Hoover Dam, the Depression-era engineering marvel, turns 75 this month. While its new bridge crossing is set to open in November, the concrete monolith also is marking a dubious milestone this year—a 54-year low point for its water level, which threatens the dam’s hydroelectric output.
Lake Mead dipped to 1,085 ft in September, less than 40% of its capacity, following a decade of boom growth and drought. As a result, Hoover Dam may have to shutter its 17 Francis-type hydroelectric turbines, each generating 130 MW, by 2013. The facility also has two 60-MW turbines and two 3-MW service generators. Lake levels have been dropping by 10 ft annually and cannot feed the turbines below 1,050 ft. “It was designed as a high-elevation dam,” says Pete DiDonato, dam facilities manager for the U.S. Bureau of Reclamation.