Discussion of "Gate and Vacuum Flushing of Sewer Sediment: Laboratory Testing" by Qizhong Guo, Chi-Yuan Fan, Ramjee Raghaven, and Richard Field

The paper under discussion represents a valid experimental contribution to the description of the hydrodynamic and sediment transport processes determined by flushing operations in sewer channels; the data derived by the authors from the described laboratory experiments can be usefully adopted for the validation of numerical models specifically developed for the simulation of the effects of flushing waves on sewer deposits. This discussion mainly concerns the influence of the laboratory setup adopted by the authors for the experiments. For both the tested flushing devices, the authors analyzed the sediment scouring as a function of the initial water depth in the flume over the sediment bed; in particular, a decreasing of the weight of the flushed sediments was pointed out as the initial water depth increased