Dewey Lake is part of the integrated flood reduction system operated by the Corp of Engineers for the entire Ohio River Basin. When the lakes in this system are operated as a vast storage system, flood crests along the Ohio can be significantly reduced. Construction of Dewey Dam began in 1946 and was completed in 1949. The dam is rolled earth-fill with an uncontrolled saddle spillway. The cost of the dam was $6,051,400. The length of the lake is 18.5 miles upstream from the dam. The watershed is 207 square miles. In the intake structure, there are three 5' x 10' caterpillar control gates. The outflow is an 11 foot diameter horseshoe tunnel. Summer Pool Elevation is 650.0 m.s.l. which is 1,100 acres. Winter Pool Elevation is 645.0 m.s.l. The auxiliary spillway is located at Hager Gap at Terry's boat launch ramp. Construction began in 2000 and was completed in 2002. Approximately 150,000 cubic yards of rock was removed from the site. This spillway will allow a maximum of 178,000 cubic feet of water per second to flow through it. The highest flood on record was 3 March 1955 (682.32 m.s.l) The most recent flood was 11 May 2009 (668.66 m.s.l.). During this flood event (11 May 2009) Dewey Lake prevented more than 2 million dollars in flood damages and overall has prevented more than 94 million dollars since construction.
