The project was authorized by the River and Harbor Act of 1945.
Construction of the project began in June 1961, and it became operational in 1969. Construction of the additional generating units started in 1975 and was completed in 1981. The entire project is considered complete.
The project includes Lower Monumental Dam, powerhouse, navigation lock, two fish ladders, a juvenile fish facility (JFF), and appurtenant facilities providing for navigation, hydroelectric generation, recreation, fish and wildlife habitat, and irrigation.
Lower Monumental Dam
The dam is located at the head of Lake Sacajawea, the reservoir created by Ice Harbor Dam. It is 3,791 feet long, with an effective height of about 100 feet. The dam is a concrete gravity-type dam, with earthfill abutment embankments.
Lake Herbert G. West extends up the Snake River for 28.1 miles to the tailwater of Little Goose Dam. It has a surface area of 6,590 acres.
The powerhouse has six 135,000-kilowatt units. Power generated during fiscal year 2017 was 2.67 billion kilowatt hours.
This is a single-lift lock, 86 feet wide by 666 feet long, with a 100-foot vertical lift. About 2,903,090 tons of commodities passed through the navigation lock during fiscal year 2021. The cargo primarily consisted of grains, petroleum products, fertilizer and wood products.
There are two fish ladders for migrating adult salmon and steelhead to use. Modifications to improve adult Pacific lamprey passage include installation of passage structures and metal plating to assist lamprey upstream. In 2007, a spillway weir was installed to improve conditions for juvenile fish passage at the dam. The 10-year average collection of outgoing juvenile salmon and steelhead for 2011 to 2020 at Lower Monumental was approximately 2.2 million fish with approximately 1.7 million of those transported via truck and barge below Bonneville Dam.
There are 8,335.5 acres of project lands surrounding Lake Herbert G. West. There are 7,024 acres of USACE-managed lands that are utilized for public recreation purposes, wildlife habitat, wildlife mitigation, and water-connected industrial development. Lake West offers seven day-use areas, five areas offering camping, five boat launch areas, and one designated swimming beach. Lower Monumental hosted more than 153,167 visitors in 2020.
About 50 Walla Walla District employees work at the Lower Monumental project. They serve as electricians, lock operators, mechanics, welders, riggers, painters, utility workers, heavy equipment operators, biologists, park rangers, environmental resource specialists, administrative support staff, maintenance workers and engineers. Together, they manage the safe and continuous operation of the project.
Lower Monumental project lands provide opportunities for all sorts of recreational activities, including fishing, hunting, hiking, birding, camping, swimming and horseback riding. Amenities within the parks include boat launches, campsites, shelters, fire rings, trash collections, restrooms, and picnic tables.