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Brian A. Smith, Ph. D., P.G.

GROUNDWATER AVAILABILITY MODELING OF THE BARTON SPRINGS SEGMENT OF THE EDWARDS AQUIFER, CENTRAL TEXAS. Brian A. Smith, Ph. D., P.G. Brian B. Hunt, P.G. Barton Springs/Edwards Aquifer Conservation District Texas Groundwater 2004: Towards Sustainability November 18-19 Austin, Texas.

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Brian A. Smith, Ph. D., P.G.

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  1. GROUNDWATER AVAILABILITY MODELING OF THE BARTON SPRINGS SEGMENT OF THE EDWARDS AQUIFER, CENTRAL TEXAS Brian A. Smith, Ph. D., P.G. Brian B. Hunt, P.G.Barton Springs/Edwards Aquifer Conservation District Texas Groundwater 2004: Towards Sustainability November 18-19 Austin, Texas

  2. FUNDAMENTAL PROBLEM What are the impacts to discharge from Barton Springs and water levels under a recurrence of 1950’s drought conditions and increasing pumping? + = IMPACTS? 1950’sdrought (7-year drought) Pumping

  3. OUTLINE • Hydrogeologic Setting • 2000 and 2001 Groundwater Availability Models (GAM) • Recalibration of GAM to 1950’s Drought Conditions • Impacts to Barton Springs Discharge • Impacts to Water Levels and Wells • Conclusions • Future Studies

  4. Barton Springs Aquifer

  5. Conceptual Aquifer Model Contributing zone • Most of the recharge to the aquifer occurs via surface streams in discrete (karst) recharge features. • Limited contribution from the Trinity Aquifer and saline-water zone. Trinity Edwards

  6. Barton Springs Aquifer • Sole source of drinking water to more than 50,000 people • Home to endangered species at springs • Important source of recreation for Austin

  7. Barton Springs Aquifer • Sole source of drinking water to more than 50,000 people • Home to endangered species at springs • Important source of recreation for Austin

  8. Barton Springs Aquifer • Sole source of drinking water for more than 50,000 people • Home to endangered species • Important source of recreation for Austin

  9. Permitted and Actual Pumpage Note: 1 cfs = 448 gal/min = 235,889,000 gal/yr = 723 acre-ft/yr

  10. Drought of Record: Rainfall 1950-1956 33.0 inches, average annual Camp Mabry, Austin, Texas

  11. Drought of record: Springflow Barton Springs

  12. Drought of Record: Water Levels Drought of record potentiometric map (feet above msl) Drought of record saturated thickness map (feet)

  13. Groundwater Availability Model • GAM is an initiative by TWDB • to develop state of the art, publicly available, numerical groundwater flow models to provide reliable information of groundwater availability in Texas. • Barton Springs GAM: • Scanlon et al., 2000 and 2001 • Recalibrated to better-match 1950’s drought conditions

  14. Groundwater Model Advisory Team • Raymond Slade- Retired, USGS • Rene Barker- Retired, USGS • Nico Hauwert- City of Austin • David Johns- City of Austin • Jack Sharp- UT Dept. of Geosciences • Bridget Scanlon- UT BEG • Robert Mace- TWDB • Eric Strom- USGS

  15. Zones of Hydraulic Conductivity

  16. GAM SimulatedSpring Flow Simulated spring flow under 1950’s drought and various pumping rates

  17. Drawdown Due to Drought

  18. Evaluation of Hydrogeologic Data to Quantify Impacts to Wells • Stratigraphy and geologic structures • Measured water levels • Specific capacity and pumping test data • Well construction data • Simulated pumping drawdown from GAM

  19. Cross Section

  20. RESULTS: impacts to wells Current permitted pumpage • 7% of wells may be negatively impacted under 1950’s drought conditions alone. • 19% of the wells in the District may be negatively impacted under 1950’s drought and 10 cfs pumping.

  21. CONCLUSIONS:Spring Flow • For each 1 cfs of groundwater pumped from the aquifer under 1950’s drought conditions, discharge from Barton Springs will diminish by about the same rate. • At current permitted pumping levels (10 cfs), Barton Springs discharge is predicted to decrease to about 1 cfs on a monthly average, although may temporarily cease at times.

  22. CONCLUSIONS:Impacts to Wells • At current permitted pumping levels (10 cfs), as many as 19% of wells in the District may be negatively impacted. Most of the impacts are to wells that only partially penetrate the aquifer. • The southwestern portion of the aquifer is most threatened from low water levels and increased pumping rates during a recurrence of 1950’s drought conditions.

  23. Future Studies Next Generation of Model • Conduit/diffuse-flow model • Variable hydraulic conductivities Aquifer Characterization • Saline-water zone studies • Dye-trace studies • Edwards-Trinity hydraulic connection • Southern groundwater divide

  24. www.bseacd.com

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