Representative Grain Size and Equivalent Roughness Height of a Sediment Bed

The representative grain size of a sediment bed can be defined as the mean-volume diameter, which varies with the geometric standard deviation of sediment size. The obtained results explain why the representative sediment size can be approximated to be D84 for typical gravel beds. The analysis is finally extended to quantify the dependence of the equivalent sand roughness on the geometric standard deviation of grain size distribution.