Recharge and Recirculation / Edwards Aquifer Optimization Program Phase III / IV Report Final

Author Todd Engineers, TRC Brandes and NRS Engineering
Year 2008
Description Continued and final analyses using improved flow model and recent agency rules for optimizing recharge and streamflow in the Edwards Aquifer
Publisher Todd Engineers
Location Edwards Aquifer, Balcones Fault Zone, Comal Springs, San Marcos Springs, San Antonio Pool
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The R&R – Phase III/IV Report consists of baseline modeling scenarios, evaluation of R&R facility operational parameters, evaluation of source water availability, scenario modeling, and engineering and cost estimates for seven scenarios.

[Excerpted from the Executive Summary and Summary]
For more than three decades, the Edwards Aquifer Authority (EAA), its predecessor, and others have evaluated groundwater management strategies to more productively use the shared resource of the Edwards Aquifer. These strategies have involved, among others, enhancing natural recharge and recirculating groundwater discharge back into the aquifer system. This study builds on previous investigations and re‐evaluates recharge and recirculation (R&R) strategies incorporating:
• analysis with an improved computer flow model,
• updated estimates of available source water, and
• recently‐adopted EAA rules for various aspects of aquifer management.

The study also evaluates combinations of strategies and provides preliminary costs for facilities to support implementation of an R&R program. Benefits to the region are evaluated in terms of increased water supply and maintaining minimum springflow at key springs including Comal and San Marcos springs….

Based on the analyses provided in this report, the following conclusions can be made.
• An R&R program can be developed that increases water supply while maintaining minimum required springflow.
• Considerations for optimizing the program should be based on specific management objectives developed by EAA and stakeholders such as when and under what conditions additional water supply is needed and what minimum flows are required for Comal Springs and during what time period.
• Using the water balance output from the model, benefits from enhanced recharge can be assessed for five main categories: enhanced pumping (for recharge recovery), Permit pumping (due to lessening of CPM stages), Comal Springs, springflow at other springs, and aquifer storage (water remaining in aquifer).
• Baseline conditions developed for this study indicate that the aquifer is in critical period stages for most of the model time period. For the San Antonio Pool, critical period stages occur 65 percent of the time. Springflow at Comal Springs is significantly lower than the historical record and ceases to flow for 25 months during the drought of record (1947‐1956).
• The EAA model, as modified, simulates newly‐adopted CPM rules and pumping cap, and provides a valuable tool for evaluating R&R scenarios.