[mb.pejvak]

I am using interFoam solver to simulate free surface water flow in a channel. The bottom of the channel has roughness, so I used nutkRoughWallFunction in boundary condition of nut for the surface. The height of the mesh close to surface is 5.0 mm. I investigate different Ks from 1.5e-4 to 3.0e-3. But the height of water is less than experimental data and the force acting on a bolder in the channel is higher than expected. But by increasing Ks these two parameter has been improved. Now my question is since Ks is 'sand-gran roughness height', if I increase Ks close to height of the cell, would it make the simulation wrong? i.e. how the height of cell and Ks correlated to each other?
If you need openFoam setup of the simulation, you can take a look at the repository in which I uploaded the case setup
https://gitlab.com/Mehdi_Pejvak/free...master/setup_3