Alternative Pumping and Recharge Simulations in Establishing Desired Future Conditions in the Texas Hill Country

In 2002, the Texas Water Development Board delineated 16 “groundwater management areas” in Texas.  As required by House Bill 1763, passed by the Texas Legislature in 2005, groundwater conservation districts in each groundwater management area were required to adopt “desired future conditions” for relevant aquifers within the groundwater management area by September 1, 2010.  A desired future condition is essentially a management goal that defines the philosophy and policy of groundwater management in a defined area. More specifically, a desired future condition is the desired, quantified condition of a relevant aquifer (such as groundwater level, groundwater storage volume, or spring flow) at a specified time or times in the future. The process is termed “joint planning” because the groundwater conservation districts within a groundwater management area must work together to establish these goals in such a manner that they are physically possible.

As part of the process to adopt desired future conditions in the Trinity Aquifer in the Texas Hill Country, over 2,000 50-year simulations using a groundwater flow model were completed and communicated to the groundwater conservation districts in Groundwater Management Area 9.  These simulations considered alternative pumping and recharge scenarios.  The recharge scenarios were developed from tree-ring precipitation estimates from 1537 to 1972 for the Edwards Plateau.  The simulations were designed to evaluate climatic variability and the potential impacts of various pumping scenarios during severe drought conditions that predated the commonly accepted worst-case drought of the 1950s.  Results of the simulations were used to evaluate pumping and drought impacts on groundwater elevation declines, spring flow, base flow to rivers and outflow across the Balcones Fault Zone.