Riverbank Stability Analysis. II: Applications

Bank retreat occurs by a combination of lateral erosion by the flow and mass failure under gravity. A new analysis of bank erosion and failure is developed, using a critical shear‐stress concept to account for lateral erosion and a slope stability criterion for mass failure. In this paper, we apply the analysis to two problems of bank retreat often encountered by practicing engineers dealing with alluvial channels. The first application is to the prediction of degradation downstream of a dam for the case in which bed lowering causes bank instability. We show that rapid bank retreat can occur once the threshold height for mass failure of the banks is reached. This supplies sediment to the flow, tends to limit the depth of degradation, and drives complex response downstream. The second application is to the modeling of flow in channel bends and the prediction of the equilibrium cross section. We show that scour depth at the outer bank may be limited by the critical bank height. If scouring causes the outer bank to fail, then the channel will migrate laterally rather than scour down vertically. The analysis presented here can be used to predict the equilibrium cross section and migration rate incorporating bank stability considerations. It could also be used to predict the likely increase in scour depth resulting from outer bank stabilization in a bendway.