海南岛南渡江河口动力沉积模式

Sedimentation Dynamic Modes of the Nandujiang Estuary,Hainan Island

河口是一个迅速变化的、动态的海岸巨系统。作为陆地河流和和海洋过程的重要链接,河口的动力沉积过程一直是陆海相互作用研究的核心和焦点内容。本文基于2011年8月在南渡江河口采集的大范围表层沉积物样品,利用经验正交函数分析技术(EOF)对河口的动力沉积特征进行研究。结果表明:南渡江河口海床表层沉积物主要以砂为主,沉积物总体偏粗;河口的动力沉积特征自陆向海可分为三种动力沉积模式:1波控模式,该模式主要分布在河口地区10 m以浅的近岸区域,呈与岸线平行的带状分布,其表层沉积物以粉砂质砂为主,分选较差;2径、潮流耦合作用下的沉积模式,在径流和潮流的共同控制作用下,沉积物主要表现为粒径较粗,该模式呈扇形分布,其中20 m以浅河口海床受控于径流和潮流的共同作用,20 m以深海床表现为潮流控制的沉积模式;3台风或风暴潮控制的沉积模式,即整个河口海床都表现出受控于台风或者风暴潮作用的沉积特征,沉积物主要是以粗砂为主。常态作用下,河口以径、潮流控制的沉积模式为主,波浪、径流和潮流以及潮流控制的沉积模式自陆向海的规律性分布体现出南渡江河口近岸以波浪作用为主,而离岸则受河口尤其是洪水作用形成的喷射流以及沿岸潮流的影响。此外,尽管南渡江河口在过去的成果中将其归纳为波控河口,但目前的研究发现:该河口区域沉积类型变化明显受控于不同的动力作用,河口形态以及琼州海峡的障蔽和"狭管效应"为河口沉积环境变化的主要控制因素。

Estuaries are naturally dynamic coastal systems that are unique in their close links to both land-based fluvial and coastal ocean process. Based on the collected large-scale sediment samples of Nandujiang Estuary in August2011,the characteristics of grain size and associated sediment dynamic process of the Nandujiang Estuary were analyzed,and then depositional modes of the Nandujiang Estuary were further researched by empirical orthogonal function( EOF) method.The studied results show that: surface sediments of the Nandujiang Estuary were mainly composed of sand component. Three distinct depositional modes of the Nandujiang Estuary from land to sea can be seen as follows: 1Mode controlled by dominant wave action with main distribution is limited to the shallow area below 10 m isobaths,where the surface sediments are basically composed of silt-sand with poor sorting. 2Mode controlled by coupling actions of runoff and tidal current with main distributed region is ranged from 10 m to 20 m isobaths,and offshore zone below 20 m isobaths was mainly controlled by the tidal forcing. The depositional mode is composed of coarse sediment component,which is presented as fan appearance. 3Mode controlled by Typhoon or storm tidal actions is distributed over the whole studied area,where the sediments are mainly composed of coarse sand.The first two depositional modes represent commonly sediment dynamics features of the Nandujiang Estuary. The basic pattern is the mode controlled by coupling actions of runoff and tidal current. Moreover,distributed depositional modes from land to sea show that the wave action is dominant in the nearshore zone,and offshore zone is mainly influenced by jet current due to flood action and alongshore tide current. In addition,although Nandujiang Estuary was attributed to wave-dominated estuary in the previous researches,present results reveal that depositional mode of the Nandujiang Estuary could be obvious controlled by different dynamic actions. Estuarine geometry appearance and impacts of barrier actions and narrow tub of the Qiongzhou Strait could be one of the dominant factors on depositional environment changes of the Nandujiang Estuary.