Prepared in cooperation with the Bureau of Reclamation, Washington State Department of Ecology, and the Yakama Nation Numerical Simulation of Groundwater Flow for the Yakima River Basin Aquifer System, Washington Scientific Investigations Report 2011–5155 U.S. Department of the Interior U.S. Geological Survey Cover: Photograph of Clark Well No. 1, located on the north side of the Moxee Valley in North Yakima, Washington. The well is located in township 12 north, range 20 east, section 6. The well was drilled to a depth of 940 feet into an artesian zone of the Ellensburg Formation, and completed in 1897 at a cost of $2,000. The original flow from the well was estimated at about 600 gallons per minute, and was used to irrigate 250 acres in 1900 and supplied water to 8 small ranches with an additional 47 acres of irrigation. (Photograph was taken by E.E. James in 1897, and was printed in 1901 in the U.S. Geological Survey Water-Supply and Irrigation Paper 55.) Numerical Simulation of Groundwater Flow for the Yakima River Basin Aquifer System, Washington By D.M. Ely, M.P. Bachmann, and J.J. Vaccaro Prepared in cooperation with the Bureau of Reclamation, Washington State Department of Ecology, and the Yakama Nation Scientific Investigations Report 2011–5155 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia: 2011 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS. 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Suggested citation: Ely, D.M., Bachmann, M.P., and Vaccaro, J.J., 2011, Numerical simulation of groundwater flow for the Yakima River basin aquifer system, Washington: U.S. Geological Survey Scientific Investigations Report 2011-5155, 90 p. iii Contents Abstract ..........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Purpose and Scope .......................................................................................................................................3 Description of Study Area ............................................................................................................................3 Location and Setting ............................................................................................................................3 Development of Water Resources .....................................................................................................4 Overview of the Geology......................................................................................................................7 Well Data and Their Use .............................................................................................................................10 Hydrogeologic Units ....................................................................................................................................10 Numerical Simulation of Groundwater Flow ...........................................................................................19 Model Hydrogeologic Units ..............................................................................................................19 Discretization .......................................................................................................................................22 Spatial Discretization and Layering ........................................................................................22 Temporal Discretization ............................................................................................................24 Boundary Conditions ..........................................................................................................................24 No-Flow Boundaries .................................................................................................................25 Head-Dependent Flux Boundaries ..........................................................................................25 Drain Conductances and Stages ...................................................................................25 Stream Conductances and Stages ................................................................................25 General-Head Boundary Conductances and Stages .................................................28 Specified-Head Stages .............................................................................................................28 Specified-Flux Boundaries .......................................................................................................28 Groundwater Pumping .....................................................................................................28 Groundwater Recharge ...................................................................................................31 Specified Stream Inflows ................................................................................................33 Initial Conditions..................................................................................................................................35 Initial Hydraulic Properties ...............................................................................................................35 Horizontal Hydraulic Conductivity ...........................................................................................36 Vertical Hydraulic Conductivity ...............................................................................................40 Storage Properties ....................................................................................................................40 Geologic Structures ..................................................................................................................40 Model Calibration and Sensitivity .............................................................................................................42 Calibration Approach .........................................................................................................................47 Sensitivity Analysis ....................................................................................................................47 Parameter Correlation Coefficient ..........................................................................................47 Observations Used in Model Calibration ........................................................................................48 Water Levels, Water-Level Changes, and Associated Errors ............................................48 Streamflow Observations and Errors .....................................................................................49 Model-Calibrated Hydraulic Properties and Parameter Uncertainty ........................................49 Statistical Measures of Model Fit ....................................................................................................53 iv Contents—Continued Model Calibration and Sensitivity—Continued Transient Calibration Model Fit .........................................................................................................54 Comparison of Simulated and Measured Hydraulic Heads ...............................................54 Comparison of Simulated and Measured or Estimated Streamflow .................................61 Model Uncertainty and Limitations ...........................................................................................................67 Appropriate Uses of the Groundwater Model ........................................................................................69 Model-Derived Groundwater Budget .......................................................................................................69 Model Applications......................................................................................................................................70 Scenario 1—Existing Conditions without Pumping ......................................................................73 Scenario 2—Existing Conditions without Basalt Pumping ..........................................................75 Scenario 3—Existing Conditions with Additional Recharge and without Exempt Pumping ....................................................................................................................77 Scenario 4—Existing Conditions with Additional Pumpage Estimated for Pending Groundwater Applications ...................................................................................78 Scenario 5—Existing Conditions Continued into the Future .......................................................79 Changes in the Cumulative Water