Roughness has no influence on results, k-epsilon
 

I try to modelling flow over a small dam (embankment). The rougness of dam surface is about d90=20mm (grain size). I tried to model smooth wall and rougnesses hs= 0, 10, 20, 30, 40, 50 mm.
In this case i have these problems:
1. different results between smooth wall and rough wall hs=0mm
2. For rougneses hs higher than 20 mm is no influence on results (water level - head is constant)

1. There was a problem with mesh thickness.
2. Ok it's my fault. I didnt know that the first cell of mesh must be twice higher than rougness.