HYDRAULIC DEPENDENCIES AMONG REGIONAL POROUS MEDIA AND KARST AQUIFERS IN CENTRAL TEXAS

Central Texas derives much of its water resources from regional (i.e., Edwards-Trinity, Edwards, and Carrizo-Wilcox) and related local aquifers. Recharge to the aquifers is by precipitation distributed over outcrop areas (autogenic recharge), runoff focused into river and stream beds (typically allogenic), and interformational flow in the subsurface. Precipitation (and recharge) is variable from semi-arid (i.e., < 50 cm/yr) in west-central Texas to sub-humid (i.e., as high as 100 cm/yr) in the east. In general, headwaters of the surface watersheds are located in the northwest and surface flow is to the southeast oftentimes crossing all three regional aquifers. The hydraulic interaction between upland areas and downgradient aquifers varies due to changes in recharge rates and water management actions. Recent field studies and analyses explored these interformational relationships and help illustrate how the porous media and karstic characteristics of these aquifers affect how the dependencies respond to changes in the hydraulic environment.