U.S. Fish and Wildlife Service

Quantifying Changes in 

Streambed Composition 

Following the Removal 

of the Elwha and Glines 

Canyon Dam on the 

Elwha River

May 2015 By R. J. Peters

U. S. Fish and Wildlife Service

G. R. Pess

 NOAA Fisheries

 M. L. McHenry

 Lower Elwha Klallam Tribe

P. D. Bakke

U. S. Fish and Wildlife Service

M. Elofson & E. Sampson

Lower Elwha Klallam Tribe
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QUANTIFYING STREAMBED COMPOSITION OF THE ELWHA RIVER, 2014

Prepared for:

Olympic National Park

Port Angeles, Washington

Prepared by:

Roger J. Peters1

, George R. Pess2, Mike L. McHenry3, Paul Bakke1, Mel Elofson3, and

Ernest “Sonny” Sampson3

1

Washington Fish and Wildlife Office, U.S. Fish and Wildlife Service, 510 Desmond 

Drive, SE, Suite 102, Lacey, WA 98503

2

Supervisory Research Fishery Biologist, Northwest Fisheries Science Center, NOAA 

Fisheries, Seattle, WA

3

Habitat Biologist, Fisheries Department, Lower Elwha Klallam Tribe, Port Angeles, WA

May 29, 2015
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Abstract

Approximately 7.1 million m3 of sediment was released during the first two years 

following dam removal (2011 and 2012) on the Elwha River, much of which has been 

transported and stored in river channels, floodplains, delta, and nearshore. Removal of Elwha 

and Glines Canyon Dams on the Elwha River was expected to eventually release a large 

proportion of the estimated 21 million m3 (± 3 million m3) of sediment stored behind the two 

dams. Nearly 50 percent of the estimated sediment release is classified as fine (silt and clay), 

which could have deleterious effects on downstream salmonid spawning habitats. The objectives 

of this project are to; 1) determine if fine sediment intrusion in spawning habitats of the 

mainstem and floodplain channels reaches levels likely to impact incubation survival, and 2) 

determine if the proportion of the substrate which is the appropriate size for spawning increases 

following dam removal. These objectives are being met through annual monitoring that was 

initiated prior to dam removal in 2010. Substrate was initially characterized at randomly selected 

riffle crests along the mainstem from just below Glines Canyon Dam to the river mouth. 

Floodplain substrates were characterized at upstream and downstream riffle crests in selected 

floodplain channels that coincided with other biological sampling (i.e., food web). Two 

(floodplain channels) or three (mainstem) bulk samples were collected behind a wood shield at 

each selected site to characterize sediment sizes. Water samples were collected before and after 

the bulk sampling to estimate the fine sediment content (i.e., <0.85 mm) that could not be 

captured in the bulk samples. These sediments affected mainstem and floodplain channels 

differently. Fine sediment concentrations at mainstem sites were less than six percent for the less 

than 0.85 mm fraction and less than 10 percent for the less than 3.35 mm fraction, except for one 

site which had 14.9 percent for the less than the 3.35 mm fraction. In contrast, fine sediment 

concentrations were generally greater than 90 percent in floodplain channels. Gravel made up a 

small percentage of most main channel and floodplain channel sites. Three of 22 main channels 

sites, all within 4 km of the former Elwha Dam site, were composed primarily of gravel. 

Mainstem sites consisted primarily of cobble. We recommend continuing the fine sediment 

sampling and initiation of streambed mobility monitoring in the mainstem.
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INTRODUCTION

Large dam removal (dams greater than 10 m in height) has recently become a viable 

option to achieve numerous objectives such as the decommissioning of unnecessary or unsafe 

structures (Doyle et al. 2008, Warrick et al. 2015) and the recovery of aquatic ecosystems (Heinz 

Center 2002, Stanley and Doyle 2003, Service 2011). One of the main issues surrounding large 

dam removal is the large volumes of sediment that can be released because many such dams 

have been in place for decades, accumulating sediment in the reservoir areas (Minear and 

Kondolf, 2009; Sawaske and Freyberg, 2012; Merritts et al. 2013). Regardless of how long it 

takes to remove dams, there is typically a massive increase in sediment supply that can lead to a 

3 to 20 times the average increase in the annual amount of transported sediment in a river 

(Warrick et al. 2015, East et al. 2015, Magirl et al. 2015, Major et al. 2012; Wilcox et al. 2014).

The composition of sediment being released during dam removal will vary, but in most cases 

will be substantially finer grained than most of the pre-dam- removal riverbed (Kibler et al. 

2011, Tullos et al. 2014, East et al. 2015). However, it is not clear how this change in sediment 

supply translates into changes to the aquatic ecosystem (Tullos et al, 2014).

Streambed and associated aquatic habitat responses to sediment pulses associated with 

dam removal can vary considerably in both temporal and spatial extent, with responses ranging 

from minimal and temporary, to large and persistent (Kibler et al. 2011, East et al. 2015, Tullos 

et al. 2014). Change in downstream aquatic habitats in the main stem, associated floodplains, and 

delta areas typically varies as a function of stream channel slope, stream power, sediment supply, 

and peak flow history (Warrick et al, 2015, East et al. 2015, Magirl et al. 2015, Stanley and 

Doyle, 2002, Ahearn and Dahlgren 2005, Doyle et al. 2005, Riggsbee et al. 2007, Major et al. 

2012, Merritts et al. 2013, Wilcox et al. 2014).

Downstream response of streambed and aquatic habitat has already been identified in 

larger dam removals. Immediately after the Condit Dam removal on the White Salmon River, 

Washington, bed material transport increased and subsequent deposition filled pools and channel 

margins, aggrading the channel between 1 to 2 meters over 2 kilometers downstream (Wilcox et 

al. 2014). However, the channel incised 5 days later because of the diminished sediment supply 

exiting the reservoir and small size of the sediment transported downstream, which inhibited 

streambed armoring (Wilcox et al. 2014). The Marmot Dam removal on the Sandy River,

Oregon resulted in immediate and persistent deposition immediately downstream of the dam four 

years after removal; however, there was a lack of deposition and change 7 to 12 km downstream 

(Cui et al. 2014). After the Milltown Dam removal in the Clark Fork River, Montana, deposition 

of fine sediment (<2mm) and intrusion of fines into the streambed pore space was minimal in 

reaches that were dominated by complex channel features, high sediment supply, and mobile 

streambeds (Evans and Wilcox 2013) These dam removal projects differ from Elwha dam 

removals in that they were instantaneous, while dam removals on the Elwha were staged. In 

addition, the amount and type of sediment differed from the Elwha River dams.

Newly deposited sediment from dam removal in the Elwha River, Washington resulted in 

a 2 to 10-fold change in bed elevation relative to the previous four years, significant channel 

1
changes (gravel bars, channel avulsion, floodplain channel aggradation), and a significant 

reduction in streambed particle size over the entire course of the river below the dams (East et al. 

2015). The geomorphic alterations and changing bed sediment grain size along the Elwha River 

has important ecological implications, affecting aquatic habitat structure, benthic fauna, and in 

particular salmonid fish spawning and rearing potential (East et al. 2015). 

Our study focuses on two questions related to these changes in the Elwha River. First,

how have sediment releases from dam removal and subsequent mainstem and floodplain channel 

deposition altered the quality of salmonid spawning habitat in the Elwha River? Second, how has 

fine sediment (< 2mm) released from dam removal impacted salmonid spawning gravels? This 

report summarizes data collected during 2014.

Study Area

The Elwha River is an 833 km2 watershed that begins at an elevation of 1,300 m in the 

Olympic Mountains of Washington State’s Olympic Peninsula. The Elwha flows north for 72 km 

emptying into the Strait of Juan de Fuca. The mountains are composed of metasedimentary

rocks, with frequent landslides supplying relative large volumes of sediment (Acker et al. 2008). 

The Elwha is situated in a maritime climate with dry summers and cool, wet winters. The 

average annual precipitation is 550 cm in the headwaters and 100 cm near the river mouth (Duda 

et al. 2008). Peak discharges are driven by both winter rain-on-snow events and late spring/early 

summer snow melt. Average annual discharge in the Elwha is 42 cms, the median (two-year)

peak discharge is 400 cms (Curran et al. 2009). 

Construction of two dams, Elwha Dam (Rkm 7.9) and Glines Canyon Dam (Rkm 21.6) 

was completed in the early 1900’s and blocked anadromous fish access to about 90% of the

watershed (Pess et al. 2008). The dams impounded approximately 21 million m3 (± 3 million m3)

of sediment (Warrick et al. 2015). The former Mills Reservoir, formed by Glines Canyon Dam 

had approximately 16 million m3 (± 1.2 million m3) of sediment of which less than half (44%)

was composed of silt and clay (<0.063 mm) and over half (56%) was coarse (Warrick et al. 

2015). The former Aldwell Reservoir, formed by Elwha dam, had ~5 million m3 (± 1.4 million 

m3) of sediment less than half of which (47%) was composed of silt and clay and over half (53%) 

was coarse (Warrick et al. 2015).

The Elwha River is composed of several alluvial valleys. The alluvial lower Elwha River, 

below former Elwha dam, has an average slope of 0.4%. The middle Elwha River, between the 

former Elwha and Glines Canyon dams, has a slope of 0.7-0.8% (East et al. 2015). Before dam 

removal, the streambed in the Lower and Middle Elwha was armored with predominately cobble 

sized material (64 - 256 mm; Childers et al. 2000, Pohl 2004; Draut et al. 2011).

The removal of both dams, which began in 2011, has resulted in an estimated release of

~7.1 million m3 (~9.2 Mt) of sediment being released during the first two years, 6 million m3

(~7.8 Mt) of which had been impounded behind Glines Canyon Dam (~37% of stored sediments) 

and 1.1 million m3 (~1.4 Mt) behind Elwha Dam (~23% of stored sediment) (Warrick et al. 

2015). The release represents a decade’s worth of sediment since normal release during the 

period would be approximately 147,000-500,000 m3 (217,000-513,000) metric tons (Curran et 

2
al., 2009; Czuba et al., 2011). Bedload transport during the second year after dam removal was 

about an order of magnitude greater than the first year (Magirl et al 2015). Sand and gravel 

began flowing over Glines Canyon Dam in October of 2012 (Randle et al. 2015). Large-scale 

river incision (~0.4 m) occurred at in the Lake Aldwell reservoir delta sediments behind former 

Elwha Dam by November 2012 (Randle et al. 2015). As of September 2013 there was an 

estimated 580,000 m3 of new sediment stored in the lower 18 kilometers of the Elwha River 

(East et al. 2015).

METHODS

Field Methods

The proportion of fine sediment and spawning gravel in the Elwha River below the 

former Glines Canyon Dam were quantified by sampling 20 of 46 (in 2010) selected riffle crest 

sites in the mainstem, and 18 floodplain channel sites in the Middle and Lower Elwha during 

August and September of 2014. The 20-mainstem sampling sites sampled were randomly 

selected from the 46-riffle crests available in 2010 from Glines Canyon Dam downstream to the 

river mouth. The sites were randomly selected to ensure that they would be distributed from 

Glines Canyon to the river mouth (Figure 1). Floodplain channels were generally sampled at 

their upstream and downstream ends and were selected to coincide with on-going biological 

sampling efforts (e.g. Morley et al. 2008). Three sub-samples were collected at each mainstem 

site and two sub-samples at narrower (<5 m wetted width) floodplain channels. When possible 

we sampled across the entire riffle crest, one in the center and two closer to each bank at 

mainstem locations and two closer to each bank in floodplain channels. Where this was not 

possible due to water depth and/or velocity, we sampled on one side or the other, sampling at the 

upstream, downstream and mid riffle crest portion of the site. Results from the subsamples were 

combined to calculate the metrics evaluated as described below.

A plywood shield modified from the design presented by Bunte and Abt (2001) was used 

to define a sampling area of approximately 0.10 m2. The shield was placed on the streambed with 

the open end downstream, to provide a protected area for sampling (Figure 2). We then collected 

a depth-integrated water sample from the sampling location to get a quantitative estimate of the 

proportion of suspended sediments in the water column prior to sampling. We measured five

water depths within the sampling area at equidistant points with a ruler to calculate an average 

water depth. Three to five of the largest surface layer rocks, which we thought represented the 

84th percentile streambed particle size (D84), were removed, measured and weighed on-site. 

Water depths in the voids left by the removed particles were measured to determine an average 

depth of excavation. The surface layer was defined as the material lying between the original 

channel bottom and the average depth of the voids left by the rocks removed (Figure 3). The 

surface layer was then uniformly excavated and placed into a canvas bag using gloved hands, 

cupped to avoid losing the fine sediment fraction. Each sample was marked with the date, study 

site, and within site, location (i.e. left bank, right bank, middle). Once the sample was completely

removed we collected a second depth-integrated water sample while the water was still turbid 

3
from the removal of the surface layer to assess the volume of fines dislodged into suspension

during sampling. 

We recorded the length, width, and original and final depths of the excavated area and 

used this to calculate the volume of water within the sampling area, which was used to calculate 

the weight of fines suspended in the water column (see below). In some cases, the site had large 

particles that were difficult to transport back to the lab (generally, 90 mm or larger). We 

measured the intermediate- or b-axis (Bunte and Abt 2001) and weight of each of these particles

in the field. Smaller rocks were weighed with a platform scale accurate to 0.001 kg, while larger 

rocks were placed in a sample bag and weighed using a spring scale accurate to 0.1 kg.

Bulk samples were taken to the lab, dried, and sieved following standard procedures 

(Bunte and Abt 2001). Sieves having openings of 75, 26.5, 13.2, 9.5, 3.35, 2, 0.85, 0.106 mm 

were used to characterize sediments. Particles in each sieve were weighed using a platform scale 

accurate to the nearest 0.001 kg. The concentration of suspended sediments (mg/l) in the water 

samples associated with each bulk sample collected was determined by lab filtration using a 

modified standard methods approach (Franson 1985). Ninety- mm-diameter fiberglass filters 

were washed (using 30 ml distilled water) and dried (103-105 oC for 4 hrs) two separate times to 

remove dust and loose fibers. Filters were weighed to 0.0001 mg at the beginning and end of 

each wash/dry cycle. Suspended sediment samples were shaken for 5 minutes using an electric 

sediment shaker fitted with a bottle holder attachment. Once shaken, 200 to 300 ml of the sample 

was quickly poured into a graduate cylinder and the volume noted. This sub-sample was slowly 

poured onto the glass filter to allow the water to be sucked through the filter by a vacuum pump. 

Once the entire subsample was processed, the graduated cylinder was washed three times using 

20 ml of distilled water, which was also poured onto the filter. The funnel supporting the glass 

filter was washed three consecutive times and allowed to drain completely. The filter was then 

removed and dried in an oven overnight at 103-105 oC. The filter was weighed after drying 

overnight and placed in a muffle furnace at 550 oC for 15 minutes at to burn off any organic 

matter. After cooling, the filter was weighed again. 

The suspended sediment concentration behind the shield after the sample was collected 

was calculated by dividing the difference in weight of the filter after ignition at high 

temperatures in the muffle furnace and the original, clean, washed and dried filter, by the volume 

of water filtered. The background concentrations obtained from the water sample collected 

before the substrate sample was collected was subtracted to calculate the actual concentration 

suspended during the sampling activity. The total weight of non-organic solids stirred up into the 

water column during sampling was computed using the volume of water within the shield as 

determined from the dimensions of the sampling area and water depth. The estimated fine 

sediment weight determined from this procedure was included in the <0.106 mm size fraction in 

the sample analysis.

Data were summarized by main channel and floodplain channels for percent less than 

0.85 mm, percent less than 3.35 mm, percent gravel (>3.35 mm, < 75 mm), and percent cobble

(>75 mm). Data were summarized as percent less than 0.85 mm because this substrate size has 

been shown to have the greatest impact on salmonid egg survival (Jensen et al. 2009). The 

percentage less than 3.35 mm size fraction was used since it was similar to the sizes reviewed by 

Jensen et al. (2009). Percent less than 0.85 mm and 3.35 mm were calculated based on the total 

4
weight of the sample less than 75 mm to reduce the potential bias caused by extremely large 

particles making up a large proportion of the sample.

RESULTS

The response of floodplain and mainstem channels to sediment releases from the removal 

of Elwha and Glines Canyon dams differed for the fine sediment and cobble size fractions, but 

not for gravel (Figure 4 and 5). Fine sediment less than 0.85 mm ranged from 0 to 5.8 percent in 

main channels and 1.9 to 100 percent in floodplain channels. None of the 22 mainstem sites had 

<0.85 mm concentrations greater than 10 percent, while 11 of 13 floodplain channel sites had 

concentrations greater than 10 percent. The concentrations of the less than 3.35 mm fraction 

ranged from 0 to 14.9 percent in the main channel sites, with one of the 22 sites having a 

concentration greater than 10 percent. In contrast, the 3.35 mm fraction ranged from 4.3 to 100 

percent, with 12 of the 13 sites having concentrations greater than 10%.

Percent gravel observed in main channel and floodplain channel sites were generally 

similar (Figures 4 and 5). Percent gravel varied from 0 to 88.9 percent in main channel sites, 

while those in floodplain channels varied from 0 to 82.9 percent. Only two of the 22 main 

channel sites and two of 13 floodplain channel sites had greater than 50 percent gravel. Thus, 

gravel made up a relatively small proportion of the overall substrate in both main and floodplain 

channel sites. 

In contrast to floodplain channel sites that were composed primarily of fine sediments, 

main channel sites were composed primarily of cobble (Figures 4 and 5). Percent cobble varied 

from 6.7 to 100 percent in the main channel sites and from 0 to 99.8 in the floodplain channel 

sites. Nineteen of the 22 mainstem sites had greater than 90 percent cobble. In contrast, only two 

of the 13-floodplain channel sites had more than 90 percent cobble.

DISCUSSION

The removal of Elwha and Glines Canyon Dams has resulted in the release of 

approximately 7.1 million m3 (10.5 million Mt) of sediment during the first two years of dam 

removal and much of this was fine sediment (Randle et al. 2015). This sediment has been 

transported throughout the Elwha River to the near-shore environment (Warrick et al. 2015) and 

therefore has the potential to impact salmonid spawning habitat (Peters et al. 2014). Mainstem 

and floodplain channel substrates have been influenced differently by this sediment release. 

Potential spawning habitat in floodplain channels has been almost completely covered with fine 

sediment, while mainstem spawning habitat has relatively low percentages of fine sediment 

present. However, only a few main channel sites are composed primarily of gravel, with the 

remaining main channels sites composed primarily of cobble. 

In general, fine sediment levels in floodplain channels exceeded 90%, while fine 

sediment levels in the main channel sites were on average less than 6%. This has several 

potential effects on salmonids of all life stages. First spawning salmonids will likely not utilize 

the floodplain habitats due the high proportion of finer sediment, while salmonids will likely 

utilize the mainstem sites due to the higher proportion of spawnable material. Salmonids that 

5
spawn in floodplain channels conversely also have a higher likelihood of deleterious effects at 

other life stages such as the egg to fry life stage due to elevated fine levels (Jensen et al. 2009). 

Mainstem sites will have a higher likelihood of being utilized at the spawning life stage and a 

lower likelihood of deleterious effects at the egg to fry life stage resulting from fine sediment 

impacts because of the lower levels of fine sediment (Jensen et al. 2009).

Although fine sediment concentrations were low in the mainstem, the results should be 

viewed cautiously. Our sampling method resulted in a relatively small sample being collected 

from the large riffle crests of the mainstem Elwha and represents conditions during a single point 

in time; summer low flow conditions. When combined, the three sub-samples from each riffle 

represented an average area of about 1.25 m2. Diplas and Fripp (1992) recommend that areal 

samples should be a minimum of 100 times the area of the largest particle, while Fripp and 

Diplas (1993) recommend 400 times the largest particle to obtain precise estimates of all particle 

sizes. Individual particles with surface areas of 0.15 m2 were common during sediment sampling 

in the Elwha River from 2010-2013 (Peters, unpublished data). Given this, sampling areas of 15 

m

2 to 60 m2 would be required to obtain an unbiased sample based on these areal methods. 

Sampling this area is logistically impractical and environmentally undesirable. Thus, the total 

area sampled during our sampling efforts was small relative to that required to obtain an 

unbiased sample. To counteract this potential bias, we calculated percent fine sediment (both 

<0.85 and 3.35 mm) based on the overall sample weight of particles less than 75 mm – the 

largest sieve used to characterize particle size in this study. This should have limited the potential 

bias associated with very large particles.

Although much less common due to the generally smaller substrate size in floodplain 

channels prior to dam removal (Peters, unpublished data), and the small size of substrates 

observed, data for the floodplain channels also have potential bias. We collected two subsamples in floodplain channels, so the area sampled was about 0.8 m2

. However, particles up to 

190 mm (~0.04m2) were present, requiring a sample area of approximately 4 m

2 to obtain 

unbiased estimates. This potential bias existed for only five of the 13 floodplain sites we 

sampled. However, with the exception of two of these sites, concentrations of the less than 0.85 

mm particles were greater than 10 percent, a level reported to result in increased incubation 

mortality (Jensen et al. 2009). Thus, even with this potential bias against fine sediment 

concentrations, the concentration of 0.85 mm particles was sufficient to potentially impact 

incubation survival of salmonids, assuming any salmonids spawned in these channels. In 

addition, our result are similar to those reported by Pess et al. (2015), who reported significant 

fine sediment (< 2 mm) accumulations in floodplain channels from the lower and middle Elwha 

River. Finally, by calculating percent fine sediment based on the total weight of sediment less 

than 75 mm we limited the potential for this bias. 

Data from 2014 suggest similar results to those observed from 2010-2013 (Peters, 

Unpublished data). It appears that fine sediments (i.e., <0.85 mm and <3.35 mm) have been 

declining since 2012 in main channel sites and that levels are still below levels reported to reduce 

incubation survival. In addition, the bed appears to be degrading back to its original elevation 

and re-exposing previous cobble substrates, an observation that is supported by East et al. 

(2015). The somewhat reduced deposition in floodplain channels between 2013 and 2014 (Pess 

et al. 2015) has resulted in increased substrate size in several of the floodplain sites we sampled. 

6
We recommend that yearly sampling continue as long as sediment transport substantially greater 

than normal is observed. Based on this, we plan to sample these sites again in 2015. We plan to 

sample at least three additional floodplain channels to overlap with new food web sampling 

planned for 2015 (Sarah Morley, NOAA, personal communication). In addition, main channel 

and floodplain channel pebble counts will be summarized in the future. Pebble counts were 

collected in floodplain channel during 2014, but could not be safely collected in the main 

channel due to higher flows. We expect to be able to collect main channel pebble counts in 2015 

and will summarize that data in future reports.

Increased salmonid redd scour is another mechanism that could lead to decreased 

incubation survival for salmonids. Redd scour is known to increase in channels where sediment 

loads increase drastically above background levels (Tripp and Poulin 1986; Frissell et al. 1996), 

which is occurring in the Elwha River (East et al. 2015). However, this variable is not being 

measured in the Elwha River. We recommend that scour monitoring be initiated in the mainstem 

if possible to assess the influence of increased sediment transport on salmonid spawning habitat 

below the former Glines Canyon Dam site. This area represents nearly 21 km of mainstem river 

and has been the primary spawning area for Chinook salmon in recent years (McHenry et al. 

2015). 

7
ACKNOWLEDGEMENTS

This report was improved by reviews from Denise Hawkins (FWS), Pat Crain (ONP) and 

Andy Ritchie (USGS/ONP). Kim Williams (LEKT), Sam Barcklow and Shane Taylor (both 

WCC) assisted with fieldwork. Alex Bell and Zach Moore (both USFWS) completed the 

suspended sediment processing. Carol Mitchell (USFWS) produced the report covers. Funding 

for this project was provided by Olympic National Park through the Lower Elwha Klallam Tribe. 

The findings and conclusions in this article are those of the author(s) and do not necessarily 

represent the views of the U.S. Fish and Wildlife Service or NOAA Fisheries.

8
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http://dx.doi.org/10.1002/2013JF003073.

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FIGURES

Figure 1. Elwha study area and sites sampled during late summer 2014

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Figure 2. Photograph showing the shield used to provide a calm area where fine sediment 

samples could be collected.

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Figure 3. The surface layer for sediment removal and analysis during this project was 

defined by removing three to five rocks representing the 84th percentile streambed particle size 

(marked with an ‘R’ in this figure. The surface layer extended to the average depth of the void 

left by removing these rocks (adapted from Bunte and Abt 2001). 

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Figure 4. Percent fine sediment less than 0.85 mm, 3.35 mm, gravel and cobble observed in bulk samples from mainstem 

sample sites. River kilometer (top row) and site names (bottom row) are both listed on the x-axis. Percent gravel and cobble is based 

on total sample weight; percent fine sediment is based on total weight less than 75 mm. No samples were collected if no site names are 

listed. This was done to show the relative position of the sampling sites. The location of the former Glines Canyon dam (Glines) and 

Elwha Dam (Elwha) are noted on the site name line. Note that the scales for the y-axis are different in the two charts.

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Figure 5. Percent fine sediment less than 0.85 mm, 3.35 mm, gravel and cobble observed in bulk samples from floodplain 

sample sites. Percent gravel and cobble is based on total sample weight; percent fine sediment is based on total weight less than 75 

mm. River kilometer (top row) and site names (bottom row) are both listed on the x-axis. No samples were collected if no site names 

are listed. This was done to show the relative position of the sampling sites. The location of the former Glines Canyon dam (Glines) 

and Elwha Dam (Elwha) are noted on the site name line.

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U.S. Fish & Wildlife Service

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