SHALLOW GROUNDWATER CHARACTERIZATION WITH CAPACITIVELY COUPLED RESISTIVITY IN FORESTED WATERSHEDS, EAST TEXAS

The use of Capacitively Coupled Resistivity (CCR) as a geophysical method for the characterization of shallow aquifers and groundwater in hydrogeologic applications is increasing in popularity. This study evaluates the use of CCR for analysis of unconfined, shallow groundwater movement and water table fluctuations within forested watersheds in East Texas. An approximately six-acre watershed in Sabine County, Texas was selected to investigate the shallow water table variations within the undivided Wilcox group, a Paleocene strata that consists mainly of mudstones, crossbedded sands, and deltaic silts. Resistivity was measured over eleven transects across the watershed to delineate the water table surface with monitoring wells installed as physical control indicators of the water table. Two traverses transect 40 meters of elevation from the top of the watershed to the base of the watershed, while the remaining seven traverses are near perpendicular to the slope of the watershed, evenly spaced at approximately constant elevations. The maximum depth of penetration for CCR is often reported as twenty meters, with an average of ten meters; however, the depth of penetration has been found to be highly variable based on minor facies variations. Both slope angle and degree of cementation within host rock can significantly affect the depth of penetration. CCR has great potential for applications in shallow groundwater management as water quantity and quality issues are ever increasing. CCR is useful in characterization of shallow aquifers in forested watersheds, which maintain aquatic ecosystems and provide abundant water resources.