Experimental and numerical analysis of the scouring effects of flushing waves on sediment deposits

In the management of urban drainage networks, great interest has been recently addressed to the removal of sediment deposits from sewer collectors. In particular, sewer cleansing can be carried out by flushing devices able to discharge a great volume of water during a short period of time. In this paper an experimental and numerical investigation on the scouring effects of flushing waves on sewer sediment deposits is presented. Experiments were carried out on a laboratory channel adopting a simple flushing device and considering different flushing conditions. Accurate measurements on the evolution of mobile-bed deposits and on sediment transported during the flushing operations were carried out. Subsequently, a numerical model was specifically developed for the analysis of the flushing wave propagation and for the description of the sediment scouring on mobile-bed channels. The model is based on the semi-coupled solution of the complete De Saint Venant equations for the water flow and of the Exner equation for the sediment continuity. Numerical results were compared with the experimental measurements in order to derive indications on the scouring processes consequent to flushing operations.