Laboratory investigation on the effects of flushes on cohesive sediment beds

Hydraulic flushing gates have recently been successfully adopted for the removal of sewer sediments. A large number of researches are aimed at the evaluation of the performances of these devices in the case of granular sediment deposits, but little information exists about the effectiveness of flushes on cohesive sediments as yet in literature. The current paper reports the results of an experimental investigation on the erosive performances of flushing waves on cohesive sediment beds. Experiments were performed in a laboratory flume adopting two flushing hydraulic conditions and comparing the erosive effects on cohesive and granular sediment beds. Different behaviours of cohesive sediments were observed during flushing operations: in particular, erosive effects in cohesive sediment beds were observed to be smaller than in granular sediments during initial flushes whereas erosion in cohesive sediments proved to be higher during subsequent flushes.