6.1 Numerical Models for Developing Management Strategies

The State of Texas and other government entities have developed groundwater models for the major Texas aquifers that have provided new insights into the groundwater resources on which much of the state relies. Several regional-scale groundwater flow models cover parts of the Edwards Aquifer (Green et al., 2019d). Post-2000 models were mostly developed as part of the Texas Water Development Board’s Groundwater Availability Model (GAM) program (Mace et al., 2008). These models target portions of the Edwards Aquifer: Northern segment (Jones, 2003), Barton Springs segment (Scanlon et al., 2001, 2003; Smith and Hunt, 2004; Winterle et al., 2009; Hutchison and Hill, 2011), and the Edwards (Balcones Fault Zone Aquifer) San Antonio segment (Klemt et al., 1979; Maclay and Land, 1988; Lindgren et al., 2004; Lindgren, 2006; Fratesi et al., 2015; Liu et al., 2017). The GAMs are implemented within Texas’ unique system of Groundwater Conservation Districts (GCDs) and Groundwater Management Areas (GMAs) to assist in establishing desired future conditions and management strategies to ensure adequate water resources for the future of the state (Mace et al., 2008).

In addition, there are GMAs for the Edwards-Trinity Aquifer (Anaya and Jones, 2004, 2009; Young et al., 2009; Hutchison et al., 2011b) and the Hill Country Trinity Aquifer (Mace et al., 2000; Jones et al., 2009), although the focus of these models included the Trinity Aquifer. There was also a U.S. Geological Survey Regional System Aquifer Analysis model that targeted the Edwards Plateau, but also covered the western portions of the Edwards Aquifer (Kuniansky and Holligan, 1994; Kuniansky, 1995).

The Edwards Aquifer is also managed by two GMAs and is near another. GMA 10 covers the Edwards Aquifer from the previously designated groundwater divide at Las Moras Springs in Kinney County to the Colorado River. GMA 10 includes nine overlapping GCDs all of which overlie the Edwards Aquifer. GMA 8 includes a much broader area including the counties north of the Colorado River where the Edwards Aquifer is present as well as also large areas to the north and west of the aquifer. GMA 8 includes 24 GCDs, only one of which covers the Edwards Aquifer (i.e., the Clearwater GCD in Bell County). GMA 9 does not include the Edwards Aquifer but manages the Trinity Aquifer which is juxtaposed with the Edwards Aquifer by faulting. As a result, the Trinity Aquifer provides cross-formational flow and baseflow that subsequently recharge the Edwards Aquifer.

Two agencies are specifically responsible for managing the Edwards Aquifer: the Edwards Aquifer Authority, which was established under a different law and is not a GCD, and the Barton Springs Edwards Aquifer Conservation District (BSEACD).