Soft Beach Change Prediction in Japan Sea Coast

日本面对日本海的沙滩存在严重的侵蚀问题，这主要是由冬季季风中陡峭的风浪造成的。由于波浪破碎导致泥沙向近岸输送，在海浪带产生了所谓的离岸水流，在防波线附近形成了一个长长的海岸沙洲。外海的沉积物被一个长长的海岸沙洲困住了。这是冬季跨岸沉积物的循环循环。当建造大规模的海岸建筑来阻止沿岸泥沙的输送时，一个跨岸泥沙的循环循环就被破坏了。这是日本沿海沙质海岸海滩侵蚀的一种机制--首席研究员小组已经开发了陆地防御工程，以控制上述海滩侵蚀。此外，还发展了海滩变化预测方法，并指出建立日本海岸软海滩变化预测应研究以下主题：(1)闭合深度：季风风诱导的沿岸流；(2)稳定海滩形成的模拟；(3)海滩滋养方法：相互评价日本、欧盟和美国的海滩保护方法。本研究项目详细阐述了日本海域冬季季风引起的海岸流预测，明确了沿岸流和近海沉积物的三维结构。这些结果将应用于头陆防御工程中的袖珍海滩形成的模拟。

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.