PREDICTION OF TENSION CRACK LOCATION AND RIVERBANK EROSION HAZARDS ALONG DESTABILIZED CHANNELS

Riverbank erosion, associated sedimentation and land loss hazards are a land management problem of global significance and many attempts to predict the onset of riverbank instability have been made. Recently, O sman and Thorne (1988) have presented a Culmann-type analysis of the s tability of steep, cohesive riverbanks; this has the potential to be a considerable improvement over previous bank stability theories, which do not account for bank geometry changes due to toe scour and lateral erosion. However, in this paper it is shown that the existing Osman-T horne model does not properly incorporate the influence of tension cra cking on bank stability since the location of the tension crack on the floodplain is indirectly determined via calculation or arbitrary spec ification of the tension crack depth. Furthermore, accurate determinat ion of tension crack location is essential to the calculation of the g eometry of riverbank failure blocks and hence prediction of land loss and bank sediment yield associated with riverbank instability and chan nel widening. In this paper, a rational, physically based method to pr edict the location of tension cracks on the floodplain behind the erod ing bank face is presented and tested. A case study is used to illustr ate the computational procedure required to apply the model. Improved estimates of failure block geometry using the new method may potential ly be applied to improve predictions of bank retreat and floodplain la nd loss along river channels destabilized as a result of environmental change.