Experimental of the influence of different near-bank riverbed compositions on bank failure

Six sets of experiments were carried out in a bend flume to study the impact of the cohesion of channel bed on the failure of cohesive banks. For comparison, the flume bed was consisted of cohesive and non-cohesive sediment, respectively. Results showed that, for channel bend with non-cohesive bed, the outer bank of the bend was eroded while a mixture of collapsed bank material was deposited near the inner bank. Net aggradation occurred at the channel bed. For channel bend with cohesive bed, both the channel bed and the outer bank were eroded. Degradation at the main flow area of the channel bed was greater than that near the outer bank. The bank toe of the outer bank of the bend with non-cohesive bed was more prone to be scoured than that of the bend with cohesive bed. Due to the adjustment of the flow structure near the outer bank of the bend, the turbulence kinetic energy of the flow can double and the circulation intensity can rise to as great as eleven times of its initial value, thus aggravating bank erosion and collapse and accelerating the transport of wasted sediment. Severe erosion occurred at the bank toe of the channel with non-cohesive bed, and the volume of collapsed bank material was two to four times of that aggravated at the bed. The wasted bank material contributed as sediment source for the riverbed. The height difference between the channel bed and the floodplain of the channel with non-cohesive bed was relatively smaller and the cross section was wider and shallower after scouring. This paper represents a preliminary study on the influence of the riverbed compositions on the channel erosion and bank failure. The results may help to guide bank protection and regulation of fluvial rivers.