1. Estimating Groundwater Recharge in Porous Media Aquifers in Texas Bridget Scanlon Kelley Keese Robert Reedy Bureau of Economic Geology Jackson School of Geosciences Univ. of Texas at Austin

2. Purpose and Scope Estimate recharge rates for major aquifers (porous media) in Texas based on unsaturated flow modeling.

3. Outline Methods – Study design – Model description – Input data Results Conclusions

4. Modeled Study Areas

5. Different Modeling Scenarios Assess relative importance of climate, soils, and vegetation on simulated recharge 1.Monolithic sand profile, no vegetation – effect of climate on recharge 2.Monolithic sand profile + vegetation – effect of vegetation on recharge 3.Layered soil profile, no vegetation – effect of soil layering on recharge 4.Layered soil profile + vegetation – most realistic case

6. Outline Methods – Study design – Model description – Input data Results Conclusions

7. Model UNSAT-H code (1-D finite difference, PNNL) 5 m profile Boundary conditions: –upper boundary condition: daily weather 1961 – 1990 –lower boundary condition: free drainage Initial conditions Model output: –recharge, runoff, ET, water storage change –pressure and water content

8. Water Balance Equation R = P – ET – R 0 –  S R = recharge P = precipitation ET = evapotranspiration R 0 = runoff  S = change in soil water storage

9. Outline Methods – Study design – Model description – Input data Results Conclusions

10. Average Annual Precipitation Map

11. 1961-1990 Average Annual Precipitation and PET for Selected Weather Stations

12. Average Soil Profile Clay Content (STATSGO)

13. Online Soils Databases and Pedotransfer Functions SSURGO (Soil Survey Geographic) database (1:24,000 scale ) Similar soils data to STATSGO + water retention points at -3.3 and - 150 m. Pedotransfer function: transforms available soils data into hydraulic parameters (K(  ), h(  )) Rosetta neural network Input: Sand, silt, and clay percentages, bulk density and water retention at -3 m head and -150 m head Database: water retention h(  ) and saturated hydraulic conductivity (Ks) Output: water retention functions and saturated hydraulic conductivity

14. Distribution of Dominant Vegetation Types in Texas

15. Vegetation Parameters Type of vegetation shrubs, grasses, crops, trees Fractional vegetation coverage Leaf Area Index (LAI) one sided green leaf area per unit ground area in broadleaf canopies Root depth Root length density

16. Outline Methods – Study design – Model description – Input data Results Conclusions

17. Different Modeling Scenarios Assess relative importance of climate, soils, and vegetation on simulated recharge 1.Monolithic sand profile, no vegetation – effect of climate on recharge 2.Monolithic sand profile + vegetation – effect of vegetation on recharge 3.Layered soil profile, no vegetation – effect of soil layering on recharge 4.Layered soil profile + vegetation – most realistic case

18. Relationships Between Average Annual Precipitation and Simulated Area-Weighted Average Annual Recharge (1961 – 1990) R = 1.0

19. Map of Recharge based on Nonvegetated Monolithic Sand Scenario 25% of P 61% of P

20. Different Modeling Scenarios Assess relative importance of climate, soils, and vegetation on simulated recharge 1.Monolithic sand profile, no vegetation – effect of climate on recharge 2.Monolithic sand profile + vegetation – effect of vegetation on recharge 3.Layered soil profile, no vegetation – effect of soil layering on recharge 4.Layered soil profile + vegetation – most realistic case

21. Relationships Between Average Annual Precipitation and Simulated Area-Weighted Average Annual Recharge (1961 – 1990) R = 0.96

22. Variations of Recharge with different Vegetation Covers within one Simulated Site, Bastrop County Soil Profiles: sand, PaE, TfB, Afc

23. Vegetated Monolithic Sand Profile 0% of P 32% of P

24. Different Modeling Scenarios Assess relative importance of climate, soils, and vegetation on simulated recharge 1.Monolithic sand profile, no vegetation – effect of climate on recharge 2.Monolithic sand profile + vegetation – effect of vegetation on recharge 3.Layered soil profile, no vegetation – effect of soil layering on recharge 4.Layered soil profile + vegetation – most realistic case

25. Relationships Between Average Annual Precipitation and Simulated Area-Weighted Average Annual Recharge (1961 – 1990) R=0.79

26. Variations of Recharge with different Soil Profiles within one Simulated Site, Bastrop County Soil Profiles: sand, PaE, TfB, Afc

27. Average Soil Profile Clay Content (STATSGO) 0.1 mm/yr 50, 25 mm/yr 150 mm/yr 170 mm/yr 10 mm/yr 60 mm/yr 260 mm/yr 15 mm/yr 30 mm/yr 315 mm/yr 430mm/yr Simulated Runoff

28. Simulated Recharge Distribution based on Nonvegetated Layered Soil Profiles 4% P 26% P

29. Different Modeling Scenarios Assess relative importance of climate, soils, and vegetation on simulated recharge 1.Monolithic sand profile, no vegetation – effect of climate on recharge 2.Monolithic sand profile + vegetation – effect of vegetation on recharge 3.Layered soil profile, no vegetation – effect of soil layering on recharge 4.Layered soil profile + vegetation – most realistic case

30. Relationships Between Average Annual Precipitation and Simulated Area-Weighted Average Annual Recharge (1961 – 1990) R=0.95

31. Map of Simulated Recharge based on the Power Law Relationship Power model Reduction Factor 11 – 109 0.2% - 7% P Reduction Factor 2 – 7 2% - 10% P

32. Sensitivity of Recharge to Variations in Leaf Area Index, Root Depth, Root Length Density, and Bare Area Simulated Average Annual Drainage (mm/yr) 1 - 4 Represent Different Soil Profiles

33. Summary/Conclusions Monolithic sand profile –54 mm/yr in W Texas to 720 mm/yr in E Texas –represents 25% to 61% of precipitation Vegetated sand profile –0 mm/yr in W Texas to 377 mm/yr in E Texas –represents 0% to 32% of precipitation Layered soil profile –18 mm/yr in W Texas to 226 mm/yr in E Texas –represents 4% to 26% of precipitation Layered soil profiles + vegetation –0.1 mm/yr in W Texas to 114 mm/yr in E Texas –represents 0.1% to 10% of precipitation

34. Summary/Conclusions Monolithic sand profile –54 mm/yr in W Texas to 720 mm/yr in E Texas –represents 25% to 61% of precipitation Vegetated sand profile –0 mm/yr in W Texas to 377 mm/yr in E Texas –represents 0% to 32% of precipitation Layered soil profile –18 mm/yr in W Texas to 226 mm/yr in E Texas –represents 4% to 26% of precipitation Layered soil profiles + vegetation –0.1 mm/yr in W Texas to 114 mm/yr in E Texas –represents 0.1% to 10% of precipitation