River bank failure

River bank failure can be caused when the gravitational forces acting on a bank exceed the forces which hold the sediment together. Failure depends on sediment type, layering, and moisture content. All river banks experience erosion, but failure is dependent on the location and the rate at which erosion is occurring. River bank failure may be caused by house placement, water saturation, weight on the river bank, vegetation, and/or tectonic activity. When structures are built too close to the bank of the river, their weight may exceed the weight which the bank can hold and cause slumping, or accelerate slumping that may already be active. Adding to these stresses can be increased saturation caused by irrigation and septics, which reduce the soil's strength. While deep rooted vegetation can increase the strength of river banks, replacement with grass and shallower rooted vegetation can actually weaken the soil. Presence of lawns and concrete driveways concentrates runoff onto the riverbank, weakening it further. Foundations and structures further increase stress. Although each mode of failure is clearly defined, investigation into soil types, bank composition, and environment must be clearly defined in order to establish the mode of failure, of which multiple types may be present on the same area at different times. Once failure has been classified, steps may be taken in order to prevent further erosion. If tectonic failure is at fault, research into its effects may aid in the understanding of alluvial systems and their responses to different stresses.