U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2015–5046

Prepared in cooperation with the Trinity River Restoration Project

Assessing Geomorphic Change along the Trinity River 

Downstream from Lewiston Dam, California, 1980 to 2011
Cover: Photo mosaic showing 2011 peak flow release from Lewiston Dam and 

concurrent gravel augmentation at Lewiston gaging station (1.5 floodplain kilometers 

downstream from Lewiston Dam). Sawmill rehabilitation site and juvenile coho, 

4 floodplain kilometers downstream from Lewiston Dam. Photo credit: Trinity River 

Restoration Program on-line photo archives.
Assessing Geomorphic Change along the 

Trinity River Downstream from Lewiston 

Dam, California, 1980 to 2011

By Jennifer A. Curtis, Scott A. Wright, J. Toby Minear, and Lorraine E. Flint

Prepared in cooperation with the Trinity River Restoration Program

Scientific Investigations Report 2015–5046

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod/.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Curtis, J.A., Wright, S.A., Minear, J.T., and Flint, L.E., 2015, Assessing geomorphic change along the Trinity River 

downstream from Lewiston Dam, California, 1980–2011: U.S. Geological Survey Scientific Investigations Report 

2015–5046, 69 p., plus appendix, http://dx.doi.org/10.3133/sir20155046.

ISSN 2328-0328 (online)
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................3

Study Area..............................................................................................................................................3

In-Stream Effects of the Trinity River Diversion...............................................................................4

Methods...........................................................................................................................................................8

Estimating Geomorphic Change.........................................................................................................9

Interpretation of Geomorphic Mapping .................................................................................12

Uncertainty and Error Analysis ...............................................................................................12

Assessing Natural and Managed Drivers of Geomorphic Change ............................................15

Streamflow and Sediment Supply...........................................................................................15

Sediment Management and Mechanical Channel Rehabilitation.....................................17

Results ...........................................................................................................................................................17

Spatial and Temporal Analysis of Geomorphic Change...............................................................17

Natural and Managed Drivers of Geomorphic Change................................................................23

Streamflow and Sediment Supply...........................................................................................31

Sediment Management and Mechanical Channel Rehabilitation.....................................37

Summary of Bar and Bank Processes ............................................................................................40

Discussion.....................................................................................................................................................44

Channel Change Potential.................................................................................................................44

Trajectories of Geomorphic Response and Primary Controls .....................................................46

Geomorphology and Habitat Linkages ............................................................................................47

Conclusions...................................................................................................................................................52

References Cited..........................................................................................................................................53

Appendix A....................................................................................................................................................57
iv

Figures

1. Map showing study area, Trinity River, California...................................................................2

2. Map showing Trinity River restoration reach, in California, from Lewiston Dam

downstream to the North Fork Trinity confluence and 13 geomorphic reaches,

within 3 river-channel segments, used as the spatial framework for interpretation

of mapping results ........................................................................................................................5

3. Graph showing elevation profile of the Trinity River restoration reach, California,

estimated from 10-meter-resolution digital elevation data....................................................6

4. Raster hydrograph showing mean daily flows measured 1.5 kilometers downstream

from Lewiston Dam along the Trinity River, California............................................................7

5. Photo showing example of the topographic relations among depositional and

constructed features for the Trinity River downstream from Lewiston Dam, 

California ......................................................................................................................................11

6. Graphs showing areal extent of riparian and channel features along the Trinity

River downstream from Lewiston Dam, California, A, in 1980, and change in

active-channel area for five periods from 1980 to 2011: B, 1980 to 1997; C, 1997 to

2001; D, 2001 to 2006; E, 2006 to 2009; and F, 2009 to 2011 ....................................................18

7. Bar graphs showing areal extent of lower elevation riparian features along the

Trinity River downstream from Lewiston Dam, California, in A, 1980; B, 1997; 

C, 2001; D, 2006; E, 2009; and F, 2011 ........................................................................................19

8. Bar graphs showing areal extent of channel-complexity features within the active

channel along the Trinity River downstream from Lewiston Dam, California, in 

A, 1980; B, 1997; C, 2001; D, 2006; E, 2009; and F, 2011...........................................................20

9. Graphs showing area of uplands along the Trinity River downstream from Lewiston

Dam, California, and change in upland area from 1980 to 2011: A, cumulative area

by reach; B, cumulative change in area per year by reach; C, area by study

reach and segments over time.................................................................................................21

10. Graphs showing area of riparian features along the Trinity River downstream from

Lewiston Dam, California, and change in riparian area from 1980 to 2011: A,

cumulative area by study reach; B, cumulative change in area per year by study

reach; C, area by study reach and segments over time.......................................................22

11. Graphs showing area of the pre-dam floodplain along the Trinity River downstream

from Lewiston Dam, California, and change in pre-dam floodplain area from 1980 to

2011: A, cumulative area by study reach; B, cumulative change in area per year by

study reach; C, area by study reach and river segments over time...................................24

12. Graphs showing area of post-dam benches along the Trinity River downstream

from Lewiston Dam, California, and change in post-dam bench area from 1980 to

2011: A, cumulative area by study reach; B, cumulative change in area per year by

study reach; C, area by study reach and river segments over time...................................25

13. Graphs showing area of constructed floodplains along the Trinity River

downstream from Lewiston Dam, California, and change in constructed floodplain

area from 1980 to 2011: A, cumulative area by study reach; B, cumulative change in

area per year by study reach; C, area by study reach and river segments over time....26

14. Graphs showing area of stable bars along the Trinity River downstream from

Lewiston Dam, California, and change in stable bar area from 1980 to 2011: A,

cumulative area by study reach; B, cumulative change in area per year by study

reach; C, area by study reach and river segments over time .............................................27
v

Figures—Continued

15. Graphs showing area of the active channel along the Trinity River downstream

from Lewiston Dam, California, and change in active channel area from 1980 to

2011: A, cumulative area by study reach; B, cumulative change in area per year 

by study reach; C, area by study reach and river segments over time .............................28

16. Graphs showing area of active bars along the Trinity River downstream from

Lewiston Dam, California, and change in active bar area from 1980 to 2011: 

A, cumulative area by study reach; B, cumulative change in area per year by 

study reach; C, area by study reach and river segments over time ..................................29

17. Graphs showing area of secondary water features along the Trinity River

downstream from Lewiston Dam, California, and change in secondary water

feature area from 1980 to 2011: A, cumulative area by study reach; B, cumulative

change in area per year by study reach; C, area by study reach and river segments

over time.......................................................................................................................................30

18. Graphs showing temporal changes in the active-channel from 1980 to 2011 for the

Trinity River downstream from Lewiston Dam, California: A, baseflow shoreline

length; B, active-channel width ...............................................................................................31

19. Graphs showing streamflow measured at the Lewiston gage on the Trinity River,

California, 1.5 km downstream from Lewiston Dam, from 1980 to 2011: A, mean daily

and annual peak flows; B, annual average flows. ROD, Record of Decision...................32

20. Boxplots showing mean daily flows from 1980 to 2011, grouped by month with minimum 

in-stream flow, for the Lewiston gage on the Trinity River, California: A, pre-ROD 

(Record of Decision) period; B, post-ROD period......................................................................34

21. Graph showing contributing drainage area for 13 geomorphic reaches, delineated

by vertical lines and described in table 2, along the Trinity River downstream from

Lewiston Dam, California...........................................................................................................35

22. Graph showing the mean annual flow measured at five mainstem gages on the

Trinity River, California, downstream of Lewiston Dam, California, from 1996 to 2011....35

23. Graphs showing mean daily flows measured at five mainstem gaging stations on

the Trinity River, California, downstream from Lewiston Dam, from 1980 to 2011, and

annual time series for four wettest years during the study period: A, 1997; B, 1998;

C, 2006; D, 2011 ............................................................................................................................36

24. Diagram showing summary of relevant management actions from 1976 to 2011

along the Trinity River downstream from Lewiston Dam, California..................................37

25. Bar graph showing annual and cumulative volumes of sediment extraction and

augmentation for Trinity River downstream from Lewiston Dam, California, from

1980 to 2011 .................................................................................................................................38

26. Summary of constructed riparian and channel features along the Trinity River

downstream from Lewiston Dam, California, in 1980, 1997, 2001, 2006, 2009, 

and 2011........................................................................................................................................39

27. Graphs showing changes in active-channel area due to bank erosion and

accretion along the Trinity River downstream from Lewiston Dam, California, for

five periods ending in 1997, 2001, 2006, 2009, and 2011 ........................................................41

28. Graphs showing changes in active-bar area due to bar scour and accretion along

the Trinity River downstream from Lewiston Dam, California, for five periods ending

in 1997, 2001, 2006, 2009, and 2011 ...........................................................................................42

29. Graphs showing changes in bar vegetation along the Trinity River downstream from 

Lewiston Dam, California, for five periods ending in 1997, 2001, 2006, 2009, and 2011 ...43
vi

Figures—Continued

30. Graphs showing cumulative downstream change in the areal extent of exposed

active bars and of the active channel along the Trinity River downstream from

Lewiston Dam, California, for five periods ending in 1997, 2001, 2006, 2009, and 2011 ...45

31. Geomorphic feature maps for the Sven Olbertson Rehabilitation Site on the Trinity

River, California, 1.0 floodplain kilometers downstream from Lewiston Dam, in 

1980, 2001, and 2011....................................................................................................................48

32. Geomorphic feature maps near Junction City on the Trinity River, California, 50.1

floodplain kilometers downstream from Lewiston Dam, in 1980, 2001, and 2011.............49

33. Geomorphic feature maps for Conner Creek Rehabilitation Site on the Trinity River,

California, 53.8 floodplain kilometers downstream from Lewiston Dam, in 1980, 

2001, and 2011..............................................................................................................................50

34. Geomorphic feature maps at Lime Point on the Trinity River, California, 58.1

floodplain kilometers downstream from Lewiston Dam, in 1980, 2001, and 2011.............51

Tables

1. Recommended flow releases to the Trinity River, California, from Lewiston Dam and

associated management objectives..........................................................................................8

2. Mapping protocol structure and geomorphic feature descriptions ..................................10

3A. Geomorphic reach descriptions and restoration history for study segments along

the Trinity River, California, downstream from Lewiston Dam: upper river segment......13

3B. Geomorphic reach descriptions and restoration history for study segments along

the Trinity River, California, downstream from Lewiston Dam: central river segment....14

3C. Geomorphic reach descriptions and restoration history for study segments along

the Trinity River, California, downstream from Lewiston Dam: lower river segment ......14

4. Uncertainty analysis for six geomorphic maps of the Trinity River, California,

downstream from Lewiston Dam. ...........................................................................................15

5. Summary of stream discharge data for the Trinity River, California, downstream

from Lewiston Dam. ...................................................................................................................16

6. Summary of bar and bank changes during five study periods for the Trinity River,

California, downstream from Lewiston Dam..........................................................................40
vii

Conversion Factors

[Inch/pound to International System of Units]

Multiply By To obtain

Volume

acre-foot (acre-ft) 1,233 cubic meter (m3

)

Flow rate

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

[International System of Units to Inch/pound]

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

square meter (m2

) 10.76 square foot (ft2) 

square kilometer (km2

) 0.3861 square mile (mi2)

Volume

cubic meter (m3) 264.2 gallon (gal) 

Flow rate

cubic meter per year (m3

/yr) 0.000811 acre-foot per year (acre-ft/yr) 

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

Datums

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

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.
viii

Abbreviations and Acronyms

DTM digital terrain model

EIS Environmental Impact Statement

FPkm floodplain kilometer

GIS geographic information system

HVT Hoopa Valley Tribe

RMSE root mean square error

ROD Record of Decision

TAF thousand acre-feet

TRA Trinity Restoration Associates, Inc.

TRD Trinity River Division of the Central Valley Project

TRFE Trinity River Flow Evaluation

TRRP Trinity River Restoration Program

USFWS U.S. Fish and Wildlife Service

Acknowledgements

This study benefited from discussions with Bureau of Reclamation staff including Andreas 

Krause, Dave Gaeuman, and Eric Peterson and members of the Trinity River Restoration Program 

Physical Workgroup who provided helpful guidance and review. 

Rose Wallick (U.S. Geological Survey, Portland, Oregon) and MacKenzie Keith (U.S. Geological 

Survey, Portland, Oregon) were instrumental in the development and analysis of the mapping 

geodatabase. 
Assessing Geomorphic Change along the Trinity River 

Downstream from Lewiston Dam, California, 1980 to 2011

By Jennifer A. Curtis, Scott A. Wright, J. Toby Minear, and Lorraine E. Flint

Abstract

The Trinity River Restoration Program, one of the 

nation’s largest adaptively managed river restoration 

programs, requires periodic assessment to determine the 

effectiveness of management actions in restoring channel 

dynamics and habitat features. This study documents 

riparian and channel changes along an intensively managed 

65-kilometer reach of the Trinity River in California, 

downstream from Lewiston Dam. The two primary periods 

of interest, from 1980 to 2001 and from 2001 to 2011, are 

separated by a shift in restoration activities mandated by 

the U.S. Department of the Interior December 2000 Record 

of Decision. The post-2001 restoration strategy increased 

managed-flow releases, gravel augmentation, watershed 

restoration, and mechanical channel rehabilitation. 

We assessed the nature and extent of geomorphic 

change and a series of ecological performance measures 

(channel complexity, shoreline length, and channel–

floodplain connectivity) by using a series of maps digitized 

from available rectified orthophotography acquired during 

low-flow conditions in 1980, 1997, 2001, 2006, 2009, and 

2011. Lateral changes in riparian and channel features were 

used to quantify alluvial processes, and a review of existing 

streamflow, sediment, and restoration records was used to 

assess causal mechanisms. During the study period, natural 

bank erosion and mechanical rehabilitation of channel margins 

converted riparian features to channel features and expanded 

the active-channel area. The primary period of bank erosion 

and expansion of the active channel was from 1980 to 1997. 

Subsequent bar accretion from 1997 to 2001, followed by 

slightly greater bar scour from 2001 to 2006, took place 

primarily in the central and lower reaches of the study area, 

downstream of Indian Creek. In comparison, post-2006 

bank and bar changes were spatially limited to reaches that 

had sufficient local transport capacity or sediment supply 

supported by gravel augmentation, mechanical channel 

rehabilitation, and tributary contributions.

The highest rates of change in the areal extents of 

channel and riparian features were observed during the 

pre-2001 period, which was longer and relatively wetter than 

the post-2001 period. A series of tributary floods in 1997, 

1998, and 2006 increased channel complexity and floodplain 

connectivity. During the post-2006 period, managed-flow 

releases, in the absence of tributary flooding, combined with 

gravel augmentation and mechanical restoration, caused 

localized increases in sediment supply and transport capacity 

that led to smaller, but measurable, increases in channel 

complexity and floodplain connectivity in the upper river near 

Lewiston Dam. Extensive pre-2001 channel widening and the 

muted geomorphic response of channel rehabilitation sites to 

post-2001 managed flows highlight the need for continued 

monitoring and assessment of the magnitude, duration, and 

timing of prescriptive flows and associated geomorphic 

responses.

Introduction

In 1958, a plan was developed to increase water supplies 

and generate power for California’s Central Valley Project, 

in part, by transferring water from the Trinity River (fig. 1) 

to the Sacramento River. The Trinity River Division (TRD) 

included construction of two main-stem dams. The reservoir 

behind Trinity Dam began filling in 1960, and Lewiston Dam 

was completed in 1963. Following closure of the Trinity 

Dam, annual water diversions commenced, and up to 75 to 

90 percent of the upper Trinity River’s annual streamflow, 

measured as inflow to Trinity Lake, was transferred to the 

upper Sacramento River (U.S. Fish and Wildlife Service and 

Hoopa Valley Tribe, 1999). 

The combination of dam construction, flow diversion, and 

land-use practices (dredge mining and upland logging) caused 

channel aggradation, riparian encroachment, and simplification 

of channel morphology with concurrent reductions in channel 

complexity and channel–floodplain connectivity downstream 

from Lewiston Dam (Trinity River Taskforce, 1970). 

Recognition that riparian and channel changes coincided 

with declines in salmon and steelhead populations led to an 

Environmental Impact Statement (EIS; U.S. Fish and Wildlife 

Service, 1980). The EIS determined the fisheries decline was 

primarily caused by streambed sedimentation, insufficient 

streamflow, and inadequate regulation of fish harvests. On the 

basis of these findings, channel bank rehabilitation and flow 

increases were recommended to restore salmon and steelhead 

populations (U.S. Fish and Wildlife Service, 1980).
2 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

sac12-0449_fig 01

CASCADE

RANGE

Area of

figure 2

Trinity River

South Fork Trinity River

Hayfork Cr

Stuart Fork

New River

Swift C r

Coffee Cr

Indian Cr

KLAMATH `RIVER

Trinity

Lake

Lewiston

Dam

PA

CIFIC

O

C

E

A

N

N

Fk Trinity River

Trinity River

Canyon Cr

Reading

Creek

Rush Cr

Douglas City

Junction

City

Eureka Weaverville

Willow

Creek

TRINITY

HUMBOLDT

SISKIYOU

TEHAMA

SHASTA

MENDOCINO

DEL NORTE SALMON

MOUNTAINS

TRINITY

MOU

NTAINS

124° 123°30' 123° 122°30'

41°

30'

41°

40°

30'

40°

0 10 20 30 40 Miles

0 10 20 30 40 Kilometers

Base map modified from U.S. Geological Survey digital 

data, various scales. Coordinate system: UTM projection 

Zone 10, North American Datum of 1983.

Trinity River

watershed

CALIFORNIA

EXPLANATION

Trinity River watershed

Study reach

Figure 1. Study area, Trinity River, California.
Introduction 3

Although baseflow increases began in 1981, salmon 

and steelhead populations continued to decline, which led 

to additional environmental and experimental flow studies 

summarized in the Trinity River Flow Evaluation (TRFE; 

U.S. Fish and Wildlife Service and Hoopa Valley Tribe, 

1999). The TRFE presented recommendations that were 

formally adopted in December 2000 by the U.S. Department 

of the Interior Record of Decision (ROD; U.S. Department 

of the Interior, 2000). The ROD explicitly required a 

restoration strategy that included managed-flow releases, 

gravel augmentation, mechanical channel rehabilitation, 

and watershed restoration. The Trinity River Restoration 

Program (TRRP), a multi-agency partnership, was tasked 

with overseeing implementation of mandated restoration 

and adaptive management. The TRRP’s mission is to 

promote geomorphic processes responsible for creating and 

maintaining habitat sufficient to restore the salmonid fishery 

to pre-dam levels. Restoration of a dynamic alluvial channel, 

exhibiting all the characteristics of the pre-dam river, but at a 

smaller scale, is a primary goal.

Purpose and Scope

The purpose of this report is to provide results from a 

geomorphic assessment of the 65-kilometer (km) restoration 

reach along the mainstem Trinity River, downstream from 

Lewiston Dam, completed by the USGS in cooperation 

with the TRRP. The study period began in 1980, prior to 

implementation of baseflow increases in 1981, and covered 

approximately two decades (1980 to 2001) prior to the ROD 

and one decade (2001 to 2011) following. The primary study 

objectives were as follows:

1. To develop a system-wide perspective of 

geomorphic features.

2. To determine the evolution of geomorphic features and 

the trajectories of geomorphic change. 

3. To quantify ecologically significant measures 

of geomorphic change relevant to Trinity River 

fisheries restoration.

4. To evaluate the cumulative effects of natural and 

managed drivers of change.

We used six available rectified orthophotographs, 

acquired during baseflow conditions, to construct a series 

of retrospective geomorphic feature maps that are published 

in a companion report and geodatabase (Curtis and 

Guerrero, 2015; http://dx.doi.org/10.5066/F7TT4P04). The 

orthophotographs bracketed five study periods that included 

two pre-ROD periods (May 1980 to October 1997 and 

October 1997 to November 2001) and three post-ROD periods 

(November 2001 to July 2006, July 2006 to April 2009, and 

April 2009 to August 2011). Using the six geomorphic feature 

maps, we quantified spatial and temporal changes in riparian 

and channel features and assessed a series of ecological 

performance measures (channel complexity, shoreline length, 

and channel–floodplain connectivity) identified as primary 

metrics for understanding linkages between ecosystem benefits 

and restoration actions (Trinity River Restoration Program and 

ESSA Technologies Ltd., 2009). 

During each of the five study periods, there were 

concurrent and sequential alterations in flow, sediment 

supply, and channel morphology. We interpreted cumulative 

change during each of the five periods in the context of 

controlling factors related to natural channel processes, flow 

and sediment management, and mechanical alterations of 

channel morphology. Results from this study are intended to 

help inform the design and implementation of future channel 

rehabilitation projects (Hoopa Valley Tribe and others, 2011a) 

and adaptive management of the TRRP restoration reach.

Study Area

The Trinity River traverses a region in the Central 

Klamath Mountain geologic province (Irwin, 1972, 1981) 

underlain by geologic terranes accreted to western North 

America during the late Mesozoic Era and early Tertiary 

Period (Ingersoll and Schweickert, 1986). A progression 

of eastward dipping thrust faults (Irwin, 1994) juxtaposes 

younger, Jurassic mixed-volcanic and sedimentary rocks 

against older, Devonian sedimentary rocks. During 

and subsequent to accretion, these geologic units were 

metamorphosed and intruded by igneous plutons, dikes, and 

sills. The Weaverville Formation, a Cenozoic gold-bearing 

fluvial deposit, was deposited on older stratigraphy (Diller, 

1902) in the study area. 

Anomalously high topography and surface exposure of 

Devonian rocks in the Klamath province indicate a period 

of geologically recent tectonic uplift. Inferred rapid uplift 

could be related to plate convergence at the nearby Cascadia 

subduction zone and Mendocino Triple Junction (Anderson, 

2008). Inferred uplift rates also provide a tectonic mechanism 

for river incision and development of bedrock channels 

draining the central Klamath Mountains. 

The Trinity River flows 270 km westward from its 

headwaters to its confluence with the Klamath River (fig. 1). 

The Trinity is the Klamath River’s largest tributary and 

has a total drainage area of 7,670 square kilometers (km2). 

Approximately one quarter of the Trinity River watershed 

(1,850 km2) is upstream from Lewiston Dam. The watershed 

is predominately mountainous and forested. Elevations 

range from 90 to 2,700 meters (m) above sea level, and the 

highest elevations were glaciated during the Pleistocene. 

The channel network is primarily bedrock with intermittent 

alluvial reaches. Downstream of Lewiston Dam, the river 

flows southwest through a series of antecedent meanders 

superimposed across northwest-trending terranes. Near 

Douglas City, the river turns and flows northwest through a 

structurally controlled landscape.
4 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

The climate in this region is Mediterranean, with 

hot, dry summers and cool, wet winters. Beginning in 

November, storm systems from the Pacific Ocean bring 

winter precipitation. Approximately 80 percent of the 

annual precipitation falls between November and March. 

The U.S. Forest Service has operated a weather station in 

Weaverville since 1905 (Weaverville RS, WVR, http://

www.cdec.water.ca.gov). The Weaverville station is at an 

elevation of 625 m, where average annual precipitation is 

935 millimeters (mm), and average annual snowfall is 570 

mm. The maximum monthly precipitation, 530 mm, fell in 

December 2005, and the maximum 24-hour precipitation, 140 

mm, fell on January 4, 1982. Elevations between 1,220 and 

1,820 m are susceptible to rain-on-snow events (U.S. Fish and 

Wildlife Service and Hoopa Valley Tribe, 1999), which can 

produce large tributary floods.

The TRRP restoration reach extends from Lewiston Dam 

downstream to the confluence with the North Fork Trinity 

River (fig. 2). This 65-km river segment along the mainstem 

Trinity River was identified as the most severely affected 

by flow regulation and diversion and was recommended 

for restoration by the initial flow evaluation (U.S. Fish and 

Wildlife Service, 1994). The study reach is a partially confined 

gravel-bed river that has a nearly constant slope of 0.002 

meters per meter (fig. 3). The nearly constant slope indicates 

that bedrock functions as a primary control of channel 

slope. This assertion is further supported by intermittent 

bedrock exposures in the active channel throughout the 

study reach. The channel pattern is primarily singlethread, and the dominant channel type is pool-riffle with 

intermittent plane‐bed and canyon reaches (Montgomery and 

Buffington, 1998).

From the early 1860s to the early 1900s, large-scale 

hydraulic mining of the gold-bearing Weaverville Formation 

and, to a lesser extent, logging increased sediment supplies 

to the study reach. Deposition of large-diameter mining 

sediment aggraded the channel and valley bottom by several 

feet (Trinity River Taskforce, 1970; Krause and others, 

2010). Beginning in the late 1800s and continuing until 1960, 

dredge mining of the mainstem channel overturned more than 

70 percent of the floodplain area (Stearns, 1969), depositing 

large piles of coarse tailings (gravel, cobble, and boulder) up 

to 12 m high that confine the modern river in some locations 

(Krause, 2012b). Many of these tailings piles were reworked 

by the 1955 and 1964 floods (Ritter, 1968), producing an 

extensive set of historic terraces and inset floodplains. 

Redistribution of stored mining sediment and tributary 

confluence aggradation during the 1964 flood led to the first 

mechanical restoration effort in 1965 that involved confluence 

channelization. Notably, smaller scale hydraulic mining 

continued in the study reach until 1970.

In-Stream Effects of the Trinity River Diversion

In-stream effects related to Trinity River flow diversions 

are documented explicitly in the TRFE (U.S. Fish and Wildlife 

Service and Hoopa Valley Tribe, 1999) and numerous project 

reports. In this report, we review the evolution of flow and 

sediment management strategies to support a thorough 

understanding of the study reach history. Note that we use 

English units, cubic feet per second (ft3/s) and thousand 

acre‐feet (TAF), to characterize flow data because they are 

commonly used by the Trinity River management community.

The influence of flow regulation and diversion on 

streamflow variability is readily apparent in mean daily flows 

recorded at the Lewiston gaging station (fig. 4; Trinity River 

at Lewiston, USGS station identification number 11525500), 

1.5 km downstream from Lewiston Dam (fig. 2). The predam flow regime included summer base flows, winter-storm 

peaks, and spring-snowmelt peaks, which created variable 

seasonal flow conditions. Post-dam flow variability decreased 

and flow releases from 1964 to 1973 were pursuant to the 

1955 Congressional Act, which authorized construction and 

operation of the TRD by the Bureau of Reclamation. The 

TRD maintained daily flows between 150 and 250 ft3/s at the 

Lewiston gage, and the annual flow‐release volume was set at 

120.5 TAF, with periodic, larger safety-of-dam releases.

Post-dam salmonid habitat deterioration and population 

declines (Trinity River Taskforce, 1970) prompted a request 

in 1980 by the California Department of Fish and Game to 

increase the annual flow release from Lewiston Dam to the 

Trinity River to 315 TAF. Subsequent investigations of the 

relation between in-stream flows and salmonid habitat by the 

U.S. Fish and Wildlife Service (USFWS) were incorporated 

into an EIS (U.S. Fish and Wildlife Service, 1980), which 

concluded that insufficient streamflow was the most critical 

limiting factor for restoring salmonid populations. The EIS 

explicitly recommended channel rehabilitation by mechanical 

restoration and increases in minimum annual flow volumes to 

140 TAF in critically dry water years, 220 TAF in dry water 

years, and 340 TAF in normal or wet water years.

In 1981, a Department of the Interior Secretarial Decision 

was issued that mandated baseflow increases and completion 

of a flow evaluation study to evaluate the potential effects of 

implementing prescriptive in-stream flows to mimic variable 

climatic conditions and provide suitable flows to restore 

dynamic fluvial processes, maintain channel complexity, and 

support all stages of the salmonid life cycle. Drier climatic 

conditions prevailed from 1986 to 1990, which delayed flow 

increases. In the early 1990s, a series of 3,000 to 6,000 ft3

/s 

experimental flows were released, and in-stream effects were 

monitored as part of an environmental assessment (EA). 
Introduction 5

tac12-0449_fig 02

N Fk Trinity R

Canyon Creek

Grass Valley Creek

Trinity River

Rush Creek

Oregon

Gulch

Deadwood

Cr

TRINITY

DAM

Browns Creek

Reading Creek

Indian Creek

Dutch Creek

Weaver Creek

Trinity River

LEWISTON

DAM

R3

R2

R1

R9

R7 R6

R5

R11

R4

R12

R8

R10

R13

Junction City Weaverville

Douglas City

Lewiston

15

20

25

30

35

40

45

50

55

60

5

10

299

299

TRLG

TRDC

TRJC

TRNF

TRAL

40°

45'

40°

50'

40°

40'

40°

35'

0 5 MILES

0 5 KILOMETERS

Base map modified from U.S. Geological Survey digital 

data, various scales. Coordinate system: UTM projection 

Zone 10, North American Datum of 1983.

123°05' 123° 122°55' 122°50' 122°45'

EXPLANATION

R1 Study reaches

R4 - Stott

R2 - Sawmill

R3 - Rush Creek

R1 - Lewiston R6 - Vitzhum Gulch R9 - Dutch Creek

R7 - Reading Creek

R8 - Dutton Creek

R5 - Poker Bar Canyon R13 - Pear Tree

R10 - Oregon Gulch

R12 - Lime Point

R11 - Canyon Creek

5

TRDC U. S. Geological Survey 

streamgaging station—See table 5

for station names

Floodplain kilometer—distance

downstream from Lewiston Dam

Upper river Central river Lower river

Figure 2. Trinity River restoration reach, in California, from Lewiston Dam downstream to the North Fork Trinity confluence and 

13 geomorphic reaches, within 3 river-channel segments, used as the spatial framework for interpretation of mapping results.
6 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

sac12-0459_fig03

0 10 20 30 40 50 60

Elevation, in meters

Distance downstream from Lewiston Dam, in floodplain kilometers

Upper river Central river Lower river

400

420

440

460

480

500

520

540

560

580

Geomorphic reach

EXPLANATION

Tributary confluences

USGS gaging stations

R1 R5 R6 R7 R8 R9 R10 R11 R12 R13 Geomorphic

reach

Tributary

confluence

R2 R3 R4

Figure 3. Elevation profile of the Trinity River restoration reach, California, estimated from 10-meter-resolution digital 

elevation data. See table 3 for description of the 13 geomorphic reaches.

The TRFE was completed in 1999, and flow recommendations 

were formally adopted in the ROD (U.S. Department of the 

Interior, 2000), but litigation delayed full implementation 

of the ROD flows until December 2005. Post-ROD flow 

management included large increases in annual flow volumes 

compared to those initially recommended in the 1980 EIS. 

In critically dry water years, the EIS recommendation of 

140 TAF was more than doubled to 369 TAF. The EIS 

recommendation of 340 TAF was increased to 647 TAF during 

normal years and to 701 TAF during wet years (table 1).

An important change in post-ROD flow management 

was the implementation of an annual spring-flow release with 

specific geomorphic objectives (table 1). The annual peak 

release typically begins in early May and can extend into 

mid-July depending on the water-year type. Water-year type 

and the spring-flow release are determined in April of each 

year on the basis of forecasted annual-flow volumes at the 

Lewiston stream gage (Krause, 2012a). The peak release can 

be described as a “benched” hydrograph, with rapid increases 

in the rising limb, and a gradual decrease in the falling limb 

that is punctuated by periods of steady flows referred to as 

“benches” (U.S. Fish and Wildlife Service and Hoopa Valley 

Tribe, 1999). The “benches” are designed to support bed 

mobility, scour, and geomorphic objectives listed in table 1. 

A post-dam sediment deficit existed downstream of 

Lewiston Dam (Gaeuman and Krause, 2011). Sediment deficit 

conditions occur when transport capacity exceeds sediment 

supply, which often results in scour and evacuation of bedmaterial to downstream reaches (Schmidt and Wilcock, 

2008; Draut and others, 2011). Excess transport capacity 

immediately downstream from dams, typical for reaches that 

lack sufficient sediment supply, can lead to coarsening of the 

channel bed, decreased bed mobility, and channel incision. 

Within the study reach, changes in the substrate grain size 

relative to pre-dam conditions are unknown, but gaging 

measurements, collected at a cableway 2.5 km downstream 

from Lewiston Dam, indicated negligible post-dam channel 

incision (Gaeuman, 2008). 

Abundant tributary and in-channel sediment sources 

exist in downstream study reaches (Graham Matthews and 

Associates, 2001), where sediment deficit conditions transition 

to equilibrium or surplus conditions (Gaeuman and Krause, 

2011). The transition from deficit to surplus conditions often 

occurs downstream from the first major tributary confluence 

(Schmidt and Wilcock, 2008) or in pre-dam aggradation zones, 

where modern bed and bank processes recruit stored sediment 

from in-channel or floodplain sources (Draut and others, 

2011). Beginning at about 3 km downstream from Lewiston 

Dam, large amounts of legacy mine tailings are stored along 

channel margins, but flows in this reach are insufficient to 

scour and transport this large-diameter material. Prior to 

construction of sediment-retention ponds in 1986, Grass 

Valley Creek (11.9 floodplain kilometers, or FPkm) was the 

first large contributor of sediment downstream from Lewiston 

Dam (Graham Matthews and Associates, 2001). At the time 

of writing this report, almost all bed-material sized sediment 

from Grass Valley Creek is trapped in a series of retention 

ponds constructed at the confluence in 1986. After 1986, 

Indian Creek (25.6 FPkm) functioned as the first important 

contributor of sediment downstream from Lewiston Dam 

(Graham Matthews and Associates, 2001).
Introduction 7

sac12-0459_fig04

Post-ROD study period

Pre-ROD study period

Raster hydrograph of daily flow

at USGS 11525500 Trinity R A Lewiston CA Daily streamflow for 

years 1911–2011, in 

cubic feet per 

second

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

10,000

40,000

2010

2000

1990

1980

1970

1960

1950

1940

1930

1920

1911

2010

2000

1990

1980

1970

1960

1950

1940

1930

1920

1911

5,000

1,000

500

100

50

30

No data

Figure 4. Raster hydrograph (http://waterwatch.usgs.gov/index.php?id=wwchart_rastergraph) showing mean daily flows 

measured 1.5 kilometers downstream from Lewiston Dam (fig. 2) along the Trinity River, California. Hydrograph shows monthly and 

annual variability of mean daily flows for 1911 to 2011. Pre- and post-ROD study periods are separated by the U.S. Department of 

the Interior Record of Decision (U.S. Department of the Interior, 2000). ROD, Record of Decision.
8 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

Table 1. Recommended flow releases to the Trinity River, California, from Lewiston Dam and associated management objectives.

[See report by Hoopa Valley Tribe and others (2011b) for additional details; acre-ft, acre-foot; D84, particle diameter that represents 84 percent of the grain-size 

distribution of channel bed sediment; days/yr, days per year; ft3/s, cubic feet per second; ROD, record of decision; yr, year]

Water-year

type

Frequency of 

water-year 

type during 

post-ROD

period

(percent)

Recommended

annual flow

released to

Trinity River 

(acre-ft)

Recommended

peak

release at

Lewiston

(ft3

/s)

Recommended 

duration of 

peak release 

(days)

Pre-ROD

exceedence

of recommended 

peak flow 

(days/yr)

Post-ROD

exceedence

of recommended 

peak flow 

(days/yr)

Objectives

Critically dry 12 369,000 1,500 36 31 118 Discourage encroachment of riparian 

vegetation on low bars.

Dry 28 453,000 4,500 5 10 19 Mobilization of gravels in pool tails and 

mid-channel bars.

Normal 20 647,000 6,000 5 5 8 Channel-bed surface mobilization on 

bars and riffles. Coarse-sediment 

transport equal to sediment supply. 

Tributary confluence maintenance. 

Channel migration. Managed floodplain 

inundation and fine-sediment deposition. 

Scour of 0–1 year old riparian seedlings 

on lower bar surfaces. Recharge of 

shallow groundwater table. All effects 

realized at lower flows.

Wet 28 701,000 8,500 5 0.1 1.7 Scour of bar margins greater than or 

equal to D84 depth. Coarse sediment 

movement. Scour of 1–2 year old 

riparian seedlings and lower bar surfaces. 

All effects realized at lower flows.

Extremely 

wet

12 815,000 11,000 5 0 0.5 Scour depth of alternate bars greater than 

two times D84. Managed floodplain 

scour. Side-channel maintenance. Scour 

of 2–3 year old riparian seedlings and 

lower bar surfaces. All effects realized at 

lower flows.

Decreases in post-dam flows resulted in aggradation 

of tributary confluences (Ritter, 1968) and accumulation 

of undesirable fine bed material primarily downstream 

of Grass Valley Creek (U.S. Fish and Wildlife Service 

and Hoopa Valley Tribe, 1999). The TRFE suggested that 

post-dam decreases in coarse bed material reduced successful 

salmonid spawning and simplified the structure of available 

physical habitat (U.S. Fish and Wildlife Service and Hoopa 

Valley Tribe, 1999). There was concern that the relatively 

large annual flow releases necessary to mobilize and scour 

undesirable fine bed material would result in the transport 

and removal of existing gravel in the reach immediately 

downstream from Lewiston Dam, which, despite effects 

related to flow regulation and diversion, continued to function 

as a primary spawning reach for regional salmonid production 

(U.S. Fish and Wildlife Service, 1989). To mitigate transport 

of gravel out of the primary spawning reach, the ROD 

mandated gravel augmentation in the upper river. 

Gravel augmentation in the reach immediately 

downstream from Lewiston Dam began in 1998 with 

in-channel placement of coarse-sized bed material. Note 

that the TRRP defines coarse bed material as all particles 

greater than 8mm in diameter (Gaeuman and Krause, 2011). 

Recently, Gaeuman (2008) determined an optimal particlesize distribution (9.5 to 125 mm) and annual quantity (5,400 

cubic meters, or m3) for long-term maintenance of coarse bed 

material in the upper river. 

Methods

The objectives of this study were to develop a 

system-wide perspective of geomorphic features and to assess 

cumulative geomorphic change and controlling factors during 

five periods spanning 1980 to 2011. We characterized the 

spatial distribution of geomorphic features along the study 
Methods 9

reach by using a series of retrospective geomorphic maps and 

completed geospatial analysis to assess cumulative change 

during each period. Geomorphic changes were interpreted in 

the context of controlling factors related to natural processes, 

flow and sediment management, and mechanical restoration.

Estimating Geomorphic Change

Geomorphic maps published in a companion report 

and geodatabase (Curtis and Guerrero, 2015; http://dx.doi.

org/10.5066/F7TT4P04) were used to classify upland, 

riparian, and channel features. The map dates bracket relevant 

geomorphic events and include three dates that span the preROD period (May 16, 1980; October 20, 1997; November 7, 

2001) and three dates that span the post-ROD period (July 25, 

2006; April 16, 2009; August 16, 2011). The orthophotographs 

used as base maps were acquired during baseflow conditions, 

about 300 ft3/s, when channel features were well exposed.

A map boundary was defined on the basis of the area 

inundated by a 500-year recurrence interval flood. This 

boundary, constructed by a one-dimensional flow model 

(California Department of Water Resources, 2007), roughly 

defined the valley bottom. The boundary was extended by 

30 m to include all features of interest. Geomorphic features 

larger than 30 m2 within the map boundary were digitized at 

a scale of 1:1,000. Mapping was limited to exposed features 

because subaqueous features, although evident in some years, 

could not be consistently digitized.

The hierarchy of the mapping protocol included upland, 

riparian, and channel features similar to recent studies on 

the Colorado River and its main tributary, the Green River 

(Schmidt and others, 1999; Grams and Schmidt, 2002). The 

protocol was designed to assess spatial and temporal changes 

in geomorphic features and ecologically important measures 

of geomorphic change relevant to restoration of Trinity 

River fisheries. Previous studies determined that the linkage 

between habitat and channel geomorphology was represented 

best by channel complexity, channel–floodplain connectivity, 

and shoreline length, which represent fundamental variables 

governing the quality and quantity of available salmonid 

habitat (U.S. Fish and Wildlife Service and Hoopa Valley 

Tribe, 1999; Trinity River Restoration Program and ESSA 

Technologies Ltd., 2009). The mapping protocol, geomorphic 

feature definition, and the ArcGIS (v. 10.0) geodatabase 

structure are explained in table 2.

Geomorphic features were delineated by orthophoto 

interpretation, and specific observational criteria are 

described in table 2. The mapping was further constrained 

by a contour map derived from a 2009 digital terrain model 

(DTM, Woolpert, 2010) and a series of water-surface extents 

constructed by a one-dimensional flow model. The mapping 

was field checked in the summer of 2012. Observational 

criteria used to classify geomorphic features included the 

age, density, and type of vegetation; spatial transitions 

among vegetation types; evidence of scour or deposition; 

and presence of stagnant or flowing water. Although features 

were primarily delineated on the basis of these criteria, the 

2009 contour map helped delineate relatively static features, 

and modeled water surfaces were used to assess riparian 

inundation extents and to interpret channel–floodplain 

connectivity. Water-surface extents were constructed on the 

basis of flow releases from Lewiston Dam, which ranged 

from 2,000 to 11,000 ft3

/s with tributary flows incorporated 

downstream. Lower elevation channel features were 

topographically inset relative to riparian and upland features. 

This nested topographic relation is illustrated in figure 5. 

Generally, higher elevation features are older and inundated 

less frequently by larger flows.

The boundary between the upland and riparian 

environments is delineated by the pre-dam floodplain, which 

is a relict depositional landform that is partially inundated at 

6,000 ft3/s and fully inundated at about 11,000 ft3/s. Under the 

regulated-flow regime in use at the time of writing, the upland 

environment is inundated only during extreme flows that have 

large tributary contributions. 

Three floodplain types were defined: a relatively 

continuous, higher elevation pre-dam floodplain; a series 

of intermittent constructed floodplains; and lower elevation 

topographic benches created by the post-ROD flow regime. 

Isolated constructed floodplains were created by mechanical 

rehabilitation (vegetation removal, re-contouring, and 

surface lowering) as part of the USFWS bank-rehabilitation 

program in the early 1990s and by the TRRP after 2005. The 

larger scale TRRP projects included constructed floodplains 

designed to be inundated by the post-ROD mean annual 

peak-flow release (about 6,000 ft3/s). The lowest elevation 

riparian features are post-dam topographic benches composed 

of coalesced bars. The post-dam benches are composed of 

previously active bars that were stabilized by 1975 as a result 

of declines in transport capacity due to flow regulation and 

concurrent vegetation encroachment. By 1980, these stable 

bars had coalesced into relatively continuous low-elevation 

floodplain features. Under the flow regime in use at the time 

of writing, these benches are inundated by flows ranging 

between about 2,000 and 4,500 ft3

/s. Portions of these features 

are elevated as a result of vegetation encroachment, which 

facilitated sediment deposition and development of riparian 

berms. The extent and frequency of inundation is influenced 

by the presence of these berms, which act as natural levees. 

The active-channel environment (table 2) includes 

the baseflow-wetted channel and morphologically activechannel margins characterized by bedload transport. Similar 

to previous studies (Grant and Swanson, 1995; Church, 

2002; Zilliani and Surian, 2012), we delineated a dynamic 

active-channel boundary that included wetted-channel features 

and unvegetated or sparsely vegetated bars. The mapping 

protocol accommodated the transitional boundary between the 

channel and riparian environments that expands and contracts 

through time.
10 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

Table 2. Mapping protocol structure and geomorphic feature descriptions.—Continued 

[See companion report by Curtis and Guerrero (2015) for additional details. Abbreviations: FPkm, floodplain kilometer; ft3/s, cubic foot per second; km, 

kilometer; km2, square kilometer; m, meters; ROD, record of decision; TRRP, Trinity River Restoration Program; USFWS, U.S. Fish and Wildlife Service; 

%, percent]

Geomorphic setting Feature description

Terrestrial environment

Uplands Uplands include areas underlain by soil, colluvium, alluvium, bedrock, or legacy mine tailings. Unless 

altered by mechanical restoration, the areal extent of upland features typically persists throughout the 

historic imagery.

Riparian environment

Islands Alluvial features bounded on all sides by water and distinguished from medial bars by denser mature 

vegetation, greater areal extents, and higher elevations. Although islands existed prior to 1980, most 

were created by side-channel construction.

Floodplains Floodplain features typically exhibit a vegetation gradient with the highest density of vegetation along the 

active-channel margin; density decreases with increasing distance from the channel margin.

Pre-dam floodplain This broad, relict depositional feature was created and inundated annually by the unregulated pre-dam flow 

regime, but is inundated periodically under the post-dam flow regime by flows between about 6,000 and 

11,000 ft3

/s. 

Constructed floodplains Discontinuous restoration features created by mechanical vegetation removal, re-contouring, and surface 

lowering as part of the USFWS bank-rehabilitation program in the early 1990s and since 2005 as part of 

the TRRP bank-rehabilitation program. 

Post-dam topographic 

bench

Depositional features composed of coalesced bars stabilized prior to 1975 because of declines in scouring 

flows and the associated encroachment of vegetation. Portions of these features are elevated because of 

vegetation-facilitated sediment deposition and development of a riparian berm along the channel margin. 

Riparian wetlands These disconnected aquatic features are outside the modern active-channel boundary. Only areas containing 

water in the base imagery were mapped, even when it was apparent that additional areas would be 

inundated seasonally.

Other Unique constructed features, such as borrow pits and gravel-recruitment piles.

Active-channel environment

Baseflow wetted channel The primary channel delivers the majority of flow and, where the channel splits, it is identified as the 

widest channel. Wetted-channel area is delineated by the wetted perimeter, as seen in the base imagery. 

Secondary water features Wetted-channel features that do not deliver the majority of channel flow. Only areas containing water in 

the base imagery were mapped, even when it was apparent that additional areas were inundated at higher 

flows.

Alcove Secondary water feature connected at one end to any wetted channel, including mainstem, tributary, sidechannel, or split-flow channel. 

Wetland Secondary water feature completely disconnected from any other wetted-channel feature. 

Side-channel Secondary channels connected to the primary channel at the upstream and downstream ends and 

distinguished from split-flow channels by conveyance of less than 20% of total summer baseflow and 

generally less than 10%. The percentage of flow conveyance was estimated from channel widths.

Split-flow channel Secondary channels created by flow separation that results in a change in the river morphology. Split-flow 

channels convey between 20 and 50% of baseflow. The percentage of flow conveyance was estimated 

from channel widths.

Bar Dynamic features created by bedload transport typically oriented parallel to the primary flow direction. The 

boundary between bars and adjacent riparian or upland features was delineated by using observational 

criteria that included morphology, vegetation type and density, and physical evidence of scour or 

deposition. 

Lateral Depositional channel feature created and maintained by active bedload transport and attached to the 

channel margin. 

Medial Depositional channel feature created and maintained by active bedload transport and surrounded by water 

on all sides.

Table 2. Mapping protocol structure and geomorphic feature descriptions.
Methods 11

Table 2. Mapping protocol structure and geomorphic feature descriptions.—Continued 

[See companion report by Curtis and Guerrero (2015) for additional details. Abbreviations: FPkm, floodplain kilometer; ft3/s, cubic foot per second; km, 

kilometer; km2, square kilometer; m, meters; ROD, record of decision; TRRP, Trinity River Restoration Program; USFWS, U.S. Fish and Wildlife Service; 

%, percent]

Geomorphic setting Feature description

Active-channel environment—Continued

Bedrock outcrops Static, non-alluvial features persistent in most or all years of base imagery. Can be buried by sediment in 

some years and exposed in others. Bedrock outcrops are typically darker than alluvial features and have 

a rough tone, jagged boundary, and lineations indicative of bedrock texture.

Other Unique constructed features, such as hydraulic grade controls, bank stabilization features, and historic 

bridge pilings. 

Additional mapping attributes

Vegetation density

Bare to sparse Vegetation covers less than 10%. 

Moderate Vegetation covers 10 to 40%. 

Dense Vegetation covers greater than 40%.

Restoration features

Constructed Features created by in-channel gravel placement or channel and bank rehabilitation.

Bar stability

Stable No physical evidence of scour, mobilization, or deposition in the current imagery when compared to the 

previous imagery. The channel margin can have bare to dense vegetation, but must have a stable areal 

extent. 

Active Obvious physical evidence of scour, mobilization, or incipient deposition when compared to previous 

imagery. The baseflow-channel margin and the bar-surface area must be bare to sparsely vegetated in the 

current imagery. 

Uplands

Geomorphic floodplain

Active bar

Constructed floodplain

Terrace

Post-dam

topographic

bench

Flow

Figure 5. Example of the topographic relations among depositional and constructed features for the Trinity River downstream 

from Lewiston Dam, California (photograph by J.A. Curtis). Photo shows left bank downstream of Canyon Creek (51 floodplain 

kilometers, or FPkm).
12 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

Channel features were assigned either to mainstem or 

tributary environments, and a simple bar classification (medial 

and lateral) was used (table 2). The presence of flowing or 

stagnant water delineated the wetted perimeter of baseflow 

channels and secondary water features (split-flow channels, 

side channels, alcoves, and aquatic wetlands). For the 

baseflow channels and secondary water features, only areas 

containing water were digitized, even when it was apparent 

that additional areas were inundated at higher flows. Three 

additional feature attributes were included in the geodatabase: 

restoration, vegetation density, and bar stability. Constructed 

features were labeled, which enabled assessment of features 

created or altered mechanically by in-channel gravel 

placement, side-channel construction, or bank rehabilitation. 

Vegetation density was estimated for all bar features, and 

bar stability was defined by vegetation density estimates, 

evidence of scour or deposition, and the presence or absence 

of vegetation along the baseflow-channel margin. Active 

bars typically have bare-to-sparse vegetation and a dynamic 

perimeter along the channel margin. In comparison, stable 

bars can have bare-to-dense vegetation, but more typically are 

characterized by moderate-to-dense vegetation and generally 

have a stable areal extent in consecutive orthophotographs. 

Interpretation of Geomorphic Mapping

A spatial framework for interpreting results was 

developed on the basis of longitudinal changes in transport 

capacity and sediment-supply conditions. The framework 

was inferred from valley and channel confinement, location 

of tributary confluences, and the presence of in-channel 

legacy mine tailings and was used to delineate study reaches. 

The mainstem was initially divided into upper, central, 

and lower channel segments and then was subdivided into 

13 geomorphic reaches (table 3). Lateral changes in channel 

and riparian features caused by bar and bank processes were 

investigated at a 1-km sub-reach scale.

Similar to recent studies by Wallick and others (2010, 

2011), floodplain distance, rather than channel distance, was 

used to reference study-reach locations because distances 

along this line were static during the study period, whereas 

channel distances varied with time. Floodplain distance was 

defined as the distance downstream from Lewiston Dam along 

a centerline digitized within the pre-dam floodplain boundary. 

The numbering system begins at Lewiston Dam and ends 

upstream from the North Fork Trinity River confluence.

Channel lengths were estimated by using channel 

centerlines, digitized within the baseflow channel boundary for 

each of the six orthophotographs. Reach-averaged estimates 

of active-channel widths were calculated by dividing the 

active-channel area by channel length. The active-channel 

area included the primary wetted channel; secondary water 

features; in-channel features, such as bedrock outcrops; and 

active bars.

Two channel attributes that characterize the quality 

and quantity of available habitat are channel complexity 

and shoreline length (Trinity River Restoration Program 

and ESSA Technologies Ltd., 2009). Channel complexity 

was estimated by summing the areal extents of active bar 

and secondary water features. The perimeter of the wetted 

channel edge, including the primary baseflow channel and all 

connected secondary water features, was used to estimate the 

shoreline length. 

We created five change maps, which preserved individual 

map attributes and bracketed the period of interest, by 

intersecting consecutive maps. Change polygons, which 

represent the nature and extent of bar and bank processes, 

were created and summarized for each of the 1-km subreaches 

by using a series of conditional statements. Bar-accretion 

polygons were identified by the conversion of a water feature 

to a bar feature, and bar-scour polygons were identified by the 

conversion of a bar to water feature. Bank-erosion polygons 

were identified by the conversion of an upland or riparian 

feature to a channel feature, and bank-accretion polygons were 

identified by the conversion of a channel feature to a riparian 

feature. We also investigated bar-vegetation dynamics by 

using conditional statements to quantify the area converted 

from a sparsely vegetated to a densely vegetated bar, 

indicative of stabilization by vegetation encroachment, and the 

area converted from a densely vegetated to sparsely vegetated 

bar, indicative of scour and mobilization.

Uncertainty and Error Analysis

Uncertainty and error result when real world data are 

transferred to digital formats (Mount and Louis, 2005; Hughes 

and others, 2006). Errors associated with digitized data 

include operational errors, discharge differences during photo 

acquisition, and digitizing errors due to features obscured by 

vegetation or shadows (table 4). Curtis and Guerrero (2015) 

determined that operational and variable discharge errors 

were negligible, and digitizing errors based on the accuracy 

and precision of the digitizing process were conservatively 

inferred to be about 10 percent.

In this report, we present an additional error analysis 

associated with interpreting lateral channel changes. Although 

the root mean square error (RMSE) is generally regarded as 

a poor indicator of overall horizontal accuracy (Hughes and 

others, 2006), it is typically the only metric available to define 

uncertainty associated with lateral channel changes quantified 

by using repeat rectified photography (O’Connor and others, 

2003; Micheli and others, 2004; Draut and others, 2008; 

Wallick and others, 2010; Wallick and others, 2011). 

The greatest RMSE among the orthophotos was used to 

determine a threshold polygon area to address the horizontal 

uncertainty due to poor alignment. Change polygons smaller 

than the threshold area likely represent rectification errors 

and were removed from the lateral change analyses. The 1980 

imagery had the greatest estimated RMSE (9.8 m; table 4). 
Methods 13

Table 3A. Geomorphic reach descriptions and restoration history for study segments along the Trinity River, California, downstream from Lewiston Dam: upper river segment.[Abbreviations: FPkm, floodplain kilometer; km2, square kilometer; m, meters; m/m, meter per meter; ROD, Record of Decision; USGS, U.S. Geological Survey; —, no data]

Study 

reach Reach name

Pre-dam 

annual 

floodplain 

width

(m)

Floodplain 

distance 

(FPkm)

Reach length 

(FPkm)

Local

contributing

drainage

area 

(km2)

Reach 

slope 

(m/m)

Geomorphic description

Pre-ROD 

restoration 

actions

Post-ROD channelrehabilitation 

projects and gravel 

augmentation

1 Lewiston 103 0–1.4 1.4 1.1 0.004 Channel confined by Lewiston fish-hatchery 

facility. Contains USGS Lewiston streamgaging station.

Side-channel and 

riffle construction, coarse-sediment placement.

Sven Olbertson 2008. 

Hatchery gravelaugmentation site.

2 Sawmill 115 1.4–6.5 5.1 44.0 0.002 Relatively small, local sediment sources include 

Deadwood Creek and Hoadley Gulch.

Side-channel and 

riffle construction, pool dredging.

Deadwood, Lewiston 

Cableway, Hoadley Gulch 2008. Sawmill 2009, Sawmill Point and diversion pool gravel-augmentation sites.

3 Rush Creek 175 6.5–12.5 6.0 171.2 0.002 Local sediment sources include Rush Creek, 

Grass Valley Creek, and erosion of legacy mine tailings. Contains non-USGS Grass Valley Creek gaging station.

Side-channel and 

riffle construction, pool dredging, feathered-edge project.

Dark Gulch 2008. 

Lowden and Trinity House Gulch 2010, Lowden gravel-augmentation site.

4 Stott 111 12.5–16.7 4.2 13.6 0.002 No major local sediment sources. Riffle construction 

and pool dredging.

—

5 Poker Bar 

Canyon

83 16.7–23.4 6.7 13.2 0.002 No major local sediment sources. Confined 

bedrock canyon. Contains USGS Limekiln Gulch (TRLG) streamgaging station.

Side-channel 

construction, two feathered edge projects.

—
14 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011 Table 3B. Geomorphic reach descriptions and restoration history for study segments along the Trinity River, California, downstream from Lewiston Dam: central river segment.

[Abbreviations: FPkm, floodplain kilometer; km2, square kilometer; m, meters; m/m, meter per meter; ROD, Record of Decision; USGS, U.S. Geological Survey; —, no data]

Study 

reach Reach name

Pre-dam 

annual 

floodplain 

width 

(m)

Floodplain 

distance 

(FPkm)

Reach length 

(FPkm)

Contributing

drainage

area 

(km2

)

Reach 

slope 

(m/m)

Geomorphic description

Pre-ROD 

restoration 

actions

Post-ROD channelrehabilitation 

projects and gravel 

augmentation

6 Vitzhum 105 23.4–29.2 5.8 225.0 0.002 Local sediment sources include Indian Creek, 

Weaver Creek, and erosion of legacy mine tailings.

Side-channel 

construction.

Indian Creek 2007.

7 Reading 

Creek

97 29.2–35.5 6.3 89.8 0.003 Local sediment sources include Reading 

Creek. Contains USGS Douglas City streamgaging station.

Feathered-edge 

project.

Reading Creek 2010.

8 Dutton 

Creek

65 35.5–39.6 4.1 221.6 0.002 Confined bedrock canyon with relatively 

small local sediment supply from Brown’s Creek. 

—

—

Table 3C. Geomorphic reach descriptions and restoration history for study segments along the Trinity River, California, downstream from Lewiston Dam: lower river segment.[Abbreviations: FPkm, floodplain kilometer; km2, square kilometer; m, meters; m/m, meter per meter; ROD, Record of Decision; USGS, U.S. Geological Survey; —, no data]

Study 

reach Reach name

Pre-dam 

annual 

floodplain 

width 

(m)

Floodplain 

distance 

(FPkm)

Reach length 

(FPkm)

Contributing

drainage

area 

(km2

)

Reach 

slope 

(m/m)

Geomorphic description

Pre-ROD 

restoration 

actions

Post-ROD channel 

rehabilitation 

projects and gravel 

augmentation

9 Dutch Creek 137 39.6–47.9 8.3 67.8 0.002 Local sediment sources include erosion of legacy 

mine tailings. This reach is fault controlled with the channel turning north to follow the trend of the Siskiyou-North Fork fault system.

Three featherededge projects.

—

10 Oregon Gulch 131 47.9–50.5 2.6 31.8 0.002 Local sediment sources include Oregon Gulch and 

erosion of legacy mine tailings. Notable cutbank erosion is occuring. Contains USGS Junction City streamgaging station.

Side-channel 

construction.

—

11 Canyon Creek 153 50.5–54.8 4.3 186.0 0.003 Local sediment source at Canyon Creek. Feathered-edge 

project.

Hocker Flat 2005.

12 Lime Point 141 54.8–58.6 3.8 9.6 0.002 No major local sediment sources. This reach 

crosses a regional thrust fault that juxtaposes less resistant Devonian age bedrock and more resistant Jurassic age geologic strata.

Side-channel 

construction, featherededge project.

Canyon Creek Suite 

(Conner Creek and Valdor Gulch) 2006 and Wheel Gulch 2011.

13 Pear Tree 92 58.6–61.3 2.7 9.9 0.002 No major local sediment sources. Bounded by two 

regional thrust faults and incised into resistant Jurassic age geologic strata. Contains USGS North Fork Trinity streamgaging station.

—

Canyon Creek Suite 

(Elkhorn and Pear Tree) 2006.
Methods 15

Table 4. Uncertainty analysis for six geomorphic maps of the Trinity River, California, downstream from Lewiston Dam. 

[Note see Curtis and Guerrero (2015) for additional details. Abbreviations: ft3/s, cubic feet per second; m, meters; mm/dd/yyyy, month/day/year; RMSE, root 

mean squared error]

Year Date

(mm/dd/yyyy)

Rectified orthophoto 

resolution

(m)

RMSE1

(m)

Stream discharge 

at Lewiston gage 

(ft3

/s)

Difference in 

water depth2

 

(m)

Inferred 

digitizing error3 

(percent)

1980 05/16/1980 0.6 9.8 288.0 0.0 10

1997 10/20/1997 0.2 1.5 285.0 0.0 10

2001 11/07/2001 0.2 1.5 298.0 0.0 10

2006 07/25/2006 0.2 1.5 405.0 0.1 10

2009 04/16/2009 0.2 0.4 291.0 0.0 10

2011 08/16/2011 0.2 0.2 446.0 0.1 10

1

Represents horizontal uncertainty for each ortho-rectified image.

2

Error associated with variable discharge during photo acquisition estimated from gaging records.

3

Digitizing error based on accuracy and precision of digitizing.

This value was inferred from pixel resolution and national 

accuracy standards (Curtis and Guerrero, 2015). We checked 

the alignment between the 1980 and1997 photography and 

concluded that 9.8 m represented an overly conservative 

estimate and determined that 5 m was a more representative 

estimate of RMSE. By using the less conservative RMSE of 

5 m, we estimated a threshold size of 25 m2 and rounded this 

up to 30 m2, which also represented the minimum polygon 

size for features included in the geodatabase. All change 

polygons smaller than 30 m2 were eliminated from the 

lateral-change analysis.

We did not explicitly quantify uncertainty associated 

with our geomorphic-change analyses because uncertainty 

is scale-and location dependent, but here we present some 

calculations that indicate the error associated with large wellexposed features was about 3 percent compared to about 10 

percent for small, obscured features. Curtis and Guerrero 

(2015) determined digitized-line precision ranged from about 

0.85 to 2.0 m. This precision equated to a 7 to 13 percent 

error, or an average error of plus or minus 10 percent, for 

a representative 30-m channel width. The mean perimeter 

of active bars in 2011 was 130 m, and active bars were 

typically well exposed, so application of the lowest linework 

precision (plus or minus 0.85 m) was appropriate. For an 

equi-dimensional feature, with a perimeter of 130 m and area 

of 1,056 m2, the estimated uncertainty was within 3 percent.

Assessing Natural and Managed Drivers of 

Geomorphic Change

In fluvial systems, geomorphic change is driven by a 

complex set of interrelated causal mechanisms including 

numerous climatic, lithologic, topologic, biologic, and 

anthropogenic factors that often exist concurrently and 

sequentially, making it difficult to disentangle their relative 

importance. We specifically investigated the cumulative 

influence of streamflow, sediment supply, sediment 

management, and mechanical channel rehabilitation during 

the five study periods.

Streamflow and Sediment Supply

Flow analysis was limited by a lack of gaging records. 

We analyzed available records from the five mainstem gaging 

stations (fig. 2) and focused our analysis on the Lewiston 

gage, which has the longest period of record that spans the 

study period (table 5). We inferred ungaged tributary‐flows 

by comparing mainstem-flows at stations upstream and 

downstream of tributary confluences. Our goal was to 

characterize the relative differences between mainstem flows 

during the five study periods. With this in mind, we assessed 

the magnitude, frequency, timing, and duration of flows and 

investigated the characteristics of geomorphically important 

flow events that took place in 1997, 1998, 2006, and 2011.

Previous investigations characterized the study 

reach as sediment-rich with abundant tributary sediment 

supplies (Pitlick and Wilcock, 2001). The exception to this 

generalization was in the upper river immediately downstream 

from Lewiston Dam, where post-dam sediment-deficit 

conditions existed (Gaeuman and Krause, 2010). The primary 

post-dam sediment sources, listed in order of importance, 

included tributary contributions, localized scour of in-channel 

sources, and gravel augmentation (Ritter, 1968; Knott, 1974; 

Trinity River Taskforce, 1979; Trinity Restoration Associates, 

Inc., 1993; Graham Matthews and Associates, 2001; Pitlick and 

Wilcock, 2001; Gaeuman and Krause, 2010). 

Although there has been extensive monitoring of 

mainstem sediment transport in the upper river since 2005 

(Graham Matthews and Associates, 2012), few measured 

data were available for the pre-2005 periods. Without direct 

measurements, sediment supply could only be evaluated 

indirectly. We assumed there was no supply of bed-materialsized sediment (greater than 0.5 mm) from sources upstream of 

Lewiston Dam. We then assumed a positive correlation between 

flow and sediment supply and inferred an increase in sediment 

supply with increasing mainstem flow.
16 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011 Table 5. Summary of stream discharge data for the Trinity River, California, downstream from Lewiston Dam. 

[Abbreviations: ft3/s, cubic feet per second; FPkm, floodplain kilometer; km2, square kilometers; m, meters; NGVD, National Geodetic Vertical Datum; ROD, Record of Decision; USGS, U.S. Geological 

Survey; WY, water year; —, no data; °, degree; ʹ, minute; ʺ, second]

USGS 

station 

identifier

Gage name Gage name abbreviation Name used in this report Location (latitude/ longitude) Drainage area (km2

)

Datum 

elevation 

above 

NGVD 1929 

(m) 

Available 

data

(WY)

Distance 

downstream 

from 

Lewiston Dam

(FPkm)

Mean daily 

discharge4

(ft3/s)

Pre-ROD 

mean annual 

peak 

(ft3/s)

Post-ROD 

mean annual 

peak

(ft3/s)

11525500 Trinity River at Lewiston TRAL Lewiston 40°43ʹ10ʺ 

122°48ʹ09ʺ

1,862 554 1911–2011 1.5 770 3,980 6,550

11525655 Trinity River at Limekiln Gulch TRLG Limekiln Gulch 40°40ʹ22ʺ 

122°55ʹ10ʺ

2,098 503 1982–1991 

2002–20111

20.4 830

— 7,120

11525854 Trinity River at Douglas City TRDC Douglas City 40°38ʹ43ʺ 

122°57ʹ24ʺ

2,411 487 1996–20112 29.9 1,230

— 7,570

11526250 Trinity River at Junction City TRJC Junction City 40°43ʹ43ʺ 

123°03ʹ39ʺ

2,738 440 1996–20113 50.3 1,430

— 9,790

11526400 Trinity River upstream from 

North Fork near Helena

TRNF Upstream from 

North Fork

40°46ʹ00ʺ 

123°06ʹ48ʺ

2,945 421 2006–2011 60.1 1,550

— 11,640

111525655 missing records WY 1992 to WY2002.211525854 operated as non-USGS station WY1997 to WY2002.311526250 operated as non-USGS station WY1997 to WY2002, peak data unavailable for WY1997 to 2002.4Mean daily discharge calculated by using the period of record.
Results 17

Sediment Management and Mechanical 

Channel Rehabilitation

We compiled, analyzed, and summarized information 

related to sediment management and mechanical rehabilitation 

from available reports (Kondolf and Minear, 2004; Gaeuman, 

2008; Gaeuman and Krause, 2011; Hoopa Valley Tribe and 

others, 2011b; Graham Matthews and Associates, 2012; 

Krause, 2012b) and from communication with TRRP staff. 

A lack of “as built” surveys, which reflect any changes 

made during construction, required that we use the original 

design specifications to identify the location and extent of 

constructed features. The digitized extent of constructed 

features do not always represent the actual “as built” extents 

because geomorphic changes could have occurred between 

construction and photo acquisition. Although these data 

required little analysis, they were critical for interpreting 

management actions that altered river morphology.

Results

Our results focus on spatial and temporal trends in 

the areal distribution of geomorphic features. The mapping 

data represent channel conditions at discrete points in time, 

whereas estimates of geomorphic change represent the 

cumulative response to numerous controlling factors during 

each study period. We present estimates of cumulative 

geomorphic change, describe controlling factors, and assess 

the primary causal mechanisms that created geomorphic 

change during each of the five study periods. The areal extent 

of individual geomorphic features, summarized for each of the 

thirteen geomorphic reaches, is presented in appendix A.

Spatial and Temporal Analysis of 

Geomorphic Change

When the areal extent of the riparian and channel 

environments were compared at the system-scale geomorphic 

change was not apparent because large riparian features 

dominated the landscape (fig.6A). In particular, the riparian 

environment was dominated by the pre-dam floodplain. The 

active-channel margin represents the boundary between 

riparian and channel features. In figures 6B to 6F, the change 

in active-channel area is shown for the five periods of interest. 

An increase in the active-channel area equated to an equal loss 

of riparian area, and likewise a decrease in the active-channel 

area equated to an equal increase in riparian area.

Excluding the pre-dam floodplain and focusing on 

smaller-scale lower-elevation features highlighted spatial 

and temporal changes in riparian diversity (fig. 7). In 

1980, post-dam benches composed 94 percent of the lower 

elevation riparian environment (fig.7A). By 2001, floodplain 

construction and bar stabilization increased riparian diversity, 

and the proportion of post-dam benches decreased to 

86 percent (fig.7C). By the end of the study period in 2011, 

the relative proportions of post-dam benches, constructed 

floodplains, stable bars, and riparian wetlands were 60, 27, 

10 and 3 percent, respectively (fig.7F).

The diversity of channel features was more variable than 

riparian features in space and time (fig. 8). In 1980, channel 

diversity was greatest in the upper and central river reaches 

and channel-complexity features, such as active bars and 

secondary water features (split-flow channels, side channels, 

alcoves, and aquatic wetlands), composed approximately 

12 percent of the active-channel area (fig.8A). From 1980 to 

2001, the active-channel area increased by 20 percent (fig.6). 

By 2001, there were relatively more channel complexity 

features in the upper and central river reaches (fig.8B) and 

these features composed 17 percent of the active-channel area. 

From 2001 to 2011, the increase in active-channel area was 

about 5 percent. By 2011, channel complexity had increased 

in the upper river, but decreased in the lower river. By 2011, 

the channel-complexity features occupied 14 percent of the 

active-channel area (fig.8F). During the longer (21 years) 

and relatively wetter pre‐ROD period, increases in activechannel area and channel complexity were 20 and 70 percent, 

respectively. The post-ROD period was shorter (10 years) 

and relatively drier, with intensified management. During this 

later period, there were smaller, but measurable, increases 

in active-channel area of about 5 percent, and channel 

complexity decreased by 3 percent.

Spatial and temporal changes in geomorphic features 

are illustrated in greater detail in this section and are used to 

interpret trajectories and rates of geomorphic change during 

the five study periods. We present summary data for individual 

upland, riparian, or channel features in the context of the 

13 geomorphic reaches and the upper, central, and lower river 

segments, as defined in table 3. In each figure, panel A shows 

the cumulative area of each geomorphic feature summed 

in the downstream direction from Lewiston Dam to the 

confluence with the North Fork Trinity River; panel B shows 

cumulative change in feature area per year, where the slope 

of the line represents and annual rate of change; and panel C 

shows a time series of feature area scaled by reach length and 

illustrates trajectories of change. Note the differences in the 

scale of the y-axis in these figures.

Uplands showed little cumulative change during the 

study period (fig. 9), particularly when compared to changes 

in total riparian area (fig. 10) and individual riparian features 

(figs. 11–14). The exception to this generality was Reach 3 

(fig. 9B), where uplands were converted to constructed 

floodplains by mechanical surface lowering from 2009 

to 2011.
18 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

sac12-0459_fig06

Areal extent of channel features

Areal extent of riparian features

Change in active-channel area

EXPLANATION EXPLANATION

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1 2 3 4 5 6 7 8 9 10 11 12 13

Geomorphic reaches

A. 1980

0

20,000

40,000

60,000

80,000

1 2 3 4 5 6 7 8 9 10 11 12 13

Geomorphic reaches

B. 1980–1997

-5,000

0

5,000

10,000

15,000

20,000

25,000

1 2 3 4 5 6 7 8 9 10 11 12 13

Area, in square meters

C. 1997–2001

-5,000

0

5,000

10,000

15,000

20,000

25,000

1 2 3 4 5 6 7 8 9 10 11 12 13

D. 2001–2006

-5,000

0

5,000

10,000

15,000

20,000

25,000

1 2 3 4 5 6 7 8 9 10 11 12 13

E. 2006–2009

-5,000

0

5,000

10,000

15,000

20,000

25,000

1 2 3 4 5 6 7 8 9 10 11 12 13

F. 2009–2011

-6,606

Figure 6. Areal extent of riparian and channel features along the Trinity River downstream from Lewiston Dam, California, 

A, in 1980, and change in active-channel area for five periods from 1980 to 2011: B, 1980 to 1997; C, 1997 to 2001; D, 2001 to 

2006; E, 2006 to 2009; and F, 2009 to 2011. Note differences in y-axis scale among periods.
Results 19

sac12-0459_fig07

EXPLANATION

Other

Stable bars

Post-dam topographic bench

Constructed floodplains

Riparian wetland

0

50,000

100,000

150,000

200,000

250,000

300,000

1 2 3 4 5 6 7 8 9 10 11 12 13

Geomorphic reaches

A. 1980

0

50,000

100,000

150,000

200,000

250,000

300,000

1 2 3 4 5 6 7 8 9 10 11 12 13

Geomorphic reaches

B. 1997

0

50,000

100,000

150,000

200,000

250,000

300,000

1 2 3 4 5 6 7 8 9 10 11 12 13

Area, in square meters

C. 2001

0

50,000

100,000

150,000

200,000

250,000

300,000

1 2 3 4 5 6 7 8 9 10 11 12 13

D. 2006

0

50,000

100,000

150,000

200,000

250,000

300,000

1 2 3 4 5 6 7 8 9 10 11 12 13

E. 2009

0

50,000

100,000

150,000

200,000

250,000

300,000

1 2 3 4 5 6 7 8 9 10 11 12 13

F. 2011

Figure 7. Areal extent of lower elevation riparian features along the Trinity River downstream from Lewiston Dam, California, 

in A, 1980; B, 1997; C, 2001; D, 2006; E, 2009; and F, 2011.
20 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

sac12-0459_fig08

EXPLANATION

1 2 3 4 5 6 7 8 9 10 11 12 13

Geomorphic reaches

A. 1980

1 2 3 4 5 6 7 8 9 10 11 12 13

Geomorphic reaches

B. 1997

1 2 3 4 5 6 7 8 9 10 11 12 13

Area, in square meters

C. 2001

1 2 3 4 5 6 7 8 9 10 11 12 13

D. 2006

1 2 3 4 5 6 7 8 9 10 11 12 13

E. 2009

1 2 3 4 5 6 7 8 9 10 11 12 13

F. 2011

Other

Active bars

Aquatic wetland

Split-flow channel

Side channel

Alcove

Exposed bedrock

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

Figure 8. Areal extent of channel-complexity features within the active channel along the Trinity River downstream from 

Lewiston Dam, California, in A, 1980; B, 1997; C, 2001; D, 2006; E, 2009; and F, 2011.
Results 21

EXPLANATION

1980–1997

1997–2001

2001–2006

2006–2009

2009–2011

EXPLANATION

1980

1997

2001

2006

2009

2011

Reach 13

Reach 12

Reach 11

Reach 10

Reach 9

Reach 8

Reach 7

Reach 6

Reach 5

Reach 4

Reach 3

Reach 2

Reach 1

Lower river

Central river

Upper river

EXPLANATION

Geomorphic reach

Tributary confluence

0

50

100

150

200

250

300

1980 1985 1990 1995 2000 2005 2010

Area, in 1,000 square meters

per floodplain kilometer 

Year

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

Cumulative area, in 1,000 square meters

0 10 20 30 40 50 60

Distance downstream from Lewiston Dam, in floodplain kilometers

-30

-25

-20

-15

-10

-5

0

5

10

Cumulative change in area per year,

in 1,000 square meters per year

Uplands

R8

B

C

R1 R5 R6 R7 R8 R9 R10 R11 R12 R13 Geomorphic

reach

Tributary

confluence

R2 R3 R4

A

Figure 9. Area of uplands along the Trinity River downstream from Lewiston Dam, California, and change in upland area 

from 1980 to 2011: A, cumulative area by reach; B, cumulative change in area per year by reach; C, area by study reach and 

segments over time.
22 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

sac12-0459_fig10

EXPLANATION

1980–1997

1997–2001

2001–2006

2006–2009

2009–2011

EXPLANATION

1980

1997

2001

2006

2009

2011

Reach 13

Reach 12

Reach 11

Reach 10

Reach 9

Reach 8

Reach 7

Reach 6

Reach 5

Reach 4

Reach 3

Reach 2

Reach 1

Lower river

Central river

Upper river

EXPLANATION

Geomorphic reach

Tributary confluence

1980 1985 1990 1995 2000 2005 2010

Area, in 1,000 square meters

per floodplain kilometer 

Year

Cumulative area, in 1,000 square meters

0 10 20 30 40 50 60

Distance downstream from Lewiston Dam, in floodplain kilometers

Cumulative change in area per year,

in 1,000 square meters per year

0

1,000

2,000

3,000

4,000

5,000

6,000

Riparian features

-80

-60

-40

-20

0

20

0

20

40

60

80

100

120

140

R8

B

C

R1 R5 R6 R7 R8 R9 R10 R11 R12 R13 Geomorphic

reach

Tributary

confluence

R2 R3 R4

A

Figure 10. Area of riparian features along the Trinity River downstream from Lewiston Dam, California, and change in 

riparian area from 1980 to 2011: A, cumulative area by study reach; B, cumulative change in area per year by study reach; 

C, area by study reach and segments over time.
Results 23

Riparian area generally decreased during the study 

period, but the decrease accelerated after 2009 (fig. 10B). The 

post-2009 decrease in riparian area was primarily caused by 

conversion of a large portion of pre-dam floodplain (fig. 11B) 

into a series of constructed floodplains by mechanical surface 

lowering. The area of post-dam benches also decreased during 

the study period, with the largest cumalative decreases from 

1980 to 1997 (fig. 12A) caused by bank erosion and bar 

scour. Post-dam benches were also converted into constructed 

floodplains by vegetated berm removal and mechanical 

surface lowering. Floodplain construction accelerated during 

the post-ROD period, especially after 2006 (fig. 13). 

Stable bars are transitional units, originally deposited in 

the active channel, but are part of the riparian environment 

when stabilized by vegetation and revert back to the active 

channel when scoured and remobilized. Bar stabilization 

accelerated from 1997 to 2001(fig.14A), and the area of stable 

bars continued to increase until the end of the study period 

in 2011 (fig. 14C). The exception to this generalization was 

a decrease in stable bar area from 2006 to 2009 in the lower 

river caused by the 2006 tributary-flow event.

The active-channel area generally increased during the 

study period as upland and riparian features were eroded 

or mechanically altered. The largest cumulative increase in 

active-channel area occurred from 1980 to 1997 (fig. 15A). 

When cumulative change is scaled by time (fig. 15B), the 

highest rate of change in the upper river was in Reach 3 during 

the relatively short period from 2009 to 2011. This period 

included the 2011 flow release, the largest since 1974 (Krause, 

2012a), and several large scale TRRP bank rehabilitation 

projects. The cumulative change in active-channel area across 

the study area from 2009 to 2011 was slightly less than the 

rate estimated for the much longer and relatively wetter period 

from 1980 to 1997.

The largest cumulative increase in active-bar area 

occurred between 1997 and 2001, primarily downstream from 

Indian Creek (25.6 percent; fig. 16A). Post-2001 changes in 

active-bar area were variable across the study area. From 2001 

to 2006, there was a slight increase in active-bar area in the 

upper river (fig.16B). With the start of gravel augmentation by 

direct injection in 2008, active-bar area increased notably in 

the upper river between 2006 and 2011 (fig. 16C). From 2001 

to 2009, active-bar area decreased in the central river, which 

was followed by an increase from 2009 to 2011. From 2001 to 

2006, active bar area decreased notably in the lower river, then 

remained relatively stable from 2006 to 2009, and decreased 

slightly from 2009 to 2011 (fig.16C). 

We combined the area of secondary water features 

(split‐flow channels, side channels, alcoves, and aquatic 

wetlands) into a single category for analysis because the 

trajectories of change for these small features were highly 

variable. There were large increases in the area of secondary 

water features from 1980 to 1997 (fig. 17A), primarily in the 

upper river. The area of secondary water features remained 

fairly static after 1997 (fig.17A), and there were minor 

decreases from 1997 to 2001, primarily in the central and 

lower river (fig. 17B). From 2001 to 2006 and 2006 to 2009, 

there were small increases in the area of secondary water 

features primarily in the central river, and from 2009 to 2011, 

there were larger increases in the area of secondary water 

features primarily in the lower river (fig. 17C). Trends in 

shoreline length were similar to those for secondary water 

features (fig. 18A).

From 1980 to 2006, average active-channel widths 

increased in all the study reaches (fig. 18B). In 1980, the active 

channel width was much greater in the upper river, but by 

1997, active-channel widths in the upper and lower river were 

about equal and remained similar for the remainder of the 

study period. Channel widths continued to increase from 1997 

to 2006, but remained stable from 2006 to 2009. From 2009 to 

2011, channel widths decreased slightly in the upper and lower 

river and increased slightly in the central river.

Natural and Managed Drivers of 

Geomorphic Change

Sediment retention by upstream dams, flow diversion, 

and flow regulation led to diminished sediment supply and 

transport capacity, particularly in the reach that extends from 

Lewiston Dam downstream to Rush Creek (0–6.5 FPkm). 

Further downstream, sediment supply from Grass Valley 

Creek (11.85 FPkm) was effectively eliminated by sediment 

retention dams constructed in 1986 (Trinity River Taskforce, 

1970). These retention ponds are actively maintained by 

dredging, under the present sediment-management program 

(Krause, 2012b). Although Deadwood Creek (1.65 FPkm) 

and Rush Creek (6.5 FPkm) contribute flow and sediment, 

transport capacity remains low downstream to Poker Bar 

Canyon, where channel confinement and transport capacity 

increase as the river flows through a confined bedrock canyon 

(16.7–23.4 FPkm). 

Contributing drainage area, sediment supply, and 

flow increase in the central river as a result of tributary 

contributions from Indian Creek (25.6 FPkm), Weaver Creek 

(28.0 FPkm), and Reading Creek (29.4 FPkm) and localized 

bank erosion of legacy mine tailings. Further downstream, the 

central river flows through a second confined bedrock reach 

(35.5–39.6 FPkm), where transport capacity increases, but 

sediment supply diminishes. 
24 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

sac12-0459_fig11

EXPLANATION

1980–1997

1997–2001

2001–2006

2006–2009

2009–2011

EXPLANATION

1980

1997

2001

2006

2009

2011

Reach 13

Reach 12

Reach 11

Reach 10

Reach 9

Reach 8

Reach 7

Reach 6

Reach 5

Reach 4

Reach 3

Reach 2

Reach 1

Lower river

Central river

Upper river

EXPLANATION

Geomorphic reach

Tributary confluence

1980 1985 1990 1995 2000 2005 2010

Area, in 1,000 square meters

per floodplain kilometer 

Year

Cumulative area, in 1,000 square meters

0 10 20 30 40 50 60

Distance downstream from Lewiston Dam, in floodplain kilometers

Cumulative change in area per year,

in 1,000 square meters per year

Pre-dam floodplain

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

-60

-50

-40

-30

-20

-10

0

10

0

10

20

30

40

50

60

70

80

90

100

R8

B

C

R1 R5 R6 R7 R8 R9 R10 R11 R12 R13 Geomorphic

reach

Tributary

confluence

R2 R3 R4

A

Figure 11. Area of the pre-dam floodplain along the Trinity River downstream from Lewiston Dam, California, and change 

in pre-dam floodplain area from 1980 to 2011: A, cumulative area by study reach; B, cumulative change in area per year by 

study reach; C, area by study reach and river segments over time.
Results 25

sac12-0459_fig12

EXPLANATION

1980–1997

1997–2001

2001–2006

2006–2009

2009–2011

EXPLANATION

1980

1997

2001

2006

2009

2011

Reach 13

Reach 12

Reach 11

Reach 10

Reach 9

Reach 8

Reach 7

Reach 6

Reach 5

Reach 4

Reach 3

Reach 2

Reach 1

Lower river

Central river

Upper river

EXPLANATION

Geomorphic reach

Tributary confluence

1980 1985 1990 1995 2000 2005 2010

Area, in 1,000 square meters

per floodplain kilometer 

Year

Cumulative area, in 1,000 square meters

0 10 20 30 40 50 60

Distance downstream from Lewiston Dam, in floodplain kilometers

Cumulative change in area per year,

in 1,000 square meters per year

0

200

400

600

800

1,000

1,200

1,400

1,600

-30

-25

-20

-15

-10

-5

0

5

10

0

5

10

15

20

25

30

35

40

Post-dam topographic benches

R8

B

C

R1 R5 R6 R7 R8 R9 R10 R11 R12 R13 Geomorphic

reach

Tributary

confluence

R2 R3 R4

A

Figure 12. Area of post-dam benches along the Trinity River downstream from Lewiston Dam, California, and change in 

post-dam bench area from 1980 to 2011: A, cumulative area by study reach; B, cumulative change in area per year by study 

reach; C, area by study reach and river segments over time.
26 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

sac12-0459_fig13

EXPLANATION

1980–1997

1997–2001

2001–2006

2006–2009

2009–2011

EXPLANATION

1980

1997

2001

2006

2009

2011

Reach 13

Reach 12

Reach 11

Reach 10

Reach 9

Reach 8

Reach 7

Reach 6

Reach 5

Reach 4

Reach 3

Reach 2

Reach 1

Lower river

Central river

Upper river

EXPLANATION

Geomorphic reach

Tributary confluence

1980 1985 1990 1995 2000 2005 2010

Area, in 1,000 square meters

per floodplain kilometer 

Year

Cumulative area, in 1,000 square meters

0 10 20 30 40 50 60

Distance downstream from Lewiston Dam, in floodplain kilometers

Cumulative change in area per year,

in 1,000 square meters per year

Constructed floodplains

0

5

10

15

20

0

100

200

300

400

-10

0

10

20

30

40

50

60

70

R8

B

C

R1 R5 R6 R7 R8 R9 R10 R11 R12 R13 Geomorphic

reach

Tributary

confluence

R2 R3 R4

A

Figure 13. Area of constructed floodplains along the Trinity River downstream from Lewiston Dam, California, and change 

in constructed floodplain area from 1980 to 2011: A, cumulative area by study reach; B, cumulative change in area per year 

by study reach; C, area by study reach and river segments over time.
Results 27

sac12-0459_fig14

EXPLANATION

1980–1997

1997–2001

2001–2006

2006–2009

2009–2011

EXPLANATION

1980

1997

2001

2006

2009

2011

Reach 13

Reach 12

Reach 11

Reach 10

Reach 9

Reach 8

Reach 7

Reach 6

Reach 5

Reach 4

Reach 3

Reach 2

Reach 1

Lower river

Central river

Upper river

EXPLANATION

Geomorphic reach

Tributary confluence

1980 1985 1990 1995 2000 2005 2010

Area, in 1,000 square meters

per floodplain kilometer 

Year

Cumulative area, in 1,000 square meters

0 10 20 30 40 50 60

Distance downstream from Lewiston Dam, in floodplain kilometers

Cumulative change in area per year,

in 1,000 square meters per year

Stable bars

0

20

40

60

80

100

120

140

160

180

200

-15

-10

-5

0

5

10

15

0

2

4

6

8

R8

B

C

R1 R5 R6 R7 R8 R9 R10 R11 R12 R13 Geomorphic

reach

Tributary

confluence

R2 R3 R4

A

Figure 14. Area of stable bars along the Trinity River downstream from Lewiston Dam, California, and change in stable bar 

area from 1980 to 2011: A, cumulative area by study reach; B, cumulative change in area per year by study reach; C, area by 

study reach and river segments over time.
28 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

sac12-0459_fig15

EXPLANATION

1980–1997

1997–2001

2001–2006

2006–2009

2009–2011

Reach 13

Reach 12

Reach 11

Reach 10

Reach 9

Reach 8

Reach 7

Reach 6

Reach 5

Reach 4

Reach 3

Reach 2

Reach 1

Lower river

Central river

Upper river

EXPLANATION

EXPLANATION

1980

1997

2001

2006

2009

2011

Geomorphic reach

Tributary confluence

1980 1985 1990 1995 2000 2005 2010

Area, in 1,000 square meters

per floodplain kilometer 

Year

Cumulative area, in 1,000 square meters

0 10 20 30 40 50 60

Distance downstream from Lewiston Dam, in floodplain kilometers

Cumulative change in area per year,

in 1,000 square meters per year

0

500

1,000

1,500

2,000

2,500

-5

5

15

25

35

0

10

20

30

40

50

60

Active-channel area

R8

B

C

R1 R5 R6 R7 R8 R9 R10 R11 R12 R13 Geomorphic

reach

Tributary

confluence

R2 R3 R4

A

Figure 15. Area of the active channel along the Trinity River downstream from Lewiston Dam, California, and change in 

active channel area from 1980 to 2011: A, cumulative area by study reach; B, cumulative change in area per year by study 

reach; C, area by study reach and river segments over time.
Results 29

sac12-0459_fig16

EXPLANATION

1980

1997

2001

2006

2009

2011

EXPLANATION

1980–1997

1997–2001

2001–2006

2006–2009

2009–2011

Reach 13

Reach 12

Reach 11

Reach 10

Reach 9

Reach 8

Reach 7

Reach 6

Reach 5

Reach 4

Reach 3

Reach 2

Reach 1

Lower river

Central river

Upper river

EXPLANATION

Geomorphic reach

Tributary confluence

1980 1985 1990 1995 2000 2005 2010

Area, in 1,000 square meters

per floodplain kilometer 

Year

Cumulative area, in 1,000 square meters

0 10 20 30 40 50 60

Distance downstream from Lewiston Dam, in floodplain kilometers

Cumulative change in area per year,

in 1,000 square meters per year

0

20

40

60

80

100

120

140

160

180

200

Active bars

-15

-10

-5

0

5

10

15

0

2

4

6

8

R8

B

C

R1 R5 R6 R7 R8 R9 R10 R11 R12 R13 Geomorphic

reach

Tributary

confluence

R2 R3 R4

A

Figure 16. Area of active bars along the Trinity River downstream from Lewiston Dam, California, and change in active bar 

area from 1980 to 2011: A, cumulative area by study reach; B, cumulative change in area per year by study reach; C, area by 

study reach and river segments over time.
30 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

sac12-0459_fig17

EXPLANATION

1980

1997

2001

2006

2009

2011

EXPLANATION

1980–1997

1997–2001

2001–2006

2006–2009

2009–2011

Reach 13

Reach 12

Reach 11

Reach 10

Reach 9

Reach 8

Reach 7

Reach 6

Reach 5

Reach 4

Reach 3

Reach 2

Reach 1

Lower river

Central river

Upper river

EXPLANATION

Geomorphic reach

Tributary confluence

1980 1985 1990 1995 2000 2005 2010

Area, in 1,000 square meters

per floodplain kilometer 

Year

Cumulative area, in 1,000 square meters

0 10 20 30 40 50 60

Distance downstream from Lewiston Dam, in floodplain kilometers

Cumulative change in area per year,

in 1,000 square meters per year

0

40

80

120

160

200

240

Secondary water features

-15

-10

-5

0

5

10

15

0

2

4

6

8

10

12

14

R8

B

C

R1 R5 R6 R7 R8 R9 R10 R11 R12 R13 Geomorphic

reach

Tributary

confluence

R2 R3 R4

A

Figure 17. Area of secondary water features (split-flow channels, side channels, alcoves, and aquatic wetlands) along 

the Trinity River downstream from Lewiston Dam, California, and change in secondary water feature area from 1980 to 2011: 

A, cumulative area by study reach; B, cumulative change in area per year by study reach; C, area by study reach and river 

segments over time.
Results 31

sac12-0459_fig18

Reach 13

Reach 12

Reach 11

Reach 10

Reach 9

Reach 8

Reach 7

Reach 6

Reach 5

Reach 4

Reach 3

Reach 2

Reach 1

Lower river

Central river

Upper river

EXPLANATION

1980 1985 1990 1995 2000 2005 2010

Length, in meters

Year

1980 1985 1990 1995 2000 2005 2010

Width, in meters

Year

2,000

3,000

4,000

5,000

A. Baseflow shoreline length

20

25

30

35

40

45

B. Active-channel width

Figure 18. Temporal changes in the active-channel from 1980 to 2011 for the Trinity River downstream from Lewiston 

Dam, California: A, baseflow shoreline length; B, active-channel width.

At the upstream end of the lower river segment, the river 

flows through a wider reach (39.6–47.9 FPkm), where the 

local sediment supply increases as a result of bank erosion. 

Continuing downstream (47.9–54.8 FPkm), transport capacity 

and sediment supply increase again as a result of contributions 

from bank erosion, Canyon Creek (51.0 FPkm), and, to a 

lesser extent, Oregon Gulch (48.2 FPkm). Although there 

are no large local sediment sources at the bottom of the 

study reach (54.8–61.3 FPkm), upstream sources of flow and 

sediment maintain dynamic river processes.

Streamflow and Sediment Supply

To assess transport capacity in greater detail, we analyzed 

the size, frequency, and duration of flows at five USGS gaging 

stations along the mainstem Trinity River (fig. 2; table 5). Our 

analyses necessarily focused on the Lewiston gage, which 

is approximately 1.5 km downstream from Lewiston Dam. 

Flows at the Lewiston gage represented regulated conditions, 

but this was the only site with continuous daily flow data 

spanning the study period. The four downstream gages had 

partial records. 

Mean daily flows at the Lewiston gage for the pre- and 

post-ROD periods were 700 ft3/s and 890 ft3/s, respectively. 

Analysis of local precipitation records indicated the increase in 

mean daily flows was caused by increases in post-ROD annual 

flow releases rather than increased precipitation. Monthly 

precipitation records from the National Weather Service 

station near Weaverville, California, indicated the long-term 

mean annual precipitation from 1911 to 2011 was 935 mm. 

Mean annual precipitation during the pre-ROD period 

(979 mm) was slightly greater than the long-term average, but 

the post-ROD mean annual precipitation (465 mm) was about 

50 percent of the long-term average.

Figure 19 presents mean daily flows, annual peaks, 

and annual average flows for the Lewiston gage. During the 

relatively wetter pre-ROD period, there were three water years 

(1983, 1997, and 1998) classified as “extremely wet,” and one 

year (1995) classified as “wet” (table 1). The years 1983 and 

1995 bracketed a decade of lower flows from 1985 to 1994. 

During the relatively drier post-ROD period, one year (2006) 

was classified as “extremely wet,” and two years (2004 and 

2011) were classified as “wet.” 
32 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

sac12-0459_fig19

1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

0

2,000

4,000

6,000

8,000

10,000

12,000

Flow, in cubic feet per second

Pre−ROD Post−ROD

Pre−ROD Post−ROD

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

2,000

2,200

Annual average flow, in cubic feet per second

A

B

Figure 19. Streamflow measured at the Lewiston gage on the Trinity River, California, 1.5 km downstream from Lewiston 

Dam, from 1980 to 2011: A, mean daily and annual peak flows; B, annual average flows. ROD, Record of Decision.
Results 33

The post-ROD flow regime altered the timing and 

variability of annual peak flows released from Lewiston 

Dam. Winter peak-flow releases were eliminated, and the 

peak release was shifted to the spring to mimic snowmelt 

conditions. Analysis of the monthly distribution of mean daily 

flows at the Lewiston gage indicated that annual peak-flow 

releases during the pre-ROD period were distributed from 

December to June, whereas the post-ROD peak-flow releases 

were larger in May and June (fig. 20). Notably, post-ROD 

flows from February to April were lower compared to preROD flows.

Post-ROD flows were also evaluated by computing 

the number of exceedance days at the Lewiston gage for 

the prescriptive ROD-flow thresholds (table 1). Mean daily 

flows greater than 1,500 ft3/s occurred about three times 

more frequently during the post-ROD period compared to the 

pre‐ROD-period, whereas the medium-range flow thresholds 

of 4,500 and 6,000 ft3/s were exceeded 90 and 60 percent more 

frequently, respectively, during the post-ROD period. Flows 

greater than 8,500 ft3/s were exceeded an average of about 

1.7 days per year during the post-ROD period compared to 

0.1 days per year during the pre-ROD period.

Tributary flows were important drivers of geomorphic 

change, particularly during wet periods. Unlike clear-water 

releases from Lewiston Dam, the amount of sediment 

delivered to the mainstem study reach from ungaged 

tributaries is unknown, but likely substantial (Ritter, 1968; 

Knox, 1974; Trinity River Taskforce, 1979; U.S. Fish and 

Wildlife Service and Hoopa Valley Tribe, 1999; Graham 

Matthews and Associates, 2001). The contributing area 

upstream from Lewiston Dam (1,850 km2) represents 

63 percent of the total contributing area upstream from the 

North Fork Trinity River (2,930 km2). Sediment supply from 

Grass Valley Creek (11.85 FPkm; fig. 2), which represents 

3 percent (94 km2) of the contributing area, is detained by a 

series of retention ponds so that only 34 percent (986 km2) 

of the Trinity River watershed contributes bedload to the 

study reach (fig. 21). The contributing areas for the upper, 

central, and lower river reaches were 131, 550, and 305 km2, 

representing 13, 56, and 31 percent, respectively. Indian, 

Weaver, and Redding Creek all flow into the central river 

upstream from the Douglas City gage (29.9 FPkm). A recent 

sediment-budget estimate of the study reach upstream from 

the Douglas City streamgage determined that the transition 

between sediment deficit and surplus conditions under present 

conditions is between the Douglas City and Limekiln Gulch 

gage (20.4 FPkm; Gaeuman and Krause, 2011), which is 

upstream from the central river reach’s boundary (23.4 FPkm). 

Based on contributing area, sediment budget estimates, and 

active bar area, the transition from a sediment deficit to a 

sediment surplus condition is downstream from Indian Creek 

(25.6 FPkm). 

Inconsistencies in the timing of tributary-flow events 

and mainstem flushing-flow releases influenced sediment 

dynamics in the study reach. Precipitation-driven tributary 

flows and the associated sediment delivery peaked during the 

winter and spring and did not coincide with the peak-flow 

releases. Peak-flow releases occurred from May to June, and 

from 2008 to 2011, these were accompanied by the direct 

injection of gravel. The delay of peak-flow releases results in 

interim channel aggradation.

Aggradation of tributary confluences has been a 

recurring problem (Ritter, 1968; Trinity River Taskforce, 

1979; U.S. Fish and Wildlife Service and Hoopa Valley Tribe, 

1999) because it produces upstream slackwater conditions on 

the mainstem, where undesirable fine bed material (less than 

8mm) accumulates. Wilcock and others (1995) recommended 

moderate peak-flow releases (4,500 to 6,000 ft3/s) to mobilize 

bed material and remove undesirable fine-grained bed material 

and higher peak flows (8,500 to 11,000 ft3/s) to produce deeper 

scour and greater transport. 

The effects of tributary-flow contributions on mainstem 

transport capacity are illustrated in figure 22, which shows 

mean annual flows for the five mainstem gages from 1996 

to 2011, the period in which multiple mainstem gages were 

in operation (table 5). During the relatively wetter 2006 and 

2011 water years, mean annual flow at the North Fork gage 

was 70 to 80 percent greater than at the Lewiston gage. Again, 

we inferred, on the basis of previous investigations, that these 

tributary-flow events contributed large, but unknown, amounts 

of sediment.

Figure 23 illustrates mean daily flows for mainstem gages 

and highlights two pre-ROD water years (1997, 1998) and two 

post-ROD years (2006, 2011), which represent the four largest 

tributary-flow events during the study period. The influence 

of tributaries on mainstem flows was clear in December 

1997, when mean daily flows increased from about 6,900 ft3/s 

at Lewiston to 10,200 ft3/s at Douglas City and to 27,000 

ft3/s at Junction City. In February 1998, mean daily flows 

increased from about 5,600 ft3/s at Lewiston to 9,900 ft3/s at 

Douglas City and to 25,000 ft3/s at Junction City. Mean daily 

flows released in December of 2006 were about 1,500 ft3

/s 

at Lewiston, but increased to 7,500 ft3/s at Douglas City, to 

12,000 ft3/s at Junction City, and to nearly 20,000 ft3/s at the 

North Fork gage (fig.23D). In comparison, mean daily flows in 

May 2011, during the largest flow release since 1974 (Krause, 

2012a), lacked tributary contributions because the flow 

release did not coincide with tributary runoff. In May 2011, 

flow releases at Lewiston peaked at 12,000 ft3/s, compared to 

12,500 ft3/s at Limekiln Gulch, 12,900 ft3/s at Douglas City, 

13,700 ft3/s at Junction City, and 12,900 ft3/s at the North Fork 

gage (fig.23E).
34 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

sac12-0459_fig20

October November December January February March April May June July August September

Mean daily flow, in cubic feet per second

October November December January February March April May June July August September

Mean daily flow, in cubic feet per second

100

1,000

10,000

A. Pre−ROD (1980−2000)

100

1,000

10,000

B. Post−ROD (2001−2011)

Figure 20. Mean daily flows from 1980 to 2011, grouped by month with minimum in-stream flow, for the Lewiston gage 

on the Trinity River, California: A, pre-ROD (Record of Decision) period; B, post-ROD period. The horizontal dashed lines 

indicate 300 cubic feet per second, which represents summer-baseflow conditions, and 6,000 cubic feet per second, which 

represents the post-ROD mean annual peak flow.
Results 35

sac12-0459_fig21

Upper river Central river Lower river

Geomorphic reach R8

EXPLANATION

Tributary confluences

USGS gaging stations

0 10 20 30 40 50 60

Contributing drainage area, in square kilometers

Distance downstream from Lewiston Dam, in floodplain kilometers

1,000

1,500

2,000

2,500

3,000

3,500

4,000

R1 R5 R6 R7 R8 R9 R10 R11 R12 R13 Geomorphic

reach

Tributary

confluence

R2 R3 R4

Figure 21. Contributing drainage area for 13 geomorphic reaches, delineated by vertical lines and described in table 2, 

along the Trinity River downstream from Lewiston Dam, California. USGS, U.S. Geological Survey.

1996 1998 2000 2002 2004 2006 2008 2010 2012

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

Mean annual flow, in cubic feet per second

EXPLANATION

Douglas City

Junction City

Lewiston

Upstream from 

North Fork

Limekiln Gulch

Figure 22. Mean annual flow measured at five mainstem gages on the Trinity River, California, downstream of Lewiston 

Dam, California, from 1996 to 2011.
36 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

sac12-0459_fig23

EXPLANATION

Douglas City

Junction City

Lewiston

Upstream from North Fork

Limekiln Gulch

1980 1985 1990 1995 2000 2005 2010

0

5,000

10,000

15,000

20,000

25,000

30,000

Mean daily flow, in cubic feet per second

1997199820062011

0

5,000

10,000

15,000

20,000

30,000

25,000

Mean daily flow, in cubic feet per second

Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept.

Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept.

A. Water years 1980–2011

B. Water year 1997 C. Water year 1998

0

5,000

10,000

15,000

20,000

30,000

25,000

Mean daily flow, in cubic feet per second

D. Water year 2006 E. Water year 2011

Figure 23. Mean daily flows measured at five mainstem gaging stations on the Trinity River, California, downstream from 

Lewiston Dam, from 1980 to 2011, and annual time series for four wettest years during the study period: A, 1997; B, 1998; 

C, 2006; D, 2011. Dashed horizontal line denotes 6,000 cubic feet per second, which represents the post-Record of Decision 

mean annual peak flow.
Results 37

Sediment Management and Mechanical 

Channel Rehabilitation

The history of sediment management and mechanical 

channel rehabilitation were reviewed earlier in this report, and 

in this section we present pertinent details. Figure 24 provides 

a spatial and temporal summary of management actions in 

the project reach. Pre-ROD management was focused on 

restoring adult-holding and spawning habitat (Trinity River 

Taskforce, 1970). Adult salmonids require deep-water holding 

pools and spawning riffles free of fine bed material (less 

than 8 mm). Pre-ROD dredging of mainstem pools increased 

and maintained deep-water adult-holding habitat. Riffle and 

grade-control construction created spawning habitat, whereas 

upland watershed restoration and sediment-retention basins 

at the Grass Valley Creek confluence reduced the delivery of 

undesirable fine-sediment (U.S. Bureau of Land Management, 

1995; Graham Matthews and Associates, 2001).

Krause (2012a) provided a detailed history of sediment 

extraction and augmentation for the study reach, which 

is summarized in figure 25. Following dam closure, flow 

diversions, combined with elevated tributary sediment supply 

related to land use, caused significant aggradation of the 

channel bed with sand-sized bed material that filled pools and 

inundated spawning areas (U.S. Fish and Wildlife Service and 

Hoopa Valley Tribe, 1999). Sediment extraction, primarily 

by pool dredging, and to a lesser degree bar scalping, began 

in 1976 and continued until 1990. Extracted volumes of 

sediment were composed of approximately 15–25 percent 

coarse-grained sediment (greater than 16-mm in diameter) and 

about 75–85 percent finer grained material (less than 16 mm).

0 10 20 30 40 50 60

Distance downstream from Lewiston Dam, in floodplain kilometers

0 10 20 30 40 50 60

Distance downstream from Lewiston Dam, in floodplain kilometers

EXPLANATION

Gravel-augmentation sites

Dredging of sediment-retention ponds

Mainstem pool dredging

Feathered-edge program

Side-channel construction

Channel-rehabilitation projects

Geomorphic reaches

Tributary confluences

Dates of orthophotography

R8

1976

1980

1984

1988

1992

1996

2000

2004

2008

2012

Year 

R1 R5 R6 R7 R8 R9 R10 R11 R12 R13 Geomorphic

reach

Tributary

confluence

R2 R3 R4

Figure 24. Summary of relevant management actions from 1976 to 2011 along the Trinity River downstream from Lewiston 

Dam, California.
38 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

sac12-0459_fig25

-150

-100

-50

0

50

100

-40

-30

-20

-10

0

10

20

1980 1985 1990 1995 2000 2005 2010

Annual volume, in 1,000 cubic meters per year

Cumulative volume, in 1,000 cubic meters per year

-200

EXPLANATION

In-channel placement of coarse sediment

High-flow injection of coarse sediment

Coarse-sediment extraction

Fine-sediment extraction

Cumulative coarse-sediment augmentation

Cumulative sediment extraction

Dates of orthophotography

Figure 25. Annual and cumulative volumes of sediment extraction and augmentation for Trinity River downstream from 

Lewiston Dam, California, from 1980 to 2011 (Krause, 2012b).

A summary of constructed features is presented in 

figure 26. An emphasis on salmonid rearing habitat began 

in the 1990s (U.S. Fish and Wildlife Service, 1989), and a 

series of 18 side channels and 9 bank-rehabilitation projects, 

referred to as “feathered edges,” were constructed to create 

shallow-water rearing habitat (fig. 24; U.S. Fish and Wildlife 

Service, 1994). Side-channel construction increased shoreline 

length and low-velocity off-channel rearing habitat and also 

created large island features. The “feathered edge” program 

targeted overly steep channel margins where vegetation 

had encroached. Riparian vegetation and sediment berms 

were mechanically removed to create gently sloping, 

gravelly channel margins intended to function as mainstem 

rearing habitat. 

In 1999, the TRFE determined the lack of rearing habitat 

continued to be a primary limiting factor for sustainable 

salmonid populations and made recommendations for 

prescriptive-flow management, channel rehabilitation, and 

augmentation of coarse bed-material-sized sediment adopted 

by the ROD in 2001. The TRFE identified 44 potential 

channel-rehabilitation sites and 3 potential side-channel sites. 

Construction of these projects began in 2005 under a phased 

approach to allow for monitoring and performance assessment 

(Trinity River Restoration Program and ESSA Technologies 

Ltd., 2009). From 2005 to 2011, 19 of the proposed 

rehabilitation projects were constructed (fig. 24).

The design of post-ROD channel-rehabilitation projects 

evolved over time. Early designs, constructed in 2005 and 

2006, were relatively simple channel–floodplain connectivity 

projects designed to facilitate inundation of channel 

margins by vegetation removal, riparian berm recontouring, 

and surface lowering of riparian features. These early 

projects were in the lower river, where ample in-channel 

and tributary sediment sources existed and where TRRP 

partners hypothesized the river would “rehabilitate itself.” 

A lack of geomorphic response at these early restoration 

sites (Hoopa Valley Tribe and others, 2011b) led to broader 

hypotheses and the evolution of project designs. More 

recent projects, constructed from 2006 to 2011, focused on 

enhancing channel–floodplain connectivity and utilized new 

design criteria (Hoopa Valley Tribe and others, 2011a) to 

mechanically increase the diversity and extent of salmonid 

habitat by incorporating channel complexity features into 

project designs.

Gravel augmentation to create and maintain spawning 

habitat in the upper river began in 1972 and continued into the 

post-ROD period. Gravel augmentation approaches evolved 

from the pre-ROD strategy of in-channel placement of static 

gravel features to provide spawning or rearing habitat to 

the post-ROD strategy of direct injection during the spring 

peak-flow release (Kondolf and Minear, 2004). In-channel 

placement of gravel to increase sediment supply and restore 

dynamic fluvial processes began in 1998. Direct injection 

during managed high-flow releases, by using front-end 

loaders or conveyor belts, began in 2008. Although the TRFE 

recommended gravel augmentation up to 51,000 cubic meters 

per year (m3

/yr), the actual volumes placed each water year 

varied (fig. 25). At time of writing, recommendations for 

average annual-injection volumes, based on gravel transport 

rates and desired bed-surface textures, were about 5,400 m3/yr 

(Gaeuman, 2008).
Results 39

sac12-0459_fig26

EXPLANATION

Constructed bars

Constructed secondary water features

Constructed floodplains

1 2 3 4 5 6 7 8 9 10 11 12 13

Geomorphic reaches

A. 1980

1 2 3 4 5 6 7 8 9 10 11 12 13

Geomorphic reaches

B. 1997

1 2 3 4 5 6 7 8 9 10 11 12 13

Area, in square meters

C. 2001

1 2 3 4 5 6 7 8 9 10 11 12 13

D. 2006

1 2 3 4 5 6 7 8 9 10 11 12 13

E. 2009

1 2 3 4 5 6 7 8 9 10 11 12 13

F. 2011

0

20,000

40,000

60,000

80,000

100,000

0

20,000

40,000

60,000

80,000

100,000

0

20,000

40,000

60,000

80,000

100,000

0

20,000

40,000

60,000

80,000

100,000

0

20,000

40,000

60,000

80,000

100,000

0

20,000

40,000

60,000

80,000

100,000

Figure 26. Bar graphs showing a summary of constructed riparian and channel features along the Trinity River downstream 

from Lewiston Dam, California, in 1980, 1997, 2001, 2006, 2009, and 2011.
40 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

Summary of Bar and Bank Processes

Lateral changes induced by bar and bank processes were 

characterized by summarizing change polygons in 1-km subreaches during the five periods of interest. We used conditional 

statements, as described previously, in a geographic 

information system (GIS) to estimate scour and accretion by 

quantifying changes in bar and bank spatial extents. 

The first mapping interval, from 1980 to 1997, 

was dominated by channel widening; 24 percent of the 

active-channel area showed lateral bank changes compared 

to about 8 to 10 percent during subsequent periods (table 6). 

About 7 percent of the active channel showed a change in 

bar area compared to about 2 to 5 percent during subsequent 

periods. The combined effects of scour-inducing tributary 

floods, experimental flow releases, and “feathered-edge” 

construction resulted in the greatest bank-erosion rates of 

the study period (fig. 27). There was a small amount of bar 

accretion, primarily in the vicinity of tributary confluences 

(fig. 28), and in the lower river, there was scour of bar 

vegetation (fig. 29). A post-flood assessment (McBain and 

Trush, Inc., 2000) indicated much of the bank erosion during 

this period was caused by the 1997 tributary flood (fig. 23), 

and from 1980 to 1997, mean daily flows at the Lewiston 

gage exceeded 6,000 ft3

/s, the flow threshold designed to 

mobilize and scour channel features (table 1), for a total of 

81 days. Additional management actions that contributed to 

bank and bar changes included pool dredging and side-channel 

construction (fig. 24).

The period from 1997 to 2001 was dominated by bar 

accretion (fig. 28) near Rush Creek (6.5 FPkm), Indian 

Creek (25.6 FPkm), and downstream from Oregon Gulch 

(50.5 FPkm). Bank erosion continued (fig. 27), although 

rates declined slightly (table 6), and bar stabilization by 

vegetation encroachment ensued throughout the study 

area (fig. 29). Compared to the previous period, a smaller 

proportion of the channel underwent bar and bank changes. 

About 4 percent of the active channel underwent bar scour or 

accretion, whereas about 10 percent underwent bank erosion 

or accretion (table 6). The rate of bar accretion was an order 

of magnitude higher (8,709 m2/yr) than during the previous 

period (772 m2/yr), but the bank erosion rate (0.24 m/yr) was 

similar to the previous period (0.3 m/yr). Although there was 

a large, long duration, tributary-flow event in 1998 (fig. 23), 

mean daily flows at the Lewiston gage exceeded 6,000 ft3/s 

for only 9 days. Management actions were confined to the 

upper river and included dredging of sediment-retention ponds 

(fig. 24) and small amounts of gravel augmentation (fig. 25).

Table 6. Summary of bar and bank changes during five study periods for the Trinity River, California, downstream from Lewiston Dam.

[Abbreviations: m/yr, meter per year; m2/m, square meter per meter; m2/yr, square meter per year]

Type of change 1980 to 1997 1997 to 2001 2001 to 2006 2006 to 2009 2009 to 2011

Bar change

Net change in active-bar area per unit channel length1

 (m2/m) 0.20 0.54 –0.72 0.15 0.20

Rate of change in active-bar area (m2

/yr) 772 8,709 –9,324 3,267 6,505

Active-channel area experiencing bar scour or accretion (percent) 7.4 3.5 5.1 2.4 4.2

Bank change

Net change in active-channel area per unit channel length2

 (m2/m) 5.05 0.95 1.13 0.25 0.53

Rate of change in active-channel width (m/yr) 0.30 0.24 0.23 0.08 0.27

Active-channel area experiencing bank erosion or accretion (percent) 24.4 10.2 10.9 8.4 8.7

1

Positive values indicate bar accretion, and negative values indicate bar scour. Data normalized by channel length estimated by using the centerline of 

baseflow channel.

2

Positive values indicate channel widening and bank erosion, and negative values indicate channel narrowing and bank accretion and riparian vegetation 

encroachment. Data normalized by channel length estimated by using the centerline of baseflow channel.
Results 41

sac12-0459_fig27

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

-20

-10

0

10

20

-20

-10

0

10

20

-20

-10

0

10

20

-20

-10

0

10

20

-20

-10

0

10

20

1980–1997

1997–2001

2001–2006

0 10 20 30 40 50 60 62

Distance downstream from Lewiston Dam, in floodplain kilometers

2009–2011

2006–2009

Active-channel width change, in percent

Change in active-channel area, in 1,000 square meters

R8 Geomorphic reach

Tributary confluence

Lateral bank accretion (channel narrowing)

Bank erosion (channel widening)

Net change in active-channel area

Change in active channel as percentage of active channel

EXPLANATION

Geomorphic

reach

Tributary

confluence

R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13

Figure 27. Changes in active-channel area due to bank erosion and accretion along the Trinity River downstream 

from Lewiston Dam, California, for five periods ending in 1997, 2001, 2006, 2009, and 2011.
42 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

sac12-0459_fig28

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

-20

-10

0

10

20

-20

-10

0

10

20

-20

-10

0

10

20

-20

-10

0

10

20

-20

-10

0

10

20

1980–1997

1997–2001

2001–2006

2009–2011

2006–2009

Change in exposed active-bar area, in 1,000 square meters

0 10 20 30 40 50 60 62

Distance downstream from Lewiston Dam, in floodplain kilometers

Active-channel width change, in percent

R8 Geomorphic reach

Tributary confluence

Bar accretion

Bar scour

Net change in exposed active bar area

Change in bar area as percentage of active channel

EXPLANATION

Geomorphic

reach

Tributary

confluence

R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13

Figure 28. Changes in active-bar area due to bar scour and accretion along the Trinity River downstream from 

Lewiston Dam, California, for five periods ending in 1997, 2001, 2006, 2009, and 2011.
Results 43

sac12-0459_fig29 Change in bar vegetation cover, in 1,000 square meters

0

2

4

8

6

10

0

2

4

8

6

10

0

2

4

8

6

10

0

2

4

8

6

10

0

2

4

8

6

10

1980–1997

1997–2001

2001–2006

2009–2011

2006–2009

0 10 20 30 40 50 60 62

Distance downstream from Lewiston Dam, in floodplain kilometers

R8 Geomorphic reach

Tributary confluence

EXPLANATION

Area of active bar stabilized by vegetation growth

Area of stable bar reactivated by scour of vegetation

Geomorphic

reach

Tributary

confluence

R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13

Figure 29. Changes in bar vegetation along the Trinity River downstream from Lewiston Dam, California, for five 

periods ending in 1997, 2001, 2006, 2009, and 2011.
44 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

The period from 2001 to 2006 was dominated by bar 

scour (fig. 28), and bar stabilization from encroachment of 

riparian vegetation continued in the upper and lower river 

(fig. 29). Bar accretion occurred in the upper river downstream 

of Rush Creek (6.5 FPkm), but bar scour dominated 

downstream of Indian Creek (25.6 FPkm). System wide, about 

5 percent of the active channel showed bar scour or accretion, 

whereas about 11 percent showed bank change (table 6). 

Rates of bar scour (9,324 m2/yr) were slightly greater than bar 

accretion during the previous period, but the bank erosion rate 

(0.23 m/yr) was similar to the previous period (table 6). There 

was a significant tributary flood followed by a secondary 

spring flow release in 2006 (fig. 23), and there were 33 days 

with flows greater than 6,000 ft3/s measured at the Lewiston 

gage. Management activities included small amounts of gravel 

augmentation in the upper river (fig. 25) and construction 

of the first large-scale channel-rehabilitation project in the 

lower river that involved surface lowering and floodplain 

construction (fig. 24). 

From a system-wide perspective, bar and bank changes 

from 2006 to 2009 were relatively small compared to previous 

periods (table 6), but stabilization of active bars as a result 

of vegetation encroachment continued throughout the study 

area (fig. 29). There was bank erosion in upper river (fig. 27), 

and the largest amount of bar accretion was near the Sawmill 

gravel-augmentation site (1.7 FPkm). In the lower river, the 

Lime Point reach (54.8 FPkm) was the only reach that had 

notable bar and bank changes. System wide, about 2 percent 

of the active channel showed bar scour or accretion, whereas 

about 8 percent of the active channel showed bank changes 

(table 6). There was net bar accretion (3,267 m2/yr), but bankerosion rates decreased (0.08 m/yr) relative to the previous 

period (0.23 m/yr). Tributary flows were relatively low, and 

there were only 7 days with flows greater than 6,000 ft3/s 

at the Lewiston gage; however, larger volumes of gravel 

augmentation by direct injection began in 2008 (fig. 25), 

causing bar accretion in the upper river (fig. 28). Additional 

management actions included construction of 14 large-scale 

channel-rehabilitation projects in the study reach (fig. 24). 

Mechanical restoration included surface lowering to increase 

channel–floodplain connectivity and construction of channel 

complexity features.

Bar and bank changes increased from 2009 to 2011. In 

the upper river, bar accretion and bank erosion occurred near 

the Lowden Ranch gravel-augmentation site (11.5 FPkm). 

There was also net bar accretion near Indian Creek 

(25.6 FPkm) and downstream of Oregon Gulch (48.2 FPkm). 

The largest amount of bank erosion (fig. 27) was near Grass 

Valley Creek (11.9 FPkm) and Lime Point (58 FPkm), and 

stabilization of active bars by vegetation encroachment 

continued throughout the study area (fig. 29). System wide, 

about 4 percent of the active channel underwent bar scour 

or accretion, whereas about 9 percent of the active channel 

underwent bank erosion or accretion (table 6). The rate of 

bar accretion doubled (6,505 m2/yr) compared to the previous 

period (3,267 m2

/y), and the bank erosion rate (0.27 m/yr) 

increased and was comparable to estimates from 1980 to 

2006 (table 6). A moderate tributary‐flow event in 2011 was 

followed by the largest flow release since 1974 in May of 

2011 (Krause, 2012a). At the Lewiston gage, there were 

12 days with flows greater than 6,000 ft3/s and 3 days with 

flows greater than 11,000 ft3/s. Gravel augmentation by 

direct injection during the flow release increased active‐bar 

area in the upper river (fig. 28), and four large-scale 

channel-rehabilitation projects were constructed (fig. 24). 

Mechanical rehabilitation included surface lowering to 

increase channel–floodplain connectivity and construction of 

channel-complexity features.

Discussion

Our assessment of the cumulative changes in active bar 

and active channel areas are summarized in figure 30, which 

shows pre-ROD increases in the active-channel area were 

well distributed downstream, whereas pre-ROD increases 

in the active-bar area were primarily downstream of Indian 

Creek (25.6 FPkm). Post-ROD increases in the area of the 

active-channel and active-bars were primarily in the upper 

river upstream of Indian Creek. These interpretations are 

consistent with our contributing area analysis (fig. 21) and a 

recent sediment budget estimate (Gaeuman and Krause, 2011), 

which indicated a transition to a sediment surplus condition 

downstream of Indian Creek (25.6FPkm). In the remainder of 

this report, we discuss pertinent controlling factors responsible 

for the documented geomorphic changes.

Channel Change Potential

The study reach is in an active zone of uplift that 

provided a tectonic mechanism over geologic time for river 

incision and development of a bedrock-channel network 

(Anderson, 2008). Active uplift zones tend to be drained by 

channels with high transport capacities and low volumes 

of stored sediment because of the confined setting (Gilbert, 

1914; Montgomery and others, 1996; Brierley and others, 

2002; Wallick and others, 2010). It follows that sediment 

storage is often transient and concentrated near point sources 

or in reaches with erodible channel margins; however, 

watershed disturbances can result in episodic aggradation 

and degradation, and such is the case for the Trinity River 

downstream from Lewiston Dam. 

The combined effects caused by the influx of largediameter mining tailings, dam construction, flow diversion, 

vegetation encroachment, and flood-induced confluence 

aggradation effectively trapped the modern channel, often 

against resistant bedrock valley margins, creating conditions 

that sustain static channel form and stable alluvial features. 

An unknown amount of historic channel aggradation between 

1848 and 1970, as a result of gold-extraction activities, 

increased the sediment supply by several orders of magnitude 
Discussion 45

sac12-0459_fig30 Cumulative change in exposed active-bar area, in 1,000 square meters Cumulative change in active-channel area, in 1,000 square meters

-50

-40

-30

-20

-10

0

10

20

30

40

50

0

50

100

150

200

250

300

350

400

Cumulative active-bar changes

Cumulative active-channel changes

0 10 20 30 40 50 60 62

Distance downstream from Lewiston Dam, in floodplain kilometers

EXPLANATION

1980–1997

1997–2001

2001–2006

2006–2009

2009–2011

R8 Geomorphic reach

Tributary confluence

Pre-Record of Decision (1980–2001)

Post-Record of Decision (2001–2011)

Geomorphic

reach

Tributary

confluence

R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13

Figure 30. Cumulative downstream change in the areal extent of exposed active bars and of the active channel 

along the Trinity River downstream from Lewiston Dam, California, for five periods ending in 1997, 2001, 2006, 2009, 

and 2011.

(Krause and others, 2010; Krause, 2012b). Flow regulation 

and diversions that began in 1960 effectively decreased the 

river’s transport capacity (U.S. Fish and Wildlife Service 

and Hoopa Valley Tribe, 1999) and enabled vegetation 

encroachment and stabilization of channel margins. In 1964, a 

massive regional flood initiated a new episode of aggradation 

at all major tributary confluences in the study reach (Ritter, 

1968). The combined effects of these disturbances produced a 

narrower, partially confined, aggraded river. Although riparian 

encroachment continues to be an issue, the tendency toward a 

static channel form and stable alluvial features was disrupted 

by pre-ROD tributary floods and continues to be moderated by 

post-ROD tributary floods, increases in the size and duration 

of peak-flow releases, and upper-river gravel augmentation.

The upper river generally has a lower potential for 

dynamic geomorphic change because it lacks tributary 

contributions to flow and sediment supply. To resolve the lack 

of capacity for creating dynamic change, post-ROD channel 

rehabilitation, gravel augmentation, and alterations in flow 

management were implemented to increase and maintain 

active-channel areas and channel complexity. The post2006 increases in gravel augmentation provided additional 

sediment supply, and regulated flows were increased to 

support transport capacity. Beginning in 2008, a new phase of 

channel-rehabilitation began to include channel complexity 

features, such as bars and secondary water features (split-flow 

channels, side channels, alcoves, and aquatic wetlands). 
46 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

The potential of flow events to create channel change 

depends on antecedent channel conditions, transport capacity, 

and sediment supply. In terms of creating system-wide 

responses, the geomorphic effectiveness of ROD-flows is 

relatively low compared to tributary flows, which produce 

larger, longer duration flows with greater sediment delivery. 

Because the upper river lacked sufficient transport capacity 

and sediment supply, intensive post-ROD management 

was required to achieve the TRRP goal of promoting active 

alluvial processes that create and maintain the quantity and 

quality of available salmonid habitat. Our analyses indicated 

that geomorphic change induced by managed-flow releases, 

with concurrent gravel augmentation, tended to be spatially 

limited. Although the majority of the pre-2001 active bars 

were remobilized and scoured by the 2006 tributary flood, 

subsequent increases in bar vegetation indicated post-ROD 

flows were not sufficient to scour emergent bar vegetation and 

to maintain active-bar areas in reaches downstream of Indian 

Creek (25.6 FPkm). However, post-ROD gravel augmentation 

and flow management did successfully increase and maintain 

active-bar area in the upper river.

Trajectories of Geomorphic Response and 

Primary Controls

The general trajectory of change during the study period 

was the conversion of riparian features into channel features 

and an expansion of the active-channel system. During the 

pre-ROD period, channel widening dominated from 1980 

to 1997, followed by bar accretion from 1997 to 2001. 

Although channel widening continued through the post-ROD 

period, 2001 to 2006 was characterized by bar scour, and 

there were relatively small geomorphic changes from 2006 

to 2011 related to the implementation of ROD‐mandated 

gravel augmentation, prescriptive flow releases, and 

channel rehabilitation. 

The largest and longest duration tributary floods during 

the study period occurred in 1997 and 1998. The relatively 

wet period in the early 1980s likely initiated some of the 

channel changes between 1980 and 1997, but these effects 

were undocumented. Effects of the 1997 tributary flood were 

assessed (McBain and Trush, Inc., 2000), and results from the 

post-flood survey indicated the 1997 flow event effectively 

scoured channel margins downstream of the Rush Creek 

confluence (6.5 FPkm). 

The 1980 to 1997 period was dominated by bank 

erosion and channel widening, and we inferred, on the basis 

of the post-flood reconnaissance, that much of the expansion 

of the active-channel area was induced by the 1997 flood. 

The greatest cumulative downstream increase in exposed 

active-bar area during the study period was from 1997 to 2001 

(fig. 30), primarily downstream of the Indian Creek confluence 

(25.6 FPkm). 

The rapid rate of accretion (8,709 m2/yr; table 6) during 

the relatively short period from 1997 to 2001 was facilitated 

by decreased transport capacity and increased sediment 

supply. Channel widening from 1980 to 1997 altered the 

river’s hydraulic geometry and effectively decreased available 

transport capacity. Local sediment supply likely increased 

after 1997 because of scour of riparian vegetation and bank 

destabilization. We also inferred that tributary sediment 

supplies increased during the relatively wetter 1998 water 

year, when there were two large tributary floods. Gravel 

augmentation accounted for a relatively small portion of the 

increase in sediment supply during this period. A total of 

3,200 m3 of coarse gravel (fig. 25), or about 800 m3/yr, was 

added to the upper river at two locations (1.4 and 4.6 FPkm).

During the period from 2001 to 2006, the study area 

was dominated by bar scour, again, primarily downstream of 

the Indian Creek confluence (25.6 FPkm; fig. 30). Bar scour 

was most likely induced during a relatively wetter period 

that culminated in the 2006 tributary flood and a 10,400 ft3/s 

peak‐flow release (fig. 23). Bar scour during this period was 

slightly greater (9,324 m2/yr) than bar accretion during the 

previous period (8,709 m2/yr; table 6).

Beginning in 2005, large-scale channel rehabilitation 

began (fig. 24), and there were concurrent increases in the 

frequency of flows inundating floodplains (fig.19) and gravel 

augmentation (fig.25). Intensified mechanical rehabilitation 

increased the connectivity of low-elevation riparian features 

(post-dam benches and constructed floodplains), and 

implementation of the post-ROD flow regime increased the 

frequency of floodplain inundation. Implementation of larger 

scale channel rehabilitation also increased channel complexity 

(fig. 8) in the form of exposed active-bar areas (fig. 16) and 

secondary water features (split-channels, side channels, 

alcoves, and aquatic wetlands; fig. 17) in the upper and 

central river. 

During the remainder of the post-ROD period, 2006 to 

2011, the active-channel area continued to increase (fig. 30), 

and bar changes were primarily confined to the upper 

river reaches that had gravel augmentation (1.4 FPkm and 

11.5 FPkm) and downstream of the Canyon Creek confluence 

(51.0 FPkm). The cumulative results of intensive management 

in the upper river were increased channel complexity 

and floodplain connectivity that was maintained with 

managed‐flow releases. Gravel augmentation was the primary 

factor leading to upper river increases in active-bar area, and 

the 2006 tributary flood was the primary factor that increased 

lower river active-bar area.
Discussion 47

During the post-ROD period, large channel changes 

were spatially limited to reaches that had mechanical 

restoration or gravel augmentation and to reaches downstream 

of tributary confluences, where localized excess sediment 

supplies or transport capacity exist. This observation was 

supported by earlier studies (Ritter, 1968; Trinity Restoration 

Associates, Inc., 1993; Hoopa Valley Tribe and others, 2011b). 

The exception to this generalization was the Lime Point reach 

(54.8 to 58.2 FPkm). The Lime Point reach was one of the 

most dynamic reaches during the study period. Although 

there was a series of rehabilitation projects constructed in 

this reach in 2006 and 2010, dynamic channel changes were 

primarily in un-rehabilitated reaches. The greatest bar and 

bank changes were in the lowermost section of the Lime Point 

reach (58 FPkm), which is in an incised meander bend that has 

a relatively small radius of curvature, which produces large 

bed-shear stresses and high transport capacity. 

We constructed a series of figures to show the cumulative 

pre- and post-ROD changes in representative reaches. 

Figure 31 shows a portion of the primary spawning reach and 

the Sven Olbertson rehabilitation site (1.0 FPkm) in the upper 

river downstream from Lewiston Dam. Intensive management 

of this reach during pre- and post-ROD periods included 

gravel augmentation, mechanical restoration, and peak-flow 

releases that increased the active-channel area, channel 

complexity, and floodplain connectivity. 

Figures 32, 33, and 34 show a series of reaches in 

the lower river where there was dynamic channel change. 

Figure 32 illustrates bank erosion and bar accretion near 

Junction City, Calif. (50.1 FPkm), upstream from the Canyon 

Creek confluence. Pre-ROD erosion of the left bank and 

deposition of lateral bars resulted in about 25 m of channel 

migration between 1980 and 2001. Post-ROD bank erosion 

continued to expand the active-channel area, and there was 

concurrent bar accretion, bar scour, and stabilization of a 

downstream lateral bar. Channel complexity also increased 

with the number of bars and secondary water features. 

Figure 33 shows the upstream portion of the Conner Creek 

rehabilitation site (53.8 FPkm), where the deposition of 

large pre-ROD bars increased channel complexity and 

sinuosity. During the post-ROD period, there was bar 

scour, bar stabilization, and bank erosion that expanded the 

active-channel area, and rehabilitation of the channel margin 

increased riparian diversity with floodplain construction. 

Figure 34 illustrates Lime Point (58.1 FPkm), where a 

pre‐ROD channel avulsion was accompanied by bar scour 

and bar deposition, which increased channel complexity 

and the active-channel area. During the post-ROD period, a 

large medial bar was stabilized by vegetation encroachment, 

and the active channel area decreased, but the 1980-era 

channel continued to function as a side channel, and new bar 

features formed.

Geomorphology and Habitat Linkages

To support the TRRP adaptive management program, we 

evaluated the relative effectiveness of natural and managed 

controlling factors and the associated cumulative geomorphic 

response during the five study periods. We also assessed a 

set of performance measures (channel complexity, shoreline 

length, and channel‐floodplain connectivity) identified by 

the TRRP as primary metrics for characterizing linkages 

between geomorphic structure and available salmonid habitat 

(Trinity River Restoration Program and ESSA Technologies 

Ltd., 2009).

Measures of channel complexity included exposed 

active-bar area (fig. 16) and secondary water features (fig. 17). 

There were greater increases in channel complexity during 

the pre-ROD period than during the post-ROD period. 

System-wide channel complexity increased markedly from 

1980 to 1997 and then decreased slightly from 1997 to 2001. 

During the post-ROD period system-wide channel complexity 

decreased slightly, but there were smaller, yet measurable, 

increases in channel complexity in the upper river.

An integrated habitat assessment (U.S. Fish and Wildlife 

Service and others, 2011) of channel-rehabilitation projects 

constructed from 2005 to 2009 concluded that the only metric 

well correlated to fish use was the length of the wettedchannel edge, or shoreline length. During the study period, 

the largest increase in shoreline length (fig. 18A) was during 

the pre-ROD period, primarily in the upper river, as a result of 

extensive side-channel construction and bar accretion. There 

were smaller, but measurable, increases in shoreline length 

during the post‐ROD period, primarily after 2006, related to 

channel rehabilitation.

Increases in channel–floodplain connectivity were 

inferred from the areal extent of constructed floodplains and 

by increases in the size and frequency of post-ROD flow 

releases. During the pre-ROD period in the early 1990s, 

small-scale riparian berm removal and feathered-edge 

construction increased floodplain connectivity (fig. 24). 

Extensive scour of riparian vegetation during the 1997 

tributary flood resulted in additional increases in floodplain 

connectivity, primarily downstream from Indian Creek 

(25.6 FPkm; fig. 29). During the post-ROD period, riparian 

vegetation was scoured near tributary confluences from 2001 

to 2006 (fig. 29), and there was a relatively large increase 

in constructed floodplain area from 2005 to 2011 (fig. 25). 

Post-ROD increases in the areal extent of lower‐elevation 

floodplains, inundated by flows greater than about 4,500 ft3/s, 

and concurrent increases in the frequency of exceedance 

(table 1) indicated a larger proportion of riparian features were 

inundated annually during the post-ROD period.
48 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

tac12-0449_fig 31

0.9

1

1.1

1.2

0.9

1

1.1

1.2

0.9

1

1.1

1.2

EXPLANATION

Active bar

Stable bar

Constructed bar

Secondary water feature (alcove, 

Constructed secondary water feature

wetland, split-flow channel, and side channel)

1.1

Wetted baseflow channelUplandsPre-dam floodplain

Constructed floodplain

Post-dam topographic benchIslandConstructed island

Other

Longitudinal distance downstream 

from Lewiston Dam (floodplain kilometer)

1980

Base map from rectified 1980, 2001, and 2011 aerial photography. Coordinate reference system: UTM projection, Zone 10, North American Datum of 1983

2011 2001

200 FEET

50 METERS

00

Figure 31. Geomorphic feature maps for the Sven Olbertson Rehabilitation Site on the Trinity River, California, 1.0 floodplain kilometers downstream from Lewiston Dam, in 1980, 2001, and 2011.
Discussion 49 tac12-0449_fig 32

50.1

50.2

50.3

50.4

50.1

50.2

50.3

50.4

50.1

50.2

50.3

50.4

EXPLANATION

Active bar

Stable bar

50.3

Uplands

Pre-dam floodplain Wetted baseflow channel

Post-dam topographic bench

1980

Base map from rectified 1980, 2001, and 2011 aerial photography. Coordinate reference system: UTM projection, Zone 10, North American Datum of 1983

2011 2001

200 FEET

50 METERS

00

Secondary water feature (alcove, 

wetland, split-flow channel, and side channel)

Longitudinal distance downstream 

from Lewiston Dam (floodplain kilometer)

Figure 32. Geomorphic feature maps near Junction City on the Trinity River, California, 50.1 floodplain kilometers downstream from Lewiston Dam, in 1980, 2001, and 2011.
50 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

tac12-0449_fig 33

54

53.8

53.9

54

53.8

53.9

54

53.8

53.9

EXPLANATION

Active bar

Stable bar

53.9

Uplands

Pre-dam floodplain

Constructed floodplain Wetted baseflow channel

Post-dam topographic bench

Secondary water feature (alcove, 

wetland, split-flow channel, and side channel)

Longitudinal distance downstream 

from Lewiston Dam (floodplain kilometer)

1980

Base map from rectified 1980, 2001, and 2011 aerial photography. Coordinate reference system: UTM projection, Zone 10, North American Datum of 1983

2011 2001

200 FEET

50 METERS

00

Figure 33. Geomorphic feature maps for Conner Creek Rehabilitation Site on the Trinity River, California, 53.8 floodplain kilometers downstream from Lewiston Dam, in 1980, 2001, and 2011.
Discussion 51 tac12-0449_fig 34

58.1

58.2

58.3

58.4

58.1

58.2

58.3

58.4

58.1

58.2

58.3

58.4

Active bar

Stable bar

58.3

Wetted baseflow channelUplandsPre-dam floodplain

Post-dam topographic bench

Other

EXPLANATION

Constructed bar

Secondary water feature (alcove, 

wetland, split-flow channel, and side channel)

Longitudinal distance downstream 

from Lewiston Dam (floodplain kilometer)

1980

Base map from rectified 1980, 2001, and 2011 aerial photography. Coordinate reference system: UTM projection, Zone 10, North American Datum of 1983

2011 2001

200 FEET

50 METERS

00

Figure 34. Geomorphic feature maps at Lime Point on the Trinity River, California, 58.1 floodplain kilometers downstream from Lewiston Dam, in 1980, 2001, and 2011.
52 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

Conclusions

This report documents a geomorphic assessment of 

a 65-km study reach along the Trinity River, California, 

downstream of Lewiston Dam. A series of geomorphic maps 

were used to characterize trajectories of geomorphic change 

and to investigate the evolution of geomorphic features and 

alluvial processes for one of the nation’s largest adaptively 

managed river restoration programs. The maps illustrate a 

system-wide perspective of evolving geomorphic features 

governed by natural processes and management actions from 

1980 to 2011. The 1980 to 1997 period was dominated by 

channel widening, primarily induced by the 1997 tributary 

flood, and accompanied by smaller increases in active‐bar 

area. This period of channel widening was followed by 

extensive bar accretion, primarily downstream of Indian 

Creek, from 1997 to 2001. Bar and channel margins, 

scoured by large tributary floods in 1997 and 1998, were 

recolonized by vegetation as early as 2001. The beginning of 

the post‐ROD period, from 2001 to 2006, was characterized 

by bar scour slightly greater than bar accretion during the 

previous period, again, primarily downstream from Indian 

Creek. From 2006 to 2011, there were smaller, but measurable 

geomorphic changes, but these were generally limited to 

gravel-augmentation sites in the upper river, mechanical 

channel-rehabilitation sites, tributary confluences, and 

lower river reaches that had sufficient transport capacity and 

sediment supply.

The general trajectory of change from 1980 to 2011 

was a system-wide increase in riparian diversity and 

conversion of riparian features to channel features, such that 

the active-channel area and channel complexity increased. 

During the longer (21 years) and relatively wetter pre‐ROD 

period, increases in active-channel area and channel 

complexity were 20 and 70 percent, respectively. In 1980, the 

pre-dam floodplain and post-dam benches were the primary 

riparian features. Pre-ROD changes in riparian diversity 

included an increase in constructed floodplain and stable bar 

areas. The post‐ROD period was shorter (10 years), relatively 

drier, had intensified management, and there were small, 

but measurable, increases in active-channel area (5 percent) 

and decreases in channel complexity (3 percent). Post‐ROD 

changes in riparian diversity included large increases in 

constructed floodplain area and smaller increases in stable 

bar area.

Parsing out responses to individual causal mechanisms 

is exceedingly complex with numerous and concurrent 

natural and managed controlling factors operating at the 

watershed to reach scale. We determined the primary drivers 

of change during the wetter pre-ROD period were sequential 

tributary floods in 1997 and 1998 that produced channel 

widening (1997) following by bar accretion (1998). During 

the relatively drier post-ROD period, there were measurable 

increases in channel complexity, shoreline length, riparian 

diversity, and channel–floodplain connectivity, which can be 

attributed to the 2006 tributary flood, mechanical restoration, 

gravel augmentation, and managed flow increases. Since 

2006, restoration efforts successfully increased exposed 

active-bar areas by using gravel augmentation in the upper 

river, and these active-bars were maintained with managedflow releases. System-wide riparian diversity and floodplain 

connectivity peaked in 2011, and constructed floodplains were 

inundated for the first time by the 2011 peak-flow release. 

Channel complexity peaked in the central and lower river 

in 2001 and subsequently decreased as a result of natural 

scour and bar stabilization by vegetation encroachment. 

In the upper river, channel complexity peaked in 2011 

as a result of gravel augmentation and construction of 

channel-complexity features.

Our analysis of tributary floods and managed peak-flow 

releases indicated tributary floods have the potential to initiate 

larger and more extensive geomorphic change than managed 

peak-flow releases. During the study period, tributary-flows in 

1997, 1998, and 2006 delivered an unknown, yet presumably 

large, amount of flow and sediment to the mainstem study 

reach. We inferred that increases in transport capacity and 

sediment supply during these tributary floods resulted in the 

greatest channel changes during the study period. 

The regulated-flow strategy in use at the time of writing 

largely decouples mainstem flows from tributary flows in 

terms of timing. The annual peak flow releases from Lewiston 

Dam begin in May, whereas tributary contributions are 

distributed through the winter and spring. An alternative 

strategy for inducing system-wide dynamic bar and bank 

processes would be to coordinate managed-flow releases 

from Lewiston Dam to coincide with tributary flooding. 

Also, the muted and spatially limited physical response to 

flow releases during the post‐ROD period highlights the need 

for continued monitoring and assessment of the magnitude, 

duration, and timing of prescriptive flows and associated 

geomorphic response.

Channel widening from 1980 to 1997 represented a 

threshold disturbance resulting in a system-wide decrease 

in transport capacity, which was likely a primary factor 

governing active-bar deposition from 1997 to 2001. 

Bed-mobility studies in the mid-1990s determined that 

80 percent of the low-flow channel margin was mobilized at 

6,000 ft3/s (Trinity Restoration Associates, Inc., 1993; Wilcock 

and others, 1995; McBain and Trush, Inc., 1997). After 1997, 

studies showed that 6,000 ft3/s did not produce the expected 

scour, mobility, or channel maintenance targets (Hoopa 

Valley Tribe and others, 2011b). These observations indicate 

that pre‐ROD channel widening could have altered channel 

hydraulics, such that flows required to produce targeted 

geomorphic objectives need to be increased. Achieving the 

TRRP goal of a downscaled dynamic river could come with 

the unexpected consequence of a larger active-channel area 

that requires periodic higher maintenance flows.
References Cited 53

Expansion of the geomorphic feature database (Curtis 

and Guerrero, 2015; http://dx.doi.org/10.5066/F7TT4P04) 

to include additional study periods and additional physical 

attributes would support disturbance–response analyses, 

interpretation of the linkages between geomorphology and 

physical habitat, and could be used to refine conceptual 

models and test hypotheses highlighted as a fundamental 

component of adaptive management (Trinity River 

Restoration Program and ESSA Technologies Ltd, 2009). 

Rectified orthophotography from 1944, 1960, and 1975 

exists. Expanding the retrospective mapping to include the 

pre-1980 orthophotography would enable assessment of 

legacy influences related to hydraulic and dredge mining and 

the 1955, 1964, and 1974 floods. More detailed mapping 

of the type and density of riparian vegetation within the 

framework of the existing geomorphic feature maps would 

enable refinement of the active-channel boundary and 

bar‐stability classification. This study used a relatively simple 

bar classification that included lateral and medial bars. For 

the more recent periods, the bar classification could be 

expanded to include additional morphologic and topographic 

attributes and to include additional field reconnaissance and 

mapping of hydraulic controls to support the assessment of 

bar-forcing mechanisms.

Geomorphic change was strongly influenced by the 

relation between transport capacity and sediment supply, 

which varied in space and time. The lack of spatially 

distributed estimates of transport capacity and sediment supply 

severely hindered the controlling factor analysis. A series of 

physical models that link tributaries and the mainstem study 

reach, and characterize flow and sediment flux, would be 

useful for interpreting the spatial distribution of transport 

capacity and sediment supply and for developing testable 

hypotheses regarding potential geomorphic changes under 

present and future conditions. Spatially distributed estimates 

of transport capacity and sediment supply would also 

support a more detailed disturbance–response analysis and 

assessment of the effectiveness of channel-maintenance flows, 

gravel-augmentation prescriptions, and channel-rehabilitation 

design criteria.

References Cited

Anderson, K.T., 2008, Inferring bedrock uplift in the Klamath 

Mountains Province, from river profile analysis and digital 

topography, Master’s Thesis, Texas Tech University, Tex., 

314 p.

Brierley, G.J., Fryirs, K., Outhet, D., Massey, C., 2002, 

Application of the river styles framework as a basis for 

river management in New South Wales, Australia: Applied 

Geography v. 22 no. 1, p. 91–122. http://dx.doi.org/10.1016/

S0143-6228(01)00016-9.

California Department of Water Resources Northern District, 

2007, Trinity River Hydraulic Flow Study North Fork 

Trinity to Lewiston Dam: Sacramento, California, 85 p., 

http://odp.trrp.net/FileDatabase/Documents/DWR_

HydraulicFlowStudyReport_forTRRP_Final_2007071.pdf.

Church, M., 2002, Geomorphic thresholds in riverine 

landscapes: Freshwater Biology, v. 47, p. 541–557. DOI: 

10.1046/j.1365-2427.2002.00919.x.

Curtis, J.A., and Guerrero, T.M. 2015, Geomorphic mapping 

to support river restoration on the Trinity River downstream 

from Lewiston Dam, California, 1980–2011: U.S. 

Geological Survey Open File Report, OFR-5046, xp.

Diller, J.S., 1902, Topographic development of the Klamath 

Mountains: Washington, D.C., U.S. Geological Survey 

Bulletin, v. 196, p. 69. http://pubs.usgs.gov/bul/0196/report.

pdf.

Draut, A.E., Logan, J.B., McCoy, R.E., McHenry, M., and 

Warrick, J.A., 2008, Channel evolution on the lower Elwha 

River, Washington, 1939–2006: U.S. Geological Survey, 

Scientific Investigations Report 2008–5127, 26 p., http://

pubs.usgs.gov/sir/2008/5127/.

Draut, A.E., Logan, J.B., and Mastin, M.C., 2011, Channel 

evolution on the dammed Elwha River, Washington, 

USA: Geomorphology, v. 127, p. 71–87, doi:10.1016/j.

geomorph.2010.12.008.

Gaeuman, D., 2008, Recommended quantities and gradation 

for long-term coarse sediment augmentation downstream 

from Lewiston Dam: Weaverville, Calif., Trinity River 

Restoration Program, Technical Report TM-TRRP-2008-2, 

16 p. http://odp.trrp.net/FileDatabase/Documents/

TM-TRRP-2008_21.pdf.

Gaeuman, D., and Krause, A.F., 2011, 2010 Bed-material 

sediment budget update, Trinity River, Lewiston Dam 

to Douglas City, California: Trinity River Restoration 

Program Technical Report TM-TRRP-2011-2: Weaverville, 

Calif., 24 p. http://odp.trrp.net/FileDatabase/Documents/

Gaeuman%20Krause%20%282011%29%202010%20

Bed-material%20sediment%20budget%20update...

TR-TRRP-2011_21.pdf.

Gallagher, S.P, 1995, Evaluation of the feathered edge 

restoration projects on the Trinity River: fish use and 

physical habitat: Sacramento, Calif., U.S. Fish and Wildlife 

Service, Division of Ecological Services, In-stream Flow 

Branch, 28 p.

Gilbert, G.K., 1914, The transport of debris by running water: 

U.S. Geological Survey Professional Paper 86, 263 p. http://

pubs.usgs.gov/pp/0086/report.pdf.
54 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

Graham Matthews and Associates, 2001, Sediment source 

analysis for the mainstem Trinity River, Trinity County, 

California, Final Report to Tetra Tech, Inc.: Fairfax, Va., 

190 p. http://www.krisweb.com/biblio/trinity_tetratech_

gma_2001_sediment.pdf.

Graham Matthews and Associates, 2012, Trinity River 

WY2011 sediment transport monitoring final report, 

Prepared for the Trinity River Restoration Program: 

Weaverville, Calif., 144 p. http://odp.trrp.net/FileDatabase/

Documents/GMA%20%282012%29%20Trinity%20

River%20WY2011%20Sediment%20Transport%20

Monitoring1.pdf.

Grams, P.E., and Schmidt, J.C. 2002, Streamflow regulation 

and multi-level flood plain formation: channel narrowing on 

the aggrading Green River in the eastern Uinta Mountains, 

Colorado and Utah: Geomorphology, v. 44, p. 337–360. 

http://dx.doi.org/10.1016/S0169-555X(01)00182-9.

Grant, G. E. and Swanson, F. J., 1995, Morphology and 

Processes of Valley Floors in Mountain Streams, Western 

Cascades, Oregon, in Costa, J.E., Miller, A.J., Potter, 

K.W., and Wilcock P.R., eds., Natural and Anthropogenic 

Influences in Fluvial Geomorphology: Washington, D. C., 

American Geophysical Union. doi: 10.1029/GM089p0083.

Hoopa Valley Tribe, McBain & Trush, Inc., and Northern 

Hydrology and Engineering, 2011a, Channel rehabilitation 

design guidelines for the mainstem Trinity River: Prepared 

for the Trinity River Restoration Program, Hoopa, Calif., 

338 p. http://odp.trrp.net/FileDatabase/Documents/

Trinity%20River%20Channel%20Design%20Guide%20

1-21-11%20reduced2.pdf.

Hoopa Valley Tribe, U.S. Fish and Wildlife Service, and Yurok 

Tribe, 2011b, Integrated habitat assessment of the Upper 

Trinity River, 2009: Draft Report: Prepared for the Trinity 

River Restoration Program, Hoopa, Calif., 336 p.

Hughes, M.L., McDowell, P.F., and Marcus, W.A., 2006, 

Accuracy assessment of georectified aerial photographs—

Implications for measuring lateral channel movement 

in GIS: Geomorphology, v. 74, p. 1–16. http://dx.doi.

org/10.1016/j.geomorph.2005.07.001.

Ingersoll, R.V., and Schweickert, R.A., 1986, A platetectonic model for Late Jurassic Ophiolite Genesis, 

Nevadan orogeny and forearc initiation, northern 

California: Tectonics, v. 5, no. 6, p. 901–912. doi:10.1029/

TC005i006p00901.

Irwin, W., 1972, Terranes of the western Paleozoic and 

Triassic belt in the southern Klamath Mountains, 

California: U.S. Geological Survey Professional Paper

800–C, p. 103–111. http://pubs.usgs.gov/pp/0800c/report.

pdf.

Irwin, W.P., 1981, Tectonic accretion of the Klamath 

Mountains, in Ernst, W.G., ed., The geotectonic 

development of California (Rubey Volume 1): PrenticeHall, Englewood Cliffs, N.J., p. 29–49.

Irwin, W.P., 1994, Geologic map of the Klamath Mountains, 

California and Oregon: U.S. Geological Survey 

Miscellaneous Investigations Series Map I–2148, scale 

1:500,000. http://pubs.er.usgs.gov/publication/i2148.

Knott, J.M., 1974, Sediment discharge in the Trinity River 

Basin, California: U.S. Geological Survey Water Resources 

Investigation 73–49, 56 p. http://pubs.er.usgs.gov/

publication/wri7349.

Kondolf, G.M., and Minear, J.T., 2004, Coarse sediment 

augmentation on the Trinity River below Lewiston Dam: 

Geomorphic Perspectives and Review of Past Projects, 

Report to the Trinity River Restoration Program, 67 p. 

http://odp.trrp.net/FileDatabase/Documents/Kondolf,%20

G%20and%20Minear,%20J%20%282004%29%20

Coarse%20sediment%20augmentation%20on%20the%20

Trinity%20River...2.pdf.

Krause, A.F., 2012a, Flow releases and diversions and the 

Trinity River, CA: Water Year 2011: Weaverville, Calif., 

Bureau of Reclamation, Trinity River Restoration Program, 

Technical Report, TR-TRRP-2012-1. http://odp.trrp.net/

FileDatabase/Documents/Krause%202012%20Flow%20

Releases%20and%20Diversions%20on%20the%20

Trinity%20River%20WY20111.pdf.

Krause, A.F., 2012b, History of mechanical sediment 

augmentation and extraction on the Trinity River, 

California, 1912–2011: Trinity River Restoration Program 

Technical Report, TR-TRRP-2012-2, 49 p. http://odp.

trrp.net/FileDatabase/Documents/Krause%20(2012)%20

History%20of%20mechanical%20sediment%20

augmentation%20and%20extraction%201912%20-%20

2011.Revised1.pdf.

Krause, A.F., Wilcock, P.R., Gaeuman, D., 2010, One hundred 

and fifty years of sediment manipulation on the Trinity 

River, Calif.: In Proceedings of the 9th Joint Federal 

Interagency Conference on Sedimentation and Hydrologic 

Modeling, Las Vegas, Nev., June 27, 2010–July 1, 

2010. http://acwi.gov/sos/pubs/2ndJFIC/Contents/3D_

Krause_3_1_10.pdf.

McBain & Trush, Inc., 1997, Trinity River maintenance flow 

study—Final report: Arcata, Calif., prepared for the Hoopa 

Valley Tribe, McBain and Trush, Inc., 482 p. http://odp.trrp.

net/FileDatabase/Documents/Trinity%20Maintenance%20

Flow%20Study%20-%20November%201997.pdf.
References Cited 55

McBain & Trush, Inc., 2000, Evaluation of 1997 flood impacts 

on Riparian Berms along the Trinity River, California—

Final Report: Arcata, Calif., prepared for the Hoopa Valley 

Tribe, McBain and Trush, Inc., 27 p. http://odp.trrp.net/

FileDatabase/Documents/MT%20%282000%29%20

Evaluation%20of%201997%20Flood%20Impacts%20

on%20Riparian%20Berms1.pdf.

Micheli, E.R., Kirchner, J.W., and Larsen, E.W., 2004, 

Quantifying the effect of riparian forest versus agricultural 

vegetation on river meander migration rates, Central 

Sacramento River, California, U.S.A.: River Research and 

Applications, v. 20, no. 5, p. 537–548. doi: 10.1002/rra.756.

Montgomery, D.R., and Buffington, J.M. 1998, Channel 

processes, classification, and response, chapter 2 in Naiman, 

R., and Bilby, R., eds., River Ecology and Management: 

New York, N.Y., Springer-Verlag Inc., p. 13–42.

Montgomery, D.R., Abbe, T.B., Buffington, J.M., Peterson, 

N.P., Schmidt, K.M., and Stock, J.D., 1996, Distribution of 

bedrock and alluvial channel in forested mountain drainage 

basins: Nature, v. 381, p. 587–589. doi:10.1038/381587a0 

http://www.fs.fed.us/rm/boise/publications/watershed/

rmrs_1998_montomeryr001.pdf.

Mount, N.J., and Louis, J., 2005, Estimation and propagation 

of error in the measurement of river channel movement 

from aerial imagery: Earth Surface Processes and 

Landforms, v. 30, no. 5, p. 635–643. DOI: 10.1002/

esp.1172.

O’Connor, J.E., Jones, M.A., Haluska, T.L., 2003, Flood plain 

and channel dynamics of the Quinault and Queets Rivers, 

Washington, USA: Geomorphology v. 51, p. 31–59. http://

dx.doi.org/10.1016/S0169-555X(02)00324-0.

Pitlick, J. and Wilcock, P.R, 2001, Relations between 

Streamflow, Sediment Transport, and Aquatic Habitat in 

Regulated Rivers, in Dorava, J.M., Montgomery, D.R., 

Palcsak, B.B, and Fitzpatrick, F. A., eds, Geomorphic 

Processes and Riverine Habitat: Washington, D. C., 

American Geophysical Union, p. 185–198. doi: 10.1029/

WS004p0185.

Schmidt, J.C., and Wilcock, P.R., 2008, Metrics for assessing 

the downstream effects of dams: Water Resources Research, 

W04404. doi:10.1029/2006WR005092.

Schmidt, J.C., Grams, P.E., and Leschin, M.F., 1999, Variation 

in the magnitude and style of deposition and erosion in three 

long (8–12 km) reaches as determined by photographic 

analysis, in Webb, R.H., Schmidt, J.C., Valdez, R.A., 

and Marzolf, G.R., eds., The Controlled Flood in Grand 

Canyon: Washington, D.C., American Geophysical Union, 

p. 185–203. doi: 10.1029/GM110p0185.

Stearns, J.G., 1969, Task force report on sediment problems 

in the Trinity River near Lewiston, State of California: 

Sacramento, California Resources Agency, 159 p. http://

odp.trrp.net/FileDatabase/Documents/Sediment%20

Problems%20in%20the%20Trinity%20River,%20Near%20

Lewiston%2019691.pdf.

Trinity Restoration Associates, Inc., 1993, Trinity River 

maintenance flow report: evaluation of the 6,000 cfs release: 

Report to Hoopa Valley Indian Tribe Fisheries Department, 

140 p. http://www.fws.gov/arcata/fisheries/reports/technical/

Trinity_River_Channel_Maintenance_Flow_Study_Final_

Report.pdf.

Trinity River Restoration Program and ESSA Technologies 

Ltd, 2009, Integrated Assessment Plan, Version 1.0–

September 2009: Draft report prepared for the Trinity River 

Restoration Program, Weaverville, Calif., 285 p. http://odp.

trrp.net/FileDatabase/Documents/IAP_1.01.pdf.

Trinity River Taskforce, 1970, Task force findings and 

recommendations on sediment problems in the Trinity 

River near Lewiston and a summary of the watershed 

investigation: California Resources Agency, 29 p.

Trinity River Taskforce, 1979, Delta formations at the mouths 

of tributary streams: California Resources Agency, 6 p.

U.S. Bureau of Land Management, 1995, Mainstem Trinity 

River watershed analysis: Redding Resource Area, 74 p. 

http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/

stelprdb5380151.pdf.

U.S. Department of the Interior, 2000, Record of Decision, 

Trinity River mainstem fishery restoration, Final 

Environmental Impact Statement/Environmental Impact 

Report, 43p. http://odp.trrp.net/FileDatabase/Documents/

Trinity%20River%20Record%20of%20Decision%2012-19-

00.pdf.

U.S. Fish and Wildlife Service, 1980, Environmental impact 

statement on the management of river flows to mitigate 

the loss of the anadromous fishery of the Trinity River, 

California, Volume I: Sacramento, California, 229 p. 

http://odp.trrp.net/FileDatabase/Documents/Enviro%20

Impact%20Statement%20Vol.%201%201980b1.pdf.

U.S. Fish and Wildlife Service, 1989, Annual report, Klamath 

River fisheries assessment program juvenile salmonid 

production monitoring, 1988: Report No. AFF-FAO-89-12: 

Arcata, Calif., U.S. Fish and Wildlife Service, 19 p. http://

odp.trrp.net/FileDatabase/Documents/Juvenile_Salmonid_

Monitoring_on_the_Klamath_and_Trinity_Rivers_-_19881.

pdf.
56 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011

U.S. Fish and Wildlife Service, 1994, Restoration of the 

mainstem Trinity River background report, Trinity River 

Restoration Program: Weaverville, Calif., U.S. Fish and 

Wildlife Service, 14 p. http://odp.trrp.net/FileDatabase/

Documents/Restoration%20of%20the%20Mainstem%20

TR%20Background%20Report%2019941.pdf.

U.S. Fish and Wildlife Service and Hoopa Valley Tribe, 1999, 

Trinity River Flow Evaluation Study: Final Report, 310 p. 

http://odp.trrp.net/FileDatabase/Documents/USFWS%20

HVT%201999%20(June%20FINAL%20-%20locked)%20

Trinity%20River%20Flow%20Evaluation%20Final%20

Report1.pdf.

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

O’Connor, J.E., 2010, Channel change and bed-material 

transport in the lower Chetco River, Oregon: U.S. 

Geological Survey Scientific Investigations Report 

2010–5065, 68 p. http://pubs.usgs.gov/sir/2010/5065/pdf/

sir20105065.pdf.

Wallick, J.R., O’Connor, J.E., Anderson, S., Keith, M., 

Cannon, C., and Risley, J.C., 2011, Channel change and 

bed-material transport in the Umpqua River basin, Oregon: 

U.S. Geological Survey Scientific Investigations Report 

2011–5041, 112 p. http://pubs.usgs.gov/sir/2011/5041/pdf/

sir20115041.pdf.

Wilcock, P.R., Kondolf, G.M., Barta, A.F., Matthews, W.V.G., 

and Shea, C.C., 1995, Spawning gravel flushing during trial 

reservoir releases on the Trinity River: Field observations 

and recommendations for sediment maintenance flushing 

flows: Prepared for the U.S. Fish Wildlife Service, 

Sacramento, Calif., Cooperative Agreements 14-16-0001-

91514 and 14-16-0001-91515, 96 p. http://www.fws.

gov/arcata/fisheries/reports/technical/Spawning_Gravel_

Flushing_During_Trial_Reservoir_Releases_on_the_

Trinity_River_Field_Observations_and_Recommendations_

for_Sediment_Maintenance_Flushing_Flows.pdf.

Woolpert, Inc., 2010, Trinity River bathymetry, airborne laser 

data and photogrammetric DTM merging, verification 

and certification: Report prepared for Trinity River 

Restoration Program, U.S. Bureau of Reclamation Task 

Order R10PD40022, 41 p. http://odp.trrp.net/FileDatabase/

Documents/TRRP_2009_DTM&ORTHO1.pdf.

Zilliani, L. and Surian N., 2012, Evolutionary trajectory of 

channel morphology and controlling factors in a large 

gravel-bed river: Geomorphology, v. 173–174, p. 104–117. 

doi:10.1016/j.geomorph.2012.06.001.
Appendix A 57

Appendix A
58 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011 Table A1. Summary of the areal extent of geomorphic features estimated in 1980, Trinity River downstream from Lewiston Dam in California.

[Abbreviations: m2, square meter; —, no data]

Geomorphic reach

Lewiston 

(reach 1)

(m2

)

Sawmill 

(reach 2)

(m2

)

Rush 

Creek 

(reach 3)

(m2

)

Stott 

(reach 4)

(m2

)

Poker Bar 

Canyon 

(reach 5)

(m2

)

Vitzhum 

(reach 6)

(m2

)

Reading Creek 

(reach 7)

(m2

)

Dutton Creek 

(reach 8)

(m2

)

Uplands 93,491 647,047 1,347,078 658,070 703,090 819,531 1,131,225 479,288

Riparian 97,436 368,627 632,002 300,784 345,756 425,715 444,294 161,774

Island 0 33,603 24,113 1,858 17,664 2,411 2,342 0Pre-dam floodplain 58,092 238,509 379,402 181,717 196,437 291,897 315,534 130,427

Constructed floodplain 0 0 0 0 0 0 0 0

Post-dam topographic bench 35,326 89,074 215,249 97,980 121,210 115,473 124,726 28,689

Stable bars 1,223 2,919 3,494 16,398 10,446 15,934 1,301 1,542

Riparian wetland 2,796 4,522 9,744 2,832 0 0 392 1,114

Other 0 0 0 0 0 0 0 0

Active channel 51,386 170,623 181,626 145,929 211,395 163,236 162,999 104,778

Baseflow wetted channel 46,227 145,914 156,354 120,763 181,457 133,955 147,053 96,019

Exposed bedrock 186 439 0 0 651 53 570 496

Alcove 183 1,416 447 5,910 306 1,392 746 102

Side channel 0 10,356 7,651 212 7,494 1,157 1,857 508

Split-flow channel 932 7,654 4,278 10,777 11,763 11,813 4,081 2,581

Aquatic wetland 0 380 0 0 0 0 0 0

Constructed secondary water features 0 7,161 0 0 0 0 0 0

Active bars 680 1,726 12,155 8,266 9,723 14,866 8,471 5,072

Other 3,179 2,736 741 0 0 0 221 0

Lateral bar 1,660 3,638 13,335 20,654 14,755 19,143 8,672 6,078

Medial bar 243 1,007 2,314 4,010 5,414 11,658 1,099 536

Constructed bar 0 293 2,495 0 0 0 0 0

Additional channel attributes

Baseflow-channel length 1,586 5,276 6,369 4,559 6,929 5,986 6,794 4,187

Shoreline length 3,613 14,359 15,643 11,312 17,425 14,550 15,314 9,341

Mean baseflow-channel width 29.1 27.7 24.5 26.5 26.2 22.4 21.6 22.9

Mean active-channel width 32.4 32.3 28.5 32.0 30.5 27.3 24.0 25.0
Appendix A 59

Table A1. Summary of the areal extent of geomorphic features estimated in 1980, Trinity River downstream from Lewiston Dam in California.—Continued[Abbreviations: m2, square meter; —, no data]

Geomorphic reach

Dutch Creek 

(reach 9)

(m2)

Oregon Gulch 

(reach 10)

(m2)

Canyon Creek 

(reach 11) 

(m2)

Lime 

Point 

(reach 12)

(m2)

Pear 

Tree 

(reach 13)

(m2)

Summary

Study 

reach

(m2)

Proportion 

of total

(percent)

Relative 

proportion

(percent)

Uplands 1,723,956 511,038 1,031,079 921,186 364,453 10,430,532 60.4 —

Riparian 916,591 256,145 501,117 392,207 166,376 5,008,825 29.0 —

Island 14,459 2,160 0 0 0 98,610 — 2.0

Pre-dam floodplain 632,919 186,786 372,951 245,322 125,144 3,355,138 — 67.0

Constructed floodplain 0 0 0 0 0 0 — 0.0

Post-dam topographic bench 242,608 62,515 113,012 138,037 39,441 1,423,338 — 28.4

Stable bars 16,179 4,684 7,141 8,848 1,791 91,900 — 1.8

Riparian wetland 10,426 0 8,014 0 0 39,839 — 0.8

Other 0 0 0 0 0 0 — 0.0

Active channel 216,776 61,350 136,630 131,820 79,371 1,817,918 10.5 —

Baseflow wetted channel 197,449 53,826 122,219 114,195 76,113 1,591,545 — 87.5

Exposed bedrock 77 0 0 0 342 2,814 — 0.2

Alcove 1,987 1,066 289 717 79 14,640 — 0.8

Side channel 2,295 0 0 195 0 31,725 — 1.7

Split-flow channel 5,470 2,920 848 5,630 878 69,627 — 3.8

Aquatic wetland 460 0 347 114 0 1,301 — 0.1Constructed secondary water features 0 0 0 0 0 7,161 — 0.4

Active bars 9,037 3,538 12,927 10,969 1,959 99,389 — 5.5

Other 0 0 0 0 0 6,877 — 0.4

Lateral bar 23,518 3,433 14,995 9,023 3,561 142,464 — 7.8

Medial bar 1,699 4,789 5,073 10,794 190 48,826 — 2.7

Constructed bar 0 0 0 0 0 2,789 — 0.2

Additional channel attributes

Baseflow-channel length 8,679 2,680 4,714 4,006 2,834 64,599 — —

Shoreline length 19,726 6,243 9,843 9,375 5,991 152,736 — —

Mean baseflow-channel width 22.8 20.1 25.9 28.5 27.2 25.0 — —

Mean active-channel width 25.0 22.9 29.0 32.9 28.0 28.4 — —
60 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011 Table A2. Summary of the areal extent of geomorphic features estimated in 1997, Trinity River downstream from Lewiston Dam in California.

[Abbreviations: m2, square meter; —, no data]

Geomorphic reach

Lewiston

(reach 1)

(m2

)

Sawmill 

(reach 2)

(m2

)

Rush Creek 

(reach 3)

(m2

)

Stott 

(reach 4)

(m2

)

Poker Bar 

Canyon 

(reach 5)

(m2

)

Vitzhum 

(reach 6)

(m2

)

Reading Creek 

(reach 7)

 (m2

)

Dutton Creek 

(reach 8)

(m2

)

Uplands 93,608 623,198 1,341,307 660,063 703,295 816,500 1,131,285 478,180

Riparian 78,701 360,596 588,401 292,450 323,602 399,224 409,184 151,584

Island 5,125 57,845 37,106 25,694 26,812 10,735 1,612 1,059

Pre-dam floodplain 56,096 228,427 360,925 175,645 184,264 280,898 306,883 125,413

Constructed floodplain 0 0 891 0 10,640 0 9,254 0

Post-dam topographic bench 16,941 68,212 171,503 69,539 92,157 95,598 87,085 24,587

Stable bars 538 3,936 9,275 17,813 9,694 11,993 2,184 524

Riparian wetland 0 2,176 8,701 3,759 35 0 2,166 0

Other 0 0 0 0 0 0 0 0

Active channel 70,005 202,481 214,037 152,269 233,344 192,508 199,276 116,059

Baseflow wetted channel 45,514 161,146 174,055 127,409 187,261 155,202 170,256 103,977

Exposed bedrock 859 975 53 283 1,300 197 1,493 331

Alcove 7,025 4,533 5,349 917 489 416 3,402 484

Side channel 1,726 22,838 15,071 11,315 18,795 12,009 2,162 1,454

Split-flow channel 8,929 7,510 5,202 4,030 13,264 4,491 5,470 1,673

Aquatic wetland 0 76 0 0 0 109 0 0

Constructed secondary water features 8,234 19,210 9,285 10,919 11,592 0 0 0

Active bars 3,624 2,182 13,920 8,316 12,036 20,085 16,439 8,139

Other 2,327 3,222 388 0 199 0 55 0

Lateral bar 1,332 4,627 11,913 21,451 7,948 22,842 16,834 6,029

Medial bar 2,831 1,491 11,281 4,678 13,782 9,236 1,789 2,635

Constructed bar 448 590 1,869 0 0 0 587 0

Additional channel attributes

Baseflow-channel length 1,586 5,276 6,369 4,559 6,929 5,986 6,794 4,187

Shoreline length 6,379 17,369 18,375 11,651 20,626 15,616 16,083 9,771

Mean baseflow-channel width 36.5 32.5 30.0 30.0 31.2 28.4 26.5 26.0

Mean active-channel width 38.7 32.9 35.3 32.8 33.0 31.8 29.0 28.5
Appendix A 61

Table A2. Summary of the areal extent of geomorphic features estimated in 1997, Trinity River downstream from Lewiston Dam in California.—Continued[Abbreviations: m2, square meter; —, no data]

Geomorphic reach

Dutch Creek 

(reach 9)

(m2)

Oregon Gulch 

(reach 10)

(m2)

Canyon Creek 

(reach 11)

(m2)

Lime Point 

(reach 12)

(m2)

Pear Tree 

(reach 13)

(m2)

Summary

Study 

reach

(m2)

Proportion 

of total

(percent)

Relative 

proportion

(percent)

Uplands 1,722,563 505,425 1,027,867 918,801 364,941 10,387,034 60.2 —

Riparian 847,880 229,782 481,825 378,284 156,179 4,697,692 27.2 —

Island 0 17,439 904 0 0 184,332 — 3.9

Pre-dam floodplain 619,005 173,264 359,810 239,678 121,465 3,231,774 — 68.8Constructed floodplain 21,784 0 3,163 1,190 2,011 48,935 — 1.0Post-dam topographic bench 192,476 34,764 103,673 121,691 31,314 1,109,540 — 23.6Stable bars 8,215 3,676 4,001 15,513 1,389 88,752 — 1.9Riparian wetland 6,399 640 10,273 212 0 34,360 — 0.7Other 0 0 0 0 0 0 — 0.0

Active channel 286,937 94,876 157,611 148,128 89,080 2,156,612 12.5 —

Baseflow wetted channel 239,904 68,006 123,924 123,060 81,781 1,761,495 — 81.7

Exposed bedrock 229 0 0 0 422 6,141 — 0.3Alcove 2,760 1,418 2,034 1,726 828 31,382 — 1.5Side channel 1,096 6,283 395 1,043 0 94,186 — 4.4Split-flow channel 10,188 2,265 8,402 1,692 1,011 74,128 — 3.4Aquatic wetland 0 106 0 1,900 102 2,292 — 0.1Constructed secondary water features 0 3,460 0 0 0 62,700 — 2.9Active bars 32,760 16,798 22,857 18,706 4,936 180,797 — 8.4Other 0 0 0 0 0 6,191 — 0.3

Lateral bar 32,419 11,205 24,202 31,841 6,325 198,968 — 9.2Medial bar 8,556 9,268 2,656 2,378 0 70,581 — 3.3

Constructed bar 0 0 0 0 0 3,493 — 0.2

Additional channel attributes

Baseflow-channel length 8,679 2,680 4,714 4,006 2,834 64,599 — —Shoreline length 20,239 7,861 11,003 9,196 6,186 170,354 — —Mean baseflow-channel width 29.8 29.0 31.4 31.5 30.2 30.2 — —Mean active-channel width 33.5 35.1 36.5 36.1 31.9 33.5 — —
62 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011 Table A3. Summary of the areal extent of geomorphic features estimated in 2001, Trinity River downstream from Lewiston Dam in California.

[Abbreviations: m2, square meter; —, no data]

Geomorphic Reach

Lewiston 

(reach 1)

(m2

)

Sawmill 

(reach 2)

(m2

)

Rush Creek 

(reach 3) 

(m2

)

Stott 

(reach 4)

(m2

)

Poker Bar 

Canyon 

(reach 5) 

(m2

)

Vitzhum 

(reach 6)

(m2

)

Reading Creek 

(reach 7)

(m2

)

Dutton Creek 

(reach 8)

(m2

)

Uplands 93,595 625,515 1,342,284 659,740 702,753 814,607 1,131,561 478,335

Riparian 76,169 359,213 584,947 292,682 321,992 400,674 402,091 148,628

Island 4,899 58,490 36,112 25,833 26,250 9,108 1,045 1,054

Pre-dam floodplain 54,734 228,963 359,569 172,801 184,556 281,024 303,525 123,893

Constructed floodplain 0 0 952 0 10,394 0 9,175 0

Post-dam topographic bench 16,094 65,586 167,455 69,858 88,463 91,776 81,458 23,171

Stable bars 443 4,185 13,239 18,503 12,329 18,766 6,405 511

Riparian wetland 0 1,799 7,621 5,688 0 0 482 0

Other 0 190 0 0 0 0 0 0

Active channel 72,549 201,466 221,378 152,360 235,496 194,765 206,178 118,793

Baseflow wetted channel 47,452 162,887 176,786 130,451 194,087 156,081 179,930 107,210

Exposed bedrock 667 888 39 355 1,088 199 1,427 411

Alcove 9,405 4,597 1,412 1,068 385 1,104 1,508 772

Side channel 0 20,242 17,129 11,092 18,980 7,765 1,349 1,430

Split-flow channel 8,541 6,945 6,444 4,032 12,698 6,709 4,844 1,592

Aquatic wetland 0 0 523 0 0 0 121 0

Constructed secondary water features 6,919 19,125 4,580 10,718 9,290 280 0 0

Active bars 3,898 3,066 18,681 5,363 7,964 22,907 16,938 7,379

Other 2,586 2,840 364 0 294 0 61 0

Lateral bar 1,375 5,765 26,092 19,795 8,080 27,687 21,475 5,690

Medial bar 2,965 1,486 5,828 4,070 12,213 13,986 1,869 2,201

Constructed bar 417 584 2,773 0 0 861 0 0

Additional channel attributes

Baseflow-channel length 1,586 5,276 6,369 4,559 6,929 5,986 6,794 4,187

Shoreline length 6,103 17,491 17,740 11,605 20,266 15,892 15,539 9,714

Mean baseflow-channel width 37.6 32.7 29.7 30.5 31.8 29.6 27.7 26.6

Mean active-channel width 40.1 33.2 35.7 33.0 33.0 33.5 30.3 28.7
Appendix A 63

Table A3. Summary of the areal extent of geomorphic features estimated in 2001, Trinity River downstream from Lewiston Dam in California.—Continued[Abbreviations: m2, square meter; —, no data]

Geomorphic Reach

Dutch Creek 

(reach 9)

(m2)

Oregon Gulch 

(reach 10) 

(m2)

Canyon Creek 

(reach 11) 

(m2)

Lime Point 

(reach 12)

(m2)

Pear Tree 

(reach 13)

(m2)

Summary

Study 

reach

(m2)

Proportion 

of total

(percent)

Relative 

proportion

(percent)

Uplands 1,721,904 504,326 1,024,853 919,134 365,065 10,383,672 60.2 —

Riparian 844,159 231,460 480,820 375,344 156,342 4,674,523 27.1 —

Island 0 0 0 0 0 162,790 — 3.5

Pre-dam floodplain 620,349 182,438 357,810 238,006 121,553 3,229,220 — 69.1

Constructed floodplain 20,719 3,216 2,611 1,323 1,910 50,300 — 1.1

Post-dam topographic bench 187,707 39,581 101,791 110,878 31,146 1,074,962 — 23.0

Stable bars 8,791 6,225 6,034 24,968 1,733 122,133 — 2.6

Riparian wetland 6,593 0 9,533 169 0 31,886 — 0.7

Other 0 0 3,042 0 0 3,232 — 0.1

Active channel 291,267 92,683 160,988 150,736 88,793 2,187,452 12.7 —

Baseflow wetted channel 246,691 69,027 129,867 126,761 80,392 1,807,622 — 82.6

Exposed bedrock 220 0 0 0 395 5,689 — 0.3

Alcove 694 1,799 1,866 1,295 162 26,065 — 1.2

Side channel 0 0 744 3,892 74 82,697 — 3.8

Split-flow channel 7,887 4,631 0 0 1,666 65,989 — 3.0

Aquatic wetland 52 107 209 61 170 1,241 — 0.1

Constructed secondary water features 0 1,656 6,431 0 0 58,997 — 2.7

Active bars 35,724 17,120 28,303 18,726 5,935 192,004 — 8.8

Other 0 0 0 0 0 6,145 — 0.3

Lateral bar 39,292 16,861 30,942 38,840 7,524 249,418 — 11.4

Medial bar 5,223 6,483 3,395 4,855 144 64,719 — 3.0

Constructed bar 6,893 438 1,151 0 0 13,115 — 0.6

Additional channel attributes

Baseflow-channel length 8,679 2,680 4,714 4,006 2,834 64,599 — —

Shoreline length 19,148 6,787 10,379 9,196 6,116 165,976 — —

Mean baseflow-channel width 30.0 29.9 30.9 33.6 30.0 30.8 — —

Mean active-channel width 34.1 36.3 37.1 38.3 32.1 34.3 — —
64 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011 Table A4. Summary of the areal extent of geomorphic features estimated in 2006, Trinity River downstream from Lewiston Dam in California.

[Abbreviations: m2, square meter; —, no data]

Geomorphic reach

Lewiston 

(reach 1)

(m2

)

Sawmill 

(reach 2)

(m2

)

Rush Creek 

(reach 3)

(m2

)

Stott 

(reach 4)

(m2

)

Poker Bar 

Canyon 

(reach 5)

(m2

)

Vitzhum 

(reach 6)

(m2

)

Reading Creek 

(reach 7)

(m2

)

Dutton Creek 

(reach 8)

(m2

)

Uplands 93,560 625,205 1,340,891 658,894 702,875 813,123 1,131,437 478,610

Riparian 75,092 355,981 582,693 291,163 311,115 389,163 395,585 149,411

Island 2,283 52,729 34,463 23,878 21,990 9,910 1,111 437

Pre-dam floodplain 53,847 225,754 357,206 170,662 183,195 272,323 301,360 126,072

Constructed floodplain 0 0 1,177 0 10,519 0 8,897 0

Post-dam topographic bench 17,671 69,289 162,196 69,561 85,730 89,967 77,639 22,171

Stable bars 1,011 4,644 19,141 18,780 9,681 16,963 6,136 683

Riparian wetland 279 3,566 8,511 8,281 0 0 442 48

Other 0 0 0 0 0 0 0 0

Active channel 73,662 204,976 225,768 154,726 246,252 205,004 213,033 117,981

Baseflow wetted channel 48,594 164,457 177,734 129,343 201,591 169,551 186,894 108,836

Exposed bedrock 515 428 50 262 854 248 1,338 390

Alcove 10,142 4,983 2,924 940 3,280 1,399 2,048 110

Side channel 0 17,826 18,352 12,494 16,809 6,309 1,497 1,038

Split-flow channel 8,070 9,912 7,169 4,711 12,869 8,019 8,189 2,028

Aquatic wetland 0 305 192 0 23 276 200 597

Constructed secondary water features 7,257 18,155 6,444 11,418 10,084 0 0 0

Active bars 3,254 3,560 19,080 6,975 10,596 19,202 12,827 4,981

Other 3,088 3,504 267 0 230 0 41 0

Lateral bar 1,284 5,533 25,365 20,042 10,002 23,740 13,531 3,134

Medial bar 2,981 2,671 12,855 5,713 10,275 12,425 5,432 2,530

Constructed bar 3,078 688 1,013 0 0 0 0 0

Additional channel attributes

Baseflow-channel length 1,581 5,242 6,323 4,547 6,902 5,982 6,768 4,160

Shoreline length 5,977 17,183 18,353 11,715 19,981 15,608 16,277 9,939

Mean baseflow-channel width 38.0 33.8 31.3 30.8 32.8 31.9 29.8 27.4

Mean active-channel width 40.1 34.5 37.2 33.8 34.3 35.1 32.0 29.2
Appendix A 65

Table A4. Summary of the areal extent of geomorphic features estimated in 2006, Trinity River downstream from Lewiston Dam in California.—Continued[Abbreviations: m2, square meter; —, no data]

Geomorphic reach

Dutch Creek 

(reach 9)

(m2)

Oregon Gulch 

(reach 10)

(m2)

Canyon Creek 

(reach 11)

(m2)

Lime Point 

(reach 12)

(m2)

Pear Tree 

(reach 13)

(m2)

Summary

Study 

reach

(m2)

Proportion 

of total

(percent)

Relative 

proportion

(percent)

Uplands 1,723,242 503,565 1,019,735 919,929 364,683 10,375,749 60.2 —

Riparian 837,908 226,454 479,394 366,877 154,279 4,615,115 26.8 —

Island 0 18,599 0 482 0 165,881 — 3.6

Pre-dam floodplain 612,217 172,032 315,728 237,094 120,577 3,148,067 — 68.2

Constructed floodplain 19,045 0 60,142 1,441 1,675 102,895 — 2.2

Post-dam topographic bench 180,311 30,442 84,190 103,134 30,115 1,022,418 — 22.2Stable bars 16,015 5,297 7,875 24,727 1,911 132,864 — 2.9

Riparian wetland 10,321 83 11,459 0 0 42,991 — 0.9

Other 0 0 0 0 0 0 — 0.0

Active channel 296,201 98,157 166,379 158,407 91,238 2,251,783 13.1 —

Baseflow wetted channel 268,495 78,995 151,253 131,868 84,095 1,901,707 — 84.5

Exposed bedrock 198 0 0 0 375 4,659 — 0.2

Alcove 946 876 636 420 256 28,959 — 1.3

Side channel 227 3,440 982 2,649 93 81,717 — 3.6

Split-flow channel 8,164 2,978 1,899 5,472 744 80,224 — 3.6

Aquatic wetland 225 56 0 475 337 2,686 — 0.1

Constructed secondary water features 0 2,895 0 0 1,294 57,547 — 2.6

Active bars 17,946 11,812 11,610 17,523 5,338 144,703 — 6.4

Other 0 0 0 0 0 7,130 — 0.3

Lateral bar 30,659 14,643 14,539 36,022 7,250 205,744 — 9.1

Medial bar 3,302 2,467 4,945 6,227 0 71,823 — 3.2

Constructed bar 5,399 0 0 0 0 10,177 — 0.5

Additional channel attributes

Baseflow-channel length 8,666 2,753 4,666 3,985 2,825 64,401 — —

Shoreline length 18,818 7,436 10,548 9,446 6,051 167,333 — —

Mean baseflow-channel width 32.4 30.9 36.1 36.9 31.2 32.6 — —

Mean active-channel width 34.5 35.2 38.8 41.3 33.1 35.3 — —
66 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011 Table A5. Summary of the areal extent of geomorphic features estimated in 2009, Trinity River downstream from Lewiston Dam in California.

[Abbreviations: m2, square meter; —, no data]

Geomorphic reach

Lewiston 

(reach 1)

(m2

)

Sawmill 

(reach 2)

(m2

)

Rush Creek 

(reach 3)

(m2

)

Stott 

(reach 4)

(m2

)

Poker Bar 

Canyon 

(reach 5)

(m2

)

Vitzhum 

(reach 6)

(m2

)

Reading Creek 

(reach 7)

(m2

)

Dutton Creek 

(reach 8)

(m2

)

Uplands 93,253 624,100 1,339,419 657,647 703,078 812,104 1,130,735 478,994

Riparian 76,524 351,357 580,028 292,074 312,265 385,277 396,403 148,408

Island 3,847 58,173 39,082 24,365 22,094 21,442 1,141 427

Pre-dam floodplain 42,684 224,356 332,654 170,218 183,212 254,756 299,903 125,059

Constructed floodplain 24,257 1,571 27,786 0 10,418 23,051 9,166 0

Post-dam topographic bench 3,558 61,974 151,994 68,644 86,603 68,296 77,708 22,485

Stable bars 1,271 3,908 21,042 20,607 9,938 17,659 7,653 437

Riparian wetland 906 1,376 7,469 8,241 0 73 833 0

Other 0 0 0 0 0 0 0 0

Active channel 72,536 210,664 229,973 155,061 244,898 208,769 212,501 118,570

Baseflow wetted channel 49,886 158,703 174,161 132,057 201,106 170,100 188,775 108,287

Exposed bedrock 292 425 420 169 1,629 263 1,361 465

Alcove 513 8,326 4,579 769 544 2,831 1,020 224

Side channel 8,065 17,400 21,558 11,739 19,325 13,745 1,736 922

Split-flow channel 6,601 9,535 6,826 4,623 11,376 7,921 7,393 2,449

Aquatic wetland 0 277 166 0 0 0 420 731

Constructed secondary water features 7,923 21,788 12,600 10,180 8,882 9,739 0 0

Active bars 4,659 12,555 21,911 5,705 10,918 13,910 11,795 5,491

Other 2,520 3,442 351 0 0 0 0 0

Lateral bar 2,177 11,070 35,599 20,468 7,427 18,431 13,345 3,736

Medial bar 3,754 5,393 7,354 5,843 13,429 13,138 6,103 2,192

Constructed bar 1,104 7,512 3,444 0 0 0 0 0

Additional channel attributes

Baseflow-channel length 1,586 5,276 6,369 4,559 6,929 5,986 6,794 4,187

Shoreline length 5,907 18,559 19,492 11,828 20,222 17,919 16,047 9,949

Mean baseflow-channel width 38.2 33.0 29.9 31.3 33.1 32.1 30.1 27.2

Mean active-channel width 41.2 35.4 36.3 34.0 34.6 34.5 31.9 29.3
Appendix A 67

Table A5. Summary of the areal extent of geomorphic features estimated in 2009, Trinity River downstream from Lewiston Dam in California.—Continued[Abbreviations: m2, square meter; —, no data]

Geomorphic reach

Dutch Creek 

(reach 9)

(m2)

Oregon Gulch 

(reach 10)

(m2)

Canyon Creek 

(reach 11)

(m2)

Lime Point 

(reach 12)

(m2)

Pear Tree 

(reach 13)

(m2)

Summary

Study 

reach

(m2)

Proportion 

of total

(percent)

Relative 

proportion

(percent)

Uplands 1,721,861 502,653 1,017,454 919,435 364,147 10,364,880 60.1 —

Riparian 843,387 227,031 480,700 361,294 150,537 4,605,284 26.7 —

Island 0 18,978 0 584 0 190,134 — 4.1

Pre-dam floodplain 611,970 172,203 306,312 223,873 109,171 3,056,371 — 66.4

Constructed floodplain 19,484 0 77,343 29,730 13,732 236,537 — 5.1

Post-dam topographic bench 182,536 30,378 75,809 94,536 25,768 950,289 — 20.6

Stable bars 17,840 5,369 8,737 12,507 1,865 128,833 — 2.8

Riparian wetland 11,557 103 12,498 65 0 43,121 — 0.9

Other 0 0 0 0 0 0 — 0.0

Active channel 292,120 98,630 167,157 164,484 95,516 2,270,878 13.2 —

Baseflow wetted channel 267,211 78,859 150,830 138,085 87,774 1,905,833 — 83.9

Exposed bedrock 78 0 0 0 332 5,433 — 0.2

Alcove 683 307 1,389 1,036 295 22,517 — 1.0

Side channel 154 2,507 762 4,529 263 102,706 — 4.5

Split-flow channel 8,019 3,491 1,143 3,443 743 73,564 — 3.2

Aquatic wetland 257 635 0 370 426 3,283 — 0.1

Constructed secondary water features 0 2,745 0 698 1,299 75,854 — 3.3

Active bars 15,719 12,831 13,032 17,020 5,684 151,230 — 6.7

Other 0 0 0 0 0 6,313 — 0.3

Lateral bar 30,316 17,085 16,232 27,110 7,549 210,546 — 9.3

Medial bar 3,243 1,114 5,537 2,417 0 69,516 — 3.1

Constructed bar 6,383 0 0 0 0 18,443 — 0.8

Additional channel attributes

Baseflow-channel length 8,679 2,680 4,714 4,006 2,834 64,599 — —

Shoreline length 18,996 7,155 10,505 10,030 6,181 172,789 — —

Mean baseflow-channel width 32.2 30.2 36.2 36.9 32.3 32.5 — —

Mean active-channel width 34.0 34.9 39.2 41.2 34.3 35.4 — —
68 Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam, California, 1980 to 2011 Table A6. Summary of the areal extent of geomorphic features estimated in 2011, Trinity River downstream from Lewiston Dam in California.

[Abbreviations: m2, square meter; —, no data]

Geomorphic reach

Lewiston 

(reach 1)

(m2

)

Sawmill 

(reach 2)

(m2

)

Rush Creek 

(reach 3)

(m2

)

Stott 

(reach 4)

(m2

)

Poker Bar 

Canyon 

(reach 5)

(m2

)

Vitzhum 

(reach 6)

(m2

)

Reading Creek 

(reach 7)

(m2

)

Dutton Creek 

(reach 8)

(m2

)

Uplands 93,171 624,917 1,316,188 657,913 703,261 813,700 1,131,927 479,191

Riparian 77,863 346,649 586,145 292,870 316,440 379,657 390,107 149,400

Island 4,223 26,913 48,684 24,433 21,083 19,073 1,134 332

Pre-dam floodplain 43,067 210,161 304,952 170,751 184,135 221,791 259,215 126,018

Constructed floodplain 25,062 47,573 57,125 0 10,316 55,168 45,366 0

Post-dam topographic bench 3,600 55,557 138,706 68,202 87,018 68,980 74,154 22,289

Stable bars 1,199 5,212 24,350 21,279 13,888 14,519 9,105 761

Riparian wetland 712 1,234 12,327 8,205 0 126 1,134 0

Other 0 0 0 0 0 0 0 0

Active channel 71,279 214,564 250,085 154,000 240,539 213,255 218,156 117,355

Baseflow wetted channel 50,089 161,272 176,684 133,202 199,874 169,494 191,718 107,782

Exposed bedrock 186 339 376 290 914 335 1,366 566

Alcove 714 9,663 8,454 1,116 603 1,450 2,275 331

Side channel 9,560 21,248 27,186 11,218 20,147 15,583 2,134 1,532

Split-flow channel 3,311 7,317 4,235 4,354 10,525 6,573 7,379 1,221

Aquatic wetland 0 562 1,104 0 46 0 0 0

Constructed secondary water features 9,566 27,636 23,128 10,502 9,893 7,715 1,240 0

Active bars 680 1,726 12,155 8,266 9,723 14,866 8,471 5,072

Other 2,499 964 223 66 229 0 39 0

Lateral bar 5,569 14,841 43,878 19,095 10,749 18,153 16,614 3,840

Medial bar 550 3,571 12,294 5,938 11,340 16,186 5,735 2,843

Constructed bar 3,997 9,414 13,036 0 0 483 2,670 0

Additional channel attributes

Baseflow-channel length 1,586 5,276 6,369 4,559 6,929 5,986 6,794 4,187

Shoreline length 5,810 19,160 21,622 11,649 19,686 17,591 16,003 9,828

Mean baseflow-channel width 34.2 32.6 30.5 31.6 32.3 32.3 30.5 27.1

Mean active-channel width 37.4 35.1 38.0 33.8 33.5 35.6 32.5 29.2
Appendix A 69

Table A6. Summary of the areal extent of geomorphic features estimated in 2011, Trinity River downstream from Lewiston Dam in California.—Continued[Abbreviations: m2, square meter; —, no data]

Geomorphic reach

Dutch Creek 

(reach 9)

(m2)

Oregon Gulch 

(reach 10)

(m2)

Canyon Creek 

(reach 11)

(m2)

Lime Point 

(reach 12)

(m2)

Pear Tree 

(reach 13)

(m2)

Summary

Study 

reach

(m2)

Proportion 

of total

(percent)

Relative 

proportion

(percent)

Uplands 1,723,568 503,078 1,016,755 919,619 364,493 10,347,782 60.0 —

Riparian 845,908 224,622 481,982 367,717 152,463 4,611,824 26.7 —

Island 0 19,053 0 8,855 0 173,783 — 3.8

Pre-dam floodplain 613,625 169,371 307,041 212,330 110,703 2,933,161 — 63.6Constructed floodplain 19,645 0 77,351 40,233 13,534 391,373 — 8.5Post-dam topographic bench 183,363 29,954 74,623 86,186 25,630 918,261 — 19.9Stable bars 19,154 6,245 10,154 19,910 2,596 148,369 — 3.2Riparian wetland 10,121 0 12,814 204 0 46,877 — 1.0Other 0 0 0 0 0 0 — 0.0Active channel 287,855 100,419 169,659 157,878 93,244 2,288,289 13.3 —

Baseflow wetted channel 265,027 81,879 146,608 129,733 85,873 1,899,233 — 83.0

Exposed bedrock 202 30 0 0 297 4,902 — 0.2

Alcove 845 1,212 1,322 1,481 383 29,850 — 1.3

Side channel 0 2,331 344 6,678 101 118,062 — 5.2

Split-flow channel 7,585 3,412 3,272 8,219 779 68,182 — 3.0

Aquatic wetland 0 0 46 460 461 2,678 — 0.1

Constructed secondary water features 0 2,331 1,065 7,356 305 100,737 — 4.4

Active bars 9,037 3,538 18,068 10,969 1,959 104,530 — 4.6

Other 78 0 0 0 0 4,098 — 0.2

Lateral bar 30,332 14,468 22,763 24,482 7,946 232,731 — 10.2

Medial bar 2,941 3,331 5,459 6,090 0 76,278 — 3.3

Constructed bar 5,520 0 1,190 0 0 36,310 — 1.6

Additional channel attributes

Baseflow-channel length 8,679 2,680 4,714 4,006 2,834 64,599 — —

Shoreline length 18,901 7,700 10,649 10,787 6,070 175,456 — —

Mean baseflow-channel width 31.9 32.4 35.3 36.4 31.7 32.2 — —Mean active-channel width 33.5 36.6 39.2 39.3 33.5 35.2 — —

Publishing support provided by the U.S. Geological Survey

Science Publishing Network, Sacramento and Tacoma Publishing Service Centers

For more information concerning the research in this report, contact the

 Director, California Water Science Center

U.S. Geological Survey

6000 J Street, Placer Hall

Sacramento, California 95819

http://ca.water.usgs.gov
Curtis and others—Assessing Geomorphic Change along the Trinity River Downstream from Lewiston Dam California, 1980 to 2011—Scientific Investigations Report 2015–5046

ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20155046