Combined Ground Penetrating Radar And Masw Surveys To Locate Dam Seeps

Abstract

Multiple-frequency ground penetrating radar (GPR) and multi-channel analysis of surface waves (MASW) methods were used at the Reichenback Pond Dam in Woodbury, Connecticut to delineate the extent of known seeps and to locate possible responsible utilities. The present dam was constructed over an earthen road stream crossing thought to contain a small culvert. MASW was used to obtain soil property data, constraints for GPR interpretations, and to detect possible shallow seep zones or utilities. The multi-frequency (100-, 200-, and 500-MHz) GPR program was implemented on the paved road on top of and along both sides of the dam. Seismic data were collected along the paved road and on its north side where the seeps were located. Strong GPR anomalies indicated air- or water-saturated zones with localized collapse. MASW results also showed velocity anomalies in the interpreted seep zones. The strength and depth of MASW velocity anomalies were sensitive to variation in coupling media (road pavement vs. grass) and the methodology of dispersion curve analysis. Post-survey drilling supports the geophysical interpretation of seep zones related to the collapse of the older original culvert, primarily at the north toe of the dam.