A MULTI-SCALE ASSESSMENT OF SURFACE AND GROUNDWATER INTERACTIONS BETWEEN THE MIDDLE BRAZOS RIVER ALLUVIUM AQUIFER AND THE BRAZOS RIVER IN CENTRAL TEXAS

The Brazos River Alluvium Aquifer (BRAA) and Brazos River are vital sources of industrial and agricultural water supply for cooperations, farmers, and ranchers in Central Texas. Groundwater and surface water interaction (GW-SW) is a growing area of research and the interactions between the BRAA and the Brazos River provide an excellent example. The BRAA system has a major perennial river overlying a complex, heterogeneous, and compartmentalized alluvial aquifer experiencing stress from land use and changing climate. This intricate system can provide insights to similar systems. To this end, this study seeks to improve understanding of the GW-SW interactions in the middle segment of the BRAA (defined as the section in Brazos, Burleson, Milam, and Robertson Counties) at both county and local scales. While regional modeling by the Texas Water Development Board (TWDB), has provided valuable insights, these models often trade accuracy of spatial and temporal heterogeneities, seasonal variations, and river-aquifer interactions for the difficult challenges, added costs, and complexity of collecting site-specific data. To address these limitations, this study applies a multi-scale approach utilizing both historical data from the TWDB’s Groundwater Database (GWDB) and original data collected on-site to better define hydrogeologic gradients, chemical compositions, and flow variations in the middle segment of the BRAA. Preliminary results show a generalized hydrogeologic gradient which suggests flow from the BRAA to the Brazos River contributing to the river baseflow. However, extended rainfalls often result in elevated river levels with temporary flow reversal periods. Further research is needed to understand the impacts of temporal head variations under varying conditions.