U.S. Water News Online
PHOENIX -- A water storage and flood control dam that actually predates Arizona statehood has been brought up to 21st century standards in a nine-year, $430-million renewal project. A rededication ceremony will take place next month at Theodore Roosevelt Dam, the highest in a series of three dams on the Salt River east of Phoenix.
Originally constructed by the U.S. Reclamation Service (now the Bureau of Reclamation) between 1903 and 1911 as the world's largest masonry dam, the structure impounds Roosevelt Lake, the first of a continuous chain of lakes extending nearly 60 miles along the Salt River towards the Phoenix metropolitan area. Safety modifications to Roosevelt Dam were approved by Congress in 1984 to give the dam an ability to withstand a "probable maximum flood," known as a PMF.
The principal modification to Roosevelt Dam, as mandated by the federal Safety of Dams Act, was raising the original structure 77 feet to a total height of 357 feet. This 20 percent increase in storage capacity adds nearly 300,000 acre feet to Roosevelt Lake and allows for more than 1.8 million acre feet of flood surcharge storage. Rehabilitation of the 95-year-old dam was complicated by its masonry construction. Problems included weak mortar joints, cracks and faults in the underlying bedrock, and numerous old tunnels that had to be plugged in its foundation.
Modifications to Roosevelt Dam now allow drainage to the dam's foundation to protect against earthquake failure, along with added low-level outlet capacity. Along with improvements in the dam, the project included construction of a new $21.3 million bridge that is the longest two-lane, single-span, steel-arch bridge in North America. Built to take traffic off the top of Roosevelt Dam, the bridge spans some 1,080 feet across Roosevelt Lake providing two-way traffic that wasn't previously possible. The original dam-top roadway was designed to allow two Model-T Fords to pass abreast, a width much too narrow for modern two-lane traffic.
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