ORIENTATION OF FRACTURES, KARST FEATURES, AND CREEKS, LOWER GLEN ROSE LIMESTONE, COMAL COUNTY, TEXAS

This study uses two primary steps in the hydrogeologic characterization of karstic fractured rock system, which are: 1) identification and mapping of the features and 2) determination of hydrogeologic or geomorphologic properties. Aerial photograph interpretation, field observation, and GIS techniques are used to investigate the linear structural controls on groundwater flow in the Honey Creek basin, lower Glen Rose limestone, Comal and Kendall Counties. Fractures at Honey Creek State Natural Area (HCSNA) were mapped and categorized from aerial photographs, digital elevation models (DEMs) (30-meter), and ArcView with GeoTools extension. Rose diagrams help identify regional fracture trends and dominant orientations of spring conduits. The dominant northeast trends of the fractures and faults found during this study correspond with those identified in published fault orientations. Dominant fracture trends within the study area and Honey Creek itself were found to be generally aligned with the northeast-trending Balcones Fault Zone, located about 30 miles (10 kilometers) to the east. Regional groundwater flow is to the northeast. Spring conduits feeding into Honey Creek intersect the channel at a conjugate angle (to the northwest). Geomorphologic features consistent with spring sapping were identified include headward erosion of streams, structural controls on incised streams, and generation of alluvium from scarp collapse. Seepage erosion may enhance slope erosion along marly risers and interbedded limestone and dolomite scarps.