Section Heading 1

Prepared in cooperation with Pierce County Public Works and Utilities, Surface Water 

Management, and King County Department of Natural Resources and Parks, Water and 

Land Resources Division

Changes in Sediment Volume in Alder Lake, Nisqually 

River Basin, Washington, 1945–2011

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2012–1068
Cover: The elevation-contour map surveyed in 1956 (contours in red) drawn 

on a copy of the October 24, 1944, map sheet (contours in black) of the bed 

of Alder Lake near the mouth of the Nisqually River in Alder Lake near Elbe, 

Washington. (Courtesy of Tacoma Public Utilities, Tacoma Power.)
Changes in Sediment Volume in Alder Lake, 

Nisqually River Basin, Washington, 

1945–2011

By Jonathan A. Czuba, Theresa D. Olsen, Christiana R. Czuba, 

Christopher S. Magirl, and Casey C. Gish

Prepared in cooperation with Pierce County Public Works and Utilities, Surface 

Water Management, and King County Department of Natural Resources and 

Parks, Water and Land Resources Division

Open-File Report 2012–1068

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

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/

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

Government.

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

reproduce any copyrighted materials contained within this report.

Suggested citation: Czuba, J.A., Olsen, T.D., Czuba, C.R., Magirl, C.S., and Gish, C.C., 2012, Changes in sediment 

volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011: U.S. Geological Survey Open-File Report 

2012–1068, 30 p.
iii

Contents

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

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

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

Description of Nisqually River Basin..........................................................................................................3

Brief History of Dams on the Nisqually River...................................................................................3

Major Debris Flows from Mount Rainier in the Nisqually River Basin ........................................5

Methods...........................................................................................................................................................6

Description of Historical Contour Maps and Conversion to Digital Format................................6

1945 Elevation-Contour Map......................................................................................................6

1956 Elevation-Contour Map......................................................................................................6

1985 Elevation-Contour Map......................................................................................................6

Digital Conversion of Historical Contour Maps to Elevation Surfaces ...............................6

Data Collection and Processing of 2011 Bathymetric Survey.......................................................7

Computation of Change in Volume between Elevation Surfaces .................................................8

Changes in Sediment Volume of the Nisqually River Delta in Alder Lake............................................9

Changes in Sediment Volume of the Little Nisqually River Delta in Alder Lake................................22

Sediment Deposition in Alder Lake 1945–2011 .......................................................................................26

Future Investigations...................................................................................................................................27

Summary........................................................................................................................................................27

Acknowledgments.......................................................................................................................................28

References Cited..........................................................................................................................................28

Figures

Figure 1. Map showing location and extent of Alder Lake within the Nisqually River basin,

Washington ................................................................................. 2

Figure 2. Photograph showing construction of Alder Dam on the Nisqually River,

Washington, July 20, 1943 .................................................................. 4

Figure 3. Photograph showing Alder Dam on the Nisqually River, Washington ............... 5

Figure 4. Map showing the 1945 (pre-dam) surface elevations of the Alder Lake area,

Washington ................................................................................. 9

Figure 5. Map showing the 2011 point-elevation data of the bed of Alder Lake, 

Washington ................................................................................. 10

Figure 6. Graph showing elevation profiles along the pre-dam Nisqually River centerline

for the 1945 (pre-dam) and 2011 surfaces of the bed of the Alder Lake, 

Washington ................................................................................. 11

Figure 7. Maps showing surface elevations of the Nisqually River delta in Alder Lake,

Washington, from 1945 (pre-dam; contours at 5-foot intervals); 1956 (contours at

1-foot intervals); 1985 (contours mostly at 10-foot intervals, with a few contours 

at 5-foot intervals); and 2011 ............................................................... 12

Figure 8. Photograph showing sediment deposited in Alder Lake near Elbe, Washington,

March 28, 1956 .............................................................................. 16
iv

Figures—Continued

Figure 9. Graph showing elevation profiles for the 1945 (pre-dam), 1956, 1985, and 2011

surfaces along a line through the approximate center of the Nisqually River 

delta in Alder Lake, Washington ......................................................... 17

Figure 10. Maps showing net change in elevation of the Nisqually River delta in Alder 

Lake, Washington, for 1945–56, 1945–85, and 1945–2011 .............................. 18

Figure 11. Photograph showing view looking south at the southeast bank of Alder Lake,

Washington, near the center of the lake, April 19, 2011 .............................. 21

Figure 12. Maps showing spatial extent of the surfaces used to compute delta volume for

the Little Nisqually River delta in Alder Lake, Washington, from 1945 (pre-dam;

contours at 5-foot intervals) and 2011 ................................................... 23

Figure 13. Graph showing elevation profiles along the pre-dam Little Nisqually River

centerline from 1945 (pre-dam) and 2011 surfaces of the Little Nisqually River

delta in Alder Lake, Washington ......................................................... 24

Figure 14. Map showing change in elevation of the Little Nisqually River delta in Alder 

Lake, Washington, 1945–2011 ............................................................ 25

Figure 15. Map showing the volume of sediment deposition between 1945 and 2011 at three

areas of Alder Lake, Washington: the Nisqually River delta; the main body of

Alder Lake, along a 40-meter wide corridor of the pre-dam Nisqually River; and

the Little Nisqually River delta ............................................................ 27

Tables

Table 1. Net cumulative change in sediment volume of the Nisqually River delta in 

Alder Lake, Washington, and estimated uncertainty, 1945–56, 1945–85, and 

1945–2011 .................................................................................... 22

Table 2. Incremental net change in sediment volume of the Nisqually River delta in 

Alder Lake, Washington, 1945–56, 1956–85, and 1985–2011 ........................... 22

Table 3. Net change in sediment volume of the Little Nisqually River delta in Alder Lake,

Washington, and estimated uncertainty, 1945–2011.................................... 26
v

Conversion Factors, Datums, and Abbreviations and 

Acronyms

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

SI to Inch/Pound

Multiply By To obtain

Length

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

meter (m) 1.094 yard (yd) 

Area

square kilometer (km2) 247.1 acre

square kilometer (km2) 0.3861 square mile (mi2)

Volume

cubic meter (m3) 35.31 cubic foot (ft3)

cubic meter (m3) 1.308 cubic yard (yd3) 

Sediment yield

cubic meter per year per square 

kilometer [(m3/yr)/km2]

0.0006844 million gallons per year per 

square mile [(Mgal/yr)/mi2]

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

°F=(1.8×°C)+32.

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.
vi

Abbreviations and Acronyms

Abbreviation or 

Acronym Definition

ADCP acoustic Doppler current profiler

DRG digital raster graphic

GIS geographic information system

GPS global positioning system

NAIP National Agriculture Imagery Program

RTK real-time kinematic

UTM10 Universal Transverse Mercator zone 10

USGS U.S. Geological Survey

WSDOT Washington State Department of Transportation

 

 

 

 
Abstract

The Nisqually River drains the southwest slopes of 

Mount Rainier, a glaciated stratovolcano in the Cascade Range 

of western Washington. The Nisqually River was impounded 

behind Alder Dam when the dam was completed in 1945 

and formed Alder Lake. This report quantifies the volume 

of sediment deposited by the Nisqually and Little Nisqually 

Rivers in their respective deltas in Alder Lake since 1945. 

Four digital elevation surfaces were generated from historical 

contour maps from 1945, 1956, and 1985, and a bathymetric 

survey from 2011. These surfaces were used to compute 

changes in sediment volume since 1945. Estimates of the 

volume of sediment deposited in Alder Lake between 1945 

and 2011 were focused in three areas: (1) the Nisqually River 

delta, (2) the main body of Alder Lake, along a 40-meter wide 

corridor of the pre-dam Nisqually River, and (3) the Little 

Nisqually River delta. In each of these areas the net deposition 

over the 66-year period was 42,000,000 ± 4,000,000 cubic 

meters (m3), 2,000,000 ± 600,000 m3, and 310,000 ± 

110,000 m3, respectively. These volumes correspond to annual 

rates of accumulation of 630,000 ± 60,000 m3/yr, 33,000 ± 

9,000 m3/yr, and 4,700 ± 1,600 m3/yr, respectively. The annual 

sediment yield of the Nisqually (1,100 ± 100 cubic meters per 

year per square kilometer [(m3/yr)/km2]) and Little Nisqually 

River basins [70 ± 24 (m3/yr)/km2] provides insight into the 

yield of two basins with different land cover and geomorphic 

processes. These estimates suggest that a basin draining a 

glaciated stratovolcano yields approximately 15 times more 

sediment than a basin draining forested uplands in the Cascade 

Range. Given the cumulative net change in sediment volume 

in the Nisqually River delta in Alder Lake, the total capacity 

of Alder Lake since 1945 decreased about 3 percent by 1956, 

8 percent by 1985, and 15 percent by 2011.

Introduction

Mount Rainier in the Cascade Range of Washington State 

is drained by five major rivers: the Puyallup, Carbon, White, 

Nisqually, and Cowlitz Rivers (fig. 1). The Carbon and White 

Rivers are tributary to the Puyallup River, which, like the 

Nisqually River, drains to Puget Sound; the Cowlitz River is 

Changes in Sediment Volume in Alder Lake, 

Nisqually River Basin, Washington, 1945–2011

By Jonathan A. Czuba, Theresa D. Olsen, Christiana R. Czuba, Christopher S. Magirl, and Casey C. Gish

a tributary to the Columbia River, which forms the southwest 

boundary of Washington State. Large sediment loads in these 

river systems have resulted in high rates of aggradation in 

selected reaches, increasing channel migration and reducing 

flood-conveyance capacity (Beason and Kennard, 2007; Czuba 

and others, 2010). Multiple debris flows from Mount Rainier 

have delivered large volumes of sediment to these rivers, with 

most documented occurrences (between 1926 and 2006) in 

tributaries of the Nisqually River (Walder and Driedger, 1993; 

Walder and Driedger, 1994; Copeland, 2009). Much of the 

sediment delivered to the Nisqually River was transported 

downstream to Alder Lake, a reservoir that formed behind 

Alder Dam after its completion in 1945. Alder Lake has 

allowed for the quantification of sediment accumulation since 

1945 from the Nisqually River, a river draining a glaciated 

stratovolcano, and the Little Nisqually River, a smaller river 

draining forested uplands of the Cascade Range (fig. 1).

Resource managers have few river-management options 

available that contend with large sediment loads, reduce flood 

risk, and do not adversely affect ecosystems (Czuba and 

others, 2010). Additionally, an apparent increase in the rate 

of aggradation along rivers within Mount Rainier National 

Park during the past two decades (Beason, 2007) may portend 

continued alluvial aggradation in lowland rivers as the 

sediment moves downstream. Resource managers responsible 

for the Puyallup and upper Nisqually River basins want to 

know the quantity of recently released alluvium and the 

historical trends of sediment transport so that they can begin 

to anticipate the timing and magnitude of the downstream 

movement of mobilized sediment. To assist with answering 

these questions, Pierce and King Counties requested that 

the U.S. Geological Survey (USGS) analyze the fluvial 

geomorphic response of rivers downstream of Mount Rainier, 

Washington.

The objectives of the overall study are to estimate 

sediment input from the upper basins of rivers draining Mount 

Rainier, and to estimate downstream transport of this sediment 

through the Puyallup River network (Puyallup, Carbon, and 

White Rivers) and the upper Nisqually River upstream of 

Alder Lake. This report addresses one component of the 

overall study: the estimation of the volumes of sediment 

deposited in Alder Lake between 1945 and 2011 from the 

Nisqually and Little Nisqually Rivers.
2 Changes in Sediment Volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011

Figure 1. Location and extent of Alder Lake within the Nisqually River basin, Washington.

tac12-0728_fig 01

Tacoma

Muck Creek

Mashel 

 River

Mineral Creek

Big Creek

Tanwax Creek

Kautz Creek

East Creek

Tahoma Creek

Little Nisqually River

PIERCE 

COUNTY

LEWIS COUNTY

KING COUNTY

THURSTON COUNTY YAKIMA 

 COUNTY Ohop Creek

122°40'W 122°20'W 122°W 121°40'W

47°10'N

47°N

46°50'N

46°40'N

0 8 16 KILOMETERS

0 4 8 16 MILES

Nisqually River

Alder 

 Lake

Mount Rainier

MOUNT RAINIER

NATIONAL PARK

PUGET

 SOUND

Washington State Dept. of Transportation 

Alder Lake

 Survey Monument BM27007-89

La Grande Reservoir

ALDER DAM

LA GRANDE DAM

Elbe

0 1 2 4 KILOMETERS

0 1 2 4 MILES

CASCADE RANGE

WASHINGTON

MAP LOCATION

EXTENT FIGURE 1B

Carbon River

Puyallup River

White River

Cowlitz River

National Agricultural Imagery Program 2009, UTM zone 10, NAD83, 1 meter resolution.

A.

B.

Nisqually 

River basin
Description of Nisqually River Basin 3

Purpose and Scope

This report documents changes in sediment volume in 

Alder Lake, Nisqually River basin, Washington, from 1945 

to 2011. Estimates of the changes are based on comparisons 

of elevation surfaces for 1945, 1956, 1985, and 2011. The 

data sources were elevation-contour maps from surveys in 

1945, 1956, and 1985 and from bathymetric data collected in 

Alder Lake on October 18–19, 2010, February 8, 2011, and 

April 19–20, 2011. These surfaces were then used to compute 

changes in sediment volume in Alder Lake since 1945. The 

volume change of the Nisqually River delta in Alder Lake was 

computed cumulatively from 1945 to 1956, 1985, and 2011 

and also incrementally for 1945–56, 1956–85, and 1985–2011. 

The volume change of the Little Nisqually River delta in Alder 

Lake was computed for 1945–2011.

Description of Nisqually River Basin

The major tributaries (and associated basin areas) 

to Alder Lake (fig. 1) include the Nisqually River 

(approximately 590 square kilometers [km2]), the Little 

Nisqually River (approximately 67 km2), and East Creek 

(approximately 35 km2). The dominant land cover of all the 

basins upstream of Alder Lake is forest, but some tributaries 

also drain active glaciers on Mount Rainier. The source of 

the Nisqually River is on the southwestern slopes of Mount 

Rainier, a glaciated stratovolcano in the Cascade Range of 

western Washington with a summit elevation of approximately 

4,393 meters (m). The total basin area of the Nisqually River 

is approximately 2,000 km2 and the river drains to Puget 

Sound (fig. 1A). The major tributaries to the Nisqually River, 

also draining glaciers on Mount Rainier, include Kautz and 

Tahoma Creeks. Additional tributaries to the Nisqually River 

not draining glaciated terrain but entering the Nisqually River 

upstream of Alder Lake include Big and Mineral Creeks. East 

Creek and the Nisqually River enter Alder Lake at the eastern 

end of the lake, and both tributaries contribute sediment to the 

deltas that form at their adjacent mouths. The Little Nisqually 

River enters from a steep canyon into a southwestern arm of 

Alder Lake that joins the main lake near its outlet at Alder 

Dam (fig. 1B). 

Alder Lake effectively traps most sediment delivered to 

it, reducing the amount of sediment delivered downstream. 

Just downstream of Alder Lake and Alder Dam is the 

smaller La Grande Reservoir and La Grande Dam, which 

was completed about the same time as Alder Dam (fig. 1B). 

Downstream of these dams, the major tributaries that enter 

the Nisqually River include the Mashel River, Ohop Creek, 

Tanwax Creek, and Muck Creek before the Nisqually River 

enters Puget Sound (fig. 1). The Nisqually River delta in 

Puget Sound is currently (2011) the site of the largest tidal 

marsh restoration project in the Pacific Northwest designed 

to assist in the recovery of Puget Sound salmon and wildlife 

populations (Nisqually Delta Restoration Partnership, 2011). 

Understanding sediment delivery of the Nisqually River to 

Alder Lake can help fill a data gap for restoration-project 

managers planning for the future of the Nisqually River delta 

in Puget Sound.

In western Washington, periods of high streamflow 

occur during autumn and winter, coinciding with periods of 

maximum precipitation, and in spring or early summer, due 

to the seasonal rise in temperature and subsequent melting of 

snowpack at high elevations. In the western Cascade Range, 

orographic lifting of moisture-laden air masses brought in by 

frontal systems from the Pacific Ocean results in heavy 

precipitation, with annual precipitation ranging from 

1.5 to 2.5 m (National Oceanic and Atmospheric 

Administration, 2011). The highest elevations of Mount 

Rainier remain snow covered through summer and have 

many large and expansive glaciers. Snowfall usually begins 

at high elevations in September and maximum snow depths 

usually are reached in early March (National Oceanic and 

Atmospheric Administration, 2011). Average winter snowfall 

ranges from 1.3 to 1.9 m at elevations of approximately 300m, 

increasing to 10–15 m at elevations from 1,200 to 1,700 m 

(National Oceanic and Atmospheric Administration, 2011).

Brief History of Dams on the Nisqually River

In 1907, the city of Tacoma, Washington, was having 

trouble securing a reliable supply of electrical power. In 1909, 

its citizens voted to approve the construction of a hydroelectric 

power-generation plant on the Nisqually River (Malloy and 

Ott, 1993). The first Nisqually River hydroelectric project 

began with the construction of the La Grande Diversion Dam 

in February 1910, which was completed in August 1912. 

The first La Grande Dam was approximately 11-m high and 

69-m wide (Malloy and Ott, 1993). In 1914, the town of 

Alder built the first Alder Dam at the confluence of Alder 

Creek and the Nisqually River, and used its reservoir as a 

mill pond (Johnstone and the South Pierce County Historical 

Society, 2011). Both dams were replaced in the second stage 

of the Nisqually River hydroelectric project by the current La 

Grande and Alder Dams (Tacoma Public Utilities, Tacoma 

Power, 2011). Construction began on the second Alder Dam 

in 1942 and was completed in 1945 (fig. 2; Johnstone and the 

South Pierce County Historical Society, 2011; Tacoma Public 

Utilities, Tacoma Power, 2011). The filling of Alder Lake 

began in January 1945 and electricity generation at Alder Dam 

began in September 1945 (Johnstone and the South Pierce 

County Historical Society, 2011). Alder Dam is a concrete 

arch dam approximately 101-m high and 490-m wide (fig. 3; 

Tacoma Public Utilities, Tacoma Power, 2011). La Grande 

Dam is a concrete gravity and embankment dam, constructed 

in 1945 approximately 3.2 kilometers (km) downstream of 

Alder Dam, and is approximately 66-m high and 220-m wide 

(Tacoma Public Utilities, Tacoma Power, 2011). Throughout 

the rest of this report, ‘pre-dam’ and ‘post-dam’ refer to the 

time prior to and after completion of the second Alder Dam in 

1945, respectively.
4 Changes in Sediment Volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011

watac12-0728_fig 02

Figure 2. Construction of Alder Dam on the Nisqually River, Washington, July 20, 1943. (Courtesy of Tacoma Public Utilities, 

Tacoma Power.)
Description of Nisqually River Basin 5

Tacoma Power of Tacoma Public Utilities manages the 

water-surface elevation of Alder Lake with the primary goal 

of maintaining downstream river flows at or above a specified 

minimum. The secondary goal is to maintain a high lake 

elevation during prime recreation months. Alder Lake has little 

capacity to provide downstream flood control; however, when 

possible, Tacoma Power lowers the elevation of Alder Lake 

during winter months to enable some capture of high inflow 

rates from rainfall and snowmelt. The maximum water-surface 

elevation of Alder Lake, which is controlled by the dam 

spillway, is approximately 367 m, and the lowest allowable 

elevation, which is controlled by the water intake at the dam, 

is approximately 338 m (Tacoma Public Utilities, Tacoma 

Power, 2011).

Major Debris Flows from Mount Rainier in the 

Nisqually River Basin

Between 1926 and 2006, 51 debris flows have been 

documented within Mount Rainier National Park, 48 of which 

were located in tributaries of the Nisqually River (Walder 

and Driedger, 1993; Walder and Driedger, 1994; Copeland, 

2009). However, this historical debris-flow record is likely 

incomplete because most events were documented only when 

they damaged park infrastructure or were large enough to 

be noticed. This historical record also is skewed toward the 

Nisqually River basin because this basin has the largest staff 

presence and is the most heavily visited in the park.

Debris flows are often triggered by heavy rainfall or 

glacial outburst flooding. Heavy rainfall on October 2–3, 1947, 

led to a series of four debris flows in Kautz Creek attributed to 

a combination of rain and glacial outburst flooding (Crandell, 

1971; Walder and Driedger, 1993). The event mobilized 

about 40 million cubic meters (m3) of sediment. Much of the 

fine-grained material was readily transported downstream and 

deposited in Alder Lake (Crandell, 1971). Debris flows were 

infrequently reported in Mount Rainier National Park between 

1948 and 1966 (Copeland, 2009). From 1967 through 2006, 

at least 28 individual debris-flow events were recorded on 

Tahoma Creek (Walder and Driedger, 1994; Copeland, 2009). 

Although the historical record of observation is incomplete, 

there seems to be an increase in Mount Rainier debris-flow 

activity from the 1970s to 2006 (Walder and Driedger, 1993; 

Walder and Driedger, 1994; Copeland, 2009).

watac12-0728_fig 03

Figure 3. Alder Dam on the Nisqually River, Washington. (Courtesy of Tacoma Public Utilities, Tacoma Power, date 

unknown.)
6 Changes in Sediment Volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011

Methods

This study compared historical and modern elevation 

data to estimate volumes of sediment deposited in Alder Lake 

from its two major tributaries. This section describes how 

three historical elevation-contour maps of the Alder Lake area 

representing conditions in 1942–44, 1956–57, and 1985 were 

converted to digital format. This section also describes how an 

acoustic Doppler current profiler (ADCP) was used to measure 

bathymetry in Alder Lake in 2010–11. These data were used 

to generate elevation surfaces in a geographic information 

system (GIS) from which the net change in sediment volume 

in Alder Lake between pre- and post-dam conditions could be 

computed.

Description of Historical Contour Maps and 

Conversion to Digital Format

Historical elevation-contour maps were used to generate 

elevation surfaces for years 1945, 1956, and 1985. Tacoma 

Power provided the USGS with digital images of three 

historical paper elevation-contour maps of the Alder Lake area 

representing conditions in 1942–44, 1956–57 and 1985 (Jeff 

Singleton, Tacoma Public Utilities, Tacoma Power, written 

commun., 2010). The 1942–44 and 1956–57 contour maps 

were surveyed by Tacoma Power or one of its contractors, and 

the 1985 contour map was surveyed by the USGS. The exact 

methods used in these historical surveys are unknown, but 

information about survey dates, datums, and limited survey 

notes were recorded on the paper maps.

1945 Elevation-Contour Map

An elevation-contour map of the entire pre-dam Alder 

Lake area was represented on four separate map sheets. The 

dates of the map sheets spanned from September 1942 to 

October 1944 (September 26, 1942, November 10, 1942, 

November 20, 1942, and October 24, 1944), and were earliest 

near the proposed Alder Lake Dam site, and most recent near 

the mouth of the Nisqually River. The contours representing 

1942–44 conditions were drawn at 5-ft intervals and were 

referenced to the Tacoma Power–Alder Lake project datum 

(vertical) in feet. It was assumed that negligible changes in 

elevation occurred between 1942 and 1945 at the location of 

the Nisqually and Little Nisqually River deltas in Alder Lake, 

and the composite elevation surface constructed from the 

historical map sheets are referred to in this report as the 1945 

surface.

1956 Elevation-Contour Map

An elevation-contour map of the bed of Alder Lake near 

the mouth of the Nisqually River in Alder Lake, surveyed in 

1956, was drawn on a copy of the October 24, 1944, 

contour-map sheet to aid in the calculation (by Tacoma City 

Light, now Tacoma Power of Tacoma Public Utilities, dated 

June 15, 1956) of the change in sediment volume in the 

Nisqually River delta in Alder Lake. Additional contours were 

added to the map sheet on February 21, 1957, extending the 

1956 contours from approximately 2.3 km to 2.9 km into the 

lake. The elevation contours representing 1956–57 conditions 

were drawn at 1-ft intervals and were referenced to the 

Tacoma Power–Alder Lake project datum (vertical) in feet. 

The elevation surface created from the 1956–57 contours is 

referred to in this report as the 1956 surface.

1985 Elevation-Contour Map

A third historical elevation-contour map obtained from 

Tacoma Power represented the entire bed of Alder Lake on 

three map sheets, dated October 29, 1985. The elevation 

contours on the map sheets were drawn mostly at 10-ft 

intervals, with a few contours drawn at 5-ft intervals near the 

mouth of the Nisqually River in Alder Lake. The contours 

were referenced to the National Geodetic Vertical Datum of 

1929 (NGVD 29) in feet. The elevation surface created from 

these contours is referred to in this report as the 1985 surface.

Digital Conversion of Historical Contour Maps to 

Elevation Surfaces

The historical elevation maps were scanned and 

georeferenced horizontally to the North American Datum 

of 1927 (NAD 27) and projected into Universal Transverse 

Mercator zone 10 (UTM10) coordinates in units of meters. 

The digital maps were spatially registered in ArcGIS 9.3, 

using the 2.5-m resolution USGS 1:24,000 topographic 

quadrangle digital raster graphic (DRG) as a base layer. 

The exception is for the 1945 elevation-contour map near 

the Little Nisqually River, where the DRG georeferencing 

was not accurate compared to the 2009 aerial imagery from 

the National Agriculture Imagery Program (NAIP; U.S. 

Department of Agriculture, 2011) or the 2011 survey data. 

Instead this contour map was spatially registered to the 

shoreline of the 2009 NAIP imagery from August 3, 2009, 

which had an elevation of 362.8 m based on historical records 

of lake-surface elevation at Alder Dam (Toby Brewer, Tacoma 

Public Utilities, Tacoma Power, written commun., 2011). At 

least four ground control points were matched between the 

scanned maps and the DRGs and usually consisted of surveyed 

section corners, if available. Using the georeferencing tools in 

ArcGIS, each georeferenced map was rectified by resampling 

the data to a grid, with a cell size of about 1.0 m, by assigning 

the nearest-neighbor value to each grid cell. The

root-mean-squared error of the ground control points was 

generally less than 10 m. Contour lines were then digitized 

from the rectified maps and attributed with contour elevations 

referenced to the vertical datum of the historical contours. 

The datums for all digitized historical contours were then 
Methods 7

converted to the North American Datum of 1983 (NAD 83) 

and the North American Vertical Datum of 1988 (NAVD 88) 

in meters. Conversion of the vertical datum of the historical 

contours to NAVD 88 in meters required three steps: the 

conversion from the Tacoma Power–Alder Lake project datum 

in feet to NGVD 29 in feet (subtract 7.42 ft), from NGVD 29 

in feet to NAVD 88 in feet (add 3.484 ft; value obtained from 

near Alder Dam, National Geodetic Survey, 2003), and from 

NAVD 88 in feet to NAVD 88 in meters. Elevation surfaces 

were generated from the historical elevation contours using the 

Topo-to-Raster tool in ArcGIS.

Data Collection and Processing of 2011 

Bathymetric Survey

Bathymetry of Alder Lake was surveyed on October 

18–19, 2010, February 8, 2011, and April 19–20, 2011, using 

a 600-kHz ADCP and a real-time kinematic (RTK) global 

positioning system (GPS) that received real-time network 

corrections by mobile phone. The ADCP measured water 

depth with four transducers arranged in a Janus configuration 

oriented at 20 degrees from the vertical (Simpson, 2002). The 

RTK-GPS was mounted directly above the ADCP and was 

used to horizontally and vertically reference the ADCP 

water-depth measurements to real-world coordinates. 

Lake-bed elevations were computed by subtracting the 

water-depths measured by the ADCP from the water-surface 

elevations measured by the RTK-GPS. An elevation surface 

was generated from the combined elevation points using the 

Topo-to-Raster tool in ArcGIS; the final surface is referred to 

as the 2011 surface in this report.

All horizontal surveyed data were collected using the 

World Geodetic System of 1984 (WGS 84) ellipsoid reference 

surface and projected into NAD 83 UTM10 in meters and 

vertical data were collected referenced to NAVD 88 in feet. 

Geoid model GEOID03 (National Geodetic Survey, 2011) was 

used to convert GPS-derived heights above the ellipsoid to 

orthometric heights, or elevations above NAVD 88. All final 

surveyed data are in meters and use coordinates in the UTM10 

projection referenced to NAD 83 and NAVD 88 datums.

Real-time corrections for the RTK-GPS were available 

from a network of base stations in the Washington State 

Reference Network and transmitted to the onboard GPS 

through a mobile-phone internet connection (Washington 

State Reference Network, 2011). Dual frequency Trimble 

R8 GPS receivers, Trimble Survey Controller, and Trimble 

GPS antennas were used for all GPS work. Quality control 

RTK-GPS measurements were made at a nearby Washington 

State Department of Transportation (WSDOT) survey 

monument BM27007-89 (fig. 1; Washington State Department 

of Transportation, 2011). The positional accuracy of the 

WSDOT monument was last updated on May 1, 2008, and 

had a reported horizontal and vertical accuracy of 0.02 m 

and 0.01 m, respectively (Washington State Department of 

Transportation, 2011). Three quality-control measurements of 

this survey mark on days of the survey were all within 0.03 m 

horizontally and 0.05 m vertically.

Bathymetric data were collected using a combination of 

cross sections, winding paths, and longitudinal profiles. 

Water-depth measurements were collected in WinRiver2 

ADCP data-processing software and imported into MatLab for 

further processing. Water-depth measurements from each of 

the four transducers were processed as individual 

lake-bed elevation points in the bathymetric dataset. 

Water-depth measurements were corrected in MatLab for 

transducer orientation and instrument pitch and roll using data 

from the compass and tilt sensor of the instrument. Waterdepth measurements were compensated for changes in the 

speed of sound in water, associated with temperature, using 

the temperature sensor of the instrument located near the 

transducers.

Independent water-temperature measurements made 

periodically near the ADCP verified that the instrument 

was reading temperature within 0.5°C. No measurements 

were made of the temperature profile throughout the water 

column; therefore, ADCP water-depth measurements were 

not compensated for temperature variations with depth. A 5°C 

error in temperature throughout the entire water column would 

bias water-depth measurements by 2 percent (Mueller and 

Wagner, 2009). During the survey, measured 

surface-water temperatures ranged from approximately 

4 to 14°C and measured water depths ranged from 

approximately 0.5 to 70 m. The presence of a thermocline, 

defined as a region of abruptly changing water temperature 

that separates cold deep water from warmer surface water, 

would bias measured water-depth measurements low, and 

therefore would bias computed lake-bed elevations high. 

Assuming the presence of an unmeasured thermocline during 

the survey that results in an average temperature throughout 

the water column of 4°C, the largest depth-measurement 

errors would be introduced where the measured surfacewater temperatures were high and water depths were deep. 

Near the Nisqually and Little Nisqually River deltas, the 

combination of measured surface-water temperature and 

depth that would introduce the largest possible depthmeasurement error due to the presence of a thermocline 

were a surface-water temperature of approximately 7°C and 

a depth of approximately 20 m that would bias measured 

water depths low and computed lake-bed elevations high by 

approximately 0.25 m. Similarly, away from the deltas in the 

deeper main body of the lake, the combination of measured 

surface-water temperature and depth that would introduce 

the largest possible depth-measurement error due to the 

presence of a thermocline were a surface-water temperature 

of approximately 9°C and a depth of approximately 70 m that 

would bias measured water depths low and computed lake-bed 

elevations high by approximately 1.4 m.
8 Changes in Sediment Volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011

The 2011 bathymetric survey had a high spatial resolution 

near the Nisqually and Little Nisqually River deltas in Alder 

Lake, and away from these areas of interest, both the spatial 

resolution and vertical accuracy decreased. Given the accuracy 

of the RTK-GPS and ADCP instruments, the possible presence 

of a thermocline, and the sparse resolution of the dataset in 

some areas, the estimated uncertainty of the 2011 elevation 

surface is 0.3 m near the deltas and 2 m away from the deltas.

Computation of Change in Volume between 

Elevation Surfaces

Cumulative changes in the volume of the Nisqually 

River delta in Alder Lake were computed for the 1945–56, 

1945–85, and 1945–2011 by subtracting the 1945 surface 

from each of the more recent surfaces. The volume change for 

the Little Nisqually River delta in Alder Lake was computed 

only for 1945–2011. The spatial extent of the volume-change 

computation depended on the overlapping areas of the two 

surfaces and was limited to just beyond the extent of the delta 

at that time. The volume-change computation generated an 

increase in volume where the 1956, 1985, and 2011 surfaces 

were higher than the 1945 surface, and a decrease where 

these surfaces were lower than the 1945 surface. The net 

change in volume was computed by subtracting the total 

decrease in volume from the total increase. The rate of net 

change in volume was computed by dividing the net change 

in volume by the number of years between the two surveys. 

The incremental net change in volume between each survey 

(between 1945 and 1956, 1956 and 1985, and 1985 and 

2011) was computed as the difference between net changes in 

volume since 1945. 

The exact methods used for each historical survey are 

unknown; however, a measure of vertical uncertainty was 

estimated based on the contour interval of the historical 

survey. An uncertainty in the vertical elevations of each 

historical surface was assumed to be one-half of the contour 

interval of the contours used to generate that surface. The 

estimated uncertainty of the net change in volume was 

computed from the combined vertical uncertainties of the two 

surfaces being compared, calculated as the square root of the 

sum of the squares of the vertical uncertainty of each surface, 

and multiplied by the surface area of the computation.

Channel reworking or bank erosion was assumed to 

remove sediment from one location in the lake and deposit 

it in another location in the lake, resulting in no net change 

in sediment volume. Therefore, estimates of net change in 

volume (total increases minus total decreases in volumes) 

represent the net volume of sediment contributed by the 

respective rivers to Alder Lake.
Changes in Sediment Volume of the Nisqually River Delta in Alder Lake 9

8 6

4

2

0

14

12

10

0 1 2 MILES

0 1 2 KILOMETERS

EXPLANATION

Pre-dam Nisqually River

centerline 

Distance along centerline,

in kilometers

369.0

289.0

1945 surface elevation,

in meters above North 

American Vertical Datum 

of 1988

4

122°18' W 122°16'W 122°14'W 122°12'W

46°48'N

46°46' N

National Agricultural Imagery Program 2009, UTM zone 10, NAD83, 1 meter resolution.

Figure 4. The 1945 (pre-dam) surface elevations of the Alder Lake area, Washington.

Changes in Sediment Volume of the 

Nisqually River Delta in Alder Lake

The Nisqually River transports sediment with particle 

diameters that span a wide range of sizes: from cobble 

and gravel (with particle diameters as large as several 

centimeters) to clay (with particle diameters as small as a 

few micrometers). Before construction of the earliest dam on 

the Nisqually River in 1910, the Nisqually River transported 

sediment downstream of the Alder Lake area, with the largest 

particles breaking down to smaller sizes before reaching 

Puget Sound. The historical channel of the Nisqually River 

was apparent in the pre-dam (1945) surface of the Alder Lake 

area (fig. 4). Since the formation of Alder Lake in 1945, the 

transport of sediment by the Nisqually River downstream of 

the Alder Lake area decreased dramatically. A relatively large 

amount of sediment deposited in a delta within Alder Lake that 

had prograded as far as 6 km from the mouth of the Nisqually 

River as of 2011 (fig. 5). The delta front is indicated by the 

sharp decline in elevation in a narrow section near the center 

of the lake (fig. 5). The coarsest sediment (cobble and gravel) 

would have deposited nearest the mouth of the Nisqually 

River in Alder Lake. The sediment composing the delta 

presumably grades to finer sediment (sand and silt) farther 

into the lake. The finest sediment (clay) presumably settles 

out in the main body of Alder Lake or passes through the 

intake structure of Alder Dam and is transported downstream. 

However, the transport and fate of specific sizes of sediment 

or the composition of sediment deposits were not assessed 

because the sizes of the sediment deposited in Alder Lake 

were not measured.

East Creek enters Alder Lake adjacent to the Nisqually 

River and also contributes sediment to the Nisqually River 

delta in Alder Lake. However, because the land cover in 

the East Creek basin is similar to the Little Nisqually River 

basin and is smaller in drainage area, it is assumed that its 

sediment contribution is minor and that most of the sediment 

in the Nisqually River delta in Alder Lake is attributed to the 

Nisqually River basin.
10 Changes in Sediment Volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011

Comparison of elevation profiles along the historical 

channel of the Nisqually River for the 1945 (pre-dam) and 

2011 surfaces showed the general change in elevation of the 

bed of Alder Lake between 1945 and 2011, with a maximum 

increase in the thickness of the delta deposit of approximately 

30 m near its distal extent (fig. 6). Due to time limitations of 

the survey and the focus on the delta area, the 2011 elevation 

points (fig. 6) were sparse and uncertainty is larger close to 

the dam (between 8 and 14 km along the historical channel of 

the Nisqually River) than near the delta (between 0 and 8 km 

along the historical channel of the Nisqually River).

Because of differences in the resolution of the elevation 

contours, the four elevation surfaces of the Nisqually River 

delta region in Alder Lake show varying detail (fig. 7A-D). 

watac12-0728_fig 05

EXPLANATION

Pre-dam Nisqually River centerline 

Distance along centerline,

 in kilometers

2011 point elevation, in meters 

 above North American Vertical 

 Datum of 1988

289.0 - 300.0

300.1 - 310.0

310.1 - 320.0

320.1 - 330.0

330.1 - 340.0

340.1 - 350.0

350.1 - 360.0

360.1 - 369.1

122°18'W 122°16'W 122°14'W 122°12'W

46°48'N

46°46'N

8 6

4

2

2

0

14

12

10

National Agricultural Imagery Program 2009, UTM zone 10, NAD83, 1 meter resolution.

0 1 2 MILES

0 1 2 KILOMETERS

Figure 5. The 2011 point-elevation data of the bed of Alder Lake, Washington.

The 1956 surface shows the most detailed features including 

a mound of sediment (fig. 7B, between 0 and 1 km along the 

approximate center of the delta) with distinct channel features 

cut into it. This mound of sediment has been attributed to 

sediment mobilized by the 1947 Kautz Creek debris flow 

(Crandell, 1971) that was transported from Kautz Creek 

downstream to the Nisqually River and deposited in Alder 

Lake. A photograph taken in 1956 (fig. 8) shows one of the 

channel features that was cut approximately 5 m down into the 

mound of sediment, which from the photograph appears to be 

composed of sand and finer-sized sediment. The exact location 

of the photograph is unknown, but based on comparable 

topographic features (fig. 8) and the 1956 surface (fig. 7B), the 

probable location is indicated in figure 7B.
Changes in Sediment Volume of the Nisqually River Delta in Alder Lake 11

watac12-0728_fig 06

280

290

300

310

320

330

340

350

360

370

0 2 4 6 8 10 12 14

Elevation, in meters above North American Vertical Datum of 1988

Distance along the pre-dam Nisqually River centerline, in kilometers

Elevation of Alder Dam spillway

1945

2011

Elevation of Alder Dam water intake

Figure 6. Elevation profiles along the pre-dam Nisqually River centerline for the 1945 (pre-dam) and 2011 surfaces of the 

bed of the Alder Lake, Washington. River centerline is shown in figures 4 and 5.
12 Changes in Sediment Volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011

watac12-0728_Fig07a

6

5

4

3

2

1

0

6

5

4

3

2

1

1

0

122°12'W 122°13'W 122°14'W 122°15'W

46°47'N

46°46'N

0 1 0.5 MILES

0 1 0.5 KILOMETERS

EXPLANATION

Elevation contourApproximate center

of the delta

Distance along approximate 

center of the delta,in kilometers

1945 surface elevation, 

in meters above North American Vertical Datum of 1988

369320

National Agricultural Imagery Program 2009, UTM zone 10, NAD83, 1 meter resolution.

A.

1

Figure 7. Surface elevations of the Nisqually River delta in Alder Lake, Washington, from (A) 1945 (pre-dam; contours at 5-foot intervals); (B) 1956 

(contours at 1-foot intervals; marker indicates the probable location of the photograph shown in figure 8); (C) 1985 (contours mostly at 10-foot intervals, with a few contours at 5-foot intervals); and (D) 2011.
Changes in Sediment Volume of the Nisqually River Delta in Alder Lake 13 watac12-0728_fig07b

2

1

0

2

1

0

122°12'W 122°13'W 122°14'W 122°15'W

46°47'N

46°46'N

0 1 0.5 MILES0 1 0.5 KILOMETERS

EXPLANATION

Elevation contourApproximate center

of the delta

Distance along approximate 

center of the delta,in kilometers

Probable location of

photograph shownin figure 8

1956 surface elevation, 

in meters above North American Vertical Datum of 1988

369320

National Agricultural Imagery Program 2009, UTM zone 10, NAD83, 1 meter resolution.

B.

2

Figure 7. Continued. 
14 Changes in Sediment Volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011

watac12-0728_fig07c

!

!

!

!

!

4

3

2

1

0

4

3

2

1

0

122°12'W 122°13'W 122°14'W 122°15'W

46°47'N

46°46'N

0 1 0.5 MILES0 1 0.5 KILOMETERS

EXPLANATION

Elevation contourApproximate center

of the delta

Distance along approximate 

center of the delta,in kilometers

1985 surface elevation, 

in meters above North American Vertical Datum of 1988

369320

National Agricultural Imagery Program 2009, UTM zone 10, NAD83, 1 meter resolution.

C.

1

Figure 7. Continued. 
Changes in Sediment Volume of the Nisqually River Delta in Alder Lake 15 watac12-0728_fig07d

6

5

4

3

2

1

0

6

5

4

3

2

1

0

122°12'W 122°13'W 122°14'W 122°15'W

46°47'N

46°46'N

0 1 0.5 MILES

0 1 0.5 KILOMETERS

EXPLANATION

Approximate center

of the delta

Distance along approximate 

center of the delta,in kilometers

2011 surface elevation, 

in meters above North American Vertical Datum of 1988

369320

National Agricultural Imagery Program 2009, UTM zone 10, NAD83, 1 meter resolution.

D.

1

Figure 7. Continued. 
16 Changes in Sediment Volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011

Figure 8. Sediment deposited in Alder Lake near Elbe, Washington, March 28, 1956. The probable location of the photograph is 

indicated in figure 7B; view is looking southeast. (Courtesy of Tacoma Public Utilities, Tacoma Power.)

watac12-0728_fig08
Changes in Sediment Volume of the Nisqually River Delta in Alder Lake 17

310 

320 

330 

340 

350 

360 

370 

0 1 2 3 4 5 6 7 

1945

1956

2011

1985

Elevation of Alder Dam spillway

Elevation of Alder Dam water intake

Elevation, in meters above North American Vertical Datum of 1988

Distance along the approximate center of the Nisqually River delta, in kilometers

Figure 9. Elevation profiles for the 1945 (pre-dam), 1956, 1985, and 2011 surfaces along a line through the approximate 

center of the Nisqually River delta in Alder Lake, Washington. (Line is shown in the maps in figure 7A-D).

An elevation profile for these surfaces along a line 

through the approximate center of the Nisqually River delta in 

Alder Lake (which is different than the former river centerline 

shown in figures 4 and 5 and used for the elevation profile 

in figure 6) shows the temporal evolution of the Nisqually 

River delta in Alder Lake (fig. 9; line shown in fig. 7A-D). 

The 1956 surface, which includes the contour data that were 

added in 1957, does not capture the distal extent of the delta 

at that time, but indicates that it was at least approximately 

2.5 km into Alder Lake from the mouth of the Nisqually 

River. By 1985, the delta front prograded a total distance of 

approximately 3.5 km. Between 1985 and 2011, the delta 

front prograded an additional distance of approximately 2 km 

farther into Alder Lake.

The spatial distribution of the changes in elevation 

between 1945 and 1956, 1985, and 2011 shows where 

increases and decreases in elevations are distributed in the 

Nisqually River delta region in Alder Lake (fig. 10A-C). 

Areas with the largest increases in elevation are at the distal 

end of the prograding delta. Areas with noticeable decreases 

in elevation are along the banks of the lake and near the area 

where the Nisqually River and East Creek enter the lake 

(fig. 1). Significant decreases in elevation are likely due to 

reworking of deposited sediment by the migration of channels 

across the delta deposit during periods of low water in the 

lake, due to erosion of the banks along the shore of the lake, 

or an artifact of the horizontal misalignment of the surveys, 

in which the two georeferenced surfaces were not perfectly 

oriented to each other. The substantial decrease in elevation 

between 1945 and 1985 (fig. 10B) is most likely an artifact 

of horizontal misalignment of the 1985 surface. Significant 

decreases in elevation between 1945 and 2011 (fig. 10C) are 

limited to the banks of Alder Lake where wave action appears 

to have eroded the banks of the lake. Ongoing erosion of the 

southeast bank of Alder Lake near the center of the lake was 

observed on April 19, 2011 (fig. 11).
18 Changes in Sediment Volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011

Figure 10. Net change in elevation of the Nisqually River delta in Alder Lake, Washington, for (A) 1945–56, (B) 1945–85, and (C) 1945–2011.

watac12-0728_fig10a

122°12'W 122°13'W 122°14'W 122°15'W

46°47'N

46°46'N

0 1 0.5 MILES0 1 0.5 KILOMETERS

EXPLANATION

Elevation change 1945–56, 

in meters 

28

0

-28

National Agricultural Imagery Program 2009, UTM zone 10, NAD83, 1 meter resolution.

A.
Changes in Sediment Volume of the Nisqually River Delta in Alder Lake 19

watac12-0728_fig10b

122°12'W 122°13'W 122°14'W 122°15'W

46°47'N

46°46'N

0 1 0.5 MILES

0 1 0.5 KILOMETERS

EXPLANATION

Elevation change 1945–85, 

in meters 

28

0

-28

National Agricultural Imagery Program 2009, UTM zone 10, NAD83, 1 meter resolution.

B.

Figure 10. Continued.
20 Changes in Sediment Volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011

watac12-0728_fig10c

122°12'W 122°13'W 122°14'W 122°15'W

46°47'N

46°46'N

0 1 0.5 MILES0 1 0.5 KILOMETERS

EXPLANATION

Elevation change 1945–2011, 

in meters 

Location of photograph 

shown in figure 11

28

0

-28

National Agricultural Imagery Program 2009, UTM zone 10, NAD83, 1 meter resolution.

C.

Figure 10. Continued.
Changes in Sediment Volume of the Nisqually River Delta in Alder Lake 21

watac12-0728_fig 11

Figure 11. View looking south at the southeast bank of Alder Lake, Washington, near the center of the 

lake, April 19, 2011. (Location of the photograph is indicated in figure 10C. Photograph taken by Christiana 

Czuba, U.S. Geological Survey.)

The net change in volume and estimated uncertainty of 

the Nisqually River delta in Alder Lake between 1945 and 

1956, 1945 and 1985, and 1945 and 2011 are 9 ± 2 million 

cubic meters, 22 ± 5 million cubic meters, and 42 ± 4 million 

cubic meters, respectively (table 1). The rate of net change in 

volume and estimated uncertainty for the Nisqually River delta 

in Alder Lake between 1945 and 2011 is 630,000 ± 60,000 m3/

yr. This is equivalent to a yield of 1,100 ± 100 (m3/yr)/km2 for 

the Nisqually River basin.

Tacoma City Light estimated that 7,215,000 m3 of 

sediment accumulated in the Nisqually River delta in Alder 

Lake between 1944 and 1956. This estimate was cited by Mills 

(1976), but because this estimate did not include the additional 

contours that were added in February 1957, the estimated 

volume of sediment that accumulated in the Nisqually River 

delta in Alder Lake during that period was underestimated. 

The additional contours added in February 1957 in the volume 

calculation were used in this study to estimate the volume 

of sediment that accumulated in the Nisqually River delta in 

Alder Lake between 1945 and 1956 of 9,000,000 m3

(± 2,000,000 m3; table 1). However, the contours added in 

1957 did not fully extend to the distal extent of the Nisqually 

River delta in Alder Lake (fig. 9), and therefore, the estimate 

of the volume of sediment that accumulated in the Nisqually 

River delta between 1945 and 1956, from this report, 

underrepresents the volume of sediment accumulated by 1956.

The 1947 Kautz Creek debris flow mobilized about 

40 million cubic meters of sediment (Crandell, 1971). Some 

of this sediment deposited immediately in Kautz Creek, 

some deposited in the Nisqually River, and some transported 

to Alder Lake (fig. 7B and 8). Between 1945 and 1956, 

at least 9 million cubic meters of sediment had deposited 

in the Nisqually River delta in Alder Lake. The source of 

this sediment was from a combination of the background 

watershed contributions and from the 1947 Kautz Creek 

debris flow. Assuming that all of the 9 million cubic meters of 

sediment was from the Kautz Creek debris flow, then at most 

one-fourth of the sediment mobilized by the 1947 Kautz Creek 

debris flow deposited in Alder Lake by 1956.

The rates of incremental net change in volume between 

1945 and 1956, 1956 and 1985, and 1985 and 2011 are 

830,000, 430,000, and 770,000 m3/yr, respectively (table 2). 

The largest rate of incremental net change in volume was 

for 1945–56. The rate of incremental net change in volume 

for 1956–85 was comparatively small, and may indicate that 

there was a shift in sediment delivery from Mount Rainier to 

the Nisqually River associated with a change in hydrologic 

conditions.
22 Changes in Sediment Volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011

Table 1. Net cumulative change in sediment volume of the Nisqually River delta in Alder Lake, Washington, and estimated uncertainty, 

1945–56, 1945–85, and 1945–2011.

[Abbreviations: m2, square meter; m3, cubic meter; m3/yr, cubic meter per year]

Period 

between 

surveys

Number of 

years 

between 

surveys

Surface area 

of volume 

computation 

(m2

)

Total 

increase in 

volume

(m3

) 

Total 

decrease in 

volume 

(m3

) 

Net change in 

volume (total 

increase minus 

total decrease) 

(m3

) 

Estimated 

uncertainty of 

net change in 

volume

(m3

)

Rate of net 

change in 

volume

(m3

/yr) 

Estimated 

uncertainty of 

rate of net change 

in volume

(m3

/yr) 

1945–56 11 2,500,000 9,300,000 100,000 9,000,000 2,000,000 830,000 180,000

1945–85 40 4,200,000 22,100,000 500,000 22,000,000 5,000,000 540,000 110,000

1945–2011 66 4,800,000 43,100,000 1,500,000 42,000,000 4,000,000 630,000 60,000

Table 2. Incremental net change in sediment volume of the 

Nisqually River delta in Alder Lake, Washington, 1945–56, 1956–85, 

and 1985–2011.

[Abbreviations: m3, cubic meter; m3/yr, cubic meter per year]

Period 

between 

surveys

Number of 

years 

between 

surveys

 Incremental 

net change 

in volume

(m3

) 

 Rate of 

incremental 

net change 

in volume

(m3

/yr) 

1945–56 11 9,000,000 830,000 

1956–85 29 12,000,000 430,000 

1985–2011 26 20,000,000 770,000 

Changes in Sediment Volume of the 

Little Nisqually River Delta in Alder 

Lake

The Little Nisqually River enters from a steep canyon 

into a southwestern arm of Alder Lake (fig. 1). The delta of the 

Little Nisqually River in Alder Lake is located where the lake 

widens as shown on the 1945 (pre-dam) and 2011 elevation 

surfaces (fig. 12). Elevation profiles along the historical 

channel of the Little Nisqually River from the pre-dam and 

2011 surfaces indicate an increase in elevation of the bed of 

Alder Lake between 1945 and 2011, with a maximum increase 

of the delta deposit of approximately 10 m (fig. 13). Between 

1945 and 2011, the Little Nisqually River delta in Alder Lake 

prograded less than 1 km into the lake (fig. 13) and did not 

have as sharp of a break between the top and more steeply 

sloping front of its delta as did the Nisqually River delta in 

Alder Lake (fig. 6). The spatial distribution of the changes in 

elevation between 1945 and 2011 shows where increases and 

decreases in elevations are distributed in the Little Nisqually 

River delta region in Alder Lake (fig. 14). Areas with the 

largest increases in elevation are located toward the distal end 

of the prograding delta. Areas with noticeable decreases in 

elevation are located along the banks of the lake where there is 

a larger uncertainty between the elevation surfaces.

The net change in volume and estimated uncertainty of 

the Little Nisqually River delta in Alder Lake between 1945 

and 2011 is 310,000 ± 110,000 m3 (table 3). The rate of net 

change in volume and estimated uncertainty for the Little 

Nisqually River delta in Alder Lake between 1945 and 2011 is 

4,700 ± 1,600 m3/yr (table 3). This is equivalent to a yield of 

70 ± 24 (m3/yr)/km2 for the Little Nisqually River basin.
Changes in Sediment Volume of the Little Nisqually River Delta in Alder Lake 23

watac12-0728_fig12

0

0.8

0.6

0.4

0.2

0

0.8

0.6

0.4

0.2

122°19'20"W 122°19'10"W

46°46'15"N

46°46'N

46°45'45"N

122°19'20"W 122°19'10"W

0 500 FEET

0 100 METERS

0 500 FEET

0 100 METERS

EXPLANATION EXPLANATION

Pre-dam Little Nisqually

 River centerline

Distance along centerline, 

in kilometers

Pre-dam Little Nisqually

River centerline

Elevation contour

Distance along centerline, 

in kilometers

1945 surface elevation, in meters above North 

American Vertical Datum of 1988

369

335

2011 surface elevation, in meters 

above North American Vertical 

Datum of 1988

369

335

0.2 0.2

A. B.

National Agricultural Imagery Program 2009, 

UTM zone 10, NAD83, 1 meter resolution.

National Agricultural Imagery Program 2009, 

UTM zone 10, NAD83, 1 meter resolution.

Figure 12. Spatial extent of the surfaces used to compute delta volume for the Little Nisqually River delta in Alder Lake, 

Washington, from (A) 1945 (pre-dam; contours at 5-foot intervals) and (B) 2011.
24 Changes in Sediment Volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011

watac12-0728_fig13

330 

335 

340 

345 

350 

355 

360 

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 

1945

2011

Elevation, in meters above North American Vertical Datum of 1988

Distance along the pre-dam Little Nisqually River centerline, in kilometers

Figure 13. Elevation profiles along the pre-dam Little Nisqually River centerline from 1945 (pre-dam) and 2011 surfaces of 

the Little Nisqually River delta in Alder Lake, Washington (shown in figures 12A–B).
Changes in Sediment Volume of the Little Nisqually River Delta in Alder Lake 25

watac12-0728_fig14

EXPLANATION

Elevation change 1945–2011,

in meters

17

0

-17

National Agricultural Imagery Program 2009, UTM zone 10, NAD83, 1 meter resolution.

Figure 14. Change in elevation of the Little Nisqually River delta in Alder Lake, Washington, 1945–2011.
26 Changes in Sediment Volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011

Sediment Deposition in Alder Lake 

1945–2011

Alder Lake allows the quantification of sediment 

deposited in the lake since 1945 from the Nisqually and Little 

Nisqually Rivers. The volumes of sediment measured in Alder 

Lake provide estimates of the sediment yield from subbasins 

with different land covers and geomorphic processes. The 

volume of sediment deposited in the main body of the lake, 

away from the deltas, between 1945 and 2011 was estimated 

from limited data collected in 2011 and combined with the 

delta volumes to provide an estimate of the total amount 

of sediment deposited in Alder Lake since 1945. The total 

amount of sediment deposited since 1945 has decreased the 

total capacity of Alder Lake.

The annual sediment yield of the Nisqually 

[1,100 ± 100 (m3/yr)/km2] and Little Nisqually River basins 

[70 ± 24 (m3/yr)/km2] provides an estimate of the yield of two 

basins with different land cover and geomorphic processes. 

These estimates suggest that a basin draining a glaciated 

stratovolcano yields approximately 15 times more sediment 

than a basin draining forested uplands in the Cascade Range. 

This finding is consistent with the finding of Czuba and others 

(2011) that the largest sediment loads in rivers draining to 

Puget Sound are carried by rivers with glaciated volcanoes in 

their headwaters.

Although this study primarily focused on sediment 

deposition in the deltas in Alder Lake, the limited data 

collected in 2011 in the main body of the lake provides an 

estimate of the volume of sediment deposition between 1945 

and 2011. Away from the deltas and within the coverage of the 

2011 bathymetric survey (fig. 5), the only area that showed 

a consistent change in elevation between 1945 and 2011 was 

along an approximately 40-m-wide corridor of the pre-dam 

Nisqually River that extended from the distal extent of the 

delta of the Nisqually River to Alder Dam. These data indicate 

that additional sediment has deposited in the main body of 

Alder Lake to an average thickness of approximately 7.5 m 

along a 40-m-wide corridor of the pre-dam Nisqually River, 

effectively filling the former river channel to an elevation 

similar to the surrounding valley (fig. 6; between 8 and 14 km 

along the historical channel of the Nisqually River). Between 

1945 and 2011, a change in volume and estimated uncertainty 

of 2,000,000 ± 600,000 m3 has occurred along the corridor 

of the pre-dam Nisqually River in the main body of Alder 

Lake. This change in volume corresponds to an annual rate 

and estimated uncertainty of 33,000 ± 9,000 m3/yr. The source 

of this sediment is likely from the Nisqually River that either 

bypasses the delta and settles out in the main body of the lake, 

from the front of the delta that travels in turbidity currents 

along the channel of the pre-dam Nisqually River, or from 

filling in while the lake was forming.

Estimates of the volume of sediment deposited in Alder 

Lake between 1945 and 2011 were focused in three areas: 

(1) the Nisqually River delta, (2) the main body of Alder 

Lake, along a 40-m-wide corridor of the pre-dam Nisqually 

River, and (3) the Little Nisqually River delta. In each of 

these areas the net deposition over this 66 year period was 

42,000,000 ± 4,000,000 m3, 2,000,000 ± 600,000 m3, and 

310,000 ± 110,000 m3, respectively (fig. 15). These volumes 

correspond to annual rates of accumulation of 630,000 ± 

60,000 m3/yr, 33,000 ± 9,000 m3/yr, and 4,700 ± 1,600 m3/yr, 

respectively. Given these rates, the Nisqually River accounts 

for approximately 99 percent of sediment deposited in Alder 

Lake (approximately 94 percent in the delta and approximately 

5 percent in the main body of the lake) at an annual rate 

of 663,000 ± 61,000 m3/yr, and the Little Nisqually River 

accounts for approximately 1 percent.

The maximum volumetric capacity of Alder Lake in 

1945 at the elevation of the dam spillway (elevation of 

approximately 367 m) was approximately 287 million cubic 

meters. Based on the cumulative net change in sediment 

volume in the Nisqually River delta in Alder Lake (table 1), 

the total capacity of Alder Lake since 1945 decreased by 

about 3 percent by 1956, 8 percent by 1985, and 15 percent 

by 2011. The total capacity of Alder Lake may decrease by 50 

percent by as early as 2175, based on the 1945-2011 sediment 

accumulation rate. However, this estimate assumes that the 

conditions during the last 66 years will be representative of 

future conditions. This may not be the case, given estimations 

of more intense precipitation (Salathé, 2006) and warmer 

temperatures in western Washington during the next century 

(Mote and Salathé, 2010) that likely would increase the 

production and delivery of sediment from Mount Rainier.

Table 3. Net change in sediment volume of the Little Nisqually River delta in Alder Lake, Washington, and estimated uncertainty, 

1945–2011.

[Abbreviations: m2, square meter; m3, cubic meter; m3/yr, cubic meter per year]

Period 

between 

surveys

Number of 

years 

between 

surveys

Surface area 

of volume 

computation 

(m2

)

 Total 

increase in 

volume

(m3

) 

 Total 

decrease in 

volume

(m3

) 

Net change in 

volume (total 

increase minus 

total decrease) 

(m3

) 

Estimated 

uncertainty of 

net change in 

volume

(m3

)

Rate of net 

change in 

volume

(m3

/yr) 

Estimated 

uncertainty of 

rate of net change 

in volume

(m3

/yr) 

1945–2011 66 130,000 470,000 160,000 310,000 110,000 4,700 1,600 
Summary 27

watac12-0728_fig15

42,000,000 m3

310,000 m3 2,000,000 cubic 

meters (m3

)

Little Nisqually 

River delta

Main body of 

Alder Lake

Nisqually 

River delta

Volume of sediment deposition in Alder Lake, 1945–2011

Alder Dam

Figure 15. Volume of sediment deposition between 1945 and 2011 at three areas of Alder Lake, Washington: the Nisqually 

River delta; the main body of Alder Lake, along a 40-meter wide corridor of the pre-dam Nisqually River; and the Little 

Nisqually River delta.

Future Investigations

The 2011 bathymetric survey primarily focused on the 

Nisqually and Little Nisqually River deltas in Alder Lake 

to quantify the delivery of sediment by these rivers. A more 

detailed understanding of sediment delivery to Alder Lake 

and the fate of different sediment sizes within the lake would 

be possible with existing technology. For example, detailed 

features of the lake bottom could be resolved at sub-meter 

resolution using a multibeam echosounder. Depending on 

the amount of mixing between different layers of lake-bed 

sediment, it may be possible to obtain seasonal or yearly 

sediment deposition rates by coring the lake deposits at a 

number of locations within the deltas and a few beyond the 

distal extent of the deltas. The evolution of the lake deposits 

also could be determined from a structural map of the deposits 

that could be obtained through sub-bottom profiling using 

geophysical tools. Using a combination of the above methods, 

collection of physical sediment samples, and images of the 

lake bed, it would be possible to quantify the transport and fate 

of specific sizes of sediment and the composition of sediment 

deposits in Alder Lake.

Summary

The Nisqually River drains the southwest slopes of 

Mount Rainier, a glaciated stratovolcano in the Cascade 

Range of western Washington. The Nisqually River was 

impounded behind Alder Dam in 1945, forming Alder Lake. 

In this study, four digital elevation surfaces were generated 

from historical contour maps from 1945, 1956, 1985, and 

from a 2011 bathymetric survey of Alder Lake using an 

acoustic Doppler current profiler. These surfaces were then 

used to compute changes in sediment volume in Alder Lake 

since 1945.

The presence of Alder Lake allows the quantification of 

sediment deposited in the lake since 1945 from the Nisqually 

and Little Nisqually Rivers. Estimates of the volume of 

sediment deposited in Alder Lake between 1945 and 2011 

were focused in three areas: (1) the Nisqually River delta, 

(2) the main body of Alder Lake, along a 40-m-wide corridor 

of the pre-dam Nisqually River, and (3) the Little Nisqually 

River delta. In each of these areas the net deposition over this 

66 year period was 42,000,000 ± 4,000,000 m3, 2,000,000 

± 600,000 m3, and 310,000 ± 110,000 m3, respectively. 
28 Changes in Sediment Volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011

These volumes correspond to annual rates of accumulation 

of 630,000 ± 60,000 m3/yr, 33,000 ± 9,000 m3/yr, and 4,700 

± 1,600 m3/yr, respectively. The annual sediment yield of the 

Nisqually [1,100 ± 100 (m3/yr)/km2] and Little Nisqually 

River basins [70 ± 24 (m3/yr)/km2] provides insight into the 

yield of two basins with different land cover and geomorphic 

processes. These estimates suggest that a basin draining a 

glaciated stratovolcano yields approximately 15 times more 

sediment than a basin draining forested uplands in the Cascade 

Range. Given the cumulative net change in sediment volume 

in the Nisqually River delta in Alder Lake, the total capacity 

of Alder Lake since 1945 decreased by about 3 percent by 

1956, 8 percent by 1985, and 15 percent by 2011. Given the 

rate of sediment deposition for 1945-2011 in Alder Lake, the 

total capacity of Alder Lake may decrease by 50 percent by 

2175, assuming the conditions during the last 66 years will be 

representative of future conditions.

Acknowledgments

We thank Tacoma Public Utilities, Tacoma Power for 

providing historical elevation-contour maps of the bed of 

Alder Lake and historical photographs, and James Foreman 

and Greg Justin, U.S. Geological Survey, for assistance with 

field surveys.

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30 Changes in Sediment Volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011

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2 Report Title

Czuba and others— Changes in Sediment Volume in Alder Lake, Nisqually River Basin, Washington, 1945–2011—Open-File Report 2012–1068