Lower Monumental Dam

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Lower Monumental Dam
USACE Lower Monumental Dam.jpg
Lower Monumental Dam and the Snake River from the southwest, looking northeast, upstream.
Location Franklin / Walla Walla counties, Washington, USA
Coordinates 46°33′45″N 118°32′15″W / 46.5623627°N 118.5374856°W / 46.5623627; -118.5374856Coordinates: 46°33′45″N 118°32′15″W / 46.5623627°N 118.5374856°W / 46.5623627; -118.5374856
Construction began June 1961
Opening date 1969
Operator(s) U.S. Army Corps of Engineers
Dam and spillways
Type of dam Concrete gravity, run-of-the-river
Impounds Snake River
Height 100 feet (30 m)
Length 3,791 feet (1,155 m)
Spillway type Service, gate-controlled
Creates Lake Herbert G. West
Total capacity 432,000 acre·ft (0.533 km3)[1]
Surface area 6,590 acres (26.7 km2)
Power station
Turbines 6 x 135-153 MW[2]
Installed capacity 810 MW
932 MW (max)

Lower Monumental Lock and Dam is a hydroelectric, concrete, run-of-the-river dam on the Snake River, and bridges Franklin County and Walla Walla County, in the state of Washington.[3] The dam is located six miles (10 km) south of the town of Kahlotus, and 43 miles (69 km) north of the town of Walla Walla.

Construction began in June 1961. 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 (176 m) long.

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

Lake Herbert G. West, which extends 28 miles (45 km) east to the base of Little Goose Dam, is formed behind the dam. Lake Sacajawea, formed from Ice Harbor Dam, runs 35 miles (56 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
  • 86 feet (26 m) wide
  • 666 feet (203 m) long

See also[edit]


  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. ^ "The Columbia River System Inside Story" (PDF). BPA.gov. pp. 14–15. Retrieved 17 July 2010. 

External links[edit]