Lower Monumental Dam

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Lower Monumental Dam
USACE Lower Monumental Dam.jpg
View from the southwest
LocationFranklin and Walla Walla counties, Washington, U.S.
Coordinates46°33′47″N 118°32′20″W / 46.563°N 118.539°W / 46.563; -118.539Coordinates: 46°33′47″N 118°32′20″W / 46.563°N 118.539°W / 46.563; -118.539
Construction beganJune 1961
Opening date1969
Operator(s)U.S. Army Corps of Engineers
Dam and spillways
Type of damConcrete gravity,
ImpoundsSnake River
Height100 feet (30 m)
Length3,791 feet (1,155 m)
Spillway typeService, gate-controlled
CreatesLake Herbert G. West
Total capacity432,000 acre⋅ft (0.53 km3)[1]
Surface area6,590 acres (26.7 km2)
Normal elevation540 ft (165 m)
Power Station
Turbines6 x 135-153 MW[2]
Installed capacity810 MW
932 MW (max)

Lower Monumental Lock and Dam is a hydroelectric, concrete, run-of-the-river dam in the northwest United States. Located on the Snake River, it bridges Franklin and Walla Walla counties in southeast Washington.[3][4] It is six miles (10 km) south of Kahlotus and 43 miles (70 km) north of Walla Walla.

Construction began in June 1961, and the main structure and three generators were completed in 1969, with an additional three generators finished in 1981. Generating capacity is 810 megawatts, with an overload capacity of 932 MW. The spillway has eight gates and is 572 feet (174 m) in length.

Lower Monumental Dam is part of the Columbia River Basin system of dams.

Behind the dam, Lake Herbert G. West is the reservoir; it extends 28 miles (45 km) east to the base of Little Goose Dam. Lake Sacajawea, formed from Ice Harbor Dam, runs 22 miles (35 km) southwest, downstream from the base of the dam.

Lower Monumental Dam with the lock in the center of the river (far side in photo), the power generation on the northwest side of the river, and spillway in the middle of the dam, between the powerhouse and the lock.
Columbia River Basin
Navigation lock
  • Single-lift
  • Width: 86 ft (26 m)
  • Length: 666 ft (203 m)

See also


  1. ^ "The Four Lower Snake River Dams". Bluefish.org. Retrieved 17 July 2010.
  2. ^ "Lower Monumental Dam". Washington.edu. Retrieved 17 July 2010.[dead link]
  3. ^ "Lower Monumental Dam". Lewiston Morning Tribune. (Idaho). (photo). March 19, 1964. p. 13.
  4. ^ "The Columbia River System Inside Story" (PDF). BPA.gov. pp. 14–15. Retrieved 17 July 2010.

External links