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Dworshak Dam and Reservoir

Dworshak Dam
This congressionally authorized project includes Dworshak Dam, Dworshak Reservoir lands, powerhouse, recreation facilities, wildlife mitigation and Dworshak National Fish Hatchery. Since 1972, $2,836,000 in potential flood damages have been prevented by the project. 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 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.

Project Information

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Dworshak National Fish Hatchery was constructed by the U.S. Army Corps of Engineers to mitigate fish losses associated with the construction and operation of Dworshak Dam. The fish hatchery started operation in April 1969. A Memorandum of Understanding was signed by the Corps and the Fish and Wildlife Service in 1969 authorizing the Fish and Wildlife Service to operate Dworshak National Fish Hatchery with reimbursable funding from the Corps. Since 1969, Fish and Wildlife Service has operated Dworshak National Fish Hatchery and has endeavored to meet the "mitigation goal" of maintaining the North Fork of the Clearwater River "B" run steelhead and producing resident fish for stocking Dworshak Reservoir.

 

Dworshak National Fish Hatchery Complex is located at the confluence of the North Fork and mainstem Clearwater River in Ahsahka, Idaho, 3 miles west of Orofino, Idaho. The Complex consists of Dworshak National Fish Hatchery, Idaho Fishery Resource Office, Idaho Fish Health Center and the Kooskia National Fish Hatchery located at Kooskia, Idaho (managed by the Nez Perce Tribe).  Dworshak hatchery production is co-managed by the U.S. Fish and Wildlife Service and the Nez Perce Tribe.

Authorization
The project was authorized by the Flood Control Act of 1962.

Progress
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. 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 promote the continuance of existing fish runs, is operational.
Log-handling facilities were completed in May 1979. The facilities were used by the timber industry through the mid-1980s when development of back-country roads provided more cost-effective transportation routes. Mitigation land acquisition and the development of a wildlife browse area is complete.

Dworshak Dam
This congressionally authorized project includes Dworshak Dam, Dworshak Reservoir lands, powerhouse, recreation facilities, wildlife mitigation and Dworshak National Fish Hatchery. Since 1972, $2,836,000 in potential flood damages have been prevented by the project. 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 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.

Reservoir
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. 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. The reservoir provides substantial recreational and wildlife benefits.

Generators
The powerhouse has two 90,000-kilowatt units and one 220,000-kilowatt unit – 400 megawatt total powerhouse capacity. During fiscal year 2011, 2.34 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, mitigation lands have been developed and are managed for winter range. About 7,000 acres were purchased are managed specifically for elk mitigation.

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, constructed and maintained by the Corps and operated by the U.S. Fish and Wildlife Service. The Dworshak hatchery is the largest steelhead hatchery in the world. After Dworshak Reservoir was filled, kokanee salmon and smallmouth bass were stocked and became self-sustaining in the reservoir. The abundance of kokanee salmon in the reservoir has made it a favored sport species in the reservoir.

Lands
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, wildlife mitigation and log-handling facilities. These include federally owned lands managed by the Corps, as well as easement lands managed by the U.S. Forest Service to which the Corps has flowage easement rights. Recreation opportunities include boating, water-skiing, fishing, developed and primitive camping, picnicking, hiking and hunting. Boat launching is available at six locations. Visitation to Dworshak during fiscal year 2009 was 146,483.

People
About 45 Walla Walla District employees work at the Dworshak Project. They serve as electricians, mechanics, welders, 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.

Budget
During fiscal year 2011, total expenditures were $11,241,215 for the Dworshak Project.

References
Annual Report of the Chief of Engineers on Civil Works Activities, Fiscal Year 2011, Department of the Army Corps of Engineers, Extract Report of the Walla Walla District.
General
River mile - 1.9
Drainage area - 2,440 square miles
Effective hydraulic height - 632 ft
Maximum structural height - 717 ft
Overall length at crest - 3,287 ft

Streamflow, cubic feet per second (cfs):
Minimum of record - 250 cfs

Standard project flood peaks:
Mean annual - 5,727 cfs
Winter - 160,000
Spring - 120,000
Maximum of record - 100,000
Probable maximum flood - 411,000

Streamflow, acre-feet:
Minimum annual - 2,157,000
Mean annual - 4,100,000
Maximum annual - 6,680,000

Project design discharges, cfs:
At pool elevation 1445 - 32,290
At pool elevation 1600:
Spillway – 150,000
Outlets – 40,000
Total at elevation 1600 – 190,000
220,000

Tailwater elevations:
Minimum, discharge 1,000 - 968 cfs
Maximum, discharge 150,000 - 1,003.4 cfs
First power online - 1 March 1973

Estimated Cost
1 July 1973 - $302,000,000

Reservoir
Elevations, feet:
Maximum design pool - 1605
Maximum operating pool - 1600
Normal operating range - 1600 to 1445
Storage capacity, acre-feet:
Gross - 3,468,000
Usable, flood control and power - 2,016,000
Length at elevation 1600 - 53.6 miles
Shoreline length - 175 miles

Surface areas, acres:
At elevation 1600 - 17,090
At elevation 1445 - 9,050

Recreation sites, number:
Initial - 7
Ultimate - 19

Non-Overflows
Type - Concrete gravity
Crest elevation - 1613
Deck width - 44 ft
Concrete volume - 6,500,000 cubic yards
Upstream slope - Vertical
Downstream slope - Vertical above elevation 1560, 1 on 0.8 below
Elevators, number - 3

Spillway
Type - Gate controlled, with stilling basin
Gates:
Type - Tainter
Size, width by height, feet - 50 x 56.4
Number - 2
Crest elevation - 1545
Crane capacity - 150 tons

Permanent Outlet Works
Water passages:
Number - 3
Type - Conduit
Size - 12 x 17 ft

Gates, type and number:
Tainter - 3
Tractor (emergency) - 1
Intake centerline elevation - 1362

Powerplant
Initial installation:
Number of units - 3
Nameplate rating, kilowatts:
Two, each – 90,000
One – 220,000
Total – 400,000
Ultimate installation:
Number of units - 6
Nameplate rating, KVA:
Two, each – 90,000
Four, each – 220,000
Total – 1,060,000
Powerhouse length - 428 ft
Turbine type - Francis

Turbine ratings, horsepower:
Small units - 142,000
Large units - 346,000

Synchronous speed, revolutions per minute:
Small units - 200
Large units - 128.6

Distributor centerline elevations:
Small units - 969
Large units - 975

Spacing, feet:
Small units - 47
Large units - 65

Penstock diameters:
Small units - 12
Large units - 19

Penstock intake elevations:
Small units - 1,420.68
Large units - 1,412.70
Gross head - 632 ft
Rated head - 560 ft
Minimum head - 477 ft

Crane:
Number - 2
Type - Bridge
Capacity, each - 350 tons

Relocations
Roads, miles:
Highway districts - 2.7
County - 24.3
Bridges, number - 2


Fish Hatchery, Steelhead
Attraction water pump capacity – 255 cfs
Capacity, adult size – 6,000 cfs

Yearly fingerling release:
Estimated number – 3,360,000
Estimated total weight – 420,000 lbs

Water Data

 

Contact Us

Dworshak Dam and Reservoir
North Fork Drive
PO Box 48
Ahsahka, ID 83520-0048
Phone: 208-476-1261

Dworshak Recreation

Dworshak