Lower Granite Dam

Lower Granite Dam
Name	Lower Granite Dam
Name official	Lower Granite Lock and Dam
Dam crosses	Snake River
Location	Whitman County, Washington, United States
Operator	United States Army Corps of Engineers
Dam type	Concrete, run-of-the-river
Length	3,100 ft
Height	100 ft
Opening	1975
Plant capacity	8100 kW

Lower Granite Dam is a concrete run-of-the-river lock and dam on the Snake River in Whitman County, Washington, United States. It forms Lower Granite Lake and serves multiple purposes including navigation, hydroelectric power generation, flood control, and fish management. The project is operated by the United States Army Corps of Engineers as part of the Columbia River Basin system coordinated with the Bonneville Power Administration, U.S. Bureau of Reclamation, and regional stakeholders.

Overview and specifications

Lower Granite Dam is located near the city of Colton, Washington about 22 miles upstream of the confluence with the Columbia River at Pasco, Washington. The structure is a concrete gravity dam with a gated spillway, a lock chamber measuring 86 by 675 feet, and a powerhouse containing Kaplan turbines that produce approximately 8.1 megawatts of peaking capacity. The reservoir, Lower Granite Lake, extends upstream to Lewiston, Idaho and inundates portions of the Snake River Plain, linking to the navigation system that includes Little Goose Lock and Dam, Lower Monumental Lock and Dam, and Ice Harbor Lock and Dam. The project was authorized as part of the Flood Control Act of 1950 and constructed under the supervision of the U.S. Army Corps of Engineers, Walla Walla District.

History and construction

Planning for the dam occurred amid regional development initiatives involving the Columbia Basin Project, the Pacific Northwest Electric Power Planning and Conservation Act, and interstate agreements among Washington (state), Idaho, and Oregon. Site selection considered river hydraulics, geology of the Palouse River watershed, and treaty-obligations with the Nez Perce Tribe. Construction began in 1965 with cofferdam works, diversion channels, and foundation excavation influenced by studies from the U.S. Geological Survey and the National Oceanic and Atmospheric Administration. Major concrete placements, spillway erection, and lock assembly continued through the late 1960s and early 1970s, with official completion and dedication in 1975 amid regional debates involving Environmental Protection Agency concerns and coordination with the Federal Energy Regulatory Commission for operational licensing.

Operations and power generation

Operational control of reservoir levels, spillway releases, and powerhouse dispatch is coordinated among the U.S. Army Corps of Engineers, Bonneville Power Administration, and regional utilities including Avista Corporation and Idaho Power Company. The Kaplan turbine generators provide primarily peaking and load-following capability that supports the Pacific Northwest power grid and integrates with seasonal flows managed for irrigation projects like the Columbia Basin Project and municipal supplies for cities such as Lewiston, Idaho and Clarkston, Washington. Hydrologic decision-making uses data from the National Weather Service, streamflow gauges maintained by the U.S. Geological Survey, and basin models developed during coordinated operations with the Northwest Power and Conservation Council.

Navigation and lock system

Lower Granite’s lock creates the upper terminus of a navigable inland waterway that connects to the Port of Portland and seaport facilities at Portland, Oregon. The 86-by-675-foot lock chamber accommodates barges carrying grain from the Inland Northwest and agricultural commodities from the Palouse to ocean-going vessels. Navigation planning involves the U.S. Army Corps of Engineers, Portland District for channel maintenance, dredging, and riverbank stabilization, and links to commerce overseen by regional ports including the Port of Lewiston and the Port of Clarkston. The lock schedule is coordinated with tow operators, the American Waterways Operators trade group, and inland shipping logistics.

Fish passage and environmental impacts

Fish passage facilities at Lower Granite include juvenile bypass systems, adult fish ladders, monitoring facilities, and transport operations that have been the focus of litigation and policy actions involving the National Marine Fisheries Service, the U.S. Fish and Wildlife Service, and tribal governments such as the Nez Perce Tribe. The dam’s effects on anadromous runs—especially Chinook salmon, steelhead, and Sockeye salmon—prompted mitigation measures including spill regime adjustments, surface passage systems, and river restoration funded through collaborative efforts with the Bonneville Power Administration under the Columbia River Basin Fish and Wildlife Program. Ecological debates have involved conservation organizations such as the Sierra Club and legal cases before the U.S. District Court for the Eastern District of Washington and the Ninth Circuit Court of Appeals over compliance with the Endangered Species Act.

Recreation and surrounding area

Lower Granite Lake and adjacent lands provide recreational opportunities managed by the U.S. Army Corps of Engineers and county parks in Whitman County, Washington and Nez Perce County, Idaho. Activities include boating, fishing for species such as Smallmouth bass and walleye, hunting, camping, and riverside trails tied to regional tourism promoted by the Washington State Department of Transportation and local chambers of commerce like the Lewiston–Clarkston Valley Chamber of Commerce. Nearby attractions and infrastructure include rail lines operated by Union Pacific Railroad, the Hells Canyon National Recreation Area, and community centers in Lewiston, Idaho and Clarkston, Washington that support visitor services.

Category:Dams in Washington (state)