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Changing Head Boundary Condition below bottom elevation of cell


Terry

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I have an arc on the boundary of my model that is set to "specified head." I have the initial head below the bottom elevation of the upper layer. The Model Checker gives me "The Changing Head Boundary Condition is below the bottom elevation of cell" error (along with the starting head is lower than the bottome elevation warning). Modflow will not run.

Reading the help and checking the tutorial files this setup should work because I am using a specified head boundary condition. Why is the boundary being interpreted as a changing head?

So far I've reviewed http://www.xmswiki.com/xms/GMS:IBOUND and http://aquaveo.invisionzone.com/index.php?showtopic=98&st=0&p=205&hl=constant%20head&fromsearch=1entry205

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GMS maps specified head boundary conditions to the changing head boundary (CHB) package in MODFLOW. It will act as a specified head boundary condition unless you decide to make it change during a transient scenario.

That being said, you have a conflict in a cell if you are immediately trying to set a head below the bottom elevation of the cell (meaning that it starts off dry). You should remove that boundary condition from that cell and place it in the layer below....or, if it is already also in the layer below and the upper cell will remain dry, inactivate the cell.

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  • 1 year later...

FH1976 - Your question is not fully clear to me. It seems that you are asking the following: A solution generates dry cells. Can you then deactivate them in the conceptual model approach? Well, yes, but it isn't an automatic "deactivate dry cells." You would have to set up a polygon around those cells to change the IBOUND flag.

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Hello Mr. Czarniecki,

iam fully aware of this. I might explain my selfe.

In the Modellchecker I get lots of cells that have a lower starting head than the cellbottom elevation. Having these Information is not bad but it is just not practical to deactivate neither setting up a polygone by hand to "catch" these cells.

So i thought there is a way to use the errorfile to generate a xyz file witch i can use somehow (this is the question) to deactivate the cells.

Greetings

Friedrich

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Definitely a question that the developers will have to answer....

Just thinking about it, if your model isn't too large, you could pull the solution into the starting heads, copy the results and drop them into a spreadsheet, do a search and replace to create an IBound file (replace any dry cell results with a "0" and make the rest "1") which you could then pull back into GMS. It is a few steps, but is a way to do it.

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Well i just found out how to deactivate the cells with litteraly 4 clicks.

In the Model Checker hold shift and doubleclick on one of the error-cells: all get highlightet in the grid --> properties --> 0 --> $profit$

Why no one told me this earlier ... would have safet me a lot of time.

Greetings from Germany

Friedrich

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  • 3 years later...

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