How to import/export head save files - Model won't converge

[Ana Schanzenbach]

Hello everyone,

I recently discovered this group and I'm hoping for some assistance!

Right now, my model will not converge and I know that I need to change the initial heads. I was told by a colleague that I should go to Model, Modflow, Package Options, the Initial Heads tab, choose the SURFER option from the drop-down tab, and upload my head-save file. I have done this, followed by creating new data sets, and running with MODFLOW 2005. Unfortunately, it just makes the model run longer without converging.

Am I missing any steps? Also, which head save file do I use? Do I use the one automatically created or do I need to export a head save file first and import it back into the model?

Any help is greatly appreciated.
Thank you,
Ana Schanzenbach

[Rodrigo Herrera]

Hi,
Assuming you are trying to run a transient model and that,you don´t get passed the first time step. I wonder how did you created this head-save file, is it a steady state solution or is it a surfer interpolation from head measurements?. A steady state solution usually helps eliminating the possibility of non-convergence when using an non-equilibrated initial head. Head measurement interpolation can create an non-equilibrated initial head, that might make your model to run longer initially, it all depends on the amount of water being injected or extracted from the domain. There are other factors related to non-convergence like solver type and its settings,  K contrasts too high, rewetting of cells (not an issue for MODFLOW -NWT or - USG) or boundary conditions being unrealistic. You should check all of that as well.

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Rodrigo Herrera

Líder Área de Modelación

GeoHidrología Consultores
www.geohidrologia.cl

[Ana Schanzenbach]

Hello,

Thank you for the response.

My model is actually a steady-state model. Here are the actions I took to create the head-save file: Properties -> Export -> Head-save format. Then, Model ->MODFLOW -> Package Options -> Initial Heads tab. Under the "Head-Save File Options" I chose "Set Heads from Head-save, BASIC, SURFER, matrix" and browsed for the exported head-save file. I have played around with selecting "Save Starting Heads to Initial Head Property Next Time MODFLOW Files are Created" and choosing different options from the pull-down menu for Initial Head Location.

In every attempt the model runs a longer time without converging.

I have noticed that the output after running the model shows that some cells are rewetting. Could this be my problem? How can I fix this?

Thank you, Ana

[Rodrigo Herrera (GeoHidrologia)]

If you have dry cells in your initial heads and if you are not using MODFLOW-NWT maybe switching to 'read heads directly from binary head-save file' instead of the option you are using can be of a little help. It is under the same MODFLOW/package Option/Initial Heads tab.

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