Federal dam managers are hopeful that a new fish ladder cooling system installed at the Lower Granite Dam will help lower high water temperatures that have stalled and stymied the upstream migration of adult salmon and steelhead over parts of the past three summers.
When water temperatures rise during summer hot spells, adult fish are often reluctant to enter the fish ladder that takes them around the dam. The problem was particularly pronounced last summer when 100-degree weather arrived in June and combined with extremely low flows to raise water temperatures and wipe out most of the sockeye salmon returning to both the Snake River and the upper Columbia River.
Water temperatures persistently above 70 degrees can be harmful, and even lethal, to salmon and steelhead. The U.S. Army Corps of Engineers releases cold water from the depths of Dworshak Reservoir on the North Fork of the Clearwater River each summer to reduce water temperatures in the lower Snake River for the benefit of both juvenile and adult salmon and steelhead. When the 48-degree water from Dworshak joins the Snake River at Lewiston, it sinks and sits beneath a layer of warm water from the Snake as it travels downstream.
At Lower Granite, according to the corps, the fish ladder is fed with water from the top layer of the river. But most of the water below the dam, where fish enter the ladder, is much cooler after it mixes with water that is poured over spillways or pushed through turbines. When the difference between the ladder and the river is more than a few degrees, adult fish will often sit below the dam and wait for the water to cool. The longer they wait, the more susceptible they are to disease and the more of their fat reserves they expend without making progress upriver.
The corps has used pumps to draw deep water from above the dam and funnel it into the ladder during recent hot spells. Over the past year, the corps improved on that fix and spent $1.18 million to install a pair of "intake chimneys" to the front of the dam that siphon cool water from about 70 feet below the surface to various parts of the ladder and the trap.
"This is the permanent system that we expect to help relieve some of the temperature issues this coming summer or anytime we see this unusually hot weather," said Bruce Henrickson, a spokesman for the corps' Walla Walla District.
If successful, the chimneys will also allow fisheries biologists to run a trap on the ladder without interruption. The trap allows biologists to inspect and track various stocks of salmon and steelhead and to capture fall chinook, which are taken to Lyons Ferry Hatchery and the Nez Perce Tribal Hatchery. During extreme hot-water events such as the one last summer, when temperatures exceeded 70 degrees in the Lower Salmon River, the trap is used to intercept endangered adult sockeye so they can be trucked to hatcheries.
When temperatures exceed 68 degrees in the Lower Granite Fish Ladder, trapping is suspended because of the stress it causes to the fish.
"That trap is very important in letting us know what is coming back to the Snake in addition to the fall chinook brood stock collection," said Becky Johnson, production manager for the Nez Perce Tribal Fisheries Division.
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Barker may be contacted at ebarker@lmtribune.com or at (208) 848-2273. Follow him on Twitter @ezebarker.
