Design of Erosion-Protection of Flood Plain and Side Slope of Levee by Vegetation

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Recently, river improvement should be planned to refine various functional aspects of rivers such as flood control, more efficient water resources utilization, recreational or leisure usage of rivers, well-conserved ecological situation, aquatic habitat and so on. As a compromise, erosion-protection works of flood plain and/or side slope of levee (embankment) by vegetation cover was investigated instead of more rigid protection works.When the sand bed is covered by vegetation layr, the Reynolds stress in the vegetation layr is effectively suppressed due to drag by vegetation. The flow with vegetation was described numerically by taking account of the effect of vegetation. In case of flexible vegetation, the deformation of individual plants and the flow over deformed vegetation layr were solved simultaneously. The method how to measure the flexural rigidity, which governs the deformation of the plants, in the fields was also studied.Furthermore, the effects of geometry of cross-section, which often have flood plain and side slopes, on the erosion-protection efficiency of vegetation layr were investigated by using the three-dimensional numerical analysis of flow with vegetation. The results of calculation obtained by changing the parameters systematically were summarized to be conveniently used for design of erosion-protection works with vegetation cover.