QUANTIFYING SEASONAL AND DIURNAL STREAM LOSS IN FIRST-ORDER, SPRING-FED STREAMS ON THE CARBONATE TERRAIN OF THE EDWARDS PLATEAU THROUGH THE USE OF MODELING TECHNIQUES

The Edwards Aquifer serves as a critical water source for much of Central Texas. By investigating the amount of water taken up by plants in the aquifer recharge zone, the impact of vegetation on water availability can be determined. West Seco Creek is located in the headwaters of the Hondo Creek Watershed, within the transition zone of the Edwards Aquifer. In this region baseflow proves to be an important aspect of the water budget, contributing to a large percentage of stream flow. Normal baseflow losses can largely be attributed to the uptake of available water by vegetation through evapotranspiration. Despite its significant role in the water balance for this region, evapotranspiration remains a difficult measurement to obtain and therefore is still largely unquantified. Quantifying water lost through evapotranspiration in the densely vegetated hills of Maple Valley is an important component of this study. In the study area three main types of vegetated zones exist: deciduous dominated riparian vegetation in the alluvial stream valleys, mid-range prairie grasses in the transitional areas, and juniper rich areas located on colluvial slopes. Each vegetation’s association affects evapotranspiration differently, and therefore monitoring efforts are necessary for each vegetative type. Using the 1-meter resolution MrSID file for the small study area and ArcView’s Image Analyst extension, land use for the area was classified. The land use was then used in the Soil and Water Assessment Tool (SWAT), along with the reconnaissance data collected on-site, to model the area under its current vegetative conditions. Once SWAT was calibrated to these conditions, the land use classification was manually altered to determine the most suitable vegetative conditions for optimal stream flow.