THE MONEY PIT: KARST FAILURE OF ANCHOR DAM, WYOMING

Anchor Dam, a 200-feet high, thin-arch concrete dam, located approximately 35 miles west of Thermopolis Wyoming, was constructed by the Bureau of Reclamation at a cost exceeding $5 million dollars during the dam building boom of the 1950s and 1960s. Sinkholes and earth fissures within the reservoir area continuously allowed drainage of the reservoir to karstified redbeds in the underlying Permian Goose Egg and Triassic Chugwater before, during and after construction. Additionally, attempts to plug solution-widened fractures in carbonate strata within the Pennsylvanian Tensleep Formation, which comprised the abutments, resulted in expensive change orders during construction. The reservoir and dam were doomed from the onset by these two karst systems. Karst were identified prior to and during dam construction by the Bureau of Reclamation.