Discussion of “Downstream Hydraulic Geometry of Alluvial Channels” by Jong-Seok Lee and Pierre Y. Julien

Abstract

The authors have made a valuable contribution to the hydraulics of alluvial rivers by reconsidering a former approach with an updated database. Regardless, their results are dimensionally incorrect as stated in the paper. Relations among the parameters for river width W, average flow depth h, mean velocity V, discharge Q, channel slope S, median grain size of bed material d50 and Shields parameter are given. The authors’ Table 2 compares the results of Lee and Julien L-J with those of Julien and Wargadalam J-W. It is notable that some parameters have practically no effect in these relations, such as d50 relative to W, h and V in the L-J relations, whereas the d50 effect appears not to be negligible in the J-W formulation. Will the authors discuss this fact? By accounting for the L-J formulation, it is of course interesting to consider an average flow velocity formula. Using the authors’ Eqs. 2a and 3a and eliminating discharge Q gives