Salmon and other fish factor into every decision for Snake River dams
Story and photos by RYAN HALL | RURAL MONTANA EDITOR
Protecting adult salmon has been a consideration at the lower Snake River dams since they were built, with a fish ladder included in the construction of each one. Later, juvenile fish protection and mitigation factors were added, helping ensure that both young and adult salmon can complete their migration and spawning routes.
Not only do the fish ladders see thousands of fish use them daily during peak runs, but juvenile fish are bypassed around dams, and spillage and turbine use are optimized to protect both young and adult fish. Thousands of fish each season are also researched and studied at the dams.
“We don’t make a decision without considering fish,” said Brian Vorheis, operations project manager for Ice Harbor Lock and Dam.
Rob Lustig, operations project manager for Lower Granite Lock and Dam, said that as the first dam juvenile fish encounter on the lower Snake River, and the last dam adult fish encounter, Lower Granite is home to upwards of a dozen research projects during fish runs.
The National Oceanic and Atmospheric Administration (NOAA), Idaho Fish and Game, the Nez Perce Tribe, United States Geological Survey and many other agencies send people to the multiple research facilities built at the dam. Adult and juvenile fish are measured, weighed and tagged in hopes of better understanding the dams’ impact on their numbers, and how mitigation measures are working.
“It is key for research and management,” said Elizabeth Holdren, Lower Granite Lock and Dam Supervisory Fish Biologist.
Juvenile fish
The dams were built with adult fish migration in mind, primarily steelhead trout and three salmon species: Chinook, sockeye and coho. A focus on juveniles was added later, with dam modifications and new programs aimed at aiding their survival.
Paul Ocker, chief of operations and maintenance for the Walla Walla District of the U.S. Army Corps of Engineers, said the emphasis has shifted more to juvenile fish, especially in light of recent NOAA biological opinions, which guide dam operations, and the recent court settlement reached by the White House with two states and four tribes from outside Montana.
That settlement, along with biological opinions calling for increased spill — or diverting water away from the powerhouse and either through or over the dam — has resulted in operational changes. The changes from the settlement began with the spring salmon run that started April 1, and ran through June 20.
“It is the desire of the environmental groups, and the plaintiffs, to have all juvenile fish pass by a non-powerhouse route,” Ocker said.
The powerhouse route has a survival rate of around 90 percent, with less than 10 percent of all fish using that route to pass the dams on the lower Snake River. Newer turbines, which have been installed at Ice Harbor Dam, are showing survival rates of 96 to 98 percent.
There are several ways for juvenile fish to avoid the powerhouse, such as being diverted by fish screens to a bypass channel. A majority of the diverted fish are barged downriver to avoid passing over or around any other dam downstream.
The Army Corps of Engineers barges millions of fish each year, beginning at Lower Granite Dam, and dropping the fish off below Bonneville Dam. Throughout the journey, fresh water from the river is pumped through the holding tank so that fish can still olfactory imprint to the river to be able to find their way back as adults, Holdren said. The survival rate for barged fish is about 98 percent — the highest of all the routes.
Other methods of avoiding the powerhouse include going through a traditional spillway or a removable spillway weir.
Ocker said that each dam has a fish passage plan that dictates how water is spilled among the 8-10 spill bays, how much water must be spilled and what turbines to operate and in what order, as flow allows.
Two main elements of the recent settlement agreement are that spillage comes before power during the salmon runs, and that the maximum spillage is based on the total dissolved gas (TDG) generated in the river as a result of the dams.
The first element is fairly straightforward, the dams will run one turbine at minimum generation, typically requiring about 10,000 cubic feet per second (CFS) of water, then spill the rest until they hit the minimum cap in the agreement — about another 110,000 CFS. At that point, any remaining water can be used to create additional power, Voorheis said.
Running water through the powerhouse does not increase the natural TDG in the river, but spilling does due to pressure changes and other factors involved with a massive amount of water dropping a significant distance.
The concern with TDG is that too much of it can cause gas bubble disease, similar to the bends in human divers, and cause the formation of bubbles in the fins, eyes, gills and cardiovascular system of fish.
“An agency would normally restrict total dissolved gas to 110 (percent) caused by spill,” Ocker said. “Biological opinions have gone up to 120 (percent in recent years). The settlement calls for 125 (percent).
“Some agencies don’t like getting above 110 (percent),” Ocker added. “It depends on who you talk to as to what’s an acceptable level.”
When asked if he and other Army Corps biologists have an opinion on what is safe for fish, Ocker said, “Yes, we all have our opinion, but as the Corps of Engineers, we are required to balance what the people need and what the environment needs.”
Holdren echoed that sentiment. She said that she has an opinion about allowing TDG to reach 125 percent based on years of research and experience, but since this is the first year there is no scientific data available yet.
The device to measure the TDG is anywhere between seven-tenths of a mile from the dam at Lower Granite to 3.6 miles downstream from Ice Harbor Dam. On-site biologists and operations officials at those two dams said they could not speculate what the TDG was at the point the spilled water hits the river, but said it was reasonable to expect it to be higher than it would be at the point it is measured.
Another concern with fish utilizing the spillway is the pressure change it introduces. Most salmon prefer to be in the top 20 feet of the water column, but the traditional spillway gates are 53 to 57 feet below the surface. This forces fish to swim to those depths, at pressures of up to 25 pounds per square inch (PSI). Once they swim through the gate, they exit the dam down the spillway and come out in the river below.
“They go from 25 PSI to atmospheric pressure instantly,” Lustig said.
That can have negative impacts on the fish, he said. Those fish can become disoriented and rise to the top of the water column, increasing the likelihood of predation by other fish or birds, such as pelicans. Predatory birds, except for endangered raptors, are hazed from the immediate area of the dams by water cannons, sounds of gunshots played over speakers and wires stretched across the river.
Fish that pass through the removable spillway weir (RSW) do not experience much pressure change, but that gate is much more expensive, and is incapable of allowing higher flows of water through the dam in its normal configuration. During high-flow flood events, the RSW is designed to be removed until the flood event is over.
Adult fish impacts
The new operational changes as a result of the settlement also have an impact on adult fish returning upriver to spawn. While the fish ladders have proven effective, the increased spillage and resulting current changes has slowed migration, according to Holdren.
Both Holdren and Ocker said the increased spills have caused eddies and disrupted the attraction flow designed to draw fish to the ladders. Each dam has a specific turbine start order so that the entrance to the fish ladder features a similar flow to a naturally flowing river, and attracts fish to it, regardless of the number of turbines producing power.
“We need attraction for adults,” Holdren said. “The whole powerhouse is operated for attraction.”
Each ladder takes 100 “steps,” or small pools, for the fish to pass over the dam.
“If we spill too much, they can have trouble with finding the ladders,” Ocker said.
Holdren noted that the spill pattern had to be adjusted at Little Goose Dam because fish would stop and cluster together, rather than entering the ladder. Other dams have seen slowed migration because of an altered attraction flow.
Impact of the dams
Ocker said that returning fish numbers have gone up and down for decades, from the time the first dam was built to now. The numbers are determined by a person sitting at a window looking into the fish ladder and physically counting them and identifying the species.
Dr. Chris Peery, fish biologist in the Technical Support Branch of the Army Corps of Engineers, acknowledged that the dams do have an impact on salmon population, but said its primarily on the juvenile side, and he doesn’t believe that’s the only determining factor in overall population numbers.
“You can’t say there is no impact from the dams on fish,” Peery said. “The question then becomes is juvenile survival rate the bottleneck in the salmon population?”
He noted that salmon populations in dammed rivers, and undammed rivers such as the Yukon River, are similar, and show similar ebbs and flows. Juvenile salmon mortality is typically high, regardless of the presence of dams.
“Most fish die in the ocean,” Peery said, noting that salmon population numbers can be linked to ocean temperatures and other oceanic conditions. “They tend to fluctuate, and we now know with ocean conditions.”
Another concern is ocean fishing, which is basically unregulated more than 200 miles from shore, according to Peery.
“It’s a free for all out there. Some nations fish 12 months a year, 24/7,” Peery said. “For all the efforts on the river trying to produce more salmon, a lot of that is just going out to subsidize ocean fishing.”
He said some environmental groups claim that taking out the dams would increase salmon populations by 150 percent; however, a NOAA study showed the expected improvement would be just 14 percent in adult returns.
“I don’t see how you can get to 150 percent improvement from the data I’ve seen on juvenile survival and adult return survival,” Peery said. “I think there’s some wishful thinking on their part.”
Republished with permission from Rural Montana Magazine, the magazine of Montana’s Electric Cooperatives Association (MECA).
Read this article in the August edition of Rural Montana: Rural Montana Magazine | August 2024 (PDF)
