Discussion of “Boundary layer development over non-uniform sand rough bed channel”, by Anurag Sharma and Bimlesh Kumar (2017) ^*

This discussion provides highlights with regard to determination of the appropriate length for boundary layer development over non-uniform sand bed channels with and without seepage. It is demonstrated that the compound effects of Kármán’s coefficient κ and virtual origin should be accounted to quantify the behaviour of roughness length over non-uniform sand bed channels with seepage.