STABLE WIDTH AND DEPTH OF GRAVEL-BED RIVERS WITH COHESIVE BANKS

An analytical model is developed to determine the influence of the ban k stability on the stable width and depth of alluvial gravel-bed river s with cohesive banks. The formulation of the model is based on the as sumption that the stable width corresponds with an optimum condition t hat is equivalent to the maximum bed load transporting capacity. The o ptimum condition develops when the channel banks are at their limiting stability with respect to either mass failure or fluvial erosion. Two basic channel types are identified: bank-height and bank-shear constr ained. Mass failure stability is estimated using a simple total stress approach. A method for estimating the critical bank shear stress base d on model calibration is proposed. Analysis of field data indicates t hat the effect of the bank vegetation on bank stability can be express ed in terms of the critical bank shear stress. The average critical ba nk shear stress value calculated for riverbanks covered by vegetation with well-developed root networks was found to be approximately three times that obtained from rivers with weakly vegetated, grass-covered b anks.