This laboratory study examined the influence of particle size and density, and channel velocity on the spatial deposition pattern around an emergent (extending through the entire water depth), circular patch of model vegetation located at the center of a channel. Three flow conditions and three particles of different size and density were considered. Across all particle and velocity conditions, three basic deposition patterns were observed: (1) high deposition in the patch wake and low deposition in the zones adjacent to the patch; (2) high deposition in both the wake and adjacent zones; and (3) low deposition in both the wake and adjacent zones. The observed deposition pattern correlated with the ratio of channel shear velocity (u Ã Þ to critical shear velocity (u Ãc Þ: Specifically, for u à =u Ãc < 0:7 or u à =u Ãc > 3, the deposition was high (or low, respectively) over the entire channel with little difference between the wake and adjacent regions. In contrast, for 0:7 < u à =u Ãc < 3 divergence in net deposition between the wake and the adjacent zones occurred, with higher net deposition in the wake and lower net deposition in the adjacent zones. The peak divergence was observed at u à =u Ãc 51:6. The deposition patterns were more closely correlated with the ratio u à =u Ãc than with w s =u à (with w s the particle settling velocity), suggesting that the spatial variation in net deposition was driven by resuspension (associated with u Ãc ) and not settling (associated with w s ).
Based on the momentum transfer theory, an analytical model is proposed for the velocity and discharge distributions in compound channels with submerged vegetation on the floodplain. The partially vegetated channel was divided into three sub-regions, i.e. the main channel region, the floodplain region with submerged vegetation and the floodplain region without vegetation. For each region, the force balance relationship was established, and the momentum transfer between different regions was presented. Verification by the experimental data and comparison with the traditional method shows that the proposed method is capable of predicting for the velocity and discharge distributions in compound channels with submerged vegetation and is superior to the conventional method. The results also show that when the momentum transfer between different regions is ignored, the computed discharge will be much lager than the measured data, and the error increases with the discharge, especially in the floodplain region.
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