Sensitivity analysis 32 Calibration of model under transient conditions 34 General procedure 34 Modeled flow components 37 Groundwater conditions 37 Surface-water conditions 37 Contents III Calibration of model under transient conditions Continued Specific yield and storage coefficient 38 Initial estimates 38 Adjustments 38 Recharge 38 Boundary conditions 41 Results 41 Sensitivity analysis 45 Digital-model evaluation of groundwater resources 45 General procedure 45 Qualitative ranking of hydrogeologic units 46 Standardized potential yield 46 Procedure 46 Results 47 Analysis by hydrogeologic unit 47 Analysis in a selected area 52 Reliability of model results 54 Suggested uses of model 58 Summary 59 References cited 61 Appendixes: A: Model program listing 64 B: Instructions for use of model program 108 C: Water-level measurement data from observation-well network 118 Metric conversion factors 128 PLATES [Plates in pocket] Contents V 42 19. Statistical comparison, by general lithology, of observed and model-generated changes in water-table altitude in calibrated transient model 45 20. Ranking of hydrogeologic units, based on effects of withdrawing 1 inch of ground water per year from modeled area 46 21. Standardized potential yield for each hydrogeologic unit, based on hypothetical withdrawal scheme 47 22. Time, since start of hypothetical withdrawal scheme, for each hydrogeologic unit to reach steady-state conditions 49 23. Percentage reduction of average annual base flow during 20-year simulation of hypothetical withdrawal scheme 49 24. Median decline of water table during 20-year simulation of hypothetical withdrawal scheme 50 25. Groundwater budget for each hydrogeologic unit after 91 days of hypothetical withdrawal scheme 51 26. Ultimate groundwater budget for each hydrogeologic unit resulting from hypothetical withdrawal scheme 52 VI Contents

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