Laboratory Experiments for Channel Aggradation in Supercritical Flow

This study presents a laboratory investigation of channel aggradation under supercritical flows. According to the scientific literature, aggradation processes in these flow conditions have been much less studied than those under subcritical flows. The experiments presented in the manuscript were performed using a tilting flume with rectangular cross section, and constituted an experimental series where all the runs had the same initial bed slope and flow rate while different overloading ratios were imposed (the overloading ratio being the ratio between a sediment feeding rate at the inlet and the transport capacity at initial flow). The experiments returned extensive data for the water and bed profiles, sediment feeding rate, and sediment transport capacity of the flows. After the beginning of an experiment, the aggradation height is larger close to the sediment feeding point and decreasing downstream. The channel thus tends to a new slope, higher than the initial one, as it tends to achieve a new transport capacity in equilibrium with the sediment feeding rate imposed at the inlet. Temporal and spatial scales of propagation need to be defined and measured; however, the recognition of an aggradation front and the quantification of a related celerity of propagation are hindered by a markedly dispersive shape of the aggradation profiles, where a neat separation between an undisturbed and an aggraded reach is not detected. Therefore, the present results, while providing phenomenological insight, call for analysis tools specifically devoted to the supercritical conditions, as in the latter the aggradation process differs from that observed under subcritical flows.