bank erosion

The erosion of material from the side of a river channel, not only by fluvial processes, but also by frost heave, groundwater sapping, surface wash, and slope failure. Rates of erosion vary with bank composition and moisture content, bank vegetation, and speed of flow; rates are highest on the outer bank of meander bends or where bars in the channel have diverted the thalweg. Bank form reflects the nature of materials: fine, cohesive materials tend to fail through slipping, banks of coarse material are steep, and may have talus slopes at the base, and where a cohesive layer overlies coarser material, undercutting may form overhangs, which collapse periodically. In the short term, these collapsed blocks may protect the base of the bank.