Conceptualizing Groundwater-Surface Water Interactions within the Ogallala Aquifer Region using Electrical Resistivity Imaging

Dynamic interactions between rivers and aquifers are controlled by the underlying hydrogeologic environment, as well as the type of hydrologic connection between the riverbed and saturated zone. The Arkansas River supplies groundwater to a heavily exploited region of the Ogallala Aquifer across Western Kansas. Site characterizations of this region using existing well and borehole data reveal large scale geologic features that significantly impact recharge processes, such as the Bear Creek fault. However, the existing hydrogeologic data do not provide the level of detail needed to fully understand the contribution of the losing river system to Arkansas Alluvial aquifer recharge. Knowledge about riverbed hydrogeology is acquirable using electrical resistivity imaging (ERI) surveys. ERI surveys and soil sample analysis were conducted at three sites along the Arkansas River to characterize the hydrogeologic environment within the Arkansas River Alluvial aquifer, which overlies the Ogallala aquifer. Temporal changes in electrical resistivity served as an indicator of the hydrologic response of the alluvial sediments to changes in river discharge as different patterns of water movement from the Arkansas River to Arkansas River Alluvial aquifer were observed. The ERI surveys revealed both fully connected and disconnected regions between the riverbed and groundwater table. The results supplement the existing geologic characterization of this region, and provide a more spatially detailed view of the hydrogeologic environment that has a direct causative effect on groundwater surface water interactions. Understanding the behavior of river-aquifer interactions is vital to the ability to predict the future holds of this important groundwater system.