Stable Width and Depth of Gravel-Bed Rivers with Cohesive Banks

Abstract

An analytical model is developed to determine the influence of the bank stability on the stable width and depth of alluvial gravel-bed rivers with cohesive banks. The formulation of the model is based on the assumption that the stable width corresponds with an optimum condition that is equivalent to the maximum bed load transporting capacity. The optimum 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 constrained. Mass failure stability is estimated using a simple total stress approach. A method for estimating the critical bank shear stress based on model calibration is proposed. Analysis of field data indicates that the effect of the bank vegetation on bank stability can be expressed in terms of the critical bank shear stress. The average critical bank 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 banks.