Riverbank erosion is the deterioration of the banks of a river or stream. It occurs when the top soil that encloses a river or stream washes away. Riverbank erosion is a natural occurrence that allows rivers to flow on a proper course. However, when accelerated because of unnatural causes, the water system is susceptible to a disproportionate sediment supply, stream channel instability and habitat loss, according to the EPA.
Riverbank erosion is driven by two primary components, the characteristics of the river bank and gravitational/hydraulic forces. A number of commercial or human activities impact both of these components, which ultimately leads to accelerated erosion.
Three types of riverbank erosion occur: vertical, headward and lateral erosion. Vertical erosion makes a river deeper, lateral erosion makes it wider and headward erosion makes it longer.
Riverbank erosion has four processes: attrition, corrosion, abrasion and hydraulic action. Erosion occurs from abrasion when river sediments collide with the channel’s floors to form craters. Hydraulic action erosion occurs when the pressure of water chips away at rock particles in the bed and banks. The force of the water slams into the banks and pushes water into cracks. This force compresses air and increases pressure to damage or collapse the bank. Banks erode from attrition when eroded rocks collide together and break-off into smaller fragments. Corrosion occurs when carbon dioxide dissolves to form a weak acid. The acid then eats away at the rock bed and ultimately collapses the bank.