FACTORS AFFECTING DISTRIBUTION OF INSTABILITY OF RIVER BANKS IN THE NIGER-DELTA

The Niger delta is intensely dissected by a network of rivers which erode and continuously reshape their banks resulting in net riverbank recessions. The rates of bank recession depend on season, soil type, bank height and stratigraphy, flow velocity and relative location along the river system. Bank failures occur by several mechanisms. These include; rotational, translational, overhang/toppling and flow mechanisms. Bank failure episodes are concentrated at the early stages of lowering of channel water level due to the sensitivity of banks to removal of passive resistance. High ground-water level accentuates seepage erosion which reduces bank stability. To realistically predict the behaviour of river banks, the method of evaluation must recognise the dynamic nature of the controlling factors.