Beach change over individual wave cycles on sand and gravel beaches

由于全球变暖，沿海地区的压力正在增加，海平面预计在下个世纪将上升0.5米。海平面上升加上风暴增加预计会加剧海岸侵蚀。仅在英格兰，洪水和海岸侵蚀风险的管理每年就花费6亿英镑，预计在未来几十年里，这一数字将显著增加。天然泳滩被广泛认为是防止侵蚀的最佳形式，因为它们形成天然的缓冲，以抵御流入的海浪能量，因此海滩营养（在海滩上放置额外的沙子）作为一种管理措施受到欢迎。人们早就知道，在平静的波浪条件下，海滩会形成（积聚），在风暴条件下，海滩会被削减（侵蚀）。虽然这个周期已经被观察到，但它并没有被精确测量，主要是因为缺乏合适的仪器来记录侵蚀和增生，同时记录引起它们的波和流。因此，我们预测海滩侵蚀和增生的能力仍然很差，这使得海岸管理者很难规划未来的海岸土地利用。该项目将使用一种令人兴奋的新测量技术，该技术是由英国普利茅斯大学和澳大利亚新南威尔士大学的研究人员于2005年合作开发的。新的仪器每秒测量海滩的水位几次，这样每次海浪经过海滩后，我们就可以看到海滩的水位是上升了（增生）还是下降了（侵蚀）。通过在海滩上安装大量这样的仪器，我们将能够看到每次海浪叠加后海滩水位的微小变化是如何在数小时、数天和数周内造成海滩增生和侵蚀的。这样的测量是前所未有的。我们将在两个对比鲜明的海滩上进行两次为期四周的实地活动，收集数据。第一项实验将于2008年3月在法国波尔多附近大西洋沿岸的沙滩上进行。这次野外活动是一个更大的多国海滩实验的一部分，为英国研究人员提供了一次一次性的机会，以收集他们对海滩变化的新测量结果，与其他主要研究小组所做的一系列其他测量结果相一致。第二次实地活动将于2008年5月在英国德文郡南岸的沙砾沙滩Slapton Sands举行。斯拉普顿沙滩是世界上仅有的20个使用摄像机和波浪浮标进行长期监测的海滩之一，为我们的测量提供了非常有用的背景信息。我们之前进行的研究表明，Truc Vert和Slapton Sands随着波浪条件的变化而增加和侵蚀1米，这使它们成为本研究的理想场所。这两项活动将不分昼夜地持续4周，以捕捉大范围的海浪情况。对这些数据的分析将使我们能够了解海浪、水流和沙子运输过程是如何共同导致海滩侵蚀和增生的。利用这些波浪、水流和沙粒运输的测量结果，加上对海滩变化的新测量结果，将建立数学方程，然后用于预测海滩侵蚀和增生。这将有助于改善我们未来对海岸的管理。这是一个为期两年的项目，由英国普利茅斯大学的研究人员和澳大利亚新南威尔士大学的访问研究员共同完成，法国波尔多大学的研究人员也参与其中。我们在两个不同的海滩上对海滩变化的新测量将确保我们在预测海滩侵蚀和增生方面取得重大进展。研究结果将发表在学术期刊上，并在日本举行的一次重要国际会议上向世界各地的专家展示。

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.