The paper is intended to discuss how well or badly the common 1-D numerical models of open channel flow are behaving in terms of flow distribution across any section in a compound channel. Comparison is made with new experiments in a physical model of a reach of the Besos river Restoration Project close to Barcelona. The case in focus involves thick vegetated floodplains (wetlands in prototype), a low-flow meandering channel and high water depths over the main channel and floodplains. 1-D models fail to predict the velocities in the main channel (which are exaggerated) and floodplains (which are underestimated). The paper describes an improvement of the 1-D computation based on the consideration of the shear stress at the main channel-floodplain interface on the one hand, and the influence of upstream velocity distribution with the help of 2-D numerical models on the other hand.
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