MODFLOW-2000, the U.S. Geological Survey modular ground-water model; user guide to the observation, sensitivity, and parameter-estimation processes and three post-processing programs

[摘要] This report documents the Observation, Sensitivity, and Parameter-Estimation Processesof the ground-water modeling computer program MODFLOW-2000. The Observation Processgenerates model-calculated values for comparison with measured, or observed, quantities. Avariety of statistics is calculated to quantify this comparison, including a weighted least-squaresobjective function. In addition, a number of files are produced that can be used to compare thevalues graphically. The Sensitivity Process calculates the sensitivity of hydraulic headsthroughout the model with respect to specified parameters using the accurate sensitivity-equationmethod. These are called grid sensitivities. If the Observation Process is active, it uses the gridsensitivities to calculate sensitivities for the simulated values associated with the observations.These are called observation sensitivities. Observation sensitivities are used to calculate a numberof statistics that can be used (1) to diagnose inadequate data, (2) to identify parameters thatprobably cannot be estimated by regression using the available observations, and (3) to evaluatethe utility of proposed new data.The Parameter-Estimation Process uses a modified Gauss-Newton method to adjustvalues of user-selected input parameters in an iterative procedure to minimize the value of theweighted least-squares objective function. Statistics produced by the Parameter-EstimationProcess can be used to evaluate estimated parameter values; statistics produced by theObservation Process and post-processing program RESAN-2000 can be used to evaluate howaccurately the model represents the actual processes; statistics produced by post-processingprogram YCINT-2000 can be used to quantify the uncertainty of model simulated values.Parameters are defined in the Ground-Water Flow Process input files and can be used tocalculate most model inputs, such as: for explicitly defined model layers, horizontal hydraulicconductivity, horizontal anisotropy, vertical hydraulic conductivity or vertical anisotropy, specificstorage, and specific yield; and, for implicitly represented layers, vertical hydraulic conductivity.In addition, parameters can be defined to calculate the hydraulic conductance of the River,General-Head Boundary, and Drain Packages; areal recharge rates of the Recharge Package;maximum evapotranspiration of the Evapotranspiration Package; pumpage or the rate of flow atdefined-flux boundaries of the Well Package; and the hydraulic head at constant-head boundaries.The spatial variation of model inputs produced using defined parameters is very flexible,including interpolated distributions that require the summation of contributions from differentparameters.2Observations can include measured hydraulic heads or temporal changes in hydraulicheads, measured gains and losses along head-dependent boundaries (such as streams), flowsthrough constant-head boundaries, and advective transport through the system, which generallywould be inferred from measured concentrations.MODFLOW-2000 is intended for use on any computer operating system. The programconsists of algorithms programmed in Fortran 90, which efficiently performs numericalcalculations and is fully compatible with the newer Fortran 95. The code is easily modified to becompatible with FORTRAN 77. Coordination for multiple processors is accommodated usingMessage Passing Interface (MPI) commands. The program is designed in a modular fashion thatis intended to support inclusion of new capabilities.

[发布机构] U.S. Geological Survey

[学科分类] 地球科学(综合)