An analysis of stratigraphic control on river bank failure

Most of the rivers of the Niger Delta flow through alluvial deposits whose general stratigraphy is that of cohesionless sand overlain by cohesive silty clay. Erosion and recession of the river banks have constituted a threat to many villages along the various creeks in the delta area.Analyses of the recessional mechanisms indicate that bank failure is initiated by a fluvial erosion of the lower cohesionless bank layer at a much faster rate than the upper cohesive bank layer. This leads to development of overhangs of the upper cohesive materials. The failure mechanism of the river bank is complex, ranging from slip failures in high banks to shearing and toppling failures in low banks. The use of the common slip circle model for stability evaluation appears to be adequate only for high banks. Results obtained for the low banks suggest that the use of this model of stability analyses for low banks may yield misleading results.