Development of Analytical Model on Determination of Stable Hydraulic Geometry of Alluvial Gravel Bed Rivers

Modeling the hydraulic geometry of Gravel Rivers is of intrest to hydraulic engineers, hydrologists and enviromental scientists who are engaged in predicting the adjustments of an alluvial channel to an altered upstream runoff or sediment supply. The widely used qualitative and regime models, while indicating the general direction of river adjustment, are not able to deal with river response at a quantitative level. On the other hand the existing analytical models do not predict channel geometry to the accuracy required for engineering applications. In this paper a bank stability analysis is incorporated into an analytical procedure for modeling the hydraulic geometry of an alluvial gravel-bed channel. The bank stability criterion accounts for the increased stability of the channel banks due to effect of the bank vegetation 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 modified friction angle of the bank sediment, ??. A sensitivity analysis of the two parameters indicate that the bank stability can exert a larg influence on the channel geometry. This is supported by testing the theory on published field data.The bank sediment size was assumed to equal the bed sediment size, and the variation of the friction angle, ?? ,was investigated. The estimated ?? values are seen to increase systematically with the bank vegetation density. 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 was found 0.6 time its unvegetated channel width.