AHSAHKA, Idaho – Due to an intensifying regional heatwave, Dworshak Dam will be further increasing their releases to support flow augmentation intended to keep the tailwater of Lower Granite at or below 68° F.
Dworshak Dam releases will increase from 1,500 cubic feet per second (cfs) on Tuesday, June 22, to 12,400 cfs by Wednesday afternoon. The river will rise approximately 2 feet during the flow changes Tuesday night, and could rise an additional 0.5 feet Wednesday afternoon. The river level is then expected to remain in the same range, with a slight lowering, through the end of the week.
Between the hours of 7 p.m. and 11 p.m. on Tuesday, releases will increase from 1,500 cfs to 7,400 cfs. On Wednesday, releases will further increase from 7,400 cfs at 10 a.m. to 9,400 cfs (maximum powerhouse capacity) at 12 p.m. From 12 p.m. to 2 p.m. 3,000 cfs of spill will be added. The total releases from Dworshak will total 12,400 cfs by 3 p.m. on Wednesday. Releases will remain constant at 12,400 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.
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 65° F, and the natural river temperatures in the Clearwater River at Orofino and in the Snake River at Anatone are approximately 63 and 68° F respectively. With natural river temperatures at 68° F and the heatwave in the 10-day forecast intensifying, increased releases of cooling water from Dworshak are necessary as flow augmentation begins.
Forebay elevations in Dworshak Reservoir will change due to the increased releases needed during the early-season heatwave. The reservoir elevation as of June 22 is 1,597 feet. The reservoir elevation will begin a steady decrease Tuesday night 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 feet. 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/.