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Complexities of the Flow System, Edwards Aquifer

Complexities of the Flow System, Edwards Aquifer. Susan Hovorka, Bureau of Economic Geology with data from: Geary Schindel and Steve Johnson, Edwards Aquifer Authority J. P Nicot, Bureau of Economic Geology Steve Worthington, Worthington Associates

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Complexities of the Flow System, Edwards Aquifer

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  1. Complexities of the Flow System, Edwards Aquifer Susan Hovorka, Bureau of Economic Geology with data from: Geary Schindel and Steve Johnson, Edwards Aquifer Authority J. P Nicot, Bureau of Economic Geology Steve Worthington, Worthington Associates Adrien Lindley and Thandar Phu, University of Texas at Austin

  2. Purpose • What is the scale, distribution , and hydrologic significance of heterogeneity in the Edwards aquifer? • How much information can be extracted from existing data? • Where are productive areas for future research to better answer this question?

  3. Techniques • Thin section petrography • Measurement of porosity and permeability core plugs from cores and outcrops • Calibration of wireline logs using core plug data and porosity/permeability transforms • Core examination • Fracture aperture measurement • Outcrop photograph digitization • Cave trend analysis • Calculation of permeability from specific capacity tests • Well hydrograph recession analysis • Pseudosynoptic analysis of troughs in the water level • Calcite saturation and other geochemical indicators

  4. Facies Cross Section

  5. Based on log analysis

  6. Variation in Water Level

  7. High Permeability Deep in the Aquifer Hovorka and Yeh

  8. Pore Types

  9. Permeability in Carbonate 1 mm Dissolution of dolomite during diagenesis Randolph FM 1604 core, 924 ft

  10. Impact of Gypsum on Permeability Calcitized gypsum = vuggy, zone, moderate to low permeability

  11. Conduit Flow Dominates • To match springflow, models must upscale transmissivity several orders of magnitude above estimated transmissivity from wells High transmissivity areas of Maclay and Land overlain on well-test-derived permeability model SWRI, 2002

  12. Conduit Flow Dominates • In wells with estimated transmissivity, matrix flow accounts for about 1% of total flow. Mace and Hovorka, permeability from core compared to permeability calculated from specific capacity

  13. F r a c t u r e s 1 m 0 D o l o m i t e l a y e r C a v e s o r f a u l t s Fractures and Caves are Obvious in Outcrop

  14. From G. Schindel

  15. Evolution of Karst, Confined Zone Hovorka and Yeh

  16. Karst features are found in the confined aquifer Missing section, terra rosa, Off-scale caliper 5 cm

  17. Fracturing focuses development of karst Offset decreases cross- fault transmissivity Fractures and brecciation increase permeability parallel to the fault Effects of faulting on permeability

  18. Topographic Expression of Balcones Fault Zone, Austin

  19. Mixing Zone Dissolution – Matrix and Karst

  20. Tracer tests to define conduits in Barton Springs segment Brian Smith BSEACD Nico Hauwert COA

  21. Uranine Tracer Test Results in the Landa Park Area Uranine NBU Well 5 Eosine  Panther Canyon Well LCRA Well  Schindel, Johnson and others, 2002

  22. Conduit Interpretation(Steve Worthington) San Marcus Sp. Comal Sp. Base permeability from SWRI, based on statistical handling of well tests

  23. Synoptic Potentiometric Surface of San Antonio Segment Esquilin, 2003 provisional synoptic

  24. Trough in Water Level Interpreted as Conduits Brian Smith, Barton Springs Edwards Aquifer CD; Nico Hauwert City of Austin

  25. Conduits Interpreted from Pseudosynoptics

  26. Interpreted Conduits Compared to Other Indicators

  27. Conclusions • Matrix permeability is inadequate to describe Edwards flow system • Numerous lines of evidence suggest that conduit flow dominates

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