Soft Beach Change Prediction in Japan Sea Coast

日本面向日本海的桑迪存在严重的侵蚀问题，其主要原因是冬季风中的陡峭风浪。离岸流，即所谓的“底流”，是在碎波区产生的，由于波浪破碎，导致沉积物向离岸输送，在碎波线附近形成一个沿岸沙洲。离岸的沉积物被一个沿岸沙坝困住了。这是冬季近岸沉积物的一个环流循环。当大规模的海岸建设阻止沿岸泥沙输运时，跨岸泥沙的循环循环被破坏。这是日本海岸桑迪海岸海滩侵蚀的一种机制。为了控制上述海滩侵蚀，首席研究员小组开发了海岬-陆地防御工程。还开发了海滩变化预测方法，并指出为建立日本海海岸软海滩变化预测，应研究以下主题。(1)闭合深度：（2）稳定海滩形成的模拟;（3）海滩养护方法：日本、欧盟和美国海滩养护方法的相互评价。本研究项目对日本海冬季风引起的沿岸流进行了预测，明确了沿岸流和近海泥沙输运的三维结构。这些结果将被应用于一个口袋海滩形成的模拟在头陆防御工程。

Japan's sandy beaches facing Japan Sea have serious erosion problems which were mainly caused by steep wind waves in winter monsoon. Off-shore-going currents, so-called 'undertow' was generated in the surf zone due to wave breaking resulting in sediment transport towards off-shore to form a long-shore bar near breaker line. Sediment going off-shore was trapped with a long-shore bar. This is a circulation cycle of cross-shore sediment in winter. When large-scale coastal constructions are built to stop longshore sediment transport, a circulation cycle of cross-shore sediment is destroyed. This is a mechanism of beach erosion of sandy coasts facing Japan SeaHead-land defense works have been developed by the head researcher's group to control beach erosion mentioned above. Beach change prediction method has also been developed and pointed out that the following themes should be investigated for establishing soft beach change prediction of Japan Sea coasts.(1) Depth of closure : coastal currents induced by monsoon wind,(2) Simulation of stable beach formation,(3) Beach nourishment methods : mutual evaluation of beach preservation methods in Japan, EU and USA.This research project elaborated on prediction of coastal currents induced by winter monsoon in Japan Sea and made clear the three-dimensional structure of coastal currents and offshore sediment transport. These results will be applied to a simulation of pocket beach formation in head-land defense works.