Location and Description
Jefferson Lake Dam is located in Jefferson County and is part of Jefferson Lake State Park. The dam was constructed to create Jefferson Lake in 1934 and presently impounds approximately 61,600,000 gallons of water and has a drainage area of 7.4 square miles.
Jefferson Lake Dam consists of a single 25-foot-tall zoned fill embankment with a 50-foot-wide concrete ogee weir principal spillway, that discharges into Rippy Run. The total length of the embankment is 236 feet. The dam also has an 18-inch-diameter concrete pipe lake drain that passes through the west side of the embankment. Jefferson Lake Dam does not have an emergency spillway.
As a Class I high-hazard potential structure, a sudden failure of Jefferson Lake Dam likely would result in the structural collapse of at least one residence or one commercial or industrial business and probable loss of human life. (Hazard ratings refer to the consequences of dam failure, not the dam's condition.)
Click here for more about the Dam Risk Reduction Program.
The concrete ogee weir principal spillway is severely deficient with regards to discharge capacity. The dam does not currently pass the state's minimum design flood standard. Concrete around the principal spillway is deteriorated and in need of rehabilitation. Additionally, the lake drain is no longer functional and is in need of complete replacement.
Based upon the configuration of the existing structure, constructing roller compacted concrete (RCC) overtopping protection on the structure is the recommended alternative for rehabilitation. This alternative involves construction of a sheet pile cutoff wall on the upstream and downstream slope to support multiple lifts of RCC overtopping protection. The concrete ogee weir spillway will be rehabilitated with patch repairs. Additionally, a new 24-inch-diameter cast iron/HDPE pipe siphon lake drain is being installed and the current 18-inch-diameter concrete lake-drain pipe will be grouted and abandoned in place.
Long Term Plan
Routine inspections and maintenance of the dam will continue. An emergency action plan will be revised and shared with local emergency management officials once it is completed.
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