GYPSUM-KARST PROBLEMS IN SITING OF THE MANGUM DAM, SOUTHWESTERN OKLAHOMA

Geologic assessment was made of two prospective damsites along Salt Fork Red River near Mangum, in southwestern Oklahoma. Because of gypsum karst in the area, the first site was abandoned and the second site is acceptable, but with limitations. The abutments and impoundment area of the first site contained abundant gypsum-karst features, such as caves and sinkholes, and would not contain water. The second site is predominantly in thick shale, and contains karst features only in the upper reaches of the reservoir; this will set limitations on the lake level, size, and storage capacity of the Mangum Reservoir. Karst features are common in many parts of Oklahoma, and studies in the Mangum area show the importance of geological investigations in planning the location of damsites and the size of reservoirs. Inadequate geological studies of gypsum-karst features at other sites in the United States have led to dam failure, or inability of a reservoir to contain water.