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Before attempting to run a parameter estimation simulation, make sure your model meets the
following requirements:
The model runs successfully (converges) and produces meaningful results. The model
should provide a solution under a variety of input parameter conditions. Parameter
estimation is as much an art as it is a science, and therefore, it should only be used to
complement your own efforts in understanding the system.
The model has one or more (preferably many more) observations against which to
compare the calculated results. Observations can be in the form of measured or estimated
values of head or concentration at discrete points in the model, or in the form of measured
or estimated groundwater fluxes into (or out of) one or more grid cells.
It is also recommended that you do a sensitivity analysis prior to a full-fledged PEST run. In
a sensitivity analysis, parameter values are individually changed to determine the effect on
model calibration and prediction. The results give an indication of which parameter changes
can have significant impact on the model results (these are sensitive parameters) and
which parameter changes have little or no impact on the model results (these are nonsensitive or insensitive parameters). This should help you to property select parameters to
include in a PEST run, as you should focus more on the sensitive parameters, and less on
the non-sensitive parameters.
The observation times (for heads) lie within the start/stop time of the numerical simulation.
If you have imported a model from Visual MODFLOW Classic, ensure that an appropriate
start date was defined in Visual MODFLOW Classic before loading the project into VMOD
Flex. If you have generated the numerical model from a conceptual model workflow, ensure
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