AHSAHKA, Idaho – Dworshak Dam discharge flows were reduced last night to reduce flooding impacts in Clearwater County, Idaho, and downstream, according to officials of the U.S. Army Corps of Engineers Walla Walla District. While discharge was reduced last night, it may also be increased or decreased again in coming days and weeks.
Discharge was reduced from 22,500 cubic feet per second (cfs) to 12,500 cfs. The flow reduction lowered downstream water surface elevation in the Clearwater River by approximately one foot. For flood risk reduction, Dworshak discharge flows had been managed to 22,500 cfs since March 12 through late yesterday to accommodate high reservoir inflows due to heavy precipitation and snowmelt. February precipitation in the North Fork Clearwater River basin was 214 percent of normal.
Water surface elevations on the Clearwater River are expected to fluctuate during the next several weeks. Additional increases or decreases may be necessary as conditions change.
For safety, the public is advised to be aware of danger associated with fluctuating river flows and elevations. Outflow water is deep, cold and fast, so extreme caution should be used near river banks. 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 up or down in water elevation and volume of flow. Current Dworshak water-management conditions can be viewed on the Walla Walla District website at www.nwd-wc.usace.army.mil/nww/rreports.htm.
Regional water managers are working to control discharge flows from the reservoir into the North Fork of the Clearwater River to meet seasonal flood-risk-management requirements and balance flows with impacts on fish in the river and downstream fish hatcheries. The Corps continues to monitor river basin conditions, weather forecasts, and impacts on fish.
The Corps works with regional water managers, other agencies and tribes, and fish managers and hatcheries in joint efforts to keep total dissolved gasses (TDG) below the Idaho State maximum threshold, when possible. When water is released from the dam, gasses can be absorbed into the water. High TDG levels can be unhealthy for fish.
In early March, the Corps sent a team to adjust TDG removal equipment at the Dworshak National Fish Hatchery operated for the Corps by the U.S. Fish and Wildlife Service and the Nez Perce Tribe. The Corps team is also measuring TDG in the river and in the hatcheries, including monitoring TDG in hatchery raceways.
This year, Dworshak Powerhouse Unit 3 is out of service from September 2016 through mid-2017 and is unable to pass water from the reservoir until it goes back into service. The 220,000-kilowatt generator is capable of passing 5,600 cfs through the powerhouse. Units 1 and 2 combined pass 4,800 cfs. Water being passed through the Powerhouse units contain less total dissolved gasses than water spilled from higher up the dam. The dam has three Powerhouse units.
Release no. 17-028