HYDROGEOPHYSICAL EVALUATION OF THE WASHITA ALLUVIUM AND TERRACE AQUIFER

Aquifers comprised of alluvium and terrace deposits are an important source of water for industries and municipalities where they are found. To manage and protect these valuable resources, a more comprehensive characterization of these systems is needed to determine aquifer dimensions, hydraulic properties, and water quality. Electrical Resistivity Imaging (ERI) was used to image the subsurface architecture of the alluvium and terrace deposits of the Washita River in western Oklahoma. This surface geophysical method provides high resolution and spatially continuous data in a variety of field conditions. Four datasets were collected orthogonal to the stream, 800-1900 m in length with 66-110 m depth of investigation. The four locations included the Washita Battlefield National Historic Site, Washita National Wildlife Refuge, and two private properties. A previously unknown buried valley, approximately 80 m deep, was detected in each of datasets. The buried valley does not necessarily align with the surface stream and contains fresher water than the shallow aquifer. The discovery of this deeper, fresher component of the aquifer demonstrates interpretations of these systems through traditional methods can miss important features due to lack of spatially continuous subsurface information.