Compute discharge through an internal zone

Hi,

I want to compute the fluid flow through an internal limit in the model.
For example the flow that pass a certain given depth. Therefore the computation can be on zones or gridpoint depending of what is the simplest.

Because it isn’t a boundary with a fixed pore pressure I cannot use the fish function gp.flow.

My guess is that I could use the zone.flow function but I would need to compute the area of the zone section normal to the discharge vector to get a volume per time.

Will that give me an accurate estimation of a different approach computing all the source and sink terms is needed?

Thank you in advance!