f ASSESSING CULTURAL (ELECTRICAL) INTERFERENCE OF DEEP WENNER RESISTIVITY SOUNDINGS AT FLOOD CONTROL STRUCTURES (DAMS) FOR SUBSIDENCE HAZARD STUDIES IN THE DESERT SOUTHWEST

Flood control structures (FRS) or dams in the desert southwest are commonly located at the margins of deep alluvial basins that are subject to groundwater pumping-induced subsidence. Safety assessment of these facilities includes characterizing the existing or potential future hazard to these structures due to subsidence. Differential subsidence can lead to changes in surface hydrology and flood storage capacity, and possible earth fissuring that could cause cracking in an FRS or its’ foundation, resulting in possible piping erosion failure of the FRS during a flood event. Resistivity is an excellent reconnaissance tool to assess compressible basin alluvium that is prone to subsidence. However, with typical water table depths of 30 to over 100 meters, and potential bedrock depths underlying alluvium ranging from 0 to over 300 meters, resistivity soundings require large arrays. The authors use array electrode a spacing up to 300 meters for this work.