Simulated Ground-Water Flow in the Hueco Bolson, an Alluvial-Basin Aquifer System near El Paso, Texas U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 02-4108 Prepared in cooperation with EL PASO WATER UTILITIES and the U.S. ARMY- FORT BLISS Simulated Ground-Water Flow in the Hueco Bolson, an Alluvial-Basin Aquifer System near El Paso, Texas By Charles E. Heywood and Richard M. Yager U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 02-4108 Prepared in cooperation with EL PASO WATER UTILITIES and the U.S. ARMY - FORT BLISS Albuquerque, New Mexico 2003 U.S. DEPARTMENT OF THE INTERIOR GALE A. NORTON, Secretary U.S. GEOLOGICAL SURVEY Charles G. Groat, Director The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey. For additional information write to: Copies of this report can be purchased from: District Chief U.S. Geological Survey U.S. Geological Survey Information Services Water Resources Division Box 25286 5338 Montgomery Blvd. NE, Suite 400 Denver, CO 80225-0286 Albuquerque, NM 87109-1311 Information regarding research and data-collection programs of the U.S. Geological Survey is available on the Internet via the World Wide Web. You may connect to the home page for the New Mexico District Office using the URL http://nm.water.usgs.gov. CONTENTS Page Abstract.................................................................................................................................................................................. 1 Introduction ........................................................................................................................................................................... 1 Purpose and scope ....................................................................................................................................................... 2 Previous investigations ................................................................................................................................................ 2 Hydrogeology of the Hueco Bolson ...................................................................................................................................... 2 Extent and thickness of hydrogeologic facies ............................................................................................................. 5 Hydraulic conductivities.............................................................................................................................................. 5 Ground-water levels..................................................................................................................................................... 5 Rio Grande Valley surface-water system..................................................................................................................... 8 Agricultural canals and drains ..................................................................................................................................... 12 Recharge ...................................................................................................................................................................... 12 Mountain-front recharge.................................................................................................................................... 12 Underflow from Tularosa and Mesilla Basins ................................................................................................... 13 Human-induced recharge................................................................................................................................... 13 Discharge ..................................................................................................................................................................... 13 Ground-water withdrawals ................................................................................................................................ 13 Evapotranspiration............................................................................................................................................. 13 Seepage to Rio Grande and agricultural drains ................................................................................................. 13 Land subsidence .......................................................................................................................................................... 14 Steady-state and transient ground-water flow model............................................................................................................. 14 Numerical method ....................................................................................................................................................... 15 Aquifer dewatering ............................................................................................................................................ 15 Multi-aquifer wells ............................................................................................................................................ 15 Spatial discretization.................................................................................................................................................... 18 Vertical datums ............................................................................................................................................................ 18 Temporal discretization ............................................................................................................................................... 18 Boundary conditions.................................................................................................................................................... 19 Specified-flow boundaries ................................................................................................................................. 19 Head-dependent flow boundaries ...................................................................................................................... 19 Streamflow routing ............................................................................................................................................ 20 Faults............................................................................................................................................................................ 23 Storage properties........................................................................................................................................................ 23 Model calibration................................................................................................................................................................... 23 Hydraulic-head measurements .................................................................................................................................... 23 Flow measurements ..................................................................................................................................................... 23 Parameter estimation ................................................................................................................................................... 23 Model evaluation and simulation results ............................................................................................................................... 26 Estimates of aquifer properties.................................................................................................................................... 26 Parameter sensitivities ................................................................................................................................................. 26 Water-level drawdowns................................................................................................................................................ 29 Ground-water budget................................................................................................................................................... 29 Seepage from the Rio Grande...................................................................................................................................... 29 Summary and conclusions..................................................................................................................................................... 51 Selected references ................................................................................................................................................................ 53 Appendix 1: Modifications to MODFLOWP ........................................................................................................................ 56 Appendix 2: Modifications to MODFLOW .......................................................................................................................... 63 Appendix 3: Multi-aquifer well package............................................................................................................................... 68 iii FIGURES Page 1. Shaded-relief map showing principal physiographic features and thickness of alluvial deposits in the Hueco Bolson....................................................................................................................................................