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。它们沿着沿着1 000多公里的海岸线延伸，保护低洼的后障地区免受洪水侵袭，并保护沿海悬崖在风暴期间免受侵蚀。它们对社会的重要性得到了广泛的认可，沿海工程结构（例如，海堤和丁坝）和管理技术（补给、再循环和改造）被广泛使用，以维持和加强其保护能力。不幸的是，正如DEFRA最近委托的一份报告所强调的那样，在英国的许多砾石屏障场地发生了定期破坏和广泛的风暴破坏，而且由于气候变化导致海平面上升和风暴增强，这种情况在未来可能会增加。DEFRA报告的结论是，目前有限的科学指导，以提供海滩管理人员与业务管理工具，以预测砾石屏障和海滩对风暴的反应。具体来说，我们目前无法预测在什么条件下砾石屏障将承受一定的风暴事件，或屏障是否会被过度冲刷，甚至突破。同样，我们也没有办法评估某些管理干预措施（海堤建设，海滩营养，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获得新的理解风暴对砾石海滩和屏障的影响，并开发一种预测工具，能够模拟这些影响。而不是开发一个新的模型，从第一原则，我们的方法是使用现有的模型，已成功地应用于桑迪和修改的模型，用于砾石滩使用现场数据。作为起点使用的模型是XBeach模型，该模型是专门为预测飓风对桑迪屏障的影响而开发的。(1)将在砾石海滩上进行为期4周的现场实验，以测量在一系列波浪条件（包括风暴）下的冲刷过程、沉积物输运和海滩响应。(2)这些现场数据将用于帮助修改，参数化和校准现有的XBeach模型，使其可用于砾石海滩。(3)将在英国9个砾石屏障系统上收集关于风暴响应的额外现场数据集，这些数据集代表一系列形态学、沉积学、波浪和水位条件。(4)这些现场数据将用于确认和验证根据（2）开发的XBeach模型。(5)将根据第（4）段所述模式为最终用户开发一个工具，用于预测护堤的形成、漫顶、溢流和砾石海滩和屏障的破坏。这个为期3年的项目由Gerd Masselink教授领导，涉及两名共同研究者，一名博士后研究员，一名项目学生，两名访问研究员和两名项目合作伙伴。该研究小组是进行拟议研究的理想选择，因为在过去5年中，他们获得了：（1）平静和充满活力的条件下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形态动力学的实验能力和仪器;（3）X海滩的专业知识，以定制用于砾石海滩的模型。两个项目合作伙伴（一个来自工业界，一个来自政府）的参与将确保这项研究的结果得到适当的传播和实际应用。

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.