A NEW DISTINCT MECHANISM OF RIVER BANK EROSION IN A FORESTED CATCHMENT

It has been thought that the two main processes responsible for river bank retreat are the removal of particles or layers of material by flow erosion or sloughing and collapse by slumping. A third process, involving the development of a subsurface cavity after washout of gravels which is succeeded by slow subsidence of a segment of the former channel bank, has been identified at a site in the New Forest, southern England. The process was monitored over a 9 month period, and was observed to be assisted by the hydrological effects of a dam of coarse woody debris across the channel. As these dams occur frequently, the process is likely to have occurred elsewhere along channels in forested areas.