Debris Effects on BRIdge resiliencE and Flooding

长期以来，工程师、科学家和普通公众都对河流和桥梁之间复杂的、有时甚至是灾难性的相互作用感到困扰。河桥的基础建在河床上，在洪水发生时，河床会受到严重的冲刷。冲刷一词指的是湍急的水流靠近桥墩时对河床土壤的侵蚀。当冲刷引起的河床下降太深时，地基可能被破坏或根本无法支撑桥梁，在这种情况下，整个结构可能严重损坏甚至倒塌。世界上发生的大多数桥梁倒塌都是由这种现象引起的。在河流中，如果有大量的漂浮物（树干、树枝或人类的残骸，通常被称为“碎片”），还会发生另一种复杂情况，即这些漂浮物在桥墩上堆积，形成堵塞。这些碎石堵塞通过引导水流流向河床来改变水流，这加剧了冲刷，增加了桥梁倒塌的风险。碎石堵塞也会对桥墩产生巨大的作用力，进一步加剧桥梁的破坏前景。大量的研究表明，碎片是导致世界各地桥梁倒塌的主要原因，在英国和美国，大约30%的桥梁倒塌是由碎片造成的。除了对桥梁安全构成威胁外，被碎片堵塞的桥梁会导致上游水位上升，从而可能导致邻近地区的洪水。由于许多桥梁位于城市地区——昂贵的资产位于那里，更多的人暴露在那里——碎片堵塞会大大增加洪水的风险。由于气候变化导致的河流流量增加，以及社会经济增长导致的桥梁数量和受洪水影响的人口增加，上述问题预计将在未来变得更加频繁。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。项目的合作伙伴，网络铁路和环境局，直接受到上述问题的影响。铁路网拥有8000多座靠近水路的桥梁。环境署在河道上拥有大约2000座桥梁。此外，环境署还负责管理主要河流、河口和海洋的洪水风险。直到最近，项目合作伙伴（以及其他直接受这些问题影响的利益相关者）可用来评估碎片引起的风险的工具都没有强有力的科学依据，而且相当有限。最近对这些方法的评估显示出严重的不一致和不准确，因此使它们不足以管理重要基础设施系统的风险。南安普顿大学最近进行的一项研究使我们对桥墩上的碎片堵塞是如何增长的理解发生了变化。这些新的结果和预测能力现在为项目合作伙伴评估风险的方式的重大改进铺平了道路，从而更有效地利用资源来减轻关键基础设施故障的风险。该项目的总体目标是通过将以前的研究转化为一种强大、准确和以用户为导向的方法来评估碎片堵塞对桥梁弹性和洪水的影响，弥合最近的研究与项目合作伙伴的实际需求之间的差距。该项目的成果将使项目合作伙伴能够就如何优先投资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.