Update: Chelan PUD has announced its study findings on November 29, 2023. More data was revealed, showing that about 45% of the juvenile salmon chose the juvenile bypass system, with a 100% survival rate. The remainder went through the powerhouse's 11 generating units; 14% passed through units 1 and 2 with 98.7% survival rate and 37% passed through units 3-10 with 93% survival.


Rocky Reach Dam Sees 93% Chinook Salmon Survival Rate

Results from a month-long Chelan PUD study show an improvement in fish survival through the Rocky Reach Dam. 

The combined adult and juvenile survival rate was 93.54 percent, which is better than the 91 percent standard required in the Rocky Reach Habitat Conservation Plan   

Chelan County PUD senior fisheries biologist Lance Keller gave PUD commissioners an update on the study Monday. 

A contractor was put in place In October 2022 to help study juvenile Chinook salmon swimming downstream through Rocky Reach Dam, with plan design lasting into February 2023. 

The study was delayed a couple of years from 2021 to 2023 so that internal machinery at the dam could be repaired so there would a “fully representative operation powerhouse” up and running by the time the test took place in 2023. The work involved Trunnion bushing repairs in Units C1-C7 at the dam. 

The dam study used special detection systems to monitor salmon traffic

Approval of the study plan was given by the HCP Coordinating Committee on April 7, 2023. 

The Coordinating Committee consists of representatives of the Washington State Department of Fish and Wildlife, U.S. Fish and Wildlife, National Oceanic and Atmospheric Administration, Douglas County PUD, Confederated Tribes of the Colville Reservation, Confederated Tribes and Bands of Yakima Nation and Chelan County PUD District 1.  

The study was threatened by low initial spring runoff from mountain snow into the river in April, but water flow recovered in May to levels that allowed it to be conducted. 

As part of the study, test fish were released below Wells Dam (the Douglas County PUD dam to the north of Rocky Reach Dam) and monitored on how they approached Rocky Reach and passed through the dam.  

Detection equipment was deployed to monitor every possible route that a fish could take through the area. It included 12 detection receivers deployed on the water in the boat restriction zone of the dam in the forebay as well as well as upstream a bit. There were also 12 shore-based detection receivers at the base of the dam itself. 

Green and red circles indicate detection equipment used to monitor fish movement north of Rocky Reach Dam - Image from Chelan PUD
Green and red circles indicate detection equipment used to monitor fish movement north of Rocky Reach Dam - Image from Chelan PUD

Study fish were collected, transported, tagged and released between April 25 and May 25 for a one-month study. The last detection was on June 11.  

The one-month-long study encompassed about 82 percent of the juvenile out migration of the yearling Chinook past Rocky Reach in 2023, which Keller called a good number.  

Collectively about 1,130 yearling Chinook were released in the study with 18 replicates. 

The fish took an average of 3.8 days to pass through the area.

Travel time estimate for the fish from near Wells Dam  to the Rocky Reach forebay averaged 90.8 hours, ranging from 17.8 hours to 933.9 hours. 

Converting those numbers into days, the average was 3.8 days and ranged between 3/4 of a day to 38.9 days. 

Keller said the fish that took 39 days survived all the way through the Rocky Reach reservoir and also through the Rocky Reach Dam, which he called "pretty good survival conditions". 

PUD Commissioner Randy Smith joked that the fish were displaying human tendencies. “It is obvious that fish are somewhat like humans, some are more confused than others,” Smith said.  

Keller said the big takeaway was the 93.78 percent survival rate for juvenile Chinook salmon.  

"This in the highest junior survival estimate we have measured at Rocky Reach since our HCP studies initiated in 2003," said Keller. "The district needs to be extremely proud of this. This is trending in the right direction." 

The adult survival rate moving in the opposite direction upstream was 99.74 percent, as 191 of 192 fish made it all the way from Chelan PUD's Rock Island Dam to the south, through Rocky Reach Dam, and then through the Douglas County PUD Wells Dam to the north. 

The study showed a combined adult and juvenile survival rate of 93.54 percent. 

The PUD plans to ask the HCP committee to memorialize the results with a statement of agreement. The next spring confirmation study will be in 2033.

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