Filtering GHBs

[Ulysses Hillard]

Hi,

I have a somewhat large model originally generated by a consultant using GMS. I exported it to USGS format. After not-insignificant effort, I have it successfully running via command line and from ModelMuse.

The model is 495 columns x 195 rows and includes over 1,000 GHB definitions in three cell groups: Two represent lakes, one above the aquifer and one below, and the third is an arbitrary outflow boundary. Seepage from the lake above the aquifer drives flow in the model.

I have been asked to prepare a scenario with levels in the high lake that are lower than in the original scenario. This has meant running the model, which then stops short, skipping to the end of the LST file, which identifies at which GHB the model stopped because the new head on the GHB is below the bottom of the cell for which that GHB is defined, deleting that GHB, decreasing the number of GHBs by one, and then running the model again.

I have 1,000 GHBs to examine in this way and one life to live. I am wondering if ModelMuse (or any of the other MODFLOW front ends) presents a more efficient way to delete GHBs and/or assign new ones, for a situation like this.

Your help is much appreciated. I greatly hope the answer is yes. I also greatly hope that ModelMuse can do this as I would like to keep all of Seattle's efforts in the realm of public domain software, if possible.

Ulysses Hillard

Sr Water Resources Engineer

Seattle Public Utilities

[Richard B. Winston]

The next release of ModelMuse will generate a warning message about GHB
cells that identify GHB cells with heads that will cause problems with
MODFLOW-NWT. If someone needs that feature now, they can contact me at
my work email: rbw...@usgs.gov.

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[Marius Jigmond]

The ideal solution (in the public domain) would be to write a little script that compares GHB head to DIS elevations and discard GHB cells. This way you would know how many cells are discarded and you can adjust your criteria to minimize elimination (if desired). Any flavor of Python, Perl, etc. will do.

[Ulysses Hillard]

Hi Marius, 

Thank you for responding and, FWIW, I completely agree. The approach you describe is the first thing that occurred to me and, when I was a graduate student (aeons ago) and had weeks of time to burn free of charge, this is what I would have done. Unfortunately, that is not an option for me now. 

And I am kind of surprised that no off-the-shelf method exists. I have a hard time believing I am the first person to use MODFLOW to examine the behavior of a leaky reservoir-fed aquifer as the the reservoir level varies.

-Ulysses