Figure 1. Benefits and threats of river sediment to ecosystems and society.

Drainage Basins

Deltas and Marshes

Source of contaminants

Enables marsh accretion, buffers 

sea-level rise

Excessive sediment buries habitat

Lack of sediment, inundation because 

of sea-level rise

Beaches

Forms beaches

Lack of sediment leads to erosion

Mountains

Source of sediment

Extreme events deliver too much 

sediment 

Provides nutrients and soil

Source of sediment

Forms berms (barriers) to floods

Buries vegetation

Offshore/Marine

Excessive sediment buries habitat, 

fragments ecosystems

Creates turbid water, loss of light for 

aquatic vegetation

Rivers

Flood Plains

Creates spawning habitat

Provides nutrients to benthic habitats

Changes in sediment size affect 

spawning habitat

Channel deposition increases flood risk

Benefit

Threat

EXPLANATION

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2011–3083

August 2011

Sediment Load from Major Rivers into Puget Sound 

and its Adjacent Waters

Jonathan A. Czuba, Christopher S. Magirl, Christiana R. Czuba, Eric E. Grossman, Christopher A. Curran, 

Andrew S. Gendaszek, and Richard S. Dinicola

Printed on recycled paper

Highlights

•	 Each year, an estimated load of 6.5 million tons of sediment is transported by rivers to Puget Sound and its adjacent

waters—enough to cover a football field to the height of six

Space Needles.

•	 This estimated load is highly uncertain because sediment

studies and available sediment-load data are sparse and

historically limited to specific rivers, short time frames, and a

narrow range of hydrologic conditions.

•	 The largest sediment loads are carried by rivers with glaciated volcanoes in their headwaters.

•	 Research suggests 70 percent of the sediment load delivered

to Puget Sound is from rivers and 30 percent is from

shoreline erosion, but the magnitude of specific contributions

is highly uncertain.

•	 Most of a river’s sediment load

occurs during floods.

Why is River Sediment 

Important to Puget Sound?

Rivers carry freshwater into

Puget Sound as well as sediment

and other materials, such as wood,

important to estuarine and nearshore

habitat, aquatic ecology, and water

quality. Historical channelization

of rivers and deltas has altered

sediment-transport pathways

by restricting sediment delivery

to flood plains and redirecting

sediment offshore. Paradoxically,

sediment is both a benefit and a

threat to ecosystems and society

(fig. 1). Sufficient, but not excessive,

amounts of sediment are important

resources for beaches, deltas, and

other coastal habitats that sustain

ecosystems, vegetation, and animals

that people depend on. Excessive

amounts of sediment can place

stress on a variety of species and

habitats. For example, eelgrass

meadows, which provide important

nearshore marine habitat for fish, shellfish, and invertebrates, as

well as food for waterfowl and detritus feeders, can be buried

or fragmented by increased sediment delivery associated with

river-delta channelization, like those offshore of the Skagit

River (Grossman and others, 2011). In contrast, when sediment

delivery is depleted, nearshore critical habitat and beaches can

be eroded by natural coastal processes and lost (Warrick and

others, 2009). Changes in sediment grain-size composition

also affect ecosystems. For example, many shellfish beds and

forage-fish spawning beaches depend on a specific sediment

grain-size composition that is linked to land-use activities and

hydrologic conditions that release and carry sediment to Puget

Sound (Gelfenbaum and others, 2009). Water quality, nearshore

and offshore habitats, and aquatic-ecosystem health are affected

by contaminants and nutrients that preferentially adsorb to fine

sediments and are delivered to Puget Sound. Once present, these

contaminants can bioaccumulate in fish and shellfish making

these seafoods toxic for human consumption.
What is Sediment Load?

A river’s sediment load is computed from water discharge

and sediment-concentration data, and represents the flux of

sediment transported by the river; it is usually expressed as

mass per time, for example, tons per year (tons/yr). Most of a

river’s sediment load occurs during floods. Sediment is either

transported within the flow as suspended load or transported

along the riverbed by rolling, sliding, or saltating (hopping)

as bedload. A suspended-sediment sampler, consisting of a

nozzle connected to a container that samples a flowing river,

is used to measure the concentration of sediment in the water

column. Similarly, a bedload sampler placed on the bottom of

a flowing river collects the coarse-grained sediment moving

along the riverbed. The sum of the measured suspended load

and bedload is the total load. Typically, bedload represents

about 5–20 percent of the total load carried by a river. Most

reported sediment loads for Puget Sound rivers only include the

suspended load and thus reflect a minimum estimate of the total

sediment load. 

Figure 2. Mean annual discharge of major rivers draining into Puget Sound. The 

size of the arrow is scaled to the mean annual discharge. Data from Williams (1981). 

124° 123° 122° 121°

49°

48°

47°

0 25 50 75 MILES

0 25 50 75 KILOMETERS

Strait of Georgia

Seattle

Tacoma

Bremerton

Olympia

Everett

Mt Vernon

Bellingham

Puget Sound

Mt. Baker

Glacier Peak

Mt. Rainier

Olympic Mountains

Cascade Range

Puget Lowland

British Columbia CANADA

Washington UNITED STATES

Strait of Georgia

Seattle

Tacoma

Bremerton

Olympia

Everett

Mt Vernon

Bellingham

British Columbia CANADA

Washington UNITED STATES

Puget Sound

Mt. Baker

Glacier Peak

Mt. Rainier

Olympic Mountains

Cascade Range

Puget Lowland

Salish Sea

Pacific

Ocean

Strait of Juan de Fuca Dungeness

River

Elwha

River

Hamma Hamma River

Duckabush River

Dosewallips River

Big Quilcene River

Deschutes River

Nooksack River

Samish River

Skagit River

Stillaguamish River

Snohomish River

Lake Washington

Ship Canal

Duwamish River

Puyallup River

Nisqually River

Deschutes River

All other

tributaries

Skokomish River

Hamma Hamma River

Duckabush River

Dosewallips River

Big Quilcene River

Dungeness

River

Elwha

River

Fraser River

3,200

3,600

190

2,700

1,400

400

2,100

570

670

180

460 2,000

500

1,300 1,400

3,130

3,200

18,000

10,000

3,600

190

2,700

1,400

400

2,100

570

670

180

460 2,000

500

1,300 1,400

3,100

EXPLANATION

Drainage-basin boundary

Subbasin boundary

Mean annual discharge,

 in cubic feet per second

190

Factors Affecting Sediment Delivery to Puget Sound

A number of geologic and geomorphic factors affect

sediment supply to Puget Sound. Watershed geology, slope, land

use, precipitation, mountain uplift rates, volcanism, glaciers,

lahars, and weathering all affect the sediment load carried by the

region’s rivers. Rivers draining glaciated terrain are notoriously

laden with large amounts of sediment. Land use, including

agricultural, forested, and urban areas, affects the sediment load,

as well as nutrients and toxics, carried by rivers. Dams within a

basin store sediment that ultimately reduces sediment delivery

to Puget Sound and its adjacent waters. However, removal

of large dams, like in the planned Elwha River dam-removal

project beginning in 2011, can result in large, short-term

releases of sediment downstream and a newly adjusted annual

sediment load in the long term.

Climate change and shifting land use threaten to alter

sediment loads in rivers. An increased sediment load may be

important in maintaining estuarine and nearshore habitats as sea

level rises in response to climate change by enabling marshes

and coastlines to accumulate sediment and build topography.

Climate pattern shifts also will alter the timing and magnitude

of floods that carry sediment to Puget Sound.

Sediment Transported by Rivers into Puget Sound

Each year, about 12 trillion gallons (total mean annual

discharge of about 52,000 cubic feet per second [ft3/s]) of

freshwater flow into Puget Sound and its adjacent waters from

the region’s rivers and streams (fig. 2, table 1). These rivers,

in turn, carry an estimated 6.5 million tons (1 ton

= 2,000 pounds) of sediment into Puget Sound and

its adjacent waters (fig. 3, table 1). This sediment

is derived from the weathering and erosion of

bedrock and soil in basins where runoff from rain

and snow carries particles into main-stem rivers

that transport the material downstream to Puget

Sound. The quantity and size of sediment moved

by rivers depends on discharge and river slope, and

although even small streams carry silts and clays,

only the steepest rivers transport gravels, cobbles,

and boulders. Mountainous rivers readily transport

gravels and cobbles, and deposit this sediment

directly into Puget Sound where these rivers drain

directly into the Sound, such as the Elwha and

Dungeness Rivers. As mountainous rivers enter

Puget Lowland, the coarse particles (gravel, cobbles,

and boulders) tend to deposit on riverbeds, such as in

the Puyallup River. This coarse-sediment deposition

reduces the river’s capacity to convey a flood

without overtopping its banks and increases the flood

hazard, necessitating river management to reduce

flood risk to nearby people and infrastructure (Czuba

and others, 2010). Fine particles (clay, silt, and

sand), however, continue to be carried downstream,

out of the Puget Lowland, and into Puget Sound.

Sediment delivered into Puget Sound is redistributed

by complex interactions of tidal and wind-driven

currents throughout the bays and inlets.

Available Sediment-Load Studies

Only a handful of water-quality and sediment-transport

studies have been conducted to quantify sediment loading

from rivers into Puget Sound, and the majority of these studies

were limited to specific rivers using sediment data collected

during only a few years in the 1960s and 1970s (table 1). In

some cases, the sediment-load estimates were based on limited

measurements adding significant uncertainty because sediment

load in a river is variable, changing by as much as an order

of magnitude between years or between storms (for example,

Nelson, 1979). In addition, the measurements may not have
Modern Sediment-Surrogate Monitoring 

Technologies

Recent advances in hydroacoustic and optical

technologies have fostered renewed interest in monitoring and

tracking sediment loads in rivers (Gray and Gartner, 2009).

Coupling these technologies with strategic sediment sampling

enables the near-continuous measurement and reporting of

sediment load in rivers at a fraction of the cost of traditional

sediment-measurement techniques applied during the 20th

century. In addition to reporting the sediment load in a given

river, these instruments also have the capability to estimate

particle-size distribution of sediment delivered by rivers.

Figure 3. Annual sediment load of major rivers draining into Puget Sound 

measured at or near the river mouth. The size of the arrow is scaled to the annual 

sediment load. Data sources listed in table 1.

124° 121°

49°

47°

0 25 50 75 MILES

0 25 50 75 KILOMETERS

Strait of Georgia

Seattle

Tacoma

Bremerton

Olympia

Everett

Mt Vernon

Bellingham

Puget Sound

Mt. Baker

Glacier Peak

Mt. Rainier

Olympic Mountains

Cascade Range

Puget Lowland

British Columbia CANADA

Washington UNITED STATES

Strait of Georgia

Seattle

Tacoma

Bremerton

Olympia

Everett

Mt Vernon

Bellingham

British Columbia CANADA

Washington UNITED STATES

Puget Sound

Mt. Baker

Glacier Peak

Mt. Rainier

Olympic Mountains

Cascade Range

Puget Lowland

Salish Sea

Pacific

Ocean

Strait of Juan de Fuca

Dungeness

River

Elwha

River

Hamma Hamma River

Duckabush River

Dosewallips River

Big Quilcene River

Deschutes River

Nooksack River

Samish River

Skagit River

Stillaguamish River

Snohomish River

Lake Washington

Ship Canal

Duwamish River

Puyallup River

Nisqually River

Deschutes River

All other

tributaries

Skokomish River

Hamma Hamma River

Duckabush River

Dosewallips River

Big Quilcene River

Dungeness

River

Elwha

River

Fraser River

? ?

12

11

30

6

120

35

1,400

2,800

18

3.3

120

?

980

490

?

35

410

12

11

30

6

??

210

EXPLANATION

Drainage-basin boundary

Subbasin boundary

Annual sediment load, 

 in thousands of tons

Published load 

 estimates could not be 

 found or do not exist

3.3

123° 122°

48°

?

included an accurate representation of floods when the

greatest sediment concentrations occur, which would

lead to underestimates of the annual sediment load.

The sediment-load estimates (table 1) were obtained

from readily available studies by federal and state

agencies, consultants, and academic researchers. Only

those studies where total- or suspended-load estimates

were determined near the mouth of the respective

river as it entered Puget Sound were included in

table 1 and figure 3. These sediment-load estimates

were converted into tons per year as necessary

and were averaged together when multiple studies

provided different estimates. The most reliable

sediment-load estimates included sediment data

spanning many years (for example, the load estimates

from the Skagit and Deschutes Rivers; table 1).

The Deschutes River sediment-load estimate is

unique because it is based on repeat surveys of the

delta volume in addition to direct measurements of

sediment load in the river. All other sediment-load

estimates from rivers draining to Puget Sound were of

suspended load only and do not account for bedload.

The estimates based on data collected for a few

years may or may not represent the river’s long-term

average sediment load.

Sediment-Load Estimates for Puget Sound 

Rivers

The largest sediment loads are not necessarily

those carried by the rivers having the largest mean

annual discharge. Instead, the three rivers carrying

the largest sediment loads, the Skagit, Nooksack, and Puyallup

Rivers, all contain glaciated volcanoes in their headwaters

(fig. 3). The Skagit River drains both Mount Baker and Glacier

Peak, although much of the sediment load derived from Mount

Baker is retained in manmade reservoirs. The Nooksack River

drains the northern sections of Mount Baker and the Puyallup

River drains the northern and western sections of Mount

Rainier.

The other major source of sediment to Puget Sound is from

shoreline erosion, which contributes sediment of all grain sizes,

including clay, silt, sand, gravel, cobbles, and boulders, to areas

away from river deltas. Dexter and others (1981) estimated

shoreline erosion contributes about 2.6 million tons of sediment

per year to Puget Sound; however, the uncertainty in this

estimate is large. The combined sediment load from rivers and

shoreline erosion is about 9.1 million tons per year, about

70 percent is from rivers and 30 percent is from shoreline

erosion.

While not draining directly into Puget Sound, the Fraser

River in British Columbia drains into the Strait of Georgia and

is a prodigious contributor of fresh water and sediment into the

greater Salish Sea (table 1). The Fraser River carries a total load

of about 20 million tons of sediment per year into the Strait of

Georgia (Church and Krishnappan, 1998).

Opportunities for Monitoring and Basic Research

The sediment-load estimates for rivers draining to Puget

Sound may be inaccurate by an order of magnitude (table 1)

because of the sparse availability of reliable sediment data

and the variable nature of sediment transport. The problem is

further exacerbated by the out-of-date status of many data sets

as significant changes in land use, urbanization, and climate

in the 21st century likely have modified sediment sources and

transport since the 1970s, when most of the region’s sediment

data were collected. Recent strategic sampling of sediment

during the entire range of low- and high-flow conditions, as well

as different seasons, has greatly improved the ability to quantify

and reduce uncertainty of sediment-delivery estimates by the

Skagit River (Curran and others, 2011). Given the important

affect of sediment, as a benefit and a threat, to Puget Sound

ecosystems, detailed monitoring and analytical understanding of

sediment load, size, quality, and movement are needed to best

understand, protect, and restore important ecosystem processes

and functions in Puget Sound.
For more information contact:

Director, Washington Water Science Center

U.S. Geological Survey, 934 Broadway, Suite 300

Tacoma, Washington 98402

http://wa.water.usgs.gov

References Cited

Capitol Lake Adaptive Management Plan 1999 to 2001, 1999:

Thurston Regional Planning Council, 103 p.

Church, M., and Krishnappan, B.G., 1998, Sediment sources,

transport processes, and modeling approaches for the Fraser

River in C. Gray and T. Tuominen, eds., Health of the Fraser

River Aquatic Ecosystem: Environment Canada, DOE FRAP

1998–11, 18 p.

Curran, C.A., Grossman, E.E., Mastin, M.C., and Huffman, R.L.,

(in press), Sediment load and distribution in the lower Skagit

River, Skagit County, Washington, USA. For submission to

Continental Shelf Research.

Czuba, J.A., Czuba, C.R., Magirl, C.S., and Voss, F.D., 2010,

Channel-conveyance capacity, channel change, and sediment

transport in the lower Puyallup, White, and Carbon Rivers,

western Washington: U.S. Geological Survey Scientific

Investigations Report 2010–5240, 104 p.

Dexter, R.N., Anderson, D.E., Quinlan, E.A., Goldstein, L.S.,

Strickland, R.M., Pavlou, S.P., Clayton, J.R., Kocan, R.M.,

and Landolt, M., 1981, A summary of knowledge of Puget

Sound related to chemical contaminants: National Oceanic and

Atmospheric Administration Technical Memorandum OMPA-13,

435 p.

Downing, J., 1983, The coast of Puget Sound: its processes and

development. University of Washington Press, Seattle, Wash.,

126 p.

Embrey, S.S., and Frans, L.M., 2003, Surface-water quality of

the Skokomish, Nooksack, and Green-Duwamish Rivers and

Thornton Creek, Puget Sound basin, Washington, 1995–98:

U.S. Geological Survey Water-Resources Investigations Report

02–4190, 192 p.

Gelfenbaum, G., Fuentes, T.L., Duda, J.J., Grossman, E.E.,

and Takesue, R.K., eds., 2009, Extended abstracts from the

Coastal Habitats in Puget Sound (CHIPS) 2006 Workshop,

Port Townsend, Washington, November 14–16, 2006: U.S.

Geological Survey Open-File Report 2009–1218, 136 p.

Gray, J.R., and Gartner, J.W., 2009, Technological advances in

suspended-sediment surrogate monitoring: Water Resources

Research, v. 45, 20 p.

Grossman, E.E., George, D.A., and Lam, A., 2011, Shallow

stratigraphy of the Skagit River Delta, Washington, USA derived

from sediment cores: U.S. Geological Survey Open-File Report

2011–1194.

Nelson, L.M., 1971, Sediment transport by streams in the

Snohomish River basins, Washington: October 1967–June 1969:

U.S. Geological Survey Open-File Report 71–215, 96 p.

Nelson, L.M., 1974, Sediment transport by streams in the

Deschutes and Nisqually River basins, Washington: November

1971–June 1973: U.S. Geological Survey Open-File Report

74–1078, 33 p.

Nelson, L.M., 1979, Sediment transport by the White River into

Mud Mountain Reservoir, Washington, June 1974–June 1976:

USGS Water-Resources Investigations Report 78–133, 26 p.

Paulson, A.J., Feely, R.A., Curl Jr., H.C., Crecelius, E.A., and

Romberg, G.P., 1988, Sources and sinks of Pb, Cu, Zn, and

Mn in the main basin of Puget Sound: National Oceanic and

Atmospheric Administration Technical Memorandum ERL

PMEL-77, 26 p.

Santos, J.F., and Stoner, J.D., 1972, Physical, chemical, and

biological aspects of the Duwamish River Estuary King County,

Washington 1963–67: U.S. Geological Survey Water-Supply

Paper 1873–C., 74 p.

Warrick, J.A., George, D.A., Gelfenbaum, G., Ruggiero, P.,

Kaminsky, G.M., and Beirne, M., 2009, Beach morphology and

change along the mixed grain-size delta of the dammed Elwha

River, Washington: Geomorphology, v. 111, p. 136–148.

Williams, J.R., 1981, Principal surface-water inflow to Puget

Sound, Washington: U.S. Geological Survey Water-Resources

Investigations Report 84–4090, 6 sheets.

Wise, D.R., Rinella III, F.A., Rinella, J.F., Fuhrer, G.J., Embrey,

S.S., Clark, G.E., Schwarz, G.E., and Sobieszczyk, S., 2007,

Nutrient and suspended-sediment transport and trends in the

Columbia River and Puget Sound basins, 1993–2003: U.S.

Geological Survey Scientific Investigations Report 2007–5186,

117 p.

Table 1. Puget Sound sediment-load data.

[Mean annual discharge data from Williams (1981). mi2, square mile; ft3/s, cubic feet per

second; tons/yr, tons per year; Annual sediment load: n.e., published load estimates could

not be found or do not exist; --, no data]

Basin (area mi2)

Mean annual 

discharge 

(ft3/s)

Annual sediment load 

(tons/yr)

Time period 

when sediment-load 

data were 

collected

Skagit (3,200)1 18,000 2,800,000 1974–93,

2006–09

Snohomish (1,800)2,3,4 10,000 490,000 1964–66,

1967–68, 2000

Puyallup (980)2,4 3,600 980,000 1964–66, 2000

Nooksack (840)2,4,5 3,200 1,400,000 1964–66,

1996–98, 2000

Nisqually (770)2,6 2,100 120,000 1964–66,

1971–72

Stillaguamish (700)2 2,700 18,000 1964–66

Lake Washington Ship Canal

(600)7

1,400 3,300 1981–82

Duwamish (500)4,5,8 1,400 210,000 1964–66,

1996–98, 2000

Elwha (320) 2,000 n.e. --

Skokomish (250)2,4,5 1,300 410,000 1964–66,

1996–98, 2000

Dungeness (200) 460 n.e.

Deschutes (170)9 400 35,000 1952–98

Samish (120) 190 n.e. --

Dosewallips (120)2 670 30,000 1964–66

Hamma Hamma (80)2 500 12,000 1964–66

Duckabush (80)2,4 570 11,000 1964–66, 2000

Big Quilcene (70)2 180 6,000 1964–66

All other tributaries (2,300) 3,100 n.e. --

Total Puget Sound (13,000) 52,000 6,500,000 --

Fraser (85,000)10 130,000 20,000,000 1965–96

1

Curran and others, 2011. 6Nelson, 1974.

2

Downing, 1983. 7Paulson and others, 1988.

3

Nelson, 1971. 8Santos and Stoner, 1972.

4

Wise and others, 2007. 9Capitol Lake Adaptive Management Plan, 1999.

5

Embrey and Frans, 2003. 10Church and Krishnappan, 1998.