Author(s): Jennifer Duan; Khalid Al
Linked Author(s): Jennifer G. Duan
Keywords: Sediment transport vegetated channel flow resistance bed load suspended load
Abstract: The computational simulation of flow and sediment transport in vegetated waterways requires a complete understanding of vegetation interaction with flow and sediment. We first conducted a set of laboratory experiments to study bed form resistance and bed load transport in mobile bed vegetated channel. Vegetation stems were simulated by using arrays of emergent polyvinyl chloride (PVC) rods in several staggered configurations. The total flow resistance was divided into bed, sidewall, and vegetation resistances. Bed resistance was further separated into grain and bed form (i. e. ripples and dunes) resistances. By analyzing experimental data using the Downhill Simplex Method (DSM), we derived new empirical relations for predicting bed form resistance and bed load transport in vegetated channel. Bed form resistance increases with vegetation concentration, and bed load transport reduces with vegetation concentration. Simultaneously, we developed one and two-dimensional hydrodynamic and sediment transport model to simulate unsteady flow and sediment transport in vegetated waterways. The computational model was based on the solution of St. Venant equation together with the governing equations for suspended and bed load transport and the Exner equation for bed elevation changes. The Godunov-type finite volume method was employed to discretize the governing equations. Since sediment transport in in non-equilibrium when bed is degrading or aggrading, a recovery coefficient for bed load transport and an adaptation length for bed load were used to quantify the differences between the actual and the equilibrium transport rate. A procedure to separate the vegetation resistance from bed resistance was implemented for estimating the grain resistance. The model was applied to simulate experimental case, and an unprecedented flood event occurred at the Santa Cruz River in July 2006. This research demonstrated the importance of vegetation density and non-equilibrium sediment transport in vegetated channels.
Year: 2025