The nearshore current along a high-rainfall,trade-wind coast-Nicaragua

Runoff from abundant rainfall on the watersheds along the east coast of Nicaragua results in a well-defined nearshore current, extending 20–40 km out from the coast. Important terms in the controlling dynamical balance are the Coriolis forces, and eddy frictional forces. Calculations of the diabathic surface slope 0(10^?5) show a smooth setup of 4–5 cm from the outer edge of the current to the shoreline. A longshore surface slope of 0(10^?8) appears to be set up by the longshore wind stress, and further computations allow an estimate of ～ 6 gr cm^?1 s^?1 for the dynamic eddy viscosity. An analytical expression including diabathic surface slope and density gradient, parabathic surface slope, wind stress, and quadratic bottom friction reproduces the salient observed features of the nearshore current. These include the pronounced maximum in the parabathic (along-shelf) current about 10 km off the coast, a complex diabathic velocity structure, and a shelf countercurrent just seaward of the outer edge. Further calculations suggest that the dominant driving arises from the freshwater-induced density gradients, accounting for upward of 80% of the flow velocity. As suggested by Royer (1982), the prevailing trade wind exerts an onshore wind stress that serves the important role of maintaining the integrity of the density gradients via the convergence of a surface Ekman layer toward the coast.     

基于Boussinesq方程近岸波浪演变的数值研究

首先对目前描述近岸波浪传播变形的数学模型进行了回顾与总结;对不同数学模型的特点、适用范围和发展情况进行了阐述与对比。应用基于Boussinesq方程的Coulwave模式针对几个经典实验地形进行了数值实验,数值结果和实验实测数据吻合较好。此外,分别采用不同的近岸波浪模型模拟了某渔港附近波浪的传播变形,结果表明:当考虑波浪的折射、绕射、反射联合作用时,Coulwave模式计算结果明显较缓坡方程及SWAN模型计算结果更加合理。     

浅谈沿海滩涂开发中的测量问题

沿海滩涂大部分为淤泥质平原海岸带,滩地比较开阔,分布集中,但滩涂地形,地貌,自然植被等具有特殊性,所以其测量也不同于一般的地面测量。本文介绍了沿海滩开发中 水准测计算方法和渠道施工测量,并提出了滩涂水准测量中值得注意的几个问题,对指导当前沿海滩涂开发测量有参考价值。     

近30 年来长江口岸滩沉积物与地貌演变特征

通过对长江口潮间带宽度、表层和浅地层柱状样沉积物、典型水下岸坡剖面的现场测量,以及对潮间带宽度及水下岸坡剖面的多幅历史海图分析,研究近30 年长江口岸滩演变特征及岸滩演变的主要原因。结果表明:(1) 岸滩沉积物整体上呈“北细南粗”的变化特征,横沙东滩北岸、长江和东海大桥下等主要大型工程附近潮间带柱状样粒序向上显著变粗;(2) 长江口部分潮间带宽度减少90%以上;水下岸坡由1980 年的“S”形向凹形、斜坡形等侵蚀型形态转变,岸坡明显变陡,侵蚀型岸滩特征凸显;南汇嘴至芦潮港岸段水下岸坡闭合水深1978-2004 年为-8 m,近10 年来滩底发生侵蚀,刷深约1 m;(3) 流域来沙量锐减导致长江口侵蚀型水下岸滩格局的形成;河口大面积围垦、青草沙水库和长江与东海大桥等大型工程建设是造成潮间带大面积损失和局部沉积物粗化的主要原因;沙体变迁是狭长型河槽局部岸滩演变的主要影响因素。     

春季东海近岸表层浮游植物群落结构及其与环境因子的关系

采用HPLC-CHEMTAX方法分析了2008年春季东海近岸海域的表层浮游植物群落结构及其与环境因子的关系。结果表明,调查区表层浮游植物优势类群为硅藻和甲藻,对叶绿素a的平均贡献率分别为42%和32%。硅藻和甲藻均适于生长在低温、低盐和高氮磷比的环境,但硅藻水华发生在温度较低、盐度较高、氮磷比较高的长江冲淡水与外海水交汇的盐度锋面上,而甲藻水华发生在温度较高、盐度较低、氮磷比较低的冲淡水与台湾暖流交汇的温度锋面上。LOWESS回归表明,叶绿素a和甲藻分别随温度和盐度升高呈先增后降的趋势,硅藻随温度和盐度变化波动较大。叶绿素a和硅藻随氮磷比升高而递增,甲藻随氮磷比的变化波动较大。     

近岸水下扇微相划分研究及意义初探——以滦平盆地下白垩统西瓜园组为例

滦平盆地下白垩统西瓜园组沉积期发育大量的粗碎屑岩沉积,通过野外实地考察以及结合无人机摄影技术,将流体搬运机制与微相划分相结合,对断陷湖盆内部粗碎屑沉积体进行详细研究。结果表明：滦平盆地西瓜园组沉积期北部受边界断层活动影响,发育典型陆相断陷湖盆的近岸水下扇沉积体系。根据露头观测及研究,可划分出扇根、扇中及扇端三种亚相。其中扇根亚相以碎屑物质直接入湖、岩性较粗、分选极差、无磨圆为特征。扇中亚相采用“水下河道微相”及“边缘微相”的划分方式,水下河道微相可见同时发育由碎屑流及浊流两种不同流体性质控制的沉积体,沉积迅速,界限清晰且含轻微冲刷,横向连续性较为稳定,砾石出现一定定向性,磨圆较差,在扇中亚相中最为发育;边缘微相沉积相对较为混杂,漂砾较为常见,可见明显的板状交错层理,横向连续性差,指示河道的改道或者边缘沉积,不发育冲刷- 充填构造。扇端亚相以砂泥岩薄互层或者厚层细砂岩为特征,可见细小砾石层。微相划分方法结合流体搬运机制及沉降方式,更加具有成因性依据,同时更好地解释了远离物源区的稳定砾石层发育。研究结果为近岸水下扇内部砂体发育规律和叠置关系研究及下一步油气勘探与开发提供了新思路。     

近海与远洋飓风边界层特征高度的差异分析

使用1998—2016年大西洋40个飓风2 032个GPS下投式探空仪观测数据,以距离海岸线300 km为界分为近海和远洋两组,利用合成分析方法探讨了飓风边界层特征高度的差异。边界层特征高度的定义方法包括最大切向风高度、入流层高度、混合层高度和理查森数法高度。对比分析不同定义方法下近海和远洋边界层高度,结果表明：根据最大切向风和入流层强度定义的边界层高度,近海边界层高度低于远洋边界层高度,且近海边界层高度随径向增加至2倍最大风速半径后趋于稳定;基于混合层定义的边界层高度明显低于动力边界层高度,且近海与远洋混合边界层特征高度无明显差异;近海理查森数边界层高度在最大风速半径内与远洋的无明显差异,而在最大风速半径外略高于远洋的。     

长江口横沙北侧岸坡冲刷特征与趋势分析

根据2018年多波束测深系统、双频ADCP获得的横沙岛北侧岸坡水下地形与水动力实测数据,并结合历史地形资料分析该区域冲刷特征与发展趋势。结果表明:横沙北侧岸坡存在近岸冲刷坑,最大冲深约7 m;2002—2018年期间,冲刷坑附近河床经历冲-淤-冲的演变模式,整体呈冲刷状态;2007年后冲刷坑开始形成,并向下游延伸。这主要是因为青草沙水库工程的建设导致北港上段束窄,下段主流南移贴岸,使得近岸河床冲刷加剧。另外,横沙东滩促淤圈围工程抑制了北港与北槽间的水量交换,横沙岛近岸水域水动力进一步增强,也是岸坡冲刷的原因之一。分析表明大潮期间水流处于次饱和状态,岸坡表层泥沙起动流速略小于落急时刻水流流速,横沙北侧岸坡的冲刷可能会继续发展。     

Investigation of wave characteristics in a semi-enclosed bay based on SWAN model validated with buoys and ADP-observed currents

In this study, the simulating waves nearshore (SWAN) model with a locally refined curvilinear grid system was constructed to simulate waves in Jervis Bay and the neighbouring ocean of Australia, with the aim of examining the wave characteristics in an area with special topography and practical importance. This model was verified by field observations from buoys and acoustic Doppler profilers (ADPs). The model precisions were validated for both wind-generated waves and open-ocean swells. We present an approach with which to convert ADP-observed current data from near the bottom into the significant wave height. Our approach is deduced from the Fourier transform technique and the linear wave theory. The results illustrate that the location of the bay entrance is important because it allows the swells in the dominant direction to propagate into the bay despite the narrowness of the bay entrance. The wave period T p is also strongly related to the wave direction in the semi-enclosed bay. The Tp is great enough along the entire propagating direction from the bay entrance to the top of the bay, and the largest Tp appears along the north-west coast, which is the end tip of the swells’ propagation.