Bank Erosion in Soils of the Lower Mississippi Valley

Abstract

Bank erosion along the Lower Mississippi River is dependent on local tendencies of the river to meander and on the geology of riverbank deposits. In the Alluvial Valley, the river erodes its thalweg in sands, and sands and gravels. During the high river stage, bendway pools may be deepened 20 ft to 40 ft or more by seasonal scour. Such periodic erosion may steepen the toes of the banks from stable slopes to unstable slopes that cause subaqueous failures. The subaqueous failures may, in turn, trigger upper bank failures, affecting a layer of cohesive to partly cohesive deposits known as the topstratum. These topstratum deposits respond in certain characteristic manners to oversteepening of the bank slope. In the Deltaic Plain, the river erodes its thalweg chiefly in clays. The surge of water during the high river stage is considerably reduced by distributaries, and erosion is further reduced by the cohesive strength of the clays. Consequently, there is a comparative stability in the river channel.