Performance Testing of Relief Wells at Dams

The Miami Conservancy District (MCD) is a regional flood control agency located in southwestern Ohio. The MCD was formed after the flood of 1913 which resulted in the loss of 460 lives and more than $100 million in property losses. Five flood retarding basins were constructed which, along with channel improvements, provide flood protection to the major cities in the Great Miami River basin. The dams were constructed across valleys which contain up to 240 feet of alluvial and glacial outwash material below the foundation. One hundred four pressure relief wells have been constructed to control underseepage at four of the dams. The function of a pressure relief well is to reduce vertical hydraulic gradients through a dam or levee by allowing for discharge of subsurface water. Excessive vertical gradients can cause failure by piping or heave. The relief wells were installed using cable tool, bucket auger and reverse rotary equipment. Both natural gravel pack and engineered gravel pack were used with casing or bore hole. Well diameters inches and well depths range from 10 the wells ranges from 8 to 21 years. There are no permanent pools behind varying size of temporary range from 8 inches to 14 to 102 feet. The age of the dams and the wells flow only during storage events. The relief wells at Taylorsville Dam have discharged twice since they were installed in 1980. Relief wells at Huffman Dam have discharged five times since they were installed in 1979 and 1981. Relief wells at Englewood Dam and Lockington Dam discharge usually at least once each year. Since the wells flow only infrequently, there is no mechanism to evaluate the condition of each well unless a performance test is conducted. This paper discusses the performance tests which the MCD has conducted on the relief wells. Analysis of the performance tests was done by Wright State University as a part of graduate student research sponsored by the District. The objective of the research was to evaluate the efficiency of the MCD pressure relief wells and to evaluate the hydraulic properties of the geologic formations under the dams. 17 pp., 10 references, 14 figures.