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Barton Springs / Edwards Aquifer Conservation District

Publication Date

January 2004

Abstract

CONTENTS PREFACE...................................................................................xi EXECUTIVE SUMMARY...............................................................xiii 1.0 INTRODUCTION...........................................................................1 1.1 Purpose and Approach............................................................2 1.2 Concepts and Definitions of Sustainable Yield.................................3 2.0 SETTING.....................................................................................4 2.1 Study Area...........................................................................4 2.2 Previous Aquifer Studies..........................................................4 2.3 Geology..............................................................................6 2.4 Hydrogeology.......................................................................7 2.4.1 Aquifer Boundaries..............................................7 2.4.2 Recharge...........................................................8 2.4.2.1 Surface Recharge........................................8 2.4.2.2 Subsurface Recharge....................................8 2.4.3 Discharge..........................................................9 2.4.3.1 Spring Flow...............................................9 2.4.3.2 Pumpage.................................................10 2.4.4 Groundwater Storage and Flow...............................11 2.4.5 1950's Drought..................................................12 2.4.6 Trinity Aquifer...................................................12 3.0 NUMERICAL GROUNDWATER MODELING.....................................13 3.1 Purpose and Approach of Modeling.............................................13 3.2 Previous Work: 2001 GAM......................................................14 3.2.1 2001 GAM Simulations.................................................16 3.3 Transient-Model Recalibration..................................................16 3.3.1 Water Levels..............................................................17 3.3.2 Spring flow................................................................18 3.3.3 Sensitivity Analyses......................................................19 3.4 Predictions..........................................................................19 3.4.1 Pumping...................................................................19 3.4.2 Impacts to Spring Flow and Water Levels............................20 3.5 Qualifications and Data Needs................................................21 3.6 Major Findings.....................................................................24 4.0 IMPACTS TO WATER LEVELS AND WATER-SUPPLY WELLS FROM 1950'S DROUGHT CONDITIONS AND PUMPING...............................25 4.1 Methods.............................................................................25 4.1.1 Data Sets..................................................................26 4.1.1.1 Structure-Contour Maps........................................26 4.1.1.2 Potentiometric Maps............................................27 4.1.1.3 Simulated Drawdown..........................................28 4.1.1.4 Well Data.........................................................28 4.1.2 Saturated Aquifer Thickness Analysis.................................29 4.1.3 Saturated Borehole Thickness Analysis...............................30 4.2 Results..............................................................................31 4.3 Discussion..........................................................................32 4.4 Major Findings.....................................................................35 5.0 CONCLUSIONS...........................................................................36 5.1 Acknowledgments.................................................................36 6.0 REFERENCES.............................................................................38 7.0 GLOSSARY OF HYDROGEOLOGIC TERMS......................................44 TABLES 3-1. Comparison of measured and simulated water-level values and residuals from the 2001 GAM and recalibrated model 3-2. Comparison of hydraulic conductivity for the 2001 GAM and recalibrated GAM 4-1. Composite potentiometric data 4-2. Simulated drawdown in wells under 1950's drought conditions and various pumping scenarios 4-3. Saturated aquifer thickness analysis under 1950's drought conditions and various rates of pumping 4-4. Saturated borehole analysis under 1950's drought conditions and various rates of pumping 4-5. Total impact to wells under 1950's drought conditions and various rates of pumping FIGURES 2-1. Location map of study area 2-2. Cross section of Barton Springs and Trinity Aquifers in Hays County 2-3. Histogram of permitted and actual pumping 3-1. Hydrograph of simulated and measured spring flow from 1950's drought 3-2. Map of zonal distribution of hydraulic conductivity in the recalibrated GAM 3-3. Scatter plot of simulated results from 2001 GAM and recalibrated GAM plotted against measured low-flow 1950's water levels 3-4. Comparison of simulated and measured water-level elevation hydrographs of the study area 3-5. Scatter plot of spring-flow simulations from the 2001 GAM and recalibrated GAM and mean of measured spring-flow values for all flow conditions and low-flow conditions 3-6. Sensitivity of transient simulated spring discharge to recharge, specific yield, and specific storage 3-7. Sensitivity of transient calibration water levels to specific storage 3-8. Sensitivity of transient calibration water levels to specific yield 3-9. Sensitivity of transient calibration water levels to recharge 3-10. Hydrograph of simulated spring flow under 1950's drought conditions and 0.66, 10, and 15 cfs pumping rates 3-11. Simulated potentiometric surface contour map under average conditions and 19 cfs of pumping and drought conditions with 19 cfs pumping 4-1. Structure contour of the elevation of the bottom of the Edwards Aquifer 4-2. Isopach map of the Edwards Aquifer 4-3. Potentiometric map of the Edwards Aquifer under 1950's drought conditions 4-4. Simulated drawdown from pumping 10 cfs at the end of the 10-yr simulation 4-5. Potentiometric map of 1950's drought conditions and 10 cfs pumping 4-6. Histogram of specific-capacity values from the unconfined portion of the Edwards Aquifer and distribution and classed values of specific-capacity data 4-7. Saturated-thickness contour map of the Edwards Aquifer under 1950's drought conditions with minimal pumping 4-8. Composite of 100-ft saturated aquifer thickness contour lines under 1950's drought conditions with 0.66, 5, 10, 15, and 19 cfs of pumping 4-9. Chart summarizing number of wells impacted under 1950's drought conditions and various pumping rates APPENDICES A. Groundwater Availability of the Barton Springs Segment of the Edwards Aquifer, Texas: Numerical Simulations through 2050 B. Sensitivity Analysis of Southern Groundwater Divide C. List of participants and affiliations at sustainable yield meetings at the BSEACD: September 10, 2003 and March 24, 2004. Open Access - Permission by Publisher See Extended description for more information.

Keywords

Barton Springs (Austin, Texas, United States), United States, Geology

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1 online resource

Subject: topical

Geology

Subject: geographic

United States

Language

English

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Text

Genre

Reports, Technical

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application/pdf

Identifier

K26-01374

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