How to Find the right U Count Value for SurfaceFromPoints (SrfGrid)

Hello, I am trying to use the mosquito plug in to run a water level simulation and it needs a surface. I have my terrain as a mesh so I am using DeMesh and SurfaceFromPoints. The SurfaceFromPoints (SrfGrid) needs a U value / U count that I have to enter with a number slider. But it gives an error to me "UCount Value is not valid for this amount of points.
I have a total number of 3466 points in my mesh and I used this before with a similar terrain and it was easy to try and found the right U Count value, it worked before. But in this one I cannot find the right UCountValue at all.

I dont know is spesifically there is only 2 dividers of this number which is 2 and 1733.

I hope someone can help me here, thank you in advance.

PS: If you need an explanation for the attachments. I have 2 terrains inside, one is the existing and the other is the proposal. I need to use the plugin for both to see the comparison. The excluded parts in the model are the river course.
before after grasshoper agriculture.gh (278.0 KB)
Model_Agriculture_before after.3dm (3.9 MB)

surface from points wants a consistent grid of points to work correctly, I would suggest something like → project a grid of points on the original mesh (where the river course was not cut out) → build the surface with SurfaceFromPoints → only at this point cut-out the portion of surface where the river is, by projecting the boundary curve of the river on the surface that was just created


[edit]
something like this, didn’t project and cut-out the river, just stopped after the flow sim

before after grasshoper agriculture_Re.gh (190.7 KB)