Recent hot weather and more in the forecast prompted regional fisheries and water managers to start annual releases from Dworshak Dam designed to cool temperatures in the lower Snake River.
Officials at the Army Corps of Engineers began raising flows leaving the dam Friday. Discharge from the dam had been about 5,300 cubic feet per second, but will bump up to about 9,450 cubic feet per second, according to a news release from the agency.
Each summer the agency, in cooperation with regional salmon managers, releases about 2 million acre-feet of water from the reservoir. The goal is to protect salmon and steelhead by lowering water temperatures in the Snake River. By the end of the season, about mid-September, the elevation of Dworshak Reservoir typically drops 80 feet.
“We are required to maintain water temperatures at Lower Granite (Dam) below 68 degrees, if possible, using available reservoir-system management methods,” said Johnathan Roberts, a reservoir regulator for the Corps at Walla Walla. “It takes about three days for cold-water releases from Dworshak to reach the downstream side of Lower Granite Dam, where the target temperature gauges are located. So, we have to plan well ahead and make adjustments at Dworshak that will be effective at the time we’ll need them further down the river.”
On Friday, the Snake River on the downstream side of Lower Granite measured 66.7 degrees.
“With hot weather forecasted to continue, water temperature at Lower Granite is likely to soon exceed 68 degrees if not regulated, creating conditions in the reservoir system that are unhealthy for (Endangered Species Act)-listed fish,” Roberts said. “Dworshak’s 43-degree outflows make a big difference in water temperature there and further down the Snake River.”