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John Werner is the winner!! He is the winner for the second week in a row with just one clue.

Dworshak Dam is the answer to our 15th week of a feature to celebrate Orofino's 100th birthday and the Bicentennial of the Lewis and Clark Corps of Discovery trek through Clearwater County.

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According to information from the Dworshak Dam Visitors Center, the dam located on the North Fork of the Clearwater River was authorized for construction in October 1962. At the time, it was called Bruce's Eddy Dam. Its purposes were flood control, hydropower generation and recreation. Ten years after his death, it was renamed for Idaho's former U.S. Senator Henry C. Dworshak who was instrumental in obtaining authorization and funding for the project.

The first task for construction was to build a diversion tunnel for the North Fork so workmen could access the bedrock. The tunnel was 1,722 feet long and 40 feet in diameter. A fish trapping facility was installed at the base of the tunnel outlet channel and workers were positioned inside to count the Chinook and steelhead as they passed through.

Estimated cost of the seven year project was $327 million (1970 dollars). Thirteen million tons of aggregate were required, all of high quality and high-grade rock. A rock quarry downstream from the left abutment was chosen as source for the hornblende biotite quartz diorite gneiss which had been determined the best and cheapest place to get the material. One of the most stringent requirements of the U.S. Army Corps of Engineers in building the dam was having the temperature of the concrete at 45 degrees for one hour after the pour. The contractor, Dworshak Dam Constructors, developed a special refrigeration system.

Work went on 24-hours per day, 365 days per year for 4 1/2 years just to pour the concrete for the dam. The first bucket of concrete was poured on June 22, 1968 and the last bucket on Jan. 24, 1973. There is a total of 6,626,645 cubic yards of concrete. One of the most dramatic features of the construction was the cableway system designed to place concrete at specific sites on the dam. The dam was built in monoliths to minimize potential failure due to crackage and leakage. Any problem within a monolith would stay within that monolith, not compromising the entire structure. In total there are 51 monolith blocks.

In addition to the dam, a powerhouse, fish hatchery, recreation sites, access roads, Dent Bridge and Grandad Bridge were built. The new facility was dedicated June 15, 1973.

Take the time to stop by the Visitors Center and learn more about the history and construction of Dworshak Dam.

Photo: Dworshak Dam Powerhouse from the top of the dam.

Monday: It is made of native rock.

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Window on the Clearwater
P.O. Box 2444
Orofino, ID 83544
Fax: 208-476-3407