17-030 Dworshak Dam discharge flows to decrease Saturday night, then increase on Monday - Flow decrease and increase to help reduce flooding impacts and give hatcheries an opportunity to release juvenile fish smolts

Published March 17, 2017
AHSAHKA, Idaho – To help reduce downstream flooding impacts, and to give fish hatcheries an opportunity to release juvenile fish smolts, Dworshak Dam discharge flows are planned to be reduced from the current 12,500 cubic feet per second (cfs) to 7,500 cfs beginning at midnight on Saturday, March 18, according to U.S. Army Corps of Engineers officials. At noon on Monday, March 20, flows are planned to begin increasing 2,000 cfs per hour until flows reach 25,000 cfs at about 10 p.m. Monday night.

The Saturday night flow reduction will lower the downstream water surface elevation in the Clearwater River by about a half foot. The reduced flows on Sunday and Monday will reduce the forecasted peak flow on the Clearwater River to minimize local flood impacts in Ahsahka, Idaho and Spalding Idaho.

The reduction will also provide an opportunity for the fish hatchery managers at the Dworshak National Fish Hatchery and Clearwater Hatchery just below Dworshak Dam to release Chinook juvenile fish smolts into the river to begin their migration to the ocean with lower Total Dissolved Gas (TDG). When water is released from the dam, gasses can be absorbed into the water. High TDG levels can be unhealthy for fish.

The flow increase on Monday afternoon and evening will increase the river surface elevation about one foot. The increase will result in high water levels and very high velocities in the North Fork Clearwater River.

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 works with regional water managers, other agencies and tribes, and fish managers and hatcheries in joint efforts to keep total dissolved gasses below the Idaho State maximum threshold, when possible. 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.

The Corps continues to accommodate high Dworshak reservoir inflows due to heavy precipitation and snowmelt, and to monitor river basin conditions, weather forecasts, and impacts on fish. Discharge flows may also be increased or decreased again in coming days and weeks. 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.

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.


Public Affairs Office

Release no. 17-030