Uvalde Pool of the Edwards (Balcones Fault Zone) Aquifer

Abstract

The Uvalde Pool comprises the western portion of the San Antonio segment of the Edwards (Balcones Fault Zone) Aquifer. Assessment of available data on the hydrogeology of Uvalde County confirms the conceptualization that the Edwards Aquifer in Uvalde County to the west of the city of Knippa acts as a partially separate groundwater basin. This portion of the Edwards Aquifer is referred to as the Uvalde Pool. The Edwards Aquifer to the east of the Uvalde Pool is referred to as the San Antonio Pool. A constriction in groundwater flow between the two pools, referred to as the Knippa Gap, and marked differences in groundwater elevations on either side of the Knippa Gap are the motivation to treat the Uvalde and San Antonio Pools as separate hydrogeological features. The Uvalde Pool is unique because it is the only place where the Edwards Aquifer is in hydraulic communication with the overlying and younger Buda Limestone and the Austin Chalk Aquifers. Given the karstic nature of the Edwards Aquifer in the Uvalde Pool and its relatively limited spatial extent, the Uvalde Pool is characterized as a highly transmissive aquifer, but with relatively limited storage capacity.