New Understanding and Predicting Storm Impacts on Gravel beaches

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.

The two Project Partners involved with this research will be beneficiaries and users of this research, and who will also facilitate its wider dissemination to the user community: (1) Hydraulics Research Ltd, Wallingford (HR) is a leading private sector company involved with coastal consultancy. HR's involvement will greatly facilitate real-world application of the research outcomes, for example, they will ensure that the results from this project will be suitable for rapid inclusion into the Environment Agency's flood and coastal erosion-risk management modelling tools. (2) Channel Coastal Observatory is the data management centre for the southeast and southwest Strategic Regional Coastal Monitoring Programmes whose partners include Lead Authorities with responsibility for flood and coastal defences along gravel beaches. The CCO will provide background data to the project and help co-ordinate post-storm surveys with several Lead Authorities (e.g., New Forest District Council, Worthing Borough Council, Shepway District Council, Canterbury City Council). During the project, six-monthly meetings with the two Project Partners will take place to ensure they are fully involved at all stages of the project. Importantly, during the second stage of the project, when the new science will be incorporated in a management tool for predicting storm impacts on gravel beaches, the Project Partners will play a crucial role in ensuring that the application will be fit for purpose. The main output with potential impact will be the production of tool model, XBeach-G, designed to predict storm response on gravel barriers from a simple set of inputs, including initial morphology, waves, sea level and sediment size. To ensure the model is used widely by coastal managers and engineers, the final model will be made freely available on the project web site. In addition, a dedicated computer programmer will be appointed for a 6-month period to develop a graphical user interface (GUI) for the model through which users are able to upload the data required to drive the model, interrogate the model results, and produce a report of the model output with relative ease. In April 2013 the University of Plymouth will host the International Coastal Symposium, one of the world's largest coastal conferences with c. 500 delegates. As part of this conference we will provide a short course, Predicting storm impacts on gravel beaches, aimed primarily at practitioners from UK consultancy companies, local authorities and the Environment Agency, and providing them with hands-on experience with the XBeach-G model. The investigators have a good track record of achieving knowledge exchange and impact, and have, for example, been involved with Royal National Lifeboat Institution, Marine Conservation Society, Marine Climate Change Impacts Partnership, Slapton Field Studies Centre, Slapton Line Partnership (SLP) and Sefton Council. The investigators also have a successful track record of working with MSc/PhD students and PDRFs who have subsequently gone on to work for coastal consultancy companies, so contributing to the economic competitiveness of the UK. The resources required to support the impact plan are captured in the financial summary and in the Justification of Resources. They include six-monthly meetings between the research team and the Project Partners, a six-month appointment of a computer programmer to develop the GUI for the 2D XBeach model and funds for Visiting Researcher Roelvink and Project Partner HR Wallingford to attend the International Coastal Symposium in Plymouth in 2013.