Geology and Ground -Water Resources of Comal County,Texas GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1138 Geology and Ground -Water Resources of Comal County,Texas By WILLIAM O. GEORGE With sections on SURFACE-WATER RUNOFF By SETH D. BREEDING CHEMICAL CHARACTER OF THE WATER By WARREN W. HASTINGS GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1138 Prepared in cooperation with the Texas Board of Water Engineers Sanfrancisco UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1952 UNITED STATES DEPARTMENT OF THE INTERIOR Oscar L. Chapman, Secretary GEOLOGICAL SURVEY W. E. Wrather, Director *H'j&v-.'' l"*J* For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. CONTENTS Page Abstract.._______._,__________________ = ;siiii. i ___ ii ________________ 1 Introduction, _____________________________________________________ 2 Purpose and scope_____________________________________________ 2 History of settlement-___-____--_-_-_______---__-_-____________ 2 Location-.___________________________________________________ 3 Agriculture and% industrial development________--_______-_-_______ 3 Methods of investigation,______________________________________ 5 Previous investigation._________________________________________ 6 Acknowledgments. ______________________________________________ 6 Climate-_____-____-__---___-_-_-_-___-_-___-____-___-_-__________ 6 Topographjr ______________________________________________________ 11 General features_______________________________________________ 11 Drainage._ ___________________________________________________ 11 Stratigraphy. _______________________________'______________________ 12 Rock formations and their water-bearing properties._______________ 13 Pre-Cretaeeous rocks__ ______________________________________ 13 Cretaceous system.________________________________________ 13 Pre-Comanche rocks..__________________________________ 13 Comanche series_________________-____-_-__-____-______ 15 Trinity group.____________________________________ 15 Travis Peak formation. ________________J_______ 15 Glen Rose limestone. ________________________ -_ 17 Fredericksburg group. _____________________________ 21 Walnut clay______________________--___-_____. 21 Comanche Peak limestone.______-____--__-__-__ 22~ Edwards limestone___________________________ 22 Washita group.___________________________________ 23 Georgetown limestone_________________________ 24 Graysoii (Del Rio) shale__________-____----.-- 25 Buda limestone______________________________ 25 Gulf series__-.__.-_____._.___________-___---___-___-._ 26 Eagle Ford shale. _________________________ 26 Austin chalk____________________.___________ 26 Anacacho limestone and Taylor marl_____________ 27 Tertiary (?) system..._______________________________ 27 Pliocene (?) series-_____-___-_-___-__--_--__------_--__ 27 Uvalde gravel_______-______-__-_-__-_-_-_-____ 27 Quaternary system, _ ______________________________________ 28 Pleistocene series___________________.._______-__-_______ 28 Leona formation_____________________________ 28 ni IV CONTENTS Page Structural geology_-______-____-___________-__-_-_-__-____________.. 28 Faults______________________________________________________ 28 Comal Springs fault____-______ ___________ _ ______________ 29 Hueco Springs fault.___ ___________________ _________________ 29 Bat Cave fault-_-__-__-_-_-._ ._-___-__-__________________ 30 Bear Creek fault___J_______________.______________________ 30 Hidden Valley fault_______________________________________ 31 Tom Creek fault____________________________________________ 31 Spring Branch fault______-___--_-____-_____________________ ' 31 Minor faults and folds_ _______ ._____....________________..__.._ 32 Cause of faulting, ____ _______________________________________ 32 Age of faulting._____________________________________________ 32 Other structural features--__--____-__-._-_--__-_-_-.-..____-_____ 33 San Marcos arch, ___________________________________________ 33 Regional dips ._._..____.______....____ _______________________ 33 Sinkholes- _ ________________________________________________ 34 Methods of water-well construction-__________________________________ 34 Occurrence of ground water, with special reference to discharge and source of Comal Springs__ _____________________ .____-___-______-..___-___ 35 The development of the reservoir in the Edwards lirnestone_--______ 36 The development of the reservoirs in the Glen Rose limestone______ 38 Ground-water discharge________-..__________-_-____---_-_-__-_-. 38 Comal Springs_____________...--_-_____-_-___---_--_-_-____ 38 Hueco Springs__________---_-----_--_--_-_-_-.-_-_-_----,_-_ 40 Other springs_____________________________________________ 41 Discharge from \vells______________-_-______-_-..--_____---__ 42 Ground-water recharge____________________-__-_-_-_----____-_-_ 42 Water levels in wells in relation to rainfall and discharge of springs- _ _____-__--- __-_--___---------_-_-_--__-----_-_ 43 Movement of ground water. __-____.--_-_------__---_-----_----- 48 Rate of movement---__-_-__-____------_---- ____-______-_-_ 50 Direction of movement-__________________-_-_-__-_-___-__-._ 52 Stream losses and gains-___________--_-___-__-_-_-__-_-_.--- 53 Summary of conclusions._____________---_--_-----------__-_-_-- 60 Surface-water supplies, by Seth D. Breeding-_________________________ 61 Guadalupe River___.________________-------------------------- 61 Comal Springs____________________ _---_---- - ------ 65 Blanco River______________________-__-----_----------------- 67 Comal Creek____.___________ __._ 67 Cibolo Creek__ - - 67 Simultaneous records.___________________---__-_-_____--_-_--- 67 Conclusions. __ __________________ _ - - - 69 Chemical character of the water, by Warren W. Hastings..- _-_-_-_- 69 References cited-_________________________- __-_--_--_ _.-- --- 72 Logs of wells___ _ _ ______ -_ _______ 115 Index. _____________ _ _ _ - _ - - 125 CONTENTS ILLUSTRATIONS Page PLATE 1. A, Guadalupe River at Hueco Springs fault. B, Cavern in flood plain on Cibolo Creek________________._______ Facing 10 2. Geologic map and section of Comal County, Tex., showing lo­ cations of recorded wells and springs.________.:____ In pocket 3. A, Rudistid limestone in Guadalupe River canyon. B, Ed­ wards and Comanche Peak limestone in Guadalupe River canyon______________________-___-___________---- Facing 24 4. A, Comal Springs. B, Private power plant below Hueco Springs______________________________________---- Facing 40 5. Map showing altitudes of water levels and lines of equal pres­ sure in Edwards limestone reservoir, 1951______--_-__ In pocket 6. Map of Cibolo Creek basin showing geology and stream gaging stations._________________________________________ In pocket FIGURE 1. Index map showing location of Comal County, Tex_________ 4 2. Altitudes of water levels in wells compared with rainfall, 1936-50_____________________________________________ 45 3. Monthly discharge-of Comal Springs compared with water levels and rainfall, 1932-50___________________________ 46 4. Daily discharge of Comal Springs, water level fluctuations, and rainfall, 1942_____________________.________.__________ 49 5. Average monthly discharge of the Guadalupe River at Com­ fort, Spring Branch, and New Braunfels stations, 1939-50- 55 6. Simultaneous runoff water levels, and precipitation records, 1946-50_____________________________________________ 57 7. Chemical character of ground water in Comal County, Tex__ 71 TABLES TABLE 1. Mean monthly temperature at New Braunfels, Tex_________ 7 2. Frost data for New Braunfels for the years 1930-49, inclusive_ 7 3. Monthly precipitation, in inches, at New Braunfels, Comal County, Tex., 1889-1950.____________________________ 8 4. Monthly precipitation, in inches, at Fischer Store, Comal County, Tex., 1890-1950_______________---____-_-_---_ 9 5. Monthly precipitation, in inches, at Boerne, Kendall County, Tex., 1892-1950_________ _ - -- ---- -_ 10 6. Monthly precipitation, in inches, at Bulverde, Comal County, Tex./1940-50_____________-_-__-_-_--------_--_-_---_ 11 7. Geologic formations in Comal County, Tex________________ 14 8. Comparison of minimum, maximum, and average discharge of Comal Springs and other important springs of the Balcones fault zone, Texas_____________________________________ 39 9. Temperatures, hardness, and discharge of Hueco. Springs, Texas. ________________-_-_-_-_______________ 52 VI CONTENTS Pagfr TABLE 10. Gaging stations in the Comal County area, Texas_________ 61 11. Runoff of the Guadalupe River.________-______'___________ 62 12. Discharge of the Guadalupe River near Spring Branch and at New Braunfels and pickup between stations; rainfall at Fischer Store and New Braunfels, Tex., 1928-50-.-_.___ 63 13. Discharge measurements, Hueco Springs, 3 miles north of New Braunfels, Tex_.._____________________________ 63 14. Discharge measurements to determine seepage on the Guad­ alupe River from Comfort, Tex., to New Braunfels, Tex., in January 1928____________-________-_---__---_--____ 64 15. Discharge measurements to determine seepage on the Guad­ alupe River from Comfort, Tex., to New Braunfels, Tex., in February 1929____________-___-___-__----_--__---_-_ 65 16. Discharge measurements to determine seepage on the Guad­ alupe River from Spring Branch, Tex., to New Braunfels, Tex., in August 1944__________________________________ 66 17. Average monthly and annual discharge, in second-feet, of Comal Springs at New Braunfels, Tex___________________ 66 18. Rainfall and runoff, Comal