Impacts of the flexible net on riverbed evolution in degrading channels

Short-term dramatic degradation of a riverbed poses a great threat to the river and functioning of infrastructure in its vicinity. In this paper, a straight flume experiment was conducted to measure the velocity, water level, riverbed elevation and riverbed morphology under different experimental conditions. This was combined with the SfM (structure-from-motion) method to generate riverbed digital elevation models and orthomosaic, and the impact of a flexible net on the riverbed evolution of a degrading channel was studied. The study reveals that, under the action of the flexible net, the degradation mode of the riverbed changes from parallel to rotational degradation with the erosion datum as the fulcrum, and with an increase in the longitudinal length of the flexible net, the riverbed's protection efficiency grows. The flexible net can effectively limit the movement of sediment under the net, and the finer sediment silting raises the erosion datum elevation. The location and morphological characteristics of the downstream scour holes are observed to be greatly affected by the deformation of the erosion datum. The scour hole shows an asymmetric distribution because of uneven scouring of the flow to the downstream riverbed. The research results could provide guidance in the management of degrading channels.