Final Report Groundwater Availability Model for the West Texas Bolsons (Red Light Draw, Green River Valley, and Eagle Flat) Aquifer in Texas Texas Water Development Board Prepared for the P.O. Box 1321, Capitol Station Austin, Texas 78711-3231 November 2008 Prepared by: James A. Beach, P.G. Leigh Symank Yun Huang John B. Ashworth, P.G. Tyler Davidson, P.E. Eddie W. Collins, P.G. Barry J. Hibbs, Ph.D. Bruce K. Darling, Ph.D., P.G. Kevin Urbancyk, Ph.D., P.G. Kenny Calhoun Steve Finch, P.G. M e x T i c e o x a s R i o G r a n d e Hudspeth Co. J e P f r f e Culberson Co. D s i a d v i o i s Texas Water Development Board Final Report Groundwater Availability Model For the West Texas Bolsons (Red Light Draw, Green River Valley and Eagle Flat) Aquifer in Texas Prepared by: James A. Beach, P.G. Leigh Symank Yun Huang John B. Ashworth, P.G. Tyler Davidson, P.E. LBG-Guyton Associates Eddie W. Collins, P.G. Bureau of Economic Geology Barry J. Hibbs, Ph.D. University of California Bruce K. Darling, Ph.D., P.G. Southwest Groundwater Consulting, LLC Kevin Urbancyk, Ph.D, P.G. Sul Ross State University Kenny Calhoun Daniel B. Stephens and Associates, Inc. Steve Finch John Shomaker and Associates, Inc. November 2008 GEOSCIENTIST AND ENGINEERING SEAL This report documents the work of the following Licensed Texas Geoscientists or Licensed Texas Professional Engineers: James A. Beach, P.G. Mr. Beach was the Project Manager and was responsible for overseeing the development of the conceptual model, and for development and calibration of the numerical model. Tyler Davidson, P.E. Mr. Davidson was responsible for the evaluation of hydraulic properties and water quality in the conceptual model. John Ashworth, P.G. Mr. Ashworth was responsible for helping integrate the geologic structure into the numerical model. Eddie W. Collins, P.G. Mr. Collins was responsible for development of the conceptual geologic structure in the model area. iaJij Bruce K. Darling, Ph.D., P.G. Dr. Darling was responsible for geology sections in the report. /a261 Steven Finch, P.G. Mr. Finch was responsible for estimates for the model. Groundwater Availability Model for the West Texas Bolsons (Red Light Draw, Green River Valley, and Eagle Flat) Aquifer in Texas TABLE OF CONTENTS 1.0 INTRODUCTION ........................................................................................... 1-1 2.0 STUDY AREA ................................................................................................. 2-1 2.1 Location............................................................................................................. 2-1 2.2 Physiography ..................................................................................................... 2-9 2.3 Climate ............................................................................................................ 2-15 2.4 Vegetation and Land Use ................................................................................ 2-23 2.5 Geology ........................................................................................................... 2-26 3.0 PREVIOUS WORK ........................................................................................ 3-1 3.1 Hydrogeologic Framework................................................................................ 3-1 3.2 Groundwater Models......................................................................................... 3-2 4.0 HYDROLOGIC SETTING ............................................................................ 4-1 4.1 Hydrostratigraphy.............................................................................................. 4-1 4.1.1 Red Light Draw........................................................................................ 4-2 4.1.2 Northwest Eagle Flat................................................................................ 4-3 4.1.3 Southeast Eagle Flat................................................................................. 4-4 4.1.4 Green River Valley .................................................................................. 4-4 4.2 Structure ............................................................................................................ 4-5 4.2.1 Data Sources............................................................................................ 4-5 4.2.2 Construction of the Structural Surfaces ................................................... 4-6 4.2.3 Discussion of Structure............................................................................ 4-6 4.3 Water Levels and Regional Groundwater Flow .............................................. 4-12 4.3.1 Hydrographs........................................................................................... 4-13 4.3.2 Groundwater Flow................................................................................. 4-13 4.3.3 Potentiometric Map................................................................................ 4-17 4.3.4 Flow Systems......................................................................................... 4-20 4.3.5 Vertical Flow......................................................................................... 4-23 4.4 Recharge.......................................................................................................... 4-25 4.4.1 Recharge Areas...................................................................................... 4-25 4.4.2 Recharge Estimates from Previous Work.............................................. 4-26 4.4.3 Summary of Recharge Method .............................................................. 4-28 4.4.4 Recharge Estimates................................................................................ 4-30 4.5 Rivers, Streams, Springs and Lakes ................................................................ 4-35 4.6 Hydraulic Properties........................................................................................ 4-38 4.6.1 Hydraulic Conductivity.......................................................................... 4-38 4.6.2 Storage Properties.................................................................................. 4-39 4.7 Discharge......................................................................................................... 4-42 4.8 Water Quality.................................................................................................. 4-50 i 5.0 CONCEPTUAL MODEL OF FLOW IN WEST TEXAS BOLSON AQUIFERS..................................................................................... 5-1 5.1 Conceptual model.............................................................................................. 5-1 6.0 MODEL DESIGN............................................................................................ 6-1 6.1 Code and Processor ........................................................................................... 6-1 6.2 Model Layers and Grid...................................................................................... 6-2 6.3 Model Parameters............................................................................................ 6-11 6.3.1 Hydraulic Conductivity.......................................................................... 6-11 6.3.2 Storage Coefficients............................................................................... 6-12 6.4 Model Boundaries........................................................................................... 6-13 6.4.1 Lateral Boundaries................................................................................. 6-13 6.4.2 Vertical Boundaries............................................................................... 6-18 6.4.3 Streams and Springs............................................................................... 6-18 6.4.4 Recharge and Evapotranspiration .......................................................... 6-18 6.4.5 Pumping Discharge................................................................................ 6-19 7.0 MODELING APPROACH............................................................................. 7-1 7.1 Calibration ......................................................................................................... 7-1 7.1.1 Approach.................................................................................................. 7-1 7.1.2 Calibration Targets and Measures ........................................................... 7-2 7.1.3 Calibration Target Uncertainty................................................................ 7-4 7.2 Sensitivity Analyses.......................................................................................... 7-5 8.0 STEADY-STATE MODEL ............................................................................ 8-1 8.1 Calibration ......................................................................................................... 8-1 8.1.1 Calibration Targets...................................................................................8-1 8.1.2 Horizontal and Vertical Hydraulic Conductivities .................................. 8-1 8.1.3 Recharge .................................................................................................. 8-8 8.1.4 Groundwater Evapotranspiration............................................................. 8-8 8.1.5 General Head Boundaries ........................................................................ 8-8 8.1.6 Calibration Results and Statistics..........................................................