It is important subject for controlling flood to estimate erosive resistance of natural riverbank. Several studies on the erosion of consisting of cohesive soil have been made in recent years. In those studies, only cross sectional erosion depth has been paid attention to. But, bank erosion depth increases with widening its area. And, failure of overhanging bank comes about by large erosion area.
The point of this paper is that expansion mechanism of erosion area is examined. Indoor erosion experiments were given using undisturbed floodplain soil of the Yoshino River, Shikoku, Japan. In addition, overhanging banks are reproduced by hydraulic model to examine the longitudinal change of flow characteristics. As the consequence of those experiments, erosion process of cohesive bank and mechanism of failure of overhanging bank are clarified.