About BUY Package

[borkial]

Hello community,
I have a question about the head that should be used in a GHB Package that is located in a saline water, or in any head-dependant boundary condition (BC) package.
My MF6 simulation has a GWF and a GWT models, with the BUY package activated and set, with the SSM pointing the concentration defined in the GHB package.
Should I use the freshwater equivalent head?
I haven't found anything in the documentation, but in the fortran code gwf-buy.f90, in the line 313 appears: " ! -- Return if freshwater head formulation; all boundary heads must be
! entered as freshwater equivalents"
I thought that internally the program managed the transformation of the set head with the concentration defined in the boundary condition, but now I'm a little bit confused.
Thanks for all!
Regards

[christianlangevin]

The MODFLOW 6 buoyancy packages is based on a hydraulic head formulation, as described here, and so all input must be hydraulic head (not equivalent freshwater head). There is an older development freshwater head formulation in the BUY package, which is what you noticed in the source code, but that option is not available to users.

[borkial]

Ok,
Thank you for sharing that information Mr. Langevin.
Regards.

[borkial]

Last question,
Regarding to the output heads obtained after the simulation in the HDS file.
As the input information has to be hydraulic head, are the output heads also hydraulic heads?
In this way, for analysis purposes, can I use the density output and the heads in each cell together to obtain the freshwater equivalent head so I could check isolines and more?
The freshwater equivalent obtained through the relation described in the SEAWAT user's guide:

Thanks in advance
Regards.

[christianlangevin]

Yes, the output in the HDS file are hydraulic heads. You would need to calculate freshwater heads (using the equation you show) if you want to see them. As you probably know, the BUY package allows you to save densities in a file that has the same format as the heads file.

[borkial]

Thank you!