Applications and Case Studies > Groundwater flow studies

ZONE_FLOW in PHAST

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daliagrig:
Dear PHAST developers and users,

I tried to understand what is in output file while using the key word ZONE_FLOW in PHAST. For this purpose I made a simple file - a 10 cm x 10 cm x 10 cm region with hydraulic conductivity 1e-9 m/s and porosity 0.126 (flow only model). Boundary conditions - specified head: top - 10 cm, bottom - 0 cm.
Then I defined 3 zones: total domain, upper 1 cm and bottom 1 cm of the region.

1. Could you explain what subscripts m and p means (e.g. xm in, xm out and xp in and xp out) in the *.zf file?

2. Why the outflow from the bottom 1 cm zone is twice as large as inflow? I supposed they should be the same?

3. And how to understand "internal face". Zone 2 (top 1 cm zone) has one internal face (I suppose that plane 1 cm below the top) and the same is with bottom zone. Then why in case of the bottom zone there is flux in and out internal face, but in case of the top zone only flux out is given?

Thank you.

dlparkhurst:
xp refers to the x faces at with greater x coordinates, and xm refers to the x faces at lesser x coordinates of a zone. Typically, the zone is a rectangular box, but not necessarily; still there are faces at each end of the zone in the x direction. yp, ym, zp, and zm are analogous.

Sorry, I think there is a bug in the steady-state zone flow for the Z direction. I think all flows should be 1.0e-8, with no values of 2.0e-8. I reran your example as a transient flow (1 day, 1 hour time steps) and the result, which I think is correct, is attached. I also ran steady-state in the X direction and also got the correct answers (without the 2.0e-8).

The zone flow accumulation is by cells and, with your grid, there are cells at z=10 and z=9. So your top zone flow definition includes two layers of cells. Considering the top layer (zone_flow 2), the file says that there is 1e-8 flow in through the specified head boundary, and 1e-8 out through the bottom faces of the zone, which are located at z=8.5 (the bottom face of the cell at z=9 is at 8.5). (The bottom face of the cell at 10 is at z=9.5; top face is at z=10.) The bottom faces of the zone are not on the boundary of the domain, so the are "internal faces".

Considering the bottom zone, the relevant faces are top at z=1.5 (top of the second layer of cells) and bottom at z=0. The file indicates 1e-8 flow in through the positive (internal) Z face (z=1.5), and 1e-8 out through the specified head boundary at the bottom of the domain.

For the zone including the entire domain, inflow and outflow are through the specified head cells at the top and bottom.

Sorry about the bug. I will try to fix it, but it may be a while.