Drought Trigger Methodology for the Barton Springs Aquifer, Travis and Hays Counties, Texas

Previous studies of the Barton Springs segment of the Edwards Aquifer have shown that with uncurtailed pumping at 2004 rates and a recurrence of drought-of-record conditions, flow from Barton Springs could cease for brief periods, and up to 20% of the water-supply wells could have availability problems. A drought trigger methodology (DTM) was devised to improve declarations of drought and drought-management measures. Such measures, including mandatory pumping reductions, are a primary means of protecting groundwater levels and spring flow. Three guiding principles were established as the basis for developing a DTM: 1) drought stage declarations must be made with sufficient time to achieve benefits of curtailment and education measures; 2) representative of aquifer-wide conditions; and 3) simple to implement. Principal components of the hydrologic cycle (recharge, storage, and discharge) were evaluated using historical data on drought indices, rainfall, stream flow, pumping, water levels, and spring flow. Conduit and diffuse flow are the basic elements of the groundwater flow system in the Barton Springs aquifer that can influence the amount of water stored in the aquifer. The DTM established in this report utilizes flow from Barton Springs and water levels in the Lovelady monitor well to indicate overall storage and drought status of the aquifer. The DTM contains six stages as outlined in the table below. Barton Springs is the primary natural discharge point and is a good measure of the overall health of the aquifer system. Barton Springs is a good measure of groundwater storage, but is highly sensitive to the conduit flow system (very transient storage), responding quickly to minor and major recharge events. The Lovelady well is also a good measure of storage but is more representative of the diffuse flow system and has a muted response to major recharge events. This suggests that the Lovelady well is not directly connected to the karst aquifer’s conduit system. By using both the Lovelady well and flow from Bar