Vegetation is a common feature in natural coastal and riverine waters, interacting with both water flow and sediment transport. However, the physical processes governing these interactions are still poorly understood, which makes it difficult to predict sediment transport and associated morphodynamics in a vegetated environment. In this context, an experimental study was conducted in laboratory with a movable bed trapped in artificial vegetation. The experimental flume is a rectangular open channel 5.75 m long and 0.29 m wide. For flow measurements, the channel is equipped with a fast camera and ADV probe. This work focuses on identifying the vegetation effects on flows and sediment transport. In fact, it was shown that the vegetation presence in a watercourse promotes deposition and sediment accumulation. This is explained by a reduction of the bed shear stress, since the friction occurs mainly by the drag force effect exerted by the vegetation. It was shown too that the vegetation reduced the bedload transport. Thanks to the partitioning of shear stress, it was possible to predict the bedload transport using standard formulas with a reasonable accuracy.
The development of vegetation in the river bed and in the banks can affect the hydrodynamic conditions and the flow behavior of a watercourse. This can increase the risk of flooding and sediment transport. Therefore, it is important to develop analytical approaches to predict the resistance caused by vegetation and model its effect on the flow. This is the objective of this work which investigates the ability of different analytical models to predict the vertical velocity profile as well as the resistance induced by flexible submerged vegetation in open channels. Then it is possible to select the appropriate model that will be applied in the real case of rivers. The model validation is determined after a comparison between the data measured in the different experiments carried out and those from literature. For dense vegetation, the role of the Reynolds number is emphasized in particular with a model using the Darcy-Brinkman equation in the canopy. With a simple permeability, this model is relevant to estimate friction. However, for larger Reynolds number, models based on the fully turbulent flow assumption provide better results.
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