SPELEOGENETIC CONTROLS ON KARST DEVELOPMENT IN SALADO CREEK WATERSHED, CENTRAL TEXAS

Karst development in the Edwards Aquifer has been significantly studied in the San Antonio and Barton Spring segments; however, karst development remains poorly studied in the Northern Segment, where municipalities rely heavily on fluvial resources. Detailed characterization of the Northern Segment is vital for future water conservation because of increasing urban sprawl along the Interstate 35 corridor. Current studies within the Salado Creek Watershed in northern Williamson and southern Bell counties, shows a dominant control of planar surfaces, including fractures and bedding planes, on cavernous porosity. Karst exhibits preferential dissolution along stratigraphic horizons that dip gently towards the Balcones Fault Zone, including highly porous, vuggy zones and brecciated zones. The Northern Segment consists of the Comanche Peak, Edwards, and Georgetown formations. The Edwards Limestone contains massive to thick-bedded limestone, dolomitic limestone, dolomite, and minor argillaceous limestone with wackestone, packstone, and grainstone textures. Caves are dominantly oriented along fractures near-perpendicular to the north-northwest strike of the Balcones Fault Zone with lateral widening, including vadose and phreatic morphologies.

Current data analyses indicate epigene karst development within the Salado Creek Watershed is tied to the geomorphic evolution of Salado Creek and primary local system discharge through Salado Springs. Surface denudation coupled with stream incision has partially partitioned shallow epigene karst system within the watershed. To the west of Salado Creek, shallow spring discharge occurs along the entrenched stream channels while well-developed paleo-phreatic tubes are now abandoned to the east; vadose pit development and sinkhole collapse have created direct recharge conduits into the system. Karst along entrenched scarps of Salado Creek indicates that in the past Salado Creek provided significant groundwater recharge to eastern dipping portions of the watershed; however, these horizons are now abandoned. These shallow components are all coupled with deeper groundwater flow paths that discharge at Salado Springs.