DWORSHAK DAM AND RESERVOIR
  North Fork Clearwater River, Idaho
 

MAP: Project Lands (75 dpi) (150 dpi) | Dworshak Dam Vicinity (75 dpi) (150 dpi) | General Vicinity Map | Dworshak National Fish Hatchery (75 dpi) (150 dpi)

CONDITION OF IMPROVEMENT: 30 September 2004

PWI NUMBER: 05090

AUTHORIZATION: The project was authorized by Public Law 87-874, 87th Congress, dated October 23, 1962, in accordance with House Document 403. The original name, Bruces Eddy, was changed to Dworshak Dam and Reservoir by Dworshak Dam and Reservoir--Idaho (Public Law 88-96, 88th Congress), in honor of the late Senator from Idaho. Public Law 87-874 authorized generator units 4, 5, and 6 for the powerhouse. Units 5 and 6 were deauthorized in 1990 with Unit 4 deauthorized in 1995.

PROJECT: The project is located in northern Idaho on the North Fork of the Clearwater River, near Orofino and about 35 miles east of Lewiston. The project includes Dworshak Dam, Dworshak Reservoir lands, powerhouse, recreation facilities, wildlife mitigation, and Dworshak National Fish Hatchery.

Dworshak Dam: The project has a straight concrete gravity dam with a structural height of 717 feet, and a crest length of 3,287 feet at elevation 1613. 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, and the 22d highest dam in the world. Only two other dams in the United States exceed it in height.

Dworshak Reservoir: The reservoir has a gross storage capacity of 3,453,000 acre-feet, of which 2,000,000 acre-feet is used for local and regional flood control; and for at-site and downstream power generation. At elevation 1600, the reservoir is 53 miles long, has a surface area of 19,824 acres, and extends into the Bitterroot Mountains. The reservoir provides substantial recreational and wildlife benefits, and transportation for timber.

Powerhouse: The powerhouse has two 90,000-kilowatt generating units and one 220,000-kilowatt generating unit. During initial construction, skeleton bays were constructed for three future 220,000-kilowatt units, but two units (5 and 6) were deauthorized in 1990. Unit 4 was deauthorized in 1995. Power generated through September 1996 was 38.93 billion kilowatt hours.

Dworshak National Fish Hatchery: The Corps constructed Dworshak National Fish Hatchery to mitigate for fishery losses from the construction and operation of Dworshak Dam. Fish mitigation facilities include a fish hatchery with a design capacity for 420,000 pounds of steelhead smolt and 100,000 pounds of resident fish annually, as well as fish collection facilities at the powerhouse. The Dworshak hatchery is the largest steelhead hatchery in the world. The hatchery is operated by the U.S. Fish and Wildlife Service. It was recently expanded under the Lower Snake River Fish and Wildlife Compensation Plan.

Lands: The project contains approximately 50,800 acres. At normal full pool (elevation 1600), the surface area of Dworshak Reservoir is 19,824 acres. There are 30,935.4 acres of project lands surrounding Dworshak Reservoir. These project lands include fee lands that are Federally-owned and managed by the Corps, as well as easement lands managed by the U.S. Forest Service to which the Corps has flowage easement rights. There are 29,318 acres of Corps-managed lands that are utilized for public recreation purposes, wildlife habitat, wildlife mitigation, and log-handling facilities. Recreation opportunities include boating, water-skiing, fishing, developed and primitive camping, picnicking, hiking, and hunting. Major recreation areas include the Visitor Center, Dent Acres, the Freeman Creek unit of Dworshak State Park, and the Three Meadows Group Camp unit of Dworshak State Park. The State of Idaho took over operation of Dworshak State Park in 1989. Boat launching is available at six locations.

Wildlife Mitigation: The greatest loss of wildlife habitat was the winter range for Rocky Mountain elk and the white-tailed deer. To offset this loss, mitigation lands have been developed, and are managed for winter range. The Corps acquired 5,120 acres of additional lands adjacent to project lands, at the confluence of the Little North Fork and the North Fork of the Clearwater River. To date, approximately 9,100 acres are being managed for elk mitigation.

PROGRESS: Dam construction began on July 20, 1966, and the project became operational for flood control in June 1972. Power came online in March 1973. The steelhead fish hatchery began operating in 1970, and its capability has since been expanded. Relocations are finished, and reservoir clearing is 100-percent complete. Three power generating units are in service. A study to determine the impact of greater fluctuation downstream of the dam with the addition of a fourth generating unit was terminated when the Governor of Idaho withdrew support for the plan. This unit is now classified as "inactive."

The development of recreational facilities along the reservoir are complete, and all facilities are operational. A multi-level power intake structure on the upstream face of the dam which duplicates natural river water temperatures downstream to assure the continuance of existing fish runs, is operational. Log-handling facilities were completed in May 1979. Mitigation land acquisition, and the development of a wildlife browse area, is complete.

Wildlife Mitigation: Mitigation for fish and wildlife was per interagency agreement. The construction of Dworshak Dam and the filling of the reservoir resulted in the loss of approximately 15,270 acres of terrestrial habitat. Mitigation efforts have concentrated on one species: the Rocky Mountain elk. This single species concern was voiced by the U.S. Fish and Wildlife Service and the Idaho Department of Fish and Game, who were focused on big game as the principal wildlife asset of the Clearwater Basin. Mitigation planning emphasized winter browse development, primarily to benefit a winter range carrying capacity of 915 elk.

The mitigation goal for winter browse to sustain 915 elk has been met. Since the mitigation effort, significant clearcutting of timber has occurred on the lands surrounding the Corps-managed lands at Dworshak. The resulting loss of thermal cover for elk is important to winter range.

Other species were also impacted due to the construction, but only recently have the agencies and tribes sought additional mitigation. Funding through the Northwest Power Planning Act has allowed for the identification of non-elk habitat and the mitigation of these losses. The Corps will continue to manage the wildlife mitigation areas to produce winter browse.

Fisheries Mitigation: The construction of Dworshak Dam also resulted in the blocking of the anadromous steelhead trout, and the conversion of a river habitat (Clearwater River) to a lacustrine habitat (Dworshak Reservoir). Mitigation for fish losses has resulted in the completion of the Dworshak National Fish Hatchery, constructed and maintained by the Corps, and operated by the U.S. Fish and Wildlife Service.

Prior to the completion of Dworshak Dam, the Corps agreed to stock 100,000 pounds of trout annually in Dworshak Reservoir to mitigate for the loss of angler days in the North Fork Clearwater River. After Dworshak Reservoir was filled, kokanee salmon and smallmouth bass were stocked, and self-sustaining populations became established in the reservoir. The abundance of kokanee salmon in the reservoir prompted fishery managers to recommend substantial reductions in trout stocking levels. The kokanee salmon has become popular with sport anglers, and is now the favored sport species in the reservoir.

Dworshak National Fish Hatchery has only been able to meet its anadromous fish mitigation goals in 7 of the last 20 years. However, three of the successful years would not have been met without help from the National Fish Hatcheries at Kooskia and Hagerman. In 1982, Infectious Hematoppietic Necrosis began to cause severe losses in steelhead trout production at Dworshak National Fish Hatchery. As a result of this disease, fish production at the hatchery has been curtailed. All subsequent resident fish mitigation has been accomplished using fish reared at other hatcheries. An interim measure provided relatively disease-free water from Dworshak Reservoir, in conjunction with the Clearwater Hatchery. The Clearwater Hatchery was constructed as part of the Lower Snake River Fish and Wildlife Compensation Plan. In addition to the Infectious Hematoppietic Necrosis problem, the hatchery is in need of a major rehabilitation, which has been proposed through the Major Rehabilitation Evaluation Report, dated February 1993.

Resident fish mitigation for the Dworshak Project is in a state of flux. A resident fish mitigation reevaluation study, addressing resident fish mitigation needs, will be completed in the mid-1990¿s. This study will address the upcoming change in reservoir level management, as well as issues associated with species stocked in Dworshak Reservoir and their interaction with indigenous species. The results of the study will be used to determine the quantity and species to be stocked for mitigation in the future.

LOCAL COOPERATION: None required.

COST: The total expenditures through September 2006 have been $544,396,214, with $327,482,196 for new work and $216,914,018 used for operation and maintenance.

PHOTOS:

REFERENCES:

Report of the Secretary of the Army on Civil Works Activities for Fiscal Year 2003, Department of the Army Corps of Engineers Extract Report of the Walla Walla District.

Report of the Secretary of the Army on Civil Works Activities for Fiscal Year 2003, Department of the Army Corps of Engineers Extract Report of the Walla Walla District.

Dworshak Dam and Reservoir Final Environmental Impact Statement, US Army Engineer District, Walla Walla. Washington, September 1975.