Parameter definition

[Chang Liao]

I am working on the calibration process.

Here is the question: As many packages have specific parameter input requirement, 

also there is another PVAL package could be used.

I don't know how ModelMuse manages the parameters and related zone arrays.

Can anyone give some overview what is the promising steps to take?

[Richard B. Winston]

1. Define parameters in the "Model|MODFLOW Packages and Programs" dialog
box. You can specify whether to use multiplier or zone arrays there.
2. If parameter or zone arrays are used, they are represented by new
data sets in ModelMuse.
3. If any parameter values are defined, a .pval file will be created
automatically by ModelMuse.

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[Chang Liao]

Thank you, I noticed that too. Modelmuse will automatically generates the pval file after specifying the parameters.

I also found that all parameters in UPW packages are assigned to all layers by default. 

Besides, why at least on instance is required for each parameter in SFR package? What if only one Kv values is desired, so we still need to assign an instance for it?

[Richard Winston]

You need to define an instance in order to specify the times when the values will be used. If only one instance of a parameter is specified, there won't actually be any instances defined in the stream package input file. Instead, the perimeter will be used for all stress periods.

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[Far_Naz]

This was very useful topic. I have also a question in this regard.

I have made ModFlow model by ModelMuse, Now want to do sensitivity analysis and calibration by Pest.

For some parameters like, Horizontal hydraulic conductivity (HK) and specific yield (SY), it is possible to define parameter values and ModelMuse will create "pval" file automatically. However, for other parameters related to UZF package like, Saturated water conductivity (vks), Brooks-Corey epsilon (eps), and for parameters associated with SFR package, when unsaturated flow is activated like  Hydraulic conductivity of streambed (HCOND1 and HCOND2), I could not define parameters.

Is it possible to add parameter related to UZF and SFR packages to "pval" file by ModelMuse, or these parameters should be changed from the base file when defining template file for PEST?

I would be thankful for any help.

[Richard Winston]

ModelMuse only defines parameters for ehich there is a corrresponding parameter in the MODFLOW input file. The UZF input instructions do not include any parameters.

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[Chang Liao]

What Richard said was precisely how ModelMuse is tailored for MODFLOW model.

Modflow does not consider some variables as parameters for some reasons (can we actually assume all unknowns are parameters? mathematically we could).

Since PEST is model-independent, any inputs can be parameters. But the choice of parameters could result in different scale of difficulties. What you need is just preparing the files for PEST, which mostly like have to be done outside Modelmuse. But there are quite a few utilities you can make use of.

So to do SA, you could possibly include most of the parameters in your definition. But when do calibration, you usually only focus on a few of them.