Debris Effects on BRIdge resiliencE and Flooding

长期以来，工程师、科学家和普通公众都被河流和桥梁之间复杂的、有时甚至是灾难性的相互作用所困扰。河桥的基础建在河床上，在洪水期间会受到严重的冲刷。术语冲刷是指河床土壤的侵蚀，这是由于桥墩附近水流湍急而造成的。当冲刷引起的河床下降太深时，基础可能会被破坏或根本无法支撑桥梁，在这种情况下，整个结构可能会严重损坏甚至倒塌。世界上发生的大多数桥梁倒塌都是由这种现象引起的。在运送大量漂浮物（树干、树枝或人类碎片，通常称为“碎片”）的河流中发生的另一个复杂情况是这些材料在桥墩处的积累形成堵塞。这些泥石流堵塞通过将流速引向河床而改变了水流，这加剧了冲刷并增加了桥梁倒塌的风险。碎片堵塞也会对桥墩产生很大的作用力，进一步导致桥梁失效的可能性。大量研究表明，碎片是世界各地桥梁故障的主要原因，在英国和美国，约有30%的桥梁故障是由碎片造成的。除了对桥梁安全构成的威胁外，碎片堵塞桥梁还导致上游水位上升，可能导致邻近地区洪水泛滥。由于许多桥梁都位于城市地区，那里有昂贵的资产，更多的人暴露在外，碎片堵塞会大大增加洪水的风险。由于i）气候变化导致的河流流量增加，ii）社会经济增长导致的桥梁数量增加和面临洪水的人口增加，预计上述问题在未来将变得更加频繁。最近的事件突出表明，迫切需要改进风险评估和缓解方法，以增强这些关键基础设施的复原力。例如，在2009年和2015年坎布里亚洪水期间，分别有244座和80座桥梁受损或丢失。项目合作伙伴，网络铁路和环境局，直接受到上述问题的影响。Network Rail拥有超过8，000座靠近或靠近水道的桥梁。环境局拥有大约2 000座水道上的桥梁。此外，环境署负责管理主要河流、河口和海洋的洪水风险。直到最近，项目合作伙伴（以及直接受这些问题影响的其他利益攸关方）可用于评估碎片引起的风险的工具并没有坚实的科学基础，而且相当有限。最近对这些方法进行的评估表明，这些方法存在严重的不一致和不准确之处，因此不足以管理重要基础设施系统的风险。最近在南安普顿大学进行的一项研究使我们对桥墩碎片堵塞的理解发生了重大变化。这些新的成果和预测能力为项目合作伙伴评估风险的方式的重大改进铺平了道路，从而为更有效地利用资源以减轻关键基础设施故障的风险铺平了道路。该项目的总体目标是弥合最近的研究与项目合作伙伴的实际需求之间的差距，将以前的研究转化为一个强大的，准确和以用户为导向的方法来评估碎片堵塞对桥梁恢复力和洪水的影响。该项目的成果将使项目合作伙伴能够就如何确定投资的优先次序以增强关键基础设施的复原力做出更明智的决定。

Engineers, scientists and the lay public alike have long been troubled by the complex and sometimes catastrophic interplay between rivers and bridges. River bridges have their foundations built on river beds, which can undergo significant scour during flood events. The term scour denotes the erosion of the river bed soil that occurs as a result of fast and turbulent water flowing close to the bridge pier. When the descent of the bed caused by scour is too deep, the foundations may be undermined or simply incapable of sustaining the bridge, in which case the whole structure can be severely damaged or even collapse. Most bridge collapses that occur throughout the world are caused by this phenomenon. A further complication that occurs in rivers that transport large amounts of floating material (tree trunks, branches or human debris, often called 'debris') is the accumulation of this material at bridge piers forming a jam. These debris jams alter the flow by directing the velocity towards the bed, which exacerbates scour and increases the risk of bridge collapse. Debris jams also produce large forces on the pier, further contributing to the prospects of bridge failure. A wide body of research now acknowledges that debris ranks high among the causes of bridge failures around the world, being responsible for approximately 30% of bridge failures in the UK and the US. In addition to the threats posed to bridge safety, the blockage of bridges by debris leads to increased upstream water levels that can result in flooding of adjacent areas. As many bridges are located in urban areas-where costly assets are located and more people are exposed- debris jams can considerably increase the risk of flooding. The above problems are expected to become more frequent in the future as a result of i) increased river flows due to climate change, ii) increased number of bridges and population exposed to flooding that will follow from socio-economic growth. Recent events highlight the urgency for improved risk assessment and mitigation methods to build up the resilience of these key pieces of infrastructure. For example, during the 2009 and 2015 Cumbrian floods respectively 244 and 80 bridges were either damaged or lost.The project partners, Network Rail and the Environment Agency, are directly affected by the issues above. Network Rail owns more than 8,000 bridges near or close to waterways. The Environment Agency owns approximately 2,000 bridges over water courses. In addition, the Environment Agency is responsible for managing the risk of flooding from main rivers, estuaries and the sea. Until recently, the tools that were available to the project partners (as well as other stakeholders directly affected by these issues) to assess debris-induced risk were not based on strong science and were considerably limited. A recent assessment of these methods has demonstrated serious inconsistencies and inaccuracies, therefore rendering them inadequate for the management of risk of important infrastructure systems. Recent research conducted at University of Southampton has delivered a step-change in our understanding of how debris jams at bridge piers grow. These new results and predictive capabilities now pave the way for significant improvements in the way that the project partners assess risk, and therefore to a more effective use of resources to mitigate the risk of failure of critical infrastructures.The overarching aim of the project is to bridge the gap between this recent research and the practical needs of the project partners by translating the previous research into a robust, accurate and user-oriented methodology to assess the effects of debris jams on bridge resilience and flooding. The outcomes of the project will enable the project partners to take more informed decisions on how to prioritise investments to build up the resilience of critical infrastructure.