A formulation is developed to apply the two-layer k - epsilon model to roug
h surfaces. The approach involves modifying the / (v) formula and the bound
ary condition on k. A hydrodynamic roughness length is introduced and relat
ed to the geometrical roughness through a calibration procedure. An experim
ent has been conducted to test the model. It provides data on flow over a r
amp with and without surface roughness.