Determining Groundwater Influence on the Guadalupe River by Spring Delineation and Spatial Variability of Karst Development in Kendall County, South-Central Texas.

摘要

Significant groundwater contributions to the Guadalupe River have been reported in the past, but no systematic investigation has ever been conducted of the upper portion of the Guadalupe River to quantify and qualify the extent of spring contributions. This research investigates temporal and spatial groundwater contributions to the Guadalupe River through spring discharge from underlying Trinity and contiguous Edwards-Trinity aquifers with reference to speleogenetic and hydrogeologic evolution of Kendall County, Texas. The upper portion of the Guadalupe River in this study is a 90 kilometer segment of the river beginning at Comfort, Texas, extending across Kendall County southeastward, and ending at Guadalupe State Park, covering about 3,070 square kilometers.;Geochemical, GIS, and streamflow investigations were conducted to assess spatial and temporal karst groundwater network associated with the Guadalupe River. There were 5, 16, and 11 subaerial springs identified in December, April, and November, 2012, with samples collected in April and November for characterization of spring geochemistry to constrain spatial geochemical spring variability. Subaqueous sampling of physicochemical parameters was conducted quarterly to evaluate spatial and temporal changes in fluvial chemistry. GIS interpolation of subaqueous measurements identified 14 probable subaqueous springs, and numerouse 1st rank anomalies along the river. Stream gauging of 16 sites evaluated streamflow conditions and variations in stream discharge relating to groundwater and overflow contributions.;Subaerial and subaqueous geochemical analyses found spatial and lithological variations throughout the Guadalupe River indicating seasonal dilution during the wet season, characteristic of an epigenic karst system recharged with overland flow. Minor fluctuations in pH exhibited seasonal variations consistent with common, circum-neutral, carbonate waters. Streamflow analyses found evidence of spring contribution sustaining baseflow to the Guadalupe River, and discharge being lost upstream to recharge the groundwater system.;Dominant controls for spatial and temporal variations in geochemistry of groundwater and fluvial waters of the Guadalupe River in Kendall County are water-rock interactions with carbonate geology. Water circulation associated with deposition of transgressive-regressive couplets of Trinity units created favorable conditions for evaporites of caprinid reef and biostrome facies of the Glen Rose Reef interval; therefore, geochemical variations reflect water travelling through carbonate aquifers. Spatial distribution of springs along the Guadalupe River is most likely controlled by karst features and fractures in the area.;Karst aquifers in Kendall County, Texas provide a complex system where interactions exist between groundwater flow networks contributing to the Guadalupe River. This system likely evolved by incision of the Guadalupe River dictating geology, and stream piracy influencing geomorphology of the river with interaction of abundant karst features in the area.