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 a nd bank shear stress as well as assessing the bank stability. The bank -stability criterion accounts for the increased stability of the chann el banks due to consolidation of the bank sediment, cementing by fines , and binding of the sediment by root masses. The two key parameters i n the bank-stability analysis are the median grain diameter of the ban k sediment D50bank, and the modified friction angle of the bank sedime nt phi'. A sensitivity analysis of the two parameters indicate that th e bank stability can exert a large influence on the channel geometry. This is supported by testing the theory on published field data. The b ank sediment size was assumed to equal the bed sediment size, and the variation of the friction angle phi' was investigated. The estimated p hi' values are seen to increase systematically with the bank vegetatio n 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-dev eloped bank vegetation, the channel widths, depths, and slopes were fo und to be in the order of 0.6, 1.4, and 0.9 times their respective unv egetated channel dimension.