Zonebudget flow outside of active model domain

[Throw Away]

Hi all, 

I am running zonebudget on a MF-NWT flow model and the output shows flow both from and to outside the active model domain.

I set up zonebudget with 10 zones covering the active model domain (zones 1-10) and this is confirmed at the end of the zonebudget log file (see screen grab below). I use zone 0 (zero) to cover the inactive model domain. I have confirmed that zones 1-10 overlap precisely with the active cells from the ibound array, so that no active cell overlaps zone 0.

However, when I run zonebudget, the .csv suggests I am getting flow both from and to zone 0 (see screen grab below of zb output). 

Does anyone have any ideas about where this flow is coming from and what it might be accounting for?

end of the .log file

zonebudget output showing significant flow to and from zone 0.

[Boyce, Scott E]

You might try and run the model with mf-owhm v2.3, it supports the NWT Solver and has an updated version of ZoneBudget. Note that the bin folder contains the mf-owhm.exe and the postprocessors folder contains the zonebudget.exe

https://code.usgs.gov/modflow/mf-owhm

MODFLOW One-Water Hydrologic Flow Model - GitLab MODFLOW-OWHM Official Download and Source Repository Production release download: v2.3.0 Preliminary beta download: v2.3.1-b4 All... code.usgs.gov

Hope that fixes your problem,

Scott

---

From: mod...@googlegroups.com <mod...@googlegroups.com> on behalf of Throw Away <throwthi...@gmail.com>
Sent: Wednesday, July 16, 2025 11:18 AM
To: MODFLOW Users Group <mod...@googlegroups.com>
Subject: [EXTERNAL] [MODFLOW] Zonebudget flow outside of active model domain

 

 

This email has been received from outside of DOI - Use caution before clicking on links, opening attachments, or responding.

--
This group was created in 2004 by Mr. C. P. Kumar, Former Scientist 'G', National Institute of Hydrology, Roorkee. Please visit his webpage at https://www.angelfire.com/nh/cpkumar/
---
You received this message because you are subscribed to the Google Groups "MODFLOW Users Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to modflow+u...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/modflow/0091ac3b-3285-455d-83a7-7fc698882295n%40googlegroups.com.

[Throw Away]

Hi Mr. Boyce,

Thank you for your suggestion. I tried running with MF-owhm but there is a rather large percent discrepancy in the volumetric budget compared with the mf-nwt model I am running. 

Do you have any suggestions as to why running with the updated zonebudget provided with owhm would resolve the flow from and to inactive zones? 

[Throw Away]

An update of my troubleshooting if anyone else is able to chime in. 

I ran zonebudget on the model and used the ibound array as the zone array (ie. zone 1 is the active model domain and zone 0 is the inactive model domain). This behaved as you would expect. The end of the log file confirms only 1 zone, and the csv output confirms no flow to or from zone 0. Additionally, just to confirm, the budget in this single zoned zonebudget run matches the stress period volumetric budgets in the modflow listing file. 

I also ran zonebudget using the original 10 zone setup described in the initial post, but here I replaced the inactive model domain (zone 0) in each layer with zone 11 in layer 1, 22 in layer 2, 33 in layer 3... etc. The output from zonebudget reverted to the behavior described in the original post with flow to and from inactive zones, which not only included e.g. zones 11, 22, 33, ..., 77, but also included flow from zone 0. Again, in this set up, there was no zone 0 specified in the zone array.

If anyone has any suggestions, I am all ears!

Thanks in advance,

[Boyce, Scott E]

You should check if your time steps are converging and if the mass errors are reported in the LIST file. MF-OWHM is stricter than MF-NWT for what it considers a converged time step. If you want to disable the additional checks you can add the BAS Option, MAX_RELATIVE_VOLUME_ERROR, followed by a large number (say 2) and that will disable the additional checks ( https://code.usgs.gov/modflow/mf-owhm/-/blob/develop/doc/Option_Block_Cheatsheets/BAS_Options_Recommended.bas?ref_type=heads#L43 ).

OWHM also checks the mass balance for every time step and raises a warning if its violated. The other flavors of MF-2005 only check the mass error if requested by the user in the Output Control (OC) and for the last time step of the stress period (usually the best time step). The mass errors might be something that has been there, but you were not aware off.

You might also need to increase your solver iterations, MXITER, since OWHM considers every time the finite difference equations are formulated (FM) as an iteration, while MF-NWT only considers each time it solves for the inverse of the Jacobian.  So there usually are about 10 FM iterations for every Jacobian iteration. That is why NWT models often claim they solve in about one tenth the number of iterations compared to the other solvers (but it is really about the same number).

Last comment is that you may want to try running the model with the COMPLEX solver option. There are slight differences in the preset options for COMPLEX, MODERATE, and SIMPLE between MF-OWHM and MF-NWT, so my guess is that the later has a configuration that works better for your model.

If you need more detailed information about OWHM specific options, check out the doc folder of the download or the published report:

Boyce, S.E., Hanson, R.T., Ferguson, I., Schmid, W., Henson, W., Reimann, T., Mehl, S.M., and Earll, M.M., 2020, One-Water Hydrologic Flow Model: A MODFLOW based conjunctive-use simulation software: U.S. Geological Survey Techniques and Methods 6–A60, 435 p., https://doi.org/10.3133/tm6A60

One last comment is that your zone 0 might represent flows entering or leaving the model domain via a boundary condition.

---

From: mod...@googlegroups.com <mod...@googlegroups.com> on behalf of Throw Away <throwthi...@gmail.com>

Sent: Thursday, July 17, 2025 12:08 PM

To: MODFLOW Users Group <mod...@googlegroups.com>

Subject: Re: [EXTERNAL] [MODFLOW] Zonebudget flow outside of active model domain

 

To view this discussion visit https://groups.google.com/d/msgid/modflow/65c27044-5988-485e-b95a-a40db5eca80bn%40googlegroups.com.

[Richard Winston]

To me, this sounds like you haven't set up your zones the way you think you have.

To view this discussion visit https://groups.google.com/d/msgid/modflow/DM6PR09MB5080600BB3840C0A6CA4706FDC50A%40DM6PR09MB5080.namprd09.prod.outlook.com.