U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2015–1054

Evaluation of Two Juvenile Salmon Collection Devices at 

Cowlitz Falls Dam, Washington, 2014
Cover: Photographs showing Upper Riffe Lake Collector in the tailrace of Cowlitz Falls Dam, and the weir box in the forebay of Cowlitz Falls Dam (inset). 

Main photograph was taken by Tobias Kock, U.S. Geological Survey, August 6, 2014; inset photograph was taken by John Serl, Washington Department 

of Fish and Wildlife, May 15, 2013.
Evaluation of Two Juvenile Salmon Collection Devices at 

Cowlitz Falls Dam, Washington, 2014

By Tobias J. Kock, Theresa L. Liedtke, Brian K. Ekstrom, and William R. Hurst

Open-File Report 2015–1054

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

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

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Suggested citation:

Kock, T.J., Liedtke, T.L., Ekstrom, B.K., and Hurst W.R., 2015, Evaluation of two juvenile salmon collection devices

at Cowlitz Falls Dam, Washington, 2014: U.S. Geological Survey Open-File Report 2015-1054, 30 p., 

http://dx.doi.org/10.3133/ofr20151054. 

ISSN 2331-1258 (online)
iii

Contents

Executive Summary.................................................................................................................................................... 1

Introduction................................................................................................................................................................. 3

Methods...................................................................................................................................................................... 9

Fish Collection, Tagging, and Release.................................................................................................................... 9

Configuration of the Fish Collection System at Cowlitz Falls Dam........................................................................ 10

Monitoring Array.................................................................................................................................................... 10

Data Analysis ........................................................................................................................................................ 14

Assessment of Differences between Release Sites .......................................................................................... 14

Behavior Patterns, Performance Metrics, and Dam Passage............................................................................ 15

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

Assessment of Differences between Release Sites .......................................................................................... 17

Behavior Patterns, Performance Metrics, and Dam Passage............................................................................ 21

Discussion ................................................................................................................................................................ 26

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

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

Figures

Figure 1. Schematic of the study area showing locations of fixed monitoring sites (open circles), 

release sites (filled circles), and the Upper Riffe Lake Collector (star), Washington.................................................. 4

Figure 2. Schematic of Cowlitz Falls Dam showing locations of the debris barrier and spillbays 2 and 3, 

where juvenile salmon collection occurred through flume 1, flume 2, the weir box, and flume 4 ............................... 5

Figure 3. Schematic and photographs of the Upper Riffe Lake Collector deployed in the tailrace of 

Cowlitz Falls Dam during 2014 .................................................................................................................................. 8

Figure 4. Schematic of the side view of spillbay 3 at Cowlitz Falls Dam showing the path of movement that 

juvenile Chinook salmon would have to take to be collected in flume 4 during July–August 2014 .......................... 11

Figure 5. Schematic of Cowlitz Falls Dam and location of general detection zones for an underwater antenna 

detection array that monitored radio-tagged juvenile Chinook salmon during July–August 2014 ............................ 13

Figure 6. Boxplots showing juvenile Chinook salmon fork lengths in millimeters (mm) (top panel) and 

weights in grams (g) (bottom panel) for groups of fish that were tagged and released at the Cowlitz 

Falls Day Use Park and Lewis County Public Utility District (PUD) Boat Launch .................................................... 18

Figure 7. Graph showing proportion of tagged juvenile Chinook salmon that moved downstream from

the Cowlitz Falls Day Use Park and Lewis County Public Utility District (PUD) Boat Launch release sites in 

Lake Scanewa and entered the forebay of Cowlitz Falls Dam over time (in days [d]).............................................. 19

Figure 8. Graph showing residence time (in days [d]) of tagged juvenile Chinook salmon in the forebay of 

Cowlitz Falls Dam during July–August 2014 for groups of fish released at the Cowlitz Falls Day Use Park 

and the Lewis County Public Utility District (PUD) Boat Launch .............................................................................. 20

Figure 9. Graph showing percentage of tagged Chinook salmon that made trips between the collection 

entrances at Cowlitz Falls Dam during 2014............................................................................................................ 24

Figure 10. Graph showing percentage of tagged Chinook salmon that were collected (filled bars) or passed 

through turbines (open bars) by hour, at Cowlitz Falls Dam during 2014 ................................................................ 25
iv

Tables

Table 1. Summary of release dates, number of fish released, and average sizes of juvenile Chinook salmon 

released during a radiotelemetry evaluation at Cowlitz Falls Dam, Washington, 2014............................................ 10

Table 2. Descriptions of performance metrics used to evaluate the collection flumes and weir box 

during 2014.............................................................................................................................................................. 16

Table 3. Descriptions of performance metrics used to evaluate the Upper Riffe Lake Collector (URLC) 

during 2014.............................................................................................................................................................. 16

Table 4. Percentage of tagged juvenile Chinook salmon that were first detected in arrival zones that were 

horizontally and vertically stratified across the face of Cowlitz Falls Dam during 2014............................................ 20

Table 5. Summary of performance metrics for flume 1/flume 2 and the weir box at Cowlitz Falls Dam 

during 2014.............................................................................................................................................................. 22

Table 6. Percentage of tagged juvenile Chinook salmon that were first detected in arrival zones that were 

horizontally and vertically stratified across the face of Cowlitz Falls Dam during 2014............................................ 22

Table 7. Summary of collection entrances where tagged fish were initially detected and total number of 

collection entrances where tagged fish were detected during the study .................................................................. 23

Table 8. Summary of fates of tagged juvenile Chinook salmon released upstream of Cowlitz Falls Dam 

during 2014.............................................................................................................................................................. 23

Conversion Factors

SI to Inch/Pound

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

Flow rate

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

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

Inch-pound to SI

Multiply By To obtain

Flow rate

cubic foot per second (ft3/s) 3.281 foot per second (ft/s) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as °F = (1.8 × °C) + 32.
1 

Evaluation of Two Juvenile Salmon Collection Devices at 

Cowlitz Falls Dam, Washington, 2014

By Tobias J. Kock, Theresa L. Liedtke, Brian K. Ekstrom, and William R. Hurst

Executive Summary

Collection of juvenile salmon at Cowlitz Falls Dam is a critical part of the effort to restore 

salmon in the upper Cowlitz River, Washington. Many of the fish that are not collected pass 

downstream and enter Riffe Lake, become landlocked, and are lost to the anadromous population. In 

addition to this loss, the juvenile fish collection system at Cowlitz Falls Dam, which originally consisted 

of four collection flumes, has failed to achieve annual collection goals since it began operating in 1996. 

In the years since, the collection flumes have been modified and prototype collection devices have been 

developed and tested, but these efforts have not substantially increased juvenile fish collection. Studies 

have shown that juvenile steelhead (Oncorhynchus mykiss), coho salmon (Oncorhynchus kisutch), and 

Chinook salmon (Oncorhynchus tshawytscha) tend to come close to the entrances of the collection 

system, but many of these fish fail to enter and eventually pass the dam through turbines or spillways. 

Tacoma Power developed a prototype weir box in 2009 to increase capture rates of juvenile 

salmon at the collection entrances. The device was evaluated with radio-tagged coho salmon (318 fish) 

and Chinook salmon (317 fish), and was found to have a high retention rate; 93 percent of the coho 

salmon, and 91 percent of the Chinook salmon that entered the device were retained and collected.

However, because of safety concerns at the dam, the weir box could not be deployed near a spillway 

gate where the prototype was tested, so the device was altered and re-deployed at a different location

where it was evaluated during 2013. During that year, discovery efficiency (number of fish detected at 

the entrance divided by the number of fish detected in the forebay) was 98 percent for tagged steelhead 

and 83 percent for tagged coho salmon. However, none of the steelhead and only 5 percent of the coho 

salmon entered and were collected through the weir box. These results indicated that the device was not 

a promising collection alternative during spring months when steelhead and coho salmon are passing the 

dam. However, collection conditions change during summer months when juvenile Chinook salmon are 

passing, so the device also was evaluated during summer 2014. 

In an attempt to improve overall collection efficiency, Tacoma Power developed and tested a 

new device in 2014, called the Upper Riffe Lake Collector (URLC). The URLC was a floating device 

designed to collect fish as they moved downstream after passing through turbines at Cowlitz Falls Dam. 

The design of the URLC included a pontoon barge that supported a large net structure designed to 

funnel fish into a live box where they could be removed and transported downstream of dams on the 

Cowlitz River.

During summer 2014, we evaluated the weir box and the URLC to determine the efficacy of 

using these devices to collect juvenile Chinook salmon at Cowlitz Falls Dam. The weir box was 

operated as one of four possible collection entrances at the face of the dam because flumes 1, 2, and 4 

also were operated during the study. To evaluate the effectiveness of the structures, we surgically 

implanted radio transmitters into 87 juvenile Chinook salmon and released them 3.9 river kilometers 
2 

(rkm) upstream of Cowlitz Falls Dam. Additionally, 334 juvenile Chinook salmon were tagged and 

released 1.2 rkm upstream of Cowlitz Falls Dam as part of another study, and these fish also were 

monitored for this evaluation. This resulted in a total sample size of 421 fish for the study. We 

compared fish size, reservoir travel time, forebay residence time, and the horizontal and vertical 

distribution of tagged fish when they arrived at the dam to determine if there were significant release 

site effects. We determined that fish size and reservoir travel times were different between groups, but 

all other factors were similar, so data were pooled for most of the analyses.

A total of 363 tagged Chinook salmon arrived in the forebay of Cowlitz Falls Dam during the 

study period; 86 percent (311 fish) of the fish were detected on underwater antennas located along the 

face of the dam. Fish were horizontally distributed across the dam face when they arrived, but the 

lowest percentage of fish was first detected in the shallow zones of spillbays 2 and 3, where the 

collection entrances were located. The vertical distribution of tagged fish was skewed toward deeper 

zones (3.6 meters or deeper). Eighty percent of the tagged fish were first detected on zones located 

deeper than the entrances to the collection structures. This pattern of deep arrival appeared to affect 

collection and passage at the dam. The combined discovery efficiency of all surface collection entrances 

was only 43 percent, and the number of fish that passed the dam through turbines (230 fish) was nearly 

five times greater than the number of fish that were collected (50 fish). Collection peaked during 

morning hours and turbine passage peaked during nighttime hours. 

The weir box was the most successful collection route for juvenile Chinook salmon in our study. 

A total of 157 tagged fish were detected near collection entrances, and 91 percent (143 fish) of these 

fish were first detected at the weir box. Fifty-two percent of the tagged fish (81 fish) that arrived at 

collection entrances were only detected at the weir box. Discovery efficiency of the weir box (76

percent) was greater than discovery efficiency of flumes 1 and 2 (35 percent). These data show that the 

weir box outperformed the other collection entrances, but the effects of dam operations on this 

performance also should be considered. Turbine unit 2, which is located beneath the weir box, was 

operated during 90 percent of the study period, whereas unit 1, which is located beneath flumes 1 and 2, 

was only operated during 3 percent of the study period. It is generally accepted that turbine flow is an 

important guidance mechanism for juvenile salmon at Cowlitz Falls Dam, so the effects of dam 

operations on the study results must be considered. Additionally, entrance efficiency (52 percent) and 

retention efficiency (24 percent) of the weir box were relatively low and limited the overall success of 

the device. Overall, fish collection efficiency was 12 percent during 2014 and was composed of 

collection through the weir box (5 percent), flumes 1 and 2 (4 percent), flume 4 (2 percent), and 

unassigned routes (1 percent). The tendency for juvenile Chinook salmon to migrate in deep water may 

limit improvements to discovery metrics of surface collection routes unless other devices such as guide 

nets, or alterations to the debris barrier, are used in the future. However, improvements to entrance and 

retention characteristics of the weir box may be feasible by altering factors such as flow and weir height.

Although a large number of tagged fish (230 fish) passed through turbines and entered the 

tailrace of Cowlitz Falls Dam, few fish (24 fish; 10 percent) entered the discovery zone (within 6.1 

meters of the entrance) of the URLC. The tailrace of Cowlitz Falls Dam is fairly constrained, which 

limits egress routes for juvenile salmon. However, little is known about the horizontal and vertical 

distribution of juvenile salmon as they move downstream through the tailrace. Median residence in the 

reach located 0.5 rkm downstream of the dam was 0.37 hours (22.7 minutes), and 90 percent of the 

tagged fish exited the reach within 1.5 hours of passing the dam. This suggests that fish moved fairly 

quickly past the URLC, and indicates the need to know exactly where fish are moving in the tailrace to

optimize the placement of the URLC and to maximize the number of fish that discover the entrance to 

the device. 
3 

Introduction

Surface collection systems can increase survival for juvenile salmon at dams, but to be effective

they must collect a large proportion of the population because fish that are not collected will pass 

through other routes where injury or death can occur. Most dams provide multiple passage routes (for 

example, collection systems, turbines, spillways) for juvenile fish migrating downstream. Juvenile 

salmon rely on factors such as water velocity and turbulence to guide their downstream movements, so 

routes that pass large volumes of water are highly effective at passing fish (Coutant, 2001; Tiffan and 

others, 2009). Surface collection systems are effective because juvenile salmon typically migrate near 

the surface, but these systems must create conditions in a dam forebay that are conducive to discovery, 

entry, and retention (Coutant and Whitney, 2000; Adams and others, 2001; Johnson and Dauble, 2006; 

Evans and others, 2008). Otherwise, the risk of passing through alternate routes is greatly increased. 

The surface collection system at Cowlitz Falls Dam, located on the upper Cowlitz River, 

Washington (fig. 1), is known to attract juvenile salmon effectively in a variety of configurations. The 

collection system was originally designed and operated with four collection flumes that are located 

inside spillbays 2 and 3 (fig. 2). The two turbine units at the dam are located beneath these spillbays, so 

water that passes through the turbines guides fish toward the center of the dam where the collection 

flumes are located. However, a floating debris barrier is located upstream of spillbays 2 and 3, and this 

device extends 2.7 m below the water surface (fig. 2). Thus, fish must sound underneath the debris 

barrier before they can approach the surface collection flumes. Many of the fish that are attracted to the 

collection entrances fail to enter the system, and this factor is largely responsible for the failure of the 

system to meet annual collection goals. Juvenile salmon that arrive at Cowlitz Falls Dam either are 

collected or they pass the dam and enter Riffe Lake. Fish that are collected are transported by truck

around the other dams in the Cowlitz River hydrosystem and released into stress-relief ponds from 

which they can volitionally outmigrate into the free-flowing river. With the exception of fish that are 

collected through supplemental methods (seining and Fyke-netting), fish that enter Riffe Lake become 

landlocked and, therefore, do not contribute to the anadromous fish population. Studies have shown that 

discovery rates of the surface collection system routinely exceed 90 percent at Cowlitz Falls Dam 

(Hausmann and others, 2001; Farley and others, 2003; Liedtke and others, 2009). However, results from 

mark-recapture studies indicate that only about 46 percent of juvenile steelhead (Oncorhynchus mykiss), 

30 percent of juvenile coho salmon (Oncorhynchus kisutch), and 21 percent of juvenile Chinook salmon 

(Oncorhynchus tshawytscha) were collected annually during 1996–2013 (Serl and Heimbigner, 2014). 

In 2003, Perry and others (2004) used radiotelemetry and an acoustic camera to monitor fish behavior 

within 1 m of the collection flume entrances at Cowlitz Falls Dam. They reported that “at most only 25 

percent of the fish that come within 1 m of the flume entrances subsequently pass into the entrance” 

(Perry and others, 2004; page 54). These studies show that discovery rates are sufficient to result in high 

collection rates, but entry and retention issues have limited collection success.
4 

Cowlitz 

River

Cispus 

River

Riffe 

Lake

Cowlitz 

Falls Dam

Cowlitz 

Falls Day

Use Park

PUD

Boat 

Launch

WASHINGTON

Lake

Scanewa

Figure 1. Schematic of the study area showing locations of fixed monitoring sites (open circles), release sites (filled 

circles), and the Upper Riffe Lake Collector (star), Washington. 
5 

Flow

Flume

1

Flume

2

Weir

Box

Flume

4

Spillbay 2 Spillbay 3

Debris

Barrier

Figure 2. Schematic of Cowlitz Falls Dam showing locations of the debris barrier and spillbays 2 and 3, where 

juvenile salmon collection occurred through flume 1, flume 2, the weir box, and flume 4. Photograph of the weir box

also is shown. 
6 

Tacoma Power developed and tested two prototype fish collection devices at Cowlitz Falls Dam 

during 2006–2010 in an attempt to improve annual fish collection efficiencies. The first device was a 

fish screen that was 12.2 m long and was deployed inside spillbay 3 as a single collection entrance 

(Kock and others, 2007). The fish screen had a 6.1-m wide by 6.1-m deep entrance and the device 

gradually narrowed in the downstream direction to provide uniform water acceleration (0–2.1 m/s), 

which has been shown to be an important factor in optimizing surface collection of juvenile fish (Haro 

and others, 1998). The second device was a weir box that was designed as a wide (8.5 m), shallow (0.6 

m) structure that attached at the upstream entrance to collection flumes 1 and 2, inside spillbay 2 

(Liedtke and others, 2010). The weir box created a wide, shallow flow field that spilled over the weir 

crest and captured smolts in a high flow, turbulent holding box where they were susceptible to 

entrainment in collection flumes. In 2009, the fish screen and weir box were evaluated simultaneously 

during a radiotelemetry evaluation in which 318 juvenile coho salmon and 317 juvenile Chinook salmon 

were monitored. The discovery efficiency (number of tagged fish detected within 6.1 m of the entrance 

divided by the number of tagged fish detected in the forebay) of the fish screen and weir box was 

similar for juvenile coho salmon (about 80 percent for each device) and Chinook salmon (about 60 

percent for each device), but capture efficiencies (number of tagged fish collected divided by the 

number of tagged fish detected within 6.1 m of the entrance) were substantially greater for the weir box 

(Liedtke and others, 2010). For coho salmon, the capture efficiency of the weir box was 93 percent, 

whereas the capture efficiency of the fish screen was 16 percent (Liedtke and others, 2010). This 

relationship was similar for Chinook salmon, as capture efficiencies of the weir box were 91 percent 

compared to 38 percent for the fish screen (Liedtke and others, 2010). Given these findings, the weir 

box appeared to be a promising option for improving capture efficiencies, and thereby increasing fish 

collection at Cowlitz Falls Dam.

In 2013, Tacoma Power developed a plan to install and evaluate a weir box during the peak 

outmigration period for juvenile steelhead and coho salmon at Cowlitz Falls Dam. The proposed 

location and size of the weir box differed from the initial test of the device during 2009 because of dam 

safety concerns that prevented it from being deployed in the location where it was originally tested. The 

2013 weir box was only 6.1 m wide and was located at baffle panel 3, which was upstream of the 

location where the 2009 weir box was deployed (flumes 2 and 3; fig. 2). We conducted an assessment of 

the 2013 weir box by tagging, releasing, and monitoring the movements of 45 juvenile steelhead and 45 

juvenile coho salmon (Kock and others, 2014). In total, 29 tagged steelhead and 36 tagged coho salmon 

were collected during the study, but nearly all these fish (all steelhead and 95 percent of coho salmon) 

were collected through flumes 1 and 2, rather than through the weir box (Kock and others, 2014). These 

results indicated that the 2013 weir box was not likely to result in substantial collection of juvenile 

steelhead and coho salmon at Cowlitz Falls Dam. 
7 

Although the 2013 weir box performed poorly for collecting juvenile steelhead and coho salmon, 

it was not tested during the summer months when juvenile Chinook salmon are passing the dam. 

Collection conditions at Cowlitz Falls Dam change substantially between spring and summer months. 

Water temperatures during the spring generally range from 5 to 10 o

C, whereas summer water 

temperatures often exceed 17 oC. River flows in the 5,000–12,000 ft3/s range are common during the 

spring, so both turbine units are typically operated during this period and spill operations are often 

required. During the summer, river flows decrease to less than 1,500 ft3/s and a single turbine unit is 

often operated intermittently. The composition of the outmigrant population changes as well. Steelhead 

and coho salmon are the predominant species that pass during spring months, and juvenile Chinook 

salmon primarily pass during summer months. Given these differences, evaluation of the weir box 

during summer months was important for assessing the future of the device at Cowlitz Falls Dam. This 

assessment was conducted during 2014, in conjunction with an evaluation of a new collection device 

that was located downstream of Cowlitz Falls Dam. 

Tacoma Power developed a floating collection device, known as the Upper Riffe Lake Collector 

(URLC), which was designed to capture juvenile salmon in the tailrace of Cowlitz Falls Dam during 

2014. The URLC was deployed 0.17 rkm downstream of the dam and consisted of three parts: a 

pontoon barge, a net structure, and a live box (fig. 3). The pontoon barge (9.1 m long; 4.8 m wide) was 

the primary support structure for the URLC. It provided floatation for the net structure and served as a 

work platform for staff when fish were being removed from the live box at the downstream end of the 

structure. The net structure was 16.2 m long and oriented into the current. It had a large opening (3.0 m 

wide; 2.4 m deep) at the upstream end and attached to the live box at the downstream end (fig. 3). The

net structure gradually narrowed along its length to funnel fish into the live box, where they could be 

removed for transportation. The entrance to the live box included a Fyke-style opening that was 

designed to retain fish. The URLC was deployed in the tailrace of Cowlitz Falls Dam from July 31, 

2014, to September 15, 2014. Tacoma Power staff members visited the trap 5 days per week to remove 

fish that were caught.

We used radiotelemetry to evaluate concurrently the weir box and URLC during 2014. Tacoma 

Power purchased 90 radio transmitters for these evaluations. A concurrent study designed to evaluate 

dam passage survival of juvenile Chinook salmon at Cowlitz Falls Dam for the Lewis County Public 

Utility District (PUD) included the tagging and release of an additional 334 juvenile Chinook salmon 

upstream of the dam. We recognized the efficiency of pooling detections of tagged fish from both the 

Tacoma Power and Lewis County PUD studies in our assessment of the weir box and URLC, so we 

coordinated transmitter specifications to insure that fish from both studies could be monitored 

simultaneously. Our objectives were to determine discovery efficiency, entrance efficiency, retention 

efficiency, and capture efficiency for the weir box and URLC. 
8 

Flow

Pontoon

barge

Net

structure

Live

box

Figure 3. Schematic and photographs of the Upper Riffe Lake Collector deployed in the tailrace of Cowlitz Falls 

Dam during 2014.
9 

Methods

Fish Collection, Tagging, and Release

Juvenile Chinook salmon were collected and tagged at the Cowlitz Falls Dam fish facility during 

July–August 2014. A total of 87 juvenile Chinook salmon (table 1) were double-tagged with a radio 

transmitter (Model NTQ-2; Lotek© Wireless Inc., Newmarket, Ontario, Canada) and a passive 

integrated transponder (PIT) tag (Model HPT12 12.5 mm 134.2 kHz ISO FDXB; Biomark©, Inc., Boise, 

Idaho). Each radio transmitter weighed 0.30 g (in air) and had an expected operating life of 23 d. 

Transmitters and PIT tags were surgically implanted into the body cavity of study fish using methods 

described in Liedtke and others (2012). Following tagging, fish were held at the Cowlitz Falls fish 

facility for about 24 h to allow for recovery and to monitor short-term mortality that could result from 

the handling and tagging process. Fish were then transported by automobile to the Cowlitz Falls Day 

Use Park (3.9 rkm upstream of the dam; fig. 1) and released. An evaluation of passage survival of 

juvenile Chinook salmon at Cowlitz Falls Dam was conducted concurrently with the weir box and 

URLC study during 2014. For that study, 334 juvenile Chinook salmon were radio-tagged and released 

upstream of Cowlitz Falls Dam (table 1). The transmitters that were used for this study were the same 

model as those previously described, so we were able to monitor movements of tagged fish from both 

studies as we evaluated the weir box and URLC. This resulted in a total of 421 radio-tagged fish being 

released upstream of Cowlitz Falls Dam during July–August 2014 (table 1). There were two differences 

between fish used in the two studies. The 87 fish used in the Tacoma Power study were double-tagged 

(radio transmitter and PIT tag) and released at the Cowlitz Falls Day Use Park, and the 334 fish used in 

the Lewis County PUD study were only tagged with a radio transmitter and were released at the PUD 

Boat Launch (1.2 rkm upstream of the dam). For both studies, the same taggers and standard operating 

procedures were used for tagging, handling, and transporting, so we did not anticipate significant 

differences between the release groups, apart from the release location. 
10 

Table 1. Summary of release dates, number of fish released, and average sizes of juvenile Chinook salmon 

released during a radiotelemetry evaluation at Cowlitz Falls Dam, Washington, 2014.

[Weight and Fork length: Numbers in parentheses are one standard deviation from the mean. Abbreviations: g, gram; mm, 

millimeter; PUD, Public Utility District] 

Release date Release site

Number of fish 

released Weight (g) Fork length (mm)

7/31/2014 Day Use Park 20 12.0 (2.3) 103.9 (6.5)

8/07/2014 Day Use Park 23 12.1 (2.3) 103.6 (6.8)

8/12/2014 Day Use Park 24 11.8 (1.5) 102.4 (3.8)

8/15/2014 Day Use Park 20 12.9 (2.9) 105.8 (7.6)

Total 87 12.2 (2.3) 103.9 (6.3)

7/16/2014 PUD Boat Launch 23 18.4 (4.1) 117.9 (8.9)

7/17/2014 PUD Boat Launch 32 20.8 (4.6) 121.7 (8.0)

7/22/2014 PUD Boat Launch 30 18.3 (4.7) 117.4 (10.7)

7/23/2014 PUD Boat Launch 29 18.6 (3.4) 117.8 (7.8)

7/29/2014 PUD Boat Launch 28 15.1 (3.9) 116.8 (30.8)

7/30/2014 PUD Boat Launch 28 14.5 (2.7) 109.5 (6.8)

8/06/2014 PUD Boat Launch 8 12.6 (2.4) 104.9 (7.3)

8/07/2014 PUD Boat Launch 26 11.7 (1.9) 103.5 (6.2)

8/08/2014 PUD Boat Launch 50 11.6 (1.9) 101.9 (5.5)

8/12/2014 PUD Boat Launch 28 12.4 (1.7) 103.6 (4.7)

8/13/2014 PUD Boat Launch 28 11.8 (1.7) 102.5 (4.9)

8/14/2014 PUD Boat Launch 24 10.9 (1.3) 100.2 (4.1)

Total 334 14.8 (4.5) 109.4 (10.3)

Overall 421 14.2 (4.3) 108.2 (9.8)

Configuration of the Fish Collection System at Cowlitz Falls Dam

The Cowlitz Falls Dam fish collection system was operated with three primary collection 

entrances during July–August 2014. The primary collection entrances included flumes 1 and 2 and the 

weir box (fig. 2). Flumes 1 and 2 were located inside spillbay 2, and the weir box was located at the 

north, upstream entrance into spillbay 3 (fig. 2). The weir box collected fish immediately upstream of 

spillbay 3 and the remaining upstream entrances into the spillbay were completely blocked by baffle 

panels (fig. 4). However, induction slot entrances into spillbay 3 remained open so it was possible for 

fish to enter spillbay 3 and be collected through flume 4 (fig. 4). We documented fish collection through 

flume 4 in 2007 and 2008, when the dam was configured in a similar fashion (Liedtke and others, 2007, 

2009). Given this possibility, fish collection through flume 4 was possible, but was considered to be a 

secondary collection entrance given that low numbers of fish would be expected to enter spillbay 3 

through the induction slots. 
11 

Water level

Flume 4

Spill gate

Turbine

Trash rack

Baffle panel

Induction

slot

Fish movement

path

Spillbay 3

Figure 4. Schematic of the side view of spillbay 3 at Cowlitz Falls Dam showing the path of movement that juvenile 

Chinook salmon would have to take to be collected in flume 4 during July–August 2014.

Monitoring Array

We used aerial and underwater monitoring systems to detect tagged fish during the study. 

Twelve aerial fixed monitoring sites (hereafter referred to as “fixed sites”) were operated within the 

study area to monitor general movement patterns of tagged fish (fig. 1). Three fixed sites were located 

in Lake Scanewa to monitor movement patterns in the reservoir and detected fish in the Cowlitz Arm of 

Lake Scanewa, in the Cispus Arm of Lake Scanewa, and near the PUD Boat Launch (fig. 1). Two fixed 

sites were located on Cowlitz Falls Dam to monitor fish as they approached the dam. The remaining 

fixed sites were located downstream of the dam. These sites were primarily used to collect data for the 

Lewis County PUD study, but the PUD allowed us to collect additional data near the URLC and were 

useful for confirming dam passage of individual fish. These sites were located 0.05, 0.5, 2.0, 3.5, 4.7, 

and 7.0 rkm (two sites) downstream of the dam. 
12 

Sixty-five underwater antennas were used to monitor fine-scale movements of tagged fish at 

Cowlitz Falls Dam. The antenna locations were selected to optimize data collection as tagged fish 

approached the dam, discovered the entrances to the collection devices, and entered the fish collection 

system. All the underwater antennas at the dam were monitored by a Multiprotocol Integrated 

Telemetry Acquisition System (MITAS; SigmaEight, Inc., Newmarket, Ontario, Canada). Detection 

data from the MITAS were grouped during analysis to create a series of detection zones to describe 

near-dam fish behavior. In the event that a tagged fish was simultaneously detected in more than one 

zone, the fish was assigned to the zone that had the highest signal strength of detection. 

The first series of antennas that tagged fish encountered as they approached the forebay were 

located along the face of the dam (fig. 5). Antenna locations were selected to describe horizontal and 

depth distributions of tagged fish as they arrived at the dam. Horizontal distributions were determined 

by grouping detections from antennas within each spillbay, which created arrival zones for spillbays 1, 

2, 3, and 4 (fig. 5). Depth distributions were determined by grouping detections from antennas that were 

located at five depths across the dam face: 0.9, 3.6, 7.9 14.9 and 25.6 m (fig. 5). Fish collection 

entrances were located at the surface, so antennas were grouped into two depth zones, referred to as 

“shallow” and “deep”. The purpose of the two depth zones was to determine if fish arrived at the dam 

near the surface, where they could encounter collection entrances, or if they arrived at the dam deeper 

than where collection entrances were located. The shallow zone included antennas located 0.9 m below 

the surface, and the deep zone included antennas located 3.6, 7.9, 14.9 and 25.6 m below the surface 

(fig. 5).

The second series of antennas were located near the collection entrances and inside the 

collection flumes to detect fish when they encountered a collection entrance, and to identify collection 

routes for fish that were collected. Single antennas were located at the entrances to flumes 1, 2 and 4 

and detected fish within 6.1 m of these locations. Two antennas were located at the weir box entrance 

and detected fish within 6.1 m of that entrance. Two more antennas were located inside the weir box and 

detected fish that entered the device. Three antennas were located inside each collection flume, and 

downstream of entrances to flumes 1 and 2, the weir box, and flume 4. These antennas detected fish that 

were collected through each route. Additional antennas also were located in the fish transport flume, 

between the collection flumes and in the fish collection facility. These antennas detected fish as they 

were moved downstream to the collection facility to confirm when collection occurred. 
13 

Spillbay

#1

Spillbay 

#2

Spillbay 

#3

Water 

level

Spillbay

#4

Turbine 

#1

Intakes

Turbine 

#2

Intakes

0.9 m

7.9 m

14.9 m

25.6 m

3.6 m

Figure 5. Schematic of Cowlitz Falls Dam and location of general detection zones for an underwater antenna 

detection array that monitored radio-tagged juvenile Chinook salmon during July–August 2014. Stars identify 

locations of shallow underwater antennas and circles identify locations of deep underwater antennas.
14 

Two aerial fixed sites and three underwater antenna arrays were used to monitor fish movements 

near the URLC. Fish entered the study area for the URLC when they passed Cowlitz Falls Dam and 

were detected on the upstream fixed site, located 0.05 rkm downstream of the dam. Fish exited the 

URLC study area when they moved downstream of the device and were detected on the downstream 

fixed site, located 0.5 rkm downstream of the dam. Underwater antennas were placed upstream of, and 

inside the URLC to detect fish as they discovered, entered, and were collected by the URLC. Two 

antennas were located at the URLC entrance and detected fish within 6.1 m of the entrance. Four 

antennas were located inside the URLC, along the length of the net structure, to detect fish that entered 

the device. Two antennas were located inside the live box and detected fish that were retained in the 

device. The detection range of the antennas inside the net structure and live box was attenuated to insure 

that tagged fish were only detected when they were inside the URLC. 

Data Analysis

Assessment of Differences between Release Sites

We compared fish size, reservoir travel time, forebay residence time, and the horizontal and 

vertical distribution of tagged fish when they arrived at the dam to assess differences between groups of 

fish that were released at the Day Use Park and the PUD Boat Launch. Fish size was compared using 

data on fork length (in millimeters) and fish weight (in grams). Fish-size data were pooled across the 

tagging period by release site and differences were assessed using a t-test (Sokal and Rohlf, 1994).

Releases at the PUD Boat Launch occurred across a greater temporal period of the study than releases at 

the Day Use Park, so we also assessed fish size during the period when both groups of fish were being 

released. Reservoir travel time was obtained for each fish that arrived in the forebay of Cowlitz Falls 

Dam by subtracting the date and time of release from the first date and time of forebay detection. 

Forebay residence time was calculated as the elapsed time between the first and last detection in the 

forebay. Event-time analysis (Allison, 2008) was used to compare reservoir travel time and forebay 

residence time between release groups. Forebay arrival was the event of interest when comparing 

reservoir travel time, and last detection in the forebay was the event of interest when comparing forebay 

residence time. For each comparison, Kaplan-Meier plots were created to display travel time and 

residence time distributions for groups of fish from the two release sites. The Log-Rank statistic was 

used to test for significant differences between groups (Allison, 2008), and statistical significance was 

determined when p was less than 0.05. Each tagged fish that arrived at Cowlitz Falls Dam was assigned 

to one of four horizontal arrival zones (spillbays 1, 2, 3, or 4) and to one of two depth arrival zones 

(shallow, or deep), based on the first detection event on underwater antennas located along the face of 

the dam. The distribution of horizontal and depth arrival zones was compared between release sites 

using Fisher’s exact test.
15 

Behavior Patterns, Performance Metrics, and Dam Passage

Arrival patterns were pooled among release sites and assigned to one of three arrival periods to 

determine if arrival patterns differed temporally. The three arrival periods included July 16–July 29, 

2014, July 30–August 12, 2014, and August 13–August 26, 2014. The distribution of horizontal and 

depth arrival zones were compared between arrival periods using Fisher’s exact test.

A series of performance metrics were used to assess fish movement patterns and collector 

performance in the dam forebay (table 2). The performance metrics were developed to describe 

movement patterns of fish from forebay arrival to the point when they were collected or rejected 

collection through the various collection routes. Collection entrances were located near the surface, in 

spillbays 2 and 3, but this area was blocked by the debris barrier so fish had to sound beneath the debris 

barrier and then move back to the surface to locate collection entrances. The first metric, debris barrier 

discovery efficiency, described the percentage of fish that were detected inside the debris barrier area, 

near spillbays 2 and 3 (fig. 2). Tagged fish that arrived in this location could be detected on underwater 

antennas that were located 0.9 or 3.6 m below the water surface (fig. 5). The remaining metrics 

described the percentage of fish that discovered, entered, and were retained in flume 1/flume 2 and the 

weir box. Descriptions of the calculations used for each metric are located in table 2. It was possible for 

tagged individuals to discover and enter multiple collection entrances without being collected during the 

study period. For this reason, tagged individuals could be enumerated in discovery and entrance metrics 

for each of the collection devices that were assessed. However, individual tagged fish could only be 

collected one time during the study and thus were enumerated a maximum of one time for the collection 

metrics. We also summarized collection and dam passage events during each hour of the day to evaluate 

diel patterns in collection and passage.

Detection events at antennas located at entrances to flume 1/flume 2, the weir box, and flume 4 

were analyzed to describe discovery patterns by tagged fish. Discovery patterns were assessed for 

individual fish based on the collection entrance that was first encountered and the number of unique 

collection entrances that were encountered while the fish was in the dam forebay. Some tagged fish 

made repeated movements between collection entrances, so we also quantified the number of discovery 

events for individual fish at the collection entrances. 

Dam passage and timing were quantified to describe the percentage of tagged fish that passed 

through various routes at the dam and to determine if diel patterns were present. Tagged fish could pass 

the dam through one of three collection routes (flume 1/flume 2, weir box, flume 4) or by passing 

through the turbines. The hour of collection was obtained from underwater antennas that were located 

inside collection flumes. The hour of turbine passage was obtained from the first detection event on the 

tailrace monitoring site that was located 0.05 rkm downstream of the dam. 

Performance metrics also were used to assess fish movement patterns and collector performance 

for the URLC. Calculations used for each of the URLC performance metrics are described in table 3. 
16 

Table 2. Descriptions of performance metrics used to evaluate the collection flumes and weir box during 2014.

Metric Definition

Debris barrier discovery efficiency Number of tagged fish detected inside the debris barrier area divided 

by the number of tagged fish detected in the forebay of Cowlitz Falls 

Dam.

Flume discovery efficiency Number of tagged fish detected within 6.1 meters of flumes 1 and 2 

divided by the number of tagged fish detected inside the debris 

barrier area.

Flume entrance efficiency Number of tagged fish that entered collection flumes 1 and 2 divided 

by the number of tagged fish detected within 6.1 meters of collection 

flumes 1 and 2.

Flume retention efficiency Number of tagged fish collected through collection flumes 1 and 2 

divided by the number of tagged fish that entered collection flumes 1 

and 2.

Flume fish capture efficiency Number of tagged fish collected through the collection flumes divided 

by the number of tagged fish detected in the forebay of Cowlitz Falls 

Dam.

Weir box discovery efficiency Number of tagged fish detected within 6.1 meters of the weir box 

entrance divided by the number of tagged fish detected inside the 

debris barrier area.

Weir box entrance efficiency Number of tagged fish that entered the weir box divided by the number 

of tagged fish detected within 6.1 meters of the weir box entrance.

Weir box retention efficiency Number of tagged fish collected through the weir box divided by the 

number of tagged fish that entered the weir box.

Weir box fish capture efficiency Number of tagged fish collected through the weir box divided by the 

number of tagged fish detected in the forebay of Cowlitz Falls Dam.

Table 3. Descriptions of performance metrics used to evaluate the Upper Riffe Lake Collector (URLC) during 2014. 

Metric Definition

URLC discovery efficiency Number of tagged fish detected within 6.1 meters of the URLC

entrance divided by the number of tagged fish detected in the tailrace 

of Cowlitz Falls Dam.

URLC entrance efficiency Number of tagged fish detected inside the net structure divided by the 

number of tagged fish detected within 6.1 meters of the URLC 

entrance.

Net retention efficiency Number of tagged fish detected inside the net structure that remained in 

the URLC divided by the total number of tagged fish detected inside 

the net structure (includes fish that remained in the URLC and fish 

that left the URLC).

Live box entrance efficiency Number of tagged fish detected inside the live box divided by the 

number of tagged fish detected inside the net structure.

Live box retention efficiency Number of tagged fish collected divided by the number of tagged fish 

detected inside the live box.

URLC capture efficiency Number of tagged fish collected in the URLC divided by the number of 

tagged fish detected in the tailrace of Cowlitz Falls Dam.
17 

Results

Assessment of Differences between Release Sites

Most of the tagged fish that were used to evaluate the collection flumes, weir box and URLC 

were released at the PUD Boat Launch. A total of 421 tagged fish were released and monitored during 

the study period and most of the releases (79 percent; 334 fish) were made at the PUD Boat Launch

(table 1). Tagged fish were released at the PUD Boat Launch from July 16 to August 14, 2014 and at the 

Day Use Park from July 31 to August 15, 2014 (table 1). The average size of tagged fish in daily release 

groups decreased during July and then stabilized during August (fig. 6). Tagged fish released at the Day 

Use Park were smaller than tagged fish released at the PUD Boat Launch based on weight (t = -5.10, p

<0.0001) and fork length (t = -4.78, p <0.0001) measurements. However, fish from the Day Use Park

release groups were not tagged and released during most of July when fish were larger, on average (fig. 

6). Statistical comparison of fish size during the period when both groups were being tagged and 

released (July 30–August 14, 2014) showed that fish weight (t = 0.17, p = 0.868) and length (t = 0.47, p

= 0.637) were similar.

Reservoir travel time varied by release site, but forebay residence time was similar between 

groups. Forebay detection records show that 85 percent of the tagged fish (74 fish) released at the Day 

Use Park and 87 percent of the tagged fish released at the PUD Boat Launch (289 fish) arrived in the 

forebay of Cowlitz Falls Dam. The Day Use Park release site was located 2.7 rkm upstream of the PUD 

Boat Launch release site. Fish that were released at the Day Use Park had a slower median travel time 

(2.3 d) to the dam forebay than fish that were released at the PUD Boat Launch (1.0 d; fig. 7). Eventtime analysis showed that reservoir travel time differed between release sites (X2 

= 7.5, p = 0.006). 

Median forebay residence time was slightly less for fish released at the Day Use Park (0.45 d) than for 

fish released at the PUD Boat Launch (0.60 d), but these differences were not significant (X2 

= 2.7, p = 

0.09; fig. 8).

Analysis of first detection events showed that juvenile Chinook salmon primarily arrived in deep 

zones (>3.6 m) and were dispersed across the face of the dam. Underwater antenna detection records 

showed that 88 percent of the fish from the Day Use Park (65 fish) and 85 percent of the fish from the 

PUD Boat Launch (246 fish) that arrived in the forebay were detected at the dam. Most tagged fish 

(80.6 percent; table 4) were first detected on antennas in the deep zone when they arrived at the dam, 

and this pattern did not vary by release site (p = 0.86). The largest percentage of fish from each release 

site were first detected at spillbay 1 and the lowest percentage of fish were first detected at spillbay 2 

(table 4). These patterns did not vary by release site (p = 0.83). Although fish size and reservoir travel 

time differed by release site, forebay residence time, arrival depth, and horizontal arrival distributions 

were similar for fish from the two release sites. Given these findings, subsequent results have been 

pooled across release sites to simplify data presentation.
18 

90

100

110

120

130

140

150

Fork length (mm)

10

20

30

40

Weight (g)

= Cowlitz Falls Day

Use Park

= PUD Boat Launch

Figure 6. Boxplots showing juvenile Chinook salmon fork lengths in millimeters (mm) (top panel) and weights in 

grams (g) (bottom panel) for groups of fish that were tagged and released at the Cowlitz Falls Day Use Park and 

Lewis County Public Utility District (PUD) Boat Launch. Squares inside the box are the mean, lines inside the box 

are the median, box boundaries are the 25th and 75th percentiles, and whiskers are the minimum and maximum 

values for each group. 
19 

Elapsed time from release to forebay arrival (d)

0 2 4 6 8 10 12 14

Proportion of tagged fish

0.0

0.2

0.4

0.6

0.8

1.0

Cowlitz Falls Day Use Park

PUD Boat Launch

Figure 7. Graph showing proportion of tagged juvenile Chinook salmon that moved downstream from the Cowlitz 

Falls Day Use Park and Lewis County Public Utility District (PUD) Boat Launch release sites in Lake Scanewa and 

entered the forebay of Cowlitz Falls Dam over time (in days [d]). 
20 

Residence time in the forebay (d)

0 2 4 6 8 10 12 14

Proportion of tagged fish

0.0

0.2

0.4

0.6

0.8

1.0

Cowlitz Falls Day Use Park

PUD Boat Launch

Figure 8. Graph showing residence time (in days [d]) of tagged juvenile Chinook salmon in the forebay of Cowlitz 

Falls Dam during July–August 2014 for groups of fish released at the Cowlitz Falls Day Use Park and the Lewis 

County Public Utility District (PUD) Boat Launch.

Table 4. Percentage of tagged juvenile Chinook salmon that were first detected in arrival zones that were 

horizontally and vertically stratified across the face of Cowlitz Falls Dam during 2014.

Release site Depth Spillbay 1 Spillbay 2 Spillbay 3 Spillbay 4 Total

Cowlitz Falls Day Use Park Shallow 9.4 0.0 1.6 9.4 20.3

Deep 26.6 12.5 26.6 14.1 79.7

Total 35.9 12.5 28.1 23.4

Lewis County Public Utility 

District Boat Launch

Shallow 7.7 0.0 4.5 7.3 19.2

Deep 31.7 14.6 18.7 15.4 80.8

Total 39.4 14.6 23.2 22.8

Overall Shallow 8.1 0.0 3.5 7.7 19.4

Deep 30.6 13.9 20.6 15.5 80.6

Total 38.7 14.2 24.2 22.9
21 

Behavior Patterns, Performance Metrics, and Dam Passage

A total of 363 tagged juvenile Chinook salmon (86 percent) were detected in the forebay of 

Cowlitz Falls Dam and 311 of these fish (86 percent) moved downstream and were detected on 

underwater antennas at the face of the dam (table 5). We examined arrival patterns on underwater 

antennas to determine if horizontal or depth distributions changed as the season progressed (table 6). 

Ninety-six tagged fish arrived at the dam during the first period (July 16–July 29), 103 tagged fish 

arrived during the second period (July 30–August 12), and 112 tagged fish arrived during the third 

period. There was no difference (p = 0.33) in horizontal arrival patterns between the three periods. The 

percentage of fish that arrived at the dam in the shallow zones was greater in the first period (27.4 

percent) than in the second (14.6 percent) or third (17.0 percent) periods, but this difference was not 

quite statistically significant (p = 0.07; table 6). The lowest percentage of fish arrived in zones where 

collection entrances were located (shallow zones in spillbays 2 and 3) under all scenarios that we 

examined (tables 4 and 6). 

About one-half of the tagged fish in the forebay eventually moved inside the debris barrier area 

(debris barrier discovery efficiency = 54 percent; table 5), where the collection entrances were located.

Dam operations during the study period primarily included the sole operation of turbine unit 2 (90 

percent of the time), with the remaining operations consisting of no turbine operation (7 percent of the 

time) and sole operation of turbine unit 1 (3 percent of the time). The weir box discovery efficiency (76 

percent) was greater than the flume 1/flume 2 discovery efficiency (35 percent; table 5). Similarly, 

entrance efficiency was greater for the weir box (52 percent) than for flume 1/flume 2 (23 percent; table 

5). However, flume 1/flume 2 retained every tagged fish that entered through those routes, whereas the 

weir box only retained 24 percent of the tagged fish that were detected inside the device (table 5). 

Capture efficiencies for both devices were low (5 percent or less; table 5). 

Analysis of first detection events at collection entrances revealed that 91 percent of the tagged 

fish (143 fish) were first detected at the weir box, whereas the remaining fish initially arrived at 

entrances to flume 1/flume 2 (6 percent; 9 fish) or flume 4 (3 percent; 5 fish) (table 7). About one-half 

(52 percent) of the tagged fish that arrived at a collector entrance were only detected at the weir box, 

and most of the remaining fish (62 fish) were only detected at the weir box and the flume 1/flume 2 

entrance (table 7). Some tagged fish made multiple trips between collection entrances, but most the 

tagged fish (80 percent) made three trips or less (fig. 9). 

The largest percentage of tagged fish passed through turbines at Cowlitz Falls Dam and entered 

Riffe Lake (55 percent; table 8). Turbine passage was uncommon during daytime hours, and 87 percent 

of the passage occurred between the hours of 9:00 p.m. and 5:00 a.m. (fig. 10). The remaining fish 

either did not pass the dam (33 percent) or were collected (12 percent; table 8). Collection occurred 

through the weir box (5 percent), flume 1/flume 2 (4 percent), flume 4 (2 percent) or through an 

unknown route (1 percent; table 8). Collection occurred during daytime and nighttime hours, and 

peaked between the hours of 4:00 a.m. and 8:00 a.m. when 44 percent of the tagged fish were collected 

(fig. 10.) 

Tagged fish that passed the dam moved quickly through the tailrace, and few of the fish 

discovered the URLC. The median travel time from tailrace entry to detection on the fixed site located 

0.5 rkm downstream of Cowlitz Falls Dam (downstream of the URLC) was 0.37 h (22.7 min), and 90 

percent of the tagged fish moved through the URLC reach in 1.5 h or less. The discovery efficiency of 

the URLC was 10 percent; only 24 of the 230 tagged fish were detected at the entrance to the device. 

None of the tagged fish entered the URLC (entrance efficiency = 0 percent) and no tagged fish were 

collected, so the remaining performance metrics for the device were not calculated. Tagged fish that 

discovered the URLC entrance were only briefly present at that location. Most of the tagged fish (22 
22 

fish; 92 percent) had five detection events or less at the URLC entrance. The remaining two fish had 12 

detections and 15 detections, respectively. Given that the transmitters emitted a signal every 3.5 sec, 92 

percent of the tagged fish spent less than 20 sec in the URLC discovery zone and none of the fish spent 

more than 1 min at that location.

Table 5. Summary of performance metrics for flume 1/flume 2 and the weir box at Cowlitz Falls Dam during 2014.

Descriptor

Number of 

fish

Numbers in 

calculation Percent

Number fish released 421

Number fish detected in forebay 363 363/421 86

Number fish detected at face of dam 311 311/363 86

Debris barrier discovery efficiency

Number fish detected inside debris barrier area 197 197/363 54

Flume and weirbox discovery efficiency

Number fish detected within 6.1 meters of flume entrances 69 69/197 35

Number fish detected within 6.1 meters of weir box 

entrance

149 149/197 76

Flume and weirbox entrance efficiency

Number fish detected inside flumes 16 16/69 23

Number fish detected inside weir box 78 78/149 52

Flume and weirbox retention efficiency

Number fish collected in flumes 16 16/16 100

Number fish collected in weir box 19 19/78 24

Flume and weirbox capture efficiency

Number fish collected in flumes 16 16/363 4

Number fish collected in weir box 19 19/363 5

Table 6. Percentage of tagged juvenile Chinook salmon that were first detected in arrival zones that were 

horizontally and vertically stratified across the face of Cowlitz Falls Dam during 2014. 

[Data are pooled among release sites and presented by arrival date, which was determined by the date and time of first 

detection in one of the zones for each tagged fish] 

Arrival date Depth Spillbay 1 Spillbay 2 Spillbay 3 Spillbay 4 Total

July 16–July 29 Shallow 12.6 0.0 5.3 9.5 27.4

Deep 29.5 14.7 16.8 11.6 72.6

Total 42.1 14.7 22.1 21.1

July 30–August 12 Shallow 6.8 0.0 1.9 5.8 14.6

Deep 35.9 8.7 20.4 20.4 85.4

Total 42.7 8.7 22.3 26.2

August 13–August 26 Shallow 5.4 0.0 3.6 8.0 17.0

Deep 26.8 17.9 24.1 14.3 83.0

Total 32.1 17.9 27.7 22.3
23 

Table 7. Summary of collection entrances where tagged fish were initially detected and total number of collection 

entrances where tagged fish were detected during the study. 

[Numbers in parentheses are the percentage of each group] 

Collection entrance Number of fish

Collection entrance where fish were first detected

Weir box 143 (91)

Flume 1/flume 2 9 (6)

Flume 4 5 (3)

Total = 157

Collection entrance where fish were detected

Weir box only 81 (52)

Weir box and flume 1/flume 2 62 (39)

Flume 4 only 5 (3)

Weir box and flume 1/flume 2 and flume 4 4 (3)

Flume 1/flume 2 only 3 (2)

Weir box and flume 4 2 (1)

Total = 157

Table 8. Summary of fates of tagged juvenile Chinook salmon released upstream of Cowlitz Falls Dam during 

2014. 

[Numbers in parentheses are the percentage of each group] 

Description Number of fish

Total number of fish released 421

Total number of fish that did not pass the dam during the study 141 (33)

Total number of fish that passed through turbines at the dam 230 (55)

Total number of fish collected in the weir box 19 (5)

Total number of fish collected in flume 1/flume 2 16 (4)

Total number of fish collected in flume 4 9 (2)

Total number of fish collected through an unknown route 6 (1)
24 

0

10

20

30

40

50

60

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29

Percent of fish

Number of trips between entrances

Figure 9. Graph showing percentage of tagged Chinook salmon that made trips between the collection entrances 

at Cowlitz Falls Dam during 2014.
25 

0

2

4

6

8

10

12

14

16

Percentage of fish

Hour of passage

Fish that were collected

Fish that passed through turbines

Figure 10. Graph showing percentage of tagged Chinook salmon that were collected (filled bars) or passed 

through turbines (open bars) by hour, at Cowlitz Falls Dam during 2014.
26 

Discussion

Behavior patterns of radio-tagged fish showed that a large percentage of the juvenile Chinook 

salmon were not susceptible to collection because many of the fish failed to pass Cowlitz Falls Dam

during the study period. One-third of the tagged fish remained in Lake Scanewa, upstream of the dam, at 

the conclusion of the study. Similar results were observed in previous years when non-passage rates of 

juvenile Chinook salmon ranged from 11 to 43 percent (Kock and others, 2007, 2012; Liedtke and 

others, 2007, 2009, 2010). The fate of fish that remain upstream of Cowlitz Falls Dam is a critical 

uncertainty because little is known about these fish during September–April. Data from our research 

indicates that tagged fish are alive in Lake Scanewa during September, after the fish collection season, 

because tagged fish commonly are observed moving between areas where fixed sites are located (U.S. 

Geological Survey, unpub. data; September 2010). However, juvenile Chinook salmon were not 

monitored during October–April. Yearling Chinook salmon constitute a low proportion of the catch at 

the Cowlitz Falls Fish Facility each year (oral commun., John Serl, Washington Department of Fish and 

Wildlife; August 2012), which suggests that fish either are dying in Lake Scanewa, or are passing 

Cowlitz Falls Dam outside the fish collection season. Recent studies have shown that some juvenile 

Chinook salmon adopt alternate life history strategies in impounded reservoirs, and migrate downstream 

during the winter or following spring as yearlings (Keefer and others, 2012; Tiffan and others, 2012;). 

Because little is known about the fate of subyearling Chinook salmon in Lake Scanewa during 

September–April, this topic may be worthy of future evaluation. 

Many juvenile Chinook salmon arrived at Cowlitz Falls Dam in zones that were deeper than the 

collection entrances, and the lowest percentage of tagged fish arrived in zones where the collection 

entrances were located. Most tagged fish (80 percent) that arrived at Cowlitz Falls Dam were first 

detected in deep zones where fish did not have access to collection entrances. The deep arrival patterns 

by tagged fish were expressed in passage distributions; 55 percent of the tagged fish passed through 

turbines and 2 percent of the tagged fish were collected through flume 4, after apparently entering 

spillbay 3 through the induction slots that were located in the turbine intake. Entry into spillbay 3 only 

could have occurred through the induction slots unless there were unknown gaps in the baffle panels at 

the upstream end of the spillbay. The presence of the debris barrier also may have affected the deep 

arrival patterns at the dam because fish that encountered the debris barrier would have had to sound 

underneath it before approaching the collection entrances. Arrival zones located inside the debris barrier 

area (shallow zones in spillbays 2 and 3) had the lowest percentage of arrival of all zones that were 

monitored. A total of eight arrival zones were available, and the shallow zones in spillbays 2 and 3 

received 0 and 3.5 percent of the tagged fish that arrived at the dam, while the other zones received from 

7.7 to 30.6 percent of the tagged fish (table 4). These data suggest that additional devices, such as guide 

nets and alterations to the debris barrier, may be necessary to concentrate juvenile Chinook salmon near 

surface collection entrances at Cowlitz Falls Dam.
27 

Cowlitz Falls Dam was operated to enhance discovery and collection rates of the weir box, and 

the device performed positively in several ways. Summer dam operations at Cowlitz Falls Dam 

generally consist of operating a single turbine unit because inflow levels are rarely high enough to 

simultaneously support operation of both units. Fishery managers generally believe that turbine flow 

guides fish as they approach the dam, which means that it may be possible to alter the number of fish 

that encounter spillbays 2 or 3 by selecting which turbine operates during a given period. Turbine 1 is 

located beneath spillbay 2 and turbine 3 is located beneath spillbay 3, so the dam primarily was operated 

(90 percent of the time) using turbine 2 during our study to increase the number of fish that could 

encounter the device. Discovery efficiency of the weir box was high (76 percent), and 91 percent of the 

tagged fish that were detected near any of the collection entrances were first detected at the weir box. 

However, entrance efficiency and retention efficiency of the weir box were relatively low (52 and 24 

percent, respectively), and the number of tagged fish that were collected through the weir box (19 fish) 

was similar to the number of tagged fish that were collected through flume 1/flume 2 (16 fish). If the 

weir box will be considered as a future collection option at Cowlitz Falls Dam, alterations to the flow 

rate and height of the weir crest may be necessary to increase entrance and retention characteristics of 

the device.

The performance of the weir box as a collection device for juvenile Chinook salmon was 

substantially different from the performance of the device when it was tested using juvenile steelhead 

and coho salmon during spring 2013. Weir box discovery efficiency was relatively high for steelhead 

(98 percent) and coho salmon (83 percent). However, all the steelhead and 95 percent of the coho 

salmon that were collected entered the collection system through flume 1/flume 2 rather than through 

the weir box (Kock and others, 2014). These data show differences that can occur between spring and 

summer collection efforts at Cowlitz Falls Dam and identify the importance of testing any new device

across the entire range of collection conditions that occur during the fish collection season. 

The use of tagged fish from two separate studies was instructive because it resulted in a 

substantial increase to the sample size for the study, and also shed light on potential differences in 

tagged fish behavior from two release sites. Inclusion of tagged fish from the Lewis County PUD study 

resulted in an almost five-fold increase to sample size compared to the original number of fish that were 

planned for the evaluation. Comparison of detection records between the two release groups suggested

that few differences existed, although fish from the PUD Boat Launch were released closer to the dam. 

Overall, tagged fish from the Day Use Park releases were smaller than tagged fish from the PUD Boat 

Launch, but this was expected because tagging and release events from the first group were not 

conducted during July when larger fish were being collected (fig. 6). Fish size was similar between 

groups of fish that were tagged in August. We also determined that reservoir travel time was faster for 

the PUD Boat Launch group than for the Day Use Park group, but this also was expected because the 

release site was 2.7 rkm closer to the dam. Tagged fish from the two release sites that arrived in the dam 

forebay had similar residence time and arrival distributions, which indicated that behavior patterns in 

the forebay were similar between groups.
28 

Data collected at the URLC suggest that discovery efficiency was very low (10 percent) and 

none of the tagged fish were detected inside the device. Efforts to increase URLC discovery efficiency 

would be the necessary first step towards improving collection in the device. The tailrace of Cowlitz 

Falls Dam, where the URLC was deployed, is a constricted channel; this can benefit collection efforts 

with the URLC because egress routes for juvenile salmon are limited. However, little is known about 

the horizontal or vertical distribution of juvenile salmon as they move downstream through the tailrace. 

Our data showed that tagged fish moved downstream through the tailrace fairly quickly (median travel 

time = 22.7 min). This indicates the need to position the URLC effectively within the primary migration 

route of juvenile salmon because they are not present in the tailrace for long periods. Future studies to 

describe two- or three-dimensional movement paths of juvenile salmon in the tailrace of Cowlitz Falls 

Dam would likely provide the best information to guide URLC positioning efforts. After discovery rates 

are substantially increased, performance metrics such as entrance efficiency and retention efficiency can 

be used to better understand URLC performance. 

Acknowledgments

Numerous people and entities contributed to this study. Tacoma Power provided funding for the 

project. Matt Bleich was our primary contact with Tacoma Power, and his thoughts and ideas 

contributed to the study design, analysis, and reporting. Logistical support was provided by Tacoma 

Power staff members Heather Daniels, Charles Dueber, and Ross Reichert at the Upper Riffe Lake 

Collector. Lewis County PUD purchased additional transmitters that were used in fish that we 

monitored during the evaluation. We thank John Serl and the staff of the Cowlitz Falls Fish facility for 

their efforts in collecting fish that were tagged for the study. Joe First, and his staff at Cowlitz Falls 

Dam, provided access and support that were necessary for the installation, operation, and maintenance 

of our equipment throughout the study period. Finally, reviews of this report by John Serl, Matt Bleich 

and Noah Adams were greatly appreciated. 

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Publishing support provided by the U.S. Geological Survey

Science Publishing Network, Tacoma Publishing Service Center

For more information concerning the research in this report, contact the

 Director, Western Fisheries Research Center

U.S. Geological Survey

6505 NE 65th Street

Seattle, Washington 98115 

http://wfrc.usgs.gov/
Tobias and others—Evaluation of Two Juvenile Salmon Collection Devices at Cowlitz Falls Dam, Washington, 2014—Open-File Report 2015–1054

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20151054