New Understanding and Predicting Storm Impacts on Gravel beaches

砾石屏障和海滩由粗于2毫米的沉积物组成，在英格兰和威尔士非常常见。它们沿着其1000多公里的海岸线延伸，保护地势低洼的后屏障地区免受洪水侵袭，并在风暴期间保护沿海悬崖免受侵蚀。它们对社会的重要性得到广泛承认，并广泛使用沿海工程结构(如海堤和丁坝)和管理技术(补给、回收和重塑)，以高昂的成本维持和加强它们的保护能力。不幸的是，正如DEFRA最近委托的一份报告中强调的那样，英国的许多砾石屏障地点都发生了经常性的决口和大范围的风暴破坏，而且由于气候变化导致的海平面上升和暴风雨增强，这种情况在未来可能会增加。DEFRA报告的结论是，目前为海滩管理者提供业务管理工具以预测砾石屏障和海滩对风暴的反应的科学指导有限。具体地说，我们目前无法预测砾石屏障在什么条件下能经受住某种风暴事件，或者屏障是否会被大水冲刷，甚至被冲破。同样，我们无法评估某些管理干预措施(海堤建设、海滩滋养、剖面重塑)对砾石屏障稳定性的影响。因此，拟议研究的主要目的是对风暴对砾石海滩和屏障的影响有新的了解，并开发能够模拟这些影响的预测工具。我们的方法不是从基本原理开发新的模型，而是使用已成功应用于沙滩的现有模型，并使用现场数据修改该模型以用于砾石海滩。作为起点的模型是X海滩模型，它是专门为预测飓风对沙障的影响而开发的。拟议的研究最好总结为以下密切相关的目标。(1)将在砾石海滩上进行为期4周的现场试验，以测量包括风暴在内的各种波浪条件下的涌浪过程、泥沙输移和海滩响应。(2)这些现场数据将被用来帮助修改、参数化和校准现有的X海滩模型，以便它可以用于砾石海滩。(3)将在9个英国砾石屏障系统上收集关于风暴响应的额外现场数据，这些数据代表了一系列地形、沉积、波浪和水位条件。(4)这些现场数据将被用来验证和验证在(2)项下开发的XBeach模型。(5)将根据第(4)项所述的模型，为最终用户开发一种工具，用于预测砾石海滩和屏障的护堤形成、溢流、溢流和冲破。这个为期3年的项目由Gerd Masselink教授领导，有两名合作研究人员，一名博士后研究员，一名项目学生，两名访问研究人员和两名项目合作伙伴。研究团队是开展这项拟议研究的理想人选，因为在过去的5年里，他们已经获得了：(1)在平静和充满活力的条件下对砾石海滩动力学的知识和理解：(2)在风暴条件下测量砾石海滩地貌动力学的实验能力和仪器；以及(3)为在砾石海滩上使用而定制模型的专业知识。两个项目伙伴(一个来自行业，一个来自政府)的参与将确保这项研究的结果得到适当传播并用于实际应用。

Gravel barriers and beaches consists of sediments coarser than 2 mm and are very common in England and Wales. They extend along more than 1,000 km of its coastline and protect low-lying back-barrier regions from flooding, and coastal cliffs from undercutting during storm events. Their importance to society is widely acknowledged and coastal engineering structures (e.g., seawalls and groins) and management techniques (recharge, recycling and reshaping) are extensively used, at significant cost, to maintain and enhance their protective ability. Unfortunately, as highlighted in a recent report commissioned by DEFRA, regular breaching and extensive storm damage has occurred at many gravel barrier sites in the UK, and this is likely to increase in the future as a result of sea-level rise and enhanced storminess due to climate change. The DEFRA report concludes that limited scientific guidance is currently available to provide beach managers with operational management tools to predict the response of gravel barrier and beaches to storms. Specifically, we are currently unable to predict under what conditions a gravel barrier will withstand a certain storm event, or whether the barrier will be overwashed, or even breached. Similarly, we have no means of evaluating the effect of certain management interventions (seawall construction, beach nourishment, profile reshaping) on gravel barrier stability.The principal aim of the proposed research is therefore to obtain new understanding of storm impacts on gravel beaches and barriers, and to develop a predictive tool that is capable of modelling these impacts. Rather than developing a new model from first principles, our approach is to use an existing model that has been applied successfully to sandy beaches and modify the model for use on gravel beaches using field data. The model used as a starting point is the XBeach model, which has been specifically been developed to predict hurricane impacts on sandy barriers.The proposed research is best summarised by the following closely linked objectives. (1) A 4-week field experiment will be held on a gravel beach to measure swash processes, sediment transport and beach response under a range of wave conditions, including a storm. (2) These field data will be used to help modify, parameterise and calibrate the existing XBeach model so it can be used for gravel beaches. (3) An additional field data set on storm response will be collected on nine UK gravel barrier systems, representing a range of morphological, sedimentological, wave and water level conditions. (4) These field data will be used to validate and verify the XBeach model developed under (2). (5) A tool will be developed for end-users, based on the model formulated under (4), for predicting berm formation, overtopping, overwashing and breaching of gravel beaches and barriers. The 3-year project is led by Professor Gerd Masselink and involves two co-investigators, one post-doctoral research fellow, one project student, two Visiting Researchers and two Project Partners. The research team is ideally placed to conduct the proposed research, because over the past 5 years they have acquired: (1) knowledge and understanding of gravel beach dynamics under calm and energetic conditions: (2) experimental capability and instrumentation for measuring gravel beach morphodynamics under storm conditions; and (3) expertise with XBeach to customise the model for use on gravel beaches. Involvement of two Project Partners (one from industry and one from government) will ensure that the results from this research will be appropriately disseminated and used for practical applications.