Mitigating Drought Impacts on Estuary Inflows using Aquifer Storage and Recovery

Surface water in Texas is regulated under prior appropriation statutes recently amended to include provisions designed to protect instream flows and estuary inflows, but these provisions only apply to new or amended water rights. However, most river basins are already fully appropriated, leaving little real opportunity to utilize these new rules to achieve the instream flow and estuary inflow protection targets recently established through a process involving “Basin and Bay Area Stakeholder Committees (BBASC)” and expert science teams. The State of Texas continues to fund BBASCs to study adaptive management strategies designed to achieve the State’s goal of providing a “sound ecological environment” for Texas’ rivers and estuaries.

One adaptive management study recently commissioned by the Guadalupe-San Antonio (GSA)-BBASC investigated the use of two untapped categories of surface water flows – treated wastewater return flows and unappropriated water rights – and Aquifer Storage and Recovery (ASR) as a means of achieving the “Strategy Target Frequencies (STFs)” for the spring and summer freshwater inflow targets the GSA-BBASC established for the San Antonio Bay - Guadalupe Estuary System during drought periods.

A water availability model was used to calculate how much water from these two categories would be available for ASR storage during the “good years,” the total volume of ASR storage needed to meet the STFs for estuary inflows through a drought of record, and the volume of ASR recovery capacity required to deliver the stored water to the estuary during the spring and summer target periods. Modeling results were used to size ASR facilities to meet the STFs, and to prepare conceptual designs and cost estimates for a series of ASR facilities located along the lower Guadalupe River, just above the estuary. The project report included recommendations for state water policy changes needed to facilitate this innovative strategy.