Modeling of momentum and mass transfer mechanisms in open channel flows with vegetation

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Experimental and numerical analysis have been carried out to clarify the flow-vegetation interaction in flood flows. A rectangular prismatic channel and a compound meandering channel have been used to estimate the effects of the location and layout of vegetation belts on the flow field. It is shown that patched vegetation alters the size and frequency of large vortices as well as flow resistance, and that the vegetation belts along the floodplain edges make little change in velocity distribution in the main channel. Numerical simulations have shown that LES and RANS approaches can reproduce the measured data very well when the vegetation belt is continuous, and that they fail to produce the velocity distributions in the flow with patched vegetation belts. It is pointed out that the failure comes from the weak points of the conventional vegetation model employing drag coefficient and vegetation density, indicating the necessity of database based on CFD to improve the vegetation model.