Vegetation acts as a natural protection measure as it reduces inundation depth downstream of it and dissipates the energy of flow like flood and tsunami. The present study performed a series of laboratory experiments in which the flow variations and energy dissipation around discontinuous and vertically double layered vegetation (VDLV) were investigated with changing the vegetation density and water depth under steady subcritical flow conditions. A case of vertically single layered vegetation (SLV) was also considered for comparison purpose. The results showed that incorporating an intermediate (G/d = 0.563, where G is the clear spacing between cylinders in transverse direction, and d is the diameter of cylinder) as well as dense (G/d = 0.041) short submerged vegetation within a sparse (G/d = 2.125) emergent vegetation considerably increased the backwater rise by 22–55% and 26–59%, respectively for the upstream located vegetation model (UM), whereas it raised the backwater rise by 28–53% and 35–63%, respectively for the downstream located vegetation model (DM), as compared to that of sparse SLV forest. The combination of upstream located dense VDLV and downstream located intermediate VDLV offered larger resistance to the flow and gave maximum overall loss of flow energy i.e. 43–61%. It is observed that increasing the density of short vegetation layer in UM increases resistance to the flow by narrowing the passage of fluid flow, due to which the backwater rise upstream of the UM increased and inundation depth downstream of the DM reduced significantly; and hence, consequently resulted in a significant amount of loss in the flow energy.

中文翻译：

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垂直不连续植被流场分析及能量损失的实验研究

植被可以减少下游的淹没深度并消散洪水和海啸等流动能量，因此是一项自然保护措施。本研究进行了一系列实验室实验，研究了在亚临界稳定水流条件下，通过改变植被密度和水深，研究了不连续和垂直双层植被（VDLV）周围的水流变化和能量耗散。为了进行比较，还考虑了垂直单层植被（SLV）的情况。结果表明，结合中间物（G / d  = 0.563，其中G是横向圆柱之间的净间距，d是圆柱直径）以及密实（G / d = 0.041）稀疏（G / d = 2.125）上游植被模型（UM）的新兴植被分别使回水上升分别增加了22–55％和26–59％，而它使回水上升分别增加了28–53％和35–63％相对于稀疏SLV森林的定位植被模型（DM）。位于上游的稠密VDLV和位于下游的中间VDLV的组合提供了更大的流动阻力，并提供了最大的总流能损失，即43-61％。观察到，通过使流体流动的通道变窄，增加UM中短植被层的密度会增加对流动的阻力，因此UM上游的死水增加，而DM下游的淹没深度显着减少。因此，导致流动能量的大量损失。