强潮海滩响应威马逊台风作用动力沉积过程研究——以北海银滩为例

Sediment dynamic processes of macro-tidal beach in response to Typhoon Rammasun action——A case study of Yintan,Beihai

研究台风影响下的海滩沉积过程不仅可加深极端海况下的海滩冲淤变化理解,而且有利于海滩资源的保护与海岸工程保护。以强潮海滩——北海银滩为例,通过采集北部湾海区1409号威马逊超强台风作用前后的沉积物、剖面高程及水文资料,探讨强潮海滩的动力沉积过程。结果表明:1)台风作用前后的海滩沙丘-滩肩-沙坝体系的地貌状态基本不变,其中沉积物组分均为砂,细砂、极细砂和中砂三组分平均含量占所有组分的95%以上;与台风作用前比较,台风后的地貌在维持先前形态的条件下,发生局部侵蚀和后退,沉积物相对变粗且细砂含量增加了10%。2)台风作用后后滨沙丘侵蚀,且沉积物滚动组分增加;冲流带和滩肩前缘沉积物的搬运由双跳跃转为单一的跳跃形式。3)台风作用前后的海滩沉积物主要变化过程可由两个模态表征,其中主要模式反映了台风作用前后的海滩以细砂为主的动力沉积变化特征,该模式受控于区域波浪和潮汐的长期耦合作用,并以波浪为主导因素。台风作用前的次要模式反映潮汐作用控制下的海滩沉积横向振荡特征;台风作用后的次要模式表征了台风影响下的海滩横向沉积物偏粗、冲流带-低潮带振荡及其沉积分异过程。

Research on beach sediment dynamics under the influence of typhoon is of vital significance not only to beach erosion and deposition variations research in extreme ocean conditions, but also to beach resources and coastal engineering protection. Here, based on hydrology, sediments and beach profiles measurements during pre- and post-Typhoon Rammasun （TR） periods, this paper discusses the sediment dynamic processes of Yintan, Beibu Gulf, a macro-tidal beach. The main results show that： 1 ） The morphological state of the dune-berm-sandbar system is basically unchanged, and both pre- and post-TR periods indicate that Yintan beach is composed by sand component, with fine sand, very fine sand and medium sand accounting for over 95% of the total; compared with pre-TR period, the beach topography during post-TR is partially eroded and retreated in the condition of maintaining the previous form; the sediments are thicker, when fine sand contributes 10%. 2） In post-TR period, backshore dune indicates erosion and rolled sediment components reveal increase; sediment movement behavior over swash zone and beach berm front transfers from double to single jump pattern. 3） Sediment dynamic processes under the influence of TR along Yintan contain two main modes. The main mode reflects that the beach is mainly composed of fine sand, when the beach is controlled by long-term coupling effect of wave and tide, and the wave is the dominant factor; the minor mode represents the horizontal oscillation characteristics of the beach sediments under the control of tide, indicating coarser horizontal sediments, oscillation and differentiation processes in swash and low tide zones.