Geophysical Investigation in Support of Beaver Dam Comprehensive Seepage Investigation

摘要

A comprehensive seepage assessment of Beaver Dam, Arkansas, was performed using a suite of geophysical methods. The Boone Formation, a severely weathered limestone, underlies Dike 1 and has been experiencing seepage since initial filling of the reservoir in 1966. Between 1968-71 a grout curtain was constructed at Dike 1 to curtail this seepage which reduced the Dike's foundation leakage. Recently discovered seeps and boils on the downstream toe of Dike 1 suggest that leakage is increasing to pregrouting levels. A geophysical investigation was undertaken to assess and delineate seepage paths and to map geologic fault zones believed to behave as hydraulic conduits. Results indicate that the geophysical tests were successful in determining the locations and strike of two faults bounding Dike 1 and that seepage is pervasive rather than occurring in a few well defined conduits. Geophysical evidence suggests that the south bounding fault may act as a broad conduit for flow. Seismic refraction surveys indicate that the contact between the weathered and the underlying more competent limestone is highly variable in depth. Self potential results indicate a correlation between SP values and pool elevation. (edc)