SHALLOW KARST DETECTION IN SOUTH CENTRAL TEXAS USING GROUND PENETRATING RADAR

Ground penetrating radar is a technology commonly used for detecting targets in construction work and archeology, but can also be used for mapping geological layers. In conductive soils, such as are commonly found in Texas, the depth of penetration can be somewhat limited. In this study, a 270 MHz antenna was utilized in two geologic layers (The Lower Glen Rose and Austin Chalk Formations) known to be prolific in karst development in South-Central Texas and to determine if shallow karst features could be detected. In both settings features at a depth of the less than 10 feet were imaged and showed voids present at expected depths. Adjusting the range allowed for an increased depth and imaging of one large karst feature showed the passage from a depth of 3 ft. to 20 ft. Varying precipitation at one study area resulted in increased conductivity, and while many voids were still detectable in both dry and highly saturated conditions, some collapse features detected in dry conditions were not visible in highly saturated conditions. Scans in dry conditions also showed breaks in the stratigraphic layers, possibly indicating pathways for additional karst development. Thus, it has been determined that for utilizing the GPR in some karst terrains, the precipitation patterns in an area may not be important for detecting sizable voids, but may be important in delineating collapse features, fill or flow patterns.