北海银滩响应台风作用的动力地貌过程

Morphodynamic processes of the Yintan Beach in response to typhoon

极端高能事件影响下的海滩动力地貌过程直接关乎岸滩稳定及海堤安全。本文基于2020年16号台风“浪卡”前后北海银滩顺直岸段的剖面高程及表层沉积物等资料,探究了中等潮差的顺直响应台风作用的地貌变化机制。结果表明:1)台风后海滩地貌表现为冲流带的大型沙坝消失,后滨沙丘-滩槽体系被削平,滩面坡度趋于平缓。2)银滩沉积物均以中砂、细砂和极细砂为主,三者占比超过95%;台风后,高潮位带沉积物变细,低潮位带沉积物变粗,沙坝附近则出现粗细交错式变化;银滩中高潮位带滩面响应台风过程的特征与强潮型海滩相似,呈现消散型海滩的特征,而低潮位带滩面则因大型沙坝的作用而呈现弱潮型海滩特征。3)台风期间波浪是影响海滩的主要动力因素,海滩地形影响了近岸水动力的表现形式,从而改变了沉积物的粒径分布。

The beach morphodynamic process under the influence of extreme high-energy events is directly related to coastal stability and seawalls safety.Based on the profile elevation and surface sediments of the Yintan Beach collected before and after the 202016th typhoon“Nangka”,this paper explores the mechanism of morphological changes of a meso-tidal beach in response to typhoon actions.The results show that:(1)In post-typhoon period,the beach morphological changes are manifested by the disappearance of a large sand bar and the flattening of the bar-trough system,leading to a more gentle beach slope;(2)Sediment in Yintan Beach is mainly medium sand,fine sand and very fine sand,which account for more than 95%;The sediment grains become finer in the high tide zone and coarser in the low tide zone,while both increase and decrease in sediment grain size can occur near the sand bar;The morphodynamic process of mid-to-high tide zone of the Yintan Beach in response to a typhoon is similar to that of a macro-tidal beach,which is characterized by dissipative condition.However,the morphodynamic process of low tide zone of the Yintan Beach behaves like a micro-tidal beach due to the existence of a large sand bar;(3)During the typhoon,wave is the main dynamic factor affecting the beach,and the topography affects the manifestation of nearshore hydrodynamics,thereby changing the grain size distribution of sediment.