| Lower Monumental Dam | |
| Dam Crosses: | Snake River |
| Res Name: | Lake Herbert G. West |
| Location Map: | USA#Washington |
| Location Map Caption: | Location in the United States##Location in Washington |
| Country: | United States |
| Location: | Franklin and Walla Walla counties, Washington |
| Spillway Type: | Service, gate-controlled |
| Operator: | U.S. Army Corps of Engineers |
| Dam Height: | 100feet |
| Construction Began: | June 1961 |
| Res Surface: | 6590acres |
| Res Elevation: | 540feet |
| Plant Turbines: | 6 x 135-153 MW[1] |
| Plant Capacity: | 810 MW 932 MW (max) |
| Dam Type: | Concrete gravity, run-of-the-river |
| Coordinates: | 46.563°N -118.539°W |
Lower Monumental Lock and Dam is a hydroelectric, concrete, run-of-the-river dam in the northwest United States. Located on the lower Snake River in southeast Washington, it bridges Franklin and Walla Walla counties;[2] [3] it is 6miles south of Kahlotus and 43miles 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 in length.
Built and operated by the U.S. Army Corps of Engineers, 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 east to the base of Little Goose Dam. Lake Sacajawea, formed from Ice Harbor Dam, runs southwest, downstream from the base of the dam.