Beach change over individual wave cycles on sand and gravel beaches

Pressures on the coastal zone are increasing due to global warming, with sea-level expected to rise by 0.5 m over the next century. Rising sea levels combined with increased storminess is expected to enhance coastal erosion. In England alone, the management of flood and coastal erosion risk costs £600 million per year, a figure that is expected to increase significantly over the next decades. Natural beaches are widely thought of as the best form of protection against erosion as they form a natural buffer against incoming wave energy, hence the popularity of beach nourishment (placing extra sand on the beach) as a management measure. It has long been known that beaches build-up (accrete) in calm wave conditions and are cut back (erode) in storm conditions. Whilst this cycle has been observed, it has not been accurately measured, largely due a lack of suitable instruments that can record the erosion and accretion at the same time as the waves and currents that cause them. As a result, our ability to predict beach erosion and accretion remains poor, making it difficult for coastal managers to plan future coastal land use. This project will use an exciting new measurement technique developed in collaboration between researchers at the University of Plymouth (UK) and the University of New South Wales (Australia) in 2005. The new instruments measure the level of the beach a few times each second, so that after each wave passes up the beach, we can see whether the level of the beach has gone up (accretion) or down (erosion). By installing a large number of these instruments on the beach, we will be able to see how small changes in beach level after each wave add together to cause beach accretion and erosion over hours, days and weeks. Such measurements have never before been made. We will collect data during two four-week field campaigns on two contrasting beaches. The first experiment will take place in March 2008 on Truc Vert, a sandy beach on the Atlantic coast of France near Bordeaux. This field campaign is part of a much larger multi-national beach experiment and provides a one-off opportunity for UK researchers to collect their new measurements of beach change, coincident with a whole range of other measurements made by other leading research groups. The second field campaign will take place in May 2008 on Slapton Sands, a gravel beach on the south coast of Devon in the UK. Slapton Sands is one of only 20 beaches in the world that are being permanently monitored using video cameras and wave buoys, providing very useful background information for our measurements. Previous research conducted by us has shown that both Truc Vert and Slapton Sands build up and erode by 1 m with changes in wave conditions, making them ideal sites for this study. Both campaigns will continue day and night for 4 weeks in order to capture a wide range of wave conditions. Analysis of the data will enable us to understand how wave, current and sand transport processes combine to cause beach erosion and accretion. Using these wave, current and sand transport measurements, together with the new measurements of beach change, mathematical equations will be developed that can then be used to predict beach erosion and accretion. This will help improve the management of our coasts in the future. This is a 2-year project between researchers at the University of Plymouth (UK) and a Visiting Researcher from the University of New South Wales (Australia), and also involving researchers from the University of Bordeaux (France). Our new measurements of beach change on the two contrasting beaches will ensure significant advances are made in our ability to predict beach erosion and accretion. The results will be published in academic journals and presented to experts around the world at a major international conference in Japan.