Black Hills Hydrology Study

The Black Hills area is a unique and valuable asset to the State of South Dakota. In addition to its historic landmarks, scenic beauty, timber, and mineral resources, the Black Hills area is a major source of water. Streams flowing from the Black Hills provide water for a multitude of uses in the Cheyenne and Belle Fourche River Basins. In addition, much of western South Dakota and parts of eastern Wyoming are underlain by bedrock aquifers that are recharged in the Black Hills area.

Water resources of the Black Hills area have been stressed by increasing population, resource development, and periodic droughts. Additional water supplies are being developed for rapidly expanding communities. The potential exists for water-quality degradation from mining activity, urbanization, irrigation, forest management activities, and recreational development. Drought conditions in the late 1980's caused reduced streamflow, declining reservoir and ground-water levels, and shortages of water supplies for domestic, municipal, industrial, agricultural, and recreational purposes.

The hydrogeology of the Black Hills area is very complex. Several regional, artesian bedrock aquifers and various local aquifers are exposed and recharged in the Black Hills area. The bedrock aquifers are separated by confining units, which are composed of less permeable rocks. The thickness and permeability of aquifers and confining units are known to change with location (Peter, 1985; Kyllonen and Peter, 1987; Greene, 1993). Numerous fractures, faults, and solution cavities allow flow of water in rocks that otherwise are relatively impermeable. This is especially true of the Madison Limestone, which is well known for its karst features, including sinkholes and water-loss zones in streams, collapse features, solution cavities, and caves. Surface- and ground-water resources are connected by water-loss zones in streams and by large springs originating from one or more aquifers. Development of ground-water resources may affect surface-water resources. Conversely, development or contamination of surface-water resources may affect ground water. Detailed hydrogeologic information is necessary for effective management of water resources in the Black Hills area.