Coastal Habitats of the Elwha River, 

Washington—Biological and 

Physical Patterns and Processes 

Prior to Dam Removal

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2011–5120
Front cover: Photograph showing the Elwha River entering the Strait of Juan de Fuca and the estuary of interconnected water bodies east and west of the river. 

(Photograph taken by John Gussman, Doubleclick Productions, Sequim, Washington, April 22, 2010.)

Inside front cover: Aerial view of Elwha Dam and powerhouse. (Photograph taken by Jet Lowe, National Park Service, Historic American Engineering Record 

[Library of Congress], 1995.) 

Inside back cover: Glines Canyon Dam face. (Photograph taken by Jet Lowe, National Park Service, Historic American Engineering Record [Library of Congress], 1995.)

Back cover (left to right):

Row 1: Sea urchin, clam/starfish (photographs taken by Nancy Elder, U.S. Geological Survey); rockfish (photograph taken by Ian M. Miller, University of California, 

Santa Cruz, Ocean Sciences Department).

Row 2: Diver/anemone, silverspotted sculpin, cushion star (photographs taken by Nancy Elder).

Row 3: Bull kelp/school of fish (photograph taken by Ian M. Miller); octopus (photograph taken by Reginald R. Reisenbichler, U.S. Geological Survey); mossy chiton 

(photograph taken by Nancy Elder).

Row 4: Hermit crab (photograph taken by Reginald R. Reisenbichler); diver in kelp (photograph taken by Ian M. Miller); fish eating anemone (photograph taken by Nancy Elder).
Coastal Habitats of the Elwha River, 

Washington—Biological and 

Physical Patterns and Processes 

Prior to Dam Removal

Edited by Jeffrey J. Duda, Jonathan A. Warrick, and Christopher S. Magirl 

Scientific Investigations Report 2011–5120

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

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Although this report is in the public domain, permission must be secured from the individual copyright owners 

to reproduce any copyrighted materials contained within this report.

Suggested reference:

Entire publication:

Duda, J.J., Warrick, J.A., and Magirl, C.S., eds., 2011, Coastal habitats of the Elwha River, Washington—

Biological and physical patterns and processes prior to dam removal: U.S. Geological Survey Scientific 

Investigations Report 2011–5120, 264 p.

Example for chapter within the publication:

Warrick, J.A., Draut, A.E., McHenry, M.L., Miller, I.M., Magirl, C.S., Beirne, M.M., Stevens, A.W., and Logan, 

J.B., 2011, Geomorphology of the Elwha River and its delta, chap. 3 of Duda, J.J., Warrick, J.A., and Magirl, 

C.S., eds., Coastal habitats of the Elwha River, Washington—Biological and physical patterns and processes 

prior to dam removal: U.S. Geological Survey Scientific Investigations Report 2011-5120, p. 47-74.
 iii

Preface

This report includes chapters that summarize the results of multidisciplinary studies to quantify 

and characterize the current (2011) status and baseline conditions of the lower Elwha River, its 

estuary, and the adjacent nearshore ecosystems prior to the historic removal of two long-standing 

dams that have strongly influenced river, estuary, and nearshore conditions. The studies were 

conducted as part of the U.S. Geological Survey Multi-disciplinary Coastal Habitats in Puget 

Sound (MD-CHIPS) project. Chapter 1 is the introductory chapter that provides background and a 

historical context for the Elwha River dam removal and ecosystem restoration project. In chapter 

2, the volume and timing of sediment delivery to the estuary and nearshore are discussed, 

providing an overview of the sediment stored in the two reservoirs and the expected erosion 

mechanics of the reservoir sediment deposits after removal of the dams. Chapter 3 describes 

the geological background of the Olympic Peninsula and the geomorphology of the Elwha River 

and nearshore. Chapter 4 details a series of hydrological data collected by the MD-CHIPS Elwha 

project. These include groundwater monitoring, surface water-groundwater interactions in the 

estuary, an estimated surface-water budget to the estuary, and a series of temperature and salinity 

measurements. Chapter 5 details the work that has been completed in the nearshore, including the 

measurement of waves, tides, and currents; the development of a numerical hydrodynamic model; 

and a description of the freshwater plume entering the Strait of Juan de Fuca. Chapter 6 includes a 

characterization of the nearshore benthic substrate developed using sonar, which formed a habitat 

template used to design scuba surveys of the benthic biological communities. Chapter 7 describes 

the ecological studies conducted in the lower river and estuary and includes characterization of 

juvenile salmon diets and seasonal estuary utilization patterns using otolith analysis to determine 

habitat specific and hatchery compared with wild patterns in juvenile Chinook salmon, assessment 

of benthic and terrestrial macroinvertebrate communities, and seasonal patterns of water nutrients. 

In Chapter 8, the vegetation communities of the eastern estuary are characterized by mapped 

vegetation cover types and samples collected for vegetation composition and diversity. Chapter 9 

summarizes the existing conditions of the study area as detailed in this report and describes some 

of the possible outcomes of river restoration on the coastal ecosystems of the Elwha River.

Together, these different scientific perspectives form a basis for understanding the Elwha River 

ecosystem, an environment that has and will undergo substantial change. A century of change 

began with the start of dam construction in 1910; additional major change will result from dam 

removal scheduled to begin in September 2011. This report provides a scientific snapshot of the 

lower Elwha River, its estuary, and adjacent nearshore ecosystems prior to dam removal that can 

be used to evaluate the responses and dynamics of various system components following dam 

removal.
iv

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 v

Chapter 1.—Coastal and Lower Elwha River, Washington, Prior to Dam Removal—

History, Status, and Defining Characteristics. By Jeffrey J. Duda,

Jonathan A. Warrick, and Christopher S. Magirl ......................................................... 1

Chapter 2.— Anticipated Sediment Delivery to the Lower Elwha River During 

and Following Dam Removal. By Christiana R. Czuba, Timothy J. Randle,

Jennifer A. Bountry, Christopher S. Magirl, Jonathan A. Czuba, 

Christopher A. Curran, and Christopher P. Konrad..................................................... 27

Chapter 3.—Geomorphology of the Elwha River and its Delta. By Jonathan A.

Warrick, Amy E. Draut, Michael L. McHenry, Ian M. Miller, Christopher S.

Magirl, Matthew M. Beirne, Andrew W. Stevens, and Joshua B. Logan ............. 47

Chapter 4.—Baseline Hydrologic Studies in the Lower Elwha River Prior to

Dam Removal. By Christopher S. Magirl, Christopher A. Curran, Rich W. 

Sheibley, Jonathan A. Warrick, Jonathan A. Czuba, Christiana R. Czuba, 

Andrew S. Gendaszek, Patrick B. Shafroth, Jeffrey J. Duda, and James R. 

Foreman............................................................................................................................. 75

Chapter 5.—Coastal Processes of the Elwha River Delta. By Jonathan A.

Warrick, Andrew W. Stevens, Ian M. Miller, and Guy Gelfenbaum ..................... 111

Chapter 6.—Nearshore Biological Communities Prior to Removal of the

Elwha River Dams. By Stephen P. Rubin, Ian M. Miller, Nancy Elder,

Reginald R. Reisenbichler, and Jeffrey J. Duda ...................................................... 131

Chapter 7.—Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal.

By Jeffrey J. Duda, Matthew M. Beirne, Kimberly Larsen, Dwight Barry,

Karl Stenberg, and Michael L. McHenry ................................................................... 175

Chapter 8.—Vegetation of the Elwha River Estuary. By Patrick B. Shafroth,

Tracy L. Fuentes, Cynthia Pritekel, Matthew M. Beirne, and

Vanessa B. Beauchamp ............................................................................................... 225

Chapter 9.—Summary and Anticipated Responses to Elwha River Dam Removal.

By Guy Gelfenbaum, Jeffrey J. Duda, and Jonathan A. Warrick. ......................... 249

Contents
vi

Conversion Factors, Datums, and Abbreviations and 

Acronyms

Conversion Factors

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

kilometer (km) 0.6214 mile (mi)

meter (m) 3.281 foot (ft)

millimeter (mm) 0.03937 inch (in.) 

Area

hectare (ha) 2.471 acre

square kilometer (km2) 0.3861 square mile (mi2)

square meter (m2) 10.76 square foot (ft2)

Volume

cubic meter (m3) 0.0008107 acre-foot (acre-ft)

Flow rate

centimeter per second (cm/s) 0.394 inch per second (in/s)

cubic meter per second (m3/s) 35.31 cubic foot per second (ft3/s)

cubic meter per day (m3/d) 35.31 cubic foot per day (ft3/d)

cubic meter per year (m3/yr) 0.000811 acre-foot per year (acre-ft/yr)

meter per second (m/s) 3.281 foot per second (ft/s)

meter per day (m/d) 3.281 foot per day (ft/d)

meter per year (m/yr) 3.281 foot per year (ft/yr)

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram per year (kg/yr) 2.205 pound, avoirdupois (lb/yr)

Density

kilogram per cubic meter (kg/m3) 0.06242 pound per cubic foot (lb/ft3)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as 

follows:

°F=(1.8×°C)+32.

Concentrations of chemical constituents in water are given in micrograms per liter (μg/L).

Datums

Vertical coordinate information is referenced to the North American Vertical Datum of 

1988 (NAVD 88) or the Mean Lower Low Water (MLLW) datum of the NOAA tidal station 

number 9444090 at Port Angeles, Washington during the 1983–2001 epoch. The MLLW 

datum lies 0.129 meters below the NAVD 88 datum for this tidal station.

Horizontal coordinate information is referenced to the North American Datum of 1983 

(NAD 83).

Elevation, as used in this report, refers to distance above the vertical datum.
vii

Abbreviations and Acronyms

ADCP acoustic Doppler current profiler

AEP annual exceedance probability

ANOSIM analysis of similarities

ANOVA analysis of variance

BA before and after

BACI before-after control-impact

BP before present

CHIPS Coastal Habitats in Puget Sound

CPUE catch per unit effort

CRT Coastal range terrane

CT conductivity (salinity) and temperature sensor

CTD conductivity (salinity), temperature, and depth sensor

CWT coded-wire tag

DTS distributed temperature sensing

ELJ engineered log jams

ESU evolutionarity significant unit

HCI hydrogen chloride

kcal g-1 kilocalorie per gram

lidar Light Detection and Ranging

LISST laser in-situ scattering and transmissometry

LOESS locally weighted scatterplot smoothing

MD-CHIPS multi-disciplinary Coastal Habitats in Puget Sound

MHW mean high water

MHHW mean higher high water

MLW mean low water

MLLW mean lower low water

NAIP National Agriculture Imagery Program

NH4+ ammonia

NO3- nitrate

NOAA National Oceanic and Atmospheric Administration

ONP Olympic National Park

OSC Olympic Subduction Complex

OTIS one-dimensional transport with inflow and storage

PSU practical salinity units

PO4

-3 phosphate

PVC polyvinylchloride

RFID radio frequency identifier
viii

RhWT rhodamine WT dye tracer

RKm river kilometer

RTK-DGPS real-time kinematic differential global positioning system

RTK-GPS real-time kinematic global positioning system

SD standard deviation

SFR Standard Forage Ratio 

TN total nitrogen

TP total phosphorus

UPC uniform point contact

USDA U.S. Department of Agriculture

USGS U.S. Geological Survey 

WDFW Washington Department of Fish and Wildlife

Abbreviations and Acronyms—Continued
Chapter 1

1

Chapter

Coastal and Lower Elwha 

River, Washington, Prior to 

Dam Removal—History, Status, 

and Defining Characteristics

By Jeffrey J. Duda, Jonathan A. Warrick, 

and Christopher S. Magirl

Abstract

Characterizing the physical and 

biological characteristics of the 

lower Elwha River, its estuary, and 

adjacent nearshore habitats prior to 

dam removal is essential to monitor 

changes to these areas during and 

following the historic dam-removal 

project set to begin in September 

2011. Based on the size of the two 

hydroelectric projects and the amount 

of sediment that will be released, the 

Elwha River in Washington State will 

be home to the largest river restoration 

through dam removal attempted in 

the United States. Built in 1912 and 

1927, respectively, the Elwha and 

Glines Canyon Dams have altered key 

physical and biological characteristics 

of the Elwha River. Once abundant 

salmon populations, consisting of 

all five species of Pacific salmon, 

are restricted to the lower 7.8 river 

kilometers downstream of Elwha Dam 

and are currently in low numbers. Dam 

removal will reopen access to more 

than 140 km of mainstem, flood plain, 

and tributary habitat, most of which 

is protected within Olympic National 

Park. The high capture rate of riverborne sediments by the two reservoirs 

has changed the geomorphology of 

the riverbed downstream of the dams. 

Mobilization and downstream transport 

of these accumulated reservoir 

sediments during and following dam 

removal will significantly change 

downstream river reaches, the 

estuary complex, and the nearshore 

environment. To introduce the more 

detailed studies that follow in this 

report, we summarize many of the key 

aspects of the Elwha River ecosystem 

including a regional and historical 

context for this unprecedented project.
2 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Introduction

Coastal environments are 

among the most important ecological 

components of Puget Sound, a 

large fjord-estuary in northwestern 

Washington State. The more than 

3,000 km of Puget Sound shoreline is 

classified into a diverse array of forms 

according to geologic, oceanographic, 

and anthropogenic features (Shipman, 

2008). Common forms include rocky 

coasts, beaches, bluffs, embayments, 

and deltas. Puget Sound and the 

Georgia Basin are part of the Salish 

Sea (fig. 1.1), which is fed by rivers 

in the Cascade Range and Olympic 

Mountains. These rivers carry melt 

water from glaciers, snowmelt, and local 

rainfall. This inland marine water body 

is connected to the Pacific Ocean by 

the Strait of Juan de Fuca to the west 

and the Strait of Georgia to the north. 

Characterized by a relatively young 

tectonic- and glacier-influenced geology, 

spatially variable oceanography, and 

unevenly distributed levels of urban and 

anthropogenic impacts, Puget Sound is 

home to a diverse array of biological 

communities and charismatic species 

(Buchanan, 2006; Dethier, 2006; Kriete, 

2007; Mumford, 2007; Penttila, 2007; 

Strickland, 1983). The regions where 

rivers flowing into Puget Sound meet 

salt water (sub-estuaries within the 

greater Puget Sound fjord-estuary) 

are an especially important habitat 

type, particularly for salmon, an iconic 

natural, cultural, and economic symbol 

for the region (Simenstad and others, 

1982). 

As an interface between fresh 

and salt waters, river-mouth estuaries 

and their surrounding habitats are 

among the most productive and 

biologically rich ecosystems on Earth 

(Goldman and Horne, 1983; Keddy, 

2000). The river-mouth estuaries of 

Puget sound are both dynamic and 

complex because they are influenced 

by physical forcings from the Pacific 

Ocean (such as wave action, currents, 

and upwelling of nutrients), seasonally 

and annually varying levels of river 

inputs (such as sediment, nutrients, and 

freshwater), and local and large-scale 

climatological forcings (Moore and 

others, 2008). The diverse biological 

communities present in these areas also 

have complex responses, interactions, 

and feedbacks with these physical 

factors. Added to this natural physical 

and biological variability are human 

influences that have dramatically altered 

the amount, quality, and distribution of 

estuarine habitats throughout the region 

(Collins and Sheikh, 2005; Todd and 

others, 2006). Reconstructions of the 

distribution and size of historical coastal 

habitats, compared with their current 

condition, show a dramatic reduction in 

the amount of river-mouth estuarine and 

wetland habitat, approaching more than 

95 percent loss in some areas. A suite of 

human drivers, which include industrial 

and non-point source pollution, resource 

extraction, recreation, and development 

affect the remaining estuarine wetlands. 

Nevertheless, the intact estuarine 

habitats play an important role in the 

life history of many species, especially 

juvenile salmonids, because these 

young fish reside in river-mouth 

estuaries during their migration from 

freshwater rearing areas to the sea 

(Beamer and others, 2003; Fresh, 2006). 

Estuarine habitats are believed to offer 

more protection from predation and 

higher growth potential compared to 

alternative nearshore habitats. Exposure 

of the juvenile salmonids to estuarine 

salinity gradients also facilitates their 

physiological transition from freshwater 

to salt water. 

Recently, there has been increased 

focus on restoring Puget Sound 

ecosystems and these efforts have 

highlighted the estuarine ecosystems’ 

capacity to support biodiversity, 

commerce, and recreational 

opportunities, despite various impacts 

and threats to overall system health 

(Puget Sound Partnership, 2009). The 

U.S. Geological Survey (USGS) multidisciplinary Coastal Habitats in Puget 

Sound (MD-CHIPS) initiative was 

developed to promote interdisciplinary 

collaboration among scientists studying 

Puget Sound ecosystems, with the goal 

of developing research efforts focused 

on priorities identified by stakeholders, 

management agencies, and the public 

for the restoration and preservation of 

Puget Sound (Gelfenbaum and others, 

2006). To date, MD-CHIPS science 

has focused on three areas: (1) the 

effects of urbanization on nearshore 

ecosystems, (2) restoration of large 

river deltas, and (3) the recovery of 

nearshore ecosystems (U.S. Geological 

Survey, 2006). This report summarizes 

the research and monitoring activities 

of MD-CHIPS scientists and partners 

relating to the Elwha River restoration 

project. 

The Elwha River flows northward 

from the heart of the Olympic 

Mountains to the Strait of Juan de Fuca 

west of Port Angeles, Washington. The 

Elwha River restoration involves the 

largest dam removal project to date 

in the United States and provides the 

unprecedented opportunity to study 

the ecological effects of dams and the 

removal of these dams as an ecosystem 

restoration technique (Hart and others, 

2002; Duda and others, 2008). Although 

characterized as a restoration project, 

many of the ecosystem responses and 

trajectories following dam removal 

may be novel and precisely predicting 

ecological outcomes is challenging. 

Thus, it is imperative that this 

restoration project is monitored and 

studied closely, so that ecosystem 

responses can be characterized and 

predictive techniques can be advanced. 

The MD-CHIPS project was developed 

to characterize the physical and 

biological characteristics of the Lower 

Elwha River, its estuary, and nearshore 

habitats prior to dam removal with the 

understanding that these characteristics 

would provide important baseline 

conditions for comparisons following 

dam removal. To introduce the more 

detailed studies that follow in this 

report, many of the key aspects of the 

Elwha River ecosystem are summarized 

here including a regional and historical 

context for this unprecedented project.
Chapter 1

Coastal and Lower Elwha River, Washington, Prior to Dam Removal—History, Status, and Defining Characteristics 3

Figure 1.1. The Salish Sea, which includes the Strait of Juan de Fuca, Strait of Georgia, Puget 

Sound, and the Olympic Peninsula, Washington and British Columbia, Canada. (Used with permission 

[Freelan, 2009])
4 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Elwha River Dam Removal and River 

Restoration Project

The Elwha River, on the Olympic Peninsula of 

Washington State, offers a unique opportunity for restoration 

because 83 percent of the watershed lies within Olympic 

National Park (ONP), a World Heritage site (accessed 

March 12, 2011, at http://whc.unesco.org/en/list) and 

International Biosphere Reserve (United Nations Educational, 

Scientific and Cultural Organization, 2010; fig. 1.2). 

Restoration of the Elwha River was congressionally mandated 

by The Elwha River Ecosystem and Fisheries Restoration Act 

(Public Law 102-495) and represents the single largest riverrestoration project currently (2011) planned for the greater 

Puget Sound region. Moreover, the Elwha River restoration 

project will be the largest dam-decommissioning project in the 

history of the United States in terms of the projected release 

of sediment and the size of the existing hydroelectric projects. 

Decommissioning will involve simultaneous removal of the 

Elwha Dam (32 m high, constructed from 1910 to 1913 at 

river kilometer [RKm] 7.9; fig. 1.3) and Glines Canyon Dam 

(64 m high, completed in 1927 at RKm 21.6; fig. 1.4). These 

actions offer the unique opportunity to assess the effectiveness 

of a large dam removal in restoring the watershed and 

recovering and salmon populations. The upper Glines Canyon 

Dam and its reservoir Lake Mills are in the National Park, 

whereas the lower Elwha Dam and its reservoir Lake Aldwell 

are in an area of mixed ownership and land use (fig. 1.5). 

Figure 1.2. Aerial photograph showing view of the Olympic Peninsula and Puget Sound, Washington, showing the Elwha 

River watershed and the boundaries of Olympic National Park.

Strait of Juan de Fuca

PA

C I F

I

C

O

C

E

A

N

P

u

g

e t S

o

u

n

d

Olympic

Peninsula

Olympic National Park boundary

Elwha River watershed

EXPLANATION

0 10 20 30 Miles

Base image from Landsat. Projection: Universal 0 10 20 30 Kilometers

Transverse Mercator Zone 10.

124° 123°

48°

47°
Chapter 1

Coastal and Lower Elwha River, Washington, Prior to Dam Removal—History, Status, and Defining Characteristics 5 tac11-0558_fig1-03

B.D.

A.C.

Figure 1.3. Diagram and photographs showing the Elwha Dam, Washington, completed in 1913. (

A) Elwha Dam is a concrete gravity dam with adjacent buttresstype intake sections flanked by spillways. (

B) The dam measures 32 meters high and is 137 meters wide at its crest. (

C) The dam creates the Lake Aldwell reservoir. 

(D) A large delta of sediment deposits has formed at the head of the reservoir.
6 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal tac11--558_fig1-04 A. C. B. D. Figure 1.4. Diagram and photographs showing the Glines Canyon Dam, Washington, completed in 1927. (

A) Glines Canyon Dam is a varied radius, single arch 

concrete dam. (

B) The dam measures 64 meters high and width varies from 15.8 meters at its base to 82.3 meters at its crest. The dam is currently (2011) operated as 

run-of-the-river (equivalent flows entering the reservoir from the Elwha River are released from spillways). (

C) The dam creates the Lake Mills reservoir. (

D) A large 

delta of sediment deposits has formed at the head of the reservoir. (Photograph 

B by Scott Church, private citizen, used with permission, date unknown.)
Chapter 1

Coastal and Lower Elwha River, Washington, Prior to Dam Removal—History, Status, and Defining Characteristics 7

tac11-0558_fig1-05

Strait of Juan de Fuca

Lake Crescent

Lake

Sutherland

Lake

Aldwell

Lake

Mills

Indian Creek

Boulder Creek

Hurricane Cr Cat Creek

Long Creek

Goldie River

Wolf Creek

Lillian River

Elwha River

Delabarre Cr

Godkin Cr Hayes River

Lost River

Buckinghorse Cr

Little River

Hughes Creek

Griff Creek

12045500

12044900

Port Angeles

GLINES CANYON DAM

ELWHA DAM

Elwha River watershed

USGS gaging station and number

Olympic

National

Park 

Olympic

National

Park 

EXPLANATION

Lower Elwha Klallam Tribe Reservation

Olympic National Park boundary

Washington

Figure

location

12045500

Base map from USGS National Elevation Data

Projection: Universal Transverse Mercator Zone 10, 

10 meter resolution

0 2 4 6 8 Miles

0 42 6 8 Kilometers

123°45' 123°30' 123°15'

48°

47°

45'

Figure 1.5. Elwha River watershed, northern boundary of Olympic National Park, major tributaries, Lower Elwha Klallam Tribe 

Reservation, Elwha Dam (Lake Aldwell), Glines Canyon Dam (Lake Mills), and City of Port Angeles, Washington.
8 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Constructed without fish-passage 

structures, the dams have altered 

the size and composition of salmon 

populations in a river that once 

produced 10 distinct runs, comprised 

of steelhead trout (Oncorhynchus 

mykiss) and all 5 species of Pacific 

salmon—Chinook (O. tshawytscha), 

coho (O. kitsutch), chum (O. keta), pink 

(O. gorbuscha), and sockeye (O. nerka). 

Also affected were sea-run cutthroat 

trout (O. clarki), anadromous bull trout 

(Salvelinus confluentus), eulachon 

(Thaleichthys pacificus), and lamprey 

(Lampetra tridentata), which have life 

cycles that also require migration to or 

from freshwater. Salmon populations 

downstream of Elwha Dam currently 

are estimated at about 1 percent of their 

pre-dam numbers (U.S. Department 

of the Interior, 1995a); the amount of 

spawning habitat has steadily decreased 

during the decades following dam 

construction (Pess and others, 2008). 

This degradation of spawning habitat 

has been caused by a massive reduction 

in the supplies of sand and gravel to the 

lower river from the sediment trapping 

effects of the two reservoirs, which in 

turn has resulted in a coarsening of the 

riverbed with time. Two fish hatcheries 

operated by the State of Washington 

Department of Fish and Wildlife 

(Chinook salmon) and the Lower Elwha 

Klallam Tribe (coho, steelhead, and 

chum) supplement salmon populations. 

Four fish species (Puget Sound Chinook, 

steelhead, eulachon, and bull trout) 

in the Elwha are federally listed as 

threatened under the U.S. Endangered 

Species Act.

Construction of the Elwha and 

Glines Canyon Dams fundamentally 

changed the Elwha River ecosystem, 

including its estuarine and nearshore 

components. Similar changes due 

to dam construction have occured 

in other rivers around the world 

(Baxter, 1977; Petts, 1984). Because 

of a high sediment trapping capacity 

(Curran and others, 2009), most of 

the sediment load transported by the 

upper Elwha River has accumulated 

in the two reservoirs. Surveys 

conducted in 1994–95 determined 

that approximately 11 million m3 of 

sediment had accumulated in Lake 

Mills (upper dam) and had accumulated 

behind the lower dam in Lake Aldwell 

(Randle and others, 1996). The latest 

estimate (2010) of combined sediment 

volume in both reservoirs is about 

19 million m3 (Bountry and others, 

2010; Czuba and others, 2011, chapter 2, 

this report). Other changes caused by 

the dams include increased armoring 

and channelization in parts of the river 

downstream of each dam; increased 

in median particle size (Pohl, 2004; 

Morley and others, 2008, Draut and 

others, 2011); increased average age 

of riparian flood plain forests (Kloehn 

and others, 2008); and some decreased 

flood plain complexity and lateral 

migration of the main channel (Draut 

and others, 2008; 2011). Geomorphic 

changes have affected instream benthic 

invertebrate assemblages and patterns 

of periphyton standing crop (Morley 

and others, 2008), as well as salmon 

populations (Wunderlich and others, 

1994; Brenkman and others, 2008; 

Connolly and Brenkman, 2008; Pess 

and others, 2008). Another component 

of functioning flood plain river 

systems, large woody debris (Abbe and 

Montgomery, 1996; Latterell and others, 

2006), also has been intercepted by 

the reservoirs (although dam operators 

regularly pass rafted logs through the 

dams), further changing flood plain 

dynamics and fish habitat downstream 

of each reservoir. However, efforts by 

the Lower Elwha Klallam Tribe to place 

engineered log jams in the lower Elwha 

River has helped rehabilitate some areas 

(Coe and others, 2006, 2009; see also 

side bar in Warrick and others, 2011a, 

chapter 3, this report).

Dam Removal and Release of 

Sediment Stored in Reservoirs

Mobilization and downstream 

transport of sediments currently 

(2011) accumulated in the reservoirs 

(figs. 1.3D, 1.4D) during and following 

dam removal is expected to significantly 

change downstream river reaches, the 

estuary complex, and the nearshore 

environment to the west (Freshwater 

Bay) and east (Ediz Hook) of the 

river mouth (fig. 1.6). Studies of the 

reservoir sediment composition (U.S. 

Department of the Interior, 1995b; 

Randle and others, 1996; Childers and 

others, 2000) indicated that 85 percent 

and 95 percent (in Lake Mills and 

Lake Aldwell, respectively) was sand, 

silt, and clay. A portion of this fine 

sediment will be readily transported 

during and immediately after dam 

removal (Randle and Bountry, 2008). 

Based on numerical model studies 

(Randle and others, 1996) and a 1995 

reservoir draw down experiment in 

Lake Mills (Childers and others, 2000), 

extremely high suspended-sediment 

concentrations could occur in the 

Elwha River following dam removal. 

A simulation model by Konrad (2009) 

suggests that during the 2- to 3-year 

deconstruction period, the suspendedsediment concentration in the river 

could exceed 10,000 mg/L for several 

weeks each year, with periodically high 

concentrations for as much as 3–5 years 

following dam removal, depending upon 

hydrological conditions (Randle and 

others, 1996). Anticipation of highsuspended sediment concentrations 

led to development of unprecedented 

mitigation measures for the restoration 

project, including construction of 

two new water-treatment facilities, 

the planned suspension of reservoir 
Chapter 1

Coastal and Lower Elwha River, Washington, Prior to Dam Removal—History, Status, and Defining Characteristics 9

tac11-0558_fig1-06

Elwha River

Lake Aldwell

Strait of Juan de Fuca

Port Angeles

ELWHA DAM

101

101

112

112

Washington

Figure

location

Vegetation

Offshore biology

Water quality

Groundwater

Surface water

EXPLANATION

Study sites

Lower Elwha Klallam Tribe Reservation

123°35' 123°30'

48°

10'

48°

05'

0 1 2 Miles

Base map from USGS National Elevation Data 0 1 2 Kilometers

Projection: Universal Transverse Mercator Zone 10, 

10 meter resolution

Figure 1.6. Estuary and nearshore study sites, lower Elwha River, Washington. Samples were collected by the U.S. 

Geological Survey multi-disciplinary Coastal Habitats in Puget Sound team and the Lower Elwha Klallam Tribe.

drawdown when salmon would be affected (“fish windows”), 

and operation of conservation hatcheries to protect native fish 

stocks. Over the long-term, the Elwha River bed downstream 

of the dams is expected to aggrade by as much as 1 m in some 

areas (U.S. Department of the Interior, 1996; Konrad, 2009), 

requiring additional mitigation measures such as raising 

existing flood-protection levees, construction of new levees, 

and transitioning sewage treatment on the Elwha Klallam Tribal 

reservation from septic to municipal (City of Port Angeles). 

Additional details of sediment delivery are provided by Czuba 

and others (2011), in chapter 2 of this report.

Upon entering the Strait of Juan de Fuca, sediment will 

be dispersed by waves and tidal currents and deposited on 

the sediment-starved beaches and seafloor of the Elwha delta 

(see Warrick and others, 2011, chapter 5, this report). After 

decades of sediment reduction due to the dams, the nearshore 

seafloor has coarsened (Warrick and others, 2008) and appears 

to have developed benthic communities characteristic of 

coarse sediment and hard bottom substrate (Rubin and others, 

2011, chapter 6, this report). Release of massive amounts of 

fine sediment during and following dam removal will have 

unknown affects on bottom communities in the nearshore and 
10 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

deep water habitats off the river mouth. 

The ultimate fate of these sediments 

depends on complex interactions among 

waves, currents, and the freshwater 

plume of the Elwha River (Gelfenbaum 

and others, 2009; Warrick and Stevens, 

2011). Once sediment supply is restored 

and a long-term equilibrium is reached, 

the coastal environment will still be 

affected by other anthropogenic features. 

For example, coastal bluff armoring that 

results in a reduced coastal sediment 

supply (Shaffer and others, 2008) still 

will be present following dam removal. 

The development of key 

monitoring needs, hypotheses, and 

the appropriate spatial and temporal 

scales for data collection and analysis 

benefited from a series of scientific 

workshops (Clallam County Marine 

Resources Committee, 2004; Stolnack 

and Naiman, 2005; Stolnack and others, 

2005; Randle and others, 2006; see 

also summary in Woodward and others, 

[2008]). Among the many study designs 

available for evaluating restoration 

actions (Roni and others, 2005), the 

most common study design for the 

various Elwha River related projects 

is an intensive “before and after” (BA) 

approach, although others are using a, 

“before-after control-impact” (BACI) 

approach where appropriate control 

sites exist. The former approach relies 

on replicating data collection through 

time from multiple sites over multiple 

years before dam removal, subsequently 

returning to these sites for multiple years 

following removal to measure responses. 

Strictly speaking, an ideal experimental 

design would require replication of the 

treatment (dam removal) in multiple 

locations. Practically speaking, the 

Elwha River dam removal is the only 

such project of its kind in the greater 

Puget Sound region. Thus, replication 

is available only within the treatment 

(termed pseudoreplication by Hurlburt 

[1984]) and results must be assessed 

through multiple lines of evidence. 

The other approach, a BACI design, 

incorporates experimental and control 

treatments (sites). This allows the 

researcher to account for natural 

variability in a parameter of interest 

that is occurring at both sites, which 

allows a differentiation of these effects 

from treatment effects. Because there 

are numerous parameters of interest 

in the Elwha River restoration project, 

ranging from terrestrial to aquatic and 

biological to physical (each of these 

operating at different spatial scales), 

there is no single effective “control” 

site for the Elwha River. For some 

studies, the Quinault River has been 

used (Kloehn and others, 2008; Morley 

and others, 2008) due to its similar 

watershed area, slope, and discharge 

(McHenry and Pess, 2008). Others have 

used the Elwha River upstream of Lake 

Mills as a reference section (Draut and 

others, 2008, 2011; Kloehn and others, 

2008) for physical processes. Overall, 

these design constraints necessarily 

limit the statistical power available 

to assess the effects of dam removal. 

However, as Roni and others (2005) 

point out, valuable knowledge can 

result from unreplicated BA and BACI 

designs couched in the framework of a 

case study, combining multiple lines of 

inquiry.

Comparison of Regional 

Estuaries

Estuaries are semi-enclosed 

water bodies with a connection to 

the ocean, where freshwater from a 

river mixes with seawater. In western 

North America, these estuaries can be 

highly variable in their size, origin, and 

functions. Although Puget Sound is the 

second largest estuary in the United 

States, most estuaries on the U.S. Pacific 

coast are relatively small (less than 

100 km2 in area), especially those that 

drain the steep mountainous terrain 

in coastal ranges (Emmett and others, 

2000). On the Olympic Peninsula, 

river mouth estuaries and their wetland 

complexes typically are less than 

1–2 km2 (Todd and others, 2006). 

Comparing the river-mouth 

estuaries of the coastal Olympic 

Peninsula, the Strait of Juan de Fuca, 

and the Puget Sound (fig. 1.7) is 

instructive to highlight the differences in 

sizes, geomorphologies, and hydrologic 

conditions. These differences influence 

the biological conditions among these 

sites, which can vary considerably. For 

visual comparisons of these estuaries, 

we used 2009 aerial imagery from the 

U.S. Department of Agriculture National 

Agriculture Imagery Program (NAIP), 

displayed at 1:24,000 or 1:85,000 scales. 

The side-by-side comparisons of the 

river mouth estuaries on the Olympic 

Peninsula (Hoh, Queets, Quinault, 

Elwha, and Dungeness Rivers) show 

that they each cover a relatively small 

area, with limited off-channel aquatic 

habitat and virtually non-existent tidal 

flats (fig. 1.8). The widths of river 

mouths along the Pacific coast are 

generally larger than those within the 

Strait of Juan de Fuca and differences in 

wave energy are also apparent from the 

size and extent of breaking waves in the 

photographs (fig. 1.8; see also Warrick 

and others, 2011b, chapter 5, this report). 

The Puget Sound river mouth estuaries, 

however, are somewhat larger than their 

coastal counterparts. The Skagit River 

estuary (fig. 1.9) is the largest of the 

eight presented in fig. 1.7. In addition 

to its larger size, a higher diversity of 

estuarine habitat types is apparent, with 

complex assemblages of tidal flats, 

tidal marshes, and tidally influenced 

distributary channels. Likewise, the 

Snohomish and Nisqually river mouth 

estuaries (fig. 1.10) are larger and more 

diverse than the estuaries of the Olympic 

Peninsula, although both are smaller 

than the Skagit.
Chapter 1

Coastal and Lower Elwha River, Washington, Prior to Dam Removal—History, Status, and Defining Characteristics 11

tac11-0558_fig1-07

Skagit 

Snohomish 

Nisqually

Elwha Dungeness

Hoh

Queets

Quinault

Olympic

Peninsula

C

A

S

C

A

D

E

R

A

N

G

E

Strait of Juan de Fuca

PA

C I F

I

C

O

C

E

A

N

P

u

g e t S

o u n

d

Washington

CANADA

U.S.A.

Figure

location

Queets River basin name

EXPLANATION

124° 122°

48°

47°

0 10 20 30 40 50 Miles

0 10 30 50 Kilometers 20 40 Base map from USGS National Elevation Data

Projection: Universal Transverse Mercator Zone 10, 

10 meter resolution

Figure 1.7. Location of eight river watersheds used to compare the size of river mouth estuaries in the Puget Sound and Olympic 

Peninsula, Washington.
12 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

tac11-0558fig1-08

Queets River estuary

Quinault River estuary

Elwha River estuary

Hoh River estuary

Dungeness River estuary

Universal Transverse Mercator zone 10, and 

U.S. Department of Agriculture NAIP 

(National Agricultural Imagery Program) 

2009 imagery 

Scale 1:24,000

0 0.5 1 Mile

0 0.5 1 Kilometer

124°21'30" 124°21' 124°20'30"

47°

32'

30"

47°

32'

124°18'30" 124°18' 124°17'30"

47°

21'

124°26'30" 124°26' 124°25'30"

47°

45'

123°8'30" 123°08' 123°07'30"

48°

09'

123°34'30" 123°34' 123°33'30"

48°

09'

48°

08'

30"

Hoh R

Queets R

Quinault R

Olympic

Peninsula

PACIFIC

OCEAN

Strait of Juan de Fuca

Dungeness R

Elwha

R

Figure 1.8. Aerial images showing five river mouth estuaries of 

the Olympic Peninsula, Washington.
Chapter 1

Coastal and Lower Elwha River, Washington, Prior to Dam Removal—History, Status, and Defining Characteristics 13

tac11-0558_fig1-09

123°35' 123°34' 123°33'

48°

09'

48°

08'

122°30' 122°25'

48°

21'

48°

18'

Elwha River estuary

Skagit River estuary

0 1 2 Miles

0 1 2 Kilometers Universal Transverse Mercator zone 10, and 

U.S. Department of Agriculture NAIP (National 

Agricultural Imagery Program) 2009 imagery 

Scale 1:85,000

Figure 1.9. Aerial images comparing the size of the Skagit River and the Elwha River 

estuaries, Washington.
14 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

tac11-0558_fig1-10

122°14' 122°13' 122°12'

48°

02'

48°

01'

Snohomish River estuary

122°43' 122°42' 122°41'

47°

06'

47°

05'

Nisqually River estuary

0 0.5 1 Mile

0 0.5 1 Kilometer Universal Transverse Mercator zone 10, and 

U.S. Department of Agriculture NAIP (National 

Agricultural Imagery Program) 2009 imagery 

Scale 1:24,000

Figure 1.10. Aerial images of the Snohomish River and Nisqually River estuaries, Washington.
Chapter 1

Coastal and Lower Elwha River, Washington, Prior to Dam Removal—History, Status, and Defining Characteristics 15

The Elwha River 

Estuary: History and 

Definitions

The mouth of the Elwha 

River has undergone substantial 

change over the historical record as 

sediment sources were curtailed by 

the dams. Further change resulted 

from human modification and 

natural river processes, such as 

channel meandering and avulsion. 

The earliest written accounts of the 

lower Elwha River are from the 

late 19th and early 20th centuries. 

Todd and others (2006) suggested 

that the Elwha River had previously 

discharged into the Strait of Juan de 

Fuca through several distributary 

channels. For example, the General 

Land Office survey of 1874 noted 

at least three distributary channels, 

and an 1891 U.S. Army map and 

the 1908 U.S. Coast and Geodetic 

Survey topographic maps showed 

two channels (Todd and others, 

2006). 

The number of distributary 

channels of the Elwha River mouth 

was reduced to a single channel 

for most of the 20th century 

(Todd and others, 2006; Draut and 

others, 2008). Humans are largely 

responsible for these changes, due 

to active modification of the flood 

plain and channel between the 

1940s and 1980s (Draut and others, 

2008), as well as from the reduced 

sediment supply from damming. 

Human modifications included 

physical movement of the channel 

and levee building on both sides 

of the flood plain. The effects of 

these modifications can be seen, 

as an example, in the formation 

and persistence of Dudley Pond 

on the west side of the river mouth 

(fig. 1.11), which was created 

through the construction of a floodcontrol levee in 1964 through the 

middle of the active river mouth 

(Draut and others, 2008). 

tac11-0558_fig1-11

B.

A. Western Elwha River estuary

Dudley Pond

Dudley Pond

levee

Figure 1.11. (A) West Elwha River estuary and (B) the northern shore of Dudley Pond 

showing bloom of green algae common for this location during summer, near Port Angeles, 

Washington. ([A] Aerial photograph taken by Ian M. Miller, University of California, Santa 

Cruz, January 14, 2009; [B] photograph taken by Jeffrey J. Duda, U.S. Geological Survey 

October 10, 2007.)
16 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Throughout the 20th century, 

the Elwha River channel continued 

to change its position in response 

to lateral meander migration and 

episodic avulsion. These natural 

processes resulted in annualized rates 

of channel movement of approximately 

2–10 m/yr. Some of the highest rates 

of channel movement were along the 

lowest 3 km of the river, including the 

river mouth, an area characterized by 

low stream gradient and a broad flood 

plain (Draut and others, 2008; 2011). 

These historical changes to the lower 

Elwha River (discussed in detail in 

Warrick and others, 2011a, chapter 3, 

this report) are central to the formation 

and evolution of the river mouth estuary, 

the coastal wetlands, and the habitats 

and ecosystem functions they support. 

For example, most of the coastal lakes 

along the Elwha River delta, which 

serve as important rearing habitat for 

salmon, are former river channels cut off 

from the current channel by avulsions. 

The dynamic history of the Elwha River 

and its flood plain plays an important 

role in the formation and evolution of 

the lower river and estuary ecosystem.

The total wetland complex at 

the mouth of the Elwha River is 

approximately 0.35 km2 (table 1.1). The 

western area of this complex (0.10 km2) 

is comprised of two main wetland 

components (referred to herein as the 

west estuary). The 0.028 km2 remnant 

of the historical estuary—known 

locally as Dudley Pond (fig. 1.11B)—is 

contained by the 275 m levee discussed 

above. The other major feature of the 

west estuary is a 0.068 km2 off-channel 

habitat on the eastern side of the levee 

that is influenced by river stage and 

tides. Although groundwater exchange 

and tidally influenced seepage maintain 

some degree of connectivity between 

this habitat and the river channel, the 

impounded Dudley Pond appears to 

have limited hydrological connectivity 

to the Elwha River or the ocean. 

Table 1-1. Study areas and descriptions for coastal areas and lower Elwha River, 

Washington.

Study area name Description

Elwha River

Lower Elwha River The tidally influenced part of the Elwha River near its mouth.

East estuary

ES1 A part of the eastern estuary complex nearest to the river’s 

mouth. This area was a larger, lentic water body, prior to 

winter storms in November, 2006 that eroded much of the 

habitat.

ES2 A large lentic waterbody east of ES1. This is a former river 

mouth channel that is tidally influenced standing water.

Intraestuarine Channel A channel that connects ES1 and ES2 that is tidally influenced 

and flows to the east on a rising tide and to the west on an 

ebbing tide.

Bosco Creek A spring-fed perennial water source flowing into the eastern 

side of ES2. This water source is connected to the Lower 

Elwha Klallam Tribal Hatchery and receives outflow from 

rearing ponds.

Western Estuary

Dudley Pond A disconnected water body west of a privately constructed 

dike on the western part of the estuary. 

West Estuary Channel 

(WESC)

A slough (secondary distributary channel) bordered to the 

west by the dike that is confining Dudley Pond

Nearshore

Freshwater Bay The nearshore west of the Elwha River mouth

Ediz Hook The eastern boundary of the Elwha River nearshore east of the 

river mouth

West Beach The beach west of the Elwha River mouth

East Beach The beach east of the Elwha River mouth

The levee eliminates access to the 

pond by migrating fish. Resident fish 

consist largely of a single species, the 

threespine stickleback (Gasterosteus 

aculeatus) (Shaffer and others, 2009). 

The east estuary is 0.25 km2 and is 

composed of interconnected lagoons 

and interestuarine channels (fig. 1.12). 

An important source of freshwater to 

the east estuary is from Bosco Creek, a 

spring-fed freshwater source that also 

serves as the supply and outflow of 

the Lower Elwha Klallam Tribe’s fish 

hatchery. A mosaic of vegetation south 

of the beach includes mixed hardwood 

forests and willow thickets. Vegetation 

communities of the Elwha River estuary 

are described by Shafroth and others 

(2011), chapter 8 of this report.
Chapter 1

Coastal and Lower Elwha River, Washington, Prior to Dam Removal—History, Status, and Defining Characteristics 17

Figure 1.12. (A) East Elwha River estuary and (B) beach 

berm looking south. ([A] Aerial photograph taken by Ian M. 

Miller, University of California, Santa Cruz, March 28, 2008; [B] 

photograph taken by Jeffrey J. Duda, U.S. Geological Survey, 

October 20, 2007.)

Hydrology of the Elwha River and 

its Estuary 

The climate of the Elwha River basin is characterized by 

warm, dry summers and cool, wet winters. Most precipitation 

at upper elevations falls as snow with rain predominating 

below elevations of about 1,200 m. Because the Elwha River 

watershed spans the rain shadow created by Mount Olympus 

and the Bailey Range, the drainage contains the steepest 

precipitation gradient on the Olympic Peninsula (fig. 1.13). 

Mean annual precipitation is more than 6,000 mm on Mount 

Olympus near the headwaters of the Elwha River and about 

1,000 mm at the river mouth. Long-term weather records 

(1948–2005) from the Elwha Ranger Station (approximately 

RKm 18.2, 110 m elevation) indicate an average annual 

precipitation of 1,430 mm (Western Regional Climate Center, 

2007); most precipitation falls from October through March 

(fig. 1.14). 

Discharge of the Elwha River has been monitored 

continuously by the USGS since 1918 at McDonald Bridge 

(streamflow-gaging station 12045500, Elwha River at 

McDonald Bridge near Port Angeles, WA); the site also 

was monitored from 1897 to 1901. The gaging site, 7.9 km 

downstream of Glines Canyon Dam and 13.8 km upstream 

of the river mouth, has a total drainage area of 697 km2, 

84 percent of the total Elwha River drainage area. Prior 

to 1975, the discharge at McDonald Bridge was strongly 

influenced by, “...frequent, rapid, and dramatic stream flow 

fluctuations for power generation purposes” (U.S. Department 

of the Interior and others, 1994, p. 8). Between 1975 and 

2000, as part of a settlement agreement with the Washington 

Department of Fisheries, Glines Canyon Dam and Elwha Dam 

were operated largely as run-of-river by managing discharge 

at the dams to equal river flow entering the reservoir. Since 

March 2000, the Bureau of Reclamation, with National Park 

Service oversight, has operated both projects as run-of-river, 

except during September and October when lower river flows 

have been augmented by drafting Lake Mills at the request of 

the Washington Department of Fish and Wildlife and Lower 

Elwha Klallam Tribe (Brian Winter, Olympic National Park, 

written commun., 2010). 

tac11-0558_fig1-12

A.

B.
18 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

tac11-0558_fig1-13

Strait of Juan de Fuca

Lake Crescent

Lake

Sutherland

Lake

Aldwell

Lake

Mills

Indian Creek

Boulder Creek

Cat Creek

Long Creek

Goldie River

Lillian River

Elwha River

Godkin Cr Hayes River

Lost River

Little River

Delabarre Cr

12045500

12044900

3,000

3,000

4,0004,500

3,000

3,500

2,000

2,000

1,500

2,500

1,500

2,000

2,000

3,500

1,000

1,000

1,500

4,000

5,000

4,500

4,500

5,500

5,500

6,000

6,500

7,000

4,000

5,000

2,500

2,500

4,500

4,000

3,500

3,500

4,000

3,500

4,500

4,500

2,500

4,000

5,000

5,000

Port Angeles

ELWHA DAM

GLINES CANYON DAM

Elwha

Ranger

Station

Olympic

National

Park 

Olympic

National

Park 

Mt Olympus

Base map from USGS National Elevation Data

Projection: Universal Transverse Mercator Zone 10, 

10 meter resolution 0 2 4 6 8 Miles

0 42 6 8 Kilometers

123°45' 123°30' 123°15'

48°

47°

45'
Chapter 1

Coastal and Lower Elwha River, Washington, Prior to Dam Removal—History, Status, and Defining Characteristics 19

tac11-0558_fig1-13+Explanation

Elwha River watershed

USGS gaging station and number

EXPLANATION

Lower Elwha Klallam Tribe Reservation

Olympic National Park boundary

Annual precipitation, in millimeters

Washington

Figure

location

12045500

 250 to 1,000

1,000 to 1,500

1,500 to 2,000

2,000 to 2,500

2,500 to 3,000

3,000 to 3,500

3,500 to 4,000

4,000 to 4,500

4,500 to 5,000

5,000 to 5,500

5,500 to 6,000

6,000 to 6,500

6,500 to 7,000

7,000 to 7,500

Precipitation contour—Index contour at 1,000 

feet, interval is 500 feet 1,000

tac11-0558_fig1-14

Maximum

EXPLANATION

Air temperature

Precipitation

Average

Minimum

Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec

Month

Air temperature, in degrees Celsius

Precipitation, in millimeters

0

50

100

150

200

250

300

-5

0

5

10

15

20

25

Figure 1.14. Graph showing annual trends in air temperature 

and precipitation in the Elwha River watershed, Washington, 

June 1948–December 2005. Long-term monthly averages, 

maximum and minimum air temperatures, and precipitation 

recorded at the Elwha Ranger Station (RKm 18.2) at an elevation of 

110 m. Modified from Duda and others (2008).

Figure 1.13. Map showing isohyetal contours of 

annual precipitation across the Elwha River watershed, 

Washington. Estimated precipitation data from PRISM 

Climate Group (2010). 
20 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

The mean annual discharge for the river at the 

McDonald Bridge gaging station (12045500) is 43 m3/s 

(1,520 ft3/s) based on 95 years of discharge data. Elwha 

River discharge is bimodal with a peak discharge in the 

wet winter months due to rainfall and a peak discharge 

in the late spring and early summer due to snowpack 

melt (fig. 1.15). The two months with the largest mean 

monthly discharge are June with 63 m3/s (2,230 ft3/s) 

and December with 60 m3/s (2,120 ft3/s). Typically, the 

smallest flow is in September, with a mean monthly 

discharge of 11 m3/s (388 ft3/s). Extreme low flows often 

are calculated using a log Pearson Type III approach 

(Hann, 1977) to determine statistical limits of minimum 

discharge. For the Elwha River, the 10-year recurrenceinterval 7-day low discharge is 7 m3/s (247 ft3/s).

The maximum recorded discharge of 1,180 m3/s 

(41,600 ft3/s) occurred November 18, 1897, and seven 

annual peak discharges in the record were greater than 

800 m3/s (28,300 ft3/s) (fig. 1.16). The second largest 

peak of 1,020 m3/s (35,900 ft3/s) occurred December 3, 

2007, affording researchers the opportunity to observe 

the Elwha River response to a significant discharge event. 

All the recorded annual peak discharges have occurred 

between October and April, and 78 percent of the peak 

discharges occurred between November and January, 

consistent with climatology of rivers throughout western 

Washington (Mass, 2008). 

Annual exceedance probabilities (AEP) of peak 

discharge (also known as flood recurrence intervals) were 

calculated using the annual peak-discharge record of the 

Elwha River at McDonald Bridge weighted according 

to variance (Tim Cohn, U.S. Geological Survey, written 

commun., 2010) using a regional regression equation 

for the Elwha River (Sumioka and others, 1998) 

(table 1.2). The size of the 0.50 AEP event (2-year flood) 

is 400 m3/s (14,100 ft3/s), the size of the 0.04 AEP event 

(25-year flood) is 948 m3/s (33,500 ft3/s), and the size 

of the 0.01 AEP event (100-year flood) is 1,240 m3/s 

(43,700 ft3/s) (fig. 1.17). These flood-frequency 

calculations included the peak discharges in 1897 and 

2007 as well as the influence of retention capacity of 

Lake Mills. After the Glines Canyon Dam is removed 

and the capacity to attenuate the flood hydrograph is lost, 

peak flows are expected to be slightly larger. Using the 

watershed regression estimates of Sumioka and others 

(1998), the 0.01 AEP event (100-year flood) for the 

Elwha River at McDonald Bridge without the presence 

of the dam would be about 1,400 m3/s (49,100 ft3/s), 

10–15 percent greater than peak discharges moderated by 

the reservoir capacity.

tac11-0558_fig1-15

0

10

20

30

40

50

60

70

80

90

100

Oct Nov Dec Jan Feb Mar Apr May June July Aug Sep

Month

Monthly mean discharge, in cubic meters per second

EXPLANATION 

75th percentile

Average

25th percentile

Figure 1.15. The 25th percentile (lower bars), median 

(50th percentile, diamonds), and 75th percentile (upper 

bars) of monthly mean discharge as measured at U.S. 

Geological Survey streamflow-gaging station 12045500, 

Elwha River at McDonald Bridge near Port Angeles, 

Washington.

200

400

600

800

1,000

1,200

1,400

19001890 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Annual peak discharge, in cubic meters per second

Water year

Figure 1.16. Annual peak discharges measured at U.S. 

Geological Survey streamflow-gaging station 12045500, 

Elwha River at McDonald Bridge near Port Angeles, 

Washington.
Chapter 1

Coastal and Lower Elwha River, Washington, Prior to Dam Removal—History, Status, and Defining Characteristics 21

Summary

Over the past century, the Elwha River ecosystem 

has undergone substantial changes due to the presence 

of the Elwha and Glines Canyon Dams. Dam removal 

will cause the Elwha River and its coastal environments 

to change once again as sediments are released from the 

reservoirs following dam removal and salmon recolonize 

the watershed. Recent scientific studies conducted in 

anticipation of dam removal have described the current 

condition of the river and coastal ecosystems. This report 

provides a scientific snapshot of the lower Elwha River, 

its estuary, and adjacent nearshore ecosystems prior to 

dam removal, serving as a document that can be used 

to measure and evaluate the responses and dynamics of 

various ecosystem components following dam removal.

Acknowledgments

Support for the MD-CHIPS Elwha project was 

provided by the U.S. Geological Survey. Cindi Barton, 

Susan Benjamin, Leslie Dierauf, Guy Gelfenbaum, John 

Haines, Frank Shipley, Michael Shulters, and Lyman 

Thorsteinson provided guidance and support for the 

MD-CHIPS program. We thank our partners, including 

the Lower Elwha Klallam Tribe, National Park Service, 

U.S. Fish and Wildlife Service, Washington Department 

of Fish and Wildlife, NOAA National Marine Fisheries 

Service, and Peninsula College for their support and 

collaboration. Mark Mastin calculated statistical values 

of flood frequency and low-flow discharge. Special 

thanks to Theresa Olsen for making the NAIP derived 

figures and finalizing all GIS-based maps for this 

Scientific Investigations Report. Our work benefitted 

from discussions with many colleagues and we would 

like to thank Guy Gelfenbaum, Eric Grossman, Frank 

Shipley, Scott Smith, and Tim Randle for their thoughtful 

discussions.

Table 1.2. Flood-frequency discharge magnitudes calculated 

for the Elwha River at USGS streamflow-gaging station 12045500, 

Elwha River at McDonald Bridge near Port Angeles, Washington. 

[Abbreviations: m3/s, cubic meter per second; ft3/s, cubic foot per second]

Annual 

exceedance 

probability

Recurrence 

Interval

(years)

Discharge 

(m3

/s)

Discharge

(ft3/s)

0.5 2 400 14,100

0.1 10 752 26,600

0.04 25 948 33,500

0.02 50 1,090 38,500

0.01 100 1,240 43,700

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

1 10 100

Log10 peak flow recurrence intervals, in years

Discharge, in cubic meters per second

Figure 1.17. Weighted recurrence-interval peak flows 

calculated for the Elwha River at U.S. Geological Survey 

streamflow-gaging station 12045500, Elwha River at 

McDonald Bridge near Port Angeles, Washington, with the 

upper and lower 95 percent confidence intervals.
22 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

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26 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

This page intentionally left blank
Chapter 1 Chapter 2

 

2

Chapter

Anticipated Sediment 

Delivery to the Lower Elwha 

River During and Following 

Dam Removal

By Christiana R. Czuba, Timothy J. Randle, 

Jennifer A. Bountry, Christopher S. 

Magirl, Jonathan A. Czuba, Christopher A. 

Curran, and Christopher P. Konrad

Abstract

During and after the planned incremental 

removal of two large, century-old concrete 

dams between 2011 and 2014, the 

sediment-transport regime in the lower 

Elwha River of western Washington will 

initially spike above background levels 

and then return to pre-dam conditions 

some years after complete dam removal. 

Measurements indicate the upper reaches 

of the steep-gradient Elwha River, 

draining the northeast section of the 

Olympic Mountains, carries between an 

estimated 120,000 and 290,000 cubic 

meters of sediment annually. This large 

load has deposited an estimated 19 million 

cubic meters of sediment within the two 

reservoirs formed by the Elwha and 

Glines Canyon Dams. It is anticipated 

that from 7 to 8 million cubic meters of 

this trapped sediment will mobilize and 

transport downstream during and after 

dam decommissioning, restoring the 

downstream sections of the sedimentstarved river and nearshore marine 

environments. Downstream transport of 

sediment from the dam sites will have 

significant effects on channel morphology, 

water quality, and aquatic habitat 

during and after dam removal. Sediment 

concentrations are expected to be between 

200 and 1,000 milligrams per liter during 

and just after dam removal and could 

rise to as much as 50,000 milligrams 

per liter during high flows. Downstream 

sedimentation in the river channel and 

flood plain will be potentially large, 

particularly in the lower Elwha River, an 

alluvial reach with a wide flood plain. 

Overall aggradation could be as much as 

one to several meters. Not all reservoir 

sediment, however, will be released to 

the river. Some material will remain on 

hill slopes and flood plains within the 

drained reservoirs in quantities that will 

depend on the hydrology, precipitation, 

and mechanics of the incising channel. 

Eventually, vegetation will stabilize this 

remaining reservoir sediment, and the 

overall sediment load in the restored river 

will return to pre-dam levels.
28 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Introduction

Sediment transport in the Elwha 

River has been drastically modified 

by the construction of Elwha and 

Glines Canyon Dams (fig. 2.1) nearly 

a century ago. An estimated 19 million 

m3 of sediment has been deposited in 

the two reservoirs formed behind the 

dams (Bountry and others, 2010). Bed 

coarsening and armoring has been 

identified in the lower Elwha River 

(Pohl, 2004; Kloehn and others, 2008; 

Draut and others, 2011) consistent 

with river response to the reduction in 

sediment supply downstream of large 

dams (Williams and Wolman, 1984; 

Collier and others, 1996; Knighton, 

1998; Pizzuto, 2002; Grant and 

others, 2003). A steady trend of delta 

erosion at the river mouth is due in 

part to sediment starvation caused by 

the upstream dams (Downing, 1983; 

Schwartz and Johannessen, unpub. 

data, 1997; Woodward and others, 

2008; Warrick and others, 2009). The 

decreased sediment supply to the lower 

river has reduced spawning habitat 

(Pess and others, 2008) and led to the 

coarsening of the Elwha nearshore zone 

(Shaffer and others, 2008; Warrick and 

others, 2008). The planned incremental 

removal of both dams between 2011 and 

2014 will have large short-term effects 

on the sediment-transport regime in 

the lower Elwha River, with conditions 

eventually returning to pre-dam levels 

some years after complete dam removal. 

Although dam decommissioning 

of smaller structures has become 

common throughout the United States 

(Hart and others, 2002; O’Connor and 

others, 2008), the dam-removal project 

on the Elwha River will be the largest 

decommissioning in North America on 

record, with expected erosion of part 

of the 19 million m3 of total reservoir 

sediment resulting in the largest 

controlled release of sediment to a river 

system to date. By comparison, other 

dam-removal projects in the State of 

Washington have been small in terms 

of total volume of trapped sediment and 

complexity of managing the released 

sediment (Magirl and others, 2010). 

The largest dam removal in the United 

States, in terms of trapped sediment, 

was the 2008 Milltown Dam removal on 

the Clark Fork River, Montana, where 

5 million m3 of sediment contaminated 

from upstream mining activity was 

trapped behind the dam. However, 

nearly half of the sediment volume 

(about 2.2 million m3) was manually 

removed and disposed of as part of the 

dam-removal process (Wilcox, 2010). 

In the Pacific Northwest, the largest 

dam-removal project to date has been 

the Marmot Dam removal on the Sandy 

River in northwest Oregon in 2007. 

The total volume of trapped sediment 

was about 730,000 m3, consisting 

of predominantly coarse-grained 

sediment (sand and gravel), released 

to the river after a dam breaching and 

drawdown that lasted just hours (Major 

and others, 2008). The Marmot Dam 

removal, because of the volume and 

characteristics of the trapped sediment 

and the hydraulics of the river, provides 

an insightful analogy into the potential 

geomorphic response of the Elwha 

River after dam removal. Additionally, 

the Marmot Dam project has been, to 

date, the most completely studied and 

monitored project of its kind in terms of 

sediment transport.

Sediment eroded from Lake 

Aldwell and Lake Mills will be 

transported and deposited downstream 

of the two dam sites, causing significant 

effects on channel morphology and 

ecosystems during and after dam 

removal. The goals of this chapter are to 

summarize the current knowledge on the 

sediment-transport regime of the Elwha 

River, the nature of sediment currently 

stored in each reservoir, the expected 

erosion and downstream transport of the 

reservoir sediments, and the anticipated 

effects to the lower Elwha River during 

and after dam removal.
Chapter 2

Anticipated Sediment Delivery to the Lower Elwha River During and Following Dam Removal Introduction 29

tac11-0558_fig 01

12045500

12044900

12045500 USGS streamflow-gaging

 station and No.

Elwha River basin boundary

EXPLANATION

ELWHA DAM

GLINES CANYON DAM

Strait of Juan de Fuca

Lake

Sutherland

Lake

Aldwell

Lake

Mills

Elwha

River

Elwha

River

Indian

Cre ek

Little

River

South

Bra

nch

Boulder Creek

123°40' 123°30'

48°10'

48°

OLYMPIC NATIONAL PARK

Figure location

WASHINGTON

0 1 2 3 4 5 MILES

0 1 2 3 4 KILOMETERS 5

Base map from USGS National Elevation Data

Projection: Universal Transverse Mercator Zone 10, 

10 meter resolution

Figure 2.1. Glines Canyon Dam and Elwha Dam on the Elwha River in northwest Washington. The dams have trapped most 

of the sediment load from the river during the 20th century that would have otherwise flowed into the Strait of Juan de Fuca. 

The lower dam, Elwha Dam, forms Lake Aldwell and the upper dam, Glines Canyon Dam, forms Lake Mills.
30 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Sidebar 2.1 Geomorphic Response to Removal of Marmot Dam, 

Sandy River, Oregon, USA – What Have We Learned?

G.E. Grant, J.J. Major, J.E. O’Connor, C.J. Podolak, M.K. Keith, K.R. Spicer, S. Pittman, 

H.M. Bragg, J.R. Wallick, D.Q. Tanner, A. Rhode, and P.R. Wilcock

Dam removal has emerged as an important river restoration strategy in the United States. 

Removals offer an excellent setting for validating analytical models of sediment transport and 

morphologic change, and testing the capacity of the models to simulate channel evolution in 

response to changing water and sediment-transport regimes. The largest instantaneous and 

uncontrolled release of sediment accompanying a dam removal to date (2011) occurred with the 

breaching of the Marmot Dam coffer dam on the gravel-bed Sandy River in Oregon in October 

2007.

Marmot Dam was a concrete diversion dam built in 1913 that stood 14.3 m high by 50 m 

wide. At the time of removal, the upstream reservoir was completely filled with approximately 

750,000 m3 of sand and gravel. The decision to remove the dam was motivated by a combination 

of increasing maintenance costs and unfavorable economics. To remove the concrete structure, 

a temporary coffer dam was constructed out of river bed and reservoir sediment approximately 

70 m upstream. The main concrete structure was dynamited in July 2007, but the river was 

allowed to naturally breach the coffer dam and erode the remaining impounded sediment 

(730,000 m3) during the first autumn storms in October 2007, setting off a dramatic sequence of 

geomorphic events, upstream and downstream.

Sediment transport and morphologic change were monitored in the days, weeks, months, and 

years following removal through event-based measurements of suspended sediment and bedload, 

repeat surveys of channel cross-section and planform change, reservoir incision, and repeat lidar 

surveys. Measurements of sediment transport immediately downstream of the dam following 

breaching showed a rapid initial increase in fine suspended sediment within minutes, followed 

by high rates of suspended-sediment load and bedload transport of sand and, later, gravel. The 

elevated sediment load was derived from eroded reservoir sediment, which mobilized when a 

meters-tall knickpoint migrated about 200 m upstream in the first hour after breaching. Over the 

following days and months, the knickpoint migrated upstream more slowly; within 7 months the 

knickpoint had migrated 2 km upstream. Knickpoint migration, vertical incision, and lateral erosion 

evacuated about 15 percent of the initial reservoir volume (125,000 m3

) within 60 hours following 

breaching, and by the end of high flows in May 2008, about 50 percent of the reservoir sediment 

volume had been evacuated.

About 25 percent of the total volume of sediment eroded from the reservoir was redeposited 

in a sediment wedge extending about 2 km downstream of the former dam site. The balance of 

material has been distributed along, and partly fills, pools within the Sandy River gorge, a narrow 

bedrock canyon extending 2–9 km downstream of the former dam site, but most sediment likely 

is broadly dispersed along the channel farther downstream. A two-fraction sediment budget 

indicates that most of the gravel eroded from the reservoir reach was deposited along the 

channel immediately downstream of the dam site, whereas sand input to and eroded from the 

reservoir reach largely passed through the gorge and was broadly dispersed farther downstream, 

chiefly along an 8-km-long channel reach downstream of the river gorge.

Sediment monitoring during dam removal provided insight into the: (1) speed with which 

unconsolidated reservoir sediment can be eroded even by modest flows; (2) importance 

of bedrock and longitudinal profile controls on the redistribution of sediment; (3) distinctly 

different fate of coarse and fine fractions of sediment; (4) importance of the sequence of flows 

in determining rates of erosion but not final state; and (5) value of coupling upstream and 

downstream sediment dynamics in models and field campaigns to understand dam removal.
Chapter 2

Anticipated Sediment Delivery to the Lower Elwha River During and Following Dam Removal Introduction 31

Figure S2.1. Breaching of the temporary earthen coffer dam on October 19–20, 2007, at the site of the manually 

removed Marmot Dam in northwest Oregon. Note the seepage and mass failures on the downstream face of the dam 

by 1714 Pacific daylight time (PDT). Incision downward into the coffer dam was nearly complete by 1804 PDT, and 

nearly all the coffer dam structure had been removed by 0734 PDT the next morning watac11-0558_fig S2-1
32 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Sediment Supply

Elwha Dam is a 32-m high concrete 

gravity dam constructed in 1913 at 

7.9 km upstream of the river mouth 

(fig. 2.1), forming Lake Aldwell with an 

original storage capacity of 10 million 

m3. Glines Canyon Dam is a 64-m high 

concrete arch dam constructed in 1927 

at 21.7 km upstream of the river mouth, 

forming Lake Mills with an original 

storage capacity of 50 million m3. A 

mapping and sampling effort conducted 

in 1994–95 on Lake Mills and Lake 

Aldwell provided much of the current 

knowledge of sediment deposited in 

the two reservoirs (Gilbert and Link, 

1995), and additional reservoir surveys 

conducted in July 2010 updated the 

estimate of total sediment volume 

accumulated in the two reservoirs 

combined to 19 million m3 since 

construction of the dams (Bountry and 

others, 2010). The upstream sediment 

supply to Lake Mills was estimated from 

the volume of accumulated sediment 

(Gilbert and Link, 1995; Bountry and 

others, 2010), as well as from field 

measurements of suspended sediment 

and bedload transport (Curran and 

others, 2009).

The Lake Mills delta extends 

upstream into Rica Canyon, has a total 

length of about 3,000 m, and is as much 

as 33-m thick (Bountry and others, 

2010). The volume of sediment stored 

in Lake Mills has been measured by 

combined topographic and bathymetric 

surveys resulting in estimates of 

10.6 million m3 of sediment in 1994 

(Gilbert and Link, 1995) and 15.6 

million m3 (± 2.7 million m3) of 

sediment in July of 2010 (Bountry and 

others, 2010). In 1994, about 51 percent 

of this material was stored in the delta 

at the reservoir entrance, 38 percent was 

stored on the reservoir floor and sides, 

and the remaining 11 percent was stored 

in Rica Canyon and on the alluvial fans 

of Cat Creek and Boulder Creek (Gilbert 

and Link, 1995; fig. 2.2). 

Sediment in the Lake Mills delta 

fines in the downstream direction and 

from upper deposits into deeper, older 

deposits (Gilbert and Link, 1995). 

Sediment stored in Lake Mills was 

composed of 48 percent silt and clay, 

37 percent sand, and 15 percent gravel, 

cobbles, and boulders (Gilbert and 

Link, 1995; fig. 2.2). The delta consists 

of gravel, cobbles, and boulders at the 

upstream end transitioning to sand, 

gravels, and cobbles in the central 

area. Post-dam deposits also form a 

gently sloping wedge of fine-grained 

sediment on the reservoir floor away 

from the delta that extends to the dam 

face (Gilbert and Link, 1995). In the 

years following extensive study of delta 

dynamics during the 1990s (Childers 

and others, 2000), the delta in Lake 

Mills has prograded about 400 m to the 

mouth of Boulder Creek, and trees and 

other vegetation have grown extensively 

over the delta surface (fig. 2.3).

The Lake Aldwell delta held an 

estimated 3.0 million m3 of sediment in 

1994 (Gilbert and Link, 1995). Because 

no record of a pre-dam survey of the 

Lake Aldwell topography exists, the 

sediment volume estimate is based on 

drill holes and surface exploration. 

Based on additional reservoir surveys 

in July 2010, the volume of sediment 

in Lake Aldwell was estimated at 

3.0 million m3 (± 0.8 million m3) 

(Bountry and others, 2010), suggesting 

that there was no measurable increase 

in reservoir sediment volume between 

1994 and 2010. About 46 percent of 

the sediment in Lake Aldwell is stored 

in the delta and 54 percent is stored 

on the reservoir floor and sides; the 

sediment is composed of 67 percent silt 

and clay, 28 percent sand, and 5 percent 

gravel, cobbles, and boulders (fig. 2.4; 

Gilbert and Link, 1995). The Lake 

Aldwell delta is about 750-m long and 

as much as 5–7-m thick and is nested 

in older river-terrace deposits (Gilbert 

and Link, 1995). The upstream area of 

the delta consists primarily of gravel, 

cobbles, and boulders, and the deltaic 

deposits transition to predominantly silt 

and sand at the distal extent. Similar to 

deposition patterns in Lake Mills, the 

post-dam, fine-grained sediment forms 

a gently sloping wedge on the Lake 

Aldwell reservoir floor that extends to 

the dam face (Gilbert and Link, 1995). 

In contrast to the dynamic changes 

observed on the Lake Mills delta, 

the Lake Aldwell delta has remained 

relatively unchanged between 1994 and 

2010 (fig. 2.5).

Estimates of the annual sediment 

load into Lake Mills can be used to 

approximate the sediment discharge 

rates in the Elwha River as well as the 

long-term anticipated sediment load 

into the Strait of Juan de Fuca after the 

initial sediment pulse following dam 

removal subsides. Based on sediment 

accumulation rates in both reservoirs, 

the long-term sediment loads were 

estimated to be 130,000 m3/yr for 

coarse sediment and 120,000

m3/yr for fine sediment, thus totaling 

250,000 m3/yr (Gilbert and Link, 1995; 

Bountry and others, 2010). These 

volumetric estimates can be compared 

to sediment discharge estimates by 

Curran and others (2009). Using field 

measurements of suspended sediment 

(1995–98, 2006–07) and bedload 

(1994–97) at the Elwha River above 

Lake Mills (U.S. Geological Survey 

streamflow-gaging station 12044900), 

regression equations were developed 

to estimate both suspended-sediment 

and bedload discharge as a function 

of streamflow (Curran and others, 

2009). Applying regression equations 

for suspended-sediment and bedload 
Chapter 2

Anticipated Sediment Delivery to the Lower Elwha River During and Following Dam Removal Sediment Supply 33

watac11-0558_fig 2-02

Rica

Canyon

N

Elwha R .

Lake

Mills

Cat Creek

Boulder Creek

48%

37%

13%

2%

Silt & Clay Sand Gravel Cobbles

Lake Mills Sediment Composition

Delta

51 % of Lake Mills sediment

Reservoir floor and sides 

38 percent (%) of Lake Mills 

sediment

Rica Canyon, Cat Creek fan, 

and Boulder Creek fan 

11 % of Lake Mills sediment

24%

61%

14%

1%

Glines Canyon Dam

92%

8%

5%

30%

55%

10%

Figure 2.2. Delta and size distribution of stored sediment over an oblique view of Lake Mills, Washington. Although most 

sediment is sand sized or finer, a considerable volume of sediment is coarse-grained gravel and cobbles. (Aerial photograph from 

a 2009 National Agriculture Imagery Program image.)

discharge as a function of streamflow during a study period 

of water years 2006 and 2007, Curran and others (2009) 

estimated that total sediment load to Lake Mills was between 

217 million and 513 million kg/yr. Of that total, 77 percent 

was transported as suspended sediment and 23 percent was 

transported as bedload. Based on a comparison of suspendedsediment measurements made upstream and downstream of 

the reservoir, Curran and others (2009) also estimated the 

trap efficiency was 0.86 for Lake Mills. Assuming a mean bulk 

density of 1,760 kg/m3 for sediment in the Lake Mills delta 

(Childers and others, 2000), the total sediment load transported 

to Lake Mills estimated by Curran and others (2009) is 

equivalent to 120,000–290,000 m3/yr, which is consistent with 

total sediment load estimates from reservoir sedimentation 

(250,000 m3/yr; Gilbert and Link, 1995; Bountry and others, 

2010). 
34 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal 11-0558_fig 2-03

123°36' 123°37'

48°

47°59'

48°

47°59'

123°36' 123°37'

0.5 MILES 0

0.5 KILOMETERS 0

0.5 MILES 0

0.5 KILOMETERS 0

aL M ek

li sl

aL M ek

li sl

Elwha River Glines Canyon Dam A. B.

Figure 2.3. Aerial photographs of delta growth from (

A) 1990 to (

B) 2009 showing an approximately 400-meter advance of the delta front into 

the reservoir and significant growth of new vegetation on the deltaic surface at Lake Mills, Washington. (Aerial photographs from a 1990 digital orthophotograph quadrangle and a 2009 National Agriculture Imagery Program image.)
Chapter 2

Anticipated Sediment Delivery to the Lower Elwha River During and Following Dam Removal Sediment Supply 35

watac11-0558_fig 2-04

N

Lake

Aldwell

Silt & Clay Sand Gravel Cobbles

67%

28%

4%

1%

Lake Aldwell Sediment Composition

40%

48%

9%

3%

89%

11%

Delta

46 percent (%) of 

Lake Aldwell sediment

Elwha Dam

Reservoir floor and sides

54% of Lake Aldwell sediment

Figure 2.4. Delta and size distribution of stored sediment and an oblique view of Lake Aldwell, Washington. Sand, silt, and clay are 

the dominant particle-size classifications. (Aerial photograph from a 2009 National Agriculture Imagery Program image.)
36 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal 11-0558_fig 2-05 123°34' 123°35' 48°05' 48°04' 123°34' 123°35' 48°05' 48°04' 0.5 MILES

0 0.5 KILOMETERS0 0.5 MILES

0 0.5 KILOMETERS0

Elwha Dam

aL ke

dl A w l e l

aL ke

dl A w l e l

Elwha River A. B.

Figure 2.5. Aerial photographs of delta growth from (

A) 1994 to (

B) 2009 showing relatively little advancement of the delta at Lake Aldwell, Washington. 

(Aerial photographs from a 1994 digital orthophotograph quadrangle and a 2009 National Agriculture Imagery Program image.)
Chapter 2

Anticipated Sediment Delivery to the Lower Elwha River During and Following Dam Removal Anticipated Sediment Effects from Dam Removal 37

Anticipated Sediment 

Effects from Dam 

Removal

Elwha and Glines Canyon Dams 

are slated for decommissioning 

beginning in September 2011, and one 

of the primary concerns during and after 

removal of the dams is the fate of the 

estimated 19 million m3 of total stored 

reservoir sediments. Of the four general 

categories of sediment-management 

alternatives originally considered for 

dam decommissioning (no action, 

river erosion, mechanical removal, and 

stabilization; Randle, 2002), the rivererosion alternative; that is, allowing the 

river to erode part of the stored sediment 

using natural river-transport processes 

(Randle and others, 1996), was selected 

because it was deemed the most costeffective way to fully restore the river 

system (U.S. Department of the Interior, 

1995, 1996, 2005a, 2005b). 

Several key scientific investigations 

provide insight into the potential erosion 

and transport of reservoir sediment in 

response to the removal of Elwha and 

Glines Canyon Dams. A field experiment 

was conducted on Lake Mills in 

April 1994 that used a trial drawdown 

of the reservoir levels to demonstrate 

the potential effects of removing 

Glines Canyon Dam on the erosion 

and transport of Lake Mills sediment 

(Childers and others, 2000). Changes 

in sediment transport and suspendedsediment concentration during and after 

dam removal were investigated by the 

Bureau of Reclamation using a massbalance model to simulate reservoir 

sediment erosion and a one-dimensional 

sediment-transport model, HEC-6, 

to simulate hydraulics and sediment 

transport of the river downstream 

of Elwha Dam (Randle and others, 

1996). Laboratory physical modeling 

experiments were conducted by Bromley 

and others (2011) to investigate the 

dynamics of sediment erosion from the 

Lake Mills delta during dam removal. 

Additionally, Konrad (2009) simulated 

the dam-removal response in the entire 

Elwha River using a one-dimensional 

model developed by Bennett (2001). 

Although there is agreement among 

these various simulations, the responses 

of the river to dam removal are still 

not certain. Adaptive management 

will monitor erosion of the reservoir 

sediments and effects to the lower 

river during and after dam removal to 

determine if alterations to the damremoval and management strategy are 

necessary (Randle and Bountry, 2010). 

Management concerns during dam 

removal include the release of finegrained sediment (silt and clay-sized 

material) affecting downstream water 

quality and the release of accumulated 

coarse-grained sediment (sand, gravel, 

and cobbles) with the potential to affect 

downstream channel geomorphology, 

flooding potential, channel-migration 

rates, habitat productivity, and coastal 

processes. 
38 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Erosion of Reservoir Sediment

Elwha and Glines Canyon Dams 

will be removed concurrently over 

a 2–3-year period. Each dam, and 

associated reservoir water-surface 

elevation, will be drawn down in 

controlled increments of 2–6 m to 

allow erosion and redistribution of 

the delta sediment in the remaining 

reservoir. The maximum drawdown 

rate for each increment will be limited 

to 0.46 m/d in an effort to prevent 

initiation of reservoir landslides. As 

reservoir levels are lowered, headcut 

erosion will propagate upstream through 

the reservoir sediment. Periods of 

constant reservoir elevation between the 

incremental lowering will allow river 

processes like meandering and channel 

migration to induce lateral erosion of 

the sediment (Randle and others, 1996). 

Observations during the 1994 drawdown 

experiment of Lake Mills (Childers and 

others, 2000) showed that unvegetated 

deltaic sediment was readily mobilized 

and transported out of the reservoir 

(fig. 2.6).

As the two dams are incrementally 

removed, each delta will prograde, 

releasing fine sediment into suspension 

and transporting coarse-grained 

sediment farther into the shrinking 

reservoir. In the early stages of 

drawdown, the large reservoir 

capacity in the existing pool will 

allow much of the fine sediment to 

fall back out of suspension and not 

pass downstream of the dam site. 

This response was observed during 

the 1994 drawdown experiment as 

the maximum suspended-sediment 

concentration measured in the draining 

Lake Mills reservoir was 6,110 mg/L, 

although the measured suspendedsediment concentration downstream 

of the dam in Glines Canyon did not 

exceed 20 mg/L (Childers and others, 

2000). As the remaining reservoir water 

volume decreases from the lowered 

water surface and infilling from the 

prograding delta, the capacity of the 

reservoir to retain suspended sediment 

will decrease and more suspended 

sediment will progressively exit the 

reservoir. Additionally, the volumes of 

fine-sediment erosion will increase and 

mix with an ever decreasing reservoir 

water volume, resulting in increased 

suspended-sediment concentrations 

released from the reservoir.

Coarse sediment transported as 

bedload, however, will remain in the 

reservoir until the prograding delta 

reaches the lowered dam structure. After 

the top one-half to two-thirds of each 

dam has been removed, the volume 

of sediment eroded and prograded 

toward the dam site may be sufficient 

to completely fill the remaining 

reservoir volume behind the partially 

lowered dam (Randle, 2006; Randle 

and Bountry, 2010). Thereafter, each 

successive increment of dam removed 

will draw down the reservoir and release 

pulses of bedload and suspendedsediment load to the river.

A primary goal during the 

dam-removal process is to erode as 

much sediment as possible across the 

delta flood plain to avoid stranding 

large wedges of sediment in the former 

reservoir inundation area. Large wedges 

of sediment would be susceptible to 

catastrophic mass wasting even after 

the dams are completely removed, 

endangering people and structures 

downstream and potentially affecting 

water quality. Physical modeling by 

Bromley and others (2011) demonstrated 

that sediment mobilization would be 

maximized if the incipient knickpoint 

of the eroding channel was located 

in the center of the reservoir delta 

and drawdown steps were relatively 

small, thus allowing the incising 

river to meander across the width of 

the delta. Bromley and others (2011) 

also determined, however, that if 

the river were positioned along one 

of the bedrock canyon walls at the 

start of drawdown, the river would 

tend to remain along that bedrock 

face throughout the dam-removal 

sequence, leaving a sediment terrace 

asymmetrically positioned along the 

opposite canyon (fig. 2.7) that would be 

susceptible to mass wasting. Having the 

river channel positioned near one of the 

bedrock walls also creates the potential 

that the river would plunge over a 

bedrock shelf away from the position 

of the pre-dam river channel, creating a 

hydraulic barrier to fish passage. 

In an effort to lessen the possibility 

of stranding the incising river channel 

on one side of the delta, trees and other 

vegetation were manually removed 

in September 2010 and a 15-m wide 

pilot channel was excavated along the 

upstream 335 m of the Lake Mills delta 

centerline (fig. 2.8; Bountry and others, 

2010). Physical modeling also simulated 

that much of the trapped sediment will 

remain in the region of the drained 

reservoir (Bromley and others, 2011). 

One salient goal during and after dam 

removal will be to establish vegetation 

on relatively stable terraces of sediment 

remaining in the reservoir areas. 
Chapter 2

Anticipated Sediment Delivery to the Lower Elwha River During and Following Dam Removal Anticipated Sediment Effects from Dam Removal 39

watac11-0558_fig 2-06

A. B.

Figure 2.6. Drawdown experiment at the Lake Mills delta, Washington, in 1994. (A) Eroded sediment redeposited at the distal end 

of the prograding delta across the entire width of the receding reservoir. (B) The incised active channel showed the underlying 

stratigraphy of the delta and multiple, inset terraces. Lack of stabilizing vegetation and the coarse, non-cohesive nature of the sediment 

allowed vigorous incision and downstream transport (adapted from Randle and Bountry, 2008).

Figure 2.7. Physical model experiments of sediment erosion (A) without a pilot channel and (B) with a pilot channel showing the 

extensive and potentially problematic high terrace of alluvial sediment that may remain if the incising channel starts along one of the 

bedrock walls, Lake Mills, Washington. (Photographs courtesy of Chris Bromley; adapted from Randle and Bountry, 2008.)

A. B.
40 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Figure 2.8. Lake Mills delta, Washington, (A) before construction of a pilot channel and removal of vegetation, September 13, 2010; 

(B) with the newly constructed center pilot channel passing flow after a 5.5-meter reservoir drawdown, November 3, 2010; and (C) after 

a flood that peaked on December 12, 2010, at 632 cubic meters per second (22,300 cubic feet per second), December 15, 2010. 

([A] Photograph courtesy of Tom Roorda, Northwestern Territories, Inc.; [B] photograph courtesy of Dick Bauman, Bureau of 

Reclamation; and [C] photograph courtesy of Dick Bauman, Bureau of Reclamation.)

watac11-0558_fig 2-08

A.

C.

B.
Chapter 2

Anticipated Sediment Delivery to the Lower Elwha River During and Following Dam Removal Anticipated Sediment Effects from Dam Removal 41

Sediment Delivery 

Downstream of Dam Sites

Typical downstream river response 

to dam removal includes increased 

turbidity and sediment concentrations 

(Randle, 2002; Stanley and Doyle, 

2002; Major and others, 2008) as 

well as geomorphic responses to the 

increased sediment loads, although 

the magnitude of these effects tends to 

decrease with time and distance from 

the dam (Pizzuto, 2002). The modeling 

efforts by Randle and others (1996) and 

Konrad (2009), along with observations 

from the 1994 drawdown (Childers and 

others, 2000) and the physical modeling 

experiments by Bromley and others 

(2011) provided much of the basis for 

expectations of the sediment delivery 

to the Elwha River downstream of both 

dam sites and the response of the river. 

Based on results from the Bureau 

of Reclamation mass-balance modeling, 

between one-half and two-thirds 

of silt and clay-sized sediment in 

the reservoirs are expected to erode 

and be transported downstream as 

suspended load, and between onequarter and one-third of the sand and 

gravel-sized sediments are expected 

to erode from the reservoirs and be 

transported downstream as bedload 

(Randle and others, 1996; Randle, 

2006). Extrapolating these earlier 

model simulation results (Randle and 

others, 1996) to the updated estimate of 

19 million m3 of accumulated reservoir 

sediment since construction of the 

dams (Bountry and others, 2010), it 

is estimated that 7–8 million m3 of 

sediment will erode from the reservoirs 

and be released to the river downstream.

Fine-Sediment Transport

Much of the fine sediment released 

during dam removal will be transported 

in suspension directly to the Strait of 

Juan de Fuca, resulting in increased 

suspended-sediment concentrations and 

turbidity throughout the lower river 

(Randle and others, 1996). Simulated 

suspended-sediment concentrations at 

Glines Canyon Dam were high during 

dam removal, exceeding 10,000 mg/L 

for several weeks each year (Konrad, 

2009). Simulated suspended-sediment 

concentrations at the river mouth did 

not exceed 500 mg/L nearly as often as 

downstream of Glines Canyon Dam, 

generally less than 20 days in a 3 month 

period. The Konrad (2009) simulations 

were consistent with earlier model 

simulation results by the Bureau of 

Reclamation (Randle and others, 1996). 

Based on the Bureau of Reclamation 

model simulation results, suspendedsediment concentrations are expected 

to be typically between 200 and 1,000 

mg/L during the dam-removal period 

with temporary peaks as high as 30,000–

50,000 mg/L (Randle and others, 

1996). For comparison, based on the 

regressions developed with suspendedsediment concentration data collected 

in the Elwha River just upstream of 

Lake Mills (Curran and others, 2009), 

the background suspended-sediment 

concentration in the Elwha River at 

a median flow of 34 m3/s would be 

4.6 mg/L and the concentration at 

101 m3/s (a discharge value exceeded 

only 5 percent of the time) would be 

121 mg/L.

After dam removal, fine-sediment 

concentrations are expected to return 

to natural, background levels within 

2–5 years after complete removal 

(Randle and others, 1996). Similarly, 

Konrad’s (2009) simulations suggested 

that suspended-sediment transport likely 

will return to normal levels during 

low to moderate flows within 4 years 

after dam removal. However, larger 

flow events may still generate high 

suspended-sediment concentrations, 

as erosion is expected to further widen 

the channels in the drained reservoir 

region (Randle and others, 1996). 

These episodic high discharge values 

may cause high suspended-sediment 

concentrations and bed instability that 

may have deleterious effects on Chinook 

salmon incubation through infill of 

spawning gravels and reduction of flow 

to salmon redds (Konrad, 2009). 

Coarse-Sediment Transport

The exact timing of the arrival of 

the coarse-grained bedload to the lower 

Elwha River is not certain. Coarse 

material will be released downstream 

once the prograding deltas have reached 

the lowered dam faces. However, 

the rate of transport downstream will 

depend on the rate of dam removal 

and the driving hydrology in the years 

during and following dam removal 

(Randle and others, 1996; Konrad, 

2009). If the winter seasons are wet, the 

resulting high river flows will be able 

to transport larger quantities and sizes 

of sediment downstream at a faster rate. 

In contrast, if dry conditions persist, the 

river will have less capacity to transport 

this coarse material downstream and 

more time will elapse before this coarse 

sediment arrives in the lower river.
42 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Although 95 percent of the 

sediment from the Lake Aldwell 

delta consists of sand, silt, and clay 

and probably will have a minimal 

geomorphic affect on the lower Elwha 

River, much of the coarser material 

from the Lake Aldwell delta may start 

to arrive in deposits in the lower river 

during the second winter (2012–13), 

accreting some existing gravel bars 

and probably transporting downstream 

relatively quickly. Farther upstream, 

no coarse bedload will exit Lake Mills 

until the prograding delta impinges 

against the lowered Glines Canyon Dam 

structure. Coarse sediment release may 

begin during the second winter season 

(2012–13), although large quantities 

of bedload probably will not pass the 

Glines Canyon Dam site until the 

winter of the final year of dam removal 

(2013–14). This enhanced bedload will 

then transport down the middle reach 

of the river for another 2–5 years after 

complete removal of Glines Canyon 

Dam (Randle and others, 1996).

Although the first appreciable 

transport of coarse reservoir material 

to the lower river may start to be 

observed in the winter of the third year 

of dam removal (2013–14), whole-scale 

geomorphic changes and concomitant 

increases in bedload and sediment 

caliber associated with downstream 

translation of reservoir sediment will 

affect the lower river 4–7 years after the 

start of dam removal. Bedload transport 

rates are then expected to return to 

background conditions 7–10 years after 

the start of dam removal. However, 

there is considerable uncertainty in the 

bedload transport and system response. 

Geomorphic Effects due to 

Released Sediment

The lower river downstream of 

Elwha Dam will undergo geomorphic 

changes due to the increased sediment 

supply during and after dam removal 

(Draut and others, 2008; Konrad, 2009). 

Initially, as only fine material is released 

from the reservoirs, bimodal grain-size 

distributions will result downstream due 

to the newly transported sand combined 

with the armored cobble and boulder 

bed (Kloehn and others, 2008). As dam 

removal progresses and fine and coarse 

sediment are released downstream, the 

river is expected to become transportlimited: sediment will deposit in areas 

where the transport capacity of the river 

is less than the sediment supply (that 

is, pools, side channels, recirculation 

zones, and flood plain edges along the 

channel). Most aggradation is expected 

to occur in river pools during periods 

of low river discharge. Aggradation on 

riffles is not as likely to occur, but is 

possible depending on the magnitude 

and frequency of peak flows during and 

after dam removal.

Simulations by Konrad (2009) 

showed that within 4 years after 

completion of dam removal the lower 

Elwha River will aggrade as much as 

about 2.5 m in the upper part of the 

lower river and relatively little near 

the river mouth. Similarly, Bureau of 

Reclamation simulations suggest that 

areas of the lower river will aggrade 

between 0–3 m in the short term and in 

the decades after dam removal up to an 

average of 1.4 m throughout the lower 

river (Randle and others, 1996; Randle, 

2006). Overall, river reaches with the 

greatest potential for morphological 

change include depositional reaches 

with lower slopes (for example, lower 

Elwha River), valley expansions (for 

example, upstream of Lake Aldwell), 

or upstream of constrictions where 

backwater exists at higher flow (for 

example, upstream of Glines Canyon) 

(Konrad, 2009). In the decades after dam 

removal, channel migration is expected 

to increase in the lower reach (Kloehn 

and others, 2008). Due to aggradation 

and fining of material in the lower river, 

the channel could shift from the current 

anabranching form (see Warrick and 

others, 2011, chapter 3, this report) to 

a braided system (Draut and others, 

2008), likely resulting in a straighter 

channel alignment (steeper slope), which 

is consistent with a braided channel 

planform (Randle and Bountry, 2008).

The sediment released from these 

dam removals will affect downstream 

flood risk and ecosystems. Simulations 

from the Bureau of Reclamation suggest 

that sedimentation would increase the 

100-year flood stage along the lower 

Elwha River by less than 1 m (Randle 

and others, 1996; Randle, 2006). In 

response to these simulations, existing 

levees along the lower Elwha River 

were raised and new levees were 

constructed to protect landowners 

downstream. In the lower river reaches, 

the initial increase in sediment load will 

disrupt aquatic and riparian ecology. 

However, sediment deposition and the 

incorporation of large woody debris and 

organic matter will lead to an overall 

increase in quantity and quality of fish 

habitat (Woodward and others, 2008). 
Chapter 2

Anticipated Sediment Delivery to the Lower Elwha River During and Following Dam Removal Anticipated Sediment Effects from Dam Removal 43

Sediment Monitoring During 

and After Dam Removal

Even with the current simulations, 

there is considerable uncertainty 

in the timing and magnitude of the 

system response to the removal of 

Elwha and Glines Canyon Dams. 

Observations from the Marmot Dam 

removal suggested smaller overall 

aggradation rates downstream and a 

faster chronology of river responses 

than numerical simulations (Major 

and others, 2008). Studies of the 

Milltown Dam removal determined that 

(1) reservoir erosion occurred at greater 

rates than simulated by numerical 

modeling due to greater-than-anticipated 

lateral erosion (Johnsen, 2011), and 

(2) a sediment pulse that traveled by 

both translation and dispersion produced 

downstream pool filling, fine sediment 

infiltration (Evans and Wilcox, 2010), 

and sedimentation of side channels, but 

minimal overall aggradation (Wilcox, 

2010). 

Monitoring of river reaches 

downstream of the Elwha and Glines 

Canyon Dam sites will provide 

important insight into these geomorphic 

processes as the Elwha River adjusts 

to and recovers from the dam-removal 

process. During initial reservoir 

drawdown, monitoring activities will be 

focused on reservoir surveys, reservoir 

elevation, turbidity, discharge, and 

investigations to characterize the areas 

of erosion and the advancement of 

the delta fronts (Randle and Bountry, 

2010). Turbidity will be measured 

continuously upstream of Lake Mills 

and at the new surface-water diversion 

structure at river kilometer (RKm) 5.3 

to monitor water quality in the river 

where water is diverted into the Elwha 

Water Treatment Plant (Randle and 

Bountry, 2010). If suspended sediment 

degrades water quality beyond an 

acceptable threshold, the pace of dam 

removal will be adjusted within the 

adaptive management framework to 

reduce effects for downstream water 

users. Additionally, an acoustic Doppler 

current profiler (ADCP) and a laser 

in-situ scattering and transmissometry 

(LISST) system will be installed at the 

water diversion structure to enable the 

quantification of suspended-sediment 

load in the lower river at least through 

2013. Physical samples will be collected 

through at least the end of 2013 to 

quantify the suspended-sediment 

concentration carried by the river under 

different hydrologic conditions. These 

samples, in turn, will be used with 

turbidity data, acoustic-backscatter 

data, and LISST data to estimate the 

continuous suspended-sediment load 

carried within the lower Elwha River.

Monitoring of riverbed aggradation 

and potential increase in flood stage 

downstream of the dams will begin once 

sand and gravel have begun to transport 

downstream of the reservoir sites, 

using a combination of stage recorders, 

channel cross-section surveys, and 

longitudinal profile surveys (Randle and 

Bountry, 2010). A series of geophone 

bedload sensors were installed along the 

crest of the diversion weir at the new 

Elwha Water Treatment Plant (RKm 5.3) 

to continuously measure acoustic energy 

generated by bedload transport during 

and after dam removal (Marr and others, 

2009; Randle and others, 2009). To 

fully quantify flux of bedload, however, 

physical measurements of bedload are 

needed to correlate acoustic energy 

measured with the geophones to gravel 

transport. There are currently no plans 

to measure bedload in the lower river 

during the dam-removal project. Over 

the long term, river-based monitoring 

will focus on the restoration of 

vegetation, habitat, sediment dynamics, 

the function of large woody debris, 

and morphological processes in the 

lower river, estuary, and nearshore zone 

(Woodward and others, 2008).

Although some monitoring 

of sediment load and geomorphic 

response of the river corridor during 

and after dam removal will occur, the 

amount of basic geomorphic research 

currently planned during the project is 

relatively modest. No measurements 

of bedload transport are currently 

planned. Suspended-sediment load will 

be measured in the lower river through 

2013, but monitoring beyond 2014 is 

unfunded and no suspended-sediment 

measurements are planned upstream of 

Lake Mills or between the two reservoirs. 

These additional monitoring sites would 

provide spatial resolution of the rate of 

sediment mobilization and downstream 

transport and enable the construction of a 

quantifiable sediment budget throughout 

the river. Finally, there are no plans to 

collect remotely-sensed geomorphic 

data sets of repeat aerial photography or 

lidar during the project. Such public data 

sets would enable a wealth of follow-on 

analyses that could provide important 

insight well after completion of the dam 

removals.

The restoration of the Elwha River 

represents a true “best case” for what 

a full-on watershed restoration scheme 

might hope to accomplish. The removal 

of Elwha and Glines Canyon Dams 

is unique, in part, because the project 

represents the largest controlled release 

of sediment in the history of North 

America. This particular project is also 

unique because it encompasses an entire 

watershed including the estuarine and 

marine habitats of a predominantly 

pristine wilderness historically home to 

all runs of Pacific Northwest anadromous 

salmonids. It is imperative that the 

response and recovery of the Elwha River 

during and after dam decommissioning 

are studied if reasonable expectations 

for other watershed-based restoration 

efforts are to be established. A sound 

technical narrative of this unprecedented 

project is needed to describe the fate of 

the sediment in the years to decades after 

dam removal. 
44 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Summary

The presence of Elwha Dam and 

Glines Canyon Dam have significantly 

altered the sediment transport and 

geomorphic processes of the Elwha 

River and the nearshore environment 

in the Strait of Juan de Fuca. The 

planned removal of the dams from 

2011 to 2014 will release an anticipated 

7–8 million cubic meters of the 

estimated 19 million cubic meters of 

stored reservoir sediment to erosion 

and transport downstream. During dam 

decommissioning, fine sediment is 

expected to be more readily mobilized 

than coarse sediment.

Studies indicate that suspendedsediment concentration during low to 

moderate flows will return to pre-dam 

levels within a few years after the 

dams are completely removed. Storm 

events will continue to generate higher 

concentrations of suspended sediment 

until the reservoir sediment is no longer 

significantly eroding over the long term. 

Generally, recovery rates of sedimenttransport regimes relative to background 

conditions are expected to take 4–7 years 

following complete dam removal. The 

magnitude, timing, and frequency of 

storm events during and soon after dam 

removal are the mechanisms causing the 

overall transport of released sediment to 

the river downstream and the time until 

long-term stabilization of the sediment 

has been obtained.

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Randle, T.J., 2010, 2010 survey report 

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and Thorne, C., 2011, Physical 

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R.E., McHenry, M., and Warrick, 

J.A., 2008, Channel evolution on 

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infiltration in a gravel-bedded river 

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S.L., 2003, A geological framework 

for interpreting downstream effects 

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and Grant, G.E., eds., A peculiar 

river—Geology, geomorphology, and 

hydrology of the Deschutes River, 

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no. 7, 220 p.

Hart, D.D., Johnson, T.E., BushawNewton, K.L., Horwitz, R.J., 

Bednarek, A.T., Charles, D.F., 

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Chapter 2

Anticipated Sediment Delivery to the Lower Elwha River During and Following Dam Removal References Cited 45

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modeling of sediment transport and 

reservoir erosion following dam 

removal—Milltown Dam, Montana: 

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S.A., Coe, H.J., and Duda, J.J., 2008, 

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dynamics in the Elwha River, 

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processes: London, Arnold, 383 p.

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recovery of suspended sediment 

transport and river-bed stability 

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Magirl, C.S., Connolly, P.J., Coffin, B., 

Duda, J.J., Curran, C.A., and Draut, 

A.E., 2010, Sediment management 

strategies associated with dam 

removal in the State of Washington, in

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on Sedimentation and Hydrologic 

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July 1, 2010 [Proceedings], 10 p.

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Spicer, K.R., Bragg, H.M., Rhode, 

A., Tanner, D.Q., Anderson, C.W., 

and Wallick, J.R., 2008, Initial fluvial 

response to the removal of Oregon’s 

Marmot Dam: Eos, American 

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Marr, J.D.G., Johnson, S.R., Ellis, C.R., 

Randle, T.J., and Hilldale, R.C., 2009, 

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of bedload impact-plate sensors: 

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G., 2008, The dams come down—

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T.J., and Davies, J., 2008, Biological 

impacts of the Elwha River dams and 

potential salmonid responses to dam 

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D.C., October 23–24, 2002, p. 81-104.

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memorandum to Elwha River 

restoration project, Olympic National 

Park, Application of the report entitled 

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the river erosion alternative”: U.S. 

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PN-95-9, 1996.

Randle, T.J., and Bountry, J.A., 2008, 

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Elwha River restoration—Sediment 

adaptive management summary: 

Denver, Colo., U.S. Department of 

the Interior, Bureau of Reclamation, 

Technical Service Center, 14 p. 

Randle, T.J., Hilldale, R.C., Marr, 

J.D.G., and Johnson, S.R., 2009, 

Continuous surrogate bedload 

measurement on the Elwha 

River following dam removal, in

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Congress, 33rd, Vancouver, British 

Columbia, 2009.

Randle, T.J., Young, C.A., Melena, J.T., 

and Ouellette, E.M., 1996, Sediment 

analysis and modeling of the river 

erosion alternative: Denver, Colo., 

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Service Center, Elwha Technical 

Series PN-95-9, 136 p.

Shaffer, J.A., Crain, P., Winter, B., 

McHenry, M.L., Lear, C., and Randle, 

T.J., 2008, Nearshore restoration of 

the Elwha River through removal of 

the Elwha and Glines Canyon dams—

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retention following dam removal: 

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46 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

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2005b, Record of decision, Elwha 

River ecosystem restoration 

implementation—Final supplemental 

environmental impact statement: 

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Service, 14 p.

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and Gelfenbaum, G., 2008, Nearshore 

substrate and morphology offshore of 

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Logan, J.B., 2011, Geomorphology of 

the Elwha River and its delta, chap. 

3 of Duda, J.J., Warrick, J.A., and 

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of the Elwha River, Washington—

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and processes prior to dam removal: 

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47-74.

Warrick, J.A., George, D.A., 

Gelfenbaum, G., Ruggiero, P., 

Kaminsky, G.M., and Beirne, M., 

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along the mixed grain-size delta of the 

dammed Elwha River, Washington: 

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p. 136-148. 

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and deposition resulting from a damremoval sediment pulse—Milltown 

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#H31E-1045. 

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Chapter 3

3

Chapter

Geomorphology of the Elwha 

River and its Delta

By Jonathan A. Warrick, Amy E. Draut, 

Michael L. McHenry, Ian M. Miller, 

Christopher S. Magirl, Matthew M. 

Beirne, Andrew W. Stevens, and 

Joshua B. Logan

Abstract

The removal of two dams on the Elwha 

River will introduce massive volumes of 

sediment to the river, and this increase 

in sediment supply in the river will likely 

modify the shapes and forms of the river 

and coastal landscape downstream of the 

dams. This chapter provides the geologic 

and geomorphologic background of the 

Olympic Peninsula and the Elwha River 

with emphasis on the present river and 

shoreline. The Elwha River watershed was 

formed through the uplift of the Olympic 

Mountains, erosion and movement of 

sediment throughout the watershed from 

glaciers, and downslope movement of 

sediment from gravitational and hydrologic 

forces. Recent alterations to the river 

morphology and sediment movement 

through the river include the two large 

dams slated to be removed in 2011, but also 

include repeated bulldozing of channel 

boundaries, construction and maintenance 

of flood plain levees, a weir and diversion 

channel for water supply purposes, and 

engineered log jams to help enhance river 

habitat for salmon. The shoreline of the 

Elwha River delta has changed in location 

by several kilometers during the past 

14,000 years, in response to variations 

in the local sea-level of approximately 

150 meters. Erosion of the shoreline 

has accelerated during the past 80 years, 

resulting in landward movement of the 

beach by more than 200 meters near the 

river mouth, net reduction in the area of 

coastal wetlands, and the development of 

an armored low-tide terrace of the beach 

consisting primarily of cobble. Changes 

to the river and coastal morphology 

during and following dam removal may 

be substantial, and consistent, long-term 

monitoring of these systems will be needed 

to characterize the effects of the dam 

removal project.
48 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Introduction

The removal of the Elwha and 

Glines Canyon Dams will introduce 

massive volumes of sediment into the 

Elwha River, some of which will be 

transported to the Strait of Juan de 

Fuca coastal waters. This sediment 

perturbation will likely modify 

the shapes and forms, that is, the 

“geomorphology,” of the landscape 

downstream of the dams. One important 

step to characterizing these future 

changes is a thorough description of the 

present geomorphology of the Elwha 

River and its coast. If these changes 

are not measured and described, future 

changes to the river, flood plain, and 

coastal landforms cannot be tracked, 

and the effects of the dam removal will 

remain unknown. 

The present geomorphology of the 

Elwha River results from an uplifting 

mountain range, large changes in sea 

level, former alterations to the landscape 

by glaciers, and continual modification 

and movement of materials by winds, 

waves, rain, snow, river discharge, and 

the force of gravity. The watershed has 

also been modified by human activity, 

most notably from the two large dams 

that prevent sediment movement 

down the river. Less obvious, but also 

important, are the numerous human 

alterations to the river channel.

This chapter introduces the 

geomorphic setting of the Elwha 

River and its coast, explores the recent 

history of the Elwha River and its delta, 

and describes the effects that human 

intervention has had on these systems. 

This geomorphic framework will help 

track future changes to this system after 

the dams are removed.

Geologic Setting 

Tectonics

The steep and glaciated Olympic 

Mountains include some of the highest 

coastal peaks along Cascadia and 

form the headwaters of the Elwha 

River drainage basin. These mountains 

were formed by the convergence of 

the oceanic Juan de Fuca plate with 

the continental North American plate 

through the Cascadia subduction zone 

(fig. 3.1). As the Juan de Fuca plate 

converged with the North American 

plate at a rate of approximately 

43 mm/ yr, part of the oceanic rocks 

and sediments accreted onto the front 

of the North American plate rather 

than subducting under it. The Olympic 

Mountains are the highest part of this 

“accretionary wedge” of marine rocks 

that spans the majority of the Cascadia 

subduction zone (fig. 3.1). 

Evidence for the accretion of 

marine rocks abounds throughout the 

mountainous terrain of the Olympic 

Peninsula, where the primary rock 

types are slightly altered sedimentary 

(that is, “metasedimentary”) rocks 

that originated underneath the seafloor 

(fig. 3.2). These uplifted rocks are 

known as the Olympic subduction 

complex (OSC; Brandon and others, 

1998), which is an exposed part of 

the accretionary wedge that underlies 

most of the offshore continental margin 

(Stewart and Brandon, 2004). The 

deformed phyllites and schists that make 

up the OSC were originally deposited on 

the seafloor in Eocene to Miocene time 

(55.8 to 5.3 million years before present 

[BP]) as a result of numerous sedimentladen turbidity currents plunging down 

the continental slope into deep water 

(Orange and others, 1993; Brandon and 

others, 1998; U.S. Geological Survey 

Geologic Names Committee, 2010). 

A distinct boundary exists between 

the sedimentary rocks of the OSC and 

the Coast Range terrane (CRT; Brandon 

and others, 1998), which are sequences 

of volcanic and sedimentary rocks 

(fig. 3.2). The CRT also was formed in 

the ocean, as evidenced by its marine 

sedimentary rocks and pillow basalts, 

the latter being the result of underwater 

volcanism. The structural boundary 

between the older CRT and the OSC 

is the extensive Hurricane Ridge Fault 

and its equivalents (Tabor and Cady, 

1978; Gertsel and Lingley, 2003; 

Polenz and others, 2004). Because the 

Hurricane Ridge Fault crosses the Elwha 

River basin near Lake Mills (fig. 3.2), 

bedrock lithology of the Elwha River 

basin upstream of Lake Mills differs 

substantially from the basin downstream 

of Lake Mills. 

Over geologic time, the rocks of the 

central Olympic Mountains are uplifting 

at a rate of approximately 0.6 mm/yr 

(Brandon and others, 1998; Batt and 

others, 2001). This uplift of the Olympic 

Mountains maintains steep slopes in the 

Elwha River watershed and erosional 

processes such as rockfalls, shallow 

and deep landslides, and debris flows 

that generate substantial quantities of 

sediment for the river (Montgomery and 

Brandon, 2002; Acker and others, 2008). 

The rate of tectonic uplift in the Elwha 

River watershed decreases between 

the central Olympic Mountains and the 

coast to rates of less than 0.3 mm/yr 

(Tabor and Cady, 1978; Brandon and 

others, 1998; Polenz and others, 2004). 
Chapter 3

Geomorphology of the Elwha River and its Delta Geologic Setting 49

tac11-0558_fig3-01

Juan de Fuca 

Plate

Pacific

Plate

North

American

Plate

Spreading 

Zone

Subduction 

Zone

Arc of

Volcanoes

~43 millimeters

per year

CANADA

UNITED

STATES

BRITISH

COLUMBIA ALBERTA

WASHINGTON MONTANA

OREGON

IDAHO

NEVADA UTAH

CALIFORNIA

Basemap modified from USGS and other digital sources, 

various scales. Projection is Washington State Plane 

South, datum is North American Datum of 1983. 0 100 200 300 Miles

0 100 200 300 Kilometers

130° 125° 120° 115° 110°

51°

49°

47°

45°

43°

41°

39°

Figure 3.1 Generalized plate tectonics map of the Cascadia subduction zone of North America.
50 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

tac11-0558_fig3-02

OSC

CRT

Strait of Juan de Fuca

Hood Canal

PA

CIFIC

O

C

EA

N

Vancouver Island

Mt

Olympus

E

wl ha River Ewl ha River

124° 123°

48°

47°

30'

Basemap modified from USGS and other digital data sources, 

various scales. Projection is Washington State Plane South, 

datum is North American Datum of 1983. 0 10 20 30 Miles

0 10 20 30 Kilometers

Lithology

EXPLANATION

Glaciers

Intrusive

Sedimentary

Unconsolidated

Volcanic

Maximum extent of 

ice sheets

Hurricane Ridge Fault 

and its equivalents

Figure 3.2 Generalized geological map of the Olympic Peninsula, Washington. The fault between the Olympic subduction 

complex (OSC) and the Coast Range terrane (CRT; Brandon and others, 1998) is shown with a green line. Maximum extent of 

the most recent Cordilleran ice sheet was to the north and east of the blue line. Map created after Tabor (1987), Brandon and 

others (1998), and Schuster (2005).
Chapter 3

Geomorphology of the Elwha River and its Delta Lower Elwha River Morphology 51

Glacial Processes During the 

Quaternary Period

Profound new forces at the close of 

the Pliocene (approximately 2.6 million 

years ago) shaped the uplifted rocks 

of the Olympic Mountains. Sweeping 

down from their northern source in the 

highlands of British Columbia, massive 

continental ice sheets buried the Puget 

Sound and its margins. At the same time, 

valley glaciers sourced in the hinterlands 

of the Olympic Mountains carved out 

deep U-shaped troughs in the valleys 

(Easterbrook, 1986; Batt and others, 

2001; Mosher and Hewitt, 2004). In the 

most recent glacial episode, these valley 

glaciers reached their maximum extent 

at about 19,000 years BP (Easterbrook, 

1986), before being overridden at their 

margins by the ice sheets advancing 

from the north. At about 14,000 years 

BP, the continental ice sheet reached 

its maximum extent, approximately 

11 km inland of the present coastline 

in the region of the lower Elwha River 

watershed (fig. 3.2). The maximum 

thickness of the ice sheet has been 

estimated to be 1,900 m in the central 

Strait of Juan de Fuca (McNulty, 1996; 

Porter and Swanson, 1998; Mosher and 

Hewitt, 2004; Polenz and others, 2004).

The weight of the ice sheet depressed 

the land surface, sinking the ground 

surface almost 150 m in the region of 

the Strait (Mathews and others 1970; 

Waitt and Thorson, 1983; Dethier and 

others, 1995; Huntley and others, 2001). 

The land surface rose quickly as the 

ice retreated northward toward Canada, 

recovering much of its former elevation 

after about 2,000 years. 

Remnants of the ice age persist 

today as small alpine glaciers around 

Mount Olympus (fig. 3.2). Additional 

evidence of the ice age is scattered 

widely across the Olympic Mountains, 

particularly where the Juan de Fuca 

continental ice lobe repeatedly 

dammed the waters of the Elwha River 

watershed, creating a lake in the lower 

Elwha River watershed. Sediment 

deposits from this pro-glacial lake, with 

poorly sorted, poorly stratified glacial 

outwash alluvium and stratified sediment 

dominated by silt and clay, are visible 

today in bluff exposures along the lower 

Elwha River and may represent the most 

substantial modern sources of sediment 

downstream of Elwha Dam (Tabor, 

1975, 1987; McNulty, 1996; Polenz and 

others, 2004). 

Profile of the Elwha River 

Wherever the waters of the Elwha 

River cross over the hard, folded rocks 

of the ancient accretionary wedge, 

the river is confined within bedrock 

canyons. Between these canyon 

segments, wide valleys of alluvium 

create conditions for active bank 

erosion and frequent channel migration 

(Kloehn and others, 2008; Draut and 

others, 2011). The longitudinal profile 

of the Elwha River is steepest in the 

headwaters and flattest near sea level 

(fig. 3.3). Below approximately 600 m 

elevation, the slope of the Elwha 

River is roughly constant at about 

0.009 until the Lake Mills delta. There 

are short, steeper reaches within the 

Grand Canyon of the Elwha River and 

Rica Canyon, where the river slope 

increases to about 0.006. Between 

Glines Canyon Dam and the coast, the 

river slope decreases to an average of 

approximately 0.0013, and the flattest 

part of the river is immediately upstream 

of the river mouth (fig. 3.3). The two 

reservoirs formed by Glines Canyon 

Dam and Elwha Dam create prominent 

steps in the longitudinal water surface 

profile, which will be removed through 

the lowering of the reservoirs and the 

erosion of sediment that should follow 

dam removal. 

Lower Elwha River 

Morphology 

The final 7.8 kilometers of the river 

between the Elwha Dam and the Strait 

of Juan de Fuca is the flattest reach and 

is termed the “lower river” (fig. 3.4). 

This final reach is the most heavily 

altered reach of the river and will 

experience the largest effects of renewed 

sediment supply following dam removal 

(Draut and others, 2008; Konrad, 2009). 

The upper 1.3 km of the lower 

river lies within a bedrock gorge, 

and the lowermost 6.5 km is within 

a broad alluvial flood plain (fig. 3.4). 

The river channel splits into two to 

three narrower channels for much 

of the alluvial section, a planform 

morphology called “anabranching” 

(compare to Smith and Smith, 1980; 

Harwood and Brown, 1993; Knighton 

and Nanson, 1993). Gravel bars and 

vegetated islands separate these narrow 

channels (Pohl, 1999, 2004; Draut and 

others, 2008; Kloehn and others, 2008). 

Unconsolidated sediment of these bars 

and islands contains large proportions 

of reworked glacial materials that are 

poorly sorted and have grain sizes 

ranging from silt and clay to cobbles 

(Draut and others, 2011). 

An anabranching river such as 

the lower Elwha is understood to 

be distinctive from single-channel 

meandering rivers and braided rivers 

but has elements of both (fig. 3.5). 

Islands in anabranching rivers can be 

large relative to the width of the channel 

and commonly are stable over decades 

and even centuries. Individual channels 

meander or may exhibit smaller-scale 

braiding but eventually rejoin together 

(Knighton, 1998). Processes that cause 

anabranching are not fully understood. 
52 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Figure 3.3. Longitudinal profile of the water-surface elevation of the main-stem Elwha River calculated from a 10-meter digital 

elevation model of the Olympic Peninsula, Washington.

tac11-0558_fig3-03

Base map modified from USGS and other digital sources, 

various scales. Projection is Washington State Plane 

South. Datum is North American Datum of 1983.

Glines

Canyon

Dam

Elwha

Dam

0

200

400

600

800

1,00

1,200

1,400

1,600

River kilometer, from the mouth

Glines Canyon

Strait of

Ju

an

de

Fu

c

a

Olympic

National Park

boundary

Carlson Canyon

Grand Canyon

Rica Canyon

Water-surface elevation of Elwha River, in meters above 

North American Vertical Datum of 1988

80 70 60 50 40 30 20 10 0

0

0 5 10 Miles

5 10 Kilometers

N

47°45’ 48°

123°

45’

123°

30’
Chapter 3

Geomorphology of the Elwha River and its Delta Lower Elwha River Morphology 53

tac11-0558_fig3-04

123°35' 123°34' 123°33' 123°32'

48°

09'

48°

08'

48°

07'

48°

06'

EXPLANATION

414

0

Elevation, in meters above 

the North American 

Vertical Datum of 1988

0 0.5 Mile

0 0.5 Kilometer

Elwha Dam

Freshwater Bay

Strait of Juan de Fuca

Lake Aldwell

N

Figure 3.4. Topography of the flood plain and delta of lower Elwha River, Washington. Lidar survey dated 

between April 4 and 6, 2009, by Terra Remote Sensing, Inc. Horizontal resolution is 1.8 meters.
54 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

The total number of channels along 

a cross-section of the lower Elwha River 

varies between one and three. Large 

islands between the channels can be 

many times wider than the individual 

channels themselves and can persist for 

decades (Draut and others, 2008, 2011). 

The lower Elwha River is similar in 

size, shape, slope, and discharge rates 

to other anabranching rivers of the 

western Washington region described 

by Beechie and others (2006) (fig. 3.6), 

which suggests that this morphology 

is not unique for the region. The flood 

plain and islands of the lower Elwha 

River are heavily wooded. Initially these 

landforms are vegetated by alder and 

cottonwood trees, and older surfaces 

abound with secondary successional 

trees including spruce, hemlock, and 

cedar (for example, Beechie and others, 

2006; Kloehn and others, 2008). 

tac11-0558_fig3-05

Meandering

Anabranching

(Island-braided) Braided

EXPLANATION

Trees and shrubs

Woody debris

Figure 3.5. Schematic diagrams showing channel planforms for meandering to braided geomorphic types. The lower Elwha River is 

characterized as anabranching, which has characteristics of meandering and braided systems.

Figure 3.6. Comparison of the channel form of the lower Elwha River 

to 42 river reaches from other rivers in western Washington. Slope in 

the average slope of the river section and discharge is calculated as the 

2-year peak discharge which represents an approximation of bankfull flow. 

Adapted from Beechie and others (2006).

Discharge of the 2-year event, in cubic meters per second

Slope, in meters per meter

1

0.1

0.01

0.001

0.0001

10 100 1,000 10,000

EXPLANATION

Elwha River

Braided

Island-braided

Meandering

Straight
Chapter 3

Geomorphology of the Elwha River and its Delta Lower Elwha River Morphology 55

Figure 3.7. Historical changes in the location of the channel 

midline, Elwha River, Washington, during 1939–1971 and 1977–

2008. The dominant channel was mapped in reaches where 

multiple channels were present (after Draut and others, 2011). 

Four historical changes to the lower river thalweg are described 

the text and labeled with A–D. 

Historical Channel Changes in the Lower River

Draut and others (2008, 2011) used 14 sets of sequential 

aerial photographs obtained between 1939 and 2009 to 

document historical changes to channel position and 

morphology in the lower Elwha River. The photographs 

provided evidence of effects from large floods and human 

modifications of the flood plain. Changes were greatest along 

the lowermost 3 km of the river, where absolute changes 

in the channel position between 1939 and 2009 averaged 

approximately 160 m and in some places measured as much as 

660 m (Draut and others, 2011). 

The centerline of the main channel has moved laterally in 

time due to the erosion of channel banks and the avulsion of 

new channels (fig. 3.7; Draut and others, 2011). Although new 

channels can form rapidly in response to high flow events or 

human modifications, the older “abandoned” channels often 

appear to be active (unvegetated) for several years after the 

avulsion, even though they receive little flow. 

A few of the channel changes between 1939 and 2009 

in the lowest part of the Elwha River are highlighted in 

figure 3.8. Most notably the two major active channels 

observed in the 1939 photograph were reduced to only one 

by 1965 (fig. 3.8). Dike construction in 1950 (Pohl, 1999) led 

to the abandonment of river flow into the formerly dominant 

eastern channel, although this eastern channel remained 

open to coastal waters for many years, as seen in the 1956 

photograph (fig. 3.8B, see also fig. 3.7A). By 1965, the mouth 

of the abandoned eastern channel was closed (fig. 3.8C); this 

former channel became coastal lakes and wetlands that have 

served as salmonid rearing habitats or high-flow refugia when 

hydraulically connected to the river. The 1965 photograph also 

shows the effects of levee construction on the western side of 

the river mouth and straightening of the channel sponsored 

by Clallam County in 1964 (fig. 3.8C). This western levee 

redirected the river toward the north and cut off Dudley Pond 

from river and tidal flow. 

Following construction of the 1964 west levee, the 

channel began to meander in the lowest 3 km (“C” in fig. 3.7). 

The rate of lateral channel migration in the final river 

meander has been measured at several meters per year from 

topographic surveys and aerial photographs (fig. 3.9). Most 

channel movement occurs during high flows of winter, and 

negligible channel change is observed during the summer. 

tac11-0558_fig3-07

1939-1971 1977-2008

EXPLANATION

1939

1956

1965

1971

1981

1990

1994

2000

2002

2005

2006

2008

EXPLANATION

1977

A

C

D

B

0 1 Mile

0 1 Kilometer
56 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

tac11-0558_fig3-08

123°34'

48°

08'

30"

123°33'30"

48°

09'

123°34'

48°

08'

30"

123°33'30"

48°

09'

123°34'

48°

08'

30"

123°33'30"

48°

09'

123°34'

48°

08'

30"

123°33'30"

48°

09'

0 300 600 Feet

0 100 200 Meters

A. B.

C. D.

1939 1956

1965 2006

Levee (1985)

Levee (1964)

Abandoned

channel

Dudley

Pond

Figure 3.8. Aerial photographs showing effects of human modifications and channel meander and avulsion 

changes in the mouth of the Elwha River, Washington, between 1939 and 2006. (After Draut and others, 2008.)
Chapter 3

Geomorphology of the Elwha River and its Delta Lower Elwha River Morphology 57

tac11-0558_fig3-09

0

Distance across channel, in meters

0

-1.0

-0.5

0.5

1.0

1.5

2.0

2.5

3.0

3.5

20 40 60 80 100 120

Elevation, in meters above North American

Vertical Datum of 1988

EXPLANATION

Sept. 2006

Apr. 2007

Sept. 2007

Apr. 2008

Figure 3.9. Measured channel change on the final meander showing several meters of lateral 

migration per year of the lower Elwha River, Washington. (After Draut and others, 2010.)

During the winter high flows between 1994 and 2000, 

an avulsion formed a new westernmost channel in the Elwha 

River; this new channel has been referred to as the Hunt 

Road Channel (“D” in fig. 3.7). A large flood in December 

2007 broadened this new channel, after which most of river 

discharge flowed down the Hunt Road Channel (fig. 3.10). 

This 2007 flood also downed hundreds trees that accumulated 

in woody debris piles throughout this reach (fig. 3.11). 

Several other human modifications have been made to 

the lower Elwha River during the 20th century. Additional 

modifications include the following: 

1. Repeated bulldozing of channel boundaries by privateparty landowners between the 1950s and 1980s;

2. Excavation of a north-trending artificial meander cutoff by 

Clallam County in 1947 to reduce the flood risk east of the 

natural (eastward migrating) meander (“B” in fig. 3.7);

3. Construction of a levee that is set back from the river on 

its east side by the U.S. Army Corps of Engineers in 1985 

(fig. 3.8D);

4. Construction of an outfall channel leading from the tribal 

fish hatchery to the main river channel;

5. Construction of a weir and diversion channels for near 

the State-run fish hatchery about 4.5 km upstream of the 

river mouth (Johnson, 1994; Pohl, 1999; Draut and others, 

2008); and

6. Restoration of in-stream habitat by the Lower Elwha 

Klallam Tribe primarily through the placement of large 

woody debris in channels (see sidebar 3.1).
58 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Figure 3.10. Historical aerial photographs showing a major channel avulsion in the lower Elwha River, Washington, 1994 and 2006.

tac11-0558_fig3-10

0 100 200 Meters0 300 600 Feet

123°33' 123°33'30" 123°33' 123°33'30"

48°08'

48°08'

1994 2006

Area of 

detail

t nu H s oR ad

Channel
Chapter 3

Geomorphology of the Elwha River and its Delta Lower Elwha River Morphology 59

Figure 3.11. Woody debris resulting from channel avulsion in 

the lower Elwha River, Washington. Flow direction is from the 

top to the bottom of the photograph. The avulsion point is shown 

at the top of the photograph. (Photograph taken by Tom Roorda, 

Northwestern Territories, Inc., April 4, 2007.)

Current Sediment Supply to the Lower River

For almost 100 years, the Elwha River dams have 

captured all upper-watershed sand and gravel before it could 

reach the lower river, leading to bed armoring and coarsening 

in the lower river (Pohl, 2004; Kloehn and others, 2008; 

Curran and others, 2009; Draut and others, 2011). In the 

absence of this supply, bank erosion of older fluvial or glacial 

deposits constitutes the primary supply of coarse sediment to 

the lower river. We know of no estimate of the amount of this 

sediment recruited by bank erosion and channel migration, 

although research on other rivers demonstrates this process 

can be important for sediment supply (Collins and Dunne, 

1989; Martin and Church, 1995; Wallick and others, 2009).

Figure 3.12. Large bluff immediately upstream of the mouth of 

the Elwha River, Washington. This bluff has eroded substantially 

during the past several decades, and it may be a primary source 

of sediment to the lower river and littoral cell. (Photograph taken 

by Amy E. Draut, U.S. Geological Survey, September 8, 2008.)

Lateral erosion of the river into a 38-m-high bluff of 

glacial till immediately upstream of the river mouth may 

contribute an important input of bed material (fig. 3.12). 

Using repeat aerial photography (fig. 3.8), Draut and others 

(2008) showed that this bluff retreated about 70 m between 

1965 and 2006. Extrapolated to the full 310 m bluff length, 

this retreat would have contributed about 820,000 m3 during 

these 41 years, which is equivalent to an annual rate of about 

21,000 m3/yr. 

The final potential sources of sediment to the lower 

watershed are the drainage area and the small tributaries 

that drain directly into the lower river. Most of this lower 

catchment area is privately owned and used for wood 

production, small farms, and open space, and little information 

is available about the rates and patterns of sediment 

contributions from this lower landscape. 
60 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

The construction of the Elwha and Glines Canyon Dams in the 

Elwha River in the early 20th century prevented fish migration 

and captured sediment and wood that previously helped form 

and maintain the ecosystem of the river flood plain. Downstream 

of the dams, these effects were magnified by flood plain logging, 

removal of logjams, and channelization, activities that were 

common practice in western Washington rivers. As a result of 

the cumulative effects of dam construction and historical flood 

plain management practices, habitat conditions for anadromous 

salmon in the lower river are degraded. For instance, the lower 

river has incised into its river bed, lost suitable-sized spawning 

gravels, increased in temperature, lost connectivity with parts of 

its flood plain, and lost habitat complexity.

Although dam removal will assist with correcting many of the 

ecological problems besetting the Elwha River and its imperiled 

salmon populations, it will not immediately correct the degraded 

flood plain habitats of the lower river. In an effort to improve 

flood plain habitats in the Elwha River prior to dam removals, the 

Lower Elwha Klallam Tribe has been conducting numerous flood 

plain restoration actions, which include removing unneeded 

dikes, installing dozens of engineered log jams throughout the 

channel and flood plain, correcting fish migration barriers, 

planting thousands of native trees and shrubs, and controlling 

the spread of exotic vegetation (figs. S3.1.1 and S3.1.2). The 

restoration efforts are designed to maximize potential habitat 

areas that can accommodate all the sediment that will be 

released by dam removal. For example, dike removals increase 

flood plain capacity and allow the river to occupy areas currently 

inaccessible to habitat forming processes.

Engineered log jams (ELJs) are designed to mimic the 

natural architecture of large, stable logjams that are critical to 

anastomosing of forested island channel morphology commonly 

found in large western Washington rivers. ELJs at the river reach 

level may be used to promote island formation, to activate side 

channels (in conjunction with dike removals), and reduce flow 

velocities. ELJs also promote habitats that are used heavily by 

adult and juvenile salmonids of all species. ELJs typically develop 

large, complex scour pools that interact with groundwater 

to provide the cool temperature refugia preferred by salmon. 

Monitoring has shown that these habitats contain 2–6 times as 

many juvenile salmon as similar habitats without complex wood 

structures.

Efforts to revegetate the flood plain have focused on 

previously disturbed areas in the flood plain that were either 

open or lightly vegetated. Elevation models and existing tree 

height data obtained by lidar were used to identify areas for 

planting a mixture of native coniferous and deciduous trees. 

More than 20,000 trees and shrubs have been planted in this 

effort. Concurrently, the tribe has been aggressively controlling 

non-native exotic vegetation that has invaded the flood plain.

Figure S3.1.1. Newly constructed engineered log jam on 

the Elwha River, Washington during winter flooding 2009. This 

structure is one of 50 that the Lower Elwha Klallam Tribe has 

installed in the lower Elwha River prior to dam removal.

Figure S3.1.2. Newly activated flood plain overflow channel 

during the first winter following removal of a 1,500 foot flood plain 

dike on the Elwha River, Washington, 2009.

Sidebar 3.1 Flood Plain Restoration in the Lower Elwha River

Michael L. McHenry, Habitat Manager, Lower Elwha Klallam Tribe
Chapter 3

Geomorphology of the Elwha River and its Delta Coastal Morphology 61

Coastal Morphology

The Elwha River delta (fig. 3.13) is a wave-dominated 

deltas within the broader Puget Sound region (Shipman, 

2008; Warrick and others, 2009a). The morphology of 

wave-dominated deltas are controlled largely by littoral 

redistribution of river sediment. Waves at the Elwha River 

delta arrive from the west, and these waves induce littoral 

currents and sediment transport toward the east (toward Ediz 

Hook), as described in Warrick and others (2011, chapter 5, 

this report). 

Glacial processes have carved irregular shoreline shapes 

into the entire coastline of Puget Sound and deposited the 

coarse sediments that compose the beaches (Finlayson, 2006; 

Shipman, 2008). The Elwha River delta is different from inner 

Puget Sound beaches and deltas, however, because it is subject 

to waves from the Pacific Ocean. As shown below, these 

Pacific-derived waves—in addition to sea level and fluvial 

histories—are important characteristics that define the Elwha 

River coastal morphology. The Elwha River delta is lobate in 

shape and its beaches are composed largely of gravel, with 

some sand. These beaches have been eroding quickly during 

the past 80 years, a phenomenon which appears to be related to 

the loss of sediment supply caused by the Elwha River dams. 

The rapid erosion of the beaches is causing a distinct erosional 

morphology on the shoreline of the Elwha River delta. 

Sea-Level History

The shoreline of the Elwha River delta has moved more 

than 100 m in elevation over glacial time as a result of the 

rises and falls in the global (or “eustatic”) sea level that have 

resulted from varying quantities of ice storage, fluctuations 

in ocean water temperature, and the rising and falling of the 

Earth’s crust as it shifts under the weight of glacial ice sheets. 

With the retreat of the Juan de Fuca Lobe of the continental 

ice sheet approximately 14,000 years BP, the Strait of Juan de 

Fuca filled with seawater. Mosher and Hewitt (2004) detailed 

the subsequent sea-level history for the Strait of Juan de Fuca, 

and this record is compared graphically to the global eustatic 

sea level shown in figure 3.14. At the time of the ice sheet 

retreat, the eustatic sea level was approximately 70 m below 

current (2011) levels because of the tremendous amount of 

water trapped in the world’s ice sheets (fig. 3.14). In contrast, 

the relative sea level in the Strait of Juan de Fuca at this same 

time was approximately 50–75 m higher than the current 

levels, as evidenced by high altitude carbon-14 (14C) dated 

marine sediments (Matthews and others, 1970; Waitt and 

Thorson, 1983; Dethier and others, 1995; Huntley and others, 

2001). The approximately 150 m difference between the 

tac11-0558_fig3-13

East Beach

River Mouth

Bar

West Beach

Figure 3.13. The mouth and delta shoreline of the Elwha River, 

Washington. (Photograph taken by Ian M. Miller, University of 

California, Santa Cruz, February 12, 2005, at 11:24 Pacific standard 

time)

Elevation, in meters above North American Vertical Datum of 1988

100

50

0

16 14 12 10 8 6 4 2 0

-50

-100

Age, in thousand years before present

Strait of

Juan de Fuca

Global

Figure 3.14. History of relative sea level for the Strait of 

Juan de Fuca off the coast of Washington (after Mosher 

and Hewitt, 2004). The global eustatic sea level curve 

(Global) is based on Peltier (2002).
62 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

global eustatic and the regional Strait of 

Juan de Fuca sea levels resulted from the 

depression of the Earth’s crust under the 

thick ice sheet that covered the region.

The high-stand of relative sea 

level within the Strait of Juan de Fuca 

was short-lived, however, because the 

crust rebounded upward at rates much 

faster than the eustatic changes in 

sea level. This rebound induced rapid 

falling of relative sea level in the Strait, 

which reached an absolute minimum of 

approximately -55 m at about 10,500 

years BP (Mosher and Hewitt, 2004; 

fig. 3.14). Following this minimum in 

sea level, changes in relative sea level 

have resulted from the combined effects 

of eustatic and glacial-isostatic changes. 

The eustatic changes brought relative 

sea level approximately to its present 

height at ca. 6,000 years BP, after which 

relative sea level has been relatively 

constant compared to the fluctuations 

between 6,000 and 14,000 years BP 

(fig. 3.14). Although the eustatic sea 

level has increased about 1.7 mm/yr 

over the past century (Intergovernmental 

Panel on Climate Change, 2007), the 

relative sea level changes in the region 

of the Elwha River have been negligible 

because of the continued uplifting of the 

landscape. This differs from the inner 

Puget Sound where relative sea level has 

been rising at about 2.0 mm/yr, and the 

outer coast where relative sea level has 

been falling at about 1.6 mm/yr during 

the past century (National Oceanic and 

Atmospheric Administration stations 

9447130, Seattle and 9443090, Neah 

Bay). 

Coastal Evolution Since the 

Pleistocene Time

The dynamic sea level following 

the most recent ice sheet retreat left clear 

imprints on the landscape of the Strait 

of Juan de Fuca. The transgression (or 

rising) of sea level in the Elwha River 

delta region started about 10,500 years 

BP and was followed by relative sea 

level stability since about 6,000 years 

BP. This transgression left the most 

defining physical features on the 

shoreline and submarine (or underwater) 

landscape. Coastal bathymetric 

surveys have identified a broad terrace 

extending several kilometers offshore 

of the present day Elwha River delta 

(fig. 3.15). This feature is an ancient 

delta that was built during the lowest sea 

levels, and three drowned littoral spits 

appear along its eastern edge (I–III in 

fig. 3.15). Such spits are built out at the 

termination of littoral sediment cells, 

and the presence and location of these 

drowned spits suggest that the shoreline 

position of the Elwha River delta was 

3–5 km offshore of the present shoreline 

during lower sea levels (Galster and 

Schwartz, 1990; Mosher and Hewitt, 

2004). Furthermore, these drowned spits 

step up in elevation from -25 m for the 

farthest offshore spit (I), to -8 and -6 m 

for spits II and III, respectively (Mosher 

and Hewitt, 2004). The consistent 

orientation of the drowned spits and 

Ediz Hook (spit labeled IV in fig. 3.15) 

indicates that transport of sediment 

along this shoreline has consistently 

been toward the east, which is in the 

same direction of littoral currents from 

the waves of the Pacific Ocean (see 

Warrick and others, 2011, chapter 5, this 

report). One hypothesis is that as relative 

sea level rose between approximately 

10,500 and 6,000 years BP, the delta 

shoreline was eroded inland at an 

average rate of about 0.7 m/yr (Galster 

and Schwartz, 1990). During at least 

three episodes of this transgression, the 

terminal spit was abandoned and a new 

spit was formed farther upslope. 

The present-day Elwha River 

delta has a lobate planform centered 

on the river flood plain (fig. 3.15). 

This geomorphic shape suggests that 

either the presence of the flood plain, 

or discharge of sediment from the river, 

has defined this sinuous morphology 

of the delta. One leading hypothesis 

holds that this sinuous form did not 

result solely from river depositional 

patterns but rather from a combination 

of sediment supply from the river 

that kept the position of the delta’s 

shoreline relatively steady during the 

past 6,000 years, coupled with more 

than 1 km of erosion of the adjacent 

coastal bluffs on both sides of the 

delta during the past 6,000 years 

(equivalent to an average erosion rate 

of 0.2 m/yr; Galster and Schwartz, 

1990). The sediment supplied by the 

combination of erosion of these coastal 

bluffs and sediment discharge from the 

river built the 5 km spit, Ediz Hook, in 

this strongly unidirectional eastward 

littoral cell (Galster and Schwartz, 

1990). The beaches of the Elwha littoral 

cell are composed of mixed sediment 

grain sizes (sand to boulder), which is 

generally consistent with many of the 

Strait of Juan de Fuca beaches, owing 

to the abundance of coarse sediment 

in the glacial landforms of the region 

(Shipman, 2008). 

Historical Shoreline Changes 

The 20th century oral histories 

from Lower Klallam Elwha Tribal 

members describe hundreds of meters 

of land lost from coastal erosion of the 

beach east of the river mouth (“east 

beach”) and a fundamental shift of the 

low-tide area of the beach from being 

favorable shellfish habitat to a cobble 

substrate poorly suited for shellfish 

habitat (Reavey, 2007; Warrick and 

others, 2009a). The changes described 

by the Lower Elwha Klallam Tribe 

are consistent with aerial-photographderived erosion rates (fig. 3.16), which 

have accelerated significantly from 

0.8 to 1.4 m/yr during 1939–90 and 

1990–2006, respectively (Warrick and 

others, 2009a). Further, this oral history 

is consistent with the current differences 

between the west beach, which has not 

changed significantly in position and 

is mostly sand and gravel, and the east 

beach, which is eroding and has a cobble 

low-tide terrace (fig. 3.17). 
Chapter 3

Geomorphology of the Elwha River and its Delta Coastal Morphology 63

tac11-0558_fig3-15

Submarine delta

I

II

III

IV

0 1 2 3 Miles

0 1 2 3 4 5 Kilometers

0

50

100

150

EXPLANATION

Map

location

Glines

Canyon

Dam

Elwha

Dam

Strait of Juan de Fuca

Olympic

National Park

boundary

Elevation, in meters below

 the North American 

Vertical Datum of 1988

Figure 3.15. Coastal bathymetry of the broad submarine delta plain, three drowned spits (I–III), and the Ediz Hook (IV), which 

represents the terminus of the current littoral cell of the Elwha River delta, Washington. Source data are a merger of Finlayson (2005), 

Cochrane and others (2008), and Warrick and others (2010). 
64 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Figure 3.17. Differences between the beach on the west and east sides of the current river mouth of the Elwha River delta, 

Washington. 

tac11-0558_fig3-16

Levee 

(1964)

Bluff Floodplain

Bluff Levee 

(1985)

Riprap

Seawall

Lower Elwha Road

Charles Road

Elwha Dike Road

Strait of Juan de Fuca

EXPLANATION

1939–1990 accretion

1900–2006 accretion

1939–1990 erosion

1990–2006 erosion

1939

1990

2006

N

Distance between lines 

indicates the maximum 

change uncertainty

0 1,000 Meters

0 3,000 Feet

Map source is aerial photographs described 

in Warrick and others (2009a).

Glines

Canyon

Dam

Elwha

Dam

Strait of Juan de Fuca

Olympic

National Park

boundary

Map

location

Figure 3.16. Shoreline change of the Elwha River delta, Washington, between 1939 and 2006. (After Warrick and others, 2009a.)

Mixed sediment 

foreshore

Cobble

low tide terrace 

A. West beach–steep and cuspate B. East beach–cobble low tide terrace
Chapter 3

Geomorphology of the Elwha River and its Delta Coastal Morphology 65

Historical changes to the position of the river and the 

shoreline also are largely responsible for the formation and 

destruction of the coastal wetlands near the river mouth. 

The series of aerial photographs, shown in figure 3.8, shows 

how abandoned river channels become coastal lakes and 

estuarine channels once the river changes course. Erosion of 

the shoreline commonly pushes some sand and gravel inland 

Figure 3.18. Aerial photographs of historical changes from shoreline erosion and overwash 

deposition resulting in coastal wetland loss in the eastern Elwha River delta, Washington. (After 

Warrick and others, 2009a). 

2006

Smaller lake

Exposed low-tide terrace

Overwash 

deposits

Treeless beach

Overwash 

deposit

Coastal lake

Coastal lakes

Tree-backed beach

0 400 Feet

0 100 Meters

1990

N

over the beach berm, into sediment lobes termed “overwash 

deposits” (fig. 3.18). These overwash deposits decrease the 

size of coastal lakes and estuarine channels by filling the water 

body with sediment (fig. 3.18). Thus, coastal erosion, which 

has been considerable since the dams have been in place, has 

resulted in wetland loss around the Elwha River delta. 
66 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Recent Coastal Monitoring 

In response to the ongoing retreat of the Elwha River 

delta shoreline and because of the potential for restoration 

of this shoreline following dam removal, the Lower Elwha 

Klallam Tribe, the U.S. Geological Survey (USGS), and the 

Washington State Department of Ecology have collaborated on 

a coastal monitoring program since 2004. One of the primary 

tools used in this monitoring is high-resolution topographic 

surveying with real time kinematic global positioning systems 

(RTK-GPS). These RTK-GPS surveys require several scientific 

technicians to hike GPS receivers across the beach to measure 

topography and to drive small vessels with receivers and 

echo sounders through the coastal waters to measure seafloor 

bathymetry (fig. 3.19). The use of these surveying techniques 

results in high-resolution topographic maps of the study area 

(fig. 3.20) that can be used to detect change (Warrick and 

others, 2010). 

A. B.

Figure 3.19. Topographic and bathymetric surveys using real time kinematic global positioning system (RTK-GPS) from (A) hiked 

backpack systems and (B) personal watercraft with integrated echo sounders along the of the Elwha delta coast, Washington. 

These surveys show that the beaches of the Elwha 

River delta can be divided into three sections: (1) the steep, 

cuspate beach west of the river mouth (“west beach”); (2) the 

dynamic river mouth; and (3) the erosional beach east of the 

river mouth that has a distinct cobble low-tide terrace (“east 

beach”). The cuspate, west beach has changed little in position 

over the recent monitoring period (figs. 3.21 and 3.22), which 

is consistent with the historical analysis of this beach from 

aerial photographs discussed above. The east beach has eroded 

rapidly with a shoreward movement of the beach profile 

(figs. 3.21 and 3.22). The low-tide terrace portion (below 

approximately 1 m elevation NAVD 88) of the east beach 

is much more stable (fig. 3.21). The net effect of shoreline 

erosion of the east beach is landward movement of the beach 

face and broadening of the low-tide terrace. The cobble-faced 

low-tide terrace of the east beach is an armored portion of 

the beach resulting from beach erosion (Warrick and others, 

2009a). 
Chapter 3

Geomorphology of the Elwha River and its Delta Coastal Morphology 67

tac11-0558_fig3-20

Glines

Canyon

Dam

Elwha

Dam

Strait of Juan de Fuca

Olympic

National Park

boundary

Map

location

0 2,000 4,000 Feet

0 500 1,000 Meters

Elevation, in meters above North American Vertical Datum of 1988

-10 -5 0 5

EXPLANATION

Strait of Juan de Fuca

Elwha River Elwha River

Aerial photography from USDA - NAIP, 2006. Bathymetric data from 

Warrick and others (2010). 

Figure 3.20. Topography and bathymetry from real time kinematic global positioning 

system (RTK-GPS) surveys of the Elwha River delta, Washington, during summer 2008. 

(Aerial photography from the U.S. Department of Agriculture National Agriculture Imagery 

Program (NAIP) survey of 2006.) 
68 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Figure 3.21. Example beach topographic profiles for the west and 

east beaches of the Elwha River delta, Washington, from surveys 

by the U.S. Geological Survey. The west beach has been relatively 

stable over time, whereas the east beach has eroded substantially. 

tac11-0558_fig3-21

0

2

4

6

West

-25 0 25 50 75 100

-25 0 25 50 75 100

East

Cross−shore distance, in meters

Cross−shore distance, in meters

Elevation, in meters above North American

Vertical Datum of 1988

0

2

4

6

Elevation, in meters above North American

Vertical Datum of 1988

EXPLANATION

Mar. 2005

Sept. 2005

Apr. 2006

Sept. 2006

Apr. 2007

Sept. 2007

Aug. 2008

Sept. 2009

tac11-0558_fig3-22

Elwha River

Strait of Juan de Fuca

Two-year change in mean high

water, in meters

> -20

-20 to -15

-15 to -10

-10 to -5

-5 to -1

-1 to 1 (No data)

1 to 5

Erosion

EXPLANATION

Accretion

0 1,000 Meters

0 3,000 Feet

Data source is the analyses of Warrick 

and others (2009a) from the data of 

Warrick and others (2010).

N

Glines

Canyon

Dam

Elwha

Dam

Strait of Juan de Fuca

Olympic

National Park

boundary

Map

location

Figure 3.22. Shoreline change along the beaches of the 

Elwha River delta, Washington, during 2004–06 from real time 

kinematic global positioning system (RTK-GPS) surveys. 

(After Warrick and others, 2009a.)

The most dynamic part of the Elwha River delta shoreline 

is the river mouth, which is influenced by tidal flow, river 

discharge, and waves that move and reorganize sediment 

around the river mouth. Evidence of these changes comes 

from 3 years (2007–09) of topographic surveys in and around 

the river mouth (fig. 3.23). It is important to note that these 

surveys suggest that the river mouth region gained significant 

volumes of sediment in the time between the surveys 

(approximately 34,000 m3 in 2007–08 and approximately 

21,000 m3 in 2008–09), even though the east beach underwent 

net erosion during the same time. These results suggest that 

the river is still contributing significant amounts of sediment to 

the coastal system (a conclusion which is consistent with the 

observations of Draut and others, 2011) and that much of the 

fluvial sediment in the delta is emplaced in the bar of the river 

mouth. 
Chapter 3

Geomorphology of the Elwha River and its Delta Coastal Morphology 69

Removal of the Elwha River dams will release large volumes of sediment into the 

lower Elwha River and the Strait of Juan de Fuca. We expect this flood of sediment 

to modify coastal landforms by accretion and to change fluvial and coastal habitat 

substrate from coarse to fine sediment. Simultaneous tracking of topographic change 

and sediment size may allow for the development of models for these changes that 

could be used for future restoration projects. Traditional methods for grain size 

analysis – including pebble counts and physical sampling – are labor intensive and 

costly. The use of digital photography alleviates many of these problems by providing 

a rapid sampling of the land or seafloor surface (Adams, 1979). The USGS has been 

developing and using digital photographic methods for the Elwha River study area 

since 2004 to assist in tracking the changes induced by dam removal.

To sample grain size on the beach or a river bar, photographs were taken at regular 

intervals across these landforms. Photographs must be taken orthogonally to the 

ground surface to limit distortion of surface features. Traditionally, the calculation 

of grain size parameters for each photograph was obtained from manual sizing and 

counts from each photograph, which required 1–2 hours of analysis time for each 

photograph. New methods suggested by Rubin (2004) have significantly shortened 

analysis time owing to an automated calculation of grain size based on spatial patterns 

in each photograph. These “cobble cam” techniques were applied to the Elwha River 

flood plain and coastal landforms by Warrick and others (2009b) with excellent results. 

Photographic sampling from Elwha River landforms show a broad diversity in grain size 

and sorting (fig. S3.2.1). Comparisons of the automated analyses with physical samples 

of the substrate show that errors in the analyses are only 14 percent, which are more 

than adequate to characterize the differences prevalent in these landforms. There 

are significant differences in the grain sizes across river bars, beach cusps, and the 

low-tide terrace to foreshore transition (see fig. S3.2.2). The successful development 

and implementation of these methods should allow for the quantification of changes 

throughout the Elwha River landforms as they occur in the future.

Sidebar 3.2 Mapping Grain Size with Digital Photos

Jonathan A. Warrick

tac11-0558_fig3-2-1

0 100 millimeters

0 100 millimeters

0 100 millimeters

A.

B.

C.

0 10 20 30 40 50 60

0

1

2

3

Cross-shore distance, in meters

Elevation, in meters above 

Mean Lower Low Water

Mean grain size, in

millimeters

Foreshore

LTT

1

16

256

8

64

EXPLANATION

Figure S3.2.1 Examples of a range 

in grain size from (A) cobble (C) 

sand of the Elwha River delta beach, 

Washington. (After Warrick and others, 

2009b). 

Figure S3.2.2 Example results of the mean sediment grain size from Cobble Cam 

photographic analyses across the east beach of the Elwha River delta (after Warrick 

and others, 2009b). A distinct grain size change is apparent between the foreshore 

and the low-tide terrace (LTT).
70 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

tac11-0558_fig3-23

GlinesCanyonDam

ElwhaDam

Strait of Juan de Fuca

Olympic

National Park

boundary

Maplocation

N

2007 2008 2009

0

Elevation, in meters above North American

Vertical Datum of 1988

-5 5

EXPLANATION 0 300 Meters

0 1,000 Feet

Aerial photography from USDA - NAIP, 2006. Bathymetric data from Warrick and others (2010). 

Figure 3.23. Topographic and bathymetric survey maps showing the evolution and growth of the river mouth bar of the Elwha River during 2007–09. All three surveys were conducted in the late summer (August–September) each year. 
Chapter 3

Geomorphology of the Elwha River and its Delta References Cited 71

Summary

The Elwha River lies at the 

intersection of uplifting land and an 

eroding coast. In the past, movement of 

sand and gravel from the steep, eroding 

glaciated mountains provided the 

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spawning habitats for fish and provided 

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energetic waves. Humans have altered 

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Elwha River delta. 

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in the river channel, removal of dikes 

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the removal of two large dams, should 

further modify the geomorphology 

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expectation of restoring some of the 

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needed to quantify the effectiveness of 

these restoration efforts. 

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Nearshore Partnership Report No. 

2008-01, 42 p.

Smith, D.G., and Smith, N.D., 1980, 

Sedimentation in anastomosed river 

systems: examples from alluvial 

valleys near Banff, Alberta: Journal 

of Sedimentary Petrology, v. 50, 

p. 157-164.

Stewart, R.J., and Brandon, M.T., 2004, 

Detrital-zircon fission-track ages for 

the “Hoh Formation”: implications 

for late Cenozoic evolution of 

the Cascadia subduction wedge: 

Geological Society of America 

Bulletin, v. 116, p. 60-75.
Chapter 3

Geomorphology of the Elwha River and its Delta References Cited 73

Tabor, R.W., 1975, Guide to the geology 

of Olympic National Park: University 

of Washington Press, 144 p., 2 pls. 

Tabor, R.W., 1987, Geology of Olympic 

National Park: Seattle, Wash., 

Northwest Interpretive Association, 

144 p. 

Tabor, R.W., and Cady, W.M., 1978, 

Geologic map of the Olympic 

Peninsula, Washington: U.S. 

Geological Survey Miscellaneous 

Investigations Series Map I-944, 2 

sheets, scale 1:125,000.

U.S. Geological Survey Geologic 

Names Committee, 2010, 

Divisions of geologic time—

Major chronostratigraphic and 

geochronologic units: U.S. Geological 

Survey Fact Sheet 2010–3059, 2 p.

Waitt, R.B., and Thorson, R.M., 

1983, The Cordilleran Ice Sheet in 

Washington, Idaho, and Montana, 

in Wright, H.E., Jr., ed., 1983, 

Late-Quaternary environments of 

the United States, volume 1—The 

Late Pleistocene (Stephen C. Porter 

[ed.]): University of Minnesota Press, 

p. 53-70.

Wallick, J.R., Anderson, S.W., Cannon, 

C., and O’Connor, J.E., 2009, 

Channel change and bed-material 

transport in the lower Chetco River, 

Oregon: U.S. Geological Survey 

Open-File Report 2009-1163, 83 p.

Warrick, J.A., George, D.A., 

Gelfenbaum, G., Kaminsky, G., and 

Beirne, M., 2009a, Beach morphology 

and change along the mixed grain-size 

delta of the Elwha River, Washington: 

Geomorphology, v. 111, p. 136-148. 

Warrick, J.A., George, D.A., Stevens, 

A.W., Eshleman, J., Gelfenbaum, G., 

Kaminsky, G.M., Schwartz, A.K., and 

Beirne, M., 2010, Beach morphology 

monitoring in the Elwha River littoral 

cell: 2004–2009: U.S. Geological 

Survey Data Series Report 288, 64 p. 

(Also available at http://pubs.usgs.

gov/ds/288/.)

Warrick, J.A., Rubin, D.M., Ruggiero, 

P., Harney, J., Draut, A.E., and 

Buscombe, D., 2009b, Cobble cam—

Grain-size measurements of sand 

to boulder from digital photographs 

and autocorrelation analyses: Earth 

Surface Processes and Landforms, 

v. 34, no. 13, p. 1811-1821.
74 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

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Chapter 4

4

Chapter

Baseline Hydrologic Studies in 

the Lower Elwha River Prior to 

Dam Removal

By Christopher S. Magirl, Christopher A. 

Curran, Rich W. Sheibley, Jonathan A. 

Warrick, Jonathan A. Czuba, Christiana R. 

Czuba, Andrew S. Gendaszek, Patrick B. 

Shafroth, Jeffrey J. Duda, and James R. 

Foreman

Abstract

After the removal of two large, 

long-standing dams on the Elwha 

River, Washington, the additional load 

of sediment and wood is expected to 

affect the hydrology of the lower river, 

its estuary, and the alluvial aquifer 

underlying the surrounding flood plain. 

To better understand the surface-water 

and groundwater characteristics of the 

river and estuary before dam removal, 

several hydrologic data sets were collected 

and analyzed. An experiment using a dye 

tracer characterized transient storage, 

and it was determined that the low-flow 

channel of the lower Elwha River was 

relatively simple; 1–6 percent of the 

median travel time of dye was attributed 

to transient-storage processes. Water 

data from monitoring wells adjacent to 

the main-stem river indicated a strong 

hydraulic connectivity between stage in the 

river and groundwater levels in the flood 

plain. Analysis of temperature data from 

the monitoring wells showed that changes 

in the groundwater temperature responded 

weeks or months after water temperature 

changed in the river. A seepage 

investigation indicated that water from the 

river was moving into the aquifer (losing 

reach) between 1.7 and 2.8 kilometers 

from the river mouth. Surface-water 

measurements and temperature and 

salinity data collected throughout the 

estuary helped to characterize the 

magnitude and nature of water movement 

in and out of the estuary. Salinity and stage 

sensors positioned in the estuarine network 

showed a strong surface-water connection 

between the river and estuary waters east 

of the river. In contrast, there was a weaker 

connection between the river and estuarine 

water bodies west of the river.
76 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Introduction

Removal of the Elwha and Glines 

Canyon Dams on the Elwha River on 

the Olympic Peninsula of northwest 

Washington is expected to affect aquatic 

ecology, sediment transport, and fluvial 

geomorphology along the river, estuary, 

and nearshore within the Strait of Juan 

de Fuca (see Duda and others, 2008; 

Kloehn and others, 2008; Warrick and 

others, 2009; Draut and others, 2011; 

Duda and others, 2011b, chapter 1, 

this report). Because the Elwha dams 

currently are operated in run-of-the-river 

mode, the underlying hydrologic regime 

in the river will change only slightly 

after dam removal (Duda and others, 

2011b, chapter 1, this report). The fate of 

the 19 million m3 of sediment entrapped 

behind both dams, however, is expected 

to have significant effects on sediment 

transport, sediment-size distribution, and 

river-bed elevation (Czuba and others, 

2011, chapter 2, this report; Warrick and 

others, 2011a, chapter 3, this report), 

as well as the biological communities 

downstream of the reservoirs and in 

marine waters (Duda and others, 2011a, 

chapter 7, this report). 

As a result of changes in areal 

extent and bed elevation within the 

river corridor, the dam-removal project 

also is expected to affect the underlying 

framework of water movement 

throughout the lower Elwha River 

and its estuary. For example, channel 

complexity (that is, the potential for 

water to follow multiple flow paths, 

including recirculation zones, down 

the river corridor) within the river will 

likely be affected as sedimentation 

and the addition of large woody debris 

from sources upstream of the former 

dam sites enhance channel-migration 

potential (Kloehn and others, 2008). 

Significant channel change occurred 

near the river mouth as a result of the 

December 2007 peak-flow event, with 

an estimated recurrence interval of 40 

years (Draut and others, 2011). Changes 

in sediment-size distribution in the bed 

of the main-stem river also may alter 

hydraulic connectivity between the river 

and groundwater in the surrounding 

flood plain. In turn, groundwater 

levels in the lower Elwha River flood 

plain may rise as sedimentation in 

the main-stem river elevates the bed 

and associated water levels (Pacific 

Groundwater Group, 2005). 

Water exchange and transport 

through the estuary complex also is 

expected to be affected. The movement 

of water through the lower Elwha 

River estuary is governed by channel 

morphology in the main-stem Elwha 

River, sedimentology of the underlying 

alluvium, ocean processes of tides and 

waves, and temperature- and solutedriven flows between freshwater and 

saltwater. Conceptually, the estuary is 

a transient storage facility that captures 

the outgoing flux of freshwater flowing 

from the river to the Strait of Juan 

de Fuca. The specific areas of water 

exchange, however, are temporally and 

spatially complex. 

The Elwha River mouth and 

estuary form an important habitat for 

young salmonids and other fish and 

wildlife species (Shaffer and others, 

2009; Duda and others, 2011a, chapter 7, 

this report), and adjacent terrestrial 

habitats support a diverse complex 

of wetland and riparian vegetation 

(Shafroth and others, 2011, chapter 8, 

this report). Within these water bodies, 

river water, groundwater, and seawater 

mix providing brackish conditions 

that change with tides, storms, and 

seasons. These water-level and salinity 

dynamics exert a strong influence over 

biotic communities in river mouth 

estuaries (Mitsch and Gosselink, 1993; 

Keddy, 2000; Shafroth and others, 

2011, chapter 8, this report). Mixing 

of freshwater and saltwater offshore of 

the river mouth within the river plume 

is described more fully by Warrick and 

others (2011b), chapter 5, this report, 

and Warrick and Stevens (2011). 

Previous Studies

Few studies have addressed the 

hydrology of the lower Elwha River. 

The Pacific Groundwater Group (2005) 

completed a groundwater model for 

the lower Elwha River flood plain to 

predict the response of groundwater 

elevations after a presumed 0.8-m 

post-dam-removal aggradation in the 

channel. The model was calibrated using 

groundwater data from wells distributed 

throughout the valley-wide flood plain. 

A strong hydraulic connection between 

river stage and the wells adjacent to the 

river channel was documented under 

low-flow and peak-flow conditions 

using groundwater data and model 

simulation results (Pacific Groundwater 

Group, 2005). The correlation in 

groundwater response to river stage 

decreased with distance from the mainstem river and was negligible along 

the coastline at the eastern boundary of 

the flood plain where tidal influences 

dominated groundwater elevations 

(Pacific Groundwater Group, 2005). The 

correlation in groundwater response to 

river stage decreased with distance from 

the main-stem river and was negligible 

along the coastline at the eastern 

boundary of the flood plain where tidal 

influences dominated groundwater 

elevations (Pacific Groundwater Group, 

2005). Based on data from aquifer 

tests, Pacific Groundwater Group 

(2005) concluded that the hydraulic 

conductivity of the lower Elwha River 

aquifer was, on average, 220 meters 

per day (m/d), and ranged from 60 to 

490 m/d.

Detailed velocity measurements 

were made at five transects near 

the river mouth (Curran and others, 

2008). Similarly, recent monitoring of 

stream temperature noted an increase 

in mean annual stream temperature, 

and a decrease in diurnal temperature 

fluctuations, in the regulated reach 

downstream of Glines Canyon Dam 

compared with the unaltered upstream 

reach (Connolly and Brenkman, 2008). 
Chapter 4

Baseline Hydrologic Studies in the Lower Elwha River Prior to Dam Removal Hydrologic Studies in the Lower Elwha River 77

This warming of stream temperature 

downstream of the dams was attributed 

to heat storage in the Lake Mills 

reservoir (Wunderlich and others, 1994). 

However, thermal data characterizing 

specific temperature distribution of 

free-flowing and quiescent water bodies 

located throughout the lower Elwha 

River corridor are rare. 

Purpose and Scope

The U.S. Geological Survey 

(USGS), in collaboration with the Lower 

Elwha Klallam Tribe, the National Park 

Service, and other Federal and state 

agencies, has worked to characterize 

the hydrologic framework of the lower 

Elwha River. This chapter documents 

research and monitoring efforts that 

were completed before dam removal 

and have not been published elsewhere. 

Much of the data were collected 

with support from the USGS multidisciplinary Coastal Habitats in Puget 

Sound (MD-CHIPS) initiative (Duda 

and others, 2011b, chapter 1, this 

report). The research, largely intended 

to establish baseline hydrologic data sets 

before dam removal, included efforts 

to (1) characterize transient storage in 

the lower river, (2) monitor flood-plain 

groundwater movement and hydraulic 

connection with the main-stem river 

as well as identify areas of exchange 

between surface water and groundwater, 

and (3) identify primary hydrologic 

fluxes and exchanges of groundwater 

and surface water of river and marine 

origin in the estuary complex (Duda and 

others, 2011b, chapter 1, this report). 

This estuary complex is biologically 

significant as a rearing habitat for some 

species of juvenile salmonids, especially 

Chinook salmon, which is on the Federal 

endangered species list (Duda and 

others, 2011a, chapter 7, this report). 

Hydrologic Studies in the 

Lower Elwha River

Numerous measurements and 

data-monitoring efforts (table 4.1) were 

completed at several locations along the 

lower Elwha River flood plain (fig. 4.1) 

that enabled the characterization of 

key hydrologic aspects of the lower 

Elwha River. Transient storage in the 

river corridor was assessed using a dye 

tracer injected into the main stem during 

low flow. Groundwater movement was 

evaluated using water-elevation data 

from wells positioned throughout the 

wider valley flood plain. Surface-water/

groundwater exchanges were identified 

using a seepage investigation (a 

technique used to identify river reaches 

that are gaining or losing surface-water 

flow to the aquifer; see, for example, Ely 

and others, 2008) and temperature data 

from the beds of surface-water bodies 

to identify regions of groundwater 

upwelling. Finally, a diverse assemblage 

of surface-water measurements, tidal 

data, thermal signatures, and specific 

conductance measurements were used to 

infer how water flows in and out of the 

estuary. 

Due to its importance to aquatic 

habitat, considerable hydrologic 

analysis was focused on the estuary, 

which includes the network of surfacewater bodies and interconnecting 

channels near the river mouth (fig. 4.2). 

The water bodies and channels east of 

the river mouth are collectively referred 

to as the east estuary. Following the 

naming convention established by 

Duda and others (2011b, chapter 1, this 

report), the east estuary consists of ES1, 

a water body closest to the river, ES2, a 

larger water body farther to the east that 

occupies a former river-mouth channel, 

and Bosco Creek, a spring-fed water 

source that originates in the flood plain 

east of the main-stem river, flows into 

the eastern edge of ES2, and is the only 

known fresh surface-water flow into the 

east estuary (fig. 4.2). The prominent 

channel that connects ES1 to the main 

stem Elwha River just upstream of the 

river mouth is referred to as the ES1 

outlet channel. West of the river, two 

disconnected surface-water bodies 

comprise a smaller estuary assemblage. 

Just west of the river, a secondary 

distributary channel named the West 

Estuary Channel (WESC) (Duda and 

others, 2011b, chapter 1, this report) is, 

at times, hydraulically connected to the 

main-stem river. Farther west, beyond 

a flood-control levee is Dudley Pond, a 

water body disconnected from the mainstem river (fig. 4.2).

Transient Storage in the Lower 

Elwha River

Current methods of assessing 

in-stream habitat focus on physical 

measurements of specific habitat 

elements (for example, Fitzpatrick and 

others, 1998), but do not integrate across 

spatial scales or provide a direct measure 

of ecosystem function. Transient storage 

in a stream or river reach refers to any 

mechanism that slows down the bulk 

flow of water. Typically this results 

from in-channel features and exchange 

with shallow streambed sediments 

within the hyporheic zone (fig. 4.3). 

Therefore, there is a greater potential 

for transient storage in a stream that 

contains heterogeneous habitat elements 

at both large scales (for example, poolriffle sequences and secondary channels) 

and small scales (heterogeneous 

substrate and in-channel vegetation). 
78 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Table 4.1. Surface-water and groundwater sampling sites along the lower Elwha River, Washington.

[Abbreviations: RKm, river kilometer; CT, conductivity and temperature sensors; CTD, conductivty and temperature sensors equipped 

with transducers to measure water depth; n/a, not applicable]

Decimal 

latitude

Decimal 

longitude Site identifier Data collection dates Data collected

48.145808 -123.559370 TStn 1 8-1-09–12-18-09 Thermal

48.146438 -123.560386 TStn 2 8-1-09–12-21-09 Thermal

48.148155 -123.561795 TStn 3 8-1-09–12-11-09 Thermal

48.146982 -123.562848 TStn 4 8-2-09–8-8-09 Thermal

48.148670 -123.560036 TStn 5 8-2-09–8-8-09 Thermal

48.147375 -123.561944 TStn 6 8-2-09–8-8-09 Thermal

48.147515 -123.563160 ES1 7-28-07–3-29-10 CTD

48.147582 -123.561344 ES2 6-3-08–4-1-10 CT/CTD

48.145493 -123.567366 WESC 5-29-09–5-4-10 CT/CTD

48.144483 -123.568045 Dudley Pond 5-14-09–4-19-10 CTD

48.139917 -123.548006 AFN 256 11-9-07–8-27-09 Groundwater and thermal

48.135036 –123.554297 AFN 254 11-9-07–8-27-09 Groundwater and thermal

48.131425 –123.550747 MWGR 11-9-07–8-27-09 Groundwater and thermal

48.138014 -123.548883 AFN 259 11-9-07–8-27-09 Groundwater and thermal

48.147250 -123.563444 Acoustic Doppler velocity meter 6-3-08–9-2-08 Velocity/depth

48.145639 -123.563461 Estuary I/O flow 6-3-08–9-2-08 Discharge

48.144589 -123.556925 Bosco Creek 6-3-08–8-3-08 Discharge

48.119203 -123.553661 State hatchery outflow 9-24-07 Discharge

48.144314 -123.563133 RKm 0.4 9-24-07–9-26-07 Discharge

48.144111 -123.562589 RKm 0.4 9-24-07–9-26-07 Discharge

48.141756 -123.565631 RKm 0.8 9-25-07–9-26-07 Discharge

48.135597 -123.560611 RKm 1.7 9-25-07–9-26-07 Discharge

48.131853 -123.551247 RKm 2.2, old channel 9-26-07 Discharge

48.128217 -123.559203 RKm 2.6 9-24-07 Discharge

48.126889 -123.558706 RKm 2.8 9-24-07, 9-26-07 Discharge

48.121350 -123.554619 RKm 3.5 9-24-07 Discharge

48.118444 -123.554806 RKm 3.8 9-24-07 Discharge

48.114167 -123.553611 RKm 4.4 9-24-07–9-26-07 Discharge

48.142714 -123.563164 Tommy Boy 9-26-07 Discharge

48.120878 -123.555072 Trib 2 9-24-07 Discharge

48.129589 -123.554500 Trib 3 9-26-07 Discharge

48.131167 -123.551561 Trib 4 9-26-07 Discharge

48.136017 -123.558011 Trib 5 9-25-07–9-26-07 Discharge

48.137722 -123.559817 Trib 6 9-25-07–9-26-07 Discharge

48.143425 -123.562283 Tribal hatchery 9-26-07 Discharge

48.120171 -123.554580 Dye deployment 9-29-09 n/a

48.126030 -123.557110 Station 1 9-29-09 Dye concentration

48.131721 -123.557124 Station 2 9-29-09 Dye concentration

48.141685 -123.565316 Station 3 9-29-09 Dye concentration
Chapter 4

Baseline Hydrologic Studies in the Lower Elwha River Prior to Dam Removal Hydrologic Studies in the Lower Elwha River 79

watac11-0558_fig4-01

123°34'W 123°32' W 123°30' W

48°09'N

48°08'N

48°07'N

0 0.25 0.5 MILES

0 0.25 0.5 KILOMETERS

EXPLANATION

!

Elwha River main channel

Study sites

Distributed temperature sensing transect

Surface-water temperature sites

Dye study sites

Surface-water sites

Conductivity, temperature, depth sites

Monitoring wells

WASHINGTON STATE

Figure

location

Lower Elwha Klallam 

Tribal Reservation

AFN 256

AFN 259

MWGR

AFN 254

Bosco Creek 

gage

Station 3

Station 2

Station 1

Dye injection site

Port Angeles

STRAIT OF JUAN DE FUCA

Projection: UTM Zone 10, WGS84 

Bare earth LIDAR from 2001

Figure 4.1. Locations of hydrologic monitoring sites, lower Elwha River and estuary, northwest Washington.
80 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0558_fig4-02

EXPLANATION

Study sites

Distributed temperature sensing transect

Temperature/salinity stations

Conductivity, temperature, depth sites 

Surface-water sites

123°34'W 123°33'30"W

48°09'N

48°8'50"N

48°8'40"N

0 100 200 300 FEET

0 100 200 300 METERS

ES1

ES2

Dudley Pond

West estuary channel (WESC)

Bosco Creek

ES1 outlet

channel

TStn 1

TStn 2

TStn 4

TStn 6

TStn 3 TStn 5

Bosco Creek gage

Acoustic

Doppler

velocity

meter 

Western flood-control levee

TStn 1

Figure 4.2. Locations of data collection sites near the Elwha River estuary, Washington.
Chapter 4

Baseline Hydrologic Studies in the Lower Elwha River Prior to Dam Removal Hydrologic Studies in the Lower Elwha River 81

watac11-0558_fig4-03

A. In-channel storage B. Hyporheic zone storage

Figure 4.3. Conceptual diagram of transient storage, defined as the temporary retention of water due to (A) in-channel storage 

elements like pools and eddies, and (B) the hyporheic zone (shallow stream sediments). (Adapted from Runkel, 1998.)

Transient storage in streams has been 

shown to increase in the presence of large 

woody debris (Valett and others, 2002), 

in-stream vegetation (Harvey and others, 

2003), channel meanders (Boano and 

others, 2006), and pool-riffle sequences 

(Gooseff and others, 2006), all of which 

contribute to the habitat needs of stream 

biota. Measures of transient storage in a 

reach, therefore, provide an indicator of 

habitat quality that is integrated across the 

spatial scales. Streams with high degrees 

of habitat heterogeneity (complexity) 

generally have a high potential to retain 

water in transient storage. 

The amount of transient storage in 

a reach can be important for ecosystem 

functions of rivers and streams. For 

example, the longer that water remains in 

contact with stream sediment, the greater 

the opportunity for transformation and 

uptake of solutes in the reach becomes. 

Therefore, a complex channel with greater 

transient storage can lead to enhanced 

nutrient uptake (Valett and others, 

1996; Butturini and Sabater, 1999; 

Bukaveckas, 2007) and increased 

stream metabolism (Mulholland and 

others, 1997). In the lower Elwha River, 

measurements of transient storage 

before and after dam removal will be an 

important tool for documenting changes 

in transient storage and its potential 

influence on solute uptake (for example, 

nutrients released from decaying salmon 

carcasses). 

Reach-averaged transient storage 

commonly is measured by injecting 

a solute tracer into the stream and 

measuring the tracer concentrations 

downstream, yielding a solute 

breakthrough curve (fig. 4.4). If the 

tracer simply advects (that is, moves 

with the flow with little mixing or 

diffusion) through the reach because 

few habitat elements slow the main 

flow, the solute breakthrough curve 

will have a relatively high peak 

concentration and a quick return to 

background concentrations (fig. 4.4; 

solid line). Observation of a relatively 

lower peak concentration within the 

solute breakthrough curve and a slow 

return to background concentrations, 

indicates increased transient storage 

(fig. 4.4; dashed line). A solute-transport 

model that includes transient storage 

components to fit the field data from 

the tracer experiments can be used to 

quantitatively determine the amount 

of transient storage in a study reach. 

Previous work has shown that a complex 

channel structure (that is, multiple flow 

paths, pools, wood jams) increases 

the potential for transient storage, and 

that solute-injection experiments show 

promise for documenting this relation 

(Gooseff and others, 2007). 
82 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Transient storage was determined 

in the lower Elwha River using a dyetracer experiment in which a slug of 

fluorescent dye was added to the mainstem river, while downstream detection 

instruments recorded dye concentration 

response over time. These temporal 

concentration data then were combined 

with a transient-storage model (Runkel, 

1998) to assess overall transient storage 

for the study reach.

On September 29, 2009, a solute 

injection experiment using a nontoxic dye tracer, Rhodamine WT 

(RhWT), was completed on the lower 

Elwha River (fig. 4.1), timed to take 

advantage of autumnal low flow. The 

dye-injection site was in a section of 

the river with confined banks (about 

3.9 km upstream of the river mouth), 

and the tracer was released into a riffle 

watac11-0558_fig4-04

Time

Solute concentration

No transient storage

With transient storage

Figure 4.4. Theoretical downstream response to an instantaneous input of solute 

tracer. With little or no transient storage in the stream reach, the tracer is influenced 

only by advection and dispersion (solid line). A stream reach with significant transient 

storage will result in spreading of the peak with distance from the injection site 

(dashed line). (Adapted from Runkel, 1998.)

to enhance mixing (fig. 4.5). Another 

riffle farther downstream again mixed 

the dye throughout the width of the 

river. A total of 6.3 liters of 20 percent 

active ingredient Rhodamine WT was 

added to target a peak concentration of 

about 50 μg/L at the most downstream 

detection site, using the equations of 

Kilpatrick and Cobb (1985). To offset 

density differences and to improve 

lateral mixing, the tracer was added 

to the river simultaneously by three 

individuals spaced across the river at the 

injection site (fig. 4.5).

Concentration of dye was measured 

at three locations downstream of the 

injection site (fig. 4.1) using automated 

field fluorometers (SCUFA) that 

measured the fluorescence of the added 

tracer in the river with a reported 

detection limit of 0.04 μg/L (Turner 

Designs, Inc, 2004). Measurements of 

fluorescence were recorded at 1-minute 

intervals throughout the duration of 

the experiment to determine the solute 

breakthrough curves at each site. A 

SCUFA mount assembly for each 

instrument was secured to the riverbed 

using a cinderblock anchor attached to 

a float. The SCUFA then was affixed 

to this mount assembly so that the 

instrument was positioned at a point 

in the water column 0.75 m below the 

water surface. The three instruments 

were calibrated with simultaneous 

placement in the river for 10–15 minutes 

before and after the experiment to 

determine the bias in fluorescence 

readings between individual meters, 

and to assess potential instrument drift 

during the experiment. 
Chapter 4

Baseline Hydrologic Studies in the Lower Elwha River Prior to Dam Removal Hydrologic Studies in the Lower Elwha River 83

watac11-0558_fig4-05

 B. 

 C. D. 

 A. 

Figure 4.5. Dye study in the lower Elwha River, Washington, September 29, 2009. (A) USGS hydrologist mixing the Rhodamine 

WT solution prior to slug injection; (B) three USGS hydrologists introducing the rhodamine into a riffle to enhance lateral mixing 

of the tracer; (C) dye tracer just downstream of the injection riffle, where the plume is spreading longitudinally and laterally in the 

slow moving water before reaching the next downstream riffle; and (D) looking downstream as the dye tracer approaches the first 

monitoring station. Main channel storage is evident on the left side of the channel in a slower moving backwater area, shown by

the arrow. (Photographs taken by (A) James R. Foreman, U.S. Geological Survey and (B, C, D) Christopher A. Curran, U.S. Geological 

Survey.)
84 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

The three SCUFAs, referred to as Station 1, Station 2, 

and Station 3 (table 4.1), were placed 0.7, 1.5, and 3.0 km 

downstream of the injection site, respectively (fig. 4.1).

River discharge was measured at Stations 1 and 2 during the 

experiment using a hand-held acoustic Doppler velocimeter, 

and at Station 3 using an acoustic Doppler current profiler 

mounted on a tethered boat. The theory of operation of 

these hydroacoustic technologies is well documented (see, 

for example, Yorke and Oberg, 2002). Standard USGS 

measurement protocols were followed for both methods, and 

measurement error was assumed to be less than 5 percent 

(Mueller and Wagner, 2009; Turnipseed and Sauer, 2010).

Rhodamine travel times to each SCUFA monitoring 

station were determined by plotting the tracer response at 

each SCUFA station compared to time (fig. 4.6), and the 

time when peak concentration was reached represented 

the average travel time to that monitoring station from the 

injection site (Kilpatrick and Wilson, 1989). Average travel 

times to each station from the injection point were 0.42, 0.93 

and 1.57 hours, respectively. Measured river discharge was 

9.46 m3/s (334 ft3/s) at Station 1, decreasing to 8.86 m3/s 

(313 ft3/s) at Station 2, and increasing to 9.85 m3/s (348 ft3/s) 

at Station 3 (table 4.2). For comparison, the daily discharge 

for that day as measured at USGS streamflow-gaging station 

12045500 (Elwha River at McDonald Bridge near Port 

Angeles, Wash.) was 10.1 m3/s (355 ft3/s). 

EXPLANATION

0

20

40

60

80

100

120

140

160

180

200

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Rhodamine concentration, in micrograms per liter

Time since tracer addition, in hours

Station 1

Station 2

Station 3

Figure 4.6. Measured rhodamine concentrations at monitoring stations 1, 2 and 3 

after a slug injection of 6.3 liters of Rhodamine dye tracer in the lower Elwha River, 

Washington, September 29, 2009. 
Chapter 4

Baseline Hydrologic Studies in the Lower Elwha River Prior to Dam Removal Hydrologic Studies in the Lower Elwha River 85

Table 4.2. Flow and cross section characteristics from 

manual discharge measurements, Elwha River, Washington, 

September 29, 2009.

[Abbreviations: m3/s, cubic meter per second; m, meter; m2, square meter; 

m/s, meter per second]

Station 

No.

Discharge

(m3

/s)

Width

(m)

Mean depth

(m)

Area

(m2)

Velocity

(m/s)

Station 1 9.46 46 0.58 26.8 0.37

Station 2 8.86 26 .43 11.5 .76

Station 3 9.85 33 .46 14.9 .67

Tracer breakthrough curves were simulated using the 

one-dimensional transport with inflow and storage (OTIS) 

model (Runkel, 1998) to estimate the amount of transient 

storage in the experimental reach. OTIS solves two differential 

equations developed by Bencala and Walters (1983) to 

calculate solute concentrations over time in the main channel 

and the storage zone of the stream reach. The changes in the 

river discharge measured through the study reach, presumably 

from water exchanges with the underlying aquifer, were 

incorporated into the modeling results. The model simulation 

results produced estimates of four hydrologic parameters 

used to calculate transient storage metrics. These output 

parameters (shown conceptually in fig. 4.7) include the 

Figure 4.7 Conceptual diagram of onedimensional transport with inflow and storage 

(OTIS) model showing advection and dispersion of 

solute (dye) within the main channel and exchange 

of solute into the storage zone. Four major model 

parameters are optimized to fit the calibration 

data including main-channel area (A), dispersion 

coefficient (D), storage zone area (As

), and the 

exchange rate into the storage zone (α). (Adapted 

from Runkel, 1998.)

A,D

As

α

Storage zone

Main channel zone Downstream

transport

Advection

and

dispersion

dispersion coefficient for the reach (D), the main channel 

cross sectional area (A), storage zone area (As), and rate of 

exchange between the main channel and storage zone (α). 

From these parameter estimates, the metrics of transient 

storage can be determined, including the relative storage 

zone capacity (As/A) and the fraction of median travel 

time due to transient storage normalized against a 200-m 

long reach (Fmed

200) which allows for future comparison 

with data from other rivers (Runkel, 2002). Discharge 

fundamentally alters solute transport within a stream; 

therefore, tracer studies ideally should be over a range 

of discharge. However, Fmed

200 has been shown to be a 

robust metric for assessing differences in transient storage 

across sites and through time (Runkel, 2002) and can be 

used as a primary indicator for tracking changes following 

dam removal. By calibrating this model for the study 

reach, metrics of transient storage are derived that serve as 

indicators of habitat complexity prior to dam removal.

To run the OTIS model, the tracer breakthrough curve 

at Station 1 was entered as the upstream model boundary 

condition. This input then was used to simulate the data at 

Station 2 and Station 3 through a non-linear least squares 

algorithm using the OTIS-P model (Runkel, 1998). OTIS-P 

uses the same numerical model as OTIS, but includes a 

parameter estimation subroutine to automatically fit the 

model to downstream tracer data by optimizing values for 

D, A, As

. 
86 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

OTIS-P was executed for two 

model scenarios. The first scenario 

modeled the experimental reach as a 

single reach, with the Station 1 data used 

as the upstream boundary condition to 

simulate the response at Station 3. After 

the dams are removed, the entire reach 

between Stations 1 and 3 might remain 

intact as a single channel; therefore, 

this simulation will represent a baseline 

condition of the lower river before dam 

removal. The second scenario breaks 

up the experimental reach into two 

separate subreaches from (1) Station 

1 to Station 2, and (2) Station 2 to 

Station 3, allowing transient storage 

properties to be assessed in each 

subreach. This sampling and modeling 

strategy provides some flexibility in 

the transient-storage analysis, and 

allows future studies to use the data 

collected even if the lower river channel 

experiences dramatic morphologic 

changes.

Transient storage model simulation 

results from OTIS-P simulations 

generally matched the measured 

Rhodamine curves for the single-reach 

scenario (fig. 4.8A), and the tworeach scenario (fig. 4.8B). Optimized 

parameters of transient storage from 

each model run indicate that little 

transient storage was in each reach 

(table 4.3). This observation is best 

illustrated by the values for Fmed

200, the 

fraction of median travel time due to 

storage. In the single-reach scenario, 

Fmed

200 between Station 1 and 3 was 

0.01, suggesting that approximately 

1 percent of the travel time can be 

attributed to storage processes in the 

reach. For the two-reach scenario, 

Fmed

200 was higher in the first reach 

(0.06) when compared to the second 

reach (0.01). The relative size of the 

storage zone for the single-reach 

scenario, given by As/A, was 0.128, and 

for the two-reach scenario As/A was 

0.237 and 0.160 for the upper and lower 

reaches, respectively. These As/A values 

indicate that the channel cross-sectional 

areas are larger than the theoretical 

storage-zone areas. 

EXPLANATION

0

10

20

30

40

50

60

70

80

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Station 3

OTIS-P single reach

 simulation at station

0

20

40

60

80

100

120

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Rhodamine concentration, in micrograms per liter 

Time since tracer addition, in hours

Station 2

OTIS-P two-reach

 simulation at station

Measured

Station 3

OTIS-P two-reach

 simulation at station

Measured

EXPLANATION

A. Single reach scenario

B. Two-reach scenario

Measured

Figure 4.8 Measured and 

one-dimensional transport 

with inflow and storage 

(OTIS-P) simulated rhodamine 

breakthrough curves at (A) 

Station 3 for the single-reach 

scenario and at (B) Stations 

2 and 3 for the two-reach 

scenario for the lower Elwha 

River, Washington.
Chapter 1 Chapter 4

Baseline Hydrologic Studies in the Lower Elwha River Prior to Dam Removal Hydrologic Studies in the Lower Elwha River 87

To check how well the model simulated observed 

response in the river, the experimental Damköhler number 

(DaI) from each simulation was calculated. The DaI is a 

measure of how well the tracer experiment describes the 

transient storage processes of the experiment and is calculated 

by

(1 / ) , AAL s DaI

u

+

= α (1)

where L is the reach length (Wagner and Harvey, 1997). 

Values of DaI close to 1.0 are ideal, but values between 

0.1 and 10.0 indicate that the tracer experiment adequately 

describes the transient storage processes of the experiment 

(Wagner and Harvey, 1997; Harvey and Wagner, 2000). The

DaI results for this study were all greater than 1.0 (4.7 to 8.9, 

table 4.3), but were within this optimal range. Thus, the 

values of DaI, and the quality of the visual fit to field data, 

indicate that the modeling approach was reasonable for this 

experiment.

The amount of transient storage in the experimental reach 

is small, likely due to high water velocity and a relatively 

simple channel (table 4.2). Generally, from 1 to 6 percent of 

the median travel time in the lower reach can be attributed to 

transient storage processes. With a change in sediment supply 

and large woody debris after dam removal, sedimentation and 

channel reorganization in the lower Elwha River are expected 

to increase channel-structure complexity. These changes are 

expected to translate into measurable increases in travel times. 

Table 4.3. Optimized parameter estimates for the transient 

storage model using one-dimensional transport with inflow and 

storage (OTIS-P) and selected transient storage zone metrics, 

Elwha River, Washington.

[Abbreviations: D, dispersion coefficient; A, main channel cross-sectional 

area; As, storage zone cross-sectional area; α, storage zone exchange 

coefficient; As/A, relative storage-zone capacity; DaI, Damköhler number; 

Fmed

200, fraction of median travel time due to storage normalized against a 

200-meter long reach; m/s2, meter per second squared; sec-1; per second]

Reach D

(m/s2

)

A

(m2)

As

(m2)

α

(sec-1) As

/A Fmed

200 DaI

Station 1 to 3 6.9 15.9 2.0 2.50E-04 0.128 0.01 8.9

Station 1 to 2 1.6 20.3 4.8 8.43E-04 .237 .06 7.2

Station 2 to 3 6.4 12.6 2.0 3.00E-04 .160 .01 4.7

Groundwater and Surface-Water Interactions

Water levels and temperatures were collected from 2007 

to 2009 using self-contained data recorders in four monitoring 

wells positioned throughout the Elwha River flood plain. 

These groundwater data, coupled with streamflow and thermal 

patterns measured in the main-stem river, allowed for the 

analysis of the relative connectivity of the aquifer to the river. 

A seepage investigation in September 2007 included near 

simultaneous discharge measurements at multiple locations 

along the river channel to determine the volumetric exchange 

of surface water and groundwater. Finally, to better quantify 

the spatial distribution of groundwater flow feeding into 

the east estuary, thermal patterns of the estuary bed were 

measured over a 20-hour period in September 2008.

Water Level Measurements near the Lower 

Elwha River

Four data recorders with vented pressure transducers 

were placed in established monitoring wells (fig. 4.1;

table 4.1) to collect water level and temperature data from 

November 9, 2007, to August 27, 2009, at 1-hour intervals. 

Raw water-level data were adjusted to elevation in meters 

above sea level (NAVD 88) based on well-head elevation 

surveys by the Pacific Groundwater Group (2005). The two 

southern-most monitoring wells were on the river side of 

the eastern flood-control levee (Warrick and others, 2011a, 

chapter 3, this report) along the outer bend of a distributary 

channel that conveys overflow with increasing discharge. The 

farthest upstream of these two wells (MWGR; fig. 4.1) was 

about 2.7 km upstream of the river mouth, and the other well 

(AFN 254) was about 2.1 km upstream of river mouth. Of the 

other two monitoring wells, AFN 259 (fig. 4.1) was farther 

south and closer to the river, and AFN 256 was farther north 

and closer to the coastline.

Data collected at the four monitoring wells indicated a 

strong correlation between groundwater elevation and river 

stage throughout the year, regardless of the river discharge 

or the season (fig. 4.9). Data from AFN 259 and AFN 256, 

the two wells closest to the coastline, between June and 

September of 2008, demonstrated the strong coupling between 

groundwater elevation in the flood plain and stage in the river 

(fig. 4.10). Additionally, tidal influences also were apparent 

in these flood plain wells, although tidal influence seemed to 

be considerably smaller than the river influence. The response 

time between the peak river stage and the peak groundwater 

elevation ranged from hours to a few days. Continuous 

groundwater-elevation data collected from intermittent records 

from October 2002 through January 2005 showed similar 

characteristics (Pacific Groundwater Group, 2005).
88 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0558_fig4-09

2

4

6

8

10

12

14

16

18

Groundwater temperature, in degrees Celsius

MWGR

AFN 254

AFN 256

AFN 259

EXPLANATION

EXPLANATION

10-01-2007 12-13-2007 02-24-2008 05-07-2008 07-19-2008 09-30-2008 12-12-2008 02-23-2009 05-07-2009 07-19-2009 09-30-2009

3

4

5

6

7

8

9

10

Groundwater elevation, in meters above the 

North American Vertical Datum of 1988

MWGR

AFN 254

AFN 256

AFN 259

Stage at USGS streamflow-gaging 

station 12045500 

Air temperature, in degrees Celsius

River stage, in meters above arbitrary datum

EXPLANATION

1

2

3

4

5

6

7

8

Figure 4.9 Groundwater elevations and temperatures from four monitoring wells in the Elwha River flood plain, 

in relation to river stage at U.S. Geological Survey streamflow-gaging station 12045500, Elwha River near Port 

Angeles, Washington, and air temperature at the Bosco Creek gaging station (12046523).
Chapter 4

Baseline Hydrologic Studies in the Lower Elwha River Prior to Dam Removal Hydrologic Studies in the Lower Elwha River 89

watac11-0558_fig4-10

EXPLANATION

06-21-2008 07-01-2008 07-11-2008 07-21-2008 07-31-2008 08-10-2008 08-20-2008 08-30-2008 09-09-2008

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Elevation, in meters above

the North American

Vertical Datum of 1988 Elevation, in meters above the North American Vertical Datum of 1988

AFN 256

AFN 259

Stage at USGS streamflow-gaging station 12045500 

NOAA tidal station 9444090

4.2

4.3

4.4

4.5

4.6

4.7

4.8

3.0

3.2

3.4

3.6

3.8

4.0

4.2

4.4

Elevation, in meters above

arbitrary datum

3.7

3.8

3.9

4.0

4.1

4.2

4.3

4.4

A.

B.

C.

D.

Figure 4.10. Water elevations representing (A) tidal stage at National Oceanic and Atmospheric Administration 

(NOAA) tidal station 9444090 in Port Angeles, Washington; (B) river stage measured at U.S. Geological Survey 

streamflow-gaging station 12045500, Elwha River near Port Angeles, Washington; (C) groundwater elevation in 

monitoring well AFN 256; and (D) groundwater elevation in monitoring well AFN 259. The data show the rapid 

response in groundwater elevation to changes in river stage. Both monitoring wells are at least 0.5 kilometers 

from the main-stem river and at least 1.0 kilometers from the coast. 
90 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Temperature data from the 

monitoring wells indicated that 

in contrast to the strong hydraulic 

connection of existed between the 

river and the aquifer, a relatively weak 

thermal connection existed between 

wells and, presumably, the main-stem 

river. Although daily water-temperatures 

measured directly in the lower Elwha 

River were not available, it was assumed 

that river temperature tracked air 

temperature, and air-temperature data 

were collected at 15-minute intervals 

with the BaroTROLL collector at USGS 

streamflow-gaging station 12046523, 

Bosco Creek near Port Angeles, 

Washington. These air-temperature 

data correlated well with the general 

trends in water temperature measured at 

MWGR (fig. 4.9). This new monitoring 

well is adjacent to the river channel 

and positioned 10–30 m from the 

distributary channel and likely is active 

for moderately large discharges. It seems 

likely that the delay or lag time between 

the temperature of water in MWGR 

and the river probably is on the order 

of a few days or weeks. At well AFN 

254, about 100 m from the distributary 

channel, the warmest groundwater 

seems to occur about 1 month after the 

maximum air temperature (fig. 4.9). 

The occurrence of the warmest water 

at the flood-plain wells (AFN 259 and 

AFN 256) occurs 5–7 months after the 

maximum seasonal air temperatures 

(fig. 4.9). 

Seepage Investigation in the 

Lower Elwha River

A seepage investigation from 

September 24 – 26, 2007, determined 

stream-flow gains and losses in the 

lower 4.4 km of the Elwha River. 

This investigation consisted of 18 

discharge measurements collected at 

8 sites on the main stem, and 4 sites 

on tributaries along the river (U.S. 

Geological Survey, 2007). Standard 

methods were followed for measuring 

discharge using a current meter for 

8 measurements, an acoustic Doppler 

velocimeter for 6 measurements, and 

an acoustic Doppler current profiler for 

4 measurements (Mueller and Wagner, 

2009; Turnipseed and Sauer, 2010). For 

the seepage investigation, all discharge 

measurements were assumed to have 

an accuracy of 5 percent. Discharge 

measurements were made during autumn 

low flow to capture base-flow conditions 

when surface-water/groundwater 

interactions are most apparent. 

During the 3-day seepage 

investigation, discharge at USGS 

streamflow-gaging station 12045500, 

the Elwha River at McDonald Bridge 

near Port Angeles, Washington, was 

constant at 10.25 m3/s on September 

24, 2007, and increased to 11.47 m3/s 

on September 25, 2007, and remained 

constant for the rest of the seepage 

investigation (fig. 4.11). To allow direct 

comparison of discharge data between 

days, discharge measurements made 

on September 24, 2007, were adjusted 

upward by 1.22 m3/s (the difference 

between background discharge of 

11.47 m3/s and 10.25 m3/s) using the 

McDonald Bridge discharge values. 

Additionally, discharge measurements 

were adjusted for tributary inflow 

by subtracting all upstream tributary 

inflows from the main-stem Elwha River 

discharge measurements. 

Elwha River discharge 

measurements that have been adjusted 

for variations in the hydrograph 

and tributary inflows show synoptic 

downstream variations in the flow 

that may be attributed to groundwater/

surface-water exchange, tidal 

fluctuations in the estuary, measurement 

error, or some other factors (fig. 4.12). 

The variations in the discharge data at 

the section of river between 4.4 and 

2.8 km upstream of the river mouth are 

within the uncertainty of the individual 

measurements; however, there may 

be a slight groundwater/surface-water 

exchange. Discharge measurements 

collected on the same day in the mainstem river between 2.8 and 1.7 km 

upstream of the river mouth indicated 

that about 10 percent of the Elwha River 

discharge seeped into the groundwater 

system. Discharge data downstream of 

1.7 km from the river mouth indicated 

strong gains to the Elwha River on 

September 25, and no change on 

September 26 (fig. 4.12). However, the 

flow measurements on September 25 

were made when the tide was falling, 

whereas the flow measurements on 

September 26 were made just after low 

tide. The differences in the adjusted 

flows near the river mouth between 

these 2 days likely were caused by 

the changing flow conditions in the 

estuary as water was stored and released 

to the river. Based on uncertainty of 

measurements, there were no clear 

trends indicating groundwater losses or 

gains in the lower 1.7 km of river or in 

the section of river upstream of a point 

2.8 km from the river mouth. 
Chapter 4

Baseline Hydrologic Studies in the Lower Elwha River Prior to Dam Removal Hydrologic Studies in the Lower Elwha River 91

watac11-0558_fig4-11

EXPLANATION

0

2

4

6

8

10

12

14

09-24-2007 09-25-2007 09-26-2007 09-27-2007

Measured discharge, in cubic meters per second 

Discharge at USGS gaging station 12045500 

Discharge at USGS gaging station 12045500, ±5 percent 

Main-stem Elwha River discharge measurement, bars indicate ±5 percent

Tributary discharge measurement

Figure 4.11. Discharges measured during the 3-day seepage investigation in September 2007, on the 

lower Elwha River in relation to the discharge at U.S. Geological Survey (USGS) streamflow-gaging 

station 12045500, Elwha River at McDonald Bridge near Port Angeles, Washington.
92 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0558_fig4-12

EXPLANATION

6

7

8

9

10

11

12

0 1 2 3 4 5

Adjusted discharge,

in cubic meters per second 

Distance upstream of river mouth, in kilometers

September 24, 2007

September 25, 2007

September 26, 2007

Figure 4.12. Adjusted synoptic discharge measurements in the lower Elwha River, Washington, for the 

September 2007 seepage investigation. Bars indicate ±5 percent.
Chapter 4

Baseline Hydrologic Studies in the Lower Elwha River Prior to Dam Removal Hydrologic Studies in the Lower Elwha River 93

Distributed Temperature 

Sensing in the Estuary

A water-temperature survey using 

fiber-optic distributed temperature 

sensing (DTS) technology (Selker and 

others, 2006; Tyler and others, 2009) 

was conducted in the east estuary in 

September 2008. The sampling sites 

covered much of the surface of the 

riverbed of the east estuary and ended in 

the main-stem river just upstream of the 

river mouth (fig. 4.2). The purpose of the 

temperature survey was to locate thermal 

signals (dampened diurnal fluctuations 

of surface-water temperatures) that could 

be attributed to groundwater discharge 

into the surface-water body. Water 

temperature also was used as a tracer to 

observe the circulation pattern of tidally 

induced mixing in the east estuary. 

A field-portable Sensortran DTS 

unit was used with a 3-mm diameter 

steel and Kevlar reinforced singleended fiber-optic cable dispensed from a 

portable reel containing about 1,500 m of 

cable. Temperature was recorded every 

5 minutes at 1-m resolution along the 

cable length. The cable was calibrated 

on site with an ice bath at the DTS unit 

location. Using this arrangement, some 

degradation of precision occurs with 

distance from the DTS unit; however, 

DTS temperatures correlated well with 

Tidbit point sensors placed at multiple 

locations along the cable for comparison. 

Although 0.01 °C measurement precision 

has been demonstrated using similar 

DTS instruments (Selker and others, 

2006), accuracy of measurements in 

both deployments were estimated to be 

0.1°C.

At the estuary site, DTS cable 

(900 m) was placed in the east estuary. 

The cable was laid over much of the bed 

of ES2, extended through connecting 

channels into ES1, extended farther 

through the ES1 outlet channel, and 

ended in the main-stem river just 

upstream of the river mouth (fig. 4.2). 

Turning points, used to guide the cable 

through the estuary complex without 

damage, were constructed of 2.5-cm 

steel pipe pounded into the substrate 

with a larger plastic-pipe sheath to 

protect the cable during placement. In 

most locations, the cable was placed on 

or near the bed substrate; an exception 

was in ES2 where thick algal mats 

and water depths often exceeding 

1.2 m prevented the cable from resting 

directly on the bed. The estuary DTS 

cable was deployed over a 20-hour 

period and collected approximately 

216,000 temperature measurements.

The weather during the DTS survey 

in the east estuary, on September 1–2, 

2008, was warm and clear, with sun 

and little wind. Figure 4.13 shows the 

distribution of temperature along the 

DTS cable at transition times during 

the tidal cycle, when water flux into 

the estuary was changing. At 1400 on 

September 1, the water temperature in 

ES2 was a relatively warm 15°C, but 

cold water of about 9°C from the river 

was moving through the connecting 

channels into ES1 (fig. 4.13A). By 

1700, at exactly high tide, cold water 

had ceased entering the connecting 

channel and nearly the entire cable was 

a relatively warm 16°C (fig. 4.13B). 

This heating was caused by strong 

solar heating on September 1, 2008. By 

2200, overall water temperature had 

decreased along the cable to about 14°C 

in the ES1 and the ES1 outlet channels 

(fig. 4.13C). During the night and early 

morning, temperature generally dropped 

steadily in the smaller ES1 water body 

and connecting channels. Within ES2, 

however, the large thermal mass of 

the water body kept the water at about 

15°C throughout the night. Recorded 

temperature in ES2 also likely reflected 

the situation that algal mats suspended 

the DTS cable above the bottom of the 

water body. As a result, the temperature 

data collected in ES2 were from a depth 

location above the actual bed of the 

water body. Water temperature in the 

main-stem river fluctuated between 9 

and 12 °C during the late afternoon and 

night, as warmer river water flowed 

over the top of the cooler marine water. 

Because the cable was laid on the 

bottom of Elwha River channel, cycles 

in the tide dictated whether relatively 

warm freshwater, or cool marine water, 

influenced thermal data in this location. 

By 1000 on September 2, as the tide 

approached its low point, solar heating 

had warmed most of the water in ES1 

and ES2 (fig. 4.13F). 

To analyze where the groundwater 

may have entered the estuary, the 

total variance of recorded temperature 

data over the 20-hour experiment 

is shown as a function of position 

along the cable (fig. 4.14). Due to the 

large thermal mass, and because the 

cable was suspended by an algal mat, 

overall thermal variance in ES2 was 

less than 2 °C. Nonetheless, assuming 

groundwater was cooler than 15°C, 

no areas of groundwater influx to ES2 

were identified with the experiment. 

Variance also was small between 180 

and 200 m at a section of cable in the 

middle of ES1 (fig. 4.14). During the 

course of the experiment, temperature 

at this location in the cable ranged 

between about 13 and 14°C, which is 

small compared to sections of the cable 

placed elsewhere where temperature 

fluctuated as much as 5°C. The area of 

low variance is the short yellow section 

of cable in ES1 surrounded by red at 

1700 on September 1 (fig. 4.13B), or the 

same yellow section of cable surrounded 

by cyan at 0700 on September 2 

(fig. 4.13E). This small variance was 

interpreted to be a region of strong 

groundwater upwelling, probably 

associated with a relict fluvial channel 

of coarse sediment and relatively large 

hydraulic conductivity. Two other 

regions of decreased thermal variance 

were apparent near 155 and 76 m 

(fig. 4.14), also suggesting groundwater 

influx though the strength of the signal 

was smaller than in the region from 180 

to 200 m.
94 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Figure 4.13. Photographs and graph showing temperature along a distributed temperature sensor (DTS) 

array positioned along the riverbed in the east estuary of the Elwha River between 1400 on September 1, 

2008, and 1000 on September 2, 2008. Tidal stage at the National Oceanic and Atmospheric Administration 

tidal station 9444090 in Port Angeles, Washington, shows the influence of tides on surface-water exchange 

with the estuary. watac11-0558_fig4-13

0

0 100 200 FEET

100 200 METERS

EXPLANATION

Temperature, in degrees Celsius

9.1 - 10.0

10.1 - 11.0

11.1 - 12.0

12.1 - 13.0

13.1 - 14.0

14.1 - 15.0

Greater than 15.0

An animation showing the full time sequenced temperature data through one 

entire tidal cycle is available at http://pubs.usgs.gov/sir/2011/5120/player.html -1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1200 1800 2400 0600 1200

09-01-2008 09-02-2008

Tidal water surface, in meters

Time

A

F

E

D

C

B

A. 09-01-2008 at 1400 B. 09-01-2008 at 1700

C. 09-01-2008 at 2200 D. 09-02-2008 at 0200

E. 09-02-2008 at 0700 F. 09-02-2008 at 1000
Chapter 1 Chapter 4

Baseline Hydrologic Studies in the Lower Elwha River Prior to Dam Removal Hydrologic Studies in the Lower Elwha River 95

watac11-0558_fig4-14

0 100 200 300 400 500 600

0

5

10

Distance along distributed temperature sensing cable, in meters

20-hour temperature variance, 

in degrees Celsius

ES1 ES2

Elwha River

Water Data Collected within the Estuary

Qualitative observations of surface-water dynamics in 

the Elwha River estuary show the strong influence of tidal 

patterns and river flow dynamics (fig. 4.15), but do not explain 

the role of groundwater interactions, or quantify the relative 

contributions of water sources flowing to, and from, the 

estuary. By collecting temperature, salinity, stage, and surfacewater velocity data at strategic locations in the estuary system, 

in addition to tidal information for the Strait of Juan de Fuca, 

a greater understanding of water movement through the 

complex was possible. Data recorders were placed in the four 

major coastal water bodies of the estuary (ES1, ES2, WESC, 

and Dudley Pond; fig 4.2). Continuous discharge values were 

calculated at the outlet channel of the east estuary. Finally, 

discharge at Bosco Creek, the primary surface-water inflow 

source to the east estuary, was periodically measured during 

the study to characterize surface-water fluxes.

Figure 4.14. Variance in temperature fluctuation along the 

distributed temperature sensor array along the bed of the east 

estuary for the 20-hour period of data collection, Elwha River, 

Washington, September 1–2, 2008. Locations at 25 to 45 meters 

were in a section of the cable in the main stem of the Elwha River. 

Locations 320 meters and greater were sections of the cable in the 

ES2 water body. A prominent area of relatively small temperature 

variation from 180 to 200 meters likely was caused by strong 

groundwater upwelling. Similar reduced variation near 155 and 

76 meters (indicated by arrows) might also reflect groundwater 

upwelling although the strength of upwelling was less pronounced 

than in the interval from 180 to 200 meters.

Salinity, Temperature, and Depth 

Measurements in the Estuary

Water-temperature and salinity data were collected 

with self-recording electrical conductivity and temperature 

(CT) sensors, some of which also included transducers 

to measure water depth (CTD). These sensors were 

placed at four locations throughout the estuary (fig. 4.2; 

table 4.1). The sensors were attached to steel rods pounded 

into the estuary substrate and sampled at 15-minute or 

1-hour intervals. The CTDs were in ES2 from June 2008 

to April 2010, and in Dudley Pond from May 2009 to 

April 2010 (table 4.1). The CTs were placed in ES1 from 

July 2007 to March 2010, and in the WESC from May 

2009 to April 2010 (table 4.1). Salinity data are presented 

in Practical Salinity Units (PSU), which is a relative 

salinity scale approximately equivalent to the total mass 

of salts in parts per thousand. Ocean water and freshwater 

typically are about 32 and 0 PSU, respectively.

Water levels in Dudley Pond and ES2 correlate with 

tidal fluctuations in the Strait of Juan de Fuca, represented 

by the water level at the NOAA tide gage in Port Angeles, 

Washington (fig. 4.16). However, water-level oscillations 

in Dudley Pond were smaller than ES2, and there was a 

lag in time between the water levels at Port Angeles and 

in Dudley Pond (fig. 4.16A). In contrast, the water level in 

ES2 correlates well with the high tides in the Strait of Juan 

de Fuca (fig. 4.16B), suggesting a direct surface-water 

connection with the river mouth. 

Salinity levels in Dudley Pond were fairly low and 

steady, while WESC, on the river side of the levee, had 

higher levels and more fluctuations of salinity, suggesting 

more mixing of freshwater and seawater in WESC than in 

Dudley Pond (fig. 4.16). The east estuary (ES1 and ES2) 

had greater oscillations in salinity than the west estuary. 

Near the outlet of the estuary (ES1), there were daily 

oscillations between almost pure freshwater (about 0 PSU) 

and almost pure seawater (about 32 PSU). In ES2, salinity 

values commonly reached only one-third to one-half of 

those found in ES1 (fig. 4.16).

A longer record (spring to autumn 2009) of water 

temperature and salinity from the CTDs also demonstrated 

the differences between Dudley Pond on the west side 

and ES2 in the eastern estuary (fig. 4.17). During this 

sampling interval, there was a general warming trend until 

August, followed by a cooling trend through December. 

Dudley Pond was commonly from 2 to 5°C warmer than 

ES2 during the summer (fig. 4.17A). The salinity levels in 

ES2 were more variable, and reached higher levels, than 

salinity levels in Dudley Pond (figs. 4.17B and 4.18). 
96 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0558_fig4-15

Low Tide High Tide

A. Discharge 27.4 m3/s February 12, 2005, at 1124

0.84 m MLLW

B. Discharge 27.7 m3/s March 22, 2005, at 0844

1.67 m MLLW 

C. Discharge 31.7 m3/s April 24, 2009, at 1027

-0.06 m MLLW

D. Discharge 30.0 m3/s December 01, 2004, at 1445

1.82 m MLLW

E. Discharge 15.4 m3/s August 04, 2009, at 1009

-0.02 m MLLW

F. Discharge 15.4 m3/s August 04, 2009, at 1723

1.87 m MLLW

Figure 4.15. Effects of tides on water levels in the Elwha River mouth and estuary, Washington. The date, time, and tidal stage, 

measured in meters above Mean Lower Low Water (MLLW) at National Oceanic and Atmospheric Administration tidal station 

9444090 in Port Angeles, is shown for each photograph. (Photographs taken by Ian M. Miller (E and F) and Patrick B. Shafroth.)
Chapter 1 Chapter 4

Baseline Hydrologic Studies in the Lower Elwha River Prior to Dam Removal Hydrologic Studies in the Lower Elwha River 97

watac11-0558_fig4-16

-1

0

1

2

3

0

10

20

30

6 8 10 12 14 16 18 20 6 8 10 12 14 16 18 20

A. West of river mouth B. East of river mouth

Water level, in meters above 

mean lower low water 

Salinity, in practical

 salinity units

Day in September 2009

EXPLANATION

NOAA tidal station 

9444090 at Port 

Angeles

Dudley Pond

ES2

ES1

WESC

Figure 4.16. Surface-water levels and salinity over a 2-week (spring-neap) tidal cycle during low flow for (A) Dudley Pond and 

WESC in the west estuary and (B) ES1 and ES2 in the east estuary of the Elwha River, Washington, September 2009.

0

5

10

15

20

25

30

EXPLANATION

Dudley Pond

ES2

0

5

10

15

20

25

May June July Aug. Sept. Oct. Nov. Dec.

2009

Water temperature, in degrees Celsius Water salinity, in practical salinity units

A. Surface-water temperature

B. Surface-water salinity

Figure 4.17. Surface-water (A) 

temperature and (B) salinity in Dudley 

Pond (west estuary) and ES2 (east estuary) 

in the Elwha River estuary, Washington, 

May–December 2009. Dudley Pond is 

consistently warmer, but it does not 

receive estuarine mixing during spring 

tides like ES2.
98 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Surface-Water Temperature Measurements 

in the East Estuary

To further characterize the temperature of surface 

water in the east estuary, six temperature data recorders 

were deployed in surface-water sites distributed 

throughout the estuary (fig. 4.2; table 4.1). These 

deployments started in early August 2009 during a 

cycle of large tidal variability. The six thermal recorders 

measured near-benthic temperature and the data helped 

explain overall spatial and temporal thermal trends in 

estuarine water. One “transect” of sensors was placed 

approximately parallel to the shoreline and included TStn 

4 to the west, TStn 6 in ES1, and TStn 5 in Bosco Creek 

near where the creek enters ES2 (fig. 4.2). Another sensor 

transect was placed north-south in “finger” channels of 

ES2 (TStn 3 and TStn 2), and a secondary surface-water 

body to the south of ES2 (TStn 1; fig. 4.2). TStn 4, 5, and 

6 were removed on August 8, 2009. TStn 1, 2, and 3 were 

removed in December 2009. 

For thermal-recorder deployments, posts were 

pounded into the substrate of the bed of the water body, 

and a slotted plastic pipe was attached to the post. The 

bottom of the plastic pipe was positioned about 5 cm 

above the estuary substrate. The thermal recorders were 

placed near the bottom of the plastic pipe and secured 

with a nylon string hung from a bolt inserted near the top 

of the plastic pipe. TStn 4 was placed in a shallow well 

dug into the subaqueous substrate with a slotted-plastic 

casing. All thermal recorders were synchronized and 

recorded data at 15-minute intervals. 

Overall, the thermal recorders operating in the east 

estuary showed diurnal fluctuations in temperature and a 

general cooling trend from summer into autumn and early 

winter (fig. 4.19). Additional temperature data collected at 

the Port Angeles tidal station (NOAA 9444090) showed 

that water temperature in the east estuary was closely 

coupled to seasonal air temperature, but was largely 

independent from marine water temperature in the Strait 

of Juan de Fuca. From August 3, 2009, to August 8, 

2009, the lowest temperatures and the largest diurnal 

fluctuations were at TStn 5 (located where Bosco Creek 

enters ES2; fig. 4.2). Similarly, the next lowest recorded 

temperature values in the east estuary were measured at 

TStn 4, closest to the outlet channel (fig. 4.2). Diurnal 

temperature variation decreased from the summer months 

to the autumn.

4-18

0

5

10

15

Water salinity, in practical salinity units

20

0 25 50 0 25 50

Relative frequency of observation , in percent

10

15

20

Dudley Pond ES2

25

5

Water temperature, in degrees celsius

0 5 10 0 5 10

Figure 4.18. Frequency distribution plots showing comparison 

of water temperatures and salinities in Dudley Pond and ES2 

in the Elwha River estuary, Washington, from May 14, 2009, to 

November 10, 2009. 
Chapter 1 Chapter 4

Baseline Hydrologic Studies in the Lower Elwha River Prior to Dam Removal Hydrologic Studies in the Lower Elwha River 99

watac11-0558_fig4-19

-5

0

5

10

15

20

25

07-30-2009 08-20-2009 09-10-2009 10-01-2009 10-22-2009 11-12-2009 12-03-2009 12-24-2009

Temperature, in degrees Celsius

EXPLANATION

TStn 1

TStn 2

TStn 3

Air temperature at NOAA tidal station 9444090

Water temperature at NOAA tidal station 9444090

TStn 4

TStn 5

TStn 6

-5

0

5

10

15

20

25

08-03-2009 08-04-2009 08-05-2009 08-06-2009 08-07-2009 08-08-2009 11-12-2009 11-13-2009 11-14-2009 11-15-2009 11-16-2009 11-17-2009

Figure 4.19. Surface-water temperature data collected in the eastern estuary of the Elwha River, Washington, 

July–December 2009. 
100 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Surface-Water Movement in 

the Estuary

To understand and quantify the 

flux of surface water to and from the 

east estuary, water velocity and depth 

were monitored in the ES1 outlet 

channel from June 3 to 13, 2008, and 

from August 3 to September 2, 2008. 

A 3-MHz acoustic Doppler velocity 

meter was mounted to the bottom of 

the ES1 outlet channel (fig. 4.2), and 

water velocity, stage, and temperature 

were recorded at 5-minute intervals. 

During the period of continuous acoustic 

Doppler velocity meter operation, 

discrete discharge and channel-geometry 

measurements were made at the ES1 

outlet channel over incoming and 

outgoing flows, and used to develop 

index-velocity and stage-area relations 

needed to compute a continuous 

discharge record at the site. Positive 

discharge was defined as flow out of the 

east estuary; negative discharge as flow 

into the east estuary.

On four occasions during summer 

2008 (June 3, June 13, July 16, and 

August 3), instantaneous discharge 

was measured at the Bosco Creek 

gaging station (12046523). In addition 

to periodic flow measurements, stage 

in Bosco Creek was continuously 

monitored during the study period with 

a 5-psi non-vented transducer, which 

was corrected for atmospheric pressure 

changes using a collocated barometric 

pressure recorder.

From June 3 to 13, 2008, the 

average net discharge of water from 

the ES1 outlet channel was 0.26 m3/s. 

Surface-water discharge into the 

estuary from Bosco Creek was 0.09 and 

0.08 m3/s on June 3 and 13, respectively. 

The stage record at Bosco Creek showed 

a gradual decrease in stage during this 

period. Assuming that precipitation 

and evapotranspiration losses from the 

estuary were small, the Bosco Creek 

contribution accounted for about onethird of net surface-water flow to the 

estuary. The net discharge from the 

ES1 outlet channel was calculated to 

be 0.12 m3/s for the sampling period 

August 3 to September 2, 2008. Average 

discharge from Bosco Creek, measured 

on July 16 and August 3, was 0.04 m3/s, 

about one-third of the total net flux at the 

ES1 outlet channel in July and August. 

These results suggest that most of 

freshwater contributions to the estuary 

were from hyporheic flow, a mixture 

of shallow groundwater and subsurface 

river flow originating upstream and 

discharging into the estuary system. 

Overall, the discharge measurements 

at the ES1 outlet channel ranged from 

-0.30 to 1.12 m3/s, demonstrating the 

close connection between tidal potential 

and surface-water from the estuary.

A 2-week record of these 

measurements in August 2008 shows 

the cyclical nature of water flux at the 

estuary outlet (fig. 4.20). The discharge 

of water into ES1 (vertical shading; 

fig. 4.20) occurred over a shorter 

duration, and at a smaller rate, than 

outflow. The resulting net discharge 

exiting ES1 to the river averaged about 

14,000 m3/d, or 0.17 m3/s for the period 

recorded. Instantaneous peak discharge 

during rising-tide conditions exceeded 

2 m3/s, which is more than 10 times the 

net flow rate. This net outflow through 

the ES1 outlet channel represented the 

relative contributions of surface-water 

flow from Bosco Creek and groundwater 

flow into the estuary. 
Chapter 1 Chapter 4

Baseline Hydrologic Studies in the Lower Elwha River Prior to Dam Removal Hydrologic Studies in the Lower Elwha River 101

watac11-0558_fig4-20

0

100

200

50

150

250

August 2008

15 17 19 21 23 25 27 29

Cumulative volumetric 

discharge, in thousands

 of cubic meters

0

2

Discharge,

in cubic meters 

per second

-2

0

0.5

-0.5

Velocity,

in meters

per second

0

1

2

Stage,

in meters

out 

in

out 

in

3

Figure 4.20. Measured stage, velocity, and discharge of water into and out of the east estuary 

through the ES1 outlet channel in the Elwha River estuary, Washington, during 2 weeks in August 

2008. Shaded vertical bands show intervals of time with inflow into the estuary. The average net 

outflow was about 14,000 cubic meters per day (0.17 cubic meters per second).
102 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Synthesis of Estuarine 

Hydrologic Data

Integrating the salinity, 

temperature, depth, and discharge data 

collected during this study allows insight 

into water movement and exchange in 

estuarine water bodies. During much 

of the year, water response in the 

estuary is governed by tidal cycles and 

groundwater and surface-water input 

from the aquifer and river. When storms 

affect the region, waves at the shoreline 

and high discharge within the river can 

alter estuarine water conditions for days 

or weeks. 

General Water Movement 

within the Estuary Complex

The observations of water level, 

temperature, and salinity from the 

sensor network showed how hydrologic 

conditions varied across the estuary. 

For example, water level and salinity 

from measurements west and east of 

the river mouth revealed contrasting 

conditions during the summer of 2009. 

Although water levels in Dudley Pond 

and ES2 responded to tidal fluctuations 

in the Strait of Juan de Fuca, water 

level oscillations in Dudley Pond 

were smaller than ES2 (fig. 4.16). 

Furthermore, the western flood-control 

levee had hydraulically isolated Dudley 

Pond from direct connection with the 

river and Strait of Juan de Fuca, which 

limited water exchange to groundwater 

seepage and direct overwash of 

the beach berm from large waves. 

Groundwater exchange was responsible 

for most of the fluctuations in Dudley 

Pond water levels, shown by the lag 

between the water levels in the Strait 

of Juan de Fuca and in Dudley Pond 

(fig. 4.16A); in contrast, ES2 had a direct 

surface-water connection with the river 

mouth, shown by the close correlation in 

stage during the higher tides in the Strait 

of Juan de Fuca (fig. 4.16B). 

These different hydrologic settings 

across the estuary also influenced 

the mixing of seawater throughout 

this system, shown by the substantial 

differences in the values and patterns 

of salinity across measurement sites. 

Dudley Pond, which was not connected 

to the Strait of Juan de Fuca by surfacewater, had lower and more constant 

salinity, as opposed to WESC, on the 

river side of the levee, where there 

was more mixing of freshwater and 

seawater than in Dudley Pond (figs. 4.16

and 4.17). Similarly, the greater summer 

warming in Dudley Pond as compared 

to ES2 (fig. 4.17) also suggested a lack 

of surface-water connection to Dudley 

Pond.

Within the WESC, high water 

levels in the Strait of Juan de Fuca 

induced rapid increases of salinity which 

then decreased somewhat steadily until 

the next high water. This freshening 

effect between high waters likely was 

from hyporheic input. The greater 

oscillations in salinity in the east estuary 

(ES1 and ES2) resulted from tidal 

flows through the ES1 outlet channel 

(fig. 4.16). The spatial gradient in 

salinity values from ES1 to ES2 (greater 

daily oscillations in ES1 than ES2; 

fig. 4.16), demonstrated that the entire 

east estuary did not fully flush during 

each tidal cycle. 

Surface-water temperatures in the 

eastern estuary (ES1 and ES2) followed 

the general decreasing trends measured 

in Dudley Pond (fig. 4.19). Diurnal 

variation in temperature also was greater 

in the summer months when clear skies 

allowed greater solar heating during 

the day and enhanced radiative cooling 

at night. As climatic temperatures 

decreased in the autumn, increased cloud 

cover reduced radiative heat transfer and 

diurnal temperature variation decreased. 

The cooler Bosco Creek temperatures 

(TStn 5; fig. 4.19) reflected the influence 

of spring-fed surface waters flowing 

down the creek. Near the outlet channel 

(fig. 4.2), temperatures were lower in 

TStn 4 and therefore were more strongly 

influenced by fluxes into the estuary 

from the river (fig. 4.19).

Different distributions of water 

temperature and salinity were measured 

within the 1 km that separates ES2 

in the east estuary from Dudley Pond 

(fig. 4.18). Dudley Pond was warmer 

and less brackish than ES2. These 

differences were directly related to 

unique circulation patterns in the two 

water bodies, particularly the absence of 

hydraulic connection of surface water 

to Dudley Pond. Similarly, substantial 

differences were observed in fish 

diversity and abundance, invertebrate 

community composition, and vegetation 

structure between the east and west 

estuary (Shaffer and others, 2009; Duda 

and others, 2011a, chapter 7, this report; 

Shafroth and others, 2011, chapter 8, 

this report). 
Chapter 1 Chapter 4

Baseline Hydrologic Studies in the Lower Elwha River Prior to Dam Removal Synthesis of Estuarine Hydrologic Data 103

-1

0

1

2

3

27

November December

29 1 3 5 7 9 11

0

500

1,000

2007

Discharge, in cubic 

meters per second Water level, in meters above 

mean lower low water

-2

1,500 EXPLANATION

NOAA tidal station 9444090

ES1

Elwha River discharge at 

USGS gaging station 

122045500

Peak flow

Figure 4.21. Discharge, stage in ES1 measured in the Elwha River, and tidal stage measured 

at National Oceanic and Atmospheric Administration (NOAA) tidal station 9444090 in Port 

Angeles, Washington, during the large peak-flow event of December 2007.

Effects of River Flooding and Morphologic 

Changes on Estuarine Hydrology

Heavy precipitation and snow melt create high discharge 

and stage on the lower Elwha River. Stage at the mouth of the 

Elwha River also rises during high tides, and these temporary 

changes in water levels influence water movement throughout 

the estuary. 

The effects of the December 2007 peak-flow event, with 

a maximum value of 1,020 m3/s and an estimated 40-year 

recurrence interval (Draut and others, 2011), were recorded in 

measurements in the east estuary. The high river flow lasted 

2 days during which time the water levels in ES1 remained 

uncharacteristically high (fig. 4.21). The event reduced salinity 

in ES1 to nearly 0 PSU for 2 weeks, even though the pattern of 

fluctuation in stage in ES1 was strongly forced by tidal cycles 

immediately after this event (fig. 4.22). 
104 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0558_fig4-22

December 2007 peak flow

EXPLANATION

NOAA tidal station 9444090

Elwha River discharge at 

USGS gaging station 12045500

ES1 water properties

 Temperature

 Water level

 Salinity 

July August September October November December January February

2007–08

Salinity, in practical

 salinity units

0

5

10

15

20

-2

0

2

4

0

10

20

30

0

500

1,000

Discharge, in cubic meters

per second

Water level, in meters above 

mean lower low water

Water temperature,

in degrees Celsius

Figure 4.22. Hydrologic, temperature, and salinity conditions in the east estuary (ES1) related to the discharge in the 

Elwha River, Washington, from August 2007 to February 2008. The effects of the December 2007 peak-flow event on 

the east estuary are apparent, with decreased salinity in the east estuary for 2 weeks, and increased water levels and 

temperature.
Chapter 1 Chapter 4

Baseline Hydrologic Studies in the Lower Elwha River Prior to Dam Removal Synthesis of Estuarine Hydrologic Data 105

watac11-0558_fig4-23

1

2

3

0 5 201510 25 5 0 201510 25

Before peak flow After peak flow

Water level, in meters above 

mean lower low water

Relative frequency of observation, in percent

Figure 4.23. Frequency distribution plots showing a comparison of 

water levels in ES1, in the east estuary of the Elwha River, Washington, 

for the 80 days before (September 7, 2007, to November 29, 2007) and 

after (December 8, 2007, to February 25, 2008) the large river peak-flow 

event of December 2007. The wider distribution of water levels after the 

peak-flow event indicates an increase in the surface-water connectivity 

between the tidal river mouth and east estuary. 

This peak-flow event also modified the surfacewater connection between the river mouth and ES1. 

During the event, 7–8 m of bank erosion and channel 

migration occurred in the river adjacent to the east 

estuary (Draut and others, 2011). This morphologic 

change altered the size and elevation of the ES1 

outlet channel, increasing the hydraulic connection 

between the river and ES1. These changes were 

reflected in the increased amplitude of water levels 

in ES1 after the event (fig. 4.22). After the 2007 

peak-flow event, there was approximately 1 m 

greater range in the cycle of stage in ES1; the stage 

peaks were higher, and the stage troughs were lower 

(fig. 4.23). Similarly, water salinity in ES1 had more 

variability following the 2007 peak-flow event, 

further reflecting larger overall volumetric exchange 

of water through the ES1 outlet channel (fig. 4.22). 

Although the December 2007 peak-flow event 

expanded the ES1 outlet channel, future high flows 

or channel reorganization might reduce the size 

of this connecting channel or block it altogether. 

Such a cut-off event would greatly reduce estuarine 

exchanges in ES1 and ES2, dampening fluctuations 

in water level, temperature, and salinity to levels 

currently observed in the WESC or Dudley Pond. A 

blockage also would limit access to rearing habitat 

for young fish. For example, a large sediment 

deposit completely blocked access to ES1 and ES2 

following a peak-flow event in November 2006. This 

particular estuary blockage changed the community 

composition and density of salmonids in 2007 (Duda 

and others, 2011a, chapter 7, this report). 

Conceptual Model of Water Exchange in 

the Estuary

The observations of water conditions and flow 

from 2007 to 2009 provided insight into the general 

framework of water exchange within the river mouth 

and estuary. The extent and timing of these water 

exchanges are related to the connections of surface 

water and groundwater to these water bodies, and 

it is apparent, for the east estuary at least, that these 

surface-water connections can change dramatically 

after high flows or by channel-evolution processes. 

A conceptual diagram (fig. 4.24) schematically shows the 

movement of water through the estuary over a tidal cycle under the 

current pre-dam-removal conditions. Water movement, in turn, affects 

salinity patterns and overall water quality in the estuary (fig. 4.24). 

Between high and low tide, the river exports water through the river 

mouth. The river discharge rate and evacuation from ES1 and ES2 is 

greatest during the falling (ebbing) tide (fig. 4.24B). During the rising 

(flooding) tide, saline ocean water enters the river mouth and spreads 

into connecting estuarine channels causing increases in water salinity 

within the estuary (fig. 4.24D). The rate of water flux through these 

estuarine channels is governed by geometry in the ES1 outlet channel 

and stage in ES1, ES2, and the river. Moreover, overall magnitude of 

estuarine-channel water flux changes with the regular morphologic 

evolution of the river-mouth region (Warrick and others, 2011a, 

chapter 3, this report). With the imminent removal of the two dams 

on the Elwha River and the arrival of increased sediment load and 

concomitant morphological changes, the Elwha River estuary likely 

will experience a dynamic increase in the rate of change and evolution. 

At some point after dam removal, when the fluvial transport of 

sediment and large woody debris stabilizes, the rate of morphological 

change in the estuary would, presumably, reach a new equilibrium. 
106 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0558_fig4-24

A. High tide

B. Falling (ebb) tide

C. Low tide

D. Rising (flood) tide

river

coastal 

waters pond

pond

levee

creek

Salinity

brackish

fresh

Tidal stage High water

Low water

A

B C

D

EXPLANATION

Figure 4.24. Conceptual and schematic diagrams of 

surface water flow in and out of the Elwha River estuary, 

Washington, over a tidal cycle. The thickness of arrows 

represents the relative rate of discharge. Blue represents 

relatively fresh river water and green represents saline 

marine water.
Chapter 1 Chapter 4

Baseline Hydrologic Studies in the Lower Elwha River Prior to Dam Removal Summary 107

Summary

To better understand the hydrology 

of the lower Elwha River and its estuary 

before the removal of two dams, the 

U.S. Geological Survey, working 

with collaborators, collected baseline 

hydrologic data and interpreted the 

current hydrologic state of the lowerriver system. In particular, transient 

storage was measured in the lower 

river, groundwater response and river 

interactions with the groundwater 

aquifer were characterized, salinity 

and stage were measured and analyzed 

in estuarine water bodies, and the 

movement of water through the estuary 

was analyzed and characterized. 

Transient storage has been 

measured in many streams throughout 

the United States; however, due to 

logistical constraints, these studies are 

typically conducted on small headwater 

streams. Relatively few transient-storage 

studies have been conducted on larger 

systems comparable to the Elwha River 

or used to quantify changes in transient 

storage following a large dam removal, 

although theoretical models have 

predicted how a channel will change 

after small dam removals. Results from 

this study represent a unique dataset 

to assess changes in a large river 

before and after dam removal and the 

subsequent effects on channel shape and 

sediment supply. The dye experiment 

showed that the low-flow channel of the 

lower 3.9 kilometers of the Elwha River 

was relatively simple, and 1 to 6 percent 

of the median travel time of dye was 

attributed to transient-storage processes. 

The monitoring of groundwater 

elevation in four wells located along 

the lower Elwha River showed a strong 

correlation between stage in the river 

and groundwater levels in the flood 

plain. A tidal signal also was observed 

in the groundwater-elevation data, 

but groundwater fluctuations from 

tides were significantly smaller than 

fluctuations due to changes in river 

stage. Water temperature data collected 

in the monitoring wells showed a delay 

of days to months between the changes 

in temperature in the well adjacent the 

river and temperature in wells farther 

from the river.

A seepage investigation along 

the lower 4.4 kilometers of river in 

September 2007 showed a 10 percent 

loss of river flow to the groundwater 

aquifer at a section of the river 1.7 to 

2.8 kilometers upstream of the mouth. 

No clear trends of losses or gains were 

observed along the rest of the study 

reach.

A distributed temperature sensing 

cable deployed for 20 hours in the 

east estuary on September 1–2, 2008, 

characterized bed temperature of 

ES2, ES1, the main-stem river, and 

the interconnecting channels of the 

east estuary. Both ES1 and ES2 were 

warmed by solar heating during the 

day, and the water temperature in ES2 

remained a relatively constant 14 to 

15°C. ES1 was cooled during the day 

and night as tidally influenced water 

from the river flowed into the estuary. 

ES2 remained relatively warm during 

the night hours due to its distance from 

the river and larger size. An analysis of 

the temperature variance at particular 

points along the cable enabled the 

identification of one pronounced 

location in the middle of ES1 where 

groundwater upwelling regulated the 

temperature of the estuary bed. The 

location probably is an old relict river 

channel. Two other possible upwelling 

sites were located along the cable, 

although the variance data could not 

conclusively confirm these upwelling 

sites. 

Salinity and depth data were 

collected at locations in ES1, ES2, the 

WESC, and Dudley Pond from 2007 

to 2010 helping to explain how water 

moved through the estuary. During 

summer low-flow conditions in the 

river, stage and salinity in ES1 and ES2 

were found to fluctuate significantly in 

response to the rising (flooding) and 

falling (ebbing) tides. Salinity in ES1 in 

September 2009 ranged between 1 and 

32 Practical Salinity Units (PSU), and 

salinity in ES2 ranged between 1 and 15 

PSU. In contrast, fluctuations of stage 

and salinity in the WESC were much 

less pronounced. Salinity in the WESC 

ranged between about 3 and 11 PSU. 

Changes in stage were relatively small 

in Dudley Pond, reflecting the fact that 

this water body is hydraulically isolated 

from the river and the Strait of Juan de 

Fuca. Similarly, salinity in Dudley Pond 

was no more than 2 PSU during the lowflow conditions of late summer 2009. 

As the estuary was influenced by storm 

conditions in autumn and winter, overall 

salinity as well as salinity fluctuations 

increased in the estuary. In contrast, 

temperature and temperature fluctuations 

decreased as the weather became 

dominated by temperate rain storms and 

cloudy conditions. 

An acoustic Doppler velocity meter 

deployed in the ES1 outlet channel 

in the summer of 2008, coupled with 

discharge and stage measurements, 

allowed the measurement of the total 

discharge of surface water flowing 

from the east estuary. Although 

discharge moved both in and out of 

the estuary, depending on river stage 

governed by tidal cycles, the net flow 

of surface water was out of the east 

estuary. In June, the net outflow from 

the east estuary averaged 0.26 m3/s. In 

August and September, the net outflow 

averaged 0.12 m3/s. Contemporaneous 

measurements of discharge in Bosco 

Creek showed that the surface-water 

inflow into the east estuary was about 

one-third the net outflow through the 

ES1 outlet channel, both in June and in 

August to September. It was presumed 

that the remaining two-thirds of extra 

inflow originated from groundwater flow 

into the estuary.

The river’s influence on estuarine 

salinity and stage increased dramatically 

in autumn and winter as peak-flow 
108 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

events in the main-stem river, coupled 

with tidal effects, pushed large volumes 

of fresh water into the east estuary. For 

example, a large peak-flow event in the 

river in December 2007 reduced salinity 

in ES1 to nearly zero for two weeks. 

The data collected within and 

adjacent to the estuary helped to explain 

some of the complex interactions of 

saline marine water, fresh river water, 

and fresh groundwater under seasonal 

conditions. This insight led to the 

formulation of a simple conceptual 

model of water movement in the estuary 

that will help guide future research 

efforts focused on understanding river 

and estuary response to dam removal.

The underlying hydrologic 

framework of the lower Elwha River, 

its mouth, and the estuarine system 

of coastal ponds and interconnected 

channels reflects a complex set of 

fluvial, marine, geologic, climatic, 

and anthropogenic influences. These 

hydrologic processes will likely 

change after the removal of the two, 

long-standing Elwha River dams. 

Although the opportunity to study 

and understand the evolution of these 

hydrologic processes during and after 

dam removal is unprecedented, the 

collection of baseline hydrologic data 

and the formulation of fundamental 

scientific understanding of the existing 

processes are essential to maximize the 

potential insight gained from a damremoval project of exceptional size and 

complexity.

This chapter documents efforts 

by the U.S. Geological Survey and 

its collaborating partners to monitor 

and interpret the hydrologic system 

within the lower Elwha River and its 

estuary. More importantly, the basic 

research characterizing the hydrologic 

framework of the dam-influenced Elwha 

River contained herein will provide 

future scientists the opportunity to 

study processes and river and estuary 

responses not envisioned before the 

project.

Acknowledgments

Michael McHenry, Matthew 

Beirne, Mitch Boyd, all with the Lower 

Elwha Klallam Tribe, contributed 

expertise, advice, and data to support 

this study.

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Chapter 1 Chapter 5

 

5

Chapter

Coastal Processes of the Elwha 

River Delta

By Jonathan A. Warrick, Andrew W. 

Stevens, Ian M. Miller, and Guy Gelfenbaum

Abstract

To understand the effects of increased 

sediment supply from dam removal on 

marine habitats around the Elwha River 

delta, a basic understanding of the 

region’s coastal processes is necessary. 

This chapter provides a summary of 

the physical setting of the coast near 

the Elwha River delta, for the purpose 

of synthesizing the processes that move 

and disperse sediment discharged by 

the river. One fundamental property 

of this coastal setting is the difference 

between currents in the surfzone with 

those in the coastal waters offshore of 

the surfzone. Surfzone currents are 

largely dictated by the direction and 

size of waves, and the waves that attack 

the Elwha River delta predominantly 

come from Pacific Ocean swell from 

the west. This establishes surfzone 

currents and littoral sediment transport 

that are eastward along much of the 

delta. Offshore of the surfzone the 

currents are largely influenced by tidal 

circulation and the physical constraint 

to flow provided by the delta’s headland. 

During both ebbing and flooding tides, 

the flow separates from the coast at 

the tip of the delta’s headland, and this 

produces eddies on the downstream side 

of the headland. Immediately offshore 

of the Elwha River mouth, this creates a 

situation in which the coastal currents 

are directed toward the east much more 

frequently than toward the west. This 

suggests that Elwha River sediment will 

be more likely to move toward the east 

in the coastal system. 
112 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Introduction

Dam removal on the Elwha River 

will result in fundamental increases in 

sediment delivery to the Strait of Juan de 

Fuca (Strait). To understand and predict 

the effects of this increased sediment 

supply on marine habitats around the 

delta, a basic understanding of coastal 

processes is necessary. This chapter 

synthesizes information about the 

physical setting of the Elwha River delta 

to provide a general understanding of 

the coastal processes that will determine 

future changes to the coastal ecosystems 

in and around the Elwha River delta 

after dam removal. 

Coastal Setting 

The Elwha River discharges into 

the Strait of Juan de Fuca, a waterway 

between the Salish Sea and the Pacific 

Ocean (fig. 5.1). The Elwha River delta 

is sheltered from much, but not all, of 

the waves and swells from the Pacific 

Ocean, although it is exposed to the 

abundant and energetic exchange of 

water between the Salish Sea and the 

Pacific Ocean. This setting—sheltered 

from the ocean and yet exposed to 

strong tidal and estuarine circulation—is 

a defining feature of the Elwha River 

delta. 

Another defining feature is the 

broad and shallow submarine delta that 

extends several kilometers offshore 

from the present shoreline (fig. 5.1B). 

The origins of this submarine delta 

are discussed in Warrick and others 

(2011, chapter 3, this report). This 

feature strongly influences the waves 

and coastal currents that act upon this 

section of coast. Acoustic, video, and 

physical sampling techniques have 

shown that the submarine delta seafloor 

is composed of coarse sand to boulders 

(Warrick and others, 2008). No finegrained sediment has been deposited on 

the submarine delta, although deposits 

of fine-grained sediment are expected 

following dam removal (Warrick and 

others, 2008). 

Another element of the Elwha 

River delta setting is the fundamental 

difference between processes and 

currents within the surfzone and 

within the coastal zone offshore of the 

surfzone (fig. 5.2). The fundamental 

difference between these zones is the 

relative importance of waves in dictating 

currents. Near the beach, breaking 

waves provide a dominant influence on 

currents (Komar, 1998). Waves in the 

surfzone are not only responsible for the 

back-and-forth motions of water as each 

wave passes, but also can drive currents 

along the beach when waves approach 

at an oblique angle (fig. 5.2). These 

wave-generated currents are the primary 

drivers of alongshore beach sediment 

movement in littoral cells (Komar, 

1998). 

Offshore from the surfzone, waves 

still impart substantial back-and-forth 

movements in the water-column and 

along the seafloor, but the currents 

primarily are driven by tidal, windgenerated, or other coastal currents. 

This may result in a situation, such as 

shown in figure 5.2, in which currents 

in the surfzone and the coastal zone are 

in opposing directions. This situation 

would cause differences in the transport 

directions of water and sediment in 

these zones. Although shear will not 

always be present between the surf- and 

coastal zones, transport within these 

zones will be produced by different, 

and largely independent, processes. 

For the Elwha River delta, the surfzone 

extends only several to tens of meters 

off of the shoreline depending on wave 

height and tidal stage. More information 

about these processes is available in the 

reviews of Nittrouer and Wright (1994) 

and Komar (1998). 
Chapter 5

Coastal Processes of the Elwha River Delta Coastal Setting 113

Figure 5.1. Elwha River and Strait of Juan de Fuca, near Port Angeles, Washington. (A) The Strait of Juan de Fuca is the 

primary waterway between the Salish Sea and the Pacific Ocean. (B) The local topography and bathymetry of the Elwha River 

delta. 

Surfzone

Current

Coastal 

Current

wave crests

breaking 

waves

oblique 

waves

zone of 

shear

Figure 5.2. Schematic diagram showing alongshore currents of nearshore waters. Surfzone 

currents (green arrow) are caused by breaking waves when they have oblique approach 

angles. The coastal currents (blue arrow) offshore of the surfzone are influenced by tidal, 

wind-driven, or other regional currents and may or may not be in the same direction as the 

surfzone currents.

Submarine Delta

Elwha River

Port Angeles

W E

Ediz Hook

W

E

Elwha

River

PACIFIC 

OCEAN 

Salish Sea

fig. B

Strait of Juan deFuca

Shaded relief from Puget Sound LIDAR Consortium

Base modified from U.S. Geological Survey

1:100,000-scale digital data

-30

-60

-90

-120

-150

-180

0

Elevation, in meters

EXPLANATION

Sites of current measurement

West

East

136

134

132

130

128

138

305 310

Easting, in kilometers

Northing, in kilometers

290 295 300 315

125° 123°

48°

49°

47°

A. B.
114 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Waves

The Strait of Juan de Fuca has an 

intermediate wave climate between 

the energetic outer coast exposed to 

the Pacific Ocean and the more placid 

conditions of the Salish Sea (Shipman, 

2008), although few measurements 

of the wave conditions within the 

Strait of Juan de Fuca are available to 

corroborate this understanding. To better 

characterize waves, the U.S. Geological 

Survey (USGS) installed acoustic 

Doppler current profilers (ADCP) along 

the seafloor at two sites at about 10 m 

water depth, and sampled waves hourly 

between January 26 and May 2, 2006 

(fig. 5.1B). Although limited in their 

duration, these measurements provide 

important information about the general 

wave conditions at the delta.

 Waves heights at the Elwha 

River delta regularly exceeded 1 m and 

occasionally exceeded 2 m (fig. 5.3A). 

In contrast, waves of the outer coast of 

Washington exceeded 10 m during this 

same winter-to-spring season (Ruggiero 

and others, 2010). The wave heights 

at the Elwha River delta rose and fell 

rapidly in response to locally generated 

wind waves and swell from in the 

Pacific Ocean (fig. 5.3). Wave heights in 

excess of 1 m generally lasted for only 

a day or less (fig. 5.3), and wave heights 

were most commonly less than 0.5 m 

(fig. 5.4A). 

The narrow shape of the Strait 

of Juan de Fuca causes waves to be 

focused into a narrow northwestern 

directional band. For example, more 

than 90 percent of the wave energy 

that approached the Elwha River delta 

during our observations came from the 

northwest (fig. 5.5). Warrick and others 

(2009a) provide further evidence that 

northwest wave directions dominate all 

seasons of the year. 

The waves at the Elwha River delta 

also are derived from a combination 

of local wind-generated waves from 

the Strait and swell from the Pacific. 

Because of the shape and size of the 

Strait of Juan de Fuca, the Elwha River 

delta “fetch” (the distance over which 

wind can blow to generate waves) is 

about 70 km. One effect of this 70-km 

fetch is that waves generated within 

the Strait will be limited to periods 

of less than 8 seconds (Komar, 1998; 

U.S. Army Corps of Engineers, 2002). 

Waves with longer periods come 

from Pacific Ocean swell, where the 

fetch is much longer. Our records of 

waves at the Elwha River delta show 

combined influences from low period 

(4–8 seconds), locally generated wind 

waves and longer period (greater than 

8 seconds) ocean swell (fig. 5.3B). The 

most common condition measured 

consisted of wave periods in excess of 

8 seconds (fig. 5.4B), which indicates 

that Pacific Ocean swell dominate wave 

conditions more frequently than wind 

waves. 

Because the waves at the Elwha 

River delta originate from the northwest 

direction, these waves break at oblique 

angles along much of the shoreline, and 

these obliquely breaking waves drive 

surfzone currents and littoral sediment 

transport. Observations of wave 

breaking angles have been obtained 

from airborne light detection and 

ranging, or “lidar,” of the ocean water 

surface, historical aerial photography of 

the beach, and numerical modeling of 

wave propagation in the Strait (fig. 5.6). 

Combined, these observations show 

that the northwest wave approach 

imparts normally aligned waves on the 

western side of the delta and oblique 

wave breaking angles on the eastern 

side (fig. 5.6). Thus, transport of littoral 

sediment should be negligible west of 

the river mouth and eastward on the 

eastern side of the river mouth. This 

conceptual model for littoral sediment 

transport is consistent with recent 

measurements of littoral sediment 

movement, which suggests that sediment 

can move more than 100 m/d along the 

east beach under the strongly oblique 

wave directions (see Miller and others, 

2011, sidebar 5.1, this report).
Chapter 5

Coastal Processes of the Elwha River Delta Waves 115

wa11-0558_fig 05-3

A.

B.

Significant wave height, in meters Dominant wave period, in seconds

1

2

20 40 60 80 100 120

20 40 60 80 100 120

5

0

10

15

20

0

March April

2006

2006 ordinal date

January February

April May

May

January February March

Figure 5.3. Wave height and wave period measurements from the western side (site W) of the Elwha River 

delta, Washington, during 2006.
116 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

wa11-0558_fig 05-4

0 2 4 6 8 10 12 14 16 18 20 0

0.2

0.4

Significant wave height, in meters Dominant wave period, in seconds

A. B. 

Relative frequency Relative frequency 

0 0.5 1.0 1.5 2 2.5 0

0.10

0.05

0.15

0.20

0.25

Figure 5.4. Histograms of significant wave height and dominant wave period from 

observations at the western side (site W) of the Elwha River delta, Washington. Waves 

generally are less than 1 meter with periods greater than 8 seconds, indicating Pacific Ocean 

origins. Location of site is shown in figure 5.1.

N

W E

S

Figure 5.5. Rose diagram showing dominant wave direction 

from observations at the western side (site W) of the Elwha 

River delta, Washington. More than 90 percent of the 

observations were dominated by waves from the northwest, 

which is the direction of approach for waves generated in 

either the Pacific Ocean or the western Strait of Juan de Fuca.
Chapter 5

Coastal Processes of the Elwha River Delta Waves 117

fig 056

EXPLANATION

Wave breaking angle along

 the shoreline, in degrees

+ or - Greater than 15

10 to 15

5 to 10

Less than 5

1 meter 

Wave height,

(Hsig) in meters

0 0.25 0.50 0.75 1

Dominant 

wave direction

A.

B.

B.

C.

C. 295 300

129

132

200 250 300 350 400

100

150

200

128

132

136

290 295 300 305 310 315

Easting in kilometers

Northing in kilometers

Shaded relief from Puget Sound LIDAR Consortium

Shoreline modified from U.S. Geological Survey

1:100,000-scale digital data

Figure 5.6. Wave patterns for the Strait of Juan de Fuca and Elwha 

River delta, Washington, from measurements and model simulation 

results. (A–B) The transformation of wave heights and directions 

in the Strait from 6 meter Pacific Ocean swell as predicted by 

the SWAN numerical model (after Gelfenbaum and others, 2009). 

Arrows in (B) show modeled wave directions. (C) Measurements 

of the angle of breaking waves along the Elwha River delta 

shoreline during northwest swell (black arrow) from lidar and aerial 

photographs (after Warrick and others, 2009).
118 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Sidebar 5.1 Tracking the Movement of Cobble on the Elwha Beach

 Ian M. Miller and Jonathan A. Warrick

It is challenging, and yet important, to measure and understand sediment transport rates 

and directions on a mixed grain-size beach like the one along the Elwha River delta. To directly 

measure these sediment movements, Radio Frequency Identifier (RFID) tags have been placed 

into native pebbles, cobbles, and small boulders, and their movements have been tracked 

over various sites, time scales, and wave conditions. RFID tags (fig. S5.1A) are small passive 

transponders used frequently in tracking fish and applied more recently to the study of bedload 

transport in rivers and beaches. The device contains a small chip and a capacitor, which 

will absorb energy transmitted by a nearby radio antenna and, using the power stored in the 

capacitor, transmit a unique numerical code back to the antenna. Small (23 mm long), durable 

glass encapsulated RFID tags were implanted directly into native beach clasts to create the 

tracers; the only evidence of the RFID tag is a small epoxy cap visible on the surface of the rock 

(fig. S5.1B). An easily carried mobile antenna was used to re-locate and identify individual clasts 

buried in the beach (fig. S5.1C–D). 

Application of the RFID technique resulted in 80–100 percent recovery of the tracers placed 

on the beach. To the east of the Elwha River mouth, tracer trajectories indicate that there is 

consistent movement to the east (fig. S5.2). By contrast, tracer samples placed on the beach west 

of the river mouth moved in both alongshore directions (Miller and others, 2011). Wave height, and 

therefore the energy contained in the waves, seems to be the best predictor of the overall velocity 

of a sample of tracers on the beach over a 24 hour interval (fig. S5.2). The velocities of these 

tracer sediments also have been surprisingly high. During the 0.64 m wave heights of February 

6-7, 2009, gravels and cobbles were measured moving more than 100 m during a tidal cycle (fig. 

S5.2C).

A

C D

B Figure S5.1. Methods 

used to track cobble 

movement on the beach 

with Radio Frequency 

Identifier (RFID) tagged 

clasts, Elwha River 

delta, Washington. (A) A 

single 23-millimeter long 

RFID tag. (B) A set of 

completed tracers ready 

for placement. The epoxy 

cap is barely visible on 

each tracer and is the only 

permanent indication of 

the RFID tag inside. (C) The 

mobile reader unit, with a 

hand-held antenna. The 

battery and unit are carried 

in a backpack. (D) A 

recovered clast (at the 

base of the orange stake) 

was buried approximately 

25 centimeters.
Chapter 5

Coastal Processes of the Elwha River Delta Waves 119

wa11-0558_fig SS_5-2

Wave

height, in 

meters

0.20

0.39

0 0.64

0 10 20 30 40 50 METERS

50 100 150 200 FEET

release location

large pebble (32-64 mm)

small cobble (64-128 mm)

EXPLANATION

N

Beach location

295 300

129

132

Shaded relief from Puget Sound LIDAR Consortium

beach foreshore

August 1-2, 2008

February 5-6, 2009

February 6-7, 2009

A.

B.

C.

D.

Figure S5.2. Diagrams and map showing examples of three 24-hour releases of the Radio Frequency Identifier 

tracers over a range of wave conditions, Elwha River delta, Washington. (A) August 1–2, 2008; (B) February 5–6, 

2009; (C) February 6–7, 2009, (D) location of active foreshore and release site. Wave heights from visual 

estimates on August 1–2, 2008, and a pressure transducer located offshore of this site during the February 2009 

measurements. 
120 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Tides and Water Levels

The water levels within and outside 

of the Elwha River delta dictate the 

estuarine flow in and out of the river 

mouth, the elevation of beach processes 

such as swash, and the potential for 

coastal flooding. These water levels 

respond to tidal and atmospheric 

conditions that can change greatly over 

the course of a day. The Strait of Juan de 

Fuca has a mixed, mesotidal regime 

(Mofjeld and Larsen, 1984; Finlayson, 

2006). The “mixed” classification 

indicates that diurnal and semi-diurnal 

cycles in water levels (that is, cycles 

that occur approximately once and 

twice per day, respectively) influence 

the overall water level in approximately 

equal amounts. The “spring tidal range” 

is defined as the difference between the 

mean higher high water (MHHW) and 

the mean lower low water (MLLW), 

which are the multiple year averages 

of the higher high tide of each day and 

lower low tide of each day (Komar, 

1998). The spring tidal range of the 

nearest tidal gauge in Port Angeles, 

Washington (National Oceanic and 

Atmospheric Administration station 

9444090) is 2.15 m, which makes this 

region “mesotidal.” The spring tidal 

range generally increases with distance 

into the Salish Sea, and the inner parts 

of the Puget Sound are macrotidal with 

spring tidal ranges greater than 4 m 

(Finlayson, 2006).

 An example of water levels 

at nearby Port Angeles is shown in 

figure 5.7. These data reveal two 

important characteristics. First, the water 

levels reside at the higher elevations for 

longer intervals of time than the lower 

elevations (fig. 5.7). The low tides are 

fairly brief in time and have punctuated 

drops and rises. This is a common 

phenomenon within the Strait of Juan 

de Fuca and the Salish Sea, and results 

from the mixing of diurnal and semidiurnal tidal components (Finlayson, 

2006). Thus, the distribution of water 

levels at the Elwha River delta is skewed 

toward the higher elevations (fig. 5.8). 

The second important characteristic 

is that water levels near Port Angeles 

can deviate from expected levels, 

especially during storm surges. Storm 

surges within the Strait of Juan de 

Fuca and the Salish Sea result from 

drops in atmospheric pressure as 

storms reside over the region, and these 

effects generally are greatest in winter 

(Finlayson, 2006). The net effect of 

storm surge is that water levels can be 

much higher than expected, and water 

level deviations of as much as 0.5 m 

(fig. 5.7) are common for the winter 

storms in the Strait (Finlayson, 2006). 

Storm surges within the Strait of 

Juan de Fuca also occur during times of 

high winds, and therefore high waves, 

because the storms that cause surge also 

cause high winds. The combination 

of these conditions—storm surge and 

high waves—often results in substantial 

littoral sediment transport and coastal 

erosion during winter storms (Finlayson, 

2006).
Chapter 5

Coastal Processes of the Elwha River Delta Tides and Water Levels 121

110558fi057

Observed 0.5 m of storm surge

Predicted

-0.5

0

0.5

December 31

Noon Midnight Noon Midnight Noon Midnight Noon Midnight

Noon Midnight Noon Midnight Noon Midnight Noon Midnight

Noon

Noon

January 1 January 2 January 3

December 31 January 1 January 2 January 3

-1

0

1

2

3

Difference between

observed and predicted

water levels, in meters Water level in meters, Mean Lower Low Water

A.

B.

Surge

Date and time, in Pacific standard time, 2009-2010

Date and time, in Pacific standard time, 2009-2010

Figure 5.7. Water levels from the 

National Oceanic and Atmospheric 

Administration tidal gauge in Port 

Angeles, Washington (station 9444090) 

showing typical spring tidal range 

coupled with storm surge from the 

January 1, 2010, storm.

Figure 5.8. Relative 

frequency of water levels and 

tidal statistics at the National 

Oceanic and Atmospheric 

Administration tidal gauge 

in Port Angeles, Washington 

(station 9444090) showing 

distribution skewed toward 

high water levels. Data are 

from an 18.6 year tidal epoch.

Water level in meters, Mean Lower Low Water -1

0

1

2

3

0 0.02 0.04 0.06 0.08 0.10

MHHW

MHW

MSL

MLW

MLLW

Relative frequency 
122 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Coastal Currents

The Strait of Juan de Fuca is 

the primary channel connecting the 

Salish Sea with the Pacific Ocean, and 

because of this physical setting the 

Strait serves as a conduit for tidal and 

estuarine exchange between these two 

water bodies. To provide the water 

necessary for the meso- to macrotidal 

conditions within the Salish Sea, strong 

tidal currents with speeds on the order 

of 100 cm/s flow in and out through 

the Strait daily (Holbrook and others, 

1980). Much like the “mixed” diurnal 

and semi-diurnal characteristics of the 

water levels in the Strait, the strong 

tidal currents have diurnal and semidiurnal components with somewhat 

more importance of the semi-diurnal 

(twice daily) cycling (Holbrook and 

others, 1980).

The large volume of river 

discharge that enters into the Salish 

Sea also dictates coastal currents in 

the Strait of Juan de Fuca. Freshwater 

discharged into the Salish Sea forms 

a freshened, buoyant layer along the 

upper 50 to 150 m of water depths in 

the Strait, and this freshened surface 

layer exits toward the Pacific Ocean 

at an average rate of about 10 cm/s 

(Holbrook and others, 1980; Thomson 

and others, 2007). Because this 

“estuarine” outflow of freshened water 

has strong vertical gradients in density 

(freshwater is less dense than seawater), 

it is characterized as a “baroclinic” flow. 

This flow of freshened water varies 

considerably over seasonal timescales, 

and is most intense during the spring 

freshet from snowmelt runoff (Masson 

and Cummins, 2004; Thomson and 

others, 2007). 

To evaluate the effects of these 

coastal currents on circulation around 

the Elwha River delta, the USGS has 

conducted current meter measurements 

(fig. 5.1B) and developed a numerical 

circulation model described in 

Gelfenbaum and others (2009). These 

combined data show that the coastal 

currents near the Elwha River delta are 

strongly tidal (fig. 5.9). Most (about 

90 percent) of the variance in the 

currents near the Elwha River delta can 

be explained by tidal ebbs and floods 

(Warrick and Stevens, 2011). These tidal 

currents have diurnal and semi-diurnal 

components, with slight dominance in 

the semidiurnal, or twice daily, cycling 

of currents. 

These observations also suggest 

that coastal currents do not flow in a 

simple, uniform manner around the 

delta, but rather the coastal currents 

generate eddies as they flow past the 

headland of the delta (fig. 5.10). The 

shape of the Elwha River delta causes 

the flow to separate near the tip of 

the delta headland during ebbing and 

flooding, which causes a return flow, or 

“eddy”, on the downstream side of delta 

(fig. 5.10). Warrick and Stevens (2011) 

determined that the headland-induced 

eddies are regular features in the coastal 

currents at the Elwha River delta during 

spring and neap tides. These eddies also 

explain why there is little agreement 

between currents measured at opposite 

sides of the delta even when differences 

in the orientation of the currents and 

in the timing of the tidal responses 

were considered (fig. 5.9; Warrick and 

Stevens, 2011). 

One implication of these headlandinduced eddies is that coastal currents 

near the shore on both sides of the delta 

are preferentially directed toward the 

delta tip. For example, the coastal waters 

immediate offshore of the river mouth 

are subject to currents that flow toward 

the northeast more frequently and at 

faster current speeds than those toward 

the opposite, or southwest, direction 

(fig. 5.10). In this situation, the waters 

discharged by the river are subject 

to northeast-directed currents, which 

strongly affect the location of the Elwha 

River plume and its ecological effects.
Chapter 5

Coastal Processes of the Elwha River Delta Coastal Currents 123

wa11-0558_fig 05-9

WEST SITE EAST SITE

S

W

N

E

Direction

Water level in meters,

Mean Lower Low Water Range, in meters

5

10

15

20

Range, in meters Velocity, in centimeters per second

5

10

15

20

Current speed, in

centimeters per second

2006 ordinal date

40 60 80 100 120

January February March April May

−2

−1

0

1

February 2006

25 26 27

February 2006

25 26 27

25 26 27 25 26 27

25 26 27 25 26 27

0

20

40

60

80

100

−100

−50

0

50

100

A.

B. C.

D. E.

F. G.

Figure 5.9. Coastal currents measured offshore of the Elwha River delta, Washington, at the West and East sites. 

(A) A four month tidal record and highlights, with a gray bar. (B–G) the 3-day records. Currents are shown as (B, C) 

depth-dependent speed, (D, E) depth-dependent direction, and (F, G) depth-averaged current. Although currents at 

both sites are strongly tidal, the magnitude, direction, and persistence of these tidal currents are not consistent.
124 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

wa11-0558_fig 05-10

Easting in kilometers

Northing in kilometers

290 295 300 305 310 315

290 295 300 305 310 315

128

130

132

134

136

138

128

130

132

134

136

138

A.

B.

1 meter

per second

EXPLANATION

Figure 5.10. Coastal currents offshore of the Elwha River delta, Washington, from 

numerical simulations during (A) tidal ebbing and (B) tidal flooding. Note the tidal currents 

in excess of 1 meter per second and eddies on the downstream side of the deltaic 

headland.
Chapter 5

Coastal Processes of the Elwha River Delta Coastal Currents 125

Traditional models of sediment 

transport indicate that sediments will 

move in response to water flowing 

around the particle. In mixed sedimentary 

environments like the Elwha River delta 

coastal zone, however, larger clasts serve 

as substrate for kelps, and by doing so they 

make themselves easier to transport over 

large distances.

Numerous cases of kelp-mediated 

sediment transport were observed during 

surveys in the Elwha River coastal zone, 

where kelps have been attached to 

transported sediments of various sizes, 

including pebbles as small as a few 

centimeters to small boulders that are 

40 cm or more in diameter (fig. S5.3). 

In some instances, the kelp-attached 

sediment was observed in motion due to 

high tidal or wave-induced currents. In 

other instances, trenches or disturbed 

sea-floor adjacent to a kelp-covered 

boulder were observed, indicating recent 

movement (fig. S5.3B). Windrows of kelp on 

the Elwha River delta beach were observed 

after big swells. Each kelp attached to a 

cobble clearly indicates that it recently was 

transported from deeper water (fig. S5.3A).

Two possible mechanisms may facilitate 

kelp-mediated clast transport: (1) the 

addition of drag as a result of the increased 

surface area of the kelp, or (2) the lift from 

buoyant kelps transmitted to the sediment 

through the kelp’s holdfast. Non-buoyant 

understory kelps, such as Cymathere 

triplicata and Pterygophora californica are 

prolific in the Elwha River delta coastal 

zone, and have been observed attached to 

mobile sediments. Bull kelp (Nereocystis 

leutkeana) is one of a few buoyant species 

of kelp observed in the Elwha coastal 

zone, Bull kelps have been observed 

rafting cobbles above the seafloor along 

the Elwha coastal zone. The dominance of 

mixed grain substrate in the Elwha coastal 

zone, combined with the abundance of 

kelp species may, in fact, indicate that this 

kelp-mediated sediment transport plays an 

important role in transporting sediments 

and shaping coastal and littoral habitats.

wa11-0558_fig SS_5-3

A.

B.

Sidebar 5.2 Kelp-Mediated Sediment Transport

 Ian M. Miller, Stephen P. Rubin, and Jonathan A. Warrick

Figure S5.3. Examples of kelp-mediated clast movement from the Elwha 

River delta, Washington, coastal zone. (A) Numerous kelp-attached clasts litter 

the beach on June 21, 2009, about 250 meters east of the river mouth. Water 

level in this photograph is estimated to be 1.0 meter above Mean Lower Low 

Water (MLLW). The dominant kelp in these windrows is Cymathere triplicata, a 

common kelp at depths between -3.0 and -8.0 meters offshore of the delta. The 

two kelp-attached clasts in the near-field are estimated to be 5 centimeters 

along their long axes. (B) Active movement of an unidentified kelp attached to 

a cobble through algal debris at about -5.0 m MLLW depth offshore of the base 

of Ediz Hook on August 11, 2008. The clast under motion in this photograph is 

estimated to be 15 centimeters along the long axis. (Photographs taken by Ian 

Miller, University of California, Santa Cruz.)
126 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Elwha River Coastal 

Plume

It is important to understand the 

patterns and dynamics of the coastal 

plume of suspended sediment from 

the Elwha River (fig. 5.11), because 

this plume will define the region of 

the coastal effects from dam removal. 

Numerous physical processes will 

influence this plume, however, which 

makes estimates complicated. For 

example, once turbid river waters reach 

the Strait, the freshwater of the river 

will be positively buoyant (that is, it 

will float), whereas suspended sediment 

particles will begin to sink toward the 

seafloor (Nittrouer and Wright, 1994; 

Hill and others, 2007). The rate of 

particle sinking will be related to the 

size, abundance, and chemistry of these 

particles, although for most river plume 

settings most of the fine sediment (silt 

and clay) will reside in the buoyant 

freshwater plume for an hour or more. 

Therefore, the buoyant plume can 

impart an initial and important transport 

direction and speed to the discharged 

sediment (Hill and others, 2007).

Repeat measurements of the 

position and characteristics of the Elwha 

River buoyant plume by Warrick and 

Stevens (2011) shows that the plume 

commonly hugs the eastern shoreline as 

it spreads toward the northeast, as shown 

in figure 5.11. The Elwha River plume is 

regularly directed toward the northeast 

because of the northeast-dominated 

currents that are offshore of the Elwha 

River mouth, which in turn are caused 

by eddies (fig. 5.10). 

As the Elwha River discharges into 

the Strait, it freshens the upper 1–3 m 

of the coastal water column (fig. 5.12). 

The depth of the plume generally 

increases with the strength of the local 

current, because stronger currents mix 

the buoyant plume deeper (Warrick 

and Stevens, 2011). The rate of water 

discharge from the river mouth into the 

plume—especially during low river 

flow—also is a function of the tidal 

stage. Falling, or “ebbing,” tides export 

river water at higher rates as described 

more fully in Magirl and others (2011, 

chapter 4, this report).

Using this information about the 

coastal currents and buoyant river 

plume, the USGS has developed 

a numerical model that tracks the 

freshwater and suspended sediment 

discharged by the river (Gelfenbaum 

and others, 2009). Model simulation 

results indicate that suspended sediment 

discharged from the river should be 

dynamic and largely mimic the patterns 

of the buoyant plume (fig. 5.13). 

Because the buoyant plume is directed 

toward the east more frequently than 

toward the west, the suspended sediment 

effects of dam removal—including but 

not limited to water column turbidity 

and sedimentation on the seafloor—

should be greatest and most persistent 

on the eastern side of the river mouth. 
Chapter 5

Coastal Processes of the Elwha River Delta Elwha River Coastal Plume 127

wa11-0558_fig 05-11

N 0 200 400 600 800 1,000 METERS

0 1,000 2,000 3,000 FEET

Figure 5.11. Aerial photograph of the 

plume discharging toward the northeast 

from the mouth of the Elwha River, 

Washington. (Photograph from the 

Washington State Department of Natural 

Resources, 1994.)

Plume

Coastal

0 10 20 30 40

Practical salinity unit

Depth, in meters

1

2

3

0

4

Figure 5.12. Salinity inside the 

buoyant plume (plume) and in 

coastal waters directly outside 

the plume (coastal), Elwha River, 

Washington. Measurements were 

taken at 1800 Pacific Standard 

Time on June 9, 2007, at about 

0.5 kilometers offshore of the river 

mouth. The freshening of the upper 

1.5 meters of water from the river 

water is shaded green. (After 

Warrick and Stevens, 2011.)
128 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Figure 5.13. Evolution of coastal turbidity from the discharge of suspended sediment from the Elwha River, Washington, as 

determined by model simulation results (after Gelfenbaum and others, 2009). Arrows indicate depth-averaged flow direction and 

magnitude.

wa11-0558_fig 05-13

Easting in kilometers Easting in kilometers

Sediment concentration log10

kilograms per cubic meter

−5 −4 −3 −2 −1

A

B C

D E

A. B.

C. D.

E.

Water level, in meters

Northing in kilometers

290 295 300 305 310

310

310

128

130

132

134

136

-2

-3

-1

0

1

2

290 295 300 305

128

130

132

134

136

290 295 300 305

128

130

132

134

136

310

310

290 295 300 305

128

130

132

134

136

290 295 300 305

128

130

132

134

136

Shoreline

1 meter

per second
Chapter 5

Coastal Processes of the Elwha River Delta References Cited 129

Summary

The coastal zone of the Elwha 

River delta is strongly influenced by 

waves from the Pacific Ocean and 

currents that respond to the exchange of 

water between the ocean and the Salish 

Sea. The shape and morphology of 

the submarine delta and shoreline also 

have substantial effects on how these 

waves and currents vary within this 

coastal system. Waves approach largely 

from the northwest, which results in 

oblique breaking wave directions along 

much of the shoreline. These oblique 

wave breaking angles will move 

littoral sediment from the river mouth 

toward the east. The coastal currents 

are largely tidal, but these currents also 

induce eddies at the tip of the delta that 

influence dominant current directions. 

The coastal currents immediately 

offshore of the river mouth are directed 

toward the east more frequently than to 

the west, which influences the direction 

of transport for suspended river 

sediment discharged by the river. 

Because of these patterns, most 

of the sediment introduced from dam 

removal likely will be transported 

toward the eastern side of the river 

mouth. It is, perhaps, no coincidence 

that since the dams were emplaced, the 

eastern beach is the region of greatest 

coastal erosion (see Warrick and others, 

2011, chapter 3, this report). This does 

not mean that no significant effects may 

occur from the river sediment toward the 

west of the river mouth. In fact, there are 

occasions during which coastal currents 

offshore of the river mouth are either 

negligible or toward the west. During 

these conditions, the Elwha River plume 

is expected to spread westward toward 

Freshwater Bay. If a high sediment 

discharge occurs during a westward 

spreading plume, fine sediment will be 

deposited in Freshwater Bay.

Although there is a good 

understanding of the basic physical 

conditions of the Elwha River delta 

nearshore and coastal zones, these 

conditions and processes have not 

been fully integrated into a predictive 

sediment transport model for the postdam removal conditions. During the 

post-dam removal phase there will be 

a unique opportunity to measure the 

direction and magnitude of transport 

from this massive release of sediment. 

These observations can be used to 

develop, test, and improve analytical 

capabilities, so that future projects 

can benefit from these insights. 

Development and implementation of 

a strong coastal monitoring program 

during the post-dam removal phase and 

coordination of these observations with 

numerical modeling efforts can help in 

understanding the marine effects of dam 

removal. 

References Cited

Finlayson, D.P., 2006, The 

geomorphology of Puget Sound 

beaches: Seattle, Wash., University of 

Washington, Ph.D. thesis, 216 p. 

Gelfenbaum G., Stevens, A.W., Elias, 

E., and Warrick, J.A., 2009, Modeling 

sediment transport and delta 

morphology on the dammed Elwha 

River, Washington State, USA, 2009 

[Proceedings]: Coastal Dynamics 

2009, Paper No. 109.

Hill, P.S., Fox, J.M., Crockett, J.S., and 

others, 2007, Sediment delivery to 

the seabed on continental margins, 

in Nittrouer, C.A., Austin, J.A., Field 

M.E., Kravitz, J.H., Syvitski, J.P.M., 

and Wiberg, P.L., eds., Continental 

margin sedimentation—From 

sediment transport to sequence 

stratigraphy: Oxford, United 

Kingdom, Blackwell Publishing 

Ltd., International Association of 

Sedimentologists, Special Publication 

Number 37, p. 49-99.

Holbrook, J.R., Muench, R.D., 

Kachel, D.G., and Wright, C., 1980, 

Circulation in the Strait of Juan 

de Fuca—Recent oceanographic 

observations in the eastern basin: 

National Oceanic and Atmospheric 

Administration, Pacific Marine 

Environmental Laboratory, Technical 

Report 33, 42 p.

Komar, P.D., 1998, Beach processes 

and sedimentation (2nd ed.): Upper 

Saddle River, N.J., Prentice Hall, 

544 p.

Magirl, C.S., Curran, C.A., Sheibley, 

R.W., Warrick, J.A., Czuba, J.A., 

Czuba, C.R., Gendaszek, A.S., 

Shafroth, P.B., Duda, J.J., and 

Foreman, J.R., 2011, Baseline 

hydrologic studies in the lower Elwha 

River prior to dam removal, chap. 4 of

Duda, J.J., Warrick, J.A., and Magirl, 

C.S., eds., Coastal habitats of the 

Elwha River, Washington—Biological 

and physical patterns and processes 

prior to dam removal: U.S. Geological 

Survey Scientific Investigations 

Report 2011-5120, p. 75-110. 

Masson, D., and Cummins, P.F., 2004, 

Observations and modeling of 

seasonal variability in the Straits of 

Georgia and Juan de Fuca: Journal of 

Marine Research, v. 62, p. 491-516.

Miller, I.M., Warrick, J.A., and Morgan, 

C., 2011, Observations of coarse 

sediment movements on the mixed 

beach of the Elwha Delta, Washington 

State: Marine Geology, v. 282, 

p. 201-214.

Mofjeld, H.O., and Larsen, L.H., 1984, 

Tides and tidal currents of the inland 

waters of western Washington: 

National Oceanic and Atmospheric 

Administration Technical Report, 

Technical Memorandum ERL PMEL56, Pacific Marine Environmental 

Laboratory, 52 p.
130 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Nittrouer, C.A., and Wright, L.D., 

1994, Transport of particles across 

continental shelves: Reviews of 

Geophysics, v. 32, p. 85-113.

Ruggiero, P., Komar, P.D., and Allan, 

J.C., 2010, Increasing wave heights 

and extreme value projections—The 

wave climate of the U.S. Pacific 

Northwest: Coastal Engineering, 

v. 57, no. 5, p. 539-552.

Shipman, H., 2008, A geomorphic 

classification of Puget Sound 

nearshore landforms: Seattle, Wash., 

U.S. Army Corps of Engineers, 

Seattle District, Puget Sound 

Nearshore Partnership Report 

No. 2008-01, 37 p.

Thomson, R.E., Mihály, S.F., and 

Kulikov, E.A., 2007, Estuarine 

versus transient flow regimes in 

Juan de Fuca Strait: Journal of 

Geophysical Research, v. 112, 

C09022, doi:10.1029/2006JC003925, 

25 p., accessed May 18, 2011, 

at http://www.agu.org/pubs/

crossref/2007/2006JC003925.shtml.

U.S. Army Corps of Engineers, 

2002, Coastal engineering manual: 

Washington, D.C., U.S. Army Corps 

of Engineers, Engineer Manual 1110-

2-1100 (in 6 volumes).

Warrick, J.A., Cochrane, G.R., Sagy, Y., 

and Gelfenbaum, G., 2008, Nearshore 

substrate and morphology offshore of 

the Elwha River: Northwest Science, 

v. 82 (special issue) p. 153-163. 

Warrick, J.A., Draut, A.E., McHenry, 

M.L., Miller, I.M., Magirl, C.S., 

Beirne, M.M., Stevens, A.W., and 

Logan, J.B., 2011, Geomorphology of 

the Elwha River and its delta, chap. 

3 of Duda, J.J., Warrick, J.A., and 

Magirl, C.S., eds., Coastal habitats 

of the Elwha River, Washington—

Biological and physical patterns 

and processes prior to dam removal: 

U.S. Geological Survey Scientific 

Investigations Report 2011-5120, p. 

47-74. 

Warrick, J.A., George, D.A., 

Gelfenbaum, G., Ruggiero, P., 

Kaminsky, G.M., and Beirne, M., 

2009, Beach morphology and change 

along the mixed grain-size delta 

of the Elwha River, Washington: 

Geomorphology, v. 111, p. 136-148. 

Warrick, J.A., and Stevens, A.W., 

2011, A buoyant plume adjacent to 

a headland—Observations of the 

Elwha River plume: Continental Shelf 

Research, v. 31, p. 85-97.
Chapter 6

 

6

Chapter

Nearshore Biological 

Communities Prior to Removal 

of the Elwha River Dams

By Stephen P. Rubin, Ian M. Miller, 

Nancy Elder, Reginald R. Reisenbichler, 

and Jeffrey J. Duda

Abstract

Increases in sediment delivery to 

coastal waters are expected following 

removal of dams on the Elwha River, 

Washington, potentially increasing 

sediment deposition on the seafloor 

and suspended sediment in the water 

column. Biological communities 

inhabiting shallow, subtidal depths 

(3–18 m) near the mouth of the 

Elwha River, between the west end of 

Freshwater Bay and the base of Ediz 

Hook, were surveyed in August and 

September 2008, to establish baselines 

prior to dam removal. Density was 

estimated for 9 kelp taxa, 65 taxa 

of invertebrates larger than 2.5 cm 

any dimension and 24 fish taxa. 

Density averaged over all sites was 

3.1 per square meter (/m2) for kelp, 

2.7/m2 for invertebrates, and 0.1/m2 for 

fish. Community structure was partly 

controlled by substrate type, seafloor 

relief, and depth. On average, 12 more 

taxa occurred where boulders were 

present compared to areas lacking 

boulders but with similar base substrate. 

Four habitat types were identified: 

(1) Bedrock/boulder reefs had the 

highest kelp density and taxa richness, 

and were characterized by a canopy of 

Nereocystis leutkeana (bull kelp) at the 

water surface and a secondary canopy 

of perennial kelp 1–2 m above the 

seafloor; (2) Mixed sand and gravelcobble habitats with moderate relief 

provided by boulders had the highest 

density of invertebrates and a taxa 

richness nearly equivalent to that for 

bedrock/boulder reefs; (3) Mixed sand 

and gravel-cobble habitats lacking 

boulders supported a moderate density 

of kelp, primarily annual species with 

low growth forms (blades close to the 

seafloor), and the lowest invertebrate 

density among habitats; and (4) Sand 

habitats had the lowest kelp density 

and taxa richness among habitats and 

a moderate density of invertebrates. 

Uncertainties about nearshore 

community responses to increases in 

deposited and suspended sediments 

highlight the opportunity to advance 

scientific understanding by measuring 

responses following dam removal.
132 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Introduction

Two dams on the Elwha River 

have reduced sediment transport from 

the upper watershed to the lower river 

and coast for nearly 100 years (Duda 

and others, 2011, chapter 1, this report). 

Increases in sediment delivery to 

coastal waters are expected following 

dam removal, potentially increasing 

sediment deposition on the seafloor 

and suspended sediment in the water 

column. Large increases are expected 

initially (3–5 years after initiation of 

dam removal; Czuba and others, 2011, 

chapter 2, this report) as sediments that 

have accumulated behind the dams are 

released. Thereafter, sediment supply 

likely will decrease but should remain 

higher than before dam removal due to 

restored transport of sediments from the 

upper watershed. Much of the sediment 

currently impounded by the dams is 

silt, sand, and clay, which are readily 

transportable (Czuba and others, 2011, 

chapter 2, this report). Spatial patterns 

of suspended and deposited sediment 

in coastal waters will depend on local 

physical processes including waves and 

currents (Warrick and others, 2011b, 

chapter 5, this report). The amount, 

timing, and temperature of river water 

discharged into coastal waters are 

expected to be little changed by dam 

removal because the dams have been 

largely operated as “run of the river” 

(Duda and others, 2011, chapter 1, this 

report). 

Sediment deposition and suspended 

sediment can have a variety of effects on 

nearshore plants and animals. Sediment 

deposition can affect organisms directly 

through burial, which can reduce light, 

oxygen, nutrients, and waste removal; 

scour, which can injure or dislodge 

organisms; and replacement of hard, 

stable substrate with finer particles that 

inhibit settlement for some organisms 

(Airoldi, 2003). Sediment deposition 

also can indirectly affect communities 

by altering outcomes of competitive and 

predator-prey interactions among species 

with different tolerances and responses 

to sedimentation (Airoldi and Cinelli, 

1997; Airoldi and Virgilio, 1998). 

Suspended sediment increases turbidity, 

which reduces light penetration and 

can negatively affect photosynthetic 

organisms. Seaweeds and sea grasses 

require high ambient light, account for a 

large portion of the primary production 

in nearshore waters, and create threedimensional structures inhabited by 

various species (Mumford, 2007); 

therefore, effects on them may propagate 

to other parts of the community. 

Turbidity also can influence competition 

among plant species with different light 

requirements, or affect competitive 

or predatory abilities of animals 

that depend on vision (Beauchamp 

and others, 1999). Direct effects of 

suspended sediment include damage to 

fish and invertebrate gills, and clogging 

or damage to feeding structures of filter 

feeders (Newcombe and MacDonald, 

1991). Beds of seaweeds or sea grasses 

can dampen current velocities, thereby 

increasing sedimentation and decreasing 

suspended sediment within the beds 

(Madsen and others, 2001).

Substrate characteristics, including 

particle size, stability, and relief, are 

important for structuring benthic 

communities. Stable substrates of large 

particle size, for example bedrock 

and boulders, support various species 

adapted to attach to the substrate’s 

surface (Witman and Dayton, 2001). 

Fine sediments such as sand and silt 

do not provide attachment points but 

do permit burrowing and support 

various species adapted to living in 

the sediment (Lenihan and Micheli, 

2001). Substrates of intermediate 

particle size (for example, gravel and 

cobble) provide some attachment space 

on their surfaces, but are subject to 

overturning and displacement by waves 

and currents, and support different 

communities compared to more stable 

rocky substrates (Scheibling and 

others, 2009). Propagules of some large 

seaweed species can start to grow on 

small rocks such as gravel or cobble. 

Drag on the seaweed increases as it 

grows, and depending on the size of 

the rock, the seaweed and the rock it is 

attached to may be lifted and transported 

(see Miller and others, sidebar 3.2, this 

report). A mixture of particle sizes offers 

a variety of habitats in close proximity. 

In high current environments, large 

substrates such as cobble and boulders 

can dampen current speeds, allowing 

retention of fine sediments that would 

otherwise wash away. The presence of 

fine sediments among larger substrates 

promotes coexistence of species adapted 

to different particle sizes. Seafloor relief 

in rocky habitats provides sloped and 

vertical surfaces that support different 

communities than horizontal surfaces. 

Relief also affects communities by 

modifying flow patterns (Witman and 

Dayton, 2001). Effects of sedimentation 

on benthic communities likely will vary 

among habitats with different substrate 

characteristics. 

Purpose and Scope

This study was initiated in 2008 

to characterize nearshore biological 

communities prior to removal of the 

Elwha River dams. The intent was to 

establish a baseline to measure changes 

following dam removal. In this chapter, 

two questions are addressed: (1) What 

communities currently are present 

in shallow subtidal areas potentially 

affected by dam removal? (2) What role 

does substrate play in structuring these 

communities? 
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Study Area 133

Study Area

The study area includes shallow 

depths (3–18 m below mean lower 

low water [MLLW]) extending from 

the west end of Freshwater Bay to the 

base of Ediz Hook, a distance of 15 km 

(fig. 6.1). This range of depths should 

include most depths with sufficient light 

for photosynthesis and where kelp and 

other benthic macroalgae are dominant 

given suitable substrate for attachment 

(Whitman and Dayton, 2001; Mumford, 

2007). The length of coast that will be 

affected by dam removal is not certain, 

but we expect that the boundaries west 

and east of the river mouth will include 

the affected area. They coincide with 

the boundaries of the Elwha nearshore 

defined by Shaffer and others (2008) 

except that their eastern boundary, the 

tip of Ediz Hook, is 5 km farther east. 

Prominent features of the study 

area are Freshwater Bay, the Elwha 

River delta, which extends north into 

the Strait of Juan de Fuca, and the area 

20

15

10

5

123°38' 123°36' 123°34' 123°32' 123°30' 123°28'

48°

10'

48°

8'

0 1 2 KILOMETERS

0 1 2 MILES

Strait of Juan de Fuca

Freshwater Bay

Elwha River

Mouth

Dry Creek

Base Ediz 

Hook

Elwha 

River 

Delta

WASHINGTON

Study

Area

Bathymetry and topography from Finlayson and 

others, 2005; Cochrane and others, 2008; Warrick 

and others, 2010. UTM Zone 10, WGS84 projection

Bare earth LIDAR from 2001

Figure 6.1. Southern waters of the Strait of Juan de Fuca near the mouth of the Elwha River, Washington. Five-meter bathymetry 

contours also are shown.

east of the delta, which is sheltered by 

the delta to the west and Ediz Hook to 

the east. High bluffs border much of 

Freshwater Bay and the shore between 

Dry Creek and Ediz Hook. Bathymetry 

is steepest offshore of the river mouth, 

less steep in mid Freshwater Bay, 

and most gradual offshore of the 

eastern flank of the delta (fig. 6.1). 

Geomorphology of the study area is 

described in detail in Warrick and others, 

2011a, chapter 3, this report. 
134 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Previous Work

Sonar and video surveys were 

conducted in 2005 in Freshwater Bay 

and offshore of the Elwha River mouth 

to map bathymetry and characterize 

substrate type and distribution (Warrick 

and others, 2008). Sonar backscatter 

data and video footage were used to 

classify substrate as hard (bedrock 

or boulders), mixed (gravel and 

cobble), or soft (sand or sand waves) 

(Cochrane and others, 2008). Most of 

the hard substrate was in Freshwater 

Bay, particularly in mid Freshwater 

Bay close to shore (fig. 6.2A). Mixed 

substrate predominated offshore of the 

river mouth and in parts of Freshwater 

Bay. Areas of soft substrate occurred 

at the west and east ends of Freshwater 

Bay. The areas farthest offshore were 

characterized by a combination of 

mixed and soft substrate. The substrate 

classifications were integrated with other 

information, including delineation of 

bedrock outcrops and counts of boulders 

visible in the raw backscatter data, to 

form a substrate type and morphology 

map (fig. 6.2B; Warrick and others, 

2008). Bedrock outcrops were apparent 

in mid Freshwater Bay close to shore. 

Boulder abundance was high (greater 

than 10,000/km2) close to shore and 

intermediate (10–10,000/km2) farther 

from shore in Freshwater Bay. Boulder 

abundance was low (less than 10/km2) in 

a band extending from outer Freshwater 

Bay to the Elwha River delta. 

Aerial photographs taken during 

1989 to 2004 were used to map the 

annual spatial extent of overstory kelp 

(Nereocystis leutkeana [bull kelp] and 

Macrocystis integrifolia [giant kelp], 

which form a canopy at the water 

surface) in the Strait of Juan de Fuca 

(Berry and others, 2005). Kelp was most 

persistent (present nearly every year) 

in the area of hard substrate (bedrock 

outcrops and abundant boulders) in 

mid-Freshwater Bay (fig. 6.2C). Kelp 

also occurred frequently just to the 

northeast of the river mouth, where 

the sonar survey detected little hard 

substrate in 2005 (Warrick and others, 

2008), and in a few patches between Dry 

Creek and the base of Ediz Hook. Rigg 

(1915) mapped kelp beds in the Strait of 

Juan de Fuca in 1911 and 1912. 

The entire study area was surveyed 

in 2006 to map Zostera marina

(eelgrass), and Freshwater Bay was 

resurveyed in 2009 (Norris and Fraser, 

2009). In both years, a large Z. marina

bed (23 ha) was present at the west end 

of Freshwater Bay in a sand-dominated 

area (fig. 6.2A–B). In both years a 

much smaller bed (2 ha) was present in 

east-central Freshwater Bay. This bed 

was inshore from the area surveyed for 

substrate and west of the sandy area 

identified by the sonar survey at the east 

end of Freshwater Bay. Z. marina was 

not detected anywhere else in the study 

area. 

Scuba surveys by Seavey and Ging 

(1995) in 1994 characterized existing 

marine resources potentially affected by 

removal of the Elwha River dams. They 

identified the macroalgae community 

as a particularly important resource 

that could be affected by increased 

sediment load after dam removal. Their 

study area included depths from 0–15 m 

and extended from mid Freshwater 

Bay east to Dry Creek; however, they 

concentrated their sampling in shallow 

water (0–9 m) close to the river mouth 

and did more sampling east than 

west of the mouth because of their 

expectation that sediment deposition 

would be greatest in these areas. They 

detected high abundance and diversity 

of macroalgae. Percent cover of 

macroalgae was greater than 75 percent 

for 40 percent of their quadrates and 

greater than 50 percent for 73 percent 

of their quadrates (n quadrates = 836; 

area of each quadrate = 0.84 m2). They 

reported 40 macroalgae taxa (genus 

or species level identifications) that 

occurred in at least one quadrate. They 

also reported 57 taxa of invertebrates 

and fish that occurred in at least one 

quadrate and provided density estimates 

for 15 invertebrate species. They 

did not provide density estimates for 

macroalgae. An important component 

of their results was a set of distribution 

maps for five macroalgae species 

and Z. marina, for percent cover of 

macroalgae, and for substrate types 

(10 classes). Z. marina was present in 

6 percent of their quadrates. 

Shaffer (2000) sampled seasonally 

(every 3 to 4 months) from March 1996 

to April 1997 in two overstory kelp 

beds (3–6 m depth) in Freshwater Bay, 

one dominated by N. leutkeana and the 

other by M. integrifolia, as well as in a 

pair of N. leutkeana and M. integrifolia

beds farther west in the Strait of Juan 

de Fuca. The percentage of cover 

between the substrate and 1 m above 

the substrate for three kelp species 

(N. leutkeana, M. integrifolia, and 

Pterygophora californica), fleshy red 

algae, and total vegetation was reported. 

The density for the three kelp species, 

Haliotis kamtschatkana (northern 

abalone), Strongylocentros franciscanus

(red urchins), and Strongylocentrotus 

droebachiensis (green urchins) (n

quadrates per bed per season = 10; area 

of each quadrate = 1.0 m2) also was 

reported. Percentage of cover of total 

vegetation in the Freshwater Bay beds 

was lowest in December (35–55 percent) 

and highest in June and September 

(65–95 percent). P. californica was the 

densest of the three kelps in all seasons 

in the N. leutkeana bed in Freshwater 

Bay; M. integrifolia was always densest 

in the other Freshwater Bay bed. 

H. kamtschatkana, S. franciscanus and 

S. droebachiensis were present in the 

N. leutkeana bed (density less than or 

equal to 2 per m2 per species) but were 

nearly absent from the M. integrifolia

bed in Freshwater Bay.
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Previous Work 135

tac11-0558_fig6-02

EXPLANATION

Substrate interpretation

River bar

Sand

Bedrock outcrops

Mixed, low boulder abundance 

 (less than 10 per square kilometer)

Mixed, medium boulder abundance

 (10-10,000 per square kilometer)

Mixed, high boulder abundance 

 (greater than 10,000 per square 

 kilometer)

0 21 KILOMETERS

0 1 2 MILES

1

14

9

8

7

6

5

4

3

2

15

13

12

11

10

EXPLANATION

Years kelp present

EXPLANATION

Substrate classification

Hard (boulders or bedrock)

Soft (sand and sand waves)

Mixed (gravel and cobble)

123°38' 123°36' 123°34' 123°32' 123°30' 123°28'

48°

10'

48°

8'

48°

10'

48°

10'

48°

8'

48°

8'

A. Substrate classification

B. Substrate interpretation

C. Kelp presence in 15 year time series, 1989 - 2004

Bathymetry and topography from Finlayson and 

others, 2005; Cochrane and others, 2008; Warrick 

and others, 2010. UTM Zone 10, WGS84 projection

Bare earth LIDAR from 2001

West Freshwater 

Bay Mid Freshwater Bay

Elwha River 

Mouth

Dry Creek

Base Ediz 

Hook 

West Freshwater 

Bay Mid Freshwater Bay

Elwha River 

Mouth

Dry Creek

West Freshwater 

Bay Mid Freshwater Bay

Elwha River 

Mouth

Dry Creek

Base Ediz 

Hook 

Base Ediz 

Hook 

Figure 6.2. Substrates, and the 

extent of canopy forming kelp, 

near the mouth of the Elwha 

River, Washington. (A) Substrate 

classifications from acoustic 

backscatter data (Cochrane 

and others, 2008). (B) Substrate 

type and morphology formed by 

integrating substrate classifications 

and other information including 

delineation of bedrock outcrops 

and counts of boulders visible in 

the raw backscatter data (Warrick 

and others, 2008). (C) Presence 

and persistence of surface canopy 

forming kelp from annual aerial 

photographs taken in 1989–2004 

(Berry and others, 2005). 
136 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

In 2005 and 2006, the Washington 

Department of Fish and Wildlife 

(WDFW) established four permanent 

sites, marked with metal fence posts 

driven into the substrate, to assess 

effects of removal of the Elwha 

River dams, particularly effects on 

commercially important shellfish 

species (Michael Ulrich, Washington 

Department of Fish and Wildlife, written 

commun., February 26, 2010). Three 

sites consisted primarily of large and 

small boulders, cobble, and solid rock. 

Two sites were located in Freshwater 

Bay and considered treatment sites 

potentially affected by dam removal, and 

the third was located near Green Point, 

21 km east of the Elwha River mouth, 

and considered a control site unlikely 

to be affected. One treatment site and 

the control site were established in 2005 

and resurveyed in 2006 and 2007. The 

other treatment site was established 

in 2006 and resurveyed in 2007. A 

treatment site characterized by soft 

substrate was established offshore of 

the Elwha River mouth and surveyed in 

2006. Sites were rectangular with areas 

ranging from 140 to 250 m2. Site depths 

ranged from 11 to 15 m. Census counts 

were made for commercially important 

species including H. kamtschatkana, 

S. franciscanus, S. droebachiensis, and 

Parastichopus californicus (California 

sea cucumbers) at the rocky sites, and 

Panopea generosa (geoduck clams) 

and Tresus capax (horse clams) at 

the soft substrate site. Presence or 

absence was recorded for other animal 

and plant species. S. franciscanus and 

S. droebachiensis were measured for 

size. The two rocky treatment sites 

were recently repurposed and will not 

be available for resurveying following 

dam removal; however, pre-removal 

data from these sites may prove valuable 

when comparing data collected at other 

sites with similar habitat. 

Study Design

Our study design is based on a 

Before-After-Control-Impact approach 

(Underwood, 1994), with sampling 

effort concentrated in the area expected 

to be affected by dam removal and in 

two control areas where effects of dam 

removal are expected to be minimal. 

The control areas are offshore of Low 

Point and Green Point, 20 and 21 km 

west and east of the Elwha River 

mouth, respectively. The data reported 

herein constitute part of the “before” 

component of the study, and repeated 

sampling is expected following dam 

removal (“after”). Analysis of future 

changes in the control areas compared 

to changes near the Elwha River should 

allow for effects of dam removal to be 

separated from other potential effects 

such as interannual variability and 

climate change. Because the purpose 

of this chapter is to characterize areas 

potentially affected by dam removal, 

results from Low and Green points will 

not be presented.

Site Selection

Sites were randomly selected after 

stratifying the study area according 

to three factors: distance from the 

Elwha River mouth, water depth, and 

substrate type. Five distance bands 

were oriented north to south and spaced 

approximately evenly from the west 

to the east end of the study area, with 

the central band straddling the Elwha 

River mouth (fig.6.3). Three depth 

strata—3–6, 9–12, and 15–18 m below 

MLLW—were delineated (fig. 6.3) 

using the best available bathymetry 

data (Cochrane and others [2008] for 

Freshwater Bay and offshore of the river 

mouth; Finlayson [2005] elsewhere). 

The intersection of the cross-shore bands 

and the depth strata produced 15 “bins,” 

within which areas with different 

substrate types were identified based on 

substrate classifications by Cochrane 

and others (2008) from sonar surveys 

in Freshwater Bay and offshore of the 

Elwha River mouth (classifications were 

hard, mixed, or soft; fig. 6.2A), or on the 

presence of overstory kelp in the two 

cross-shore bands east of the river mouth 

that lacked substrate classifications from 

sonar. Berry and others (2005) mapped 

the spatial extent of overstory kelp for 

15 years during 1989–2004 (fig. 6.2C). 

We inferred substrate type from 

overstory kelp frequency of occurrence 

by assuming that kelp were attached 

to hard substrate; categories were hard 

(kelp present in 9–15 years), mixed 

(kelp present in 1–8 years), and soft 

(kelp never present). Warrick and others 

(2008) determined that for depths less 

than 15 m, overstory kelp was present 

in 58 percent of the area classified as 

hard from sonar data, but was present in 

18–23 percent of the area classified as 

mixed or soft from sonar data, providing 

some support for inferring substrate type 

from kelp presence. 

At least one site was randomly 

selected within each cross-shore 

band by depth stratum by substrate 

type combination using a geographic 

information system. Not all three 

substrate types were present in every 

cross-shore band by depth combination 

(fig. 6.3). One site in the cross-shore 

band near Dry Creek was placed outside 

of its intended depth strata; for analyses, 

it was grouped with the stratum closest 

to it in depth. 
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Previous Work 137

EXPLANATION

Depth Strata

15 - 18 meters

3 - 6 meters

9 - 12 meters

Cross-shore band

West Freshwater 

Bay

Mid Freshwater 

Bay

Elwha River 

Mouth

Dry Creek Base Ediz

 Hook

Site

123°38' 123°36' 123°34' 123°32' 123°30' 123°28'

48°

10'

48°

8'

0 1 2 KILOMETERS

0 1 2 MILES

Bathymetry and topography from Finlayson and 

others, 2005; Cochrane and others, 2008; Warrick 

and others, 2010. UTM Zone 10, WGS84 projection

Bare earth LIDAR from 2001

Figure 6.3. Three depth strata and five cross-shore bands at varying distances from the mouth of the Elwha River, Washington. 

Sites were randomly selected within each of the 15 distance by depth stratum “bins.” Data were collected in at least two 30 

meter-long shore-parallel transects at each site. One site in the Dry Creek band was placed outside of its intended depth strata; 

for analyses, it was grouped with the stratum closest to it in depth (3–6 meters).
138 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Data Collection

Data collection methods were 

adapted from protocols developed by 

the Partnership for Interdisciplinary 

Studies of Coastal Oceans (2011) for 

monitoring ecosystems associated with 

rocky reef habitats (Carr and others, 

2001). Data were collected at 30 m-long 

transects. Swath surveys were conducted 

to estimate density. Individual organisms 

present in a swath of fixed width along 

the entire transect were identified to the 

lowest practicable taxonomic level and 

counted. Measurements taken at discrete 

points along the transect were used to 

estimate percent coverage of different 

substrate types and seafloor relief 

categories. 

We navigated to each randomly 

selected site using a Wide Area 

Augmentation System-enabled Global 

Positioning System (±5 m accuracy) and 

dropped the boat anchor. Two teams of 

two divers descended the anchor line 

and established transects in opposite, 

approximately shore-parallel directions 

using compass bearings taken at the 

surface (fig. 6.4A). Water visibility was 

measured by each team at the anchor 

as the distance at which one diver 

could see two fingers held up by the 

other. Visibility ranged from 4–14 m 

(mean=8 m) among sites. Depth at 

transect starting and ending points was 

recorded from dive computers. 

Fish Swath

The fish survey was initiated 

10 m from the anchor. One diver swam 

slightly ahead of the other and counted 

all conspicuous fish within a 2 m wide 

by 2 m high swath. The second diver 

reeled out a measuring tape along the 

transect line while watching for fish. 

Invertebrate and Kelp Swaths

At the 40 m mark, the tape was 

secured and both divers proceeded back 

along the transect, one identifying and 

counting invertebrates in a swath on 

one side of the tape and the other doing 

the same for kelp on the other side 

of the tape (fig. 6.4B). Fish observed 

during the invertebrate or kelp surveys 

but not observed during the fish survey 

(typically small, cryptic individuals 

touching the substrate) were noted 

and included in fish density estimates. 

Invertebrate and kelp surveys were 

either 1 or 2 m wide based on the 

surveyor’s judgment of whether the 

survey could be completed in a single 

dive. Surveys were only 2 m wide when 

organisms were sparse, visibility good, 

and depth shallow. Invertebrates greater 

than 2.5 cm (any dimension) for which 

individuals could be recognized (not 

encrusting or colonial species) were 

counted. N. luetkeana and P. californica

with stipes greater than 30 cm long 

were counted. Other kelp species with 

combined stipe and blade lengths 

greater than 24 cm were counted. When 

Z. marina was observed, shoots present 

in the kelp swath were counted. 

A variable area sampling method 

was used for swath surveys when 

high densities of invertebrates or kelp 

were encountered. The transect was 

divided into three 10 m increments 

(0–10, 10–20, 20–30). The surveyor 

counted individuals of a taxon until 

30 individuals were counted or the end 

of the 10 m segment was reached. If 

30 were counted before the end, the 

surveyor recorded the distance along 

the transect to that point and stopped 

counting the taxon until the start of the 

next 10 m segment. 

Uniform Point Contact Survey

The uniform point contact (UPC) 

survey was started when invertebrate 

and kelp surveys were finished. Both 

divers participated, each working on 

separate 10-m segments of the 30 m 

transect. The UPC involved classifying 

sediment grain size and seafloor relief at 

60 points spaced every 0.5 m along the 

transect (fig. 6.4C). Sediment directly 

under each point was classified as 

sand (less than 0.2 cm), gravel-cobble 

(0.2–25 cm), boulder (25 cm-1 m), or 

bedrock (greater than 1 m diameter). 

Relief was measured as the greatest 

elevation difference within a rectangle 

1 m across the transect by 0.5 m along 

the transect and centered on the transect 

point (fig. 6.4C). Relief classifications 

were less than 0.1 m, 0.1–1 m, and 

greater than 1 m. 
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Data Collection 139

watac11-0558_fig6-04

D. Scuba divers conducting surveys

0.5 meter

0.5 meter

UPC Points

1 meter

Relief measured 

within frame

Transect 

line

C. Uniform point contact (UPC) points and seafloor relief sample frame schematic

Transect 1 Transect 2

30 meters 30 meters

Anchor

10 meters

A. Boat anchor and two 30 meter survey transects schematic

Transect 

line

Invertebrate swath

Kelp swath

B. Invertebrate and kelp swath transect schematic

Figure 6.4. Schematic diagrams and photographs showing establishment of transects at a site. (A) Boat anchor and two 30 

meter transects at one site; (B) invertebrate and kelp swaths along a transect; (C) uniform point contact (UPC) points spaced 

every 0.5 meter along a transect, and 0.5- by 1.0-meter rectangles centered on each UPC point. Seafloor relief was measured 

as the maximum elevation difference within a rectangle; (D) Scuba divers at work.
140 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Other Aspects of Data 

Collection

If divers had adequate air and 

allowed bottom time, a second transect 

was done along the same bearing (third 

or fourth transect at the site), in which 

case that transect was started 20 m from 

the end point of the previous transect 

to maintain a 20 m spacing interval 

between transects. 

Nine sites were surveyed between 

August 7 and 11, 2008, 14 sites 

between August 21 and 25, 2008, and 

10 sites between September 5 and 7, 

2008, for 75 transects completed at 

33 sites (table 6.1). Additional sites 

were surveyed at control locations 

during these times (data not presented). 

Diving occurred on dates with low 

tidal exchanges to minimize current 

in August–September to optimize 

favorable weather and wind conditions. 

Local current predictions generated 

from current harmonics measured by 

instruments deployed around the Elwha 

River delta (Warrick and others, 2011b, 

chapter 5, this report) assisted with 

planning dives to coincide with reduced 

currents. All surveys were conducted 

during daylight hours. Surveys in 2009 

were accomplished using the same 

methods as in 2008. Data from 2009 are 

preliminary and are not reported here. 

Table 6.1. Completed transects and sites by cross-shore band 

and depth and substrate stratum, east, west, and at the mouth of 

Elwha River, Washington, August and September 2008.

[Site locations are shown in figure 6.3]

Cross-shore 

band

Depth 

stratum

Substrate 

stratum

Number of 

transects

Number 

of sites

West Freshwater Bay 3–6 meters Hard 2 1

Mixed 2 1

Soft 2 1

9–12 meters Hard 2 1

Soft 3 1

15–18 meters Hard 2 1

Mixed 2 1

Mid-Freshwater Bay 3–6 meters Hard 6 3

9–12 meters Hard 2 1

Mixed 4 2

15–18 meters Hard 2 1

Mixed 2 1

Elwha River Mouth 3–6 meters Hard 2 1

Mixed 2 1

Soft 3 1

9–12 meters Mixed 2 1

Soft 4 1

15–18 meters Mixed 4 2

Dry Creek 3–6 meters Mixed 3 1

Soft 2 1

9–12 meters Mixed 4 2

Soft 2 1

15–18 meters Soft 2 1

Base Ediz Hook 3–6 meters Mixed 2 1

Soft 4 1

9–12 meters Hard 2 1

Mixed 2 1

15–18 meters Soft 2 1

Total 75 33
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Substrate Composition and Relief 141

Data Analyses

Scores were assigned to sediment 

grain size and relief classifications. 

Substrate classified as sand, gravelcobble, boulder, or bedrock received 

a score of 1, 2, 3, or 4, respectively. A 

mean and standard deviation (SD) were 

then computed for each transect as the 

mean and SD of the substrate scores 

for each of the 60 UPC points. Relief 

classified as less than 0.1 m, 0.1–1 m, or 

greater than 1 m received a score of 1, 

2, or 3, respectively; mean and SD relief 

scores were computed as for substrate. 

Analyses were based on site means 

from data averaged over transects at 

a site. For purposes of analysis, data 

were frequently grouped by the crossshore band and depth strata used in site 

selection, but to represent substrate type 

UPC classifications were used rather 

than the three a priori substrate strata. 

Pearson’s correlation coefficient 

(r; Sokal and Rohlf, 1995), which takes 

a value between -1 and +1, was used as 

a measure of association between two 

variables (for example, kelp density and 

mean substrate score). Values near 1 

indicate that high values of one variable 

are associated with high values of the 

other. For example, an r-value near 1 

for the correlation between kelp density 

and mean substrate score would indicate 

that sites with high kelp density also 

had high mean substrate scores. Values 

near -1 indicate that high values of 

one variable are associated with low 

values of the other, and values near 0 

indicate no association between the two 

variables. Student’s t-test (Sokal and 

Rohlf, 1995) was used to determine 

whether the mean (for example, mean 

kelp density) for one subset of sites (for 

example, deep sites) was different from 

the mean for a second subset of sites (for 

example, shallow sites). The notation 

P<0.05 was used to indicate that the 

correlation between two variables or 

the difference between two means was 

greater than what would be expected by 

chance (less than 5 times out of 100 by 

chance). 

Substrate Composition 

and Relief

Substrate composition at sites 

ranged from entirely sand (grain size 

less than 0.4 cm) to mostly coarse grain 

sizes (boulders or bedrock) (fig. 6.5A). 

Bedrock primarily was at three shallow 

sites in mid-Freshwater Bay. Boulders 

were present in Freshwater Bay and 

offshore of the Elwha River mouth but 

were rare east of the river mouth. Areas 

of nearly pure sand were close to shore 

at the west and east ends of Freshwater 

Bay and at the base of Ediz Hook. 

Gravel-cobble substrate dominated at 

many of the deeper sites, particularly 

offshore of the Elwha River and Dry 

Creek.

Seafloor relief at sites ranged 

from nearly flat (100 percent less than 

0.1 m) to moderate (mostly greater than 

0.1 m) (fig. 6.5B). High relief (greater 

than 1 m) occurred only at a few sites 

in Freshwater Bay. Relief greater than 

0.1 m was common offshore of the river 

mouth and to the west but was nearly 

absent at sites to the east of the river 

mouth. 
142 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0588_fig6-05

48°

8'

48°

10'

123°38' 123°36' 123°34' 123°32' 123°30' 123°28'

EXPLANATION

Substrate composition

Location of site

Location of site

Bedrock

Gravel-cobble

Boulder

Sand

West Freshwater 

Bay Mid Freshwater 

Bay

Elwha River 

Mouth Dry Creek

Base Ediz

 Hook

0 1 2 KILOMETERS

0 1 2 MILES

48°

8'

48°

10'

EXPLANATION

Relief

Greater than 1.0 meter

Less than 0.1 meter

0.1 - 1.0 meter

West Freshwater 

Bay Mid Freshwater 

Bay

Elwha River 

Mouth Dry Creek

Base Ediz

 Hook

Bathymetry and topography from Finlayson and 

others, 2005; Cochrane and others, 2008; Warrick 

and others, 2010. UTM Zone 10, WGS84 projection

Bare earth LIDAR from 2001

A.

B.

Figure 6.5. Substrate and relief at sites near the mouth of Elwha River, Washington, August and September 2008. 

(A) Substrate composition from classifications made at points spaced every 0.5 meter along 30-meter transects 

(usually 2 transects and 120 points per site). (B) Seafloor relief from classifications made at the same points as 

substrate classifications. At each point, maximum relief (elevation difference) within a 0.5- by 1.0-meter rectangle 

centered on the point was measured and binned as shown in the explanation.
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Number of Taxa and Mean Density 143

Number of Taxa and 

Mean Density

Density was estimated for 9 taxa of 

brown algae, 65 invertebrate taxa, and 

24 fish taxa (table 6.2). Organisms often 

were identified to species (67 taxa), 

but sometimes identification could 

be made only to genus (7 taxa) or to 

broader taxonomic categories (24 taxa). 

All the brown algae were from the 

order Laminariales which contains the 

large brown algae commonly known 

as kelp (O’Clair and Lindstrom, 2000; 

Gabrielson and others, 2006). 

Mean density of 

organisms (averaged over all sites) 

was 3.10/m2 for kelp, 2.69/m2 for 

invertebrates, and 0.078/m2 for fish 

(table 6.2). Mean density within 

invertebrate subgroups (phyla, 

subphyla, or classes) ranged from 

1.40/m2 for Polychaeta (polychaete 

worms) to 0.10/m2 or less for Cnidaria

(anemones and jellyfish), Porifera

(sponges), and Urochordata (tunicates). 

High polychaete density was due to 

high densities of worms that build 

and live in soft (non-calcareous) tubes 

constructed from mucous combined 

with sediment or other local materials 

(families Chaetopteridae, Maldanidae, 

Onuphidae, Sabellidae, and 

Terebellidae; Lamb and Hanby, 2005). 

All of these worms were combined into 

one broad taxonomic category due to 

difficulties with consistently identifying 

to lower taxonomic levels. Some of the 

soft tube worms detected in the study 

area are shown in figure 6.6. Densities 

were low for Cnidaria, Porifera, and 

Urochordata partly because we could 

not reliably count individuals for the 

many colonial or encrusting species 

from these groups. Mean density within 

fish families ranged from 0.026/m2

for Cottidae (sculpins) to 0.005/m2 or 

less for several other families. Fish 

were combined into broad taxonomic 

categories (for example, flatfish) either 

because individuals swam away before 

they could be identified or because they 

were difficult to identify visually. 

Z. marina (eelgrass) was present 

only at the west end of Freshwater 

Bay at two shallow sites with high 

percentages of sand. Shoot density was 

8.9/m2 at a site with 100 percent sand 

and 0.5/m2 at a site with 75 percent 

sand. 

Table 6.2. Number of taxa and mean density (averaged over all sites) from swath surveys for brown algae, invertebrates, and fish at 

sites near the mouth of the Elwha River, Washington, August and September, 2008.

[Subgroup: Order for brown algae, family for fish and mixed for inverebrates (P = phylum, SP = subphylum, C = Class). Density: Calculated as number per 

square meter]

Major group Subgroup Common name Number by taxonomic levelDensity Species Genus Higher Total

Brown algae Laminariales Kelp 8 1 0 9 3.10

Invertebrates Cnidaria (P) Anemones, jellyfish 7 2 1 10 0.10

Crustacea (SP) Barnacles, crabs, shrimps 8 0 6 14 0.37

Echinodermata (P) Sea cucumbers, stars, urchins 12 0 1 13 0.35

Mollusca (P) Chitons, clams, octopi, snails 13 4 5 22 0.42

Polychaeta (C) Polychaete worms 0 0 2 2 1.40

Porifera (P) Sponges 0 0 1 1 0.02

Urochordata (SP) Tunicates 2 0 1 3 0.03

Total 42 6 17 65 2.69

Fish Bothidae, Pleuronectidae Flatfish 0 0 1 1 0.011

Chimaeridae Ratfish 1 0 0 1 0.003

Cottidae Sculpins 5 0 1 6 0.026

Gadidae Cods 1 0 0 1 0.005

Hexagrammidae Greenlings, lingcod 3 0 0 3 0.012

Pholididae Gunnels 0 0 1 1 0.015

Stichaeidae Pricklebacks, warbonnets 1 0 1 2 0.002

Other 6 0 3 9 0.004

Total 17 0 7 24 0.078

Total 67 7 24 98 5.87
144 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Figure 6.6. Soft tube worms commonly observed near the mouth of the Elwha River, Washington. The 

tentacular crown, visible for Chone aurantiaca (A) and several of the other species shown in the figure, 

serves the dual function of filter feeding and respiration. The crown can be retracted into the tube 

when the worm senses danger. Diopatra worms (C) festoon their tubes with local materials, sometimes 

completely concealing the tube as shown. Pista pacifica (F) feeds on detritus and small invertebrates 

on the surface of the substrate by extending the long bucal tentacles, visible here, from its tube. (J) The 

small and large diameter whitish tubes harbor unidentified species. 

watac11-0588_fig6-06A

A. Chone aurantiaca B. Demonax medius

C. Diopatra sp. D. Eudistylia vancouveri

E. Myxicola infundibulum F. Pista pacifica
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Abundant Species 145

watac11-0588_fig6-06B

I. A field of S. costarum J. S. costarum (middle foreground) and 

unidentified spp.

G. Schizobranchia insignis (above) H. Spiochaetopterus costarum

unidentified sp. (below)

Abundant Species

Ten species of kelp were observed at the study sites 

and counted during swath surveys (fig. 6.7). N. luetkeana

(bull kelp) has a thin, flexible stipe (stem) that extends to 

or near the water surface, and blades (leaves) that are held 

there by pneumatocysts (floats). P. californica has a rigid 

stipe that extends upward 1–2 m and blades that can form a 

dense canopy at that level. The other eight species have short 

stipes, and their blades lie on or near the seafloor. Counts 

of Saccharina latissima and Saccharina subsimplex were 

combined (as Saccharina spp.) because we could not always 

distinguish small individuals. Both species were observed at 

the study sites based on characteristics of large individuals. 

M. integrifolia (giant kelp) was observed in the study area 

at the water surface but not on transects at our sites. Mean 

density for kelp taxa ranged from 0.91/m2 for P. californica to 

0.09/m2 for Alaria marginata (fig. 6.8A). 

Figure 6.6.—Continued

Of the invertebrates identified to species, the 12 species 

with the highest mean densities across all sites included two 

crab species, two sea urchins, two sea stars, and one species 

each of sea cucumber, snail, jellyfish, clam, tunicate, and 

chiton (fig. 6.9). Densities for these species were an order 

of magnitude lower than for the kelp species (fig. 6.8B). 

Densities ranged from 0.09/m2 for Cancer oregonensis

(pygmy rock crab) to 0.02/m2 for Cryptochiton stelleri

(gumboot chiton). Combined density was 0.10/m2 for the 

remaining invertebrates identified to species (the species with 

the 13th through the 42nd highest densities). 

Of the fish identified to species, the seven species with 

the highest mean densities were Hexagrammos decagrammus

(kelp greenling; 0.007/m2), Gadus macrocephalus (Pacific 

cod; 0.006/m2), Hydrolagus colliei (spotted ratfish; 0.003/m2), 

Ophiodon elongatus (lingcod; 0.003/m2), Jordania zonope

(longfin sculpin; 0.002/m2), Blepsias cirrhosus (silverspotted 

sculpin; 0.002/m2), and Hexagrammos stelleri (whitespotted 

greenling; 0.002/m2) (fig. 6.10). Combined mean density was 

0.006/m2 for the remaining fish identified to species. 
146 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0588_fig6-07A

A. Agarum fimbriatum B. Alaria marginata

C. Costaria costata D. Cymathere triplicata

E. Nereocystis luetkeana (bull kelp) F. Pleurophycus gardneri (lower left)

Figure 6.7. Nine kelp taxa (eight species and one genus comprising two species) surveyed for density 

near the mouth of the Elwha River, Washington. (B) Two individuals of Alaria marginata are shown (the 

two blades with light midribs in the center of the image); a Synchirus gilli (manacled sculpin) is perched 

on the upper of the two blades. (D) At least five individuals of Cymathere triplicata are attached to a 

single cobble. (H) Either Saccharina latissima or S. subsimplex. These two species sometimes cannot be 

distinguished without dissection. 
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Abundant Species 147

watac11-0588_fig6-07B

G. Pterygophora californica H. Saccharina sp.

I. Laminaria setchellii

Figure 6.7.—Continued
148 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0558_fig6-08

0 0.02 0.04 0.06 0.08 0.10

Density, in number per square meter

0 0.2 0.4 0.6 0.8 1.0

Pterygophora californica

Saccharina spp.

Laminaria setchellii

Cymathere triplicata

Agarum fimbriatum

Costaria costata

Nereocystis luetkeana 

(bull kelp)

Pleurophycus gardneri

Alaria marginata

Cancer oregonensis

(pygmy rock crab)

Cryptochiton stelleri

(gumboot chiton)

Styela montereyensis 

(stalked tunicate)

Cancer productus 

(red rock crab)

Strongylocentrotus droebachiensis

(green urchin)

Panopea generosa

(geoduck clam)

Haliclystus stejnegeri 

(stalked jelly)

Pycnopodia helianthoides

(sunflower star)

Henricia leviuscula 

(blood star)

Fusitriton oregonensis 

(hairy triton snail)

Cucumaria miniata 

(orange sea cucumber)

Strongylocentrotus franciscanus

(red urchin)

A.

B.

Figure 6.8. Mean density (averaged over all sites) for (A) 9 kelp taxa and (B) the 12 most common invertebrate species near 

the mouth of the Elwha River, Washington, August and September 2008. Note that densities are an order of magnitude lower 

for invertebrates than for kelp. Saccharina spp. includes two species, S. latissima and S. subsimplex, that were difficult to 

distinguish in the field. 
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Abundant Species 149

watac11-0588_fig6-09A

A. Cancer oregonensis (pygmy rock crab)

C. Cucumaria miniata (orange sea cucumber)

E. Henricia leviuscula (blood star)

B. Strongylocentrotus franciscanus (red urchin)

E D. Fusitriton oregonensis (hairy triton snail)

F. Pycnopodia helianthoides (sunflower star)

Figure 6.9. Twelve invertebrate species with the highest densities near the mouth of the Elwha River, 

Washington. Species are shown in order of decreasing density (fig. 6.8B). Cancer oregonensis (pygmy 

rock crab; A) is shown in a hole excavated in soft bedrock by a burrowing clam. Haliclystus stejnegeri

(stalked jellyfish; G) adopts a sessile lifestyle by attaching to seaweed. Panopea generosa (geoduck 

clam; H) is shown with the tips of its siphons protruding from the sand. 
150 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0588_fig6-09B

F G. Haliclystus stejnegeri (stalked jellyfish) H. Panopea generosa (geoduck clam)

I. Strongylocentrotus droebachiensis J. Cancer productus (red rock crab)

(green urchin)

K. Styela montereyensis (stalked tunicate) L. Cryptochiton stelleri (gumboot chiton)

Figure 6.9.—Continued
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Abundant Species 151

watac11-0588_fig6-10

F. Blepsias cirrhosus (silverspotted sculpin)

A. Hexagrammos decagrammus (kelp greenling) B. Juvenile Gadus macrocephalus (Pacific cod)

G. Hexagrammos stelleri (whitespotted greenling) 

C. Hydrolagus colliei (spotted ratfish)

E. Jordania zonope (longfin sculpin)

D. Juvenile Ophiodon elongatus (lingcod) 

Figure 6.10. Seven fish species with the highest 

densities near the mouth of the Elwha River, 

Washington. Species are shown in order of 

decreasing density. 
152 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Spatial Patterns of 

Density and Taxa 

Richness

Kelp density was highest in 

mid- and west Freshwater Bay close 

to shore (fig. 6.11A) at sites with high 

percentages of hard substrate (bedrock 

or boulders; fig. 6.5A). Kelp density 

was low off Dry Creek and at two 

sandy sites southwest of the Elwha 

River mouth. The site with the highest 

invertebrate density, 18.5/m2, was 

in mid-Freshwater Bay (fig. 6.11B). 

Most invertebrates at this site were 

polychaete worms with soft tubes 

(worm density=17.9/m2). Invertebrate 

density was 5.8/m2 at the site with 

the next highest invertebrate density. 

Invertebrate density was generally high 

offshore of the Elwha River mouth and 

to the west, and generally low off Dry 

Creek. Fish density was less variable 

across the study area than either kelp or 

invertebrate density (fig. 6.11C). Taxa 

richness (total number of taxa for kelp, 

invertebrates, and fish combined) was 

higher off the Elwha River mouth and to 

the west than to the east (fig. 6.11D). 

Mean density and taxa richness 

within cross-shore band by depth “bins” 

are shown in figure 6.12. Kelp density 

was highest at shallow depths in midFreshwater Bay. Invertebrate density 

was generally higher at mid-depth and 

deep sites than at shallow sites. Taxa 

richness tended to be higher at deep sites 

than at shallow or mid-depths, although 

the highest taxa richness occurred at 

shallow depths in mid-Freshwater Bay. 

Invertebrate density and taxa richness 

were generally higher offshore of the 

river mouth and to the west than to the 

east. 

Spatial and depth-related patterns 

of density varied among kelp taxa 

(fig. 6.13). P. californica achieved high 

densities at shallow depths in Freshwater 

Bay and occurred in nearly all 

combinations of depths and cross-shore 

bands. N. luetkeana also achieved high 

densities at shallow depths in Freshwater 

Bay and occurred widely at lower 

densities, although less widely than 

P. californica. Understory kelp (species 

with short stipes and with blades lying 

close to the substrate) exhibited a variety 

of spatial and depth-related patterns. 

A. marginata was detected at shallow 

and mid-depths but not at deep sites, 

and off the Elwha River mouth and to 

the east but not to the west. In contrast, 

Agarum fimbriatum was most abundant 

at deep sites, nearly absent at shallow 

sites, and was detected off the Elwha 

River mouth and to the west but not 

to the east. Cymathere triplicata was 

present at shallow and mid-depths but 

not deep sites in nearly all cross-shore 

bands. Laminaria setchellii was most 

abundant at deep sites off the mouth 

and was absent at shallow depths. 

Saccharina spp. was detected across all 

depths and cross-shore bands with no 

clear preference for particular depths or 

regions. Similarly, Costaria costata and 

Pleurophychus gardneri were widely 

distributed although both species were 

rare at shallow sites east of the river 

mouth. 

Density patterns also varied 

among abundant invertebrates that 

were identified to species (figs. 6.14

and 6.15). C. oregonensis (pigmy rock 

crab), the species with the highest mean 

density across all sites (fig. 6.8B), also 

had the most restricted distribution. It 

primarily was detected at shallow depths 

in mid-Freshwater Bay (fig. 6.14), and 

within that cross-shore band by depth 

statum it was detected at only the three 

sites with high percentages of bedrock 

(fig. 6.5A) where it attained a high 

density (1/m2). The limited distribution 

of C. oregonensis may have been due to 

an association with holes in the bedrock. 

Burrowing clams excavate holes in 

the relatively soft rock (fig. 6.16A). 

After the clams die, their holes provide 

daytime hiding places for C. oregonensis

(fig. 6.9A) from which the crabs venture 

at night to feed (Jensen, 1995). 

Most of the other 11 species 

of invertebrates with high mean 

densities (fig. 6.8B) could be placed 

into four distribution categories. 

Pycnopodia helianthoides (sunflower 

star) and Cancer productus (red rock 

crab) were widespread, occurring at 

nearly all combinations of depths and 

cross-shore bands (figs. 6.14 and 6.15). 

S. franciscanus (red urchin), Cucumaria 

miniata (orange sea cucumber), 

Fusitriton oregonensis (hairy triton 

snail), S. droebachiensis (green urchin), 

and Styela montereyensis (stalked 

tunicate) occurred off the Elwha River 

mouth and to the west, but not to the 

east, at all depths. Haliclystus stejnegeri

(stalked jellyfish) was detected primarily 

at shallow depths where it often attached 

to vegetation (fig. 6.9G). P. generosa

(geoduck clam) occurred primarily 

at deep sites. Henricia leviuscula

(blood star) and C. stelleri (gumboot 

chiton) were harder to place into one 

of these four distribution categories. 

H. leviuscula was detected off the river 

mouth, to the west at all depths, and 

to the east but only at deep sites off 

Dry Creek. C. stelleri was widespread, 

but less so than P. helianthoides or 

C. productus. 
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Spatial Patterns of Density and Taxa Richness 153

watac11-0558fig6-11

0 1 2 KILOMETERS

0 1 2 MILES

123°38' 123°36' 123°34' 123°32' 123°30' 123°28'

48°

8'

48°

10'

48°

8'

48°

10'

123°38' 123°36' 123°34' 123°32' 123°30' 123°28'

EXPLANATION

Kelp density

0.1 per square meter

10.0 per square meter

1.0 per square meter

EXPLANATION

Invertebrate density

1.0 per square meter

10.0 per square meter

5.0 per square meter

EXPLANATION

Fish density

0.01 per square meter

0.1 per square meter

EXPLANATION

Taxa richness (all groups)

10 taxa

100 taxa

A.

C.

B.

D.

West 

Freshwater 

Bay

Mid 

Freshwater 

Bay

Elwha 

River 

Mouth

Dry Creek Base Ediz

 Hook

West 

Freshwater 

Bay

Mid 

Freshwater 

Bay

Elwha 

River 

Mouth

Dry Creek Base Ediz

 Hook

West 

Freshwater 

Bay

Mid 

Freshwater 

Bay

Elwha 

River 

Mouth

Dry Creek Base Ediz

 Hook

West 

Freshwater 

Bay

Mid 

Freshwater 

Bay

Elwha 

River 

Mouth

Dry Creek Base Ediz

 Hook

Bathymetry and topography from Finlayson and 

others, 2005; Cochrane and others, 2008; Warrick 

and others, 2010. UTM Zone 10, WGS84 projection

Bare earth LIDAR from 2001

Figure 6.11. Density of (A) kelp, (B) invertebrates, and (C) fish, and (D) combined taxa richness for all three groups, at each of 

the 33 sampling sites near the mouth of the Elwha River, Washington, August and September 2008. Symbol size is proportional 

to density or taxa richness.
154 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0558_fig6-12

A. 3 - 6 meter depth stratum

B. 9 - 12 meter depth stratum

C. 15 - 18 meter depth stratum

Base Ediz Hook

Dry Creek

Elwha Mouth

Mid Freshwater

Bay

West Freshwater

Bay

Base Ediz Hook

Dry Creek

Elwha Mouth

Mid Freshwater

Bay

West Freshwater

Bay

Base Ediz Hook

Dry Creek

Elwha Mouth

Mid Freshwater

Bay

West Freshwater

Bay

Density, in number per square meter

0 2 4 6 8 10 12

13

23

37

30

22

26

25

31

15

34

34

34

23

28

17

Kelp

Fish

Invertebrates

EXPLANATION

Numbers indicate taxa richness 

(total number of kelp, invertebrate, 

and fish taxa)

Figure 6.12. Mean densities of the major taxonomic groups (kelp, invertebrates, and fish) in each cross-shore 

band for (A) shallow, (B) mid-depth, and (C) deep sites near the mouth of the Elwha River, Washington, August 

and September 2008. 
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Spatial Patterns of Density and Taxa Richness 155

watac11-0558_fig6-13

Base Ediz Hook

Dry Creek

Elwha Mouth

Mid Freshwater

Bay

West Freshwater

Bay

Base Ediz Hook

Dry Creek

Elwha Mouth

Mid Freshwater

Bay

West Freshwater

Bay

Base Ediz Hook

Dry Creek

Elwha Mouth

Mid Freshwater

Bay

West Freshwater

Bay

A. 3 - 6 meter depth stratum

B. 9 - 12 meter depth stratum

C. 15 - 18 meter depth stratum

0 2 4 6 8

Density, in number per square meter

Agarum fimbriatum

Saccharina spp.

Pterygophora californica

Pleurophychus gardneri

Nereocystis luetkeana

Laminaria setchellii

Cymathere triplicata

Costaria costata

Alaria marginata

EXPLANATION

Figure 6.13. Mean densities of the nine kelp taxa in each cross-shore band for (A) shallow, (B) mid-depth, 

and (C) deep sites near the mouth of the Elwha River, Washington, August and September 2008.
156 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0558_fig6-14

Density, in number per square meter

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Cancer oregonensis

Pycnopodia helianthoides

Henricia leviuscula

Fusitriton oregonensis

Cucumaria miniata

Strongylocentrotus franciscanus

EXPLANATION

Base Ediz Hook

Dry Creek

Elwha Mouth

Mid Freshwater

Bay

West Freshwater

Bay

Base Ediz Hook

Dry Creek

Elwha Mouth

Mid Freshwater

Bay

West Freshwater

Bay

Base Ediz Hook

Dry Creek

Elwha Mouth

Mid Freshwater

Bay

West Freshwater

Bay

B. 9 - 12 meter depth stratum

C. 15 - 18 meter depth stratum

A. 3 - 6 meter depth stratum

Figure 6.14. Mean densities of the six most common invertebrate species (see fig. 6.8B) in each cross-shore band for (A) 

shallow, (B) mid-depth, and (C) deep sites near the mouth of the Elwha River, Washington, August and September 2008.
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Spatial Patterns of Density and Taxa Richness 157

watac11-0558_fig6-15

Base Ediz Hook

Dry Creek

Elwha Mouth

Mid Freshwater

Bay

West Freshwater

Bay

Base Ediz Hook

Dry Creek

Elwha Mouth

Mid Freshwater

Bay

West Freshwater

Bay

Base Ediz Hook

Dry Creek

Elwha Mouth

Mid Freshwater

Bay

West Freshwater

Bay

A. 3 - 6 meter depth stratum

B. 9 - 12 meter depth stratum

C. 15 - 18 meter depth stratum

Cryptochiton stelleri

Styela montereyensis

Cancer productus

Strongylocentrotus droebachiensis

Panopea generosa

Haliclystus stejnegeri

EXPLANATION

Density, in number per square meter

0 0.1 0.2 0.3 0.4 1.5 0.6 0.7 0

Figure 6.15. Mean densities of the next six most common invertebrate species (see fig. 6.8B) in each cross-shore band for 

(A) shallow, (B) mid-depth, and (C) deep sites near the mouth of the Elwha River, Washington. August and September 2008.
158 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0588_fig6-16

A. Burrowing clams B. Boltenia villosa (hairy tunicate)

C. Calliostoma ligatum (blue top snail) D. Parastichopus californicus (giant 

 sea cucumber)

E. Serpulidae, unidentified sp. F. Crangon sp. (crangon shrimp)

G. Halcampa decemtentaculata (10-tentacled

 burrowing anemone)

Figure 6.16. Additional invertebrates of interest (invertebrates other 

than those shown in fig. 6.9) at sites near the mouth of the Elwha River, 

Washington. Burrowing clams (A) excavate holes in soft bedrock. 

Taxa shown in photographs B-E were common at moderate relief 

sites and were not common at low relief sites (table 6.3). Worms in 

the family Serpulidae (E) have hard tubes made of calcium carbonate 

and tentacular crowns for feeding and respiration. Crangon shrimp 

(F) were uncommon at moderate relief sites and common at low relief 

sites (table 6.3). Of the invertebrates identified to genus or species, 

Halcampa spp. (H. decemtentaculata and H. crypta) was the only 

group to attain a mean density greater than 0.1/m2

 at sites classified as 

having mixed substrates and low relief. 
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Density and Taxa Richness in Relation to Substrate and Relief 159

Table 6.3. Taxa common at moderate relief sites and uncommon at low relief sites, and 

taxa uncommon at moderate relief sites and common at low relief sites near the mouth of 

the Elwha River, Washington, August and September 2008. 

[Only the 22 sites where mean substrate score ranged from 1.25 to 2.15 (fig. 6.20B) were included. Mean 

relief score ranged from 1.12 to 1.35 at moderate relief sites (n = 9) and from 1.00–1.05 at low relief sites 

(n = 13). Percent occurrence: Percentage of total moderate relief sites or total low relief sites where a taxon 

was detected]

Occurrence-relief 

category

Percent occurrence

Moderate Taxon

Relief

Low

Relief

Common-moderate, 

uncommon-low

88.9 0.0 Cucumaria miniata (orange sea cucumber)

88.9 15.4 Agarum fimbriatum (an understory kelp)

77.8 15.4 Henricia leviuscula (blood star)

77.8 15.4 Parastichopus californicus (giant sea cucumber)

66.7 0.0 Serpulidae (calcareous tube worms)

55.6 0.0 Boltenia villosa (hairy tunicate)

55.6 0.0 Fusitriton oregonensis (hairy triton)

55.6 7.7 Calliostoma spp. (top snails)

44.4 0.0 Strongylocentrotus droebachiensis (green urchin)

44.4 7.7 Styela montereyensis (stalked tunicate)

Uncommonmoderate, 

common-low

11.1 76.9 Alaria marginata (an understory kelp)

0.0 46.2 Crangon spp. (crangon shrimps)

0.0 30.8 Hexagrammos stelleri (whitespotted greenling)

Density and Taxa Richness in Relation 

to Substrate and Relief

Results presented for relations of organism density 

and taxa richness to substrate and relief characteristics were 

obtained from analyses of means and SDs of substrate and 

relief scores rather than from analyses of substrate and relief 

composition. Mean substrate score is an index of average 

grain size of sediment. It ranged from 1.0 for sites with 

100 percent sand to 3.4 for the site with the most bedrock 

(fig.6.17A). SD substrate score is an index of heterogeneity 

of sediment grain size. It ranged from 0.0 for sites with 

only one grain size (100 percent sand) to 1.2 for the site 

with the most even mixture of the four grain size classes. 

Similarly, mean and SD relief score are indexes of average 

relief and variability of relief, respectively (fig.6.17B). The 

analyses were based on means and SDs because they lend 

themselves to simple statistical techniques and straightforward 

interpretations of average tendencies and heterogeneity. 

Kelp density increased with increasing mean substrate 

score and was highest at shallow sites with high percentages 

of boulders or bedrock (fig. 6.18A). The positive correlation 

between kelp density and mean substrate score was greater 

than would be expected by chance for all sites, for shallow 

sites (r = 0.91, P<0.05), and for mid-depth sites (r = 0.68, 

P<0.05), but not for deep sites. Invertebrate density was 

unrelated to mean substrate score when all sites were 

considered (fig. 6.18B) but was positively correlated with 

mean substrate score at shallow sites (r = 0.80, P<0.05). Fish 

density was unrelated to mean substrate score for all sites 

(fig. 6.18C) and within each depth stratum. Taxa richness 

increased with increasing mean substrate score for all sites 

(fig. 6.18D) and shallow sites (r = 0.81, P<0.05). SD substrate 

score was less correlated with kelp density and taxa richness 

than was mean substrate score for analyses conducted with all 

sites included, suggesting that heterogeneity of sediment grain 

size was less closely associated with kelp density and taxa 

richness than was average sediment grain size. 

Relations of density and taxa richness to seafloor relief 

were similar to those for sediment grain size. Kelp density 

was positively correlated with mean relief score for all sites 

(fig. 6.19A) and shallow sites (r = 0.95, P<0.05). Invertebrate 

density was unrelated to relief for all sites (fig. 6.19B) but 

was positively correlated with relief at shallow sites (r = 0.80,

P<0.05). Fish density was unrelated to relief (fig. 6.19C). 
160 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Site

1 262524232221201918171615141312111098765432 3130292827 32 33

1 262524232221201918171615141312111098765432 3130292827 32 33

1

0

2

20

40

60

80

100

0

Relief composition, in percent

Relief score

0

4

3

2

1

Substrate composition, in percent

20

40

60

80

100

0

Substrate score

Sand

Standard Deviation

Mean substrate

Bedrock

Boulder

Gravel-Cobble

EXPLANATION

less than 0.1 meter

Standard Deviation

Mean relief

greater than 1.0 meter

0.1 - 1.0 meter

EXPLANATION

A.

B.

Figure 6.17. (A) Substrate composition and mean and standard deviation (SD) substrate score and (B) relief composition 

and mean and SD relief score for each site near the mouth of the Elwha River, Washington, August and September 2008. 

Sites are ordered from lowest to highest mean substrate score.
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Density and Taxa Richness in Relation to Substrate and Relief 161

watac11-0558_fig6-18 Density, in number per square meter

4

0

Density, in number per square meter

Density, in number per square meter

5

2

3

4

0

1

18

19

6

15

45

20

25

30

35

40

5

10

Number of taxa

0.2

0.1

0

2

12

10

8

6

1.0 1.5 2.0 2.5 3.0 3.5 1.0 1.5 2.0 2.5 3.0 3.5

Mean substrate score Mean substrate score

A. Kelp density by depth strata

C. Fish density by depth strata D. Richness of all taxa by depth strata

B. Invertebrate density by depth strata

r = 0.85* r = 0.02

r = - 0.06 r = 0.61*

Shallow (3 - 6 meter) stratum

EXPLANATION

Mid-depth (9 - 12 meter) stratum

Deep (15 - 18 meter) stratum

Figure 6.18. Density of (A) kelp, (B) invertebrates, and (C) fish, and (D) taxa richness for all three groups combined, in 

relation to mean substrate score at sites near the mouth of the Elwha River, Washington, August and September 2008. 

Each data point represents a site (n=33). Pearson’s correlation coefficient (r) is a measure of association between two 

variables, for example, density and mean substrate score. Asterisks indicate that the correlation is stronger than would 

be expected by chance (P<0.05).
162 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0558_fig6-19

r = 0.16 r = 0.78*

r = - 0.06 r = 0.65*

Shallow (3 - 6 meter) stratum

EXPLANATION

Mid-depth (9 - 12 meter) stratum

Deep (15 - 18 meter) stratum

Density, in number per square meterDensity, in number per square meter

Density, in number per square meter

Number of taxa

5

Mean relief score Mean relief score

1.0 1.5 2.0 1.0 1.5 2.0

15

45

20

25

30

35

40

10

2

19

3

0

1

4

5

6

18

2

12

10

8

6

4

0

0.2

0.1

0

A. Kelp density by depth strata

C. Fish density by depth strata D. Richness of all taxa by depth strata

B. Invertebrate density by depth strata

Figure 6.19. Density of (A) kelp, (B) invertebrates, and (C) fish, and (D) taxa richness for all three groups combined, in relation 

to mean relief score at sites near the mouth of the Elwha River, Washington, August and September 2008. Each data point 

represents a site (n=33). Pearson’s correlation coefficient (r) is a measure of association between two variables, for example, 

density and mean substrate score. Asterisks indicate that the correlation is stronger than would be expected by chance 

(P<0.05).
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Density and Taxa Richness in Relation to Substrate and Relief 163

Taxa richness was positively correlated with relief for all sites 

(fig. 6.19D), shallow sites (r = 0.84, P<0.05), and deep sites 

(r = 0.84, P<0.05). In comparison to mean relief score, SD 

relief score was less correlated with kelp density and nearly 

equivalently correlated with taxa richness (r = 0.66 between 

SD relief score and taxa richness) for analyses conducted with 

all sites included. This suggests that heterogeneity of relief 

was no more closely associated with kelp density or taxa 

richness than was average relief. 

Mean substrate score was positively correlated with 

mean relief score (fig. 6.20A), indicating that sites with fine 

sediment also had low relief and sites with coarse sediment 

had high relief. Therefore, it is not surprising that mean 

substrate and mean relief were similarly related to density and 

taxa richness. However, mean substrate score was uncorrelated 

with mean relief score for the subset of sites with mean 

substrate scores between 1.25 and 2.15 (fig. 6.20). Some of 

these sites had low relief (mean relief scores between 1.00 and 

1.05) whereas others had moderate relief (mean relief scores 

between 1.12 and 1.35; fig. 6.20B). Density and taxa richness 

were compared between the moderate and low relief sites to 

determine whether there was an effect of relief independent 

from the effect of sediment grain size. 

Kelp density was similar between moderate and low 

relief sites (fig. 6.21A). Invertebrate density was higher at 

moderate relief sites than at low relief sites (fig. 6.21B). 

Mean invertebrate density at moderate relief sites was 1.6/ m2

higher than at low relief sites when one site was excluded (the 

moderate relief site where density was 18.5/m2) and 3.3/ m2

higher than at low relief sites when all sites were included. 

Fish density was similar between moderate and low relief sites 

(fig. 6.21C). The difference in taxa richness between moderate 

and low relief sites was striking (fig. 6.21D). On average, 12 

more taxa occurred at moderate relief sites than at low relief 

sites. 

r = 0.77*

Shallow (3 - 6 meter) stratum

EXPLANATION

Mid-depth (9 - 12 meter) stratum

Deep (15 - 18 meter) stratum

2.0

1.0

1.5

Mean relief score

1.4

1.2

1.3

1.2

1.0

1.1

1.0 1.5 2.0 2.5 3.0 3.5 1.4 1.6 1.8 2.0 2.2

Mean substrate score

Low relief sites

Moderate relief sites

A. B.

Figure 6.20. Mean relief score in relation to mean substrate score at sites near the mouth of the Elwha River, Washington, 

August and September 2008. (A) All 33 sites. (B) The 22 sites with mean substrate scores between 1.25 and 2.15. 
164 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0558_fig6-21

Low relief (mean relief score 1.00 - 1.05)

EXPLANATION

Moderate relief (mean relief score 1.12 - 1.35)

Density, in number per square meter

2

0

Density, in number per square meter

0.2

0.1

0

1

6

5

4

3

1.2 1.4 1.6 1.8 2.0 2.2

Mean substrate score

Density, in number per square meter 5

2

3

4

0

1

18

19

6

15

45

20

25

30

35

40

5

10

Number of taxa

1.2 1.4 1.6 1.8 2.0 2.2

Mean substrate score

A. Kelp density by substrate score

C. Fish density by substrate score D. Richness of all taxa by substrate score

B. Invertebrate density by substrate score

Effect size = 1.6* Effect size = 1.1

Effect size = 0.02 Effect size = 12*

Figure 6.21. Density of (A) kelp, (B) invertebrates, and (C) fish, and (D) taxa richness for all three groups combined, in 

relation to mean substrate score at sites near the mouth of the Elwha River, Washington, August and September 2008. Only 

the 22 sites with mean substrate scores between 1.25 and 2.15 are shown. Effect size is the difference between the mean for 

moderate relief sites and the mean for low relief sites. Asterisks indicate that effect size is greater than would be expected 

by chance (P<0.05). Note that for invertebrates, effect size and its asterisk were calculated by excluding the moderate relief 

site where density was 18.5, much higher than at any other site. Effect size was 3.3 with that site included.
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Habitat Types and Associated Taxa 165

Taxa Associated with 

Seafloor Relief

The finding that taxa richness was 

higher at moderate relief sites than 

at low relief sites was intriguing. It 

suggests that some taxa preferentially 

occurred at sites with at least moderate 

relief, thereby increasing taxa richness 

at those sites. Further analysis was 

performed to screen for taxa that were 

common at the moderate relief sites but 

uncommon at low relief sites, or the 

opposite. 

Ten taxa were classified as common 

at moderate relief sites and uncommon 

at low relief sites, and 3 taxa were 

classified as uncommon at moderate 

relief sites and common at low relief 

sites (table 6.3; fig. 6.7A–B; fig. 6.9C–E, 

I, and K; fig. 6.10G; fig. 6.16B–F). 

Thus, more taxa occurred mainly at 

moderate relief sites than at low relief 

sites, contributing to the increase in taxa 

richness with relief. Relief at moderate 

relief sites usually was provided by a 

few boulders perched on top of sand 

or gravel-cobble substrate. Several of 

the taxa detected mainly at moderate 

relief sites, including Serpulidae, 

Boltenia villosa, and S. montereyensis, 

are sessile and require hard, stable 

substrate for attachment. Other taxa, 

notably F. oregonensis, were nearly 

always observed on boulders or bedrock. 

Thus, the presence of boulders may 

have allowed the occurrence of species 

that require or prefer hard substrate, in 

addition to species requiring or tolerating 

finer substrates, thereby increasing 

taxa richness. Of the five common 

invertebrate species that were detected 

offshore of the river mouth and to the 

west but not to the east (figs. 6.14 and 

6.15), four (C. miniata, F. oregonensis, 

S. montereyensis, and S. droebachiensis) 

were detected mainly at moderate relief 

sites. Their distribution pattern may have 

been due to the availability of seafloor 

relief offshore of the river mouth and to 

the west and the lack of such habitat to 

the east (fig. 6.5B). 

Habitat Types and 

Associated Taxa

The study sites were qualitatively 

classified into four habitat types 

based on physical and biological 

characteristics (table 6.4 and fig. 6.22). 

Bedrock/Boulder Reef

Three shallow sites in central 

Freshwater Bay were located on a 

bedrock reef. One shallow site in 

west Freshwater Bay was included in 

the same habitat type as the bedrock 

sites because of its predominantly 

hard substrate (boulders) and similar 

species at similar densities. Bedrock/

boulder reef habitat supported beds of 

N. luetkeana and P. californica that 

respectively formed nearly continuous 

canopies at the water surface and 

1–2 m above the seafloor, and a diverse 

assemblage of understory kelp and 

invertebrates (fig. 6.23A–B). It also 

supported a density of kelp more than 

twice that for any other habitat type and 

the highest taxa richness among habitat 

types (fig. 6.24). 

Sand and Gravel-Cobble with 

Moderate Relief

Most of the mid-depth and deep 

sites in Freshwater Bay and offshore 

of the Elwha River mouth had mixed 

sand and gravel-cobble substrate 

with sufficient boulder abundance to 

provide moderate relief (fig. 6.23C–D). 

The relative fractions of sand and 

gravel-cobble varied considerably 

within this classification. From a 

biological perspective, the presence of 

large boulders, which provided hard, 

stable substrate and relief that some 

organisms seemed to depend on, was 

more important than the composition of 

the base substrate. Kelp and invertebrate 

assemblages included species that 

were rare at sites lacking relief. The 

mixed substrate-moderate relief habitat 

type supported the highest density of 

invertebrates among habitats with taxa 

richness nearly equivalent to that for 

bedrock/boulder reefs (fig. 6.24). 

Sand and Gravel-Cobble with 

Low Relief

The substrate was composed of 

mixed sand and gravel-cobble with 

little relief at most sites east of the 

Elwha River mouth, at one deep site 

offshore of the river mouth, and at one 

mid-depth site in central Freshwater Bay 

(fig. 6.23E–F). The relative fractions of 

sand and gravel-cobble varied within 

this classification but varied less than for 

the moderate relief classification. Kelp 

was dominated by understory species, 

notably A. marginata that did not occur 

west of the river mouth. This habitat 

supported a density of kelp close to that 

for the moderate relief classification, 

but density of invertebrates was the 

lowest among habitat types and taxa 

richness was considerably lower than for 

moderate relief (fig. 6.24). 
166 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Figure 6.23. Opposite page. Four habitat types that were qualitatively classified at sites near the mouth of the Elwha River, 

Washington. (Characteristics of the habitat types are listed in table 6.4, and locations of the habitat types are shown in fig. 6.22). 

(A–B) Bedrock/boulder reef supporting a kelp forest. (A) View under the canopy formed by Pterygophora californica. P. californica 

stipes (stems) are attached to bedrock encrusted with pink coralline algae; orange mysid shrimp are visible in the water column. 

(B) View above the P. californica canopy. The vertically oriented “ropes” are actually Nereocystis leutkeana (bull kelp) stipes that 

extend from the bedrock to pneumatocysts (floats) at the water surface. Several blades (leaves) grow from each pneumatocyst 

forming a nearly unbroken canopy at the surface. (C–D) Mixed sand and gravel-cobble substrate with moderate relief provided by 

a few boulders. (C) A boulder on substrate composed primarily of sand. Macroalgae and a Cryptochiton stelleri (gumboot chiton) 

are visible on the boulder. (D) Gravel-cobble substrate and a boulder covered with Strongylocentrotus franciscanus (red urchins). 

(E–F) Mixed sand and gravel-cobble substrate lacking boulders and therefore showing low relief. (E) A mid-depth site offshore 

of Dry Creek; Cymathere triplicata is visible. (F) A mid-depth site at the base of Ediz Hook; C. triplicata, Costaria costata, and 

Saccharina sp. are visible. (G–H) Sand substrate. (G) A Zostera marina (eelgrass) bed at the shallower of the two sandy sites in 

west Freshwater Bay; a Polyorchis penicillatus (redeye medusa) is visible in the water column. (H) The deeper of two sandy sites 

in east Freshwater Bay; a Cancer magister (Dungeness crab) is visible in the foreground.

watac11-0558_fig6-22

123°38' 123°36' 123°34' 123°32' 123°30' 123°28'

West Freshwater 

Bay Mid Freshwater 

Bay

Elwha River 

Mouth Dry Creek

Base Ediz

 Hook

EXPLANATION

Habitat classification

Bedrock/Boulder

Sand-cobble, low relief

Sand-cobble, moderate relief

Sand

Other

0 1 2 KILOMETERS

0 1 2 MILES

48°

8'

48°

10'

Bathymetry and topography from Finlayson and 

others, 2005; Cochrane and others, 2008; Warrick 

and others, 2010. UTM Zone 10, WGS84 projection

Bare earth LIDAR from 2001

Figure 6.22. Qualitative classification of four habitat types at sites near the mouth of the Elwha River, 

Washington. The “other” category contains atypical sites that did not fit well into any of the four types. 

Descriptions of physical and biological characteristics for each habitat type are shown in table 6.4.
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Taxa Associated with Seafloor Relief 167

watac11-0588_fig6-23

A. B.

C. D.

E. F.

G. H.
168 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Table 6.4. Qualitative classification of four habitat types based on physical and biological characteristics at sites near the mouth of the 

Elwha River, Washington.

[Site locations are shown in figure 6.22. Note that two atypical sites were classified as “other” and are not included in this table. Taxa identified to genus or 

species are listed in order of decreasing mean density. All such taxa with mean density greater than a minimum value (0.17 per square meter for kelp, 0.10 per 

square meter for invertebrates, 0.005 per square meter for fish) are listed. Of the taxa identified to a broader taxonomic level than genus, the taxon with the 

highest mean density is listed after the semicolon]

Characteristic

Habitat type

Bedrock-boulder reef Sand and gravel; 

moderate relief

Sand and gravel; 

low relief Sand

Physical

Number of sites 4 9 12 6

Depth strata Shallow Medium-deep Shallow-deep Shallow-medium

Depth1 5.3

(3.8–6.1)

13.6

(9.1–16.7)

10.9

(5.4–16.8)

6.4

(3.0–10.4)

Substrate composition2 47.2, 22.5, 18.4, 11.8 2.6, 12.6, 49.1, 35.6 0.1, 0.4, 64.7, 34.8 0.6, 0.6, 2.9, 95.9

Substrate score3 3.1

(2.6–3.4)

1.8

(1.3–2.3)

1.7

(1.3–2.0)

1.1

(1.0–1.3)

Relief composition4 34.5, 59.4, 6.0 65.6, 34.1, 0.3 98.6, 1.2, 0.2 98.8, 1.3, 0.0

Relief score5 1.7

(1.3–2.0)

1.3

(1.2–1.8)

1.0

(1.0–1.0)

1.0

(1.0–1.1)

Boulder abundance Low-high Medium Very low Very low

Taxa assemblage

Kelp Pterygophora californica, 

Nereocystis leutkeana, 

Costaria costata, Cymathere 

triplicata, Saccharina spp., 

Pleurophychus gardneri

Agarum fimbriatum, 

Saccharina spp., Costaria 

costata, Pleurophychus 

gardneri

Saccharina spp., Cymathere 

triplicata, Pterygophora 

californica, Alaria 

marginata

Cymathere triplicata

Invertebrates Cancer oregonensis, 

Cucumaria miniata, 

Strongylocentrous 

franciscanus, Henricia 

leviuscula, Strongylocentrous 

droebachiensis, Styela 

montereyensis, Pycnopodia 

helianthoides; calcareous 

tube worms (Serpulidae)

Cucumaria miniata, 

Strongylocentrous 

franciscanus, Calliostoma 

spp., Fusitriton oregonensis; 

soft tube worms

Halcampa spp.; soft tube 

worms

Soft tube worms

Fish Hexagrammos decagrammus, 

Jordania zonope; 

unidentified sculpins

Hexagrammos decagrammus, 

Gadus macrocephalus 

juveniles; unidentified 

sculpins6, gunnels6

Gadus macrocephalus 

juveniles, Hexagrammos 

decagrammus, Hydrolagus 

colliei; unidentified 

sculpins

Ophiodon elongatus 

juveniles, Blepsias 

cirrhosus (only in 

eelgrass); flatfish

Eelgrass West Freshwater Bay 

only

1

Mean (range) in meters, referenced to mean lower low water.

2

Mean percentage bedrock, boulder, gravel-cobble, and sand, respectively.

3

Mean (range); substrate score is an index of average sediment grain size.

4

Mean percentage in three categories: less than 0.1 meter, 0.1–1.0 meter, and greater than 1 meter, respectively.

5

Mean (range); relief score is an index of average seafloor relief.

6

Unidentified sculpins and gunnels tied for the highest mean density among taxa identified to a broader taxonomic level than genus.
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Key Findings 169

Sand

Sites dominated by sand were 

widely dispersed from west to east. 

Two sites were at the west end of 

Freshwater Bay, two were at the east 

end, and two were at the base of Ediz 

Hook. Eelgrass was interspersed with 

patches of bare sand at the shallow site 

in west Freshwater Bay (fig. 6.23G). 

Eelgrass was absent from the other five 

sandy sites, although it was present at 

one of the sites classified as “other.” 

Small amounts of substrate allowing 

kelp attachment (for example, boulders 

or woody debris), or cobbles with 

kelp attached that were imported from 

other areas (Warrick and others, 2011, 

Chapter 5, sidebar 5.2, this report), 

were sometimes present at sandy sites, 

accounting for the occurrence of kelp 

at low density. Invertebrate density 

was more twice that for the mixed 

substrate-low relief habitat and taxa 

richness was the lowest among habitat 

types (fig. 6.24). 

Other

Two sites were classified as “other” 

because they did not fit well into any of 

the four habitat types. The shallow site 

directly offshore of the Elwha River 

mouth was a moderate relief site, but it 

watac11-0558_fig6-24

Kelp

Fish

Invertebrates

EXPLANATION

Numbers indicate 

taxa richness (total 

number of kelp, 

invertebrate, 

and fish taxa)

37

33

21 17

14

0

2

4

6

8

10

12

BedrockbouldersSand-cobble

Moderate relief

Sand-cobble

Low relief

Sand

Density, in number per square meter

Habitat type

Figure 6.24. Mean densities for 

kelp, invertebrates, and fish for four 

qualitative habitat type classifications 

at sites near the mouth of the Elwha 

River, Washington, August and 

September 2008. (Characteristics, 

locations, and photographs of 

the habitat types are shown in 

table 6.4, figure 6.22, and figure 6.23, 

respectively.) 

had the lowest mean relief score among 

the moderate relief sites (fig. 6.20B) 

and a taxa richness considerably lower 

than for any of the other moderate relief 

sites (fig. 6.21D). A shallow site in west 

Freshwater Bay was classified as “other” 

because it was on a boundary between 

habitat types. One transect was in sand 

with eelgrass, the other on boulder reef. 

Key Findings

The results of this study indicate 

that biological communities in the study 

area were partly controlled by substrate, 

relief, and depth. Communities differed 

markedly among hard substrate (bedrock 

or boulders), mixed substrate (sand and 

gravel-cobble), and sand. The presence 

of relief (boulders) in areas with mixed 

substrate increased species richness 

by providing habitat for species that 

otherwise would not be represented. 

Kelp proliferated at shallow depths 

(3–6 m) given suitable substrate but also 

was abundant at deep sites (15–18 m). 

Community composition of kelps and 

invertebrates varied with depth. 

The distribution of substrate, relief, 

and depth within the study area created 

a mosaic of habitats and communities. 

Freshwater Bay was particularly rich. 

Present at shallow sites in Freshwater 

Bay, from west to east, were an eelgrass 

bed, a bedrock/boulder reef supporting 

a dense and diverse kelp forest, and 

a sandy area lacking eelgrass but 

supporting Cancer magister (Dungeness 

crab; fig. 6.23H) and juvenile O. 

elongatus (lingcod; fig. 6.10D) among 

other species. At greater depths in 

Freshwater Bay, mixed sand and 

gravel-cobble substrate and the presence 

of boulders supported a distinct 

community nearly as diverse as the kelp 

forest. Mid-depth and deep sites directly 

offshore of the Elwha River mouth 

merit attention. Diversity was high at 

these sites (fig. 6.11D). Substrate was 

almost entirely (greater than or equal to 

94 percent) gravel-cobble that appeared 

stable and may have provided habitat 

for species needing hard substrate 

even when boulders were absent. Tidal 

currents here are among the highest 

in the study area (Warrick and others, 

2011b, chapter 5, this report). The 

distribution of substrate types important 

for structuring biological communities 

in Freshwater Bay and offshore of the 

river mouth is well characterized by the 

substrate morphology map of Warrick 

and others (2008) (fig. 6.2B). 

Mixed substrate lacking boulders 

predominated at sites east of the Elwha 

River mouth. The community here was 
170 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Although the focus of this study was on benthic invertebrates larger than 

2.5 cm, qualitative observations were made of smaller-bodied invertebrates 

that may play a role in the marine biological community or may serve as useful 

indicators of change following dam removal, including brittle stars, mysid 

shrimp, and small tube worms. Of particular interest are benthic amphipods of 

the genus Ampelisca. These small, tube-building amphipods were abundant at 

a few sites that included sediments finer than sand.

The genus Ampelisca, typically associated with bottoms of soft sediments 

(Dauvin and BellanSantini, 1996), is globally distributed and can be abundant 

in shallow coastal environments. In Chile, for example, a species of this 

genus is associated with sediments composed of more than 50 percent silt 

and clay (Carrasco and Arcos, 1984). Almost all members of this genus build 

tubes constructed of sediment grains, using the tube as a protection against 

predatory grazing. During feeding the amphipods extend part of their body 

from the top of the tube and use their antennae to collect detritus, plankton 

or other epibenthic invertebrates from the surrounding seafloor or water 

column (Sheader, 1998). Their tube-building habit modifies the substrate 

and influences the exchange of material between sediments and the water 

column. One study from the east coast of the United States suggests that 

Ampelisca tubes provide structure to sea-floor sediments, making them more 

desirable as a recruitment substrate for commercially important quahog 

clams (Mercenaria mercenaria) (Mackenzie and others, 2006). The abundant 

amphipods also provide food for a number of larger animals including gray 

whales (Eschrichtius robustus) (Oliver and Slattery, 1985; Darling and others, 

1998). Ampelisca are thought to be a primary food source for a variety of fish 

species (Carrasco and Arcos, 1984), in some cases contributing as much as 

88 percent of the prey base (Franz and Tanacredi, 1992).

Field observations made during this study and sonar-derived backscatter 

interpretation from a previous study (Warrick and others, 2008) suggest that 

sediments finer than sand are rare within the Elwha coastal zone. Sediments 

usually were composed of coarser sand or a mix of sand and gravel even at 

sites classified as “soft”. Although fine sediments were generally lacking in 

the Elwha River nearshore area, tubes of Ampelisca were observed at one 

shallow site at the western edge of Freshwater Bay (fig. S6.1A), in clearings 

between dense thickets of eelgrass (Zostera marina). The substrate at this 

site was primarily sand, but it may have included silt and clay because these 

grain sizes often are associated with eelgrass in Puget Sound (Mumford, 2007)

Water visibility, measured by divers, likely can be used as a proxy for the 

presence of fine sediments, because re-suspension of mud and silt can cloud 

the water. Mean visibility for all shallow sites at the two control areas (Green 

Point and Low Point) was lower than for shallow sites in the Elwha coastal 

zone (fig. S6.2), suggesting the presence of fine sediments in control area 

substrates. The reduced visibility at Green Point and Low Point was not simply 

the product of a single low visibility dive skewing the data. Out of 85 visibility 

measurements made in 2008, the lowest 10 occurred in these two areas.

Ampelisca was observed in abundance at shallow sites offshore of 

Green Point (fig. S6.1B). Gray whales were observed at these sites exhibiting 

behavior associated with bottom feeding—repeatedly diving and creating 

clouds of silt visible at the surface (fig. S6.3A). A year later at the same 

location trenches were observed in the seafloor, approximately 3 m long, 

1–2 m wide and 0.2–0.5 m deep, which were interpreted as gray whale 

feeding excavations. Along the edges of these trenches, the sediment tubes 

of Ampelisca and inactive or dead amphipods were observed on the bed 

watac11-0558 -S1_fig6-01

A. Ampelisca tubes

B. Flatfish imprint in soft sediment

C. Tube-dwelling amphipods

50 10 CENTIMETERS

20 4 INCHES

50 10 CENTIMETERS

20 4 INCHES

0 .5 1 CENTIMETER

0 .5 1 INCH

Figure S6.1. (A) Ampelisca tubes photographed at 

macro-range in an eelgrass bed at the west end of 

Freshwater Bay, September 9, 2009. (B) Outline of a flatfish 

in soft sediment off of Green Point, Siebert Creek, Strait 

of Juan de Fuca. Within the outline are numerous tubes 

of the amphipod Ampelisca, August 12, 2009. (C) Tubedwelling amphipods, perhaps of the genus Ameplisca, 

attached to a small boulder off shore of Low Point, Lyre 

River, Strait of Juan de Fuca, September 10, 2009.

Sidebar 6.1 Fine Sediments and the Role of Benthic Amphipods

 Ian M. Miller, Jeffrey J. Duda, Nancy Elder, Reginald R. Reisenbichler, and Stephen P. Rubin
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams Habitat Types and Associated Taxa 171

watac11-0558_s1-fig6-02

Green Point Elwha Coastal

Zone

Low Point

2

0

10

8

6

4

Mean visibility, in meters

A. Gray whale off of Green Point

B. Edge of whale bite-mark

2520151050

1086420 12 INCHES

30 CENTIMETERS

(fig. S6.3B). Previous research in the Strait of Juan de Fuca (Oliver and 

Slattery, 1985) documented the effects of gray whale feeding on benthic 

community structure, showing the colonization of feeding excavations 

by motile scavengers, followed by the return of sessile tube worms in 

about 2 months. Amphipods also were observed in abundance at Low 

Point, but with a slightly different growth form, with clumps of tubes 

attached to boulders (fig. S6.1C). It is not clear if these amphipods 

also are a species of Ampelisca, although the tubes apparently were 

constructed of sediment and individual amphipods were observed at the 

opening of the tubes.

The role played by Ampelisca in supporting upper trophic levels 

in the Strait of Juan de Fuca is not clear, but this species has been a 

major dietary item of gray whales feeding elsewhere in the northern 

Pacific (Oliver and others, 1984; Oliver and Slattery 1985). Whether the 

removal of the dams on the Elwha River will increase fine sediments in 

the substrate around the Elwha delta is not known. The configuration 

of the Elwha delta and its exposure to waves and tidal currents 

might make it unsuitable for the settlement of silts, mud or clay. We 

hypothesize, however, that if dam removal results in a shift toward a 

substrate composed at least partially of fine sediments, development 

of habitat types and biological communities that are currently sparse 

may be facilitated in the Elwha coastal zone. We hypothesize that if fine 

sediments released in the Elwha coastal zone remain after dam removal, 

they may play a role in restructuring marine habitats by providing one 

of the essential ingredients for the success of abundant populations of 

Ampelisca.

References Cited

Carrasco, F.D., and Arcos, D.F., 1984, Life history and production of a cold-temperate 

population of the sublittoral amphipod Ampelisca araucana: Marine Ecology-Progress 

Series, v. 14, p. 245-252.

Darling, J.D., Keogh, K.E., and Steeves, T.E., 1998, Gray whale (Eschrichtius robustus) habitat 

utilization and prey species off Vancouver Island, B.C.: Marine Mammal Science, v. 14, 

iss. 4, p. 692-720.

Dauvin, J.C., and BellanSantini, D., 1996, Ampeliscidae (Amphipoda) from the Bay of Biscay: 

Journal of Crustacean Biology, v. 16, p. 149-168.

Franz, D.R., and Tanacredi, J.T., 1992, Secondary production of the amphipod Ampelisca 

abdita mills and its importance in the diet of juvenile winter flounder (Pleuronectes 

americanus) in Jamaica Bay, New York: Estuaries, v. 15, p. 193-203.

Mackenzie, C.L., Pikanowski, R., and McMillan, D.G., 2006, Ampelisca amphipod tube 

mats may enhance abundance of northern quahogs Mercenaria mercenaria in muddy 

sediments: Journal of Shellfish Research, v. 25, p. 841-847.

Mumford, T.F., Jr., 2007, Kelp and eelgrass in Puget Sound: Seattle District, U.S. Army Corps 

of Engineers, Puget Sound Nearshore Partnership Report No. 2007-05, accessed June 16, 

2010, at http://www.pugetsoundnearshore.org/technical_papers/kelp.pdf.

Oliver, J.S., and Slattery, P.N., 1985, Destruction and opportunity on the sea floor—Effects of 

gray whale feeding: Ecology, v. 66, p. 1965-1975.

Oliver, J.S., Slattery, P.N., Silberstein, M.A., and O’ Connor, E.F., 1984, Gray whale feeding 

on dense ampeliscid amphipod communities near Bamfield, British Columbia: Canadian 

Journal of Zoology, v. 62, p. 41-49. 

Sheader, M., 1998, Grazing predation on a population of Ampelisca tenuicornis (Gammaridae, 

Amphipoda) off the south coast of England: Marine Ecology-Progress Series, v. 164, 

p. 253-262.

Warrick, J.A., Cochrane, G.R., Sagy, Y., and Gelfenbaum, G., 2008, Nearshore substrate 

and morphology offshore of the Elwha River: Northwest Science, v. 82 (special issue), 

p. 153-163.

Figure S6.2. Mean visibility at shallow sites for two control 

areas (Green Point and Low Point) and the Elwha coastal zone. 

Error bars are one standard deviation.

Figure S6.3. (A) A gray whale feeding off Green Point, 

September 4, 2008. Plumes of sediment trailed from this whale 

as it surfaced after feeding along the bottom. (B) An excavated 

edge cut into the soft substrate off shore of Green Point, likely 

due to gray whale feeding, September 11, 2009. This illustrates 

the extent to which soft sediment is used as habitat. Amphipods, 

annelid worms, and other small invertebrates were observed on 

and around the excavated bed in these pits.
172 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

less dense and diverse than to the west 

but nonetheless abundant and distinct. 

Seavey and Ging (1995) thoroughly 

surveyed shallow depths between the 

river mouth and Dry Creek and reported 

high percentage coverage of macroalgae 

(74–100 percent) for most of this area. 

We confirmed their finding that A. 

marginata (fig. 6.7B) and C. triplicata

(fig. 6.7D) are dominant kelp species 

in this area. These species are annuals 

whose blades grow during the spring 

and summer months (Mumford, 2007). 

Therefore, these species avoid damage 

or dislodgement by winter wave action 

and can thrive on finer substrate (gravelcobble) than is required by perennial 

species like P. californica (fig. 6.7G). 

The invertebrate community at mixed 

substrate sites east of the river mouth 

was dominated by Halcampa spp. 

(burrowing anemones; fig. 6.16G), 

the most abundant taxon among those 

identified to genus or species, and 

soft tube worms including Eudistylia 

vancouveri (northern feather duster 

worm, fig. 6.6D), which was more 

abundant east than west of the river 

mouth. H. Colliei (spotted ratfish; 

fig. 6.10C) was common in mixed 

substrate habitat east of the river mouth. 

Sand habitat was also present east of the 

river mouth in shallow water at the base 

of Ediz Hook. 

Implications for Effects of 

Dam Removal

Considerable influx of sediment 

to the nearshore is expected initially 

(for 3–5 years after start of dam 

removal) due to release of sediments 

that have accumulated in the reservoirs. 

Thereafter, sediment influx will likely 

decrease as the natural (pre-dam) rate of 

sediment delivery is re-established. This 

temporal pattern of sediment delivery 

raises a number of questions about 

biological community responses. What 

will happen to habitats and biota shortly 

after dam removal and in the long 

term? Will the marine system return to 

its natural, pre-dam condition? How 

long will restoration (recovery) take? 

What “services” (for example, kelp 

production) will be lost or impaired? 

What services will be enhanced? 

Our pre-removal survey establishes a 

baseline for evaluating short- and longterm consequences of dam removal. 

Follow-up surveys should help answer 

the questions posed above.

The spatial extent, vertical 

thickness, frequency, duration, timing 

(seasonality), and grain size of deposited 

sediments following dam removal will 

be important for determining effects on 

nearshore communities (Airoldi, 2003). 

Sediment deposition is expected to be 

greatest east of the Elwha River mouth 

due to the prevailing direction of coastal 

currents; however, sedimentation also 

may occur to the west in Freshwater 

Bay because currents are occasionally 

negligible or directed westward (Warrick 

and others, 2011b, chapter 5, this 

report). Thus, the community associated 

with mixed substrates lacking relief 

(boulders) that currently predominates 

east of the river mouth may experience 

the greatest sediment loads following 

dam removal, but kelp forest and reliefdependent communities to the west also 

may be affected. Furthermore, each 

of these communities may respond 

differently even to similar sedimentation 

levels. Finally, suspended sediment 

from riverine inputs as well as from 

re-suspension of deposited sediments 

may affect biological communities. 

These uncertainties highlight the 

opportunity to advance scientific 

understanding by measuring responses 

following dam removal. 

Whatever changes come, they 

will likely involve tradeoffs, favoring 

some species and disfavoring others in 

the short term and over the long term 

as restoration occurs. Kelp may be 

particularly intolerant of sedimentation 

because their spores require sedimentfree surfaces for settlement, their 

microscopic gametophyte and young 

sporophyte life stages are susceptible to 

burial, and they require high light levels 

for growth (Mumford, 2007). Even so, 

some kelp species can persist in areas 

with fine sediment (Dayton, 1985), 

perhaps depending on the depth or 

timing of coverage by fine sediment and 

the life history traits of the kelp (timing 

of reproduction; annuals compared to 

perennials; physiological adaptations). 

Sediment influx following dam removal 

may reduce kelp abundance overall, 

but may favor some species over 

others. Organisms that can propagate 

vegetatively, thereby bypassing 

vulnerable juvenile life stages, may be 

relatively resistant to sedimentation 

(Airoldi, 2003). Some turf-forming 

seaweed can trap sediments, which 

may discourage grazing or give them a 

competitive advantage over organisms 

less tolerant to sedimentation (Airoldi, 

2003). If localized accumulations of 

sediment are great enough, some areas 

could convert from hard substrate to 

soft substrate habitat causing dramatic 

shifts in the benthic community. If dam 

removal results in accumulations of very 

fine sediments (silt, mud, or clay), which 

are currently rare in the Elwha coastal 

zone (Warrick and others, 2008), a group 

of small invertebrates that provide food 

for a number of other organisms may 

benefit (sidebar 6-1).

Summary

Benthic communities inhabiting 

shallow, subtidal depths near the 

mouth of the Elwha River were 

biologically diverse. They included 

10 kelp species with differing growth 

forms and habitat associations, and 

a wide variety of invertebrate and 

fish species. Substrate type, seafloor 

relief, and water depth were important 

determinants of organism density and 

species composition. As such, the spatial 

distribution of these characteristics 

created a rich mosaic of habitats and 

associated communities. The removal 

of two dams on the Elwha River will 

release large quantities of sediment, 
Chapter 6

Nearshore Biological Communities Prior to Removal of the Elwha River Dams References Cited 173

some of which will be discharged 

into the Elwha River nearshore. The 

greatest influx is expected during the 

first 3–5 years after start of dam removal 

from sediment that has accumulated in 

the reservoirs. Thereafter, sediment input 

should decrease but remain higher than 

before dam removal owing to restored 

connectivity with the upper watershed. 

Measuring community responses to 

short and long term changes in deposited 

and suspended sediments following 

dam removal offers an unprecedented 

opportunity to gain insight relevant 

to managing these important marine 

resources.

Acknowledgments

We thank the many people that 

provided help or support including 

Mike McHenry and Doug Morrill 

(Lower Elwha-Klallam Tribe); Kurt 

Fresh (National Marine Fisheries 

Service); Sam Brenkman, Patrick 

Crain, and Steve Fradkin (National 

Park Service); Mike Ferguson (Porthole 

Dive Charters); Lieutenant Christian 

Polyak (U.S. Coast Guard); Guy 

Cochrane, Tim Elfers, Pete Dal Ferro, 

Guy Gelfenbaum, Jamie Grover, Mike 

Hayes, Marshal Hoy, Rusty Rodriguez, 

Andrew Stevens, Glen VanBlaricom, 

Jon Warrick, and Lisa Wetzel (U.S. 

Geological Survey); Kevin BrittonSimmons (University of Washington 

Friday Harbor Laboratories); Don 

Rothaus, Anne Shaffer, and Michael 

Ulrich (Washington Department of 

Fish and Wildlife); and Tom Mumford 

(Washington Department of Natural 

Resources). 

References Cited

Airoldi, L., 2003, The effects of 

sedimentation on rocky coast 

assemblages: Oceanography and 

Marine Biology, v. 41, p. 161-236. 

Airoldi, L., and Cinelli, F., 1997, 

Effects of sedimentation on 

subtidal macroalgal assemblages—

An experimental study from a 

Mediterranean rocky shore: Journal 

of Experimental Marine Biology and 

Ecology, v. 215, p. 269-288.

Airoldi, L., and Virgilio, M., 1998, 

Responses of turf-forming algae to 

spatial variation in the deposition of 

sediments: Marine Ecology Progress 

Series, v. 165, p. 271-282.

Beauchamp, D.A., Baldwin, C.M., 

Vogel, J.L., and Gubala, C.P., 1999, 

Estimating diel, depth-specific 

foraging opportunities with a visual 

encounter rate model for pelagic 

piscivores: Canadian Journal of 

Fisheries and Aquatic Sciences, v. 56, 

p. 128-139.

Berry, H.D., Mumford, T.F., Jr., and 

Dowty, P., 2005, Using historical 

data to estimate changes in floating 

kelp (Nereocystis leutkeana and 

Macrocystis integrifolia) in Puget 

Sound, Washington: Washington State 

Department of Natural Resources, 

Nearshore Habitat Program, accessed 

June 15, 2010, at http://www.dnr.

wa.gov/Publications/aqr_nrsh_

floating_kelpbed.pdf.

Carr, M., Syms, C., and Caselle, 

J., 2001, MLMA nearshore reef 

monitoring network (NRMN) 

proposal: Report to the Cooperative 

Research and Assessment of 

Nearshore Ecosystems (CRANE) 

program, accessed June 15, 2010, 

at http://www.piscoweb.org/files/

file/Kelp-Forest-Monitoring/crane_

protocol.pdf.

Cochrane, G.R., Warrick, J.A, Sagy, 

Yael, Finlayson, D., Harney, J., 

2008, Sea-floor mapping and benthic 

habitat GIS for the Elwha River 

Delta nearshore, Washington: U.S. 

Geological Survey Data Series 320, 

accessed June 15, 2010, at http://pubs.

usgs.gov/ds/320/.

Czuba, C.R., Randle, T.J., Bountry, 

J.A., Magirl, C.S., Czuba, J.A., 

Curran, C.A., and Konrad, C.P. 2011, 

Anticipated sediment delivery to 

the lower Elwha River during and 

following dam removal, chap. 2 of 

Duda, J.J., Warrick, J.A., and Magirl, 

C.S., eds., Coastal habitats of the 

Elwha River, Washington—Biological 

and physical patterns and processes 

prior to dam removal: U.S. Geological 

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Chapter 7

7

Chapter

Aquatic Ecology of the Elwha 

River Estuary Prior to Dam 

Removal

By Jeffrey J. Duda, Matthew M. Beirne, 

Kimberly Larsen, Dwight Barry, Karl 

Stenberg, and Michael L. McHenry

Abstract

The removal of two long-standing dams on 

the Elwha River in Washington State will 

initiate a suite of biological and physical 

changes to the estuary at the river mouth. 

Estuaries represent a transition between 

freshwater and saltwater, have unique 

assemblages of plants and animals, and 

are a critical habitat for some salmon 

species as they migrate to the ocean. This 

chapter summarizes a number of studies 

in the Elwha River estuary, and focuses 

on physical and biological aspects of the 

ecosystem that are expected to change 

following dam removal. Included are data 

sets that summarize (1) water chemistry 

samples collected over a 16 month period; 

(2) beach seining activities targeted toward 

describing the fish assemblage of the 

estuary and migratory patterns of juvenile 

salmon; (3) descriptions of the aquatic 

and terrestrial invertebrate communities 

in the estuary, which represent an 

important food source for juvenile 

fish and are important water quality 

indicators; and (4) the diet and growth 

patterns of juvenile Chinook salmon 

in the lower Elwha River and estuary. 

These data represent baseline conditions 

of the ecosystem after nearly a century 

of changes due to the dams and will be 

useful in monitoring the changes to the 

river and estuary following dam removal.
176 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Introduction

As juvenile salmon migrate from 

freshwater rearing areas, they undergo 

the physiological, behavioral, and 

life history changes necessary for 

transition to life in the ocean. Estuaries 

are recognized as an important part of 

this migration (Simenstad and others, 

1982; Bottom and others, 2005b). 

Some salmon species, such as Chinook 

(Oncorhynchus tshawytscha) and chum 

(O. keta) can spend extended periods 

(weeks to months) in the estuarine 

environment, whereas others such as 

pink salmon (O. gorbuscha) largely 

forego extended use of estuarine areas 

in favor of ocean rearing (Groot and 

Margolis, 1991). It is hypothesized that 

salmon use estuarine habitats because 

they provide a higher growth potential, 

facilitate the physiological transition 

to saltwater conditions, and reduce 

the risk of predation (Quinn, 2005). 

All of these factors may play a role in 

higher growth and survival during the 

subsequent marine life history phase 

(Ruggerone and others, 2009). Estuarine 

fish assemblages fluctuate seasonally, 

based on migration timing, habitat 

structure and connectivity, and physical 

factors such as salinity and temperature. 

Estuaries vary in size (see Duda and 

others, 2011, figs. 1.8–1.10, chapter 1, 

this report) and in the relative influence 

of freshwater and marine drivers 

important for ecological processes. 

This affects the amount, complexity, 

biological productivity, and physical 

conditions of estuarine habitats, which 

varies among river systems. Although 

the role of estuaries has been deemed 

important for some Puget Sound 

Chinook populations (Simenstad and 

others, 1982; Beamer and Larsen, 

2004), the significance of the Elwha 

River estuary and nearshore (coastal 

marine water zone extending from high 

tide elevation to the limit of the photic 

zone) to Chinook salmon populations 

is relatively unknown. We set out to 

describe the existing conditions of some 

key ecological components of the lower 

Elwha River and its estuary prior to dam 

removal.

Research efforts focused on 

collecting physical (water chemistry; 

see also Magirl and others, 2011, 

chapter 3, this report, for salinity 

and temperature data) and biological 

data from throughout the estuary and 

adjacent riverine and nearshore areas 

in the Elwha River study area (fig. 7.1) 

prior to dam removal. Water samples 

were collected monthly to measure 

nutrient concentrations from stations 

dispersed in the lower river (2 sites), in 

the estuary (4 sites), and in the nearshore 

(1 site). Seasonal use of the estuary 

and nearshore by salmon during their 

migration to the marine environment 

also was estimated. We studied fish 

distribution, abundance, and migration 

timing for all salmonids using the Elwha 

River estuary and examined the diet 

and growth rates of juvenile Chinook 

salmon. The aquatic and terrestrial 

macroinvertebrate communities of 

the estuary also were surveyed. These 

animals play a central role as prey for 

salmon and are indicators of water 

quality that should be responsive to 

physical changes associated with 

dam removal. Other studies are 

being conducted on fish ecology by 

colleagues elsewhere in the watershed 

(for examples, see Burke and others, 

2008; Connolly and Brenkman, 2008; 

McHenry and Pess, 2008; Pess and 

others, 2008, Brenkman and others, 

2008a, b; Duda and others, in press), 

in the nearshore proximal to the Elwha 

River, and in the Strait of Juan de Fuca 

(for example, Shaffer and others, 2009). 

Juvenile Chinook salmon samples 

from these studies were obtained to 

assist in estimating several life history 

traits, including age and growth (otolith 

microstructure), feeding (stomach 

contents), and genetics (fin clips). This 

information should help provide a better 

understanding of Chinook salmon life 

histories and help inform adaptive 

management of the population following 

dam removal and recolonization of the 

Elwha River watershed.
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal Introduction 177

watac11-0558_fig7-01

WASHINGTON STATE

Figure

location

Dudley

Pond

WESC

ES1

ES2

Bosco

Creek

IEC

EXPLANATION

Uppermost saltwater influence

Outmigrant screw trap 

Water nutrient sampling site 

Lower Elwha Klallam Tribe 

Reservation Boundary

Hunt Road Channel

West-side Dike

Figure 7.1. Sampling locations where water nutrients, benthic and terrestrial insects, and fish samples were 

collected in the Elwha River, Washington, study area.
178 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Water Nutrients

Inorganic nutrients are important 

constituents for cell growth and often 

limit population growth and drive 

competitive interactions; therefore, 

they play a central role in determining 

presence and abundance patterns of biota. 

The availability of essential nutrients in 

the water column can limit the amount 

of biological productivity and thus 

the character of the entire ecosystem. 

Measurement of nutrients through time 

also can reflect patterns in seasonal 

biological productivity, as nutrients 

are diminished during periods of high 

growth (for example of algae and other 

primary producers during the summer 

growing season) and are higher during 

periods of biological dormancy. The 

availability of nutrients in any watershed 

depends on both biological and physical 

properties. Natural forces such as rainfall, 

geology, atmospheric deposition, and 

sedimentation drive levels of available 

nutrients, which are then consumed 

by autotrophic organisms and further 

modified by allochthonous energy inputs 

from the surrounding landscape. Other 

factors largely caused by human activity, 

such as resource extraction, fertilization, 

and industrial pollution also can affect the 

nutrient levels in a watershed.

Previous water nutrient sampling 

of main stem, side channel, and tributary 

habitats throughout the Elwha River 

watershed has indicated that, for its 

size and condition, the Elwha River is 

oligotrophic, or low in nutrients (Munn 

and others, 1999; Duda and others, in 

press). Although these earlier studies had 

broad spatial coverage of the watershed, 

they were temporally restricted to base 

(summer) flows and did not include 

water samples from the estuary or 

nearshore. This chapter provides 

comparable nutrient samples from the 

estuary and nearshore and a time series 

over a 16-month period. This baseline 

assessment of spatial and temporal trends 

in nutrient levels of the water column 

will be useful for comparisons during and 

following dam removal. 

Water Sample 

Collection and Laboratory 

Analysis of Nutrient 

Concentrations

Water samples were collected 

monthly from seven locations in the 

lower Elwha River and estuary (fig. 7.1). 

Sites included one main stem (Lower 

Elwha River – main stem) and one side 

channel (Lower Elwha River – side 

channel) location in the lower Elwha 

River; the groundwater fed outflow of 

the tribal hatchery (Bosco Creek) that 

serves as a primary source of surface 

water to the east estuary; the tidally 

influenced lentic sloughs east of the 

river mouth in the east estuary (ES1 and 

ES2); the disconnected lake to the west 

of the river mouth (Dudley Pond); and 

the surf zone (Nearshore – Strait of Juan 

de Fuca) 25 m east of the river mouth 

in the Strait of Juan de Fuca. Samples 

were collected across a range of tidal 

conditions at approximately 30-day 

intervals, with interruptions in sample 

collection at all sites in November 2006 

(inclement weather) and July 2007 

(processing error).

Water samples were collected for 

analysis of total nitrogen (TN), total 

phosphorous (TP), dissolved inorganic 

nitrogen (nitrate [NO3

-

], ammonia 

[NH4

+]) and phosphate (PO4-3). Water 

collection (500 mL) and sample bottles 

(60 mL) were acid washed (10 percent 

HCl) prior to sample collection. At each 

site, all sampling equipment and bottles 

were rinsed three times with ambient 

water. Samples were collected at the 

same depth for each site, generally 

60 percent of the water column depth at 

least 1 m from shore. An inverted water 

collection bottle was submerged, filled, 

and capped at depth, to ensure that no 

water was collected from the surface. 

Samples for dissolved nutrients were 

filtered in the field using a 0.45-μm 

pore size syringe filter. Once collected, 

samples were kept on ice in the field and 

frozen in the laboratory prior to analysis 

by the University of Washington Marine 

Chemistry Laboratory, Seattle, Wash. 

This procedure and laboratory were 

the same that were used by Morley and 

others (2008) and Duda and others (in 

press) for samples collected throughout 

the Elwha River watershed.

Total nitrogen and total 

phosphorous were analyzed using 

the persulfate digestion method of 

Valderrama (1981). The procedure 

of Armstrong and others (1967) was 

modified for the analysis of NO3 and 

NO2. Water samples were passed 

through a cadmium (Cd) column where 

the nitrate (NO3) was reduced to nitrite 

(NO2). This NO2 was then diazotized 

with sulfanilamide and coupled with 

N-(1-naphthyl)-ethylenediamine to 

form an azo dye. The sample was then 

passed through a 15 mm flowcell and 

absorbance measured at 540 nm. The 

procedure is the same for the NO2

analysis less the Cd column. Nitrate 

concentration equals the (NO3 + 

NO2) concentration minus the NO2

concentration. A modification of the 

Slawyk and MacIsaac (1972) procedure 

was used for the analysis of ammonium 

(NH4). Water samples were treated with 

phenol and alkaline hypochlorite in the 

presence of ammonia (NH3) to form 

idophenol blue (Berthelot reaction). 

Sodium nitroferricyanide was used as 

a catalyst in the reaction. Precipitation 

of calcium (Ca) and magnesium (Mg) 

hydroxides was eliminated by the 

addition of sodium citrate complexing 

reagent. The sample stream then was 

passed through a 55°C heating bath, 

then through a 50 mm flowcell and 

absorbance was measured at 640 nm. 

Phosphate was analyzed using a 

modification of the Bernhardt and 

Wilhelms (1967) method. Ammonium 

molybdate was added to water 

samples to produce phosphomolybdic 

acid, which then was reduced to 

phosphomolybdous acid following the 

addition of dihydrazine (or hydrazine) 

sulfate. The sample was passed through 

a 50 mm flowcell and absorbance was 

measured at 820 nm.
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal Water Nutrients 179

Spatial Patterns of 

Water Nutrients

Fourteen water samples were 

collected from June 2006 until 

September 2007 at most locations 

(table 7.1). The concentration of each 

nutrient by month was graphed and 

smoothed curves were created using a 

cubic spline interpolation in SPSS Inc. 

(2010). The data are presented in the 

form of sparklines, a method of data 

visualization that uses small, highresolution graphics coupled with words 

and numbers (Tufte, 2006). By creating 

small, time series graphics for each 

location and water chemistry constituent 

(with maximum, average, and minimum 

values provided), spatial and temporal 

trends in water chemistry can be 

compared in a single figure. 

The time series showed seasonal 

variations in nutrient levels and 

differences among sites (figs. 7.2A and 

7.2B). Concentrations of nutrients (TN, 

TP, PO4 and NO3),

 at the nearshore zone 

of the Strait of Juan de Fuca generally 

were higher than sites in the Elwha 

River and its estuary. An exception 

was Bosco Creek with the highest 

NH4 concentration, possibly due to the 

hatchery operations at the source of the 

surface water supply, which concentrates 

the animal waste byproducts associated 

with large-scale fish production. Higher 

concentrations of TP, TN, NO3, and 

PO4 were measured in Bosco Creek 

than in the other five sites of the lower 

Elwha River and estuary. Following 

Bosco Creek and the nearshore, the 

two locations in the east estuary (ES1 

and ES2) had the next highest levels 

of nutrient concentrations. Samples 

from the Elwha River (main stem and 

side channel) were consistently the 

lowest of all sites for most nutrients. 

This result is consistent with previous 

studies documenting the oligotrophic 

nutrient status of the river (Munn and 

others, 1999; Duda and others, in press). 

Levels of nitrogen and phosphorous 

generally increased along the gradient 

from freshwater–estuarine–marine 

waters, which is a result consistent with 

expectations. 

Temporal Patterns of Water 

Nutrients

The highest temporal variability in 

water nutrient patterns was in the Strait 

of Juan de Fuca and Bosco Creek, which 

was indicated by the widest confidence 

intervals around their mean values across 

all samples (table 7.1). Oscillations at 

both these sites were during months 

that did not follow a consistent 

seasonal pattern (figs. 7.2A and 7.2B). 

The estuarine and lower Elwha River 

samples, however, displayed a more 

typical seasonal pattern. During spring 

and summer, when primary production 

in the river and estuary increases with 

increasing day length, levels of most 

nutrients were lower than levels during 

winter, when primary productivity 

wanes. Interestingly, Dudley Pond in 

the western part of the estuary, which is 

disconnected from the Elwha River by 

a dike, was out of phase with the east 

estuary during the autumn and winter 

periods, especially for TP, PO4, and NH4.

Table 7.1. Average concentration of total and dissolved nutrients at seven sites in the lower Elwha 

River, its estuary, and the nearshore surf zone of the Strait of Juan de Fuca, Washington, 2006 and 2007.

[All values are in micrograms per liter (standard deviation). Locations are shown in figure 7.1. Samples were collected at 

approximately 30 day intervals from June 2006 to September 2007, with interruptions in sample collection at all sites in 

November 2006 and July 2007. Abbreviations: MS, main stem; SC, side channel; ES1, east estuary 1; ES2, east estuary 2]

Location Total 

phosphorus

Total 

nitrogen

Dissolved 

phosphate

Dissolved 

nitrate

Dissolved 

nitrite

Dissolved 

ammonia

Lower Elwha – MS 13 (4) 83 (48) 2 (2) 16 (17) 0.2 (0.1) 2 (3)

Lower Elwha – SC 12 (4) 105 (60) 2 (2) 24 (17) 0.2 (0.2) 4 (5)

Bosco Creek 32 (12) 275 (81) 14 (8) 76 (54) 3 (2) 79 (51)

ES1 16 (6) 139 (73) 5 (5) 28 (35) 0.2 (0.2) 13 (12)

ES2 18 (3) 178 (87) 6 (3) 43 (55) 0.6 (0.7) 18 (18)

Dudley Pond 16 (4) 163 (91) 3 (2) 7 (7) 0.3 (0.2) 10 (11)

Nearshore 49 (18) 284 (123) 30 (16) 132 (82) 2 (2) 12 (12)
180 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0558_fig7-02a

Total phosphorous

(micrograms per liter) 

Total nitrogen

(micrograms per liter) 

67

347

178

12

26

18

16

80

49

67

500

284

8

23

13

9

171

83

8

17

12

4

183

105

22

68

32

113

421

275

10

25

16

62

370

163

8

32

16

17

254

139

EXPLANATION

A.

June 2006 September 2007

Maximum

Average

Minimum

ES2

Lower

Elwhamain 

stem 

Lower

Elwhaside 

channel 

Bosco

Creek 

Dudley

Pond

ES1

Nearshore

Figure 7.2. Sparkline graphs showing time series of water chemistry species (A) total 

phosphorous and total nitrogen and (B) phosphate, nitrate, and ammonia, from the lower 

Elwha River, its estuary complex, a spring fed tributary draining into the east estuary, and 

the nearshore surf zone of the Strait of Juan de Fuca near the mouth of the Elwha River, 

Washington, 2006–07.
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal Water Nutrients 181

watac11-0558_fig7-02b

Phosphate

(micrograms per liter)

Nitrate

(micrograms per liter)

Ammonia

(micrograms per liter)

59

18

2

169

43

1

11

6

2

56

30

3

264

132

9

36

12

0

7

2

1

47

16

1

8

2

0

0.7

9

2

0.3

17

4

40

14

9

216

76

29

187

79

26

0.1

36

10

24

7

1

6

3

1

0.3

42

13

100

28

1

43

24

2

20

5

2

June 2006 September 2007

Maximum

Average

Minimum

ES2

Lower

Elwhamain 

stem 

Lower

Elwhaside 

channel 

Bosco

Creek 

Dudley

Pond

ES1

Nearshore

EXPLANATION

B.

Figure 7.2—Continued
182 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Nutrients and Dam Removal

The Elwha river is oligotrophic 

(Munn and others, 1999; Duda and 

others, in press), as measured values of 

nitrogen and phosphorous throughout 

the watershed are at low levels that are 

likely contributing to relatively low 

levels of primary productivity (Morley 

and others, 2008). This assessment, 

based on synoptic measurements taken 

during summer low flows, probably 

is affecting the nutrient status of the 

estuary. Results from the 2 freshwater 

Elwha River sites were similar to those 

reported by Duda and others (in press) 

for 12 other lower Elwha River sites 

during summer low flows (from 2005 

and 2006). In that study, sites in the 

regulated sections of the Elwha River 

(downstream of the Glines Canyon 

and Elwha Dams) were significantly 

different from the upper unregulated 

section for phosphate, but not dissolved 

inorganic nitrogen. Duda and others (in 

press, fig. 5) reported that phosphate 

and dissolved inorganic nitrogen values 

in regulated sections of the Elwha 

River were significantly lower than in 

other unregulated rivers of the Pacific 

Northwest with salmon runs. However, 

they could not explain the significant 

differences in phosphate between the 

regulated and unregulated sections of the 

Elwha River.

How the levels of these nutrients 

in the lower Elwha River and its estuary 

will respond after dam removal is not 

known. Significant changes are expected 

in sediment supply, bed particle size, 

and nutrients supplied by salmon, all of 

which could affect the nutrient status 

of the sites. The supply of sediment 

is expected to increase dramatically 

in some places during and following 

dam removal (Czuba and others, 2011, 

chapter 2, this report; Konrad, 2009). 

Immediately following dam removal, 

fine-grained sediments stored in the 

reservoir bottoms and the deltas will be 

released and transported downstream. 

Previous research has indicated 

that sediments released from reservoirs 

can change the nutrient status 

downstream (Stanley and Doyle, 2002). 

For example, phosphorous often is 

retained in reservoir sediments and the 

release of these sediments during dam 

removal could increase nutrient levels 

downstream during the short term. In the 

longer term, the reservoirs will not trap 

phosphorous, which will be transported 

to downstream reaches. The net effect of 

this material on nutrient levels after dam 

removal when sediment is transported 

to the lower Elwha River, estuary, 

and nearshore, is not clear. Based on 

an analysis of Lake Mills reservoir 

and delta sediments, Cavaliere (2010, 

p. 54) reported that, “The Elwha River 

sediments from Lake Mills have limited 

P (phosphorous) available for algal 

and plant growth. The water quality 

after the dams are removed is unlikely 

to be harmed by the release of excess 

P (phosphorous)...” from reservoir 

sediments. The low levels of nutrients 

held in reservoir sediments coupled 

with high rates of suspended sediment 

transport could limit any release of 

stored nutrients to the lower Elwha 

River and estuary.

If following dam removal and 

recolonization of upper parts of the 

watershed causes salmon to return to 

the river in larger numbers than the 

current populations, as projections 

suggest, then at least during some times 

of the year the nutrient status of the 

river may change. Based on estimates 

of future salmon returns following full 

recovery, 1,275–10,900 kg of nitrogen 

and 210–1,350 kg of phosphorous 

derived from salmon could be input 

annually into the Elwha River (estimates 

based on assumptions of Munn and 

others [1999] and projected spawners 

presented by Ward and others [2008]). 

If phosphorous and nitrogen are limiting 

primary productivity in the Elwha River, 

then increases in these nutrients may 

have important implications for the 

Elwha River ecosystem. It is not clear 

that an increase in salmon numbers will 

result in clear increases in water column 

nutrients, but salmon-derived nutrients 

may provide significant temporal 

increases in the biomass and growth 

rates of resident biota (for example, 

Bilby and others, 1996; Schuldt and 

Hershy, 1995; Wipfli and others, 1998; 

Chaloner and Wipfli, 2002; Duda and 

others, in press).

Aquatic and Terrestrial 

Macroinvertebrate 

Assemblages of the 

Elwha River Estuary

The current configuration of the 

Elwha River estuary has been relatively 

static for much of the period since 

dam construction, especially in recent 

decades (see Warrick and others, 2011, 

chapter 3, this report). The sediment 

deficit and related effects of the dams 

that led to the simplified, incised channel 

of the lower river (Pohl, 2004; Draut 

and others, 2008, 2011; Kloehn and 

others, 2008) also has contributed to 

the stability of the estuarine complex. 

This is most notable in the age and size 

classes of woody vegetation on the east 

estuary, particularly red alder and red 

elderberry (see Shafroth and others, 

2011, chapter 8, this report). Effects 

to the estuary following dam removal 

will include sediment deposition, a 

likely associated increase in channel 

formation, and perhaps over the long 

term the development of multiple river 

mouths. This could result in dramatic 

changes to plant community associations 

and age class distributions, which can 

affect macroinvertebrate community 

assemblages. 
Chapter 7

Aquatic and Terrestrial Macroinvertebrate Assemblages of the Elwha River Estuary Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal 183

The estuary is an important habitat 

for some juvenile salmon during their 

migration to the ocean in large part 

because of the food supply available, 

especially aquatic and terrestrial 

invertebrates (Simenstad and others, 

1982). The Lower Elwha Klallam 

Tribe initiated a baseline assessment 

of macroinvertebrate assemblages 

in the estuary, including benthic 

macroinvertebrates and terrestrial insects 

in the emergent and shrub transitionhabitat zones. Describing the current 

conditions of the macroinvertebrate 

communities is an important 

monitoring goal, for their sensitivity to 

environmental changes and importance 

as a prey source for juvenile salmon.

Benthic Macroinvertebrates of 

the Elwha River Estuary

Sampling and Analysis 

Methods for Benthic 

Macroinvertebrates

Samples of benthic 

macroinvertebrates residing in the 

sediments throughout the Elwha River 

estuary were collected to establish 

baseline data on species diversity, 

relative abundance, and availability to 

juvenile salmonids throughout their 

migration season (spring and summer). 

Sampling occurred on three occasions 

(May, July, and September) in 2007. 

Figure 7.3. Lower Elwha Klallam Tribe fisheries technicians sampling sediments in the Elwha River, Washington, 

estuary using a petite Ponar grab sampler. (Photograph taken by Matt Beirne, Lower Elwha Klallam Tribe, April 17, 

2006.)

During each occasion, 22 samples 

were collected from sites in the east 

and west estuary. This sampling was 

near our juvenile salmon beach seining 

sites in the estuary. The 22 samples 

were distributed among the east estuary 

(ES1 [3 locations], ES2 [8 locations], 

the channel connecting ES1 and ES2 

[2 locations; hereafter referred to as the 

intraestuarine channel [IEC]), and the 

west estuary (Dudley Pond [4 locations] 

and WESC [5 locations]) (fig. 7.1).

A spring-loaded 6-in petite Ponar 

grab sampler was attached to a nylon 

rope and deployed while wading (where 

depth allowed) or from a boat (fig. 7.3). 
184 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

The grab sampler surface area and volume were 0.023 m2 and 

2.4 L, respectively. Where the substrates were not conducive 

to acquiring an adequate sample volume, the grab sampler 

had to be manually forced into the substrate. Sediment grabs 

were weighed, photographed, and characterized by color and 

texture.

Sediment grab samples were sorted using a series of four 

metal sieves with successive openings of 3.55, 2.0, 1, and 

0.5 mm (500 μm). A garden hose with an adjustable nozzle 

was used to separate the inorganic sediment fraction gently 

from the organic material, detritus, and macroinvertebrates. 

The material remaining in the bucket was then sieved through 

a custom 0.5 mm stainless steel sieve fashioned from a plastic 

tray with the bottom replaced by a welded sheet of 500 μm 

mesh. The primarily organic material that was retained in the 

sieves was gently separated using water sprayed into clear 

plastic tubs 32.5 cm × 75 cm for subsequent sorting. 

Immediately after sieving, the remaining material was 

sorted using forceps, typically within 24 hours of sample 

collection. A squirt bottle with 70 percent ethanol was used 

to agitate any remaining organisms from the organic material 

after all macroinvertebrates were removed. Sample processing 

time typically averaged 2 hours per sample, including 

sieving and sorting. Sorted samples were preserved in 

10 percent formalin, which served as a fixative for soft-bodied 

organisms. After 1 week, specimens were filtered, rinsed, and 

transferred to 70 percent ethanol. Most insects from the orders 

Ephemeroptera, Plecoptera, and Trichoptera were identified 

to genus. All other taxa were identified to family level where 

possible, or the next identifiable taxonomic level (for example, 

class, order). Arthur Frost, a local expert in macroinvertebrate 

identification, completed all taxonomic identification.

Sediment grab samples also were used to provide general 

characterizations of epibenthic/ benthic habitat types in the 

estuary. Eight classes of sediment descriptions were used to 

characterize sediment (table 7.2). The greatest homogeneity 

was in WESC and was exclusively comprised of silty material 

typically overlayed with a detritus layer of leaf litter and some 

marine derived algae. The isolated estuary remnant of the 

west estuary (Dudley Pond) showed the greatest variability 

ranging from fine silt to gravel and was typically associated 

with a green, gelatinous organic fraction, likely derived from 

the decomposition of the heavy green algal mats that form 

on the surface of this water body (Duda and others, 2011, 

chapter 1, fig. 1.12, this report). The east estuary tended to 

lack the detrital/algal epibenthic component detected in the 

west estuary and was variable in texture from fine silt to 

sandy gravel. It was predominantly (66 percent) comprised 

of silt, with the remainder ranging from silty sand to siltysandy gravel. The west estuary, which is surrounded by dense, 

early successional willow/alder vegetation, seems to receive 

considerably greater detrital inputs and may not receive the 

same intensity or frequency of tidal flushing as in the east 

estuary habitats. The east estuary is significantly larger than 

WESC and appears to have a broader zone of emergent 

vegetation and shrub transitional habitat, coupled with greater 

tidal surges from the west and flushing from the east (Bosco 

Creek). This likely contributes to the small amount of detritus 

in the epibenthic environment.

Benthic Macroinvertebrate Assemblages of the 

Elwha River Estuary

During all months, we collected 40 macroinvertebrate 

taxa (5,943 individuals) in the east estuary, 29 taxa 

(3,343 individuals) in WESC and 25 taxa (1,840 individuals) 

in Dudley Pond in the benthic grab samples collected in 2007. 

These taxa belonged to 29 major taxonomic groups (Order or 

greater) in three phyla (Arthropoda, Nematoda, Mollusca). 

Of the 53 unique taxa (including a single “unknown”), 16 

were detected in all three locations, 16 were detected in only 

the east estuary, 6 were only in Dudley pond, and 6 were 

only in WESC. Most taxa were identified to family (22) or 

genus (17), with the remainder identified to order or suborder 

(6), class (6), or phyla (1; nematodes). A rarefaction species 

accumulation curve for all sites, using the Chao1 estimator 

(Chao, 1984) in the program Primer (version 6; Clarke and 

Gorley, 2006), indicated that we were still detecting new taxa 

as we added more samples, a result typical of abundant and 

diverse groups of organisms (fig. 7.4). However, the species 

accumulations were different among the three locations, as 

the curves appeared to level off in the east estuary, but were 

still climbing in Dudley Pond and WESC. The taxa diversity 

Table 7.2. Classification of sediment type from benthic 

macroinvertebrate samples collected in the Elwha River estuary, 

Washington, May–September 2007.

[All values are number of grab samples. Abbreviation: WESC, west estuary 

channel]

Sediment 

category

East 

estuary WESC Dudley Pond

Silt 26 12 1

Silty-sand 2 0 0

Sandy-silt 6 0 1

Sandy 2 0 0

Silty sand-gravel 1 0 0

Sandy gravel 1 0 3

Silty organic 0 3 5

Organic gelatinous 0 0 2
Chapter 7

Aquatic and Terrestrial Macroinvertebrate Assemblages of the Elwha River Estuary Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal 185

that was estimated with the Shannon diversity index (H′) 

indicated that diversity was low and did not vary among sites 

or months (fig. 7.5). When averaging across sampling sites 

and locations, amphipods and dipterans were the dominant 

taxa representing 50 and 21 percent of identified specimens, 

respectively (table 7.3). The proportion of dipterans and 

amphipods was similar in May and September; however, in 

July the proportion of dipterans in samples increased, whereas 

amphipods decreased. Spatially, samples collected from 

WESC seemed depauperate in amphipods when compared 

to Dudley Pond and the east estuary (table 7.3). This may be 

due to the paucity of sandy sediments in WESC relative to 

Dudley Pond and the east estuary. Grab samples indicated that 

Figure 7.4. Species accumulation curves for benthic invertebrate samples , showing the observed and estimated 

taxa richness in the Elwha River estuary, Washington in 2007. (Estimated values from rarefaction using the Chao1 

estimator.)

watac11-0558_fig7-04

1

140

20

40

60

80

100

120

60

40

20

0

1 31262116116 36 41

3 6 9 12

80

60

40

20

0 3 6 9 12 15

40

30

20

10

0

0

Samples

Cumulative taxa richness

0

3631262116116 6156514641 66 71

0

Taxa Observed

Estimated from Chao1

EXPLANATION

A. Total across all habitats B. East Elwha Estuary

C. WESC D. Dudley Pond

amphipods and isopods seemed to prefer sandy substrates to 

silty or muddy substrates. In September, the total abundance 

of macroinvertebrates of WESC was only 8.1 percent and 

12.9 percent of that detected in Dudley Pond and the east 

estuary sites, respectively. One possible explanation for this 

was the hydrologic isolation of WESC and lower flows of the 

Elwha River may have resulted in higher water temperatures 

and lower dissolved oxygen levels than conditions at other 

sites. Water quality data (from a Conductivity, Temperature, 

Depth (CTD) logger; details in Magirl and others, 2011, 

chapter 4, this report) collected at the time of sampling, seem 

to corroborate this, although some differences in sampling 

dates in September limits our ability to infer this from the data. 
186 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

The density of dipterans was greater in WESC than other 

areas of the estuary in May and July, but was not different 

from the east estuary in September (table 7.4). The greater 

densities of dipterans in WESC may be attributed partly to the 

significant epibenthic detrital layer in contrast to Dudley Pond 

and east estuary, which may provide greater cover or habitat 

heterogeneity for macroinvertebrate fauna. More amphipods 

were detected in Dudley Pond than at the other sites and 

Dudley Pond was the only site with significant densities of 

isopods.

A suite of complementary nonparametric multivariate 

statistics was used to analyze the assemblage structure of 

benthic macroinvertebrates across months and sites using 

Primer software. The data were placed into a rectangular data 

matrix of taxa (rows) by samples (columns). These data were 

square root transformed to reduce the effects of numerically 

dominant taxa and matrix wide non-detections (Clarke and 

Warrick, 2001; McCune and Grace, 2002). Treating each 

sampling month separately for sediment samples, a triangular 

resemblance matrix was created, with each cell of the matrix 

giving the pair-wise similarity between sites based upon the 

Bray-Curtis distance. Next, non-metric multidimensional 

scaling (nMDS) was used to graphically analyze whether the 

assemblage structure of individual sites were grouped by east 

estuary, west estuary, and Dudley Pond locations. Pairs of sites 

with similar macroinvertebrate assemblages (in terms of taxa 

present and their abundances, exclusive of joint-absences) 

occur closer together in nMDS plots than dissimilar pairs of 

sites, which occur farther apart. These analyses were done 

using the full data set (a mixture of taxonomic classifications) 

and taxa aggregated by orders. The results were similar 

between these two data sets and results are shown for the full 

data set unless otherwise indicated.

Based on the graphical analysis of nMDS plots, benthic 

invertebrates in estuarine sediments differed among the three 

estuary locations in May and July, but not in September 

(fig. 7.6). We followed up the graphical analysis with an 

Analysis of Similarities (ANOSIM), a non-parametric analog 

to Analysis of Variance (ANVOA), which calculates a ratio 

of rank similarities (R) that takes a value between 1 and 0. 

At R = 1, within-group sites are more similar to each other 

than any sites from other groups, whereas when R approaches 

0 similarities among sites do not differ among groups. We 

used a permutation test with 999 iterations to develop a 

null distribution to test whether the observed R value was 

statistically significant. 

watac11-0558_fig7-05

Sampling month

May July September

0

1.4

1.2

1.0

0.8

0.6

0.4

0.2

Shannon diversity index, H’

East Estuary

Dudley Pond 

WESC

EXPLANATION

Figure 7.5. Shannon diversity index scores of the 

macroinvertebrate community from sediments in the East Estuary, 

WESC, and Dudley Pond sampling locations of the Elwha River 

estuary, Washington, in May, July, and September 2007.

Table 7.3. Average number per sample (standard deviation) 

of amphipods and dipterans, two major components of the 

macroinvertebrate community inhabiting sediments in the Elwha 

River estuary, Washington, May, July, and September 2007.

[Values in parenthesis are standard deviation. Abbreviations: n, number; 

WESC, west estuary channel]

Location Taxon May July September

East estuary 

(n = 13)

Amphipods 45 (72) 2 (5) 220 (440)

Dipterans 25 (22) 52 (26) 34 (38)

WESC

 (n = 5)

Amphipods 0 2 (4) 3 (4)

Dipterans 89 (65) 107 (69) 28 (27)

Dudley Pond 

(n = 4)

Amphipods 14 (14) 187 (317) 180 (135)

Dipterans 20 (11) 45 (18) 11 (8)

Average percentage of total assemblage 

All sites 

combined

Amphipods 26 (31) 11 (24) 28 (37)

Dipterans 46 (32) 64 (31) 41 (35)
Chapter 7

Aquatic and Terrestrial Macroinvertebrate Assemblages of the Elwha River Estuary Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal 187

Figure 7.6. Nonmetric multidimensional scaling plots 

(nMDS) showing assemblage structure of sediment dwelling 

macroinvertebrates of the Elwha River estuary, Washington, 

during (A) May, (B) July, and (C) September 2007. (Unitless 

nMDS plots based on Bray-Curtis similarity of square root 

transformed data.)

East Estuary

Dudley Pond

WESC

DP DP

DP

DP

WESC

WESC

WESC

WESC

WESC

ES2

ES2

ES2

ES2

ES2

ES2

ES2

ES1

ES1

ES1

ES1

ES1

IEC

WESC

WESC

WESC

WESC

WESC

DP

DP

DP

DP

ES1 ES1

ES2 IEC

ES1

ES1

ES2

ES2

ES2

ES2 ES1

ES2 ES2

DP

WESC

ES2

WESC

ES1

DP DP

DP

WESC

WESC

WESC

IEC

ES2

ES1

ES1

ES2

ES2

ES2

EXPLANATION

A. B. July nMDS (stress = 0.13) May nMDS (stress = 0.17)

C. September nMDS (stress = 0.12)

Table 7.4. Average density of common macroinvertebrate taxa from benthic samples collected in the Elwha River estuary, Washington, 

May, July, and September 2007. 

[Average density is number per square meter. Values in parenthesis are standard deviation. Samples were collected using a petite Ponar grab sampler. 

Abbreviations: WESC, west estuary channel; n, number]

Taxon

WESC (n = 5 sites) Dudley Pond (n = 4 sites) East estuary (n = 13 sites)

May July September May July September May July September

Acarina 26 (58) 43 (75) 9 (19) 43 (61) 11 (22) 11 (21) 20 (42) 76 (102) 80 (116)

Amphipoda 0 104 (161) 147 (164) 606 (588) 8,083 (13,711) 7,802 (5,840) 1,951 (3,106) 93 (215) 9,506 (19,040)

Diptera 3,860 (2,816) 4,622 (2,970) 1,229 (1,170) 887 (488) 1,948 (777) 487 (368) 1,102 (948) 2,261 (1,117) 1,495 (1,665)

Isopoda 9 (19) 9 (19) 0 1,840 (2,141) 1,309 (1,491) 5,702 (7,298) 0 0 3 (12)

Odonata 86 (118) 43 (97) 95 (166) 0 0 32 (65) 3 (12) 3 (12) 23 (52)

Oligochaeta 1,930 (3,084) 1,350 (2,082) 95 (213) 357 (450) 86 (146) 2,943 (5,316) 113 (99) 1,129 (1,900) 632 (1,154)

Ostracoda 9 (19) 182 (224) 35 (56) 1,742 (2,393) 1,407 (2,813) 3,105 (5,923) 173 (395) 113 (197) 782 (1,887)

Trichoptera 17 (39) 9 (19) 0 11 (22) 0 0 13 (27) 86 (126) 0
188 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

The ANOSIM analysis confirmed 

the patterns from the nMDS plots. 

Differences among estuary locations 

were significantly different in May (R = 

0.50, P = 0.001) and July (R = 0.27, P = 

0.03) but were not significantly different 

in September (R = 0.07, P = 0.26). 

Although statistically significant, the 

moderate (May) to low (July) R values 

indicate that the assemblages in the 

different locations of the estuary showed 

a fair amount of overlap. 

To determine which specific taxa 

were driving similarities within and 

differences among estuary locations, we 

used the SIMPER analysis in Primer. 

This test decomposes the Bray-Curtis 

dissimilarity between each pair of sites 

in the triangular resemblance matrix by 

estimating the per-taxon contribution 

to the dissimilarity. The average 

contribution then is estimated across all 

comparisons within and among groups; 

taxa with a large average contribution 

and a small average variance generally 

are good discriminating taxa driving 

differences in assemblage structure 

between pairs of locations.

In May, the differences in 

assemblage structure between the 

east estuary and WESC sites were 

caused by differences in abundance 

patterns of Dipterans (27.2 percent of 

the average dissimilarity), Amphipoda 

(25.6 percent), and Oligochaeta 

(23.2 percent). There were more 

Corophium sp. amphipods in the 

east estuary and high abundances 

of Oligochaetes, Tanypodinae, 

Tanytarsini, and Chironomini diperans 

in WESC. Differences in assemblage 

structure between the east estuary and 

Dudley Pond in May were caused by 

Ostracoda (26.6 percent of the average 

dissimilarity), Isopoda (23.8 percent), 

and Amphipoda (20.0 percent), with 

higher abundances of Ostracoda and 

Sphaeromatidae (Isopoda) in Dudley 

Pond and higher Corophium sp. 

abundances in the east estuary. Finally, 

abundances of Ostracoda (20.1 percent 

of the average dissimilarity), Diptera 

(18.4 percent), Isopoda (17.2 percent), 

and Oligochaeta (16.8 percent) were 

most responsible for the dissimilarity 

between WESC and Dudley pond. 

Again, the higher abundances of 

Ostracoda and Sphaeromatidae in 

Dudley Pond coupled with the higher 

abundances of Oligochaeta, Tanytarsini, 

Chironomini, and Tanypodinae in 

WESC were responsible for the 

differences between the locations.

In July, differences between 

the east estuary and WESC were 

again caused by different abundance 

patterns of Diptera (27.8 percent of 

the average dissimilarity), Oligochaeta 

(25.6 percent), and Amphipoda 

(8.6 percent) and Ostracoda 

(9.4 percent). Top taxa contributing 

from these groups were Tanytarsini, 

Tanypodinae, Chironomini, Corophium

sp., and Chironomidae pupa.

Terrestrial Macroinvertebrates 

of the Elwha River Estuary

Sampling and Analysis 

Methods for Terrestrial 

Macroinvertebrates

Flight-intercept traps (hereafter 

fallout traps) were used to survey 

terrestrial insects, in the east estuary. 

Terrestrial insect sampling was not 

conducted in WESC or Dudley Pond. 

Traps were set during May, June, July, 

and September 2007. These periods 

generally span the season of highest 

invertebrate density and the time of 

maximum juvenile salmon use of the 

estuary. Five traps were placed in each 

of three main habitat types: littoral, 

shrub, and forest canopy (fig. 7.1). 

Littoral habitats occurred in shoreline 

areas with an open canopy and emergent 

marsh vegetation (for example, Juncus

sp.; Carex sp.). Shrub habitats were 

areas dominated by woody shrubs 

such as black hawthorn (Crataegus 

douglasii), Nootka rose (Rosa nutkana), 

and twinberry (Lonicera involucrata). 

Forest habitats were dominated by red 

alder (Alnus rubra), big leaf maple 

(Acer macrophyllum), salmonberry 

(Rubus spectabilis), and red elderberry 

(Sambucus racemosa). Traps were set, 

on average, within 1, 6, and 50 m of the 

estuarine shoreline for the littoral, shrub, 

and forest canopy zones, respectively. 

Because we were interested in 

associating terrestrial macroinvertebrate 

diversity and abundance patterns with 

food availability for juvenile salmonids, 

our analysis was limited to samples 

associated with the littoral and shrub 

zones.

Each trap was constructed from 

a shallow 32 × 75 cm plastic tub filled 

with about 5 cm of water and several 

drops of dish soap to break up the 

surface tension and facilitate retention 

of fallen insects. Because the traps were 

placed on the ground, we attempted to 

minimize the potential for inundation 

from tidal fluctuations raising the water 

level above the lip of the tub, topping 

the traps, and swamping any captured 

insects. Around the perimeter of the trap, 

PVC pipes were driven into the ground; 

PVC eyelets were attached to the tub 

and secured through the PVC pipes. 

This helped allow the tubs to rise and 

fall with the tide, while they remained 

in the sampling location (fig. 7.7). After 

3 days, the contents of each trap were 

passed through a 500 micron sieve and 

preserved in 70 percent ethanol. 
Chapter 7

Aquatic and Terrestrial Macroinvertebrate Assemblages of the Elwha River Estuary Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal 189

watac11-0558_fig7-07

Figure 7.7. Two flight-intercept (fallout) traps placed in littoral habitat of the Elwha River estuary, Washington. 

Each trap is attached with rings to PVC stakes, allowing the trap to rise and fall during tidal fluctuations. 

(Photograph taken by Matthew M. Beirne, Lower Elwha Klallam Tribe, April 26, 2006.)
190 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Terrestrial Macroinvertebrate 

Assemblages of the Elwha 

River Estuary

Across all months, 106 (17 orders) 

and 73 (14 orders) taxa in the shrub 

(n = 2,960 individuals) and littoral 

(2,333) fallout traps, respectively, were 

collected. Forty-eight taxa were detected 

in both habitats, 25 taxa were detected 

only in littoral habitat, and 58 taxa were 

detected only in shrub habitats. Most 

taxa were identified to family (88) and 

Cumulative taxa richness

0

20

40

60

80

100

120

Cumulative taxa richness

140

0

20

40

60

80

100

120

1

Samples

19171513119753

B. Shrub

A. Littoral

EXPLANATION

Taxa observed

Estimated from Chao1

Month

May June July September

2.0

Shannon diversity index, H’

0

0.5

1.0

1.5

2.5

3.0

Littoral

Shrub

EXPLANATION

Figure 7.8. Species accumulation curves for adult invertebrate 

samples in littoral and shrub habitats and both habitats combined, 

showing observed and estimated taxa richness in the east estuary 

of the Elwha River, Washington, in 2007. (Estimated values are from 

rarefaction using the Chao1 estimator.)

Figure 7.9. Shannon diversity index scores of the 

macroinvertebrate community from flight-intercept 

(fallout) traps deployed in shrub and littoral habitat 

sampling locations of the east estuary of the Elwha River, 

Washington, in May, June, July, and September 2007.

genus (25), and the rest were identified 

to Order (13), superfamily (2), class 

(2), or phyla (1; nematodes). As with 

the sampling of benthic invertebrates 

in the sediment, the rarefaction species 

accumulation curve lacked a clear 

asymptote, indicating that this sampling 

effort probably underrepresented the 

diversity of the insect communities in 

these habitats (fig. 7.8). The rarefaction 

curves were of a similar shape between 

littoral and shrub habitats. Shannon 

diversity was higher in the shrub 

samples than in the littoral samples 

across all months (fig. 7.9). A large 

amount of literature exists on patterns 

of invertebrate diversity and many 

factors could be responsible for the 

greater insect diversity, including a 

greater vegetative diversity (Siemann 

and others, 1998), biomass (Haddad and 

others, 2001), and structural complexity 

(Lawton, 1983) in the shrub transitional 

zone.

The same suite of nonparametric 

statistics described previously for 

sediment samples was used to determine 
Chapter 7

Aquatic and Terrestrial Macroinvertebrate Assemblages of the Elwha River Estuary Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal 191

the assemblage structure of the 

terrestrial insect community. As with 

the benthic macroinvertebrate samples, 

these tests were performed on the full 

data set and a data set aggregated to 

order. Results were similar for nMDS 

and nearly identical for ANOSIM 

results, so only the results from the 

full data set are presented here unless 

otherwise noted. After square root 

transforming the taxa-by-site matrix for 

all months combined, an nMDS was 

run using the Bray-Curtis similarity 

measure. Unlike the multivariate 

results for sediment samples (which 

did not show clear separation among 

habitats between months), the terrestrial 

Shrub Littoral

EXPLANATION

Sept.

July

June

May

macroinvertebrates were different 

across space and time. The nMDS plot 

showed clear separation between the 

shrub and littoral insect communities, 

as well as differences among months. 

In the shrub and littoral communities, 

samples from September grouped 

separately from the May, June, and 

July samples, which were largely 

grouped together (fig. 7.10). A two-way 

ANOSIM analysis confirmed the clear 

separation shown in the nMDS plots 

for both location (R = 0.93, P = 0.001) 

and month (R = 0.63, P = 0.001). A 

pairwise test showed that June and July 

were most similar (R = 0.34, P = 0.001) 

Figure 7.10. Nonmetric multidimensional scaling plots (nMDS) showing assemblage structure of adult invertebrates 

captured with flight-intercept (fallout) traps placed in (A) shrub and (B) littoral habitats of the east estuary of the Elwha 

River, Washington, in 2007. (Unitless nMDS plots based on Bray-Curtis similarity of square root transformed data.)

and May and September (R = 0.93, 

P = 0.001) were most different in their 

terrestrial macroinvertebrate assemblage 

structure (across all habitat groups).

A SIMPER analysis of the data 

was completed to find which groups 

of invertebrates were responsible 

for differentiating littoral and shrub 

habitat. There was a higher abundance 

of Collembola (21.9 percent of the 

average dissimilarity), Hymenoptera 

(11.3 percent), Acarina (10.9 percent), 

and Araneae (9.6 percent) in the shrub 

samples and a higher abundance of 

Dipterans (12.7 percent) and Odonata 

(7.4 percent) in the littoral samples.
192 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Juvenile Salmon in the 

Elwha River Estuary

The restoration of prime spawning 

and rearing habitat in the Elwha River 

upstream of two dams that have been in 

place for nearly a century is expected to 

benefit salmon as populations recolonize 

a watershed that once produced 

large runs (Wunderlich and others, 

1994; Pess and others, 2008; Ward 

and others, 2008; Winter and Crain, 

2008). A critical component of salmon 

population recovery in the Elwha River 

following dam removal will be from the 

maintenance or increase in life history 

and genetic diversity, which will in turn 

depend in part upon habitat use and 

performance within the Elwha River 

estuary (Bottom and others, 2005a). 

The capacity of the Elwha River estuary 

to support increased population sizes 

and life-history diversity of salmon 

populations will be determined by 

physical and biological factors, such 

as food sources, sediment deposition, 

temperature, salinity, and other habitat 

features.

The emigration of juvenile Chinook 

salmon from natal spawning grounds 

is a critical phase of their life history. 

Date of spawning, competition, food 

availability, local genetic adaptation, 

and variable life history strategies in 

populations determines the timing 

and duration of the emigration period, 

which also varies among species in the 

same river (Groot and Margolis, 1991). 

As described by Myers and others 

(1998), the high potential for interaction 

among these factors, coupled with 

spatial and temporal variability driven 

by natural and anthropogenic factors, 

creates complexity in determining 

factors responsible for trends in salmon 

population size, or phenotypically 

driven shifts in life history expression. 

In addition to these basic ecological 

questions of interest to fisheries 

biologists, the timing and abundances of 

emigrating juvenile salmon, along with 

estimates of run size, serves fisheries 

managers tasked with conservation of 

salmon populations. Finally, estimating 

vital rates associated with juvenile 

emigration has been used to track the 

effects of restoration actions geared 

toward salmon conservation (Bottom 

and others, 2005a).

Estimates of the species-specific 

timing and relative abundance patterns 

of anadromous juvenile Pacific 

salmonids during their migration from 

the Elwha River were made using 

various techniques throughout the lower 

river, the estuary, and adjacent nearshore 

areas (fig. 7.1). 

Migration of Juvenile Salmon 

from the Lower Elwha River

Estimating In-River Migrants 

Using a Rotary Screw Trap

The Lower Elwha Klallam Tribe 

has been operating a 2.4 m rotary screw 

trap at river kilometer 0.5 since 2005 to 

characterize the emigration of juvenile 

salmonids from the Elwha River 

(fig. 7.11). The trap is manufactured 

from a perforated metal cone mounted 

between two pontoons. Two tapered 

flights are wrapped around the inside 

of the cone, causing the trap to rotate 

with the flow of the river. The trap is 

suspended between two pontoons and 

this barge-like structure is anchored to 

shore using steel cables. As downstream 

flow progresses through the trap, smolts 

traveling downstream are swept into 

the wide end of the cone and are forced 

into a trap box at the narrow end of 

the cone, where they can be identified, 

measured, and returned to the river 

(Volkhardt and others, 2007). The trap 

is monitored daily to process captured 

smolts. Occasionally, wood debris or 

other factors will cause the trap to stop 

working and no data are collected. For 

these instances, the daily catch total is 

estimated based on the total hours of 

operation during the day in question. 

If entire days are missed (a rare 

occurrence), then catch is estimated for 

missed days using a non-linear (LOESS) 

regression (G.R. Pess and others, 

National Oceanic and Atmospheric 

Administration, written commun., 

2010). 

Operation of the screw trap in the 

Elwha River typically is from February 

or March until mid-June when the 

Washington Department of Fish and 

Wildlife (WDFW) releases juvenile 

Chinook salmon from the Elwha River 

hatchery. Because of the size of the 

release (about 3 million fingerlings per 

year) and the proximity of the release 

point to the trap, operation of the rotary 

screw trap ceases upon hatchery release. 

The data collected from the rotary 

screw trap provide emigration timing, 

species composition, length, and genetic 

samples for part of the emigration 

period, mostly the wild-origin 

component of the population. Population 

estimates are determined by calculating 

the efficiency of the trap, which is 

estimated by releasing multiple groups 

of 1,000 dye-marked (Bismark brown) 

juvenile chum salmon above the trap and 

then counting the number of the marked 

fish caught in the trap downstream. This 

total then can be used to convert the 

catch into an estimate of total population 

size (Volkhardt and others, 2007; G.R. 

Pess and others, National Oceanic and 

Atmospheric Administration, written 

commun., 2010). The estimated trap 

efficiency was 3.5 percent in 2006 and 

4.7 percent in 2007.
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal Juvenile Salmon in the Elwha River Estuary 193

watac11-0558_fig7-11

Figure 7.11. A 2.5 meter rotary screw trap operated at river kilometer 0.5 by the Lower Elwha Klallam Tribe 

fisheries office for counting juvenile salmon emigrating from the Elwha River, Washington. (Photograph taken by 

Michael L. McHenry, Lower Elwha Klallam Tribe, May 26, 2010.)

Results from the Elwha River Screw Trap, 

2006–07

An estimated 119,357 (± 3,443, 95 percent confidence 

interval) and 14,309 (± 3,440, 95 percent confidence 

interval) age-0 Chinook salmon migrated past the Elwha 

River screw trap in 2006 and 2007, respectively (fig. 7.12). 

This estimate is based on 3,376 (2006) and 266 (2007) 

captures at the screw trap and does not include hatchery fish 

or “stream type” age-1 Chinook salmon smolts. However, 

these numbers should be used with caution. The large 

difference in smolt numbers between 2006 and 2007 may 

be explained, in part, by the large flood that occurred on 

November 6, 2006 (peak flow of 346 m3/s [12,219 ft3/s] 

reported by Curran and others, [2009]), which may have 

scoured redds and affected recruitment of the 2007 brood 

year. In 2006, the trapping did not begin until mid-March, 

but trapping in previous years indicated that migration 

timing typically starts earlier than this date in the Elwha 

River. Additionally, trapping efficiency is variable from 

year-to-year. Finally, a road closure in spring 2007 precluded 

deployment of the large screw trap. A smaller 1.5 m trap was 

used for the 2007 outmigration estimate. Rather than provide 

estimates of the emigrating population size, the data are 

provided to show general trends in run timing and juvenile 

abundance in 2006 and 2007, when estuary use and diet 

analyses were conducted. 
194 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0558_fig7-12

15,179

EXPLANATION

2006 

2007

Day with no fish caught

2,000 1,000 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

Total estimated outmigrants

February 21

March 1

March 15

April 1 

April 15

May 1

May 15

June 1

June 15

June 26

Figure 7.12. Run timing and estimated daily emigration numbers of juvenile Chinook salmon 

(age-0) based on rotary screw trap data collected by the Lower Elwha Klallam Tribe in 2006 

and 2007, Elwha River, Washington. Data from G.R. Pess and others, National Oceanic and 

Atmospheric Administration, written commun., 2010.
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal Juvenile Salmon in the Elwha River Estuary 195

Figure 7.13. Lower Elwha Klallam Tribe fisheries technicians and students from Peninsula College deploying 

a beach seine used to sample fish assemblages in the Elwha River estuary, Washington. (Photograph taken by 

Patrick Shafroth, U.S. Geological Survey, July 20, 2006.)

Migration of Juvenile Salmon to the Elwha 

River Estuary

Detection of Estuary Migrants from Beach 

Seining

Beach seining techniques were used to sample fish 

populations in the Elwha River estuary on the east side of 

the river (fig. 7.13). Due to the shallow nature of much of 

the estuary and the presence of woody debris obstructing 

proper deployment of the net, access to suitable seining sites 

was limited to three primary sites in ES1 (1 site) and ES2 (2 

sites) and one secondary site (IEC) (fig. 7.1). Seining started 

in mid-March and ended in December (2006) or September 

(2007). Generally, samples were collected every 2 weeks 

during daylight hours. Samples were collected on 13 occasions 

each year during 2006 and 2007 (table 7.5). The dimensions 

of the beach seine were 38 m long × 2 m deep, with a 2 m × 

2 m bag in the center of the net. Mesh size was 3.18, 6.35, and 

31.75 mm, for the bag, center panel, and wings, respectively.
196 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Results from Beach Seining in 

Elwha River Estuary, 

2006–07

Sixteen species of fish were 

identified in the east estuary during 

2006–2008 (table 7.6), including five 

species of salmonids (Chinook, coho, 

chum, steelhead, cutthroat trout) and one 

species of charr (bull trout, Salvenlinus 

confluentus captured in 2008). The catch 

per unit effort (CPUE) was calculated 

by dividing the number of fish caught 

by the number of seine hauls. Data 

from 2006 and 2007, but not 2008, are 

presented.

The most abundant fish taxa 

detected, adjusted for CPUE 

and summed across all sampling 

occasions, was threespined stickleback 

(Gasterosteus aculeatus; CPUE, 306 

in 2006 and 1,823 in 2007), Pacific 

staghorn sculpin (Leptocottus armatus; 

CPUE, 180 and 134), unidentified 

sculpin spp. (Cottidae sp.; CPUE, 

150 and 136), and starry flounder 

(Platichthys stellatus; CPUE, 99 and 

93). The most abundant salmonid 

species detected were Chinook (CPUE, 

136 in 2006 and 73 in 2007), coho 

(CPUE, 70 and 32), and chum (CPUE, 

24 and 20) (table 7.6).

The patterns of seasonal estuary 

use were similar between 2006 and 2007 

for all three salmonid species (fig. 7.14). 

Juvenile Chinook were caught in the 

estuary from March through October, 

with peak abundances in June. Coho 

showed a similar pattern, with a peak 

in June, but numbers dropped off more 

steeply during summer compared with 

Chinook, to a level where they were 

rarely detected. Chum were present 

in relatively lower numbers across all 

months, with an earlier peak in March 

or April and were not detected after 

June. The number of Chinook likely was 

influenced by hatchery releases from 

the State of Washington Elwha River 

Fish Hatchery about 3.2 km upstream. 

These fish were not externally marked 

prior to release (however, they do 

receive thermal marks on their otoliths); 

therefore, estimates of the proportion 

of hatchery- to wild-origin could not 

be made. A sub sample (n=115) of fish 

collected over the entire season in 2006, 

however, showed a ratio of 75:40 for 

wild- versus hatchery-origin juvenile 

Chinook salmon (see Juvenile Growth 

by Habitat, 2006 Brood Year). 

Coastal storms that occurred in 

winter of 2006 resulted in flooding that 

significantly changed the morphology 

of the Elwha River mouth and reduced 

access to the east estuary in spring 

and summer of 2007. A large flood on 

November 6, 2006, coupled with high 

tidal conditions (+2.81 m, MLLW) and 

significant storm surges, resulted in a 

sediment bar forming, which appeared 

to preclude fish passage to the east 

estuary (ES1 and ES2) during 2007, 

except during high tides and high 

river flow events. As noted by Shaffer 

and others (2009), this sediment bar 

likely disrupted fish movements into 

the east estuary. Their results showed 

significant differences in abundances 

of juvenile salmon between sites in 

this study in the east estuary and their 

significantly smaller site in WESC. 

Results also indicate that the entire 

fish assemblage of the east estuary 

was different between 2006 and 2007, 

probably due to the formation of the 

sediment bar. The change in CPUE 

values between 2006 and 2007 were 

negative for Chinook (-46.3 percent), 

coho (-54.6 percent), and chum 

(-14.9 percent salmon (table 7.6). 

Table 7.5. Monthly sampling effort (number of occasions and seine hauls) used to estimate the fish assemblage structure of the east 

Elwha River estuary, Washington, 2006 and 2007. 

[Locations are shown in figure 7.1. Abbreviations: ES1, east estuary 1; ES2, east estuary 2; IEC, intraestuarine channel]

Month

2006 2007

Sampling 

occasions

ES1 seine 

hauls

ES2 seine 

hauls

IEC seine 

hauls

Sampling 

occasions

ES1 seine 

hauls

ES2 seine 

hauls

IEC seine 

hauls

March 1 2 1 0 2 4 4 2

April 2 3 3 0 2 4 4 4

May 2 4 3 0 2 4 7 3

June 1 2 2 0 2 3 4 1

July 1 2 2 0 2 2 6 2

August 2 3 4 0 0 0 0 0

September 2 4 4 0 2 2 2 1

October 1 2 2 0 0 0 0 0

November 0 0 0 0 0 0 0 0

December 1 0 2 0 0 0 0 0
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal Juvenile Salmon in the Elwha River Estuary 197

Table 7.6. Total counts and catch per unit effort of the fish 

assemblage during beach seining in the eastern Elwha River 

estuary, Washington, 2006 and 2007.

[Abbreviations: CPUE, catch per unit effort; –, not applicable]

2006 2007 CPUE 

change

(percent)

Total 

catch CPUE Total catch CPUE

Salmonids

Chinook 266 136 129 73 -46.3

Coho1 127 70 37 32 -54.6

Chum 34 24 38 20 -14.9

Steelhead2 26 24 44 30 27.1

Cutthroat Trout 1 0.5 2 0.8 60.0

Sculpins

Pacific Staghorn 

Sculpin

350 180 282 134 -25.7

Prickly Sculpin 0 0 22 12 –

Cottid spp. 274 150 324 136 -9.5

Flatfish

English Sole 1 0.5 0 0 -100

Starry Flounder 191 99 190 93 -6.0

Flatfish spp. 37 18 0 0 -100

Forage Fish

Surf Smelt 3 1.5 0 0 -100

Osmerid spp. 15 12 0 0 -100

Other

Shiner Perch 2 1 0 0 -100

Threespine 

Stickleback

591 306 2,675 1,823 496.7

1

Total does not include two coho “jacks.”

2

Most were hatchery fish from the Lower Elwha Klallam Tribe hatchery 

that were released into the estuary.

watac11-0558_fig7-14

2006

EXPLANATION

2007

Catch per unit effort, in fish per seine haul

0

10

20

30

40

50

60

0

10

20

30

40

50

60

0

10

20

30

40

50

60

Mar. Apr. May June July Aug. Sept. Oct.

Month

B. Coho

C. Chum

A. Chinook

Figure 7.14. Catch per unit effort (number of fish 

captured on occasion i / number of seine hauls on 

occasion i) of juvenile (A) Chinook, (B) coho, and (C) 

chum salmon detected in the east estuary of the Elwha 

River estuary, Washington, in 2006 and 2007.

Other pelagic fish, such as English sole (Parophrys vetulus), 

surf smelt (Hypomesus pretiosus), other osmerids, and shiner 

perch (Cymatogaster aggregata) were detected in 2006 but not 

in 2007. 

Mean lengths of juvenile salmon in the Elwha River 

estuary generally increased through the sampling season 

(fig. 7.15). An outlier was a steep increase in average length of 

coho salmon in April of 2006 attributed to two coho “jacks” 

(adult fish who stay in the ocean for less than 1 year and return 

to the river earlier than their cohort) caught in the east estuary.
198 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

watac11-0558_fig7-15

A. Chinook

B. Coho

40

60

80

100

40

80

120

160

Total length and standard deviation, in millimeters

Mar. Apr. May June July Aug. Sept. Oct.

Month

EXPLANATION

2006

2007

Figure 7.15. Average total length of juvenile (A) Chinook 

and (B) coho salmon captured during beach seining in 

the east estuary of the Elwha River, Washington, during 

2006 and 2007. Coho results for April 2006 include two 

“jacks.”
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal Juvenile Salmon in the Elwha River Estuary 199

Estuary and Nearshore Habitat 

Use by Juvenile Chinook 

Salmon Inferred from Otolith 

Analysis

Salmonid otolith microstructure can 

identify different juvenile life history 

strategies and events (for example see, 

Neilson and others, 1985; Volk and 

others, 1995). Previous work on more 

extensive and complex estuarine habitats 

in Puget Sound has shown that juvenile 

Chinook display distinct developmental/

life history “checks” and patterns of 

growth on the otolith microstructure 

(Beamer and Larsen, 2004; Lind-Null 

and others, 2008; Lind-Null and Larsen, 

2009, 2010). These distinct checks 

(a disruption in the microstructure 

growth pattern) usually corresponded 

with a transition between habitat types 

followed by distinct growth patterns, 

allowing us to quantify differential 

habitat use. Checks on juvenile salmonid 

otoliths can be induced (1) naturally, 

when fish migrate from one habitat zone 

to another (for example, freshwater to 

saltwater); (2) naturally, during other life 

history events (for example, hatching 

or emergence); and (3) artificially, by 

thermal marking or other manipulation 

(such as ponding checks when hatchery 

fish are moved between rearing vessels).

Otolith Microstructure Methods

Processing and Analysis of Juveniles

In the laboratory, fish fork length 

(mm) and weight (g) were measured, the 

sagittal otoliths were extracted from the 

left and right side of each fish, otoliths 

were measured by length and weight, 

and the left otolith was embedded in 

resin, which was then baked to harden. 

Each resin block was mounted onto a 

slide and then ground and polished on 

both sides to a thin cross-section, which 

revealed the otolith microstructure for 

analysis. If the left otolith was composed 

of vaterite, a crystalline transparent 

morph of calcium carbonate, which 

lacks clearly defined growth increments, 

the right sagittal otolith was substituted 

for analysis (Neilson, 1992). 

Next, images of the ground otoliths 

were imported into Image Pro Plus 

image analysis software (ver. 5.1.2) 

using a CCD color video camera and 

a Zeiss compound microscope. Two 

main analyses were of interest: (1) the 

identification of hatchery fish through 

thermal marks on the otolith, and (2) the 

interpretation of otolith microstructure 

for estimates of residence and growth. 

On each saved image, a consistent radial 

axis was drawn and then increments 

were marked along the axis using 

standard techniques (Stevenson and 

Campana, 1992). The distance between 

marks provides increment width, an 

indirect measurement of daily growth. 

Checks indicative of habitat transition 

also were identified. The number of 

marks and their average width provided 

estimates of residence time and growth 

in designated habitat zones.

River, Estuary, and Nearshore Otolith 

Microstructural Patterns of Juveniles

Samples were collected from 

the lower Elwha River, the tidally 

influenced region of the estuary near 

the mouth of the river (ES1, ES2, IEC, 

WESC; locations shown in fig. 7.1), 

and a few other sites in the river just 

upstream of the river mouth. Samples 

also were collected from nearshore areas 

accessible by beach seine in the Strait of 

Juan de Fuca east and west of the Elwha 

River mouth (provided by colleagues; 

Kurt Fresh, National Oceanic and 

Atmospheric Administration Fisheries 

and Shaffer and others, 2009). Based 

on work in other Puget Sound river 

systems (Beamer and Larsen, 2004; 

Lind-Null and others, 2008; Lind-Null 

and Larsen, 2009, 2010) we divided 

our sampling a priori into freshwater 

(FW), forested riverine tidal (FRT), 

emergent forested transition (EFT), 

estuarine emergent marsh (EEM), and 

nearshore (NS) habitat areas. These 

areas are defined as FW, main stem and 

side channels, above tidal influence, in 

the lower Elwha River; FRT, main stem 

and side channels/sloughs within tidal 

influence, generally occurring in the 

uppermost estuary; EFT, a transition 

between riparian forest and salt marsh, 

characterized by cattails and scrub/

shrub habitat (ES2, IEC); EEM, true salt 

marsh (lowermost estuary), cyclically 

inundated by the tide and characterized 

by salt tolerant plants (ES1, WESC); 

and NS, saltwater, shallow sub-tidal and 

intertidal areas.

We processed 266 juvenile 

Chinook salmon, collected between 

March and October 2006 and between 

May and September 2007. We attempted 

to collect equivalent numbers of fish 

in each habitat zone, equally divided 

between two periods (before and after 

the release of hatchery fish on June 

15th). About one-half of the samples 

were collected prior to the June release 

of hatchery fish.
200 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Approximately 3 million juvenile Chinook are released 

from the Elwha River Hatchery operated by the WDFW 

after they are thermally marked and raised to a certain size. 

Thermal marking occurs at one of two rearing facilities 

(Sol Duc and Hurd Creek). Each facility produces a unique 

mark by exposing the fish to short-term temperature 

manipulations during early embryonic development, creating 

easily recognized patterns of dark, distinct increments on 

their otoliths. These patterns stand in stark contrast to those 

Figure 7.16. Thermally marked juvenile Chinook salmon otolith (ear stone) collected prior to release from the 

Washington Department of Fish and Wildlife Elwha River hatchery, Washington. Brackets highlight the clear and 

unique marking patterns present due to a thermal marking process whereby water temperatures are fluctuated 

during embryonic development to slow and speed growth. This results in a specific pattern that is representative of a 

particular hatchery, or even brood year, and can be used for positive stock identification. (Photograph taken by Karl 

Stenberg, U.S. Geological Survey, January 24, 2008.)

Thermal

Mark

produced in otoliths from wild fish (compare fig. 7.16 with 

fig. 7.17; see also Volk and others, 1999). We familiarized 

ourselves with the unique thermal marking patterns (fig. 7.16) 

on the otolith microstructure of Elwha River Hatchery fish. 

This was done for the 2006 and 2007 outmigrant years by 

processing 25 reference otoliths collected from the two 

facilities in 2006 and from images available at the North 

Pacific Anadromous Fish Commission website (for 2006 

and 2007). Eighteen sub-yearlings collected in 2006 from 
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal Juvenile Salmon in the Elwha River Estuary 201

Hatch

Emergence

First Feed

Freshwater

Growth

Reference

Pattern

Figure 7.17. Otolith (ear stone) displaying characteristic growth patterns of wild-origin Chinook salmon captured 

in freshwater or upper estuary habitats of the Elwha River, Washington. The otolith microstructure depicts points of 

development (hatch, emergence from the gravel, first feeding) and a freshwater microstructural pattern used as a 

reference when analyzing otoliths from fish caught in other habitats downstream. (Photograph taken by Karl Stenberg, 

U.S. Geological Survey, January 24, 2008.)

the Dungeness River Hatchery also were processed to 

determine if any mixing occurred between the non-thermally 

marked Dungeness River Hatchery juveniles and wild-origin 

Elwha River juveniles in the Elwha River nearshore habitat. 

Differences in microstructural patterns are more subtle when 

comparing unmarked hatchery otoliths to wild fish otoliths. 

Daily growth increments formed in otoliths from hatchery 

Chinook salmon, immediately after the onset of exogenous 

feeding, are usually wider and more uniform in width than 

increments of wild-origin fish. Additionally, hatchery Chinook 

salmon frequently produce a release/ponding check when 

they are released from the hatchery or transported to holding 

ponds (Zhang and others, 1995). Later in the season, Chinook 

salmon from other river systems could be captured near the 

Elwha; however, the goals of this study are met simply by 

the ability to separate Elwha and Dungeness individuals from 

other stocks.
202 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Processing and Analysis of Adults

The overall objective was to collect 

otoliths from wild Elwha adult returns to 

analyze the otolith microstructure from 

the juvenile portion of the adult otoliths 

for life history, growth, and habitat 

utilization. The 2008 and 2009 adult 

returns were sub-sampled to correspond 

to juvenile Chinook outmigrants 

previously collected from the 2005 

and 2006 brood years (2006 and 2007 

collections). Forty-four and 53 otolith 

samples, respectively, were collected 

from September to mid-October in 

Table 7.7. Origin, age, gender, and size (fork length) of adult Chinook salmon collected by Lower 

Elwha Klallam Tribal biologists in the lower Elwha River, Washington, 2008 and 2009. 

[Origin was determined by otolith analysis, which reveals whether a fish was born in a hatchery or the wild. 

Marked: Thermal otolith mark. Origin: Elwha River juvelile Chinook salmon were thermally marked and reared at 

two different hatcheries, the Sol Duc and the Hurd Creek Hatcheries. Abbreviations: mm, millimeter; Y, yes; N, no; 

N/A, not applicable; cwt, coded-wire tag]

Date sampled Fish 

identifier

River 

kilometer

Age

(years) Sex Fork length(mm) Marked Origin

2008

September 16 16 0.0–1.0 3 M 670 Y Hurd Creek (cwt)

September 17 17 1.6–4.8 4 F 850 Y Sol Duc

18 1.6–4.8 4 F 940 N Wild

19 1.6–4.8 4 M 1,040 N Wild

20 1.6–4.8 4 F 920 N Wild

21 1.6–4.8 4 F 760 Y Hurd Creek

22 1.6–4.8 4 F 920 Y Sol Duc

23 1.6–4.8 4 M 900 N Wild

24 1.6–4.8 3 M 790 Y Sol Duc

25 1.6–4.8 4 F 930 Y Hurd Creek

26 1.6–4.8 3 M 850 Y Hurd Creek

September 18 27 0.0–3.2 4 M 1,020 N Wild

28 0.0–3.2 4 M 1,030 N Wild

29 0.0–3.2 4 F 890 N Wild

30 0.0–3.2 3 M 800 Y Sol Duc

31 0.0–3.2 3 F 750 Y Sol Duc

32 0.0–3.2 3 M 750 Y Sol Duc

33 0.0–3.2 3 M 790 Y Sol Duc

34 0.0–3.2 5 M 1,070 N Unknown

35 0.0–3.2 3 M 780 Y Sol Duc

36 0.0–3.2 3 F 700 Y Sol Duc

September 22 37 0.0–1.0 3 M 860 Y Sol Duc

38 0.0–1.0 4 F 780 Y Sol Duc

2008 and 2009, from spawned-out 

adult Chinook salmon in the lower 

Elwha River (mouth to river kilometer 

4.8). Elwha Klallam Tribal biologists 

collected samples during the height of 

the fall Chinook spawning season in the 

Elwha River. 

All 97 samples from the 2008 and 

2009 collections were initially aged 

(table 7.7). The otoliths were placed 

in deionized water and viewed with 

a dissection microscope. With the aid 

of transmitted and reflected light, the 

number of annuli present were visually 

determined. Both sagittal otoliths were 

used to determine the age of each 

fish. The left sagittal otolith was then 

processed (embedded and ground, 

sulcus-side down) and visually analyzed 

to determine hatchery or wild origin and 

on occasion to obtain a more accurate 

age determination. The continued 

analysis of the successful wild-origin 

spawners for life-history information 

and habitat utilization from the juvenile 

portion of their otolith microstructure 

was not possible due to small sample 

size (see results, below).
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal Juvenile Salmon in the Elwha River Estuary 203

Date sampled Fish 

identifier

River 

kilometer

Age

(years) Sex Fork length(mm) Marked Origin

2008—Continued

September 29 39 0.3–3.2 4 M 940 Y Sol Duc

40 0.3–3.2 3 F 640 Y Sol Duc

41 0.3–3.2 4 F 790 Y Sol Duc

42 0.3–3.2 3 M 790 Y Sol Duc

44 0.3–3.2 4 M 810 Y Sol Duc

45 0.3–3.2 3 F 690 Y Sol Duc

46 0.3–3.2 3 M 840 Y Sol Duc

September 30 47 3.2–3.7 4 M 960 N Wild

48 3.2–3.7 4 F 750 Y Hurd Creek

49 3.2–3.7 3 F 650 Y Sol Duc

50 3.2–3.7 3 M 700 Y Sol Duc

51 3.2–3.7 3 F 700 Y Sol Duc

52 3.2–3.7 3 M 670 Y Sol Duc

53 3.2–3.7 3 M 640 Y Sol Duc

54 3.2–3.7 3 F 650 Y Sol Duc

55 3.2–3.7 4 M 840 N Wild

October 1 56 2.9–3.2 3 M 690 Y Sol Duc

57 2.9–3.2 4 F 910 N Wild

58 2.9–3.2 4 F 840 Y Sol Duc

59 2.9–3.2 5 M 1,050 N Unknown

October 6 60 0.0–4.8 3 F 690 Y Sol Duc

2009

September 22 61 2.9–3.2 4 N/A N/A Y Sol Duc

62 2.9–3.2 4 N/A N/A Y Sol Duc

63 2.9–3.2 4 N/A N/A Y Sol Duc

64 2.9–3.2 5 N/A N/A N Wild

65 2.9–3.2 4 N/A N/A Y Sol Duc

66 2.9–3.2 4 N/A N/A Y Sol Duc

67 2.9–3.2 4 N/A N/A Y Sol Duc

68 2.9–3.2 4 F 760 Y Sol Duc

69 2.9–3.2 4 F 750 Y Sol Duc

September 23 70 2.4–2.7 4 F 750 Y Sol Duc

71 2.4–2.7 4 F 790 Y Sol Duc

72 2.4–2.7 4 F 710 Y Sol Duc

73 2.4–2.7 4 F 680 Y Sol Duc

74 2.4–2.7 4 M 780 Y Sol Duc

75 2.4–2.7 4 M 770 Y Sol Duc

76 2.4–2.7 4 F 730 Y Sol Duc

77 2.4–2.7 4 F 660 Y Sol Duc

Table 7.7. Origin, age, gender, and size (fork length) of adult Chinook salmon collected by Lower 

Elwha Klallam Tribal biologists in the lower Elwha River, Washington, 2008 and 2009.—Continued

[Origin was determined by otolith analysis, which reveals whether a fish was born in a hatchery or the wild. 

Marked: Thermal otolith mark. Origin: Elwha River juvelile Chinook salmon were thermally marked and reared at 

two different hatcheries, the Sol Duc and the Hurd Creek Hatcheries. Abbreviations: mm, millimeter; Y, yes; N, no; 

N/A, not applicable; cwt, coded-wire tag]
204 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Date sampled Fish 

identifier

River 

kilometer

Age

(years) Sex Fork length(mm) Marked Origin

2008—Continued

September 24 78 0.5–1.0 4 M 870 Y Sol Duc

79 0.5–1.0 4 M 800 Y Sol Duc

80 0.5–1.0 4 M 820 Y Sol Duc

81 0.5–1.0 4 M 870 Y Sol Duc

September 30 82 2.2–2.4 4 M 830 Y Sol Duc

83 2.2–2.4 4 M 740 Y Sol Duc

October 1 84 2.2–2.4 4 F 860 Y Sol Duc

85 2.2–2.4 4 F 790 Y Sol Duc

86 2.2–2.4 4 F 860 Y Sol Duc

87 2.2–2.4 4 M 890 Y Sol Duc

October 5 88 2.4–2.7 4 M 840 Y Sol Duc

89 2.4–2.7 4 M 680 Y Sol Duc

90 2.4–2.7 4 M 780 Y Sol Duc

91 2.4–2.7 4 F 840 Y Sol Duc

92 2.4–2.7 4 F 780 Y Sol Duc

93 2.4–2.7 4 M 730 Y Sol Duc

94 2.4–2.7 4 F 810 Y Sol Duc

95 2.4–2.7 4 M 860 Y Sol Duc

96 2.4–2.7 4 M 810 N Wild

97 2.4–2.7 4 F 810 Y Sol Duc

October 1 98 2.4–2.7 4 F 850 Y Sol Duc

October 13 99 0.0–0.8 4 F 850 Y Sol Duc

100 0.0–0.8 4 M 870 Y Sol Duc

631 0.0–0.8 4 F 870 Y Sol Duc

632 0.0–0.8 4 F 870 Y Sol Duc

633 0.0–0.8 4 F 830 Y Sol Duc

634 0.0–0.8 4 F 880 Y Sol Duc

635 0.0–0.8 4 M 950 Y Sol Duc

636 0.0–0.8 4 M N/A Y Sol Duc

637 0.0–0.8 4 F 830 Y Sol Duc

638 0.0–0.8 4 F 900 Y Sol Duc

October 15 654 0.0–0.8 4 F 950 Y Sol Duc

655 0.0–0.8 4 F 830 Y Sol Duc

656 0.0–0.8 4 F N/A Y Sol Duc

October 13 657 0.0–0.8 4 F 880 Y Sol Duc

October 13 658 0.0–0.8 4 M 1,020 Y Sol Duc

Table 7.7. Origin, age, gender, and size (fork length) of adult Chinook salmon collected by Lower 

Elwha Klallam Tribal biologists in the lower Elwha River, Washington, 2008 and 2009.—Continued

[Origin was determined by otolith analysis, which reveals whether a fish was born in a hatchery or the wild. 

Marked: Thermal otolith mark. Origin: Elwha River juvelile Chinook salmon were thermally marked and reared at 

two different hatcheries, the Sol Duc and the Hurd Creek Hatcheries. Abbreviations: mm, millimeter; Y, yes; N, no; 

N/A, not applicable; cwt, coded-wire tag]
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal Juvenile Salmon in the Elwha River Estuary 205

Hatch

Emergence

First Feed

Freshwater

Growth

Estuary

Growth

Estuary

Check

Reference

Pattern

Figure 7.18. Otolith (ear stone) displaying characteristic microstructure growth patterns of wild-origin Chinook 

salmon captured in the lower estuary (2006 and 2007) or nearshore (2006) habitats of the Elwha River, Washington. 

The otolith microstructure depicts points of development (hatch, emergence from the gravel, first feeding), a 

freshwater reference pattern, an estuarine check where increments are transitioning between freshwater and 

estuary residence, and increased increment widths beyond the check that are indicative of higher growth potential 

in some estuarine habitats. (Photograph taken by Karl Stenberg, U.S. Geological Survey, January 24, 2008.)

Otolith Microstructure Results

Juvenile Growth by Habitat, 2006 and 

2007 Brood Years

We separated 115 (2006) and 142 

(2007) emigrating Chinook juveniles 

into marked hatchery origin (fig. 

7.16) and unmarked wild or natural 

origin (figs. 7.17 and 7.18) based on 

otolith microstructure patterns. Of 

the 115 Chinook from 2006, 41 were 

of hatchery origin (40 Elwha River 

Hatchery and 1 Dungeness River 

Hatchery), 3 were stream type (age-1) 

outmigrants, and 71 were wild Elwha 

River (age-0). Of the 142 Chinook 

from 2007, 98 were of hatchery origin 

(90 from the Elwha River and 8 from 

the Dungeness River) and 44 were 

wild Elwha River (age-0). Of the 

97 fish collected in the nearshore, 65 

were from the Elwha River Hatchery 

and 8 were from the Dungeness River 

Hatchery. We analyzed 107 wild-origin 

juvenile Chinook otoliths (8 samples 

were unavailable due to poor otolith 

quality or processing damage). Three 

life history checks (hatch, emergence, 

and first feed) were visually and 

quantitatively located on these samples 

(figs. 7.17 and 7.18). The increments 

became more consistent and identifiable 

across the radial axis beyond the checks 

associated with emergence and first 

feed. Reference samples of juveniles 

collected from freshwater sites were 

used to characterize a microstructural 

reference pattern beyond emergence 

and first feed unique to the FW habitat 

zone. Samples collected in the estuary 

(FRT, EFT, and EEM) and NS were 

analyzed visually and quantitatively for 

checks and increased growth (inferred 

from larger increment widths) beyond 

the microstructural reference pattern 

observed on the samples caught in FW 

habitat. 
206 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

The results for wild juvenile 

Chinook salmon revealed two distinct 

otolith microstructural patterns in 2006 

and three distinct patterns in 2007 based 

on the criteria mentioned previously. 

The first pattern represented fish resident 

or captured in FW and FRT (uppermost 

estuary) habitats for both sampling years 

(fig. 7.17), because no distinct check or 

increased growth were apparent on the 

otoliths of fish caught in FW and FRT 

habitats. The second pattern (fig. 7.18), 

characterized by the presence of an 

estuarine check followed by increased 

daily growth, represented fish captured 

in EFT, EEM (lowermost estuary), and 

NS habitat types in 2006 and in EFT 

and EEM habitat types only in 2007. 

The 2007 collection further revealed 

a third check associated with entrance 

into the NS habitat type. The estuarine 

check was comprised of a series of 

increments with spacing representative 

of FW and estuarine growth, indicative 

of a transition period for the fish. The 

increments beyond the estuarine check 

were consistently wider and had higher 

contrast than increments associated with 

residence in the FW or FRT habitats 

prior to the check. An estuarine check 

alone or the check followed by a number 

of increments representing increased 

growth was not displayed on the otolith 

microstructure of fish collected in EFT, 

EEM, and NS habitats in 2006 until mid 

May (5 of 10), even though samples 

were collected in March and April (5 

and 3 samples, respectively). The other 

five samples in May were split between 

no representation of estuarine residence 

and presence of an estuarine check 

at the edge of the otolith. Most of the 

remaining samples collected from June 

through September 2006 (20 of 23) 

displayed an estuarine check followed 

by an increase in growth. Two of the 

three samples not displaying increased 

growth, one in July and one in August, 

displayed no sign of estuary residence, 

and the third sample, from August, 

displayed the estuarine check at the 

otolith edge. 

No samples were collected in 

the estuary before May 2007, so it is 

not known what the otolith pattern of 

early migrants was in 2007. However, 

42 of 44 samples from 2007 displayed 

the estuarine check, with an increase 

in growth following the check. The 

absence of increased growth associated 

with fish captured in the lower estuary 

(EFT and EEM) before mid-May and 

the four caught thereafter could be due 

to lower food availability, which is 

consistent with stomach content results 

or lower temperatures affecting growth 

rates of these early emigrating fish. A 

more likely scenario emerges, however, 

given the placement of the estuarine 

check near the edge of the otolith. Fish 

collected in March and April may have 

been caught immediately upon their 

entrance into the lower estuary habitat 

and therefore these fish did not have a 

chance to experience the higher growth 

potential of the estuary. Some of the fish 

collected in the middle of the season 

also were fresh arrivals, whereas those 

collected later in the season were more 

likely to have had enough residence time 

to display increased growth. 

A similar scenario of collecting 

fish shortly after their arrival may also 

explain the few individuals displaying 

a check indicative of entrance into NS 

habitat. A NS check was identified in 

a single individual in 2006. Although 

otoliths were collected from EFT and 

EEM habitats, no unique patterns 

of growth or checks associated with 

transition and growth were determined 

for these two habitat types.

It is not known whether a lack 

of unique patterns among the five 

habitat zones is due to small sample 

size, limitations of the technique, or 

minimal differentiation among habitat 

zones. This differentiation, seen in 

other river systems of Puget Sound (for 

example, Skagit River), often is caused 

by habitat specific differences in food 

availability, water temperature, water 

chemistry, salinity, spatial complexity, 

or a combination of these variables. The 

Elwha River does not have a large and 

heterogeneous estuary, as opposed to 

other Puget Sound systems (see Duda 

and others, 2011, chapter 1, this report), 

which could have contributed to the 

minimal differentiation observed on the 

otolith microstructure.

Once the different patterns of 

growth associated with transition from 

freshwater (FW and FRT capture sites) 

to lower estuary (EFT and EEM sites) 

and nearshore habitats were identified, 

the mean increment width (MIW) was 

used as an indirect measure of growth 

within these broad habitat categories. 

The number of daily increments 

assigned in habitats also was used to 

determine habitat-specific residence 

time.

The region of the otolith 

corresponding to freshwater growth 

was similar in MIW regardless of the 

habitat where individual fish were 

caught, with an average of 3.20 microns 

(fig. 7.19). The region of the otoliths 

assigned as lower estuary and nearshore 

growth showed an increase in MIW 

by 27 percent (4.06 microns). The 

average size of juvenile Chinook 

salmon increased as they migrated 

successively among freshwater, estuary, 

and nearshore environments (fig. 7.19B). 

The average estuarine residence time 

determined from Chinook captured in 

the estuary (a minimum estimate, as 

the fish were sacrificed) was 16 days 

(range = 4 to 41 days) (fig. 7.19B). 

Not surprisingly, the average estuarine 

residence time determined from Chinook 

salmon captured in the NS habitat 

showed a longer average residence of 

25 days (range = 5 to 50 days), as this 

number is a more complete estimate 

because the individuals were captured 

after they left the estuary. 

Based on a preliminary analyses, 

mostly wild-origin fish were using 

the lower estuary (EFT and EEM), 

whereas mostly hatchery fish were 

using the NS. Therefore, competition 

between hatchery and wild fish may be 

minimized in the estuary because most 

hatchery juveniles seem to bypass this 

habitat in favor of the Strait of Juan de 

Fuca. However, additional study would 

be required to confirm this hypothesis. 
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal Juvenile Salmon in the Elwha River Estuary 207

watac11-0558_fig7-19

30

56

26

34

26

3.0

4.5

4.0

3.5

Mean increment width, in microns

Freshwater increment width

Estuary increment width

EXPLANATION

Residence time, in days

Fork length

EXPLANATION

A. Habitat specific growth of juvenile Chinook salmon

B. Size and estuary residence time of juvenile Chinook salmon

0

60

40

20

Freshwater

(FW and FRT)

Estuary Nearshore

(EFT and EEM)

Location of capture

Mean fork length, in millimeters

120

100

80

Estuary residence, in days

0

15

10

5

20

25

Figure 7.19. Estimates of (A) average daily growth in freshwater and “estuary” 

habitats for wild-origin juvenile Chinook salmon captured in the Elwha River, 

Washington, its estuary, and nearshore habitats from March to October 2006 and 

May to September 2007. Estimates include possible nearshore growth on samples 

collected in 2006. Values are based on mean increment width (in microns) measured 

from the microstructure portions on the otolith assigned to each habitat. (B) The 

average fork length of wild-origin juvenile Chinook salmon captured in each habitat 

and the average estuarine residence time for juvenile Chinook salmon captured in 

the Elwha River estuary and nearshore habitats. Residence from fish captured in the 

estuary is a minimum estimate because fish were sacrificed before completing their 

residence in the estuary. Fish captured in the nearshore provide a more complete 

estimate of estuarine residence. 
208 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

An interesting observation was 

made with three FW and four FRT 

Chinook salmon collected on July 12, 

2006. These Chinook salmon displayed 

fork lengths and otolith lengths/radial 

distances that were much smaller than 

all other fish collected around this 

time, looking more similar to samples 

caught in April than to other samples 

caught in July. Upon examination of 

“developmental checks” (hatch and 

emergence relative to capture), we 

surmised that these fish were progeny 

of late-spawning parents. Additional 

sampling would be required to determine 

whether these results suggest a unique 

life-history strategy. 

Juvenile Dispersal Patterns in Elwha 

Estuary and Strait of Juan de Fuca, 

2007 Brood Year

Because the aforementioned 

sediment bar formation in the east 

estuary reduced the catch of wild-origin 

fish in 2007, an otolith analysis was 

used to determine origin of 97 juveniles 

sampled from June 12 to September 11, 

2007, in littoral drift cells (drift cells 

are discreet nearshore areas that receive 

local sources of sediment) adjacent 

to the Elwha in the Strait of Juan de 

Fuca (n = 98) by WDFW (Shaffer and 

others, 2009) and NOAA (K. Fresh, 

unpublished data, 2007) as well as 

from May 17 to August 28, 2007, in the 

Elwha River estuary (n = 45). The goal 

was to assess the dispersal of wild- and 

hatchery-origin (Elwha River hatchery 

or Dungeness River hatchery) juvenile 

Chinook salmon in nearshore waters to 

the east and west of the Elwha River. 

Samples were collected by beach seine 

from 16 locations (ordered from west 

to east): Pysht River, Crescent Bay, 

Freshwater Bay, east of the Elwha 

River mouth, Port Angeles Harbor, 

and Dungeness River. Elwha River 

estuary samples were collected from 

the east (ES1, ES2, IEC) and WESC. A 

random sample of individuals from each 

sampling occasion was collected, when 

available, for otolith extraction. Samples 

were processed as described previously 

and were compared to reference 

collections to determine hatchery or wild 

origin.

Most individuals collected from 

the Strait of Juan de Fuca were to the 

east of the Elwha River, although effort 

was concentrated in these areas. Across 

all sampling locations in the Strait of 

Juan de Fuca, most samples were Elwha 

River hatchery-origin (65) and wildorigin (44) fish. Only eight individuals 

of Dungeness River hatchery origin 

were detected (fig. 7.20). Of the Elwha 

River estuary fish, the largest numbers 

were collected in WESC (Shaffer 

and others, 2009), mostly because 

the sediment bar that was deposited 

following winter flooding restricted 

access to the east estuary. Throughout 

the estuary, 20 wild-origin and 25 

hatchery-origin fish were identified. 

For management and recovery 

purposes, Chinook salmon populations 

are apportioned into evolutionary 

significant units (Waples, 1995). The 

Puget Sound Chinook evolutionarily 

significant unit (ESU) ranges from the 

Puget Lowlands west to and including 

the Elwha River. The Strait of Juan de 

Fuca west of the Elwha River and the 

coastal rivers comprise the Washington 

Coast ESU. Populations in these 

two geographically adjacent ESUs 

have distinct genetic and life history 

characteristics (Myers and others, 1998), 

although Elwha River Chinook salmon 

appear to be a transition between the two 

units. Based on coded-wire tag (CWT) 

recoveries from commercial harvest, 

Washington Coast ESU Chinook tend to 

favor a more northern ocean migration, 

to southeast Alaskan waters, compared 

to Puget Sound ESU populations. Ocean 

migration of Elwha River Chinook 

is more typical of other Puget Sound 

ESU populations, with most CWT 

tags occurring in British Columbia 

and the rest occurring in southeast 

Alaska, coastal Washington, and Puget 

Sound (Puget Sound Indian Tribes and 

Washington Department of Fish and 

Wildlife, 2010). It is not known what 

proportion of the eastward migrating 

Elwha River Chinook juveniles become 

resident in Puget Sound, migrate north 

to the Pacific Ocean through the Strait of 

Georgia, or return westward to the Strait 

of Juan de Fuca towards the Pacific 

Ocean.

Analysis of Adult Chinook Salmon 

Otoliths 

Forty-four Chinook adult returns 

collected in 2008 were segregated into 

wild and hatchery origin based on their 

otolith microstructure (table 7.7). Of 

these fish, 32 were of hatchery origin, 

10 were of wild origin, and 2 were of 

unknown origin. Therefore, 76 percent 

of the known-origin Chinook analyzed 

were hatchery-reared based on the 

presence of a thermal mark. Twentytwo Chinook were aged age-3, 20 were 

age-4, and 2 were age-5. Two of the 

age-3 fish were Hurd Creek marked, 

20 were Sol Duc marked, and no fish 

were wild-origin Elwha age-3 fish. Of 

the age-4 fish, 3 were marked at Hurd 

Creek, 7 were marked at Sol Duc, and 

10 were wild-orgin Elwha fish. The two 

age-5 individuals did not have thermal 

marks, however, it is not known whether 

they were of hatchery origin because the 

2003 brood year pre-dates the Elwha 

River thermal marking program.

In 2009, all age-3, age-4, and 

age-5 adult hatchery Chinook would be 

thermally marked. Of the 53 Chinook 

adult returns collected in 2009, 51 

(96 percent) were of hatchery origin, 

and two adults were wild-orgin Elwha 

fish. Fifty-two Chinook were age- 4 and 

1 was age-5. No age-3 fish were present 

in the sub-sample. Fifty-one of the age-4 

fish were marked at Sol Duc, and one 

was wild-orgin Elwha fish. The one 

age-5 fish was of wild origin. 
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal Juvenile Salmon in the Elwha River Estuary 209

Figure 7.20. Aerial photographs and pie charts showing results of otolith analysis identifying origin of juvenile 

Chinook salmon captured during beach seining by Washington Department of Fish and Wildlife (Shaffer and others, 

2009) and (K. Fresh, National Oceanic and Atmospheric Administration, unpub. data, 2007). (Origins were from 

Washington Department of Fish and Wildlife, Elwha, or Dungeness hatcheries and Elwha River wild-origin.) Pie 

charts depict the proportion of individuals from each location.

watac11-0558_fig7-20

Elwha River

EXPANATION

1 fish

Elwha Hatchery

Elwha Wild

10 fish 30 fish

Dungeness Hatchery

Pysht River

Elwha Estuary

Crescent Bay Elwha River

Ediz Hook/Port Angeles Harbor Dungeness River

Strait of Juan de Fuca
210 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Combined returns from both collection 

years, showed only one wild adult 

(2009, age-4) corresponding to our 

2 years of juvenile out-migrant sampling 

(2006–07), obviously too few samples to 

proceed with any life history or estuarine 

utilization analyses. Our preliminary 

work from 2008 and 2009 revealed that 

a significant part of the adult Chinook 

salmon naturally spawning in the Hunt 

Road Complex (outside of the index area 

that WDFW uses for spawner surveys in 

the lower Elwha River) were of hatchery 

origin. Combining both collection years, 

87 percent of the adult Chinook otoliths 

examined were of hatchery origin 

(excluding two unknown origin age-5 

fish from the 2008 collection).

Diet and Feeding Strategies of 

Elwha River Juvenile Salmon 

Collection of Stomach Contents 

for Diet Analysis

Few studies of juvenile salmonid 

diet in estuarine environments of the 

central Strait of Juan de Fuca have 

been completed and no known studies 

are published for the Elwha River. The 

relatively static nature of structural 

features of the Elwha River estuary 

over recent decades (Warrick and 

others, 2009; Shafroth and others, 2011, 

chapter 8, this report) provides an ideal 

opportunity to determine the nature 

of juvenile salmon diets prior to the 

anticipated changes to these conditions 

following dam removal. Estuarine 

seining activities in 2006 and 2007 

provided an opportunity to characterize 

the diet of juvenile salmonids in the 

estuary. A subsample of the juvenile 

salmonids detected with beach seining 

throughout the migration period were 

selected at random and then sampled for 

diet. The stomachs of fish sacrificed for 

otolith analysis were dissected. Some of 

these fish were collected in the Elwha 

River above tidal influence. For the 

purpose of this report, most diet analyses 

were conducted with juvenile Chinook 

salmon due to their higher relative 

abundance (hatchery and wild) and their 

value to other ongoing scientific studies 

in the Elwha River basin. Stomach 

content samples from 149 individuals 

were collected (99 in 2006 and 50 in 

2007) for juvenile Chinook salmon, with 

44 from the Elwha River and 105 from 

the estuary. Stomach content samples 

also were collected from juvenile coho, 

steelhead, and cutthroat trout from the 

Elwha River estuary, but samples were 

not in high enough numbers during the 

sampling period for comparative diet 

analysis.

Stomachs were flushed with gastric 

lavage (fig. 7.21), following standard 

techniques (Meehan and Miller, 1978; 

Cordell and others, 1999, 2001) for 

collection of stomach contents of 

juvenile salmonids. Across all sampling 

occasions, mean length of Chinook 

was 80 mm (standard deviation [SD] 

21) and 88 mm (SD 16) in 2006 and 

2007, respectively. Juvenile salmonids 

were anesthetized with tricaine 

methanesulfonate (MS-222) until lightly 

sedated. The stomach contents of the 

fish were then gently flushed using a 10 

or 20 cc syringe filled with freshwater. 

Stomach contents were either strained 

through a 106 micron sieve or through a 

section of nylon attached to a PVC pipe. 

The stomach contents were preserved in 

70 percent ethanol.
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal Juvenile Salmon in the Elwha River Estuary 211

Results of Diet Analysis for Elwha River 

Juvenile Chinook Salmon

The diets of juvenile salmonids (all species) 

in the Elwha River estuary were comprised of a 

diverse macroinvertebrate assemblage. In 2006, 

more than 1,100 macroinvertebrates, representing 

23 higher level taxonomic groups (order or 

greater) were collected from stomach lavage and 

dissections of fish caught in the estuary and lower 

Elwha River. In 2007, 1,563 macroinvertebrates, 

representing 16 higher level taxonomic groups 

watac11-0558_fig7-21

Figure 7.21. Gastric lavage of a juvenile Chinook salmon. Flushed contents of its stomach consist of various 

invertebrate taxa. (Photograph taken by Matt Beirne, Lower Elwha Klallam Tribe, July 13, 2006.)

were collected in diet samples. When looking at 

Chinook salmon diets, most of higher taxonomic 

groups were detected in diets during both years. 

However, 12 macroinvertebrate orders were detected 

only in 2006 samples and 2 orders were unique to 

2007 samples (table 7.8). When both years were 

combined, the average number of different taxa 

per stomach was similar between juvenile Chinook 

salmon captured in the river (mean = 4.48, SD = 2.5) 

and in the estuary (mean = 4.72, SD = 2.9) and the 

overall frequency of taxa richness per stomach was 

similar (fig. 7.22). 
212 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Table 7.8. Major macroinvertebrate types in stomach contents 

of juvenile Chinook salmon samples collected in the lower Elwha 

River, Washington, and its estuary complex, 2006 and 2007. 

[Macroinvertebrate types are by order, unless indicated otherwise. Samples 

were collected in 2006 (99 individuals) and 2007 (50 individuals). Fewer 

unique taxa are represented in 2007 likely because samples were collected 

only in the estuary, whereas in 2006 samples collected in the lower Elwha 

River also were included]

Macroinvertebrate taxa

Percentage

2006 2007

Acarina (mites and ticks) 0.2 0

Amphipoda (amphipod crustaceans) 8.9 3.6

Aranaceae (spiders) 0.7 0

Chilopoda (Class; centipedes) 0.1 0

Coleoptera (beetles) 1.4 0.9

Collembola (springtails) 0.3 0.2

Diptera (true flies) 78.5 90.1

Ephemeroptera (mayflies) 4.6 0.2

Hemiptera (true bugs) 1.2 0.8

Hymenoptera (ants, wasps) 0.4 0.6

Lepidoptera (moths and butterflies) 0.2 0

Megaloptera (snakefly) 0.1 0

Malacostraca (Class; mysid shrimps) 0 0.9

Nematoda (Phylum; roundworms) 0.5 0.2

Nueroptera (brown lacewing) 0.1 0

Odonata (dragonfly and damselfly) 0.1 0.4

Oligochaeta (Class; aquatic worms) 0.1 0

Osteichthyes (Class; fishes) 0.1 0

Ostracoda (Class; seed shrimp) 0 0.3

Plecoptera (stoneflies) 0.9 0.3

Psocoptera (barkflies) 0.3 0.1

Thysanoptera (thrips) 0.5 0

Trichoptera (caddisfly) 1.0 0

Turbellaria (Class; flatworms) 0.1 0

watac11-0558_fig7-22

2

0

4

6

8

5

0

10

15

20

Frequency, number of fish Frequency, number of fish

87654321 131211109

Number of taxa per stomach

B. Elwha River Estuary

A. Lower Elwha River

Figure 7.22. Frequency of taxa richness (number 

of unique taxa) in stomach contents collected from 

juvenile Chinook salmon captured in (A) the lower 

Elwha River above tidal influence and (B) the Elwha 

River estuary, Washington.

Of the 16 higher taxonomic groups of macroinvertebrates 

present in the diet, 10 were different orders of insects. 

Dipterans (2-winged flies), representing 11 families were the 

most abundant taxa, representing 80 and 88 percent of the total 

number of macroinvertebrates identified from Chinook salmon 

diet samples in 2006 and 2007, respectively. Amphipods, 

representing 14 and 5 percent, were the second most abundant 

taxonomic group in the Chinook diet in 2006 and 2007, 

respectively. Chironomids were the predominant family 

of dipterans represented in the diet of all salmonids, with 

Ceratopogonids, Empidids, and Sphaerocerids represented 

in smaller numbers (fig. 7.23). The life stage of consumed 

dipterans shifted from predominantly pupa in early summer 

to primarily adult forms in late summer, a pattern that was 

consistent between years (fig. 7.24). Chironomid larva were 

consumed at relatively low levels throughout spring and 

summer. Chironomid larvae provide a valuable food source 

for fish and other aquatic organisms due to the relatively high 

levels of protein and high digestibility (Armitage and others, 

1995). Although caloric value varies with species, season, 

and life history, it usually ranges between 4.6 and 6.1 kcal g-1 

(Armitage and others, 1995). 
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal Juvenile Salmon in the Elwha River Estuary 213

watac11-0558_fig7-23

89.6

93.0

37.4

88.4

90.5

89.6

92.5 90.7

0

5

10

15

20

25

30

May June July August May June July August

2006 2007

Average number per stomach

EXPLANATION

Ceratopogonidae

Chironomidae

Sphaeroceridae

Diptera Families

Empididae

EXPLANATION

Adult

2006

2007

Larva

Pupa

5

25

20

15

10

May June July August

Average number of insects

 per stomach

Figure 7.23. Average number of individuals per stomach of four main dipteran families in samples from juvenile 

Chinook salmon Elwha River estuary, Washington, during May–August 2006 and 2007.

Figure 7.24. Average number of 

chironomids per stomach by life forms 

(adult, larva, pupa) for all sites in the 

lower Elwha River and its estuary during 

May–August 2006 and 2007.
214 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Comparison of Diet Overlap Among 

Habitat Locations

Habitat-specific diet of juvenile Chinook salmon were 

examined by comparing the dietary overlap between samples 

collected from freshwater compared with estuary (2006) and 

the east and west parts of the estuary (2007). Schoener’s index 

of diet overlap (Schoener 1970) is calculated as:

1

1 0.5 ,

where

is proportion of food category in diet of

 juvenile Chinook salmon in habitat ,

is proportion of food category in diet of

 juvenile Chinook salmon in habitat ,

n

xi yi

i

xi

yi

P P

P i

x

P i

y

n

=

 

α= − −     ∑

is number of food categories.

(1)

Values of α greater than or equal to 0.6 indicate 

significant dietary overlap. Standard diversity metrics, based 

on the orders of invertertebrates, also were calculated for 

comparisons. Dietary overlap between freshwater and estuary 

habitats was significant for March–May (α = 0.61) and June–

September (α = 0.68) (table 7.9). In March–May, a higher 

number of orders was measured for juvenile Chinook salmon 

prey in freshwater samples with less diversity and evenness 

compared with the estuary samples. A higher proportion 

Table 7.9. Summary statistics of diet composition (insect orders) and dietary overlap of Chinook salmon collected during two seasons 

(March–May and June–September) in the lower Elwha River (2006), Washington, and its estuary (2006 and 2007). 

[Diet items for fish in each habitat type were tallied by order and the total number of orders present (S), the Shannon diversity (H' Prey), evenness (E Prey), 

and the sum of all prey individuals (N Prey) for all sampled stomachs (N) were calculated. Diet composition was compared between the lower Elwha River 

(multiple locations between RKms 0.5 and 0.0) and the East estuary in 2006 and between the East estuary and WESC in 2007 using Schoener’s (1970) index of 

proportional similarity (α). Dipt_Freq.: frequency of dipteran occurrence. Abbreviation: FW, freshwater; WESC, west estuary channel]

Year Months α Location N S Prey H' Prey E Prey N Prey Dipt_Freq.

(percent)

2006 March–May 0.61 FW 17 13 0.76 0.30 306 79

East estuary 19 9 0.95 0.43 322 94

June–September 0.68 FW estuary 27 13 1.21 0.47 819 85

East estuary 36 15 0.54 0.20 270 100

2007 March–May 0.91 WESC 16 4 0.30 0.22 342 75

East estuary 12 10 0.58 0.25 151 83

June–September 0.95 WESC 11 7 0.22 0.11 227 100

East estuary 12 9 0.41 0.19 211 92

of dipterans was selected in freshwater (85 percent of total 

dietary items) than in estuary habitat (56 percent diptera and 

38 percent amphipods). Interestingly, this pattern was inverse 

during June–September, as more dipterans were present in 

estuary diets (91 percent) than in freshwater diets (63 percent 

diptera and 23 percent mayflies, mostly of the genus Baetis). 

In 2007, a comparison of dietary overlap between the east and 

west estuary detected a high degree of overlap in March–May 

(α = 0.91) and June–September (α = 0.95). 

Comparison of Prey Use versus Prey 

Availability in the Elwha River Estuary

As a vital requirement for animal growth, foraging is 

one of the primary factors in determining the fitness of an 

organism. Variables such as prey caloric value, handling time, 

and encounter rate all interact to affect food preference, with 

some theories suggesting that optimal foraging strategies 

are evolutionarily driven (Emlen, 1966). Most descriptive 

studies for juvenile Chinook salmon are limited to comparing 

the relative frequencies of prey taxa in the diet and in the 

environment. We examined patterns in prey use of juvenile 

Chinook salmon in using two approaches. The first was with 

modified Costello Diagrams (Costello, 1990; Amundsen and 

others, 1996), which graphically examines the proportion and 

frequency of occurrence of prey in the diet independent of 

prey availability. The second, Standard Forage Ratio (SFR; 

Manley 1974), constructs ratios of prey specific use and 

patterns of prey abundance in the environment.
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal Juvenile Salmon in the Elwha River Estuary 215

Modified Costello diagrams were used to interpret 

diet information of juvenile Chinook salmon collected in 

the freshwater and estuarine habitats of the Elwha River 

(fig. 7.25). This graphical method constructs a diagram of 

percentage of occurrence of each food item (unique taxon) on 

the ordinate and the prey-specific abundance on the abscissa. 

Prey-specific abundance is the proportional abundance of a 

particular taxon in only those fish stomachs in which it was 

present. Amundsen and others (1996) provided guidance for 

interpreting the distribution of prey items in the modified 

Costello diagram in terms of prey importance, feeding 

strategy, and niche contribution. The distribution of points 

along the prey-specific abundance axis indicates whether 

fish exhibit specialized (51–100 percent) or generalized 

(1–50 percent) feeding. A diagonal line from the origin to the 

upper right corner of the diagram indicates prey importance, 

as rare taxa are found in the lower left quadrant of the diagram 

and abundant taxa are found in the upper right quadrant of 

the diagram. The other diagonal, from the upper left to lower 

Occurrence frequency, percent

Prey-specific abuncance, percent

High

withinindividual 

variability

Dominant

Rare

Specialization

Generalization

100

50

0

High

betweenindividual 

variability

EXPLANATION

Corophium sp.

Larval

Orthocladiinae

Adult 

Chironomidae

Pupa

Chironomidae

100

80

60

40

20

10

10 20 40 60 80 100

A. East Elwha Estuary

Pupa

Chironomidae

Larval

Orthocladiinae

Naiad Baetis sp.

100

80

60

40

20

10

10 20 40 60 80 100

B. Lower Elwha River

Pupa

Chironomidae

Adult Hilaria sp.

100

80

60

40

20

10

10 20 40 60 80 100

C. WESC

right, indicates the contribution of a prey taxon to the niche 

breadth of the predator. Points in the upper left quadrant 

indicate high selectivity among individual variability on 

the prey items consumed, which determines niche breadth, 

whereas points occurring in the lower right quadrant indicate 

generalized feeding on the same prey items across individuals 

(Amundsen and others, 1996; Vile and others, 2005).

Feeding strategies inferred from modified Costello 

diagrams (fig. 7.25) showed that juvenile Chinook salmon 

specialized on chironomids in the lower Elwha River and the 

eastern and western parts of the estuary. Chironomid pupa 

were particularly dominant in the estuary and to a lesser extent 

in the lower Elwha River where larval orthocladiinae and 

mayflies of the genus Baetis were also important. Most other 

prey species were rare and fed on in a generalized fashion by 

Chinook. The only other non-dipteran prey of any importance 

was the amphipod genus Corophium in the eastern Elwha 

estuary. 

Figure 7.25. Modified Costello diagram showing feeding strategy of juvenile Chinook salmon in three habitats 

of the Elwha River, Washington. Diagrams modified from Costello, 1990, and Amundsen and others, 1996. Upper 

left panel shows three interpretive axes related to niche contribution prey importance (rare to dominant), and 

feeding strategy (generalization to specialization).
216 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Prey use and prey availability patterns were estimated 

using SFR in the estuary where macroinvertebrate abundance 

in the diet as well as in the environment was sampled 

(fig. 7.26). Diet data from 2006 and 2007 was pooled; 

benthic and terrestrial (from shrub and littoral habitat) 

macroinvertebrate data were collected from the east and 

west estuary in 2007. Data were split into three seasons: 

early (March through May), mid (June through July) and late 

(August through September). Terrestrial and benthic prey 

availability data for the early and late seasons were collected 

in May and September 2007, respectively. For the mid season, 

benthic invertebrate samples collected in July and the average 

of terrestrial samples collected in June and July were used. 

The SFR for prey orders was calculated using the formula 

provided by Manley (1974):

Acarnia

Terrestrial

Aquatic

Diet

Terrestrial

Aquatic

Diet

Terrestrial

Aquatic

Diet

Amphipoda

Hemiptera

Diptera

Collembola

Coleoptera

Araneae

Ostracoda

Odonata

Hymenoptera

Thysanoptera

Plecoptera

Trichoptera

Early

Season

Late

Season

Mid

Season Taxon

EXPANATION

75 percent

50 percent

25 percent

Figure 7.26. Bubble plots 

showing proportion of 

invertebrate taxa in fallout traps 

(terrestrial), sediment samples 

(aquatic), and diet of juvenile 

Chinook salmon captured in the 

lower Elwha River and the east 

estuary, Washington. Samples 

were pooled for fish collected 

in 2006 and 2007. Gastric lavage 

samples were standardized by 

number of invertebrates divided 

by the weight of each fish.

1

,

where

is proportion of prey in the diet, 

is proportion of prey in the environment, 

equals 1, 2... .

i i

i k

i i i

i

i

x

P

x

x

i k

=

β =

β

β

∑

(2)

Values of Pi greater than 0.5 indicate specialization, 

whereas values less than 0.5 indicate that use is in proportion 

to availability.
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal Juvenile Salmon in the Elwha River Estuary 217

Table 7.10. Average Standard Forage Ratio values for juvenile Chinook salmon diet for 

individuals captured in the Elwha River estuary, Washington, in three seasons during 2006 

and 2007. 

[Standard Forage Ratio from Manley (1974). Values in bold indicate prey that were positively selected 

for by juvenile Chinook salmon in each season. Environmental values of prey availability based on data 

collected in 2007. Values could not be computed during a given season when a prey taxon was not present 

in the diet (a) or in the environment (b). Abbreviations: N, number of individuals captured; n, (standard 

deviation) number of fish with taxon present; na, not applicable]

Macoinvertebrate

taxon

Early season 

(March–May)

N = 20

Mid season 

(June–July)

N = 58

Late season 

(August–September)

N = 20

Acarina a 0.24 (0.15, n = 2) a

Amphipoda 0.39 (0.40, n = 13) 0.50 (0.33, n = 20) 0.004 (0.001, n = 6) 

Araneae 0.25 (0.12, n = 2) 0.66 (0.08, n = 1) 0.10 (na, n = 1)

Coleoptera 0.97 (0.01, n = 2) 0.54 (0.24, n = 12) 0.83 (0.11, n = 5)

Collembola 0.38 (0.35, n = 3) 0.32 (0.40, n = 2) a

Diptera 0.35 (0.38, n = 18) 0.42 (0.42, n = 57) 0.42 (0.45, n = 20)

Hemiptera 0.42 (0.35, n = 5) 0.49 (0.31, n = 7) 0.22 (0.17, n = 5)

Hymenoptera 0.44 (na, n = 1) 0.40 (0.30, n = 6) 0.19 (0.18, n = 3)

Odonata a a 0.77 (na, n = 1)

Ostracoda a 0.28 (na, n = 1) 0.01 (na, n = 1)

Plecoptera a, b 1.0 (na, n = 1) b

Thysanoptera a 0.97 (na, n = 1) a

Trichoptera 0.82 (0.08, n = 3) 0.30 (0.33, n = 6) 0.95 (0.07, n = 3)

The SFR ratios indicate that the 

two main prey taxa, Amphipods and 

Dipterans, generally were not positively 

selected for, but rather were selected 

because they were the most abundant 

prey available (table 7.10). An exception 

was selectivity for Amphipods in the 

mid season (SFR = 0.5), although 

the calculated value was marginally 

positive. These results are in contrast 

to the interpretation of feeding strategy 

based on Costello diagrams, although 

the importance of Dipterans and 

Amphipods was apparent using both 

methods. Those cases that did show 

highly positive selectivity generally 

were those represented by few fish 

and therefore probably are not reliable 

representations of juvenile Chinook 

salmon preference. Coleopterans were 

positively selected for in all seasons and 

Trichoptera were positively selected for 

in the early and late seasons.

Other studies in estuarine 

environments in the Pacific Northwest 

also have determined that Dipterans, 

particularly chironomids, and 

Amphipods are important prey sources. 

Shreffler and others (1992) diet study 

of the Puyallup River estuary in south 

Puget Sound also determined that 

chironomids were the most abundant 

prey consumed by fall Chinook salmon, 

with Amphipods (particularly of the 

genus Corophium), Plecopterans, and 

Cladocerans as secondary prey. Grey 

and others (2002) also determined 

that Dipterans, Amphipods, and 

Trichopterans were of importance in 

control and restored sites of the Salmon 

River estuary in Oregon. Roegner 

and others (2004), working in various 

habitats of the Columbia River estuary, 

also found that chironomids and 

Amphipods were the dominant prey 

source for juvenile Chinook salmon. 

A more comprehensive analysis, 

for example bioenergetic modeling (see 

Beauchamp, 2009; Cordell and others, 

2011), would give a better estimate of 

how food availability, consumption, and 

environmental factors are playing a role 

in the growth efficiencies of juvenile 

Chinook salmon in the Elwha River and 

how those factors relate to the ongoing 

restoration efforts. 
218 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Summary

The capacity of the Elwha River 

estuary to support increased population 

sizes and life-history diversity of salmon 

populations will be determined by 

physical and biological factors, such 

as food sources, sediment deposition, 

temperature, salinity, and other habitat 

features. Our results showed that 

juvenile salmon use the Elwha River 

estuary for extended periods and show 

increased growth when they feed 

in the estuary. Chinook, coho, and 

chum salmon were the most common 

salmonids detected during 2 years 

of beach seining in the estuary. Fish 

assemblages in the Elwha River estuary 

varied between 2 years of sampling 

(2006 and 2007) likely due to stormdriven physical changes that precluded 

access to outmigrating juvenile salmon 

as well as marine fish movements in the 

estuary.

The differences in fish assemblage 

structure in the Elwha River estuary 

suggest that even modest volumes 

of sediment may create barriers 

that preclude fish access to critical 

estuarine habitat. This has management 

implications in the context of Elwha 

River restoration that may warrant a 

more active approach to maintaining 

fish access during periods of heavy 

sediment deposition following dam 

removal. Adaptive management 

planning, already underway for the 

lower main stem, would be well 

informed by taking into consideration 

the potential sediment impacts on fish 

access to estuarine habitat. Although 

significantly elevated turbidity levels 

are anticipated in the months to years 

following dam removal, the magnitude 

of these levels is difficult to anticipate, 

particularly in the Elwha River estuary. 

The extent to which elevated post-dam 

removal turbidity levels in the estuary 

may adversely affect juvenile salmonid 

life history and feeding efficiency also 

is uncertain. Simenstad and others 

(1982) postulated that naturally elevated 

turbidity in estuaries during periods 

of typical juvenile salmonid residence 

might reduce predator efficiency and 

benefit their survival. The concentration 

threshold at which the benefits of 

elevated turbidity are replaced by 

adverse life history effects is uncertain 

and will be a potential subject of study 

during the dam removal and restoration 

process. 

The effects of dam removal in the 

Elwha River estuary, like that of the 

entire river, is likely to be complex, 

with ecological processes and functions 

changing across multiple spatial and 

temporal scales. In the near term, 

high sediment loads due to erosion 

of delta deposits in the two reservoirs 

could have a negative impact on 

many habitats of the river and estuary, 

which could change the carrying 

capacity for species across trophic 

levels. Conversely, in the long term, as 

salmon recolonize the watershed and 

populations rebuild, greater life-history 

diversity of salmonids will be a key 

component of successful recolonization 

and the maintenance of self-sustaining 

populations (Schindler and others, 

2010).

Future studies of the Elwha River 

estuary, during and following dam 

removal, should examine the effects 

of physical changes due to sediment. 

Macroinvertebrate and fish communities 

are likely to respond if sediment 

deposition has large effects on physical 

factors such as substrate composition 

and turbidity. Therefore, collection of 

complementary data to that presented 

herein would allow examination of 

potential affects to these communities. 

Additional data collection, such as 

sediment traps and turbidity sensors, 

would help explain the level of changes 

experienced by biological communities 

in the estuary. Repeating many of the 

data collection efforts described in this 

chapter will be essential in documenting 

the effects of dam removal and salmon 

recolonization on the Elwha River 

estuary.

Acknowledgments

This project involved the 

coordination with and assistance from 

researchers from several institutions, 

including state and Federal agencies. 

We acknowledge and are grateful 

for the assistance of Anne Shaffer 

(Washington Department of Fish and 

Wildlife [WDFW]) who assisted with 

seining activities and collected valuable 

complementary data, and provided 

specimens for otolith analysis. Kurt Fresh, 

Anna Kagley, and Joshua Chamberlin 

(National Oceanic and Atmospheric 

Administration) also assisted by 

contributing samples for otolith analysis. 

Jeff Grimm (WDFW) provided reference 

otolith samples. Scott Williams and staff 

of the Dungeness hatchery provided 

assistance with obtaining hatchery 

samples. We would like to thank the 

following individuals for assisting with 

field work: Ernest “Sonny” Sampson, 

Larry Ward, Mel Elofson, Mitch Boyd, 

Raymond Moses (Lower Elwha Klallam 

Tribe); Rebecca Paradis, Bryan Hara, 

David Kirner, Jimmy McDougall, Brian 

Matne, and Michelle Surrette (Peninsula 

College); Dorothy Chase, Christopher 

Konrad, Cecile Mathieu, Steve Rubin, 

Guy Gelfenbaum, and Jon Warrick 

(U.S. Geological Survey). Database 

management and mapping were provided 

by Randall McCoy (Lower Elwha Klallam 

Tribe) and Theresa Olson (USGS). 

Special thanks are due to Arthur Frost for 

completing all of the macroinvertebrate 

taxonomic identification. This chapter 

benefitted from discussions with Rich 

Sheibley (USGS), Jeff Cordell (University 

of Washington), and Tom Friesen (Oregon 

Department of Fish and Wildlife). 

Funding was provided by the USGS 

Multi-disciplinary Coastal Habitats in 

Puget Sound (MD-CHIPS) program 

and from a grant to the Lower Elwha 

Klallam Tribe from the Environmental 

Protection Agency. Use of trade names 

is for convenience of the reader and does 

not constitute endorsement by the U.S. 

government.
Chapter 7

Aquatic Ecology of the Elwha River Estuary Prior to Dam Removal References Cited 219

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Chapter 8

8

Chapter

Vegetation of the Elwha 

River Estuary

By Patrick B. Shafroth, Tracy L. Fuentes, 

Cynthia Pritekel, Matthew M. Beirne, and 

Vanessa B. Beauchamp

Abstract

The Elwha River estuary supports one of 

the most diverse coastal wetland complexes 

yet described in the Salish Sea region, in 

terms of vegetation types and plant species 

richness. Using a combination of aerial 

imagery and vegetation plot sampling, 

we identified 6 primary vegetation types 

and 121 plant species in a 39.7 ha area. 

Most of the estuary is dominated by woody 

vegetation types, with mixed riparian forest 

being the most abundant (20 ha), followed 

by riparian shrub (6.3 ha) and willowalder forest (3.9 ha). The shrub-emergent 

marsh transition vegetation type was 

fourth most abundant (2.2 ha), followed 

by minor amounts of dunegrass (1.75 ha) 

and emergent marsh (0.2 ha). This chapter 

documents the abundance, distribution, 

and floristics of these six vegetation types, 

including plant species richness, life form, 

species origin (native or introduced), 

and species wetland indicator status. 

These data will serve as a baseline to 

which future changes can be compared, 

following the impending removal of 

Glines Canyon and Elwha Dams upstream 

on the Elwha River. Dam removals may 

alter many of the processes, materials, 

and biotic interactions that influence the 

estuary plant communities, including 

hydrology, salinity, sediment and wood 

transport, nutrients, and plant-microbe 

interactions.
226 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Introduction 

Unique wetland complexes occur 

where river mouths meet the sea. 

The vegetation of these areas ranges 

from riparian habitats that differ little 

from habitats associated with the river 

upstream to salt marshes that have a 

distribution limited to tidally influenced 

areas with elevated water salinity. The 

processes that drive the distribution and 

dynamics of plant communities in river 

estuary wetland complexes are also 

varied, ranging from fluvial-dominated 

processes such as flooding and channel 

migration to marine processes such as 

tidally driven water-level fluctuations. 

Patterns of seawater intrusion influence 

salinity levels in estuarine water and 

soils and can be a strong determinant 

of plant distributions (Mitsch and 

Gosselink, 1993; Keddy, 2000). At the 

scale of an entire river-mouth wetland 

complex, these conditions and processes 

can produce multiple plant communities 

with high beta diversity and high species 

richness (Keddy, 2000).

River mouth wetland complexes 

of the Salish Sea region (which 

extends from Olympia, Washington, 

to Canada’s Desolation Sound) are 

relatively uncommon and small in 

area (Collins and Sheikh, 2005; Todd 

and others, 2006). Many of these 

systems have been modified by human 

activities such as channelization, large 

wood removal, and levee and dike 

construction, which typically reduce 

wetland extent and alter key processes 

such as tidal inundation (Thom and 

others, 2002; Todd and others, 2006; 

Brennan, 2007). By one estimate, Puget 

Sound tidal wetlands have been reduced 

to about 19 percent of their historical 

area, from approximately 29,500 ha to 

approximately 5,650 ha (Collins and 

Sheikh, 2005). 

The Elwha River delta and estuary 

are relatively small and have been 

subject to alteration by the construction 

and operation of two large dams 

upstream that have significantly reduced 

sediment and wood transport through 

the estuary. Dike and levee construction 

also have constrained channel migration 

(Kloehn and others, 2008; Draut and 

others, 2011; Warrick and others, 2011, 

chapter 4, this report) and reduced the 

tidally influenced area (Duda and others, 

2011, chapter 1, this report; Magirl and 

others, 2011, chapter 4, this report).

Removal of the two dams upstream 

on the Elwha River, anticipated to 

begin in 2011, will release and transport 

coarse woody debris and much of 

the approximately 19 million m3 of 

sediment stored behind the dams 

(Bountry and others, 2010; Czuba and 

others, 2011, chapter 2, this report). 

This influx of sediment might directly 

influence estuarine plant communities 

through deposition of fine sediments, 

for example, or might indirectly affect 

these areas by inducing higher rates of 

channel change (Shafroth and others, 

2002; Hood, 2010) and by altering the 

transport of sediment in the Strait of 

Juan de Fuca and adjacent beaches and 

beach berms (Warrick and others, 2011, 

chapter 3, this report).

This study is part of a U.S. 

Geological Survey (USGS) and Lower 

Elwha Klallam Tribe multi-disciplinary 

effort to characterize the ecosystems 

of the Elwha River estuary before dam 

removal. Our objectives were to identify 

the principal vegetation types within the 

estuary, estimate their areal extent, and 

characterize their structure and species 

composition, including species richness. 

We further elucidate floristic patterns by 

comparing the distribution of life forms, 

native versus introduced species, and 

the wetland indicator status among the 

primary vegetation types in the Elwha 

River mouth/estuary wetland complex.

Methods

Patch Delineation and 

Vegetation Plot Selection

In August 2007, polygons were 

delineated representing distinct 

vegetation patches visible on 1 m 

resolution, 2006 National Agriculture 

Imagery Program (NAIP) imagery 

within the study area. The study area 

was then ground-truthed to refine the 

polygon boundaries and to classify 

each polygon as one of six vegetation 

types: mixed riparian forest (labeled 

“Riparian forest” in figures), willowalder forest, riparian shrub, shrubemergent marsh transition (shrub-marsh 

transition), emergent marsh, and 

dunegrass (fig. 8.1, table 8.1). Figure 8.1

shows the polygons and plot locations, 

overlayed on a more recent aerial 

photograph (April 2008), which better 

depicts current conditions. Table 8.1

also provides the classification of these 

vegetation types according to Cowardin 

and others (1979). Next, random x-y 

coordinates were generated to identify 

plot locations. At least three plots were 

sampled in each of our original six 

vegetation types. For two of the more 

extensive vegetation types (riparian 

forest and riparian shrub) five plots 

were sampled. A total of 22 plots were 

sampled.
Chapter 8

Vegetation of the Elwha River Estuary Introduction 227

watac11-0558_fig8-1

0 100 200 METERS

0 100 200 FEET

Bosco Creek

Elwha River

Vegetation plots

Study area

Riparian shrub

Shrub-marsh transition

Open water

Dunegrass

Riparian forest Emergent marsh

Willow-alder forest

EXPLANATION

Vegetation Type

Strait of Juan de Fuca

123 ̊34’12”W

48 ̊09’N

48 ̊09’34”N

123 ̊33’46.08”W 123 ̊33’20.16”W

Figure 8.1. Study area showing six vegetation patch types, gravel bars, open water, and vegetation plot locations, 

Elwha River estuary, Washington.
228 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Vegetation Plot Sampling

At each plot location, a 100 m2 plot 

was established. Each vascular plant 

present in a plot was assigned to 1 of 

10 cover classes: trace, 0–1 percent, 

1–2 percent, 2–5 percent, 5–10 percent, 

10–25 percent, 25–50 percent, 

50–75 percent, 75–95 percent, and 

95–100 percent. Because individual 

plants and vegetation strata commonly 

overlapped, total plant cover values 

within a plot commonly exceeded 

100 percent. In most cases, plot 

dimensions were 10 × 10 m, but where 

the vegetation patch was narrow, plot 

dimensions were sometimes 4 × 25 m 

or 5 × 20 m. With these data, the total 

number of species across all of our 

plots were tallied (estuary-scale species 

richness), as were the total number of 

species per vegetation type (communityscale species richness), and the average 

number of species per vegetation type 

(plot-scale species richness).

In August 2008, the mixed riparian 

forest and willow-alder plots were 

revisited, and tree cover by species and 

the diameter of all trees (stems greater 

than 2.5 cm at breast height) were 

measured in 0.1 ha (for mixed riparian 

forest) or 0.01 ha (for willow-alder 

forest) plots. Tree stem density and basal 

area were calculated with the diameter 

data.

Floristic Categories

Each species was identified by its 

life form (or habit): graminoid, forb, 

shrub, or tree, and whether it was native 

or introduced was noted (per the U.S. 

Department of Agriculture [USDA] 

Plants database, http://plants.usda.

gov/; and the University of Washington 

Herbarium, Washington Flora Checklist, 

http://biology.burke.washington.edu/

herbarium/waflora/checklist.php). If the 

USDA Plants database indicated that a 

species can have multiple growth forms 

(for example, a tree or shrub form), the 

species was categorized as having the 

larger of the two forms (for example, 

a tree rather than a shrub). Species 

richness patterns are summarized by 

life form, species origin (native or 

introduced), and wetland indicator 

status (for those species for which this 

information was available per the USDA 

Plants database; http://plants.usda.gov/).

Wetland indicator status is a five-point 

scale that estimates the probability that 

a plant occurs in wetlands: Obligate 

wetland species = 1; Facultative wetland 

species = 2; Facultative = 3; Facultative 

upland species = 4; Upland = 5. The 

relative cover of plants by life form 

and native versus introduced status are 

also summarized, and wetland indicator 

status weighted by the relative cover of 

each species is examined.

Table 8.1. Vegetation types named in this study in relation to the Cowardin and others (1979) classification used by the U.S. Fish and 

Wildlife National Wetlands Inventory (NWI). 

Elwha vegetation type 

(this study) Cowardin classification Comments

Mixed riparian forest PFO1A, Palustrine, Forested, Broad-leaved 

deciduous, Temporarily flooded

Many of these areas appear to be classified as non-wetland 

by the NWI. Areas classified as wetland that overlap this 

vegetation type in our study typically fall into the PFO1A 

category.

Willow-alder forest E2USP, Estuarine, Intertidal, Unconsolidated 

shore, Regularly flooded

These early successional areas conform to areas currently 

mapped as estuarine, intertidal by the NWI, but due to 

vegetation encroachment would likely now be classified 

as an estuarine or palustrine forested, depending on the 

amount of tidal influence.

Riparian shrub; Shrubemergent marsh transitionPSS1C, PSS1Ch, PSS1R, Palustrine, Scrub 

shrub, Broad-leaved deciduous, Seasonally 

flooded, Seasonally-flooded-impounded or 

Seasonal-tidal flooded or PF01A (see above)

Much of the area classified as riparian shrub is not classified 

by the NWI. Classified areas that do overlap with these 

vegetation types typically fall into the palustrine, scrubshrub, broad-leaved deciduous categories with variable 

flooding regimes. Some areas are also classified as 

palustrine, forested, broad- leaved deciduous.

Emergent marsh PEM1A, Palustrine, Emergent, Persistent, 

Temporarily flooded

These areas are often found in the ecotone from open water 

(estuarine or palustrine) to drier areas (riparian shrub and 

mixed riparian forest)

Dunegrass M2USN, Marine, Intertidal, Unconsolidated 

shore, Regularly flooded

Dunegrass dominated berms adjacent to the shore either 

fall into this category or are considered “upland” and not 

mapped by the NWI.
Chapter 8

Elwha Estuary Vegetation Sampling Results Vegetation of the Elwha River Estuary 229

Vegetation Plot Classification 

To assess the extent to which the 

plant community data from the plots 

was consistent with the subjective 

classification of the six vegetation types 

(based on the aerial photography and 

ground-truthing, above), a nonmetric 

multidimensional scaling (nMDS) 

ordination of the vegetation plot 

data was run using Primer, version 

6.0 (Clarke and Gorley, 2006). The 

ordination was derived from a BrayCurtis similarity matrix generated from 

square-root transformed percent cover 

(mid-point of cover class, by species) 

values for each species in each plot.

Vegetation Plot Elevation 

Surveys

To explore the relation between 

plot elevation and vegetation type, the 

elevation (above sea level) of each plot 

was estimated using two methods. In 

September 2009, 18 of the plot locations 

were surveyed with a Magellan ProMark 

3 Differential Global Positioning System 

operating in Real-Time Kinematic 

mode (RTK-DGPS), mounted on a 

survey pole, receiving corrections from 

a base station on a permanent survey 

monument. The estimated systematic 

and random error (combined) in the 

vertical and horizontal dimensions was 

±10 cm. Points could not be captured 

with the RTK-DGPS system for four 

of the plots due to canopy density. For 

these, plot elevations were estimated 

from a digital elevation model produced 

from a lidar flight in April 2009, which 

had an estimated absolute vertical error 

of ±30 cm (Entrix, Inc., 2009).

Elwha Estuary Vegetation 

Sampling Results

Vegetation Plot Classification

The six vegetation types that 

were identified to initially stratify 

the vegetation of the Elwha estuary 

(fig. 8.1) corresponded well to plot 

groupings revealed by the non-metric 

multi-dimensional scaling ordination 

(fig. 8.2). The final stress value for the 

two-dimensional analysis was 0.16, 

a value sufficiently low (that is, less 

than 0.2) to indicate a useful summary 

of multivariate pattern (Clarke and 

Warwick, 2001). Given the consistency 

between the classifications based on 

plot data and field mapping, these six 

vegetation types were retained for 

both the estuary-scale and communityand plot-scale descriptions. Here, the 

vegetation types are briefly described, 

and then compared with respect to 

various floristic metrics.

Figure 8.2. Ordination 

diagram showing plot 

groupings based on nonmetric multi-dimensional 

scaling, Elwha River 

estuary, Washington. Patch 

type names are those 

originally used to describe 

vegetation based on aerial 

photograph interpretation 

and ground truthing.

2-D Stress = 0.16

EXPLANATION

Shrub-marsh transition

Emergent marsh

Riparian forest

Vegetation Type

Riparian shrub

Willow-alder forest

Dunegrass
230 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Mixed Riparian Forest 

The mixed riparian forest vegetation 

type is the most extensive in the study area, 

occupying approximately 20 ha in April 

2008 (fig. 8.1). In the Elwha River estuary, 

mixed riparian forests can be dominated 

by various deciduous species, such as 

Acer macrophyllum (bigleaf maple), 

Populus balsamifera ssp. trichocarpa

(black cottonwood), Alnus rubra (red 

alder) in the overstory, with Sambucus 

racemosa (red elderberry), Rubus 

spectabilis (salmonberry), and Oemleria 

cerasiformis (Indian plum) common in the 

understory (fig. 8.3). One conifer stand 

was sampled with Pseudotsuga menziesii

(Douglas-fir) in the overstory. Thuja plicata

(western redcedar), Abies grandis (grand 

fir) and Picea sitchensis (Sitka spruce) are 

other conifer species that occur within the 

study area. Some of these mixed riparian 

forest patches are relatively old (probably 

more than100 years) and often contain 

large trees (up to 163.5 cm in diameter 

within our sample plots). Mean ± standard 

deviation of tree stem density, basal area, 

and total percent cover of vascular plants 

were 676±125 stems/ha; 33.6±20.4 m2/ha, 

and total percent cover was 192.4±36.7, 

respectively.

Figure 8.3. Mixed riparian forest vegetation type in the Elwha River estuary, Washington. (Photograph taken by 

Thomas O. Bates, formerly with ASRC Management Services, July 9, 2006.)
Chapter 8

Elwha Estuary Vegetation Sampling Results Vegetation of the Elwha River Estuary 231

Willow-Alder Forest 

 Young willow-alder forests are 

early successional communities that 

occupy recently deposited gravel bars, 

typically close to the active river channel 

(fig 8.4). River channel migration over 

the past seven decades eroded many 

of the willow-alder forests on the east 

side of the channel but also deposited 

new gravel bars on the west side where 

several patches of this vegetation 

type existed during our study (Draut 

and others, 2008; fig. 8.1), occupying 

approximately 3.9 ha in April 2008 

Figure 8.4. Willow-alder forest vegetation type growing on a gravel bar in the Elwha River estuary, Washington. 

(Photograph taken by Patrick B. Shafroth, U.S. Geological Survey, July 16, 2006.)

(fig. 8.1). Alnus rubra had the highest 

mean cover (61.5 percent) across 

the three plots sampled in this patch 

type. Salix sitchensis (Sitka willow; 

23.3 percent mean cover) dominated 

one of the three plots, and S. hookeriana

(Hooker’s willow; 6.3 percent mean 

cover) was subdominant in one of the 

plots. Mean ± standard deviation of 

tree stem density in willow-alder stands 

was 2,767±2,450 stems/ha, mean ± 

standard deviation of basal area was 

24.0±19.6 m2/ha, total plant cover was 

114.8±43.3 percent.
232 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Riparian Shrub 

Riparian shrub communities are 

characterized by high shrub cover and 

can occur in different contexts within the 

estuary. For example, along the margins 

of the estuarine water bodies and Bosco 

Creek, riparian shrub communities 

typically occurred either adjacent to 

the water or a short distance from the 

water if a strip of emergent vegetation 

was present. In places, they also 

occurred along a topographic gradient 

from water’s edge to the riparian 

forest, between the shrub-emergent 

marsh transition community and the 

mixed riparian forest community. 

Finally, riparian shrub patches can be 

interspersed with mixed riparian forests 

(fig. 8.1). The riparian shrub vegetation 

type occupied approximately 6.3 ha 

in April 2008. Several shrubs were 

relatively abundant in the sampled 

plots: Rosa nutkana (Nutka rose), 

Rosa pisocarpa (clustered wild rose), 

Crataegus douglasii (black hawthorne; 

fig. 8.5), Lonicera involucrata (black 

twinberry), Malus fusca (Pacific crab 

apple), Oemleria cerasiformis (Indianplum), Rubus spectabilis (salmonberry), 

and Symphoricarpos albus (common 

snowberry). Total plant cover in riparian 

shrub plots was 128.0±40.8 percent 

(mean ± standard deviation).

Figure 8.5. Riparian shrub vegetation type within the Elwha River estuary, Washington, study area. 

(Photograph taken by Tracy L. Fuentes, U.S. Geological Survey, August 18, 2007.)
Chapter 8

Elwha Estuary Vegetation Sampling Results Vegetation of the Elwha River Estuary 233

Shrub-Emergent Marsh Transition

Shrub-emergent marsh transition 

vegetation usually occurs between 

the narrow bands of emergent marsh 

vegetation that are subject to regular and 

relatively large, tidally driven waterlevel fluctuations, and patches of riparian 

shrub or riparian forest that typically are 

inundated by river flooding (fig. 8.6). The 

shrub-emergent marsh transition zone is 

apparently inundated by tidal waters, but 

to relatively shallow depths for relatively 

short durations. This vegetation type 

occupied approximately 2.2 ha in April 

2008. Vegetation is characterized by high 

total cover, predominantly herbaceous. The 

forb Argentina egedii (Pacific silverweed) 

dominated vegetative cover in the three 

plots sampled in this patch type (average 

of approximately 45 percent). Woody plant 

cover is comprised largely of scattered, 

relatively small Salix sitchensis and Alnus 

rubra individuals. Several emergent marsh 

species are also present in these plots, 

including Carex spp. (sedges), Juncus spp. 

(rushes), Eleocharis palustris (creeping 

spike-rush), and Typha latifolia (cattail). 

Total plant cover in shrub-emergent marsh 

transition plots was 161.0±58.4 percent 

(mean ± standard deviation).

Figure 8.6. Shrub-emergent marsh transition vegetation type within the Elwha River estuary, Washington, study 

area. (Photograph taken by Tracy L. Fuentes, U.S. Geological Survey, August 17, 2007.)
234 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Emergent Marsh

In the Elwha River estuary, 

patches of emergent marsh vegetation 

are typically limited to narrow bands 

(less than 5 m) along the margins of 

the estuarine ponds (fig. 8.7). They 

occupy the smallest area of any of 

the vegetation types—approximately 

0.2 ha in April 2008 (fig. 8.1). Sediment 

particle size is usually fine and plants 

are subject to substantial tidally driven 

water-level fluctuations (Magirl and 

others, 2011, chapter 4, this report). 

Individual patches are often relatively 

species poor, with high dominance by 

one or two species. Abundant species 

in the three plots sampled within 

this vegetation type included Juncus 

arcticus (arctic rush), Argentina egedii, 

Carex obnupta (slough sedge), Rumex 

salicifolius (willow dock), Eleocharis 

palustris, and Typha latifolia. Total plant 

cover was 118.7±30.6 in the emergent 

marsh plots (mean ± standard deviation).

Figure 8.7. Emergent marsh vegetation bordering open water in the Elwha River estuary, Washington. 

(Photograph taken by Patrick B. Shafroth, U.S. Geological Survey, July 20, 2006.)
Chapter 8

Elwha Estuary Vegetation Sampling Results Vegetation of the Elwha River Estuary 235

Dunegrass 

Dunegrass communities occur at 

relatively high topographic positions 

on or adjacent to beach berms. They 

occupied approximately 1.75 ha in 

April 2008 (fig. 8.1). These communities 

are strongly dominated by Leymus 

mollis (American dunegrass), which 

averaged more than 75 percent cover in 

the three plots sampled (fig. 8.8). Forb 

Figure 8.8. Dunegrass vegetation type in the Elwha River estuary, Washington. (Photograph taken by Tracy L. 

Fuentes, U.S. Geological Survey, August 17, 2007.)

diversity was high in the dunegrass 

communities (see below), and some 

forbs had relatively high cover, such 

as Ambrosia chamissonis (silver bur 

ragweed), Lathyrus japonicus (beach 

pea), Rumex salicifolius, Senecio 

sylvaticus (woodland ragwort), 

and Solidago canadensis (Canada 

goldenrod). Total plant cover in the three 

plots sampled was 162.4 ± 89.8 percent 

(mean ± standard deviation).
236 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Floristics and Species Richness

A total of 121 unique vascular plant taxa in 46 families 

were identified within our 22 sample plots (table 8.2). Six 

of these taxa were identifiable only to the genus level, but 

were distinct from all other plants we identified. Given 

this, these taxa are considered “species” in the context of 

calculating richness values hereafter. The riparian shrub and 

shrub-emergent marsh transition vegetation types had the 

highest total richness (52 species), while the emergent marsh 

vegetation type had the lowest total richness (31 species; 

fig. 8.9). Plot-scale species richness differed in similar ways 

as total richness across the six vegetation types (fig. 8.9). The 

shrub-emergent marsh transition and mixed riparian forest 

vegetation types contained the most unique species (not found 

in any other vegetation type; 12 and 13 species, respectively); 

the willow-alder forest vegetation type contained only one 

unique species (fig. 8.9). The greater number of plots in the 

mixed riparian forest and riparian shrub vegetation types could 

bias the comparisons of total species richness and number of 

unique species.

Vegetation type

Number of species

0

10

20

30

40

50

60

Riparian

Forest

(n=5)

Willow-Alder

Forest

(n=3)

Riparian

Shrub

(n=5)

Shrub-Marsh

Transition

(n=3)

Emergent

Marsh

(n=3)

Dunegrass

(n=3)

Cumulative species richness

Unique species

Average species richness

EXPLANATION

Figure 8.9. Species richness in the six vegetation types described for the Elwha River estuary, Washington. Light brown 

bars indicate the total number of species among all plots within a given vegetation type (cumulative species richness). 

Black bars indicate the number of species that are only in a given vegetation type (unique species). Green bars indicate 

the mean + standard error (black whisker) number of species (average species richness) per plot, by vegetation type. 

Number of plots sampled per vegetation type is indicated in parentheses beneath the x-axis labels. The area sampled is 

equal to the number of plots sampled times 100 square meters
Chapter 8

Elwha Estuary Vegetation Sampling Results Vegetation of the Elwha River Estuary 237

Table 8.2. Characteristics of 121 unique plant taxa identified in 22 vegetation plots sampled in the Elwha River estuary, Washington, August 2007.[Nomenclature for scientific names and plant family is based on the U.S. Department of Agriculture (USDA) Plants database (http://plants.usda.gov/). An “X” in a row beneath one of the six vegetation community column headings indicates that the plant was present in at least one plot sampled in that community. Life form: T, tree; F, forb; S, shrub; V, vine; SS, subshrub; G, graminoid. Origin: N, native plant; I, introduced plant; N/A, information not available Noxious weeds: Plants designated as noxious weeds by the Washington State Noxious Weed Board (2011) are labeled either B, (class B noxious weeds are nonnative species whose distribution is limited to parts of Washington State) or C, (Class C noxious weeds that already are widespread in Washington or are of special interest to the State’s agricultural industry). Wetland indicator status: Based on information from USDA Plants database. Wetland indicator status is a fivepoint scale that estimates the probability that a plant occurs in wetlands compared to non-wetlands (OBL, obligate wetland species; FACW, faculative wetland species; FAC, FAC+, FAC-, faculative; FACU, faculative upland species; UPL, upland]

Scientific name 

(genus and species) Family Mixed riparian forest Willow alder forest Riparian shrub Shrub-marsh transition Emergent marsh Dunegrass Life form Origin Noxious weeds Wetland indicator status

Acer macrophyllum Aceraceae X X X T N FACU

Alisma plantago-aquatica Alismataceae X F I OBLDaucus carota Apiaceae X F I B N/A

Oenanthe sarmentosa Apiaceae X X F N OBLHedera helix Araliaceae X S/V I C N/AAchillea millefolium Asteraceae X X X X F N FACU

Adenocaulon bicolor Asteraceae X F N N/AAmbrosia chamissonis Asteraceae X X F N N/AAnaphalis margaritacea Asteraceae X F N N/A

Cirsium arvense Asteraceae X X F I C FACU+

Cirsium vulgare Asteraceae X X X F I C FACU

Erigeron sp. Asteraceae X F N/A N/A

Hypochaeris radicata Asteraceae X X X X F I C FACU

Lapsana communis Asteraceae X X F I FAC

Leucanthemum vulgare Asteraceae X X X X X F I C N/A

Mycelis muralis Asteraceae X X F I N/ASenecio jacobaea Asteraceae X X F I B FACU

Senecio sylvaticus Asteraceae X X F I N/ASolidago canadensis Asteraceae X X X F N FACU

Sonchus oleraceus Asteraceae X F I UPL

Taraxacum officinale Asteraceae X X F I FACU

Alnus rubra Betulaceae X X X X T N FAC

Myosotis scorpioides Boraginaceae X X F I FACW

Cakile maritima Brassicaceae X F I FACU

Lepidium campestre Brassicaceae X X F I N/A

Lepidium virginicum Brassicaceae X F N FACU

Lonicera ciliosa Caprifoliaceae X S N FAC+

Lonicera involucrata Caprifoliaceae X X X X X S N FAC+

Sambucus racemosa Caprifoliaceae X T/S N FACU

Symphoricarpos albus Caprifoliaceae X X X SS/S N FACU

Stellaria crispa Caryophyllaceae X F N FAC+

Chenopodium sp. Chenopodiaceae X F N/A N/AConvolvulus sp. Convolvulaceae X X F/V N/A B N/ACornus stolonifera Cornaceae X X T/S N FACW

Thuja plicata Cupressaceae X T N FAC

Carex deweyana var. deweyana Cyperaceae X G N FACU

Carex lenticularis Cyperaceae X X G N FACW+
238 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal Scientific name (genus and species) Family Mixed riparian forest Willow alder forest Riparian shrub Shrub-marsh transition Emergent marsh Dunegrass Life form Origin Noxious weeds Wetland indicator status Carex lyngbyei Cyperaceae

X

G

N OBL

Carex obnupta Cyperaceae

X

X

X

G

N OBL

Carex stipata var. stipata Cyperaceae

X

X

G

N OBL

Eleocharis palustris Cyperaceae

X

X

G

N OBL

Pteridium aquilinum Dennstaedtiaceae 

X F N FACU

Dipsacus fullonum Dipsacaceae

X F I FAC

Athyrium filix-femina Dryopteridaceae

X

X

X F N FAC

Polystichum munitum Dryopteridaceae

X

X F N FACU

Equisetum arvense Equisetaceae

X

X

X

X F N FAC

Equisetum hyemale var. affine Equisetaceae

X F N FACW

Arbutus menziesii Ericaceae

X

T

N N/A

Gaultheria shallon Ericaceae

X SS/S

N FACU

Vaccinium parvifolium Ericaceae

X S N N/A

Cytisus scoparius Fabaceae

X

X S I C N/A

Lathyrus japonicus Fabaceae

X

X F/V

N FACULathyrus sylvestris Fabaceae

X F/V I N/A

Lotus corniculatus Fabaceae

X

X

X F I FAC

Trifolium repens Fabaceae

X

X

X F I FAC

Vicia hirsuta Fabaceae

X

X F/V I N/A

Vicia nigricans ssp. gigantea Fabaceae

X

X

X F/V

N N/A

Geranium robertianum Geraniaceae

X

X F I B N/A

Ribes divaricatum Grossulariaceae

X

X

X S N FAC

Myriophyllum aquaticum Haloragaceae

X F I B OBL

Iris pseudacorus Iridaceae

X F I OBL

Juncus acuminatus Juncaceae

X

G

N OBL

Juncus arcticus ssp. littoralis Juncaceae

X

G

N FACW+

Juncus articulatus Juncaceae

X

G

N OBL

Juncus effusus Juncaceae

X

G

N FACW

Mentha arvensis Lamiaceae

X

X

X F N FACWMentha xpiperita 

[aquatica+spicata]

Lamiaceae

X

X F N FACW+

Prunella vulgaris Lamiaceae

X

X

X F N FACU+

Maianthemum dilatatum Liliaceae

X

X F N FAC

Chamerion angustifolium ssp.

angustifolium

Onagraceae

X F N FACU+

Circaea alpina Onagraceae

X F N FAC+

Epilobium ciliatum ssp. watsonii Onagraceae

X

X F N FACWEpipactis gigantea Orchidaceae

X

X F N OBL

Piperia elongata Orchidaceae

X

X F N N/A

Pseudotsuga menziesii Pinaceae

X

X

T

N FACU

Plantago lanceolata Plantaginaceae

X

X

X F I FAC

Plantago major Plantaginaceae

X

X F I FACU+

Plantago maritima Plantaginaceae

X F N FACW+

Agrostis capillaris Poaceae

X

X

X

X

X

X

G I FAC

Table 8.2. Characteristics of 121 unique plant taxa identified in 22 vegetation plots sampled in the Elwha River estuary, Washington, August 2007.—Continued
Chapter 8

Elwha Estuary Vegetation Sampling Results Vegetation of the Elwha River Estuary 239

Scientific name 

(genus and species) Family Mixed riparian forest Willow alder forest Riparian shrub Shrub-marsh transition Emergent marsh Dunegrass Life form Origin Noxious weeds Wetland indicator status

Agrostis stolonifera Poaceae X X X X G I FAC

Bromus sitchensis Poaceae X X G N N/A

Dactylis glomerata Poaceae X X X X G I FACU

Elymus repens Poaceae X X G I FACFestuca rubra Poaceae X X G I FAC+

Holcus lanatus Poaceae X X X X X G I FAC

Leymus mollis Poaceae X X G N N/ALolium perenne ssp. multiflorum Poaceae X G I FACU

Phalaris arundinacea Poaceae X X X X G N C FACW

Phleum pratense Poaceae X G I FACPoa palustris Poaceae X X G N FAC

Schedonorus pratensis Poaceae X X X X G I FACU+

Polygonum sp. Polygonaceae X X F N/A N/A

Rumex crispus Polygonaceae X X F I FAC+Rumex salicifolius var. 

salicifolius

Polygonaceae X X X X F N FACW

Polypodium glycyrrhiza Polypodiaceae X X F N N/A

Claytonia sibirica Portulacaceae X F N FAC

Potamogeton sp. Potamogetonaceae X F N/A OBLRanunculus repens Ranunculaceae X X X X F I FACW

Argentina egedii ssp. egedii Rosaceae X X X X X F N FACCrataegus douglasii Rosaceae X T/S N FAC

Crataegus monogyna Rosaceae X T I FACU+

Holodiscus discolor Rosaceae X S N N/AMalus fusca Rosaceae X T/S N FACW

Oemleria cerasiformis Rosaceae X X X T/S N FACU

Rosa nutkana var. nutkana Rosaceae X X SS N FAC

Rosa pisocarpa Rosaceae X X SS N FAC

Rubus armeniacus Rosaceae X X SS I C FACU

Rubus parviflorus Rosaceae X X SS N FACRubus spectabilis Rosaceae X X X X X SS/V N FAC+

Rubus ursinus Rosaceae X X X SS N FACU

Galium boreale Rubiaceae X X X X F N FAC

Galium sp. Rubiaceae X F N/A N/APopulus balsamifera ssp. 

trichocarpa

Salicaceae X X T N FAC

Salix hookeriana Salicaceae X T/S N FACWSalix lasiandra ssp. lasiandra Salicaceae X T/S N FACW+

Salix sitchensis Salicaceae X X X X X X T/S N FACW

Tolmiea menziesii Saxifragaceae X X F N FAC

Digitalis purpurea Scrophulariaceae X X F I FACU

Solanum dulcamara Solanaceae X SS/F/V I FAC+

Typha latifolia Typhaceae X X F N OBL

Urtica dioica Urticaceae X F N FAC+

Table 8.2. Characteristics of 121 unique plant taxa identified in 22 vegetation plots sampled in the Elwha River estuary, Washington, August 2007.—Continued
240 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Life Form

Of the 121 unique taxa in our sample plots, there 

were 15 tree, 15 shrub, 67 forb, and 24 graminoid species. 

Within all of the vegetation types, species richness of forbs 

was higher than the other life forms. Forb richness was 

especially high in the shrub-emergent marsh transition and 

dunegrass plots. Species richness of shrubs was relatively 

high in the riparian shrub plots and somewhat high in 

the mixed riparian forest plots. Graminoid richness was 

relatively high in the shrub-emergent marsh plots and in 

the emergent marsh plots. Finally, tree species richness 

was notably low in the emergent marsh and dunegrass 

plots (fig. 8.10A). Relative cover of trees was high in 

mixed riparian forest and willow-alder forest plots (greater 

than 60 percent); relative cover of shrubs was highest 

in riparian shrub (39 percent) and mixed riparian forest 

(26 percent) plots; relative cover of forbs was highest 

in the shrub-emergent marsh transition (65 percent) and 

emergent marsh (42 percent) plots; relative cover of 

graminoids was highest in the dunegrass (64 percent) and 

emergent marsh (53 percent) plots (fig. 8.10B).

Native Compared with Introduced Species

 Of the 121 unique taxa, 113 had information 

indicating whether they are native or introduced. Of 

these 113 species, 71 (63 percent) are native and 42 

(37 percent) are introduced. Thirteen of the introduced 

species are State-listed noxious weeds (Washington State 

Noxious Weed Control Board, 2011). The numbers of 

introduced species were highest in the shrub-emergent 

marsh transition and dunegrass vegetation types (20 and 

21 species, respectively) and lowest in the emergent marsh 

and riparian forest vegetation types (10 and 12 species, 

respectively; fig. 8.11). Differences among vegetation 

types were more pronounced when cover of native 

versus introduced species was considered. The relative 

cover of introduced species was highest in the shrubemergent marsh transition and dunegrass vegetation types 

(33 percent and 18 percent, respectively) and lowest in 

the emergent marsh, riparian forest, and riparian shrub 

vegetation types (1.9, 3.4, and 3.6 percent, respectively; 

fig. 8.11).

watac11-0558_fig8-10

0

2

4

6

8

10

12

14

16

18

Vegetation type

0

20

40

60

80

100

20

Riparian

Forest

Willow-Alder

Forest

Riparian

Shrub

Shrub-Marsh

Transition

Emergent

Marsh

Dunegrass

Plant cover, in percent Number of species

Tree 

Shrub 

Forb 

Graminoid 

EXPLANATION

B.

A.

Figure 8.10. Life form composition of vegetation, Elwha River 

estuary, Washington. (A) Contribution of different life forms 

to species richness in the six Elwha River estuary vegetation 

types described in this study (plot means + standard error [black 

whisker]). (B) Relative plant cover associated with different life 

forms in the six Elwha River estuary vegetation types described in 

this study (plot means + standard error [black whisker]).
Chapter 8

Elwha Estuary Vegetation Sampling Results Vegetation of the Elwha River Estuary 241

watac11-0558_fig8-11

Vegetation type

Riparian

Forest

(n=5)

Willow-Alder

Forest

(n=3)

Riparian

Shrub

(n=5)

Shrub-Marsh

Transition

(n=3)

Emergent

Marsh

(n=3)

Dunegrass

(n=3)

Number of species

0

10

20

30

40

50

Plant cover, in percent

0

10

20

30

40

50

Native

Relative cover introduced

Introduced

EXPLANATION

Figure 8.11. Number of native and introduced species and relative plant cover of introduced 

species in the six vegetation types described for the Elwha River estuary, Washington. 

Numbers of native and introduced species are cumulative across all plots in a particular 

vegetation type. Relative plant cover of introduced species is the mean + standard error (black 

whisker). 
242 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Wetland Indicator Status

Wetland indicator status 

information was available for 94 of the 

121 unique taxa. The average wetland 

indicator value associated with species 

present in plots was highest (least likely 

to occur in wetlands) for the dunegrass 

vegetation type, followed by the mixed 

Average wetland indicator value

Average cover-weighted wetland indicator value

EXPLANATION

Wetland indicator value

0

1

2

3

4

Vegetation type

Riparian

Forest

(n=5)

Willow-Alder

Forest

(n=3)

Riparian

Shrub

(n=5)

Shrub-Marsh

Transition

(n=3)

Emergent

Marsh

(n=3)

Dunegrass

(n=3)

Figure 8.12. Wetland indicator values of plants in the six vegetation types described for 

the Elwha River estuary, Washington. Lower values indicate a greater tendency to occur in 

wetlands. Light brown bars indicate the average (of all plots within a vegetation type) of the 

average wetland indicator value of all plants for which a value was available in each plot. 

Green bars indicate the average (of all plots within a vegetation type) of the average wetland 

indicator value of plants in a plot, by vegetation type, weighted by the relative cover of those 

plants. Black whiskers indicate one standard error. Plots from the cover-weighted calculations 

were excluded if plants without a known wetland indicator value comprised greater than 20 

percent of the plot’s relative cover, which included all of the dunegrass plots.

riparian forest and riparian shrub 

vegetation types (fig. 8.12). As would be 

expected, the emergent marsh vegetation 

type had the lowest value, and the 

shrub-marsh transition vegetation types 

had the second lowest value (fig. 8.12). 

The pattern of wetland indicator values 

weighted by relative cover of each 

species was similar (fig. 8.12).

Vegetation Types Along a 

Topographic Gradient

Consistent with the wetland 

indicator status results, average plot 

elevation above NAVD 88 was highest 

for dunegrass and mixed riparian forest 

(fig. 8.13). Willow-alder forest and 

riparian shrub plots were intermediate 

and shrub-emergent marsh transition 

and marsh plots were at the lowest 

elevations (fig. 8.13). 
Chapter 8

Elwha Estuary Vegetation—Discussion of Results Vegetation of the Elwha River Estuary 243

watac11-0558_fig8-13

Elevation above mean sea level, in meters

0

1

2

3

4

5

Vegetation type

Riparian

Forest

Willow-Alder

Forest

Riparian

Shrub

Shrub-Marsh

Transition

Emergent

Marsh

Dunegrass

Figure 8.13. Average plus standard error (black whisker) 

elevation of plots within the six vegetation types described 

for the Elwha River estuary, Washington. See the “Methods” 

section for a detailed description of topographic survey data 

collection.

Elwha Estuary 

Vegetation—

Discussion of Results

Species Richness and 

Vegetation Type Diversity

Despite its small size, the Elwha 

River estuary is quite diverse in terms 

of vegetation types present and species 

richness. 121 unique plant taxa in 

6 vegetation types were documented in 

2,200 m2 total (twenty-two 100 m2 plots) 

within 39.7 ha of land area within the 

Elwha estuary study area (fig. 8-1). This 

is the greatest plant species diversity 

yet documented, both in terms of total 

species richness and species richness 

within a particular vegetation type, 

within the admittedly sparse Pacific 

Northwest coastal wetland literature 

(MacDonald and Barbour, 1974; 

Brennan, 2007). Thom and others (2002) 

documented between 8 and 14 plant 

species per year in the 15 ha Elk River 

estuary (Washington Coast) over an 

11-year period following removal 

of a dike in seventy-two 1 m2 plots. 

Tanner and others (2002) documented 

61 unique plant taxa in the 23.7 ha 

restoration project area associated with 

the Spencer Island dike breaching in the 

Snohomish River estuary (central Puget 

Sound). Plant species richness varied 

by year, beginning with 37 species 

prior to dike removal in 1994, then 

dropping to a low of 14 species in 1995, 

and increasing to 38 by 1998. Most 

species observed in 1994 were within 

forested wetland plant communities (35 

species), whereas by 1998 most species 

occurred within emergent marsh plant 

communities. Plots varied in size and 

shape, so calculations of sampled area 

were not possible. Hutchinson (1988) 

sampled 17 intertidal delta marshes 

in the Strait of Georgia and the Puget 

Sound, not including those of the Strait 

of Juan de Fuca, and documented a total 

of only 80 plant species, two of them 

macroalgae. Of the sampled deltas, 

the Cowichan (32 species), Campbell 

(30), Fraser (28), and Skokomish (28) 

deltas had the greatest plant species 

richness. However, Hutchinson sampled 

only 1,810 m2 (905 1 × 2 m plots). The 

relatively high plant diversity present 

in the Elwha River estuary is striking, 

given that it historically and presently 

represents less than 1 percent of Salish 

Sea coastal wetlands (Collins and 

Sheikh, 2005). 

The relatively high species 

richness probably is a function of 

intense searching in a larger sample 

area (Stohlgren and others, 1997), 

as well as the presence of a greater 

diversity of vegetation types compared 

with other Pacific Northwest coastal 

wetland studies. For example, “mixed 

riparian forest,” “willow-alder forest,” 

and “riparian shrub” vegetation types 

may not have been sampled in some 

of the other studies. Based on cluster 

analyses, Hutchinson (1988) identified 

five classes of deltas and seven plant 

communities. All seven of Hutchinson’s 

plant communities would be classified 

as emergent marsh under our sampling 

scheme; all are graminoid-dominated or 

graminoid/forb co-dominated. No other 

types were sampled. Of his seven, two 
244 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

are possibly present within the Elwha 

estuary: Scirpus americanus-Scirpus 

maritimus and Juncus balticus-A. egedii. 

Burg and others (1980) identified 12 

plant associations and 24 plant species 

characteristic of those associations in 

the salt marshes of the Nisqually River 

estuary in southern Puget Sound. In 

their results, they did not include a full 

plant species list, so we cannot compare 

floristic diversity between our study and 

theirs. However, new vegetation studies 

of the Nisqually estuary are currently in 

progress, and the preliminary plant list 

includes 51 species (U.S. Geological 

Survey, 2009). Of the 12 associations 

they identified, 2 of them also could be 

within our study area: pure stands of 

Carex lyngbyei and C. lynbyei-Festuca 

rubra. These are the most productive 

plant associations that Burg and others 

(1980) sampled. The C. lyngbyei

association was the most productive 

per unit dry weight (1,390 g dry 

weight/ m2, contributing 6.7 percent 

total marsh production), followed by 

C. lynbyei-Festuca rubra (1,086 g dry 

weight/ m2, contributing 10.5 percent 

total marsh production). Both species 

are present within the Elwha estuary 

and were encountered in vegetation 

patches classified as emergent marsh or 

shrub-emergent marsh transition. The 

other plant associations they identified 

are much more characteristic of low 

tidal salt marshes, which are not present 

within our study area. 

A somewhat unusual aspect of 

the Elwha estuary vegetation is the 

lack of a well-developed salt marsh 

community, given the historic extent 

of salt marshes in the Salish Sea region 

and their representation in Pacific 

Northwest coastal wetland literature. 

Nor does an Elwha River salt marsh 

community appear to have been present 

historically, which Collins and Sheik 

(2005) attributed to the high wave 

energy environment on the Strait of Juan 

de Fuca coast. Characteristic salt marsh 

taxa, including Salicornia virginica

(pickleweed), Distichlis spicata

(saltgrass), and Triglochin maritima

(seaside arrowgrass) are entirely absent 

from our sample plots in the Elwha 

estuary (table 8.2).

Introduced Species

Although the literature on estuarine 

vegetation vulnerability to invasion is 

not well developed, riparian systems 

have been shown in a number of studies 

to harbor a greater number of introduced 

species than adjacent upland ecosystems 

(DeFerrari and Naiman, 1994; Stohlgren 

and others, 1998; Brown and Peet, 

2003), largely due to high levels of 

disturbance, rapid seed dispersal 

potential, and high resource availability. 

The number of introduced species and 

the proportion of the local flora in our 

study exceed that reported in several 

other studies of riparian ecosystems 

from around the world (DeFerrari and 

Naiman, 1994; Planty-Tabacchi and 

others, 1996; Hood and Naiman, 2000; 

Brown and Peet, 2003). For example, 

DeFerrari and Naiman (1994) reported 

species richness and cover of introduced 

(exotic) plants in riparian communities 

along the Dungeness and Hoh Rivers on 

the Olympic Peninsula, Washington, and 

found 40 and 30 species, respectively, 

comprising 28 percent of the flora in 

both systems. These lower values were 

found despite the fact that they sampled 

approximately three times as many 

plots (plot size was 50 m2). PlantyTabacchi and others (1996) reported 

that 30 percent of 851 total species 

found along three drainages in western 

Oregon (Willamette River, MacKenzie 

River, Lookout Creek) were introduced. 

Thus, our finding of 37 percent of the 

Elwha estuary flora as introduced is 

higher than commonly reported and is of 

potential concern to resource managers 

(Woodward and others, 2008). Physical 

habitat changes expected following dam 

removals on the Elwha could increase 

physical disturbance and perhaps 

facilitate the spread of some of these 

taxa, as is projected further upstream in 

the Elwha watershed (Woodward and 

others, 2011).

Dam Removal Context

Removal of the two dams on the 

Elwha River is expected to result in the 

release and transport of sediment and 

large woody debris trapped behind the 

reservoirs to sediment-starved river 

reaches downstream (Konrad, 2009; 

Czuba and others, 2011, chapter 2, this 

report). Both of these inputs could lead 

to higher rates of sediment deposition, 

increased channel dynamics (Draut and 

others, 2011; Warrick and others, 2011, 

chapter 3, this report) and associated 

vegetation change (Shafroth and others, 

2002; Kloehn and others, 2008; Naiman 

and others, 2010). Maximum depth 

of sediment deposition in the channel 

bed in the lower Elwha River near 

the estuary is expected to be less than 

1 m (Konrad, 2009; Czuba and others, 

2011, chapter 2, this report). We are not 

aware of any predictions of flood plain 

aggradation depth, though it might be 

expected to be relatively high in reaches 

with relatively low gradients, and broad 

flood plain and island complexes, such 

as those in the first few kilometers 

upstream of the estuary (Konrad, 2009; 

Draut and others, 2011). Flood plain 

aggradation rates and depths will depend 

largely on the interaction of overbank 

flooding (including flood magnitude 

and duration), suspended sediment 

concentration, and flood plain roughness 

(including the density and structure of 

riparian vegetation).

Most research in the Pacific 

Northwest has focused on characterizing 

tidal wetlands (Burg and others, 1980; 

Hutchinson, 1988) or their responses 

to restored tidal influence from dike 

removals (Thom and others, 2002; 

Tanner and others, 2002). A few 
Chapter 8

Vegetation of the Elwha River Estuary Acknowledgments 245

studies from the Pacific Northwest 

have examined interactions between 

sediment, wood, and estuary vegetation. 

The addition of sediment on subsided 

intertidal areas accelerated marsh 

vegetation colonization in Coos Bay’s 

south slough, Oregon (Cornu and Sadro, 

2002). Hood (2010) described feedbacks 

between sediment deposition-induced 

channel meandering and marsh island 

vegetation development in the Skagit 

River delta, Washington. Hutchinson 

(1988) characterized morphology, 

physical environment, and vegetation, 

and concluded that flow volume and 

discharge regime of contributing rivers, 

along with the exposure of the delta 

fronts, accounted for much of the 

variation in delta vegetation across the 

region. Large woody debris appears 

to strongly influence the distribution 

of some species, such as Myrica gale

(sweetgale), a nitrogen-fixing shrub, in 

the Skagit River estuary (Hood, 2007). 

More generally, the influence of large 

woody debris on channel and vegetation 

dynamics in Pacific Northwest river 

systems is well documented (for 

example, Abbe and Montgomery, 2003).

Pacific Northwest tidal wetlands 

appear to respond rapidly to changes to 

key physical conditions, with elevation 

above mean sea level and tidal influence 

strongly driving changes in vegetation 

patterns. Bucknam and others (1992) 

documented shifts in wetland types 

at two sites on Bainbridge Island, 

Washington (Restoration Point and 

Winslow). At Restoration Point, a 

tidal flat was abruptly uplifted about 

1,700 years ago, rapidly converting it 

to freshwater swamps and meadows, 

with no intermediate, brackish stages. 

Conversely, a freshwater wetland at 

Winslow was inferred to have been 

only slightly elevated above mean 

sea level before being converted to 

more saline vegetation types as a 

result of subsidence. Rapid vegetation 

change also occurred following dike 

breaching projects at the Elk River 

estuary on Washington’s southwest 

coast (Thom and others, 2002) and 

Spencer Island in the Snohomish River 

estuary, Puget Sound (Tanner and 

others, 2002). Within about 5 years 

of dike breaching and associated 

reconnection to tidal inundation, most 

of the Elk River estuary changed from 

a Phalaris arundinacea-dominated wet 

pasture to a low-elevation salt marsh 

community dominated by Distichlis 

spicata (salt grass) and Salicornia 

virginica (pickleweed). High coastal 

marsh, dominated by Deschamspia 

caespitosa (hairgrass) and D. spicata, 

was also present but much less 

abundant (Thom and others, 2002). In 

contrast, P. arundinacea-dominated 

communities on Spencer Island either 

converted to mudflats or to a different 

freshwater vegetation type (Tanner and 

others, 2002). Experimental additions 

of sediment to an Oregon estuary 

resulted in different marsh vegetation 

composition and development rates on 

surfaces that differed in elevation above 

sea level (Cornu and Sadro, 2002). 

Thus, rapid changes to the physical 

environment associated with dam 

removals could prompt rapid vegetation 

changes in the Elwha River estuary.

Summary

Six primary vegetation types were 

identified in the Elwha River estuary: 

mixed riparian forest, willow-alder 

forest, riparian shrub, shrub-emergent 

marsh transition, emergent marsh, and 

dunegrass. These were identifiable 

on high resolution aerial imagery and 

were confirmed by the composition of 

plants in vegetation plots and grouping 

of plots determined by a non-metric 

multi-dimensional scaling ordination. 

Overall species richness was 

quite high in the Elwha River estuary; 

we identified 121 unique taxa in 22, 

100 square meter plots. Between 30 

and 52 plant taxa occurred within each 

vegetation type, typically including 

several taxa unique to each type. 

Native species predominated, but 

approximately 37 percent of taxa were 

introduced. Introduced species were 

most common and abundant in the 

shrub-emergent marsh transition and 

dunegrass vegetation types. Plants in 

lower elevation plots were most likely 

to be categorized as obligately or 

facultatively occurring in wetlands.

Future analyses will focus on 

relating the distribution of patch types 

and patterns of species richness with 

key physical processes in the Elwha 

River estuary, such as hydrologic 

and sediment dynamics, and salinity 

regimes. Changes to these processes 

and associated disturbance regimes 

and environmental gradients following 

dam removals could change parts of the 

Elwha estuary vegetation. Quantitative 

understanding of how physical processes 

and environmental gradients interact 

with species dispersal, establishment, 

and survival would greatly improve 

our understanding of how Elwha River 

estuary vegetation may respond to 

dam removals, and might ultimately be 

linked to physical process models to 

predict biological responses over time.

Acknowledgments

This work could not have been 

completed without key contributions by 

numerous collaborators. In particular, 

we thank Ian Miller for conducting 

some of the RTK-DGPS topographic 

surveying, Rebecca Paradis for 

tireless assistance with vegetation plot 

sampling, Daniel Bennett for help with 

various field tasks, Randall McCoy 

for multi-faceted assistance with aerial 

photography, Jeff Duda for assistance 

with the ordination analysis, Jim 

Bromberg for assistance with finalizing 

figures, Tammy Fancher for assistance 

with preparation of figure 1, and Fred 

Sanford for inspiration. Thanks to 

Andrea Woodward and Rebecca Brown 

for helpful discussions about this work. 
246 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

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removal—Management perspective: 

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Woodward, A., Torgersen, C., 

Chenoweth, J., Beirne, K., and 

Acker, S., 2011, Predicting spread of 

invasive exotic plants into de-watered 

reservoirs following dam removal on 

the Elwha River, Olympic National 

Park, Washington: U.S. Geological 

Survey Open-File Report 2011-1048, 

64 p. (Also available at http://pubs.

usgs.gov/of/2011/1048/.)
248 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

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Chapter 1 Chapter 9

9

Chapter

Summary and Anticipated 

Responses to Elwha River 

Dam Removal

By Guy Gelfenbaum, Jeffrey J. Duda, and 

Jonathan A. Warrick

Abstract

Starting in September 2011, the removal 

of two large dams on the Elwha River will 

begin an unprecedented river restoration 

project because of the size of the dams, 

the volume of sediment released, the 

pristine watershed upstream of the dam 

sites, and the potential for renewing 

salmon populations. Ecosystem studies 

of the Elwha watershed indicate that the 

effects of almost 100 years of damming 

are measurable and of consequence. 

These effects include smaller spawning 

salmon populations, massive sediment 

retention behind the dams, coarsening 

of the riverbed downstream of the dams, 

low nutrient concentrations in the river 

waters, and coastal erosion that has 

accelerated markedly with time. During 

and after the removal of these dams, 

the Elwha River and its ecosystems will 

be altered by a renewal of sediment 

discharge downstream of the dams and 

a reintroduction of salmon spawning 

upstream of the dams. This chapter 

summarizes the pre-dam and current state 

of the river and its coastal ecosystems, 

and describes the likely outcomes of 

river restoration on the Elwha River 

ecosystems.
250 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Introduction

The removal of two large dams on the 

Elwha River presents an opportunity to restore 

natural fluvial processes to a mostly pristine 

watershed and rebuild iconic salmon runs. 

After removal of the dams, salmon populations 

are expected to increase dramatically over 

their present numbers (U.S. Department of 

the Interior, 1995a; Ward and others, 2008), 

restoring several important runs to this Pacific 

Northwest river that once produced large 

numbers of fish (U.S. Department of the Interior 

and others, 1994; Wunderlich and others, 

1994). The removal of the Elwha and Glines 

Canyon Dams also presents an opportunity 

to restore beaches along the Strait of Juan de 

Fuca with sediment that has been trapped for 

nearly a century by dam-impounding reservoirs 

(fig. 9.1). Coastal erosion of as much as 22 m 

over the past 16 years east of the river mouth is 

encroaching on the Lower Elwha Klallam Tribal 

reservation (Warrick and others, 2009), and on 

vital wetlands and estuaries that provide critical 

habitat for rearing juvenile salmon.

Although expectations are high for 

returning salmon populations to the river, 

restoring river function, and restoring beach 

sediment supply, a number of uncertainties are 

associated with the restoration of the Elwha 

River ecosystem. The rebuilding of salmon 

populations, for example, is of particular 

interest. The spatial and temporal patterns 

of reemerging life-history diversity and 

competition among natural- and hatchery-origin 

fish are complex and not fully understood. 

However, these processes ultimately will 

affect salmon recolonization, future population 

status (Brenkman and others, 2008; Pess and 

others, 2008), and will be a large determinant 

of ecosystem restoration success. Similarly, 

the supply of sediment to the lower river and 

beaches downstream of the dams is uncertain. It 

is not known how much of the sediment trapped 

behind the dams will be eroded and transported 

downstream. Of the sediment that is transported 

downstream, it is not known how much will be 

transported all the way to the Strait of Juan de 

Fuca, and if that amount will be enough to slow 

or stop the coastal erosion. 

watac11-0558_fig9-01

Elwha River Port Angeles

Ediz Hook

Elwha

River

PACIFIC 

OCEAN

Salish Sea

fig. B

Strait of Juan deFuca

Shaded relief from Puget Sound LIDAR Consortium

Base modified from U.S. Geological Survey 1:100,000-scale digital data

-30

-60

-90

-120

-150

-180

0

136

134

132

130

128

138 305 310

Easting, in kilometers

290 295 300 315

125° 123°

48°

49°

47°

A.

B.

Figure C

C.

Aerial photography from 2006 U.S. Department of Agriculture NAIP

Freshwater 

Bay

Elwha

Dam

Glines

Canyon

Dam

Northing, in kilometers

Elevation, in meters

Levee

Levee

Dudley 

Pond

Figure 9.1. The coastal setting of the Elwha River, Washington.
Chapter 9

Summary and Anticipated Responses to Elwha River Dam Removal Introduction 251

The return of fish populations and 

restoration of sediment supply will 

cause numerous changes to the Elwha 

River ecosystem. For example, large 

amounts of silt and sand, along with 

gravel and cobbles may be deposited in 

the bed of the lower river, which would 

alter the grain-size distribution in the 

riverbed, the structure of pools and 

riffles, and the suitability of spawning 

habitat. The return of large numbers of 

fish to the lower river and estuary may 

alter nutrient concentrations, thereby 

changing the chemistry, and ultimately 

the productivity, of these systems. The 

fining of bed sediments may alter the 

suitability of the ecosystem for kelp 

species if large amounts of fine sediment 

are delivered offshore. The response 

of ecosystem processes, structure, 

habitat, and the biological resources they 

support will be complex, and are largely 

unpredictable. The scientific knowledge 

of many of these ecosystem linkages 

is limited and the results of this largescale restoration project are uncertain, 

which highlights the need for ongoing 

multidisciplinary scientific research.

The scale of the Elwha River 

Restoration Project is unprecedented. 

The Elwha and Glines Canyon Dams 

will be the largest dams removed in the 

United States, and to our knowledge, 

the world. Moreover, the removal 

of these dams will cause the largest 

controlled release of sediment into 

a river and adjacent marine waters. 

This project represents one of the 

best remaining opportunities in the 

conterminous United States to restore 

salmon in large portions of a watershed 

that are protected as wilderness. 

The Elwha River dam-removal and 

ecosystem-restoration project also is 

an opportunity for increasing scientific 

understanding (Gelfenbaum and others, 

2006). Billions of dollars are spent 

on ecosystem restoration around the 

nation, sometimes with highly uncertain 

outcomes. With the large numbers of 

dams around the nation reaching the 

end of their constructed lifespan or 

economic productivity, the impetus 

for dam removal is accelerating and 

becoming much less controversial than 

in the past (Hart and others, 2002; Heinz 

Center, 2002). Moreover, relicensing 

efforts for existing dams have a critical 

need for the best available sedimentand river-response data to assess the 

costs and benefits of dam removal 

compared with continued operation. 

Meaningful monitoring efforts are 

needed to document ecosystem recovery 

and to assess the benefits of restoration 

expenditures (Duda and others, 2008). 

As noted in the previous chapters 

of this report, as well as numerous 

other reports documenting scientific 

investigations of the Elwha River 

basin, the Elwha River ecosystem 

has been affected by the Elwha and 

Glines Canyon Dams, and removal 

of those dams will affect it further. 

However, it is also likely that dam 

removal and ecosystem restoration 

may not simply restore the ecosystem 

to its pre-dam state, but may instead 

result in something new. The concept 

of “alternative stable states” proposes 

that there are suites of abiotic and 

biotic conditions in an ecosystem 

that lead to particular assemblages of 

uniquely adapted species. As the system 

is perturbed with small changes, the 

density or species composition of the 

system may temporarily change, but 

will drift back into the equilibrium 

state when the perturbation ceases. 

Larger perturbations that exceed a 

given threshold, on the other hand, can 

lead to a phase shift in the system that 

gives rise to a new stable state (Holling, 

1973; Bender and others, 1984; Beisner 

and others, 2003). Due in part to the 

steepness of the basin, and the proximity 

between the upper reaches of the 

river and the coast, the dam removal 

project will create short duration, high 

intensity changes and long term, low 

intensity ecosystem changes. It may be 

that the high sediment load during and 

following dam removal will be large 

enough to change the existing aquatic 

and terrestrial flood plain ecosystems 

into a new stable state. This is certainly 

the case for the former reservoir sections 

that will change from lentic (lake-like) 

to lotic (river-like) water bodies. In the 

years following dam removal, as more 

coarse-grained sediments arrive from the 

former reservoirs, this lower intensity 

stressor may or may not change the 

ecosystem. It is not known if multiple 

phase shifts will arise in the Elwha River 

after dam removal, or if the ecosystem 

will settle into a new equilibrium 

following the high intensity changes 

shortly after dam removal. 

Additionally, the large numbers 

of salmon anticipated to return to the 

river and the large volume of sediment 

expected to be mobilized after dam 

removal, will create a system response 

with large “signals” relative to the 

“noise” of natural background changes. 

For these reasons, a comprehensive 

research and monitoring program such 

as that described in this report will 

have a high likelihood of successfully 

documenting ecological changes caused 

by dam removal.

A comprehensive description of 

the ecosystem response to dam removal 

will require the monitoring of multiple 

interrelated variables across a varied 

geographic domain that will depend 

on the sediment grain size mobilized 

(Woodward and others, 2008). For 

example, ecosystem responses will vary 

across the different sections of the river 

(upstream of, between, and downstream 

of the dams), the reservoirs, beaches, 

and the adjacent nearshore zone of the 

Strait of Juan de Fuca. The response 

in each of these domains will depend 

on the grain size of the sediment that 

accumulates there, which may include 

very fine-grained (silt and clay) to very 

coarse-grained (cobble and gravel) 

sediments. Sediment accumulations may 

ultimately affect each of the relevant 

ecosystem components, including: 
252 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

(1) processes such as sediment 

transport, nutrient dynamics, and 

spawning; (2) habitat structure defined 

by substrate type, channel morphology, 

flow velocity, and water depth; and 

(3) biological function such as species 

assemblages into communities of, 

for example, invertebrates or riparian 

vegetation. Ultimately, the effects on 

these ecosystem processes, habitats, and 

biological functions will influence the 

economic, cultural, and societal benefits 

that these ecosystem services provide. 

Not all components of the ecosystem 

will respond on the same time scale. 

The response will vary with time, from 

pre-dam removal, during removal 

(1–3 years), post-removal (3–7 years), 

and long-term (7–20 years). Some 

responses will occur quickly, and others 

will take much longer. 

One of the primary purposes of 

this report is to document the physical 

and biological conditions of the lower 

Elwha River and coastal ecosystems in 

anticipation of the large-scale changes 

that may be caused by dam removal. 

This summary chapter (1) provides 

a summary of the important findings 

or characteristics of the lower 

Elwha River and nearshore zone as 

described in the previous chapters 

of this report, (2) describes linkages 

among the components to form a 

system perspective, and (3) describes 

predictions of the lower river and coastal 

physical and biological responses to 

dam removal. Although scientists and 

managers may strive for quantitative 

predictions of the responses to dam 

removal, at this stage, many predictions 

will be qualitative and conceptual. The 

remainder of this summary chapter 

is organized by geographic domain, 

starting with the lower river and 

estuary, then moving to the beaches 

and nearshore. Within each geographic 

domain, the important physical and 

biological characteristics of the 

ecosystem, as they exist prior to dam 

removal, and how they might change 

during and after dam removal will be 

described.

Lower Elwha River and 

Estuary

The 7.8-km-long lower Elwha 

River, between Elwha Dam and the 

Elwha River estuary, is characterized 

by various morphologies, including a 

narrow bedrock gorge, reaches with 

multiple channels and large vegetated 

islands, and reaches with a single 

meandering channel. In the upper 

1.3 km of the reach, the channel is 

confined to a narrow bedrock gorge, 

limiting channel migration and sediment 

storage. The last 6.5 km before the river 

meets the sea is characterized by an 

‘anabranching’ morphology that is the 

result of a unique combination of river 

gradient, flow conditions, large woody 

debris, and sediment supply, which 

are functional attributes associated 

with extensive channel switching, 

or avulsions. Detailed analysis of 

channel position over the last century 

from historical aerial photographs 

documented that the lower river channel 

has moved tens to hundreds of meters 

by gradual channel migration and by 

more abrupt avulsions (Draut and others, 

2008, 2011). Avulsions are thought to 

occur when obstacles, such as piles of 

woody debris, temporarily block flow, 

as may have happened in winter floods 

of 1979 and 1980, forcing the river to 

cut a new path downstream. Repeated 

avulsions result in the formation of 

numerous interconnected channels, 

backwaters, and side channels, which 

provide important biological functions, 

a dynamic lotic ecosystem, and shifting 

riparian and estuarine habitats for many 

plant and animal species (Beechie and 

others, 2006; Tooth and others, 2008).

The hydrology of the lower river is 

typical for moderately sized watersheds 

in the Pacific Northwest, with the largest 

peak flows in winter due to heavy 

rainfall and smaller peak flows caused 

by spring snowmelt. The lowest flows 

of the year occur from August through 

October. Because the dams were built 

primarily for power generation and were 

typically operated as run-of-river, the 

dams have had little effect on the duration 

and magnitude of peak flows (Duda and 

others, 2011a, chapter 1, this report). 

Dam operations have had moderate effect 

on some aspects of the hydrograph, such 

as low flows and the rates at which flows 

increased and decreased, and they have 

had considerable effects on the supply of 

sediment and of large woody debris.

Sediment supply to the lower Elwha 

River from upstream has been reduced 

by the two dams, except for small 

quantities of fine-grained suspended 

sediment that bypasses the dams during 

floods. However, the lower river has 

compensated somewhat for the loss of 

upstream sediment supply by recruiting 

sediment from within its flood plain. 

Over the last century about 19 million 

cubic meters of sediment has been 

trapped behind Elwha and Glines Canyon 

Dams (U.S. Department of the Interior, 

1995b; Bountry and others, 2010; Czuba 

and others, 2011, chapter 2, this report). 

Deltas formed at the inlets of Lake Mills 

and Lake Aldwell (combined) consist of 

about 50 percent coarse sand and gravel, 

and about 50 percent fine-grained silt and 

clay. This is the largest known reservoir 

sediment volume known to be associated 

with any dam removal project. 

Reductions in the upstream 

sediment supply have resulted in bed 

coarsening and armoring downstream 

of the dams (Pohl, 2004; Kloehn and 

others, 2008, Morley and others, 2008; 

Draut and others, 2011). Additionally, 

Kloehn and others (2008) determined 

that the proportion of the flood plain 

older than 75 years, as determined 

by vegetation mapping and historical 

aerial photographs, increased with time 

downstream of the dams over the last 

half century, whereas the proportion of 

younger surfaces decreased with time. 

The conclusion drawn by Kloehn and 

others (2008) is that the reduced sediment 

supply has increased the stability of 

the river flood plains downstream of 

the dams. Kloehn and others (2008), 

however, did not collect channel 

stability data directly and an alternative 
Chapter 9

Summary and Anticipated Responses to Elwha River Dam Removal Lower Elwha River and Estuary 253

explanation for the aging vegetation 

population could be changes in logging 

practices. Draut and others (2011) 

refined the characterization of the lower 

river, having determined that the upper 

reaches of the lower river were more 

stable because of bed armoring caused 

by lack of sediment supply. However, 

mobility in the lower reaches of the 

river was similar to the unregulated river 

upstream of the dams. Despite the lack 

of sediment supply from upstream of the 

dams, the lowermost river recruits enough 

sediment from bank erosion to maintain 

near-natural mobility of the channel in 

the lower reaches before the estuary 

(Draut and others, 2011). The response 

of the Elwha riverbed generally is 

consistent with other rivers with reduced 

sediment supply downstream of dams 

(Williams and Wolman, 1984; Collier and 

others, 1996; Pizzuto, 2002; Grant and 

others, 2003).

The lower Elwha River merges 

into a geomorphically diverse estuarine 

complex. The estuary includes the river 

mouth, several coastal ponds on either 

side of the river mouth, and several small 

side channels that connect these water 

bodies (fig. 9.1C). Within the estuary, 

river water, seawater, and groundwater 

mix to provide brackish conditions and 

habitat for young salmonids and other 

fish and wildlife species (Magirl and 

others, 2011, chapter 4, this report; Duda 

and others, 2011b, chapter 7, this report). 

The zone of saltwater-freshwater mixing 

varies as a function of tidal stage, river 

discharge, and storm surges, as well as 

channel morphology.

The estuary has a broad suite of 

vegetation types, including (1) mixed 

riparian forest, (2) young willow/alder 

forests, (3) riparian shrub, (4) shrub–

emergent marsh transition, (5) emergent 

marsh, and (6) dunegrass. It contains a 

diverse assemblage of plant species, as 

Shafroth and others (2011, chapter 8, 

this report) found more than 120 plant 

species during surveys of each of the 

vegetation types. The riparian shrub 

and shrub–emergent marsh transition 

vegetation types had the highest total 

richness (52 species), although the 

emergent marsh vegetation type had the 

lowest total richness (31 species). About 

one-third of plant species currently 

around the estuary are non-native. 

The estuary is tidally influenced 

and brackish, although water level and 

salinity patterns across this system vary 

in space and time. Numerous channels, 

which play an important role in estuarine 

circulation, regulate the exchange of 

water between the river mouth and the 

coastal ponds. This is determined by the 

differences in the water levels, salinity, 

and temperature between the eastern 

and western areas of the estuary across 

all seasons. Dudley Pond is contained 

behind a flood-control levee on the west 

side of the river mouth. Lacking a direct 

surface-water connection to the river, 

the pond is less saline, warms to higher 

temperatures, and has smaller variability 

in water levels compared to the lentic 

waters of the eastern estuary that contain 

numerous surface water connections 

(Magirl and others, 2011, chapter 4, this 

report; fig. 4.3). The morphology of the 

interestuarine channels does change 

with time as sediment is moved in the 

river mouth by river discharge events 

and coastal waves. High flows in the 

river also alter the water conditions in 

the estuary by raising water levels and 

flushing out saline water for as long as 

several days (see example in Magirl and 

others, 2011, this report, fig. 4.7).

The removal of Elwha and Glines 

Canyon Dams will not instantaneously 

result in resupply of sediment to the 

lower river and coast. Instead, the 

dam removal process itself will take 

several years, with complete removal 

anticipated in about 2.5 years after 

deconstruction commences (Duda and 

others, 2011a, chapter 1, this report). 

While the dams are being removed, it 

is anticipated that some fine-grained 

sediment will be remobilized from 

reservoir deposits, especially during 

winter and spring floods. Most of 

the fine sediment will be transported 

through the lower river and enter the 

nearshore region (Randle and others, 

2006), to be dispersed by tidal currents 

and waves (fig. 9.2). A much smaller 

amount of the fine sediment will be 

deposited in the flood plain of the lower 

river, although fine-sediment deposition, 

where it occurs, likely will influence the 

hydrology, vegetation, and habitats of the 

river flood plain.

The rate of transport and timing 

of arrival of coarse-grained bedload to 

the lower Elwha River will depend on 

the number, magnitude, and duration 

of floods in the years during and after 

dam removal (Randle and others, 2006; 

Konrad, 2009). Coarse-sediment release 

may begin during the second winter 

season after the start of deconstruction, 

although large quantities of bedload 

probably will not pass the Glines Canyon 

Dam site until the winter of the final year 

of the project (2013–14). This enhanced 

bedload transport will continue down the 

middle reach of the river (between the 

two dams) for another 2–5 years after 

complete removal of Glines Canyon Dam 

(Randle and others, 2006; Czuba and 

others, 2011, chapter 2, this report). 

As sediment is transported 

downstream of the reservoir sites, 

alluvial sections of the Elwha River 

will accumulate sediment and aggrade 

(fig. 9.3). Sand and gravel is expected 

to fill pools, and may cause more active 

channel migration and channel avulsions. 

Because of aggradation and fining of 

material in the lower river, the channel 

could see increased braiding, at least 

temporarily (Draut and others, 2011). 

This likely would result in a straighter 

channel alignment (steeper slope), which 

is consistent with a braided channel 

planform (Randle and Bountry, 2008). In 

the decades after dam removal, Kloehn 

and others (2008) suggest the rate of 

channel migration may increase in the 

river sections below the dams. Draut and 

others (2011) determination of local fine 

sediment supply along the flood plain of 

the lower river indicates that the rate of 

channel migration may remain stable over 

the long term.
254 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

In the lower river, the initial increases in sediment load 

likely will disrupt aquatic and riparian ecology. Vegetation 

changes related to dam removal will depend largely on how 

much an influx of large woody debris and sediment alters the 

distribution and character of geomorphic surfaces, in particular 

estuarine shorelines (fig. 9.4). Another factor relates to the 

spatial and temporal nature of tidal connections and whether 

or not the connections change as the river mouth reconfigures 

after dam removal. These connections affect water level 

fluctuations and salinity levels, which likely would influence 

the “emergent marsh” and “shrub-emergent marsh transition” 

vegetation types. Additionally, any changes that appreciably 

alter the hydrologic connections between the river and estuary 

or the sedimentation and turbidity in estuarine habitats could 

affect the timing and habitat use patterns of migrating juvenile 

salmonids, as well as the resident fish assemblage of the 

estuary (Shaffer and others, 2009; Duda and others, 2011b, 

chapter 7, this report).

As sediment deposition and incorporation of largewoody debris and organic matter occur, the quantity and 

quality of fish habitat is expected to increase downstream of 

the dams (Woodward and others, 2008). The major ecological 

change in the lower river and estuary likely will result from 

the return of large numbers of fish. If recolonization of upper 

areas of the watershed causes salmon to return to the river 

in numbers larger than current populations, as projections 

suggest, then the nutrient concentrations in the river and 

estuary may change at least during some parts of the year. 

Figure 9.2. Conceptual sediment budget for fine and coarse sediment stored in the two Elwha River 

reservoirs during the first 3 years after dam removal, Elwha River, Washington. (After numerical modeling 

simulations by Randle and others, 1996). The range of values presented in this figure show the variation 

in simulated output of four contrasting hydrologic scenarios. Fine and coarse sediment separated by the 

grain-size threshold of 0.063 millimeters.

watac11-0558_fig9-02

6.5

1.0 – 2.0

7.0

3.7 – 4.3

neg.

3.7 – 4.3 

6.5

EXPLANATION

1 million cubic meters

Discharge to ocean

Initial storage in reservoir

Erosion into river

Flood-plain and river 

sedimentation

Fine sediment Coarse sediment

Sediment volume, in 

millions of cubic 

meters

neg. Negligible

0.4 – 1.0

0.5 – 1.5
Chapter 9

Summary and Anticipated Responses to Elwha River Dam Removal Lower Elwha River and Estuary 255

watac11-0558_fig9-03

A. Short-term (3 year) aggradation 

B. Long-term (50 year) aggradation 

Distance from the river mouth, in miles

Elevation, in feet above the

North American Vertical Datum of 1988

0

20

40

60

80

100

0

20

40

60

80

100

Initial river profile 

(before dam removal) 

Elwha 

Dam site

Elwha 

Dam site

River 

mouth

River 

mouth

Sedimentation 

0 1 2 3 4 5

0 1 2 3 4 5

A. Current estuary B. Potential future estuary 

Single 

channel

Coastal 

waters

Pond

Pond

Levee

Creek

Multiple 

channels

Estuary channels 

and ponds

Creek

Delta progradation

Figure 9.3. Schematic cross sections showing simulated response of the elevation to increased sediment loads after 

dam removal, Elwha River channel, Washington. (After Randle and others, 1996). Results shown for (A) short-term response 

following 3 years of renewed sediment supply and (B) long-term response after 50 years.

Figure 9.4. Schematic diagrams showing the (A) current estuary morphology and (B) potential 

morphologic changes to the estuary after several decades following dam removal and lower river 

sedimentation. The future changes to the estuary have not been predicted and therefore will not 

precisely mimic the patterns shown in (B); however, the future changes likely will exhibit many of the 

qualities shown in (B) such as multiple channels and delta progradation.
256 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

If phosphorous and nitrogen limit the biomass of primary 

producers in the Elwha River ecosystem, then increases in 

these nutrients may have important implications. Currently, 

the river is classified as oligotrophic (Munn and others, 

1999; Duda and others, in press), and any increase in nutrient 

concentrations could significantly change the aquatic ecology 

of the river and estuary. Based on estimates of future salmon 

returns following full recovery, 1,275–10,900 kg of nitrogen 

and 210–1350 kg of phosphorous derived from salmon could 

be put into the river annually (estimates based on assumptions 

of Munn and others, 1999, and projected spawners presented 

by Ward and others, 2008). Although it is not likely that 

increased numbers of salmon will cause increases in dissolved 

water-column nutrients because of rapid flushing during the 

high flow season, salmon-derived nutrients may enter aquatic 

and riparian foodwebs through direct consumption by fish 

and aquatic invertebrates, or by indirect pathways like the 

guts of scavengers. This could provide temporal increases in 

the biomass and growth rates of resident biota (for example, 

Schuldt and Hershy, 1995; Bilby and others, 1996; Wipfli and 

others, 1998; Chaloner and Wipfli, 2002; Duda and others, 

in press).

Elwha River Beaches and Nearshore

The beaches and delta adjacent to the mouth of the 

Elwha River are the product of geomorphic processes that 

have continually formed and modified these landforms over 

multiple millennia. These processes include tectonic land-level 

changes, glaciation and related sea-level changes, erosion 

and sediment transport by the river, and coastal sediment 

transport by waves and currents (Warrick and others, 2011a, 

chapter 3, this report). Over the past century, the Elwha River 

beaches and nearshore have been modified by the presence 

of the two dams through a reduction in sediment delivery. 

Although coastal waters still receive sediment from the river, 

derived from erosion of channel-bank sediments deposited 

in the flood plains, most of the upriver sediment supply 

is intercepted by the reservoirs (Curran and others, 2009; 

Bountry and others, 2010). Several potential pathways for 

sediment discharged from the river exist, including along the 

beach, onto the nearshore submarine delta, and out into the 

deeper Strait of Juan de Fuca (fig. 9.5). The transport, fate, 

and implications of this sediment will be largely dependent on 

the physical processes and ecosystems within these settings 

(Miller and others, 2011; Warrick and others, 2011b, chapter 5, 

this report). 

Potential sediment 

pathways

Elwha River

Ediz Hook

Port 

Angeles

Figure 9.5. Schematic diagram showing the potential transport pathways for sediment offshore 

of the Elwha River mouth, Washington. Actual transport directions will be determined by 

sediment grain size and the strength, direction, and persistence of coastal currents and waves.
Chapter 9

Summary and Anticipated Responses to Elwha River Dam Removal Elwha River Beaches and Nearshore 257

Discharge from the Elwha River enters the Strait of 

Juan de Fuca as a buoyant freshwater plume, influencing the 

water properties of the nearshore from Freshwater Bay to 

Ediz Hook and Port Angeles. The position of the freshwater 

plume is largely determined by tidal conditions. Warrick 

and Stevens (2011) examined the behavior of the freshwater 

plume and determined that about 50 percent of the time the 

plume is directed toward the east, and about 40 percent of 

the time the plume maintains a radial spread from the river 

mouth. The remainder of the time, less than 10 percent, the 

river plume is directed toward the west (fig. 9.6). These 

tidally influenced river plume conditions have implications 

for sediment dispersal and nearshore conditions during and 

after dam removal. As millions of cubic meters of sediment 

are released from the reservoirs, the fine-grained material will 

be transported in the river plume and arrive in the nearshore. 

Warrick and Stevens (2011) suggest that the nearshore area 

within 1 km of the Elwha River mouth will see the greatest 

suspended sediment and turbidity levels. 

The reduced sediment supply to the Elwha River 

nearshore has changed the physical character of the delta and 

nearshore sea floor, which in turn has changed the biological 

assemblages dependent upon this habitat. The shoreline and 

submarine areas of the Elwha River delta are dominated by 

coarse sediment (gravel, cobbles, and boulders; Warrick and 

others, 2008; 2011b, chapter 5, this report). A time-series 

analysis of historical aerial photographs and contemporary 

topographic surveys of the beaches have identified significant 

coastal erosion since dam construction (Warrick and others, 

2009). Net erosion rates have increased over time, from 

0.8 m yr-1 from 1936 to 1990 to 1.4 m yr-1 during 1990–2006 

and local erosion rates as much as 3.8 m yr-1 during 2004–07 

(Warrick and others, 2009). It is uncertain whether a lack 

of fine sediment supply from the river also has resulted in a 

coarsening of the beaches over time.

These physical changes have influenced the plants and 

animals living in the nearshore environment. Recent scuba 

dive surveys (Rubin and others, 2011, chapter 6, this report) 

determined that a species-rich and biologically diverse 

community that included 10 kelp species, each with different 

growth forms and habitat affinities, inhabited the Elwha 

River nearshore. Community structure, including density, 

taxa richness, and habitat associations, was controlled in part 

by substrate composition, seafloor relief, and depth. Taxa 

richness (total number of kelp, invertebrate, and fish taxa) 

was more strongly associated with seafloor relief than with 

substrate type, although because relief usually was present in 

the form of scattered boulders perched on mixed sand, gravel, 

and cobble substrate, substrate also indirectly contributed to 

this relation. On average, 12 (59 percent) more taxa occurred 

where boulders were present compared to areas lacking 

boulders but with otherwise similar conditions. 

watac11-0558_fig9-06

50 percent

41 percent

9 percent

A. Eastward

B. Radial

C. Westward

Relative 

frequency

Figure 9.6. Schematic diagrams showing 

the behavior of the buoyant coastal plume of 

the Elwha River, Washington. (After Warrick 

and Stevens, 2011). The plume is bent toward 

the east (A) and west (C) during strong tidal 

currents, and is radial (B) during weak currents. 

Oceanographic observations suggest that the 

plume is bent toward the east more frequently 

than toward the west.

Four main species-habitat associations were identified 

in the Elwha River nearshore zone. The highest kelp density 

and taxa richness were in bedrock/boulder reefs, and were 

characterized by a surface canopy of bull kelp and a secondary 

canopy of perennial kelp 1–2 m above the seafloor. Mixed 

sand and gravel-cobble habitats with moderate relief had the 

highest density of invertebrates and a taxa richness nearly 

as high as in bedrock/boulder reefs. Mixed sand and gravelcobble habitats with low relief were areas lacking in boulder 

cover (which generally reduced relief scores and excluded 

species that preferred seafloor relief) supported a moderate 

density of kelp (primarily annual species with blades close 

to the seafloor) and the lowest invertebrate density among 

the four habitat types. Sand habitats in localized sand bodies 

were limited in extent. These sandy areas had the lowest 

kelp density and kelp taxa richness, with a moderate density 

of invertebrates. Sandy substrate along the west side of 

Freshwater Bay supported eelgrass meadows, an important 

habitat for juvenile salmon and other fish species.

A significant amount of the sediment released by the 

dam removal project eventually will be discharged into the 

Strait of Juan de Fuca at the Elwha River mouth (fig. 9.2). 

Waves and currents that move sediment along and across the 

delta will dictate the fate of this sediment. The waves of the 

Elwha River delta region are primarily from the northwest. 
258 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

This occurs for swells (10–18 second 

wave periods), which are derived from 

storms in the North Pacific Ocean, and 

wind waves (2–6 second wave periods), 

which are generated in the Strait of Juan 

de Fuca from westerly winds (Warrick 

and others, 2008; 2011b, chapter 5, this 

report). The oblique direction of these 

waves results in strong littoral transport 

along the delta, driving sediment 

transport toward the east (Miller and 

others, 2011). The currents offshore of 

the beaches are driven primarily by the 

tides; however, the shape of the delta 

influences water that must flood and 

ebb past the Elwha River delta due to 

these tides. Eddies that are 2–5 km in 

diameter are formed on the downstream 

sides of this deltaic headland during 

most tidal floods and ebbs. These 

currents influence the location of the 

turbid river plume, the location of the 

initial sediment settling, and subsequent 

movement of sediment (Gelfenbaum and 

others, 2009).

A flood on December 3, 2007, 

foreshadowed the potential changes that 

dam removal may bring to the Elwha 

River mouth and nearshore area. A large 

scale rain-on-snow storm caused rivers 

of the Olympic Peninsula to swell, 

with the peak discharge on the Elwha 

River recorded as 1,020 m3/s, and an 

estimated 40-year recurrence interval 

(Draut and others, 2011; Duda and 

others, 2011a, chapter 1, this report). 

Detailed mapping of elevations of the 

Elwha River mouth in September 2007, 

and again in September 2008, revealed 

an accumulation of about 34,000 m3 of 

sediment directly offshore of the river 

mouth. This sediment accumulation 

likely was associated with the peak 

discharge from the intervening 

December 2007 flood. It also changed 

salmon access to the east estuary, as 

revealed by observations on the ground 

and changes in fish community structure 

and density (Shaffer and others, 2009; 

Duda and others, 2011b, chapter 7, this 

report). 

A calibrated hydrodynamic and 

sediment transport model described 

by Gelfenbaum and others (2009) 

provides some predictions of the fate 

of sediment during and following dam 

removal. Forced with waves, currents 

and river discharge, the model predicts 

the dispersal of fine-grained silt and 

sand across the delta. Model simulation 

results indicate that a larger sediment 

supply, such as that which is expected 

following dam removal, would spread in 

a zone to the east and west of the river 

mouth, largely driven by tidal currents 

(fig. 9.7). Because of the asymmetry in 

the tidal currents off the river mouth, 

sand will be mostly deposited east of the 

river mouth, whereas silt will be more 

evenly deposited to east and west of the 

river mouth. The weaker tidal currents 

directed to the west should be strong 

enough to transport silt in this direction, 

but probably are not strong enough to 

transport much sand to the west. Thin 

accumulations of silt and sand are 

expected across most of the delta, with 

thicker accumulations in deep water off 

the eastern edge of the delta and east of 

Ediz Hook, just inside of Port Angeles 

harbor.

 The initial large sediment influx 

to the nearshore zone from released 

reservoir sediments will stress nearshore 

communities, but in the long-term, 

the communities should benefit from 

restoration of the natural, pre-dam 

sediment delivery regime (fig. 9.8). 

Separating the short-term effects from 

long-term benefits will be a primary 

challenge facing scientists in the years 

following dam removal. In the short 

term, negative effects will be greatest 

for species most vulnerable to deposited 

and suspended sediments. Kelp, for 

example, are vulnerable because they 

require relatively sediment-free surfaces 

for spore settlement. Their microscopic 

gametophyte and young sporophyte life 

stages also are susceptible to burial. 

Plants that can propagate vegetatively, 

on the other hand, may be resistant to 

sedimentation because they bypass these 

vulnerable juvenile life stages. 

As high sediment transport 

and increased turbidity continue 

for 2–3 years during dam removal, 

community composition of plants 

and invertebrates is likely to change 

(Airoldi, 2003), and species richness 

may decline. The spatial extent, vertical 

thickness, frequency, duration, seasonal 

timing, and particle characteristics (for 

example, grain size and shape, mineral 

and chemical composition) of deposited 

sediment will largely determine the 

ecological response. Of the four 

main community-habitat associations 

described, each will have different 

responses to increased sedimentation. 

Bedrock/boulder reefs may be most 

vulnerable if deposited sediments bury 

organisms attached to the reef or prevent 

establishment of their propagules. On 

the other hand, vertical surfaces of hard 

substrate, such as the sides of large 

boulders, will not collect sediment and 

may serve as refugia for some reefadapted taxa. If localized accumulations 

of sediment are great enough, some 

areas could convert from hard substrate 

to soft substrate, causing dramatic 

community shifts and decreasing 

habitat heterogeneity. Accumulations 

of very fine sediment (silt and clay) 

could benefit tube-building amphipods 

(Ampelisca spp.), which provide food 

for various other organisms (see Rubin 

and others, 2011, Chapter 6, sidebar 6.1, 

this report). 
Chapter 9

Summary and Anticipated Responses to Elwha River Dam Removal Elwha River Beaches and Nearshore 259

watac11-0558_fig9-07

0 0.5 1 

0 50 100 0 50 100

Sediment accumulation,

in centimeters 

Sand, in percent Silt, in percent

EXPLANATION

EXPLANATION EXPLANATION

Easting, in kilometers

Northing, in kilometers

Easting, in kilometers

Northing, in kilometers

290 295 300 305 310 315

128

130

132

134

136

138

0 5 MILES

0 5 KILOMETERS

295 300

128

130

132

134

295 300

0 2 MILES

0 2 KILOMETERS

0 2 MILES

0 2 KILOMETERS

Bathymetry from Cochrane and others, 2008;

UTM Zone 10, WGS84 projection

Bare earth LIDAR from 2001

Bathymetry from Cochrane and others, 2008;

UTM Zone 10, WGS84 projection

Bare earth LIDAR from 2001

Bathymetry from Cochrane and others, 2008;

UTM Zone 10, WGS84 projection

Bare earth LIDAR from 2001

A.

B. C.

Figure 9.7. (A) simulated sediment accumulation offshore of the Elwha River 

mouth, Washington, after flood event from the river. (After Gelfenbaum and 

others, 2009). Results derived from a three-dimensional hydrodynamic model of 

water and two classes of sediment, sand, and silt. The sand (B) preferentially 

accumulates east of the river mouth, and the silt (C) accumulates on both sides of 

the river mouth.
260 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Summary

The Elwha River dam removal and ecosystem restoration project is 

an unprecedented opportunity for scientific discovery. It also is inherently 

multidisciplinary, with changes to the physical and biological components 

of the ecosystem expected. The multidisciplinary team assembled as part of 

this project has attempted to develop baseline information about the river 

from multiple perspectives. From species diversity in the nearshore region 

to vegetation communities in the estuary, and growth, habitat use, and 

migratory patterns of juvenile salmon, many species will be affected by the 

dam removal project. Complex interactions among trophic levels and the 

environments upon which they depend are expected during and after dam 

removal. As environments change due to sediment release from the reservoirs, 

species will reassemble into new configurations in the estuary and nearshore 

environments. Similarly, the hydrology, geomorphology, and coastal 

oceanography will change in the river, estuary, and nearshore zone below 

the dams. The largest controlled release of sediment in history, characterized 

by high suspended sediment in the near term followed by more gradual 

movement of larger material over the coming decades, will also bring about 

changes. These changes to the physical habitat and biological characteristics 

of the ecosystem will need to be monitored to allow for a full evaluation of 

the restoration of the Elwha River. 

watac11-0558_fig9-08

Pre-removal Removal I Removal II Post-removal

bed

clear water turbid water

sand

clear water

A. B. C. D.

turbid water

Figure 9.8. Schematic diagram showing the coastal water and seafloor near the 

Elwha River mouth, Washington, and hypothetical changes before, during, and 

after dam removal. (A) The pre-removal condition has relatively clear water and a 

gravel bed. (B) Sediment loading during removal initially will increase suspendedsediment concentrations and turbidity in the water column. (C) Sand introduced to 

the coastal waters likely will accumulate and change the grain size of the seafloor. 

(D) Several years following the dam removal, the coastal waters will be much less 

turbid, although the grain size of the seafloor likely will be sandier than observed 

before the dam removal.

Acknowledgments

Funding for this work came from 

the U.S. Geological Survey, Coastal 

Habitats in Puget Sound project. 

We are grateful to all of the authors 

who contributed to this report. Their 

dedication and passion for improving 

the scientific understanding of largescale ecosystem change associated with 

the Elwha River Restoration Project 

is evident in their work. We thank the 

Lower Elwha Klallam Tribe for valuable 

discussion and insights into the Elwha 

River and estuary. This chapter benefited 

from conversations with Steve Rubin 

and Christopher S. Magirl.

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264 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

Dwight Barry Peninsula College, Center of Excellence

Vanessa B. Beauchamp ASRC Management Services, contracted to U.S. Geological Survey

Matthew M. Beirne Lower Elwha Klallam Tribe, Natural Resources Department

Jennifer A. Bounty Bureau of Reclamation, Sedimentation and River Hydraulics Group

Heather M. Bragg U.S. Geological Survey, Oregon Water Science Center

Christopher A. Curran U.S. Geological Survey, Washington Water Science Center

Christiana R. Czuba U.S. Geological Survey, Washington Water Science Center

Jonathan A. Czuba U.S. Geological Survey, Washington Water Science Center

Amy E. Draut U.S. Geological Survey, Pacific Coastal and Marine Science Center

Jeffrey J. Duda U.S. Geological Survey, Western Fisheries Research Center

Nancy Elder U.S. Geological Survey, Western Fisheries Research Center

James R. Foreman U.S. Geological Survey, Washington Water Science Center

Tracy L. Fuentes U.S. Geological Survey, Northwest Area

Guy Gelfenbaum U.S. Geological Survey, Pacific Coastal and Marine Science Center

Andrew S. Gendaszek U.S. Geological Survey, Washington Water Science Center

Gordon E. Grant U.S. Department of Agriculture Forest Service, Pacific Northwest 

Research Station

Mackenzie K. Keith U.S. Geological Survey, Oregon Water Science Center

Christopher P. Konrad U.S. Geological Survey, Washington Water Science Center

Kimberly Larsen U.S. Geological Survey, Western Fisheries Research Center

Joshua B. Logan U.S. Geological Survey, Pacific Coastal and Marine Science Center

Christopher S. Magirl U.S. Geological Survey, Washington Water Science Center

Jon J. Major U.S. Geological Survey, Cascades Volcano Observatory

Michael L. McHenry Lower Elwha Klallam Tribe, Natural Resources Department

Ian M. Miller University of California, Santa Cruz, Ocean Sciences Department

Jim E. O’Connor U.S. Geological Survey, Oregon Water Science Center

Smokey Pittman Graham Matthews and Associates

Cynthia Pritekel ASRC Management Services, contracted to U.S. Geological Survey

Charles J. Podolak Johns Hopkins University, Department of Geography and 

Environmental Engineering

Timothy J. Randle Bureau of Reclamation, Sedimentation and River Hydraulics Group

Reginald R. Reisenbichler U.S. Geological Survey, Western Fisheries Research Center

Abagail Rhode Herrera Environmental Consultants

Stephen P. Rubin U.S. Geological Survey, Western Fisheries Research Center

Patrick B. Shafroth U.S. Geological Survey, Fort Collins Science Center

Rich W. Sheibley U.S. Geological Survey, Washington Water Science Center

Kurt R. Spicer U.S. Geological Survey, Cascades Volcano Observatory

Karl Stenberg U.S. Geological Survey, Western Fisheries Research Center

Andrew W. Stevens U.S. Geological Survey, Pacific Coastal and Marine Science Center

Dwight Q. Tanner U.S. Geological Survey, Oregon Water Science Center

J. Rose Wallick U.S. Geological Survey, Oregon Water Science Center

Jonathan A. Warrick U.S. Geological Survey, Pacific Coastal and Marine Science Center

Peter R. Wilcock Johns Hopkins University, Department of Geography and 

Environmental Engineering

Author Affiliations
Chapter 1 Chapter 9

Summary and Anticipated Responses to Elwha River Dam Removal Author Affiliations 265

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266 Coastal Habitats of the Elwha River, Washington—Biological and Physical Patterns and Processes Prior to Dam Removal

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Duda and others— Coastal Habitats, Elwha River, WA—Biological and Physical Patterns and Processes Prior to Dam Removal—Scientific Investigations Report 2011–5120