The effects of Vegetation properties on supercritical Air-Water FLOWs (V-A-W-Flow)

洪水，如2002年的易北河洪水，可以造成高额的经济损失和人身损失或损害，特别是如果技术防洪措施失败，洪水蔓延到内陆地区。滞洪区有助于影响洪水曲线，降低洪峰流量。为此，部分高流量的水流通过溢流段重新定向，进入自然或人为的保留区，在那里暂时储存。溢流部分通常建造为混凝土结构或土结构，由灰色护岸保护。随着环保意识的增强和老化基础设施维护成本的上升，基于自然的解决方案，如植被（溢流）堤防近年来受到越来越多的重视。溢流堤和溢洪道的建造必须使设计溢流率能够在不引起破坏的情况下传递到整个结构。与结构设计相关的流动参数、通气量、能量耗散和流动阻力，包括摩擦因素，都受到表面特性的影响。对光滑溢洪道、阶梯式溢洪道和岩槽等典型溢洪道结构进行了广泛的研究。此外，一些研究已经研究了植被对非曝气流动中流速和流动阻力的影响，尽管主要是针对亚临界流动。然而，由于设计参数的不确定性，植被特性对超临界空气-水沿植被槽（如溢流堤）流动和曝气的影响很少被探讨。因此，本提案旨在更好地了解植被溜槽的流动和曝气过程，并在考虑流动曝气的情况下，将能量耗散和流动阻力等设计参数作为植被特性的函数进行量化。为了了解有植被的溜槽上的流动和曝气过程，并量化依赖于溜槽表面植被特性的能量耗散和流动阻力，在溜槽模型上进行了溢流模拟。在这些试验研究中，水力边界条件和植被特性发生了系统的变化。为此，测试了不同植被高度和植被密度的卷草皮形式的天然溜槽覆盖物。植物学分析允许对被测植被进行参数化。在实验测试中，采用双尖端电导率探头测量流量和通气数据。根据收集到的数据，结合理论考虑，分析了植被特性对超临界空气-水沿植被溜槽流动参数、通气性、能量耗散和流动阻力的影响，建立了气流、通气性和植被参数之间的关系。

Flooding, such as the Elbe flood in 2002, can cause high monetary costs and bodily loss or damage, especially if the technical flood protection measures fail and the flooding extends into the hinterland. Flood retention areas help to influence the flood hydrograph and to reduce the peak flow rate. For this, part of the high water flow is redirected via overflow sections into natural or man-made retention areas where it is temporarily stored. Overflow sections are often constructed as concrete structures or as earthen structures protected by grey revetments. With increasing environmental awareness and rising costs for maintenance of aging infrastructure, nature-based solutions such as vegetated (overflow) dikes have received greater emphasis in recent years. Overflow dikes and spillways have to be constructed in such a way that the design overflow rate can be transferred across the structure without inducing damage. The flow parameters, flow aeration, energy dissipation and flow resistance, including friction factors, relevant for the structural design are influenced by the characteristics of the surface. Extensive research has been conducted for typical spillway structures, such as smooth spillways, stepped spillways and rock chutes. Further, the effects of vegetation on flow velocity and flow resistance in nonaerated flows have been investigated in several studies, though primarily for subcritical flows. Yet, the effects of vegetation properties on flow and aeration in supercritical air‐water flows down vegetated chutes such as overflow dikes are barely explored affecting the design process with uncertainties in the design parameters. Therefore, the proposal at hand aims at an improved understanding of flow and aeration processes on vegetated chutes and the quantification of design parameters, such as energy dissipation and flow resistance, as function of vegetation properties under consideration of flow aeration.In order to understand the flow and aeration processes on vegetated chutes and to quantify energy dissipation and flow resistance depending on the vegetation properties of the chute surface, overflow simulations on a chute model are performed. The hydraulic boundary conditions and vegetation properties are systematically varied during these experimental investigations. For this, natural chute covers in the form of rolled turf with different vegetation heights and vegetation densities are tested. Botanical analyses allow for parameterization of the tested vegetation. During the experimental tests, flow and aeration data is measured with double-tip conductivity probes. With the data gathered and under consideration of theoretical considerations, the effects of vegetation properties on flow parameters, flow aeration, energy dissipation and flow resistance in supercritical air‐water flows down vegetated chutes are analyzed and the relation of flow, aeration and vegetation parameters is established.