Unsteady 1D flow model of a river with partly vegetated floodplains-application to the Rhine River

A relatively simple unsteady flow model was proposed which estimates velocities, friction factors and the components of discharge in the main channel and on the floodplains simultaneously. Bottom roughness of the main channel and the floodplains, the flow resistance of vegetation on the floodplains and the flow resistance caused by the momentum transfer between the main channel and the floodplains were included in the model using Nuding's method. A pre-processing program was developed to convert topographic field data that can be derived from a digital terrain model into cross-sectional input data of the flow model. The model was applied to a 28-km reach on the Upper Rhine for three steady flow cases and for two unsteady flood event cases to investigate resistance effects of partly vegetated floodplains. Computed discharges and water levels correlated well with the measured data. It was found that a significant component of discharge was transported by the floodplains in some cross-sections during high flows.