Columbia basin project, central Wash., a multipurpose development of the U.S. Bureau of Reclamation providing irrigation, hydroelectric power, and flood control. Its key unit, the Grand Coulee Dam, provides the project with power and pumps the waters of the Columbia River into an irrigation system comprising a series of lakes, reservoirs, and numerous canals. Irrigation was begun in 1948. In 1969 the project had an installed hydroelectric power generation capacity of 2,333,000 kW. O'Sullivan Dam (200 ft/61 m high; 19,000 ft/5,791 m long; completed 1949) on Crab Creek, the project's southernmost dam, is one of the largest earthfill dams in the United States and impounds Potholes Reservoir.