15-039 Dworshak cools river temperatures for ESA-listed fish

Published June 30, 2015
AHSAHKA, Idaho – Record high temperatures over the weekend and more hot weather conditions forecasted for the rest of the week have prompted changes in flow operations at Dworshak Dam and Reservoir near Orofino, Idaho.

The National Oceanic and Atmospheric Administration’s (NOAA) Columbia River System Biological Opinion (BiOp) requires the Corps to meet several objectives to enhance ESA-listed fish survival, including maintaining minimum water flows for resident fish and salmon, and releasing Dworshak Reservoir water to maintain lower Snake River water temperatures and help speed juvenile fish downriver to the ocean.

“We are required to maintain water temperatures at Lower Granite below 68 degrees, if possible, using available reservoir-system management methods,” said Steve Hall, Walla Walla District Corps reservoir manager. “Dworshak Reservoir’s near-40-degree water is helping us keep Snake River water temperature just below that limit.”

Yesterday, Snake River temperature on the downstream side of Lower Granite was 67.8 degrees, said Hall.

Water discharges from Dworshak Reservoir were incrementally adjusted over the weekend, up to 13,300 cubic feet per second (c.f.s.), to help cool rising water temperature in the lower Snake River and maintain healthy conditions for migrating salmon and steelhead, said Hall.

“We’re trying to keep the reservoir as full as possible by releasing only enough cold water to meet the Bi-Op requirements,” said Hall. “Yesterday (June 29), we reduced flows to 9,600 c.f.s to adjust for changes in weather and temperatures. Cold-water releases from Dworshak will continue to be adjusted as needed to keep temperatures below the BiOp threshold, while conserving as much water as possible.”

Cold-water releases from Dworshak take about 3 days to reach the downstream side of Lower Granite Dam, where the target temperature gauges are located. Reservoir managers must plan well ahead and make adjustments in releases at Dworshak that will be effective at the time they are needed further down the river.

At this time, Dworshak Reservoir is about 9 feet down from full-pool and will likely be within 13-16 feet of full-pool during the upcoming Independence Day holiday weekend, based on reservoir modeling.

Natural Resources staff note having the reservoir level down a bit can actually be a good thing for visitors.

“As the reservoir lowers, woody debris usually becomes beached along the shoreline, instead of floating around and making boating difficult,” explained Paul Pence, Dworshak’s natural resources manager. “While we like to see the lake full, boating actually becomes easier and safer when the water is down several feet.”


Public Affairs Office

Release no. 15-039