The Walla Walla District of the U.S. Army Corps of Engineers is increasing releases from Dworshak Dam to match inflow into the reservoir, with a goal of maintaining the reservoir at its full pool.
Dworshak Dam, on the North Fork Clearwater River in Idaho, impounds water for a 402 MW hydroelectric powerhouse.
Before the flow increases, Dworshak Dam was releasing 1,600 cubic feet per second. Beginning the evening of June 30, Corps personnel are increasing flows to be in the range of 3,000 to 4,000 cfs. Dworshak reservoir is less than 0.5 foot from full pool, and the increased discharge will keep the reservoir within 1 foot from full pool.
This operation is expected to result in the Clearwater River near Peck increasing by about 1 to 1.5 feet. The rate of change in downstream river stage limit of 1 foot per hour, as measured at the United States Geological Survey Clearwater River Near Peck, will not be violated due to project operations.
The current operation will result in total dissolved gas 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 TDG below the Idaho State maximum threshold of 110%, when possible.
While the increased discharge is intended to balance full pool, further increases may be required in the upcoming week for the initiation of temperature augmentation. The goal of temperature augmentation is to keep the tailwater of Lower Granite Lock and Dam at or below 68 degrees Fahrenheit to support fish populations. Currently, Lower Granite’s tailwater is about 63 F. The natural river temperatures in the Clearwater River at Orofino and in the Snake River at Anatone are about 63 F and 65 F, respectively.
With temperatures in the region forecasted to rise, the natural river temperatures will increase. Releases of cooling water from Dworshak Dam help offset the natural river temperatures, which may be required starting in the first full week of July. For the remainder of the summer, outflows from Dworshak Dam will vary to meet the needs of temperature augmentation at Lower Granite, with Dworshak Reservoir drafting close to 80 feet from full pool by the end of September.
