Turbulent flows and riparian vegetation induced drag for river flooding

洪水几乎占所有自然灾害的三分之一。自然灾害造成了一半以上的死亡，大约三分之一的经济损失是自然灾害直接造成的（Berz， 2000年）。目前，大约有500万人生活在英格兰和威尔士的洪水风险地区，拥有200万套房产。为了减轻洪水风险，必须充分了解河流的流量特征，以便建立准确的模型，从而准确估计水位，提供准确的洪水警报和城镇淹没地图。然而，河流不能脱离其更广泛的环境来考虑，因此河流及其洪泛平原的现代管理必然与植被的作用直接有关。树木和灌木通常以相对直线的方式生长在河流的边缘。在农村地区，这种模式是普遍农业实践的结果，在那里，河岸标志着田地的边界，树木和灌木构成了树篱系统的一部分。尽管乔灌木在河岸环境中具有一定的生态功能，但它们对水流阻力的影响较大。树木和灌木的存在由于尾流而产生湍流，从而降低了河流及其洪泛区的输送能力，从而提高了当地的洪水水位。尽管对水生植物进行了许多研究，但迄今为止还没有人关注洪泛平原边缘的树木和灌木等河岸植被如何影响水流行为、阻力和水位。树木和灌木比水生植物提供更大的水流阻力，导致更高的水位。因此，本项目旨在通过实验室实验研究河岸植被的影响，以减轻洪水风险，并为河岸植被的管理提供适当的指导。实验将在拉夫堡大学进行，将包括测量河岸植被阻力、湍流、河床摩擦和水面变化，使用测量阻力装置、声学多普勒测速仪（ADV）、皮托管、普雷斯顿管、3-D数字扫描仪和摄影测量。这些测量的流量参数将用于研究阻力系数、流阻和水位等关键参数对河岸植被管理和洪水风险评估的影响。

Floods account for almost a third of all natural disasters. They are responsible for more than half of the fatalities and approximately a third of all economic losses are a direct result of natural catastrophes (Berz, 2000). At present, about 5 million people in 2 million properties live in flood risk areas in England and Wales. In order to mitigate flood risk, it is essential that a sufficient understanding of flow characteristics in rivers should be achieved, to enable accurate models and therefore accurate estimation of water level to provide accurate flood warnings and inundation maps of towns and cities. A river, however, cannot be considered in isolation from its wider environment so that the modern management of rivers and their floodplains is necessarily directly concerned with the role of vegetation. Trees and shrubs can be commonly found growing at the edge of rivers in relatively straight lines. In rural areas, this pattern is the result of common agricultural practice, where the riverbank marks the field boundary and the trees and shrubs form part of the hedgerow system. Despite their ecological functions in riparian environment, trees and shrubs have a large impact on flow resistance. The presence of trees and shrubs generates turbulence owing to wakes which reduces the conveyance capacity of a river and its floodplain, with consequent raising of local flood levels. As yet no one has paid attention to how riparian vegetation such as trees and shrubs along the edges of floodplains influence the flow behaviour, resistance and water level though many studies on aquatic plants have been undertaken. Trees and shrubs offer more flow resistance than aquatic plants, leading to higher water level. This project is therefore to study the effects of riparian vegetation through laboratory experiments in order to mitigate flood risk and to provide an appropriate guidance on the management of riparian vegetation. The experiments will be conducted at Loughborough University and will involve measuring riparian vegetation drag force, turbulence, bed friction, and water surface variation with a measuring drag device, Acoustic Doppler Velocimetry (ADV), a pitot tube, a Preston tube, a 3-D digital scanner, and Photogrammetry. These measured flow parameters will be used to investigate effects on the key parameters such as drag coefficient, flow resistance and water level for the management of riparian vegetation and flood risk assessment.