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EQUIVALENT MANNING’S ROUGHNESS COEFFICIENT OF VEGETATED ALTERNATIVE BAR

Recently, many river channels tend to be densely vegetated due to regime shifts in hydrological, fluvial and ecological processes and it is a critical engineering issue to evaluate conveyance capacity of vegetated channels. Although drag force coefficient is popularly used in evaluating drag force of vegetation, it is not always a convenient parameter in determining high water level, HWL, for a design flood. In this study, an equivalent Manning’s coefficient n v , which corresponds to drag force of overgrown vegetation in alternative bars, was theoretically evaluated by the two-dimensional two-layer (2D2L) hydrodynamic model. It was found that n v monotonically increases with increasing discharge as long as vegetation emerged. On the other hand, n v slightly decrease with discharge after vegetation submerged. Findings is to provide useful information for flood management of vegetated river channel.