1. Edward’s Aquifer Ground-water Flow Model Texas Ground Water 2004 November 19, 2004 George B. Ozuna

2. Edwards Aquifer Model In cooperation with:  Edwards Aquifer Authority  Department of Defense  USGS Richard Lindgren, USGS Sue Horvorka and Alan Dutton, BEG Scott Painter, SwRI Steve Worthington, Consultant

4. Edwards Aquifer Model Uniform ¼-mi grid 370 rows; 700 columns; 259,000 cells One layer Grid alignment:  Major faults and flow near Comal and San Marcos Springs

5. Structure Aquifer top elevation Aquifer bottom elevation Faults Provided by BEG – Sue Horvorka

6. Faults Simulated using Horizontal Flow Barrier Package Model inputs:  fault location  hydraulic characteristic (C) ohydraulic conductance term oAssumption: hydraulic characteristic (C) is a function of fault displacement inversely proportional

7. Las Moras Springs Leona Springs San Antonio & San Pedro Springs Comal Springs San Marcos Springs Fault Simulated Faults And Springs

8. General-head boundary No-flow boundary – saline water line General-head boundary No- flow Colorado River – Head-dependent flux boundary No- flow Recharge zone Model Boundary Conditions

9. Hydraulic Conductivity Provided by Southwest Research – Scott Painter

10. Conduits Provided by EAA Consultant - Steve Worthington

11. Hydraulic Properties

12. Simulated Recharge Zones

13. Recharge Zone - Stream Channels

14. Pumpage – by use Provided by BEG – Alan Dutton

15. Pumpage – by rate Provided by BEG – Alan Dutton

16. Steady-State Calibration Calibration period: 1939 – 1946 Pre-1950’s drought, minimal irrigation development Near-normal precipitation San Antonio precipitation: normal 1961-9030.98 in/yr average 1939-4630.47 in/yr

17. Steady-State Target Wells 144 wells

18. Steady-State Calibration

19. Transient Calibration Calibration period: 1947 – 2000 Calibration targets:  Long-term record wells oCounty Index wells omatch hydrographs  Selected time periods operiods of above- and below-normal precipitation omatch hydraulic heads for a set of wells

20. Transient Calibration Selected time periods  Below-normal precipitation o1952-57 May thru November 1956 175 wells  Above-normal precipitation o1973-77 November 1974 thru July 1975 172 wells

21. Transient Target Wells Drought Conditions, 175 Wells, May – November 1956

22. Transient Target Wells Wet Conditions, 172 Wells, November 1974 – July 1975

23. Transient Target Springs 5 springs simulated:  San Marcos  Comal  Leona  San Pedro*  San Antonio* *Based on relation with Bexar index well

24. Uvalde Index Well Medina Index Well Comal Well San Marcos Well Transient Results Water-Level Hydrographs Bexar Index Well

25. Transient Results Water-Level Hydrographs

30. Leona Springs Comal Springs San Marcos Springs Transient Results Springflow Hydrographs

34. Edwards Aquifer Model Model Inputs  Structure  Boundary Conditions  Hydraulic Properties  Stresses Model Calibration  Targets  Steady-State Results  Transient Results