The project was authorized by the Flood Control Act of 1962.
Construction of the dam began in 1966, and the project became operational for flood damage reduction in June 1972. Power came online in March 1973. Three power generating units are in service. A multi-level power intake structure on the upstream face of the dam is used to provide cool water and increased flows to promote salmon and steelhead migrations on the Lower Snake River. Dworshak project also supports the world’s largest steelhead hatchery. Dworshak National Fish Hatchery rears and releases millions of fish annually to supplement natural populations and provide opportunities for recreational fishermen.
This congressionally authorized project includes Dworshak Dam, Dworshak Reservoir lands, powerhouse, recreation facilities, wildlife mitigation and Dworshak National Fish Hatchery. The project has a straight-axis concrete gravity dam with a structural height of 717 feet and a crest length of 3,287 feet at elevation 1,613 Mean Sea Level (MSL). The dam is located on the North Fork Clearwater River at River Mile 1.9. The dam is the highest straight-axis concrete dam in the Western Hemisphere. Only two other dams in the United States exceed it in height.
Dworshak Reservoir has a gross storage capacity of 3,468,000 acre-feet, of which about 2 million acre-feet is used for local and regional flood control; and for at-site and downstream power generation. Since the project became operational in June 1972, it has prevented more than $2.8 million (cumulative nominal $) in local potential flood damages. During FY15, regulation at Dworshak Dam also prevented about $18 million in potential flood damages on the Columbia River. At elevation 1,600 MSL, the reservoir is about 54 miles long, has a surface area of about 20,000 acres and extends into the Bitterroot Mountains. It provides substantial recreational and wildlife benefits. In early July, reservoir drawdown begins to decrease temperatures on the Lower Snake River and support the migrations of anadromous fish such as salmon and steelhead.
The powerhouse has two 100,000-kilowatt units and one 250,000-kilowatt unit – the largest hydro-electric generator in the U.S. Army Corps of Engineers’ (USACE) inventory. The powerhouse has a 450-megawatt total rated capacity. During fiscal year 2017, more than 1.35 billion kilowatt hours of electricity were produced.
Fisheries & Wildlife Mitigation
The filling of the reservoir resulted in the loss of about 15,000 acres of terrestrial habitat. The greatest loss of wildlife habitat was the winter range for Rocky Mountain elk and white-tailed deer. To offset this loss, 7,000 acres of mitigation lands have been developed and are managed for winter range.
The construction of Dworshak Dam resulted in blocking anadromous steelhead trout and converting a river habitat to a reservoir. Mitigation for fish losses led to completion of the Dworshak National Fish Hatchery. The hatchery was constructed and is maintained by USACE. It is operated by the U.S. Fish and Wildlife Service and Nez Perce Tribe. The Dworshak hatchery is the primary producer of Clearwater B-run steelhead, highly sought by anglers for their large size when returning as adults. After Dworshak Reservoir was filled, kokanee salmon and smallmouth bass were stocked and became self-sustaining. Sterile rainbow trout are stocked annually to provide a put and take fishery that cannot interbreed with native cutthroat present in the tributary streams. The abundance of kokanee salmon and smallmouth bass make it a favored area for sport fisheries. Dworshak reservoir has produced multiple state record smallmouth bass.
The project contains about 50,800 acres. At normal full pool, the surface area of Dworshak Reservoir is about 20,000 acres. There are about 30,000 acres of project lands surrounding the reservoir used for public recreation purposes, wildlife habitat and wildlife mitigation. These include federally owned lands managed by USACE, as well as easement lands managed by the U.S. Forest Service to which USACE has flowage easement rights. This also includes a recreation lease to the Idaho Department of Parks & Recreation. Recreation opportunities include boating, water-skiing, ATV trails, fishing, developed and primitive camping, picnicking, hiking and hunting. Boat launching is available at six locations. Visitation to Dworshak during fiscal year 2020 was about 314,935.
About 55 Walla Walla District employees work at the Dworshak project. They serve as electricians, mechanics, a forester, utility workers, heavy equipment operators, park rangers, biologists, environmental resource specialists, administrative staff, engineers and maintenance workers. Together, they ensure the safe and continuous operation of the project.