USING ELECTRICAL RESISTIVITY SURVEYS TO DETERMINE SUBSURFACE CONNECTIVITY IN A KARST TERRAIN, FORT HOOD MILITARY INSTALLATION, TEXAS

The Fort Hood Military Installation is a karst landscape located within the Lampasas Cut Plain, a sub-region of the Edwards Plateau. The installation is characterized by dissected mesa-type topography with Lower Cretaceous Trinity and Fredericksburg Group carbonates that outcrop in areas of high relief, namely escarpments and incised valleys. The majority of karst at Fort Hood developed within the Edwards limestone, and along permeability boundaries where the Comanche Peak and Edwards are interbedded. Surface mapping and LiDAR analyses have identified numerous karst features including caves, sinks, springs, and shelters.

All of the known karst features that occur at Fort Hood are coupled to the surface and heavily overprinted by epigenic processes; many exhibit solutional widening as a result of the interaction between surface and groundwater. Many of the sub-surface features are fracture controlled, associated with local and regional trends. Most of these karst manifestations are mapped as discrete entities, and the use of invasive techniques to determine communication between proximal features has been relatively unsuccessful. Electrical resistivity surveying has been proven an effective method used for the location and delineation of subsurface karst features. A karst density map was used to determine locations where communication between proximal karst features might exist. Two dimensional (2D) electrical resistivity surveys will be conducted at strategic locations to characterize and delineate karst related subsurface voids. Documentation of these resources will help facilitate land use planning and identify environmentally sensitive features in the training areas.