GMS:Automated Parameter Estimation
| MODFLOW | |
|---|---|
| Pre-processing | |
| MODFLOW Commands | |
| Building a MODFLOW Model | |
| Map to MODFLOW | |
| Calibration | |
| Packages Supported in GMS | |
| Saving a MODFLOW Simulation | |
| Importing MODFLOW Files | |
| Unsupported MODFLOW Features | |
| Run MODFLOW | |
| Post-processing | |
| MODFLOW Display Options | |
| MODFLOW Post-Processing Viewing Options | |
| Reading a MODFLOW Simulation | |
| Tutorials | |
| Packages | |
| Flow: | BCF6, HUF, LPF, UPW |
| Solvers: | SMS |
| Other: | UZF1 |
One of the tools provided in GMS for model calibration is automated parameter estimation. With automated parameter estimation, an external utility, sometimes called an "inverse model", is used to iteratively adjust a set of parameters and repeatedly launch the model until the computed output matches field-observed values. Parameter estimation is used in conjunction with the point observations and the flow observations.
Automated parameter estimation is supported in GMS for the MODFLOW simulations using PEST a general purpose parameter estimation utility developed by John Doherty of Watermark Computing.
Inverse models should only be used carefully and with a full understanding of the assumptions, equations, and methods involved. It is suggested that the user read the available documentation on the inverse model being used. Only the steps involved in setting up an inverse model are described in this document.
Contents
- 1 Basic Steps
- 1.1 1. Create a Working MODFLOW Model
- 1.2 2. Enter the Observations
- 1.3 3. Turn on the Inverse Model
- 1.4 4. Parameterize the model
- 1.5 5. Create a Parameter List
- 1.6 6. Set parameter estimation options
- 1.7 7. Edit the Group Weight Multipliers
- 1.8 8. Edit the Convergence Options
- 1.9 9. Save and Run MODFLOW Model
- 1.10 10. Viewing the Optimal values
- 2 Sensitivity Analysis
- 3 Parameter Estimation Dialog
- 4 See also
Basic Steps
The basic steps involved in using an inverse model for parameter estimation are follows:
1. Create a Working MODFLOW Model
The first step is to create your MODFLOW model and run a simulation. Before launching the inverse model, you need to have a MODFLOW model that successfully converges and you need to determine a good set of starting values for your parameters. Once you have a solution it is also a good idea to copy the computed heads from your solution to your starting heads array. This ensures that as the inverse model modifies the parameters and runs MODFLOW repeatedly, it is more likely that MODFLOW will quickly converge each time it is launched.
2. Enter the Observations
Once you have a working MODFLOW model, you should enter your head and flux observations. Head observations are entered as points using an observation coverage in the Map module. Flow observations are assigned directly to arcs and polygons in source/sink coverages. Each of the observations is assigned a weight that is saved to the inverse input files.
3. Turn on the Inverse Model
You must select an inverse model. Bring up the Global Options dialog and select either the Parameter Estimation or Stochastic Inverse Model button depending on whether a stochastic simulation is being run.
4. Parameterize the model
The next step is to parameterize your model. See the Parameters page for more details.
5. Create a Parameter List
The next step is to create the parameter list. See the Parameters page for details.
6. Set parameter estimation options
Once the parameter list is set up, you may wish to edit the general Parameter Estimation options. These options include the output control and convergence criteria.
7. Edit the Group Weight Multipliers
The group weight multipliers can be edited to adjust the relative weight of the head and flux observations.
8. Edit the Convergence Options
Edit the MODFLOW Convergence Options if necessary in order to ensure a stable solution.
9. Save and Run MODFLOW Model
Once all of the inverse model options have been set, the next step is to save the MODFLOW model using the Save/Save As command in the File menu. Next, run MODFLOW and the inverse model will run with MODFLOW. The inverse model will then be launched in a separate window or the model wrapper in which you will see information relating to the MODFLOW runs and the status of the objective function. Depending on the problem, the inverse model may take anywhere from several minutes to several hours (or days) to run to completion. When the inverse process is completed successfully, GMS automatically launches a MODFLOW forward run with the optimal values computed by the inverse model. Thus, the solution will reflect the optimal values computed by the inverse model.
10. Viewing the Optimal values
When the inverse model is finished, it writes out a text file containing the set of parameter values corresponding to the minimum calibration error. These values can be viewed with the Import Optimal Values button. This copies the optimal parameter values to the Starting Value field in the Parameter List.
Sensitivity Analysis
At each PEST iteration, PEST computes the sensitivities of each of the parameters. This information is available in the "model.sen" file (where model is the name of the MODFLOW model). PEST records the composite sensitivity and the relative composite sensitivity of each parameter in this file. This information is useful in determining which parameters have the greatest effect on the model as well as which parameters have the least effect on the model. Thus, the "insensitive" parameters can be removed or held constant in a subsequent PEST run.
For a more detailed description of parameter sensitivity see section 5.3.2 of the PEST manual.
Parameter Estimation Dialog
Options affecting parameter estimation can be changed via the Parameter Estimation Dialog.
See also
| GMS – Groundwater Modeling System | ||
|---|---|---|
| Modules: | 2D Grid • 2D Mesh • 2D Scatter Point • 3D Grid • 3D Mesh • 3D Scatter Point • Boreholes • GIS • Map • Solid • TINs • UGrids |  |
| Models: | FEFLOW • FEMWATER • HydroGeoSphere • MODAEM • MODFLOW • MODPATH • mod-PATH3DU • MT3DMS • MT3D-USGS • PEST • PHT3D • RT3D • SEAM3D • SEAWAT • SEEP2D • T-PROGS • ZONEBUDGET | |
| Aquaveo | ||
