Effect of bank stability on geometry of gravel rivers

A bank stability analysis is incorporated into an analytical procedure for modeling the hydraulic geometry of an alluvial gravel-bed channel. The new analysis includes a procedure that calculates the mean bed and bank shear stress as well as assessing the bank stability. The bank-stability criterion accounts for the increased stability of the channel bank due to consolidation of the bank sediment, cementing by fines, and binding of the sediment by root masses. The two key parameters in the bank-stability analysis are the median grain diameter of the bank sediment D50bank, and the bank sediment φ'. A sensitivity analysis of the two parameters indicate that the bank stability can exert a large influence of the channel geometry. This is supported by testing the theory on published field data. The results indicate that increased bank stability induced by the vegetation has a significant influence on channel geometry; the vegetated channels are narrower, deeper, and less steep. For well-developed bank vegetation, the channel width, depth, and slope were found to be in the order of 0.6, 1.4, and 0.9 times their respective unvegetated channel dimension.