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Lower Granite Dam and Lake - Quick Facts

Lower Granite Lock and Dam was the fourth of four dams constructed as part of the Lower Snake River Project, authorized in the Rivers and Harbors Act of 1945. Construction began in 1965 and three turbine units were operational in 1975. Three more turbine units were installed and operational in 1979.
Lake Lower Granite extends from the dam upstream for 40 miles to Lewiston, Idaho. The U.S Army Corps of Engineers constructed roughly 8 miles of levees around Lewiston, Idaho, to help protect lives and property from potentially destructive high water conditions.

Project Description

• Stream: Snake River (RM 107.5)
• Location: Almota, Washington
• Owner: U.S. Army Corps of Engineers, Walla Walla District
• Type of Project: Run-of-river
• Authorized Purposes: Hydropower, Navigation (1945 Rivers and Harbors Act)
• Other Purposes: Recreation, Fish and Wildlife, Water Quality, Irrigation

Hydrologic Data

• Drainage area = 103,200 sq mi
• Maximum historical peak discharge:
  Unregulated = 409,000 cfs (1894)
  Regulated = 295,000 cfs (1894)
• Forebay Elevation (NGVD29)
• Maximum pool = 746.5 ft
• Normal full pool = 738.0 ft
• Normal minimum pool = 733.0 ft
• Maximum rate of change per hour = 70,000 cfs

Powerhouse

• Number of units = 6
• Nameplate capacity = 810 MW
• Overload capacity = 932 MW
• Hydraulic capacity = 130,000 cfs

Dam

• Lower Granite
• Completed: 1975
• Height: 151 feet
• Length: 3,200 feet
• Features: powerhouse, spillway, navigation lock, fish passage facilities
• Forebay Elevation Normal Operating Range: 733-738 feet msl
• Spillway Capacity (max): 850,000 cfs

Authorized Purposes

Hydropower

Lower Granite Dam has six 135-megawatt turbines, for a total generating capacity of 810 MW.

Navigation

Lower Granite Dam navigation lock is the last of eight locks encountered in the Columbia-Snake Inland Waterway, a 465-mile river highway that allows barge transport of commodities between the Pacific Ocean and Lewiston, ID. In 2015, more than 1.1 million tons of commercial commodities passed through the Lower Granite lock.

Water Quality

Water quality is monitored and managed consistent with Clean Water Act and state standards for the health of aquatic species. During spill for juvenile fish passage at the four Lower Columbia and four Lower Snake River projects, the USACE implements a Water Quality Program to manage total dissolved gas.

Recreation

Popular recreation activities around Lower Granite Dam and Lake include fishing, swimming, picnicking, boating, hunting, and camping. There are several day-use areas, campsites, parks, habitat management units, boat launch facilities, and marinas.

Fish & Wildlife

Lower Granite Dam has one fish ladder with entrances on both shores to provide a passage route for upstream-migrating fish, including adult salmon and steelhead, lamprey, shad, and others. Passage routes operated for downstream-migrating fish are the spillway, a spillway weir, and a juvenile bypass system. In 2015, about 2.7 million juvenile salmon and steelhead were collected in the bypass system—of those, roughly 1.5 million were transported downstream by barge or truck and released below Bonneville Dam.
Recent improvements to Lower Granite fish facilities include installation of pumps to draw cooler water from deep in the forebay to cool the adult ladder in the hot summer months.