Stability of river banks :

Land loss due to stream-bank erosion and channel bed degradation is a major concern in river and ocean engineering. Fig. 1.8 depicts the Brahmaputra river bank erosion in Chilmari area of Bangladesh. The bank soils remain unsaturated during most of the year. Thus these banks usually have high shear strengths due to negative pore water pressures. During the floods or severe rainfalls, the excess strength obtained from matric suction disappears due to the saturation during the flow events. In these situations, the concepts of unsaturated soil mechanics are must to provide adequate explanation and analysis of bank failures. The classical soil mechanics can't provide such explanations for slope stability during the moisture variations.

Fig. 1.8 Brahmaputra river bank erosion in Bangladesh
(Courtesy: Tonmoy Sarker photography (2012): River Bank Erosion)

 

The alternative bank failure mechanism is depicted in fig. 1.9. This diagram refers to the alternative wetting and drying stages during which the stream flow into bank and out of the bank observed. It has been observed that such alternative events are believed to be responsible for most of the failures related to river banks.