GROUNDWATER – SURFACE WATER INTERACTIONS IN THE PEDERNALES RIVER BASIN, TEXAS

Interactions between aquifers and rivers are recognized as important components of the hydrologic system. Central Texas rivers and aquifers are especially well connected because the region consists of karstic carbonate geology where gaining and losing streams, springs, and caves are common. The Pedernales River is an important source of water for the city of Austin and downstream water users of the Colorado River, to which it drains. This study compares the geochemistry of waters from the main stem and tributaries to the Pedernales River, springs across the basin, and wells screened in specific aquifers. The study also evaluates geospatial information for river gains and losses where measured, springs, and surface geology. By statistical analysis of geochemical signatures, geospatial information, and geologic data, we plan to identify which aquifer units and drainage basins contribute water to the Pedernales River, and to determine which units and regions may be the most important for future conservation efforts aimed at maintaining flows in the river.

By conducting this study during baseflow conditions, the water sources are assumed to originate exclusively from groundwater, as opposed to runoff or soil interflow. Comparing the results of the current study with historic data from 1962 will allow an evaluation of changes in the water system over time as well as changes as a result of land and water use alterations. The Pedernales River Basin is surrounded by rapidly developing areas and increasing water demands, but the majority of the watershed remains undeveloped. Identifying critical areas for water quality and quantity protection while the land is still undeveloped creates an opportunity for proactive water resource protection. This project is supported by a grant from the Cynthia and George Mitchell Foundation.