.::·.t·.·t:: . •..... ·.•... •••. ,··,.,: '. •.~\..... - .· :·.: ... · ,.·\·r~· .... ·.· . .. ..: ... .: .. · ....· . EDWARDS UNDERGROUND WATER DISTRICT REPORT 95-02 REGIONAL DISTRIBUTION OF PERMEABILITY IN THE EDWARDS AQUIFER r­ r E REGIONAL DISTRlBUTION OF PERMEABILITY IN THE EDWARDS AQUIFER r r Final Report r by r Susan D. Hovorka, Robert E. Mace, and Edward W. Collins r assisted by r E. M. Boghld, N. D. johns, jun Uao, and N. L. BaghaJ r r Prepared for Edwards Underground Water Dtstrtct r under Contract No. 93-17-FO r Alan R. Dutton, Prlndpal Investigator Bureau of Economic Geology r Noel Tyler, Director The University of Texas at Austin r Austin, Texas 78713-8924 r january 1995 t r r r' I CONTENTS r. EXECUTI'VE S~Y ••......••.••••.......•....•....••..•.•.........•..................•.••••••..•••••....•••......••••••.•.••••.....••..•.. tx. r ABS'IMcr ..........................................•..........................................................•.•.....•........••••..........••.•...... 1 Nm.ODUcnON .......••....................... ·········································~······················································ ... 3 r Geologic Setting................................ ............. ....... .. .......... .......... ..... .. ......................... ..... ......... ....... 3 r Hydraulic Conductivity-A DeflntUon ...........•••••....•.••............................................................•...... 7 Pr'evlous Work •••••••••..••.••. .. ....••••••••• •• •••••• ••••••••. ••••••..•••••.• •••••••••••••••••. ••.••.••. ••••••• .•••••••... ..••••••••.•. ••• ... 8 Sttucture ......•......................•..........................................•........••.......•..................•...................... s Stratigraphy and Geomorphology .......••••...••••...............•.......•••••••..•••••.••.........•.•..••.................. 9 r Hydraulic Pl'ol)e:rtles ••••... .•......•...... ... ..... .• ... ...•... .. .••••••...... .•••••• •.••••••••••••...•••..... .•••..•. ... ..•.•••••.. .•. 9 Storat::lvlty ............................................................•••.••••......•••............................•••.•.••................ 11 r Hydrologic Simulations •........•.•..•.................................•••••..••••••...•.•••...•••......•••••.•............••••.••. 11 r twfE'niODS •••••.••••••••.••••••.••••••••••••••••.....••••••.•.•••.••••.••......•......••••••••.•••••••••••••••••••••••••••••••••.•••.....•...•••....... 12 Sti'Uctural Data Set ....•....••.•....................•........•..................•............•..••......••••.•.•••••••.......••.....••••.••.. 13 r Isopa.dl MaiJS ••••......•.........••.••••••..••....••••••.•••••.•••••••••••••.•••••.••••••••••.••••.•••••••........•••...•••....••.•••••••••.. _ 14 Spedftc Capadty, Transmissivity, and Hydraulic Conductivity Data Set ..................................... 17 Data Collection ........................................................................................................................ 17 SJ)e'Ciftc Capadty ..•........................•••••...•.••...••••••...............•................••.•............................ 17 . r l'ransmisslvtty and HydrauUc Conductivity ...................................................................... 18 r Calculation of Transmissivity from Specific capadty ............................................................. 19 Well I.oss ..••••••••••••••.......•..•..••••••••••••••.•••.•..•............•.•••••••.•••••••..••••••....•.•••..........•......•.•...... 2:() r Partial Penetradon ...............••......••......•.....................•••••.....•............................................. 21 Analytical Relationship between Transmissivity and Specific capadty ........................... 21 r Empirical Relationship between Transmissivity and Specific Capadty ............................ 22 r Geostatistlcal Analysis .•............••..•••......•.................................................••••••....••..................... 23 Assessment of Vertical Variations in Hydraulic Conductivity ................................................ 25 r Plug and l.og-Based Calculation of PermeabllJty' •.........•.••..••..............••...............•.••..••••.••.•••......... 29 r Ul r l Quantitative Desaiption of Faults, Fractures, and Karst in Outcrop ............................................ 32 l Fracture Mapplrlg ..........................................................................................•.............•.•.......... 33 I Fracture Aperture, Porosity, a11d PenneabUity ................•........•••....•••....••.....••...........•••••...•..•.. 33 l Fracture and Conduit Roughness ..•.....••.•........................................................••.•...•................. 35 I . l Karst Features ................••••.....................................••.....••..•......••••.........•.....••••.......................... 36 ! Dlglta.l Data. Coverages ..............................................••..•.•......•.•..•......................•....••••...........•....... 36 l 1 RESUL1'S •••••••••••••••••••••••• •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 36 Structural FrameworkI of Edwards Aquifer ...................................................................................... 36 l Matrix and Conduit PenneabWty of the Edwards Aquifer ........................................................... .41 Petrographic andI Fades Controls on PerJD.eablllty .................................................................. 43 l I Poroslty'-PenneabWty Relatlonstups ................................................................................. 53 l TranSJDisslvlty' &om: Aquifer Tests ...............................••••••••.••••••.......•••••.•••••••••.............................. 00 I Relationship be~een Transmissivity' and Specific capadty' ................................................... ~ l Analysis of Data •••.••...•...............••........•••••.•••...........•..••••••..•••.............•.....••••........•..•..•••...•••...•• 63 Statistical ~ption of Data ........................................................................................... 63 l Areal Dlst:ribuUon of Transmissivity ...•............•••••••.•....•..•..•..•........••....•........••.................• 66 Spatial RelaUonshlps .......................................................................................................... 70 l i Vertical Varlation of HydrauUc Conductivity' ................................................................... 74 I l Relationship to Mattix Pel'meabWty ................................................................................... 81 Outaop Invest:lga.t:IOns ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••.•••••••••••••••• 83 l I Structural Des.alptlon of Fractures •.......................•......•......••.•••..•..............••...............•.....•••••. 83 Fracture Aperture, Porosity, and Penneablllty' ......................................................................... 87 l I Fracture an~ Conduit Roughness ...................................................................................... 91 I ' l l<a.rst •••••••••• ~- •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 91 DISCUSSION...................................................................................................................................... 106 l CONCLUSIONS..................................................................................................................................I 111 Fl1R11-fER WORK................................................................................................................................ 113 l l lv l r r ACKNOWLEDGMENTS ..................................................................................................................... 114 r REFERENCES .. .. .. .. .. ............ ............... ....... .......... .................. .. ..... ............ ... .. ... .......... .. ..... .. .. 114 r Figures 1. Structural, hydrologic, and fades setting of the Edwards aquifer .............................................. 4 r 2. Stratigraphic units within the Edwards Group .•............................•.........••..••.••.......................•.. 6 3. Conceptual models relating the mean hydraulic conductivity to the hydraulic r conductivity and thicknesses of two layers .•............................................................................. 26 4. Variation of transmissivity and spedfic capadty for lnaeasing test interval length ............... 27 r S. Structural aoss section A-A' of the Balcones Fault ZOne at New Braunfels, Texas ................... 40 r 6. GeneraUzed view of a relay ramp ............................................................................................... 4Z 7. Generalized view of sea-level-controlled depositional fades .................................................... 45 r 8. Generalized fades aoss section B-B' of the Edwards Group .............•.......•.............................. .47 9. Schematic diagram of several common pore structures resulting from different r diagenetic histories ..................................................................................................................... 48 10. Relation of measured plug permeability to porosity and calculated permeability ................... 54 r 11. Semllog scatter plot of plug porosity