|Scientific Investigations Report 2006–5009|
By Keith J. Halford
MODOPTIM is a non-linear ground-water model calibration and management tool that simulates flow with MODFLOW-96 as a subroutine. A weighted sum-of-squares objective function defines optimal solutions for calibration and management problems. Water levels, discharges, water quality, subsidence, and pumping-lift costs are the five direct observation types that can be compared in MODOPTIM. Differences between direct observations of the same type can be compared to fit temporal changes and spatial gradients. Water levels in pumping wells, wellbore storage in the observation wells, and rotational translation of observation wells also can be compared. Negative and positive residuals can be weighted unequally so inequality constraints such as maximum chloride concentrations or minimum water levels can be incorporated in the objective function. Optimization parameters are defined with zones and parameter-weight matrices. Parameter change is estimated iteratively with a quasi-Newton algorithm and is constrained to a user-defined maximum parameter change per iteration. Parameters that are less sensitive than a user-defined threshold are not estimated. MODOPTIM facilitates testing more conceptual models by expediting calibration of each conceptual model. Examples of applying MODOPTIM to aquifer-test analysis, ground-water management, and parameter estimation problems are presented.
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Purpose and Scope
The Optimization Problem
Zonation and Parameter-Weight Matrices
Parameter-Weight Matrices from Iso-Value Contours
Parameter Sensitivity and Ranking of Parameters Parameter Scaling
Implementation of Minimization Algorithm in MODOPTIM
MODOPTIM—Organization and Structure
MODOPTIM and MODFLOW files
Interpolation of Point Observations
Special Cases for Water-Level Observations
Water-Levels in Pumping Wells
Wellbore Storage in Observation Wells
Rotation of Observation Wells
Comparison of Observation Differences
Weighting of Observations
Different Observation Types
Output and Analysis of Results
Parameter Estimates and Optimization Results
Residuals and Sensitivities
Comparison to Other Programs
Appendix A. Input structures used in MODOPTIM files
Appendix B. Input for main optimization file
Appendix C. Input for composite MODFLOW/MODOPTIM file with parameters to be estimated
Appendix D. Input for grid discretization file
Appendix E. Time-variant hydraulic-property package (VAR1)
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