21-033 Dworshak Dam to increase releases for flow augmentation

Published June 21, 2021

AHSAHKA, Idaho – Dworshak Dam releases will increase from 1,500 cubic feet per second (cfs) on Tuesday to the maximum powerhouse capacity of 9,400 cfs by Thursday night. The river will rise approximately 0.5 feet during the flow changes Tuesday night. The river level is then expected to remain in the same range through the end of the week. This increase in releases is being made to support flow augmentation intended to keep the tailwater of Lower Granite at or below 68° F.

Between the hours of 7 p.m. and 11 p.m. on Tuesday, releases will increase from 1,500 cfs to 5,300 cfs. On Wednesday, releases will increase from 5,300 cfs at 7 p.m. to 7,400 cfs at 10 p.m.. Between the hours of 7 p.m. and 11 p.m. on Thursday, releases will increase from 7,400 cfs to 9,400 cfs. Releases will remain constant at 9,400 cfs through Friday and will be monitored and adjusted daily to meet downstream requirements. Water managers will continue to assess and model local and regional river temperatures and weather patterns in order to make the best use of the water in Dworshak Reservoir during what may be a dry summer.

As river temperatures increase in the summer months, cooling water from Dworshak Reservoir can be released to provide relief in the Snake River. Operations to provide cooling water are referred to as flow augmentation. The specific target of flow augmentation is to keep the tailwater of Lower Granite at or below 68° F. Currently, Lower Granite’s tailwater is approximately 64° F, and the natural river temperatures in the Clearwater River at Orofino and in the Snake River at Anatone are approximately 62 and 67° F respectively. With natural river temperatures nearing 68° F and a heatwave in the 10-day forecast, flow augmentation will begin the evening of Tuesday, June 22.

Forebay elevations in Dworshak Reservoir will change due to the increased releases needed during the early-season heatwave. The reservoir elevation as of June 21 is 1,596 feet. Inflows will gradually decrease as releases increase, causing the elevation to hold relatively steady near 1,597 feet through Thursday. The reservoir elevation will begin a steady decrease on Friday leading to a tentative elevation near 1,590 feet by the end of the month. With the potential for further releases needed over the weekend if the heatwave continues, the elevation by July 5 may near the range of 1,585. However, water managers will continually reassess for optimal operation.

The rate of change in downstream river stage will remain below 1 foot per hour as measured at the United States Geological Survey (USGS) Clearwater River Near Peck, ID (gage #13341050).

The current operation will result in total dissolved gas (TDG) remaining below 110%. The Corps will continue to work with regional water managers, other agencies, tribes, and fish managers and hatcheries in joint efforts to meet reservoir objectives and keep total dissolved gas (TDG) below the Idaho State maximum threshold of 110%, when possible.

For safety, the public is advised to be aware of the danger associated with fluctuating river flows and elevations. The river at this time of year is deep, cold and fast, so extreme caution should be used near riverbanks. Boaters, anglers and other people using waterways both in Dworshak Reservoir and below the dam on the Clearwater River are advised to be alert to changes in water elevation and volume of flow. Current Dworshak water-management conditions can be viewed on the Walla Walla District website at https://www.nwd.usace.army.mil/CRWM/Water-Control-Data/Project-Data/.


Release no. 21-041