I don't know how to implement in the pil file the varying depth in the 2 DH of an pen channel flow

As a suggustion, can you not make a fat channel and block out the parts you dont want?

not i can't make a block, it is a variation like a stairs generate a variation of the depth tahnks

You could use lots of blocks to make stairs

if it is a varying topography, is it fan the adequate command and how to use this?

Perhaps I misunderstand you?

1/ You can make a solid volume STL file and import this onto a cartesian grid using the PARSOL cut-cell method to cut this object shape from the background grid.

or 2/ Use a Body fitted grid

or

3/ Represent the depth varying through blocking out a cartesian domain with object shapes from the library of such objects, wedges, rectangles, arcs, whatever.

If you are using the hydraulic analogy, you can use porosity fields, with a porosity field, you can simulate flows with different depths, at least it worked for me.

With porosity fields ive simulated bumps or obstacles for inducing an hydraulic jump.

Please, if you have any document about analogy, can you please pass it or explain me thanks