Dworshak Dam - Specifications

Specifications

Dworshak Dam is a concrete gravity dam with a sloped downstream face and vertical upstream face, standing 717 feet (219 m) high from the foundations, 632 feet (193 m) above the riverbed and measuring 3,287 feet (1,002 m) long along its crest. The top of the dam is 44 feet (13 m) wide and sits at an elevation of 1,613 feet (492 m). The main body of the structure contains approximately 6,500,000 cubic yards (5,000,000 m3) of concrete. High water releases are controlled by a set of outlet works with four gates, capable of releasing 40,000 cubic feet per second (1,100 m3/s), and a spillway controlled by two 50.0 × 56.4 ft (15.2 × 17.2 m) tainter gates. The spillway has a capacity of 150,000 cubic feet per second (4,200 m3/s) at maximum reservoir elevation. Dworshak Reservoir is the name of the lake formed behind the dam. At normal maximum water levels of 1,600 feet (490 m) above sea level, the reservoir stretches 53 miles (85 km) upstream, covering 17,090 acres (6,920 ha) and containing 3,468,000 acre feet (4.278 km3) of water with 175 miles (282 km) of shoreline.

The hydroelectric plant located at the base of the dam is a 428-foot (130 m) long concrete structure and contains one 346,000 horsepower (hp) and two 142,000 hp turbines that power one 220 megawatt (MW) and two 90 MW generators, respectively, for a total capacity of 400 MW. The rated hydraulic head for the powerhouse is 560 feet (170 m), with a maximum of 632 feet (193 m) when the reservoir is full and a minimum of 417 feet (127 m) required for power generation. Up to 10,500 cubic feet per second (300 m3/s) of water can be released through the power plant at maximum capacity. The overload capacity of the two small units is 103.5 MW and for the large unit is 253.0 MW, for a total of 460 MW. If installed, Units 4, 5 and 6, each with a capacity of 220 MW, would bring the total generating capacity to 1,060 MW, making it one of the largest hydroelectric plants in Idaho.