Hells Canyon Dam

Hells Canyon Dam is a concrete gravity dam on the Snake River (river mile 247) in Hells Canyon on the Idaho-Oregon border. The dam impounds the Snake River in Hells Canyon Reservoir; its spillway elevation is 512 m (1,680 ft) above sea level.

It is the third and final hydroelectric dam of the Hells Canyon Project, which includes Brownlee Dam (1959) and Oxbow Dam (1961), all built and operated by Idaho Power Company. The Hells Canyon Complex on the Snake River is the largest privately owned hydroelectric power complex in the nation, according to the US Energy Information Administration. The contractor for the Hells Canyon Dam was Morrison-Knudsen.

The Hells Canyon Dam powerhouse contains three generating units, with a total nameplate capacity of 391 megawatts (MW). Power generation began with two units in 1967, the third came on line the following year.

Lacking passage for migrating salmon, the three dams of the Hells Canyon Project blocked access by anadromous salmonids to a stretch of the Snake River drainage basin from Hells Canyon Dam up to Shoshone Falls, which naturally prevents any upstream fish passage to the upper Snake River basin.

High dam proposal

As built, Hells Canyon Dam is significantly lower than it was originally proposed in the 1940s, with three dams (Hells Canyon, Brownlee Dam and Oxbow Dam) taking the place of a single 710-foot (220 m) high dam. As proposed by the U.S. Army Corps of Engineers, the Hells Canyon High Dam would have been a straight-profile concrete gravity dam with two gate-controlled tunnel spillways, one in each abutment. The proposed reservoir was planned to have a capacity of 4,050,000 acre feet (5.00×109 m3) with an area of 23,500 acres (9,500 ha). The reservoir was to extend 89 miles (143 km) upstream. The power plant was to be capable of generating 850 MW using ten units. The project included provisions for fish hatcheries, with the intention of maintaining salmon runs. Project cost was estimated at $342,076,000. The high dam project was not pursued.

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