Construction of the Coralville Dam complex by the U.S. Army Corps of Engineers was completed in 1958, and it was designed primarily for flood control. Lake levels are regulated routinely by adjusting the outflow into the Iowa River through gates near the east end of the dam. The maximum discharge capacity is 20,000 cubic feet per second. The emergency spillway abuts the west end of the dam and is 500 feet wide, with its lip 31 feet below the dam's crest. The spillway releases flood water that otherwise would exert excessive pressure on the main dam structure. The Coralville Reservoir has a capacity of over 15 billion gallons of water, enough to supply Iowa City and Coralville for over five years.