冲流带海滩高频振动探讨

在粤东汕尾寮嘴口岬间海滩冲流带设置两条剖面,利用2003年10月13日一个潮周期实测高频剖面数据(采样间隔为1min和6min),分析了海滩的高频振动特征。并结合同期实测碎波带水位波动,探讨了海滩高频振动的动力原因。分析表明,此海滩过程主要以堆积为主,并表现有显著周期的振动：其日内变化受潮汐控制,表现为涨潮堆积、落潮侵蚀;波能对海滩高频振动过程有着重要的影响。     

粤东后江湾冲流带滩面高频振动及动力作用分析

利用涌浪影响下短时段内的冲流带滩面高频高程数据和碎波带波流资料,在奇异谱分析(SSA)的基础上,以比研究了不同形态滩面的冲淤变化趋势、趋势分布形状、冲淤变化周期和冲淤变化强度,以及同一条剖面不同桩点间各因素间的变化关系;用交叉谱方法探索了每分钟滩面高频冲淤变化与碎波带长重力波间的作用关系.分析结果表明,滩角韵律地形引起的冲流分流作用促进了滩脊向滩谷的泥沙转运,冲流带滩面存在明显的长重力波频段的周期性冲淤振动,滩面冲淤振动强度由滩面下部向上部递减,碎波带长重力波对滩面高频冲淤变化起重要作用.     

粤东后江湾冲流带滩面高频振动及动力作用分析

利用涌浪影响下短时段内的冲流带滩面高频高程数据和碎波带波流资料,在奇异谱分析(SSA)的基础上,对比研究了不同形态滩面的冲淤变化趋势、趋势分布形状、冲淤变化周期和冲淤变化强度,以及同一条剖面不同桩点间各因素间的变化关系;用交叉谱方法探索了每分钟滩面高频冲淤变化与碎波带长重力波间的作用关系。分析结果表明,滩角韵律地形引起的冲流分流作用促进了滩脊向滩谷的泥沙转运,冲流带滩面存在明显的长重力波频段的周期性冲淤振动,滩面冲淤振动强度由滩面下部向上部递减,碎波带长重力波对滩面高频冲淤变化起重要作用。     

粤东后江湾涨落潮下的碎波带波能与滩面地形时空变化分析

利用涌浪和处于陡滩面、滩面下陡坎和深槽海滩地形条件下的海滩碎波带压力波和滩面地形资料,对碎波带中的入射总波能、长重力波能及两者比值随潮位涨落的变化关系,碎波带动力因子与滩面地形之间的作用关系及典型相关和多维偏交叉谱关系等作了初步分析。结果表明,碎波带中的入射总波能与潮位涨落呈现出一致的变化规律;而碎波带中的长重力波能变化与潮位涨落变化趋势相反;碎波带各动力因子、滩面潜水位和碎波带波浪、潮位及滩面地形引起的滩面陡坎处破波点位置变动等因素的耦合作用,对滩面向海发育和滩面地形变化有重要影响。     

海滩冲流带高频振动及碎波带波浪作用的模态分析

一般来说,研究者对海滩中长尺度变化的研究比较多,通过时间间隔为数小时、1d,1周、1个月甚至1a一次的重复测量来分析海滩的变化特征,但海滩冲流带是动力和地形发生高频率变化的一个区域,每次波浪引起的上冲和回流过程均要引起滩面泥沙的运动,造成滩面的局部堆积和侵蚀,而滩面地形的改变又反过来影响到下一次的冲流过程。这些现象对研究海滩碎波带动力和滩面地形相互作用机理、认识近岸泥沙的运动规律以及探讨岸滩的长期冲淤演变是十分有意义的。     

基于自组织机制理论的滩角地形数值模拟

一般认为滩角是近岸带泥沙、水动力和地形耦合作用的产物,对近岸带特别是碎波带和冲流带的动力变化响应迅速,还可以反映海滩状态,但具体的成因一直得不到很好的解释.首先详细介绍了关于滩角成因的争论以及自组织机制理论,其中驻立边缘波假说和自组织机制假说是最为认同的两种滩角成因假说.基于WERNER(1993)提出的滩角形成的自组织机制假说,建立包含冲流动力、泥沙输运和地形演变的滩角形成和发育的元胞自动机模型.模型中修正了以前研究中的坡度参数表达式和水动力输入方式.经过200个冲流循环的数值模拟,原来平直的滩面上形成了明显的滩角形态,滩角间距约为5.5～6.0 m,520个循环周期后,滩角形态基本上达到稳定状态.对模拟过程进行分析,结果表明:(1)模拟得到的滩角形态比先前的研究结果更接近天然状态下的滩角;(2)随机的水质点冲流运动使海滩地形呈无规律变化,但通过动力、泥沙、地形之间的反馈过程逐渐形成了滩角地形;(3)滩角形成过程中,海滩基本上处于堆积过程中.开始堆积速度较快,当滩角形态达到准平衡状态时(大约300个循环后),海滩体积增速变慢,并逐渐地达到稳定状态,海滩体积变化呈现小的波动调整;(4)模拟得到的有效冲流距离(S)和滩角间距(λ),满足滩角自组织机制假说的基本关系.因此,可以认为滩角是在海滩泥沙、地形与波、流的自组织过程中形成的,是一种堆积地形.自组织理论为从不同的侧面认识和研究海岸带现象与过程提供一扇窗口,是一个值得研究的方向.     

基于高频观测数据的徐闻青安湾海滩对台风“贝碧嘉”的响应研究

风暴是造成海滩剧烈变化的重要因子。由于观测环境的恶劣，目前极少有风暴过程中海滩响应的现场高频观测工作。本研究在2018年台风“贝碧嘉”期间对徐闻青安湾海滩开展了历时6天半的高频观测，获得了全时水动力要素和164组逐时海滩滩面高程变化数据。通过分析表明:(1)青安湾海域风暴增水及波浪受控于海南岛?雷州半岛特有的地形地貌和台风“贝碧嘉”的多变路径，增水稳定在0.38～0.5 m之间，而波高先由0.78 m衰减至0.43 m，再增加至0.56 m；(2)海滩剖面地形变化总体表现为滩肩侵蚀，形成水下沙坝，滩肩响应过程分为快速向下侵蚀、缓慢侵蚀至最大值、振荡回淤恢复3个阶段，台风期间滩肩振荡恢复幅度可达最大侵蚀深度的1/4；(3)海滩的风暴响应过程主要由4个模态耦合而成:第一模态体现大潮滩肩侵蚀生成水下沙坝过程；第二模态体现风暴滩肩侵蚀，补偿大潮滩肩侵蚀位置和进一步促进沙坝形成过程；第三模态揭示了波浪二次破碎位置的上冲流和离岸底流使泥沙发生双向输移过程；第四模态表明台风大浪使得碎波带内泥沙大量悬浮，在沿岸流和离岸流作用下部分悬沙进入深水区，可能造成海滩泥沙的永久亏损。     

广东水东湾弧形海岸切线段海滩剖面的过程分析

本文运用因子分析和交叉谱分析方法对广东水东湾晏镜海滩剖面实测数据进行了地貌过程分析.因子分析结果提取了4个主因子,累积方差达90%.这4个主因子分别代表了碎波带的脊-沟过程、冲流带的滩肩过程、引起后滨面切割的侵蚀性裂流-滩角过程和造成上部滩面净侵蚀的潮汐过程.先前波况对海滩剖面的影响通过交叉谱分析表明,平均海面以上海滩单宽体积变化落后于波能变化1.6-3.4d.海滩剖面动态分析显示平均海面以下是净侵蚀场所,平均海面以上则处于动态平衡.海滩主状态目前为脊-沟或低潮台地的中间类型.     

海滩近岸带中尺度地形动力过程研究进展

海滩近岸带中尺度地形动力过程是海岸海洋科学研究的重要研究内容之一.近20年来该领域发展较快,取得了一些重要的成果.对近岸带中尺度地形动力过程的碎波带地形与沙坝、冲流带地形与滩角、海滩风暴响应、观测技术手段等主要领域的进展进行了总结和评述,并对我国海滩研究提出要从加强观测手段和制定长期观测计划两方面来加强的建议.     

波浪作用下级配泥沙海滩滩面变化试验研究

砂质海滩的泥沙具有一定的级配,在波浪作用下,滩面泥沙粒径将发生分选,引起海滩质量变化。在水槽中用不同波高和周期的波浪分别对不同级配的沙滩进行作用,探究滩面在波浪外动力作用下的变化规律。结果表明:全级配沙滩在相同波高波浪作用下形成的沙坝型海滩滩型中,破波点向海的区域表层泥沙分选会随波浪周期增大变差;相同周期(T=1.68s)波浪作用下,全级配沙滩在大波高(H=13.2cm)和小波高(H=6.7cm)的波浪作用下分别形成沙坝型和滩肩型海滩,滩面泥沙分选变好;原始沙滩级配与滩面泥沙变化密切相关,同种波浪动力作用下,中细、粗中沙滩沙坝表层泥沙迎波面粗于背波面,粗细沙滩粗颗粒集中在沙坝和滩顶之间。     

复经验正交函数方法对湛江南三岛海滩剖面季节变化动态特征研究

利用复经验正交函数(CEOF)分析方法对湛江南三岛2009年2月22日至2010年4月21日期间的实测海滩剖面数据进行了分析。结果表明该海滩的季节变化有3个主要模态:第1模态是海滩风暴剖面和涌浪剖面之间的相互转换,其贡献占总方差的71.18%。其原因是海区侵蚀性风暴大浪和建设性涌浪的交替变化。第2模态是平均高、低潮线之间的地形变化,其原因是由于潮汐变化导致入射波浪冲流活动范围变化,占总方差的14.28%。第3模态是侵蚀大浪过后的水下沙坝向岸迁移,并受潮汐影响在滩面上摆动,占总方差的6.80%。最后指出必须重视风暴对华南海滩演变季节性过程的影响。     

Morphodynamics of intertidal bars on a megatidal beach, Merlimont, Northern France

The morphology, bedforms and hydrodynamics of Merlimont beach, in northern France, characterised by intertidal bars and a spring tidal range of 8.3 m, were surveyed over a 10-day experiment with variable wave conditions that included a 2-day storm with significant wave heights of up to 2.8 m. The beach exhibited two pronounced bar-trough systems located between the mean sea level and low neap tide level. Waves showed a cross-shore depth modulation, attaining maximum heights at high tide. The mean current was characterised dominantly by strong tide-induced longshore flows significantly reinforced by wind forcing during the storm, and by weaker, dominantly offshore, wave-induced flows. Vertical tidal water-level variations (tidal excursion rates) showed a bimodal distribution with a peak towards the mid-tide position and low rates near low and high water. The two bar-trough systems in the mid-tide zone remained stable in position during the experiment but showed significant local change. The absence of bar migration in spite of the relatively energetic context of this beach reflects high macro-scale bar morphological lag due to a combination of the large vertical tidal excursion rates in the mid-tide zone, the cross-shore wave structure, and the pronounced dual bar-trough system. The profile exhibited a highly variable pattern of local morphological change that showed poor correlation with wave energy levels and tidal excursion rates. Profile change reflected marked local morphodynamic feedback effects due mainly to breaks in slope associated with the bar-trough topography and with trough activity. Change was as important during low wave-energy conditions as during the storm. Strong flows in the entrenched troughs hindered cross-shore bar mobility while inducing longshore migration of medium-sized bedforms that contributed in generating short-term profile change. The large size and location of the two pronounced bars in the mid-tide zone of the beach are tentatively attributed respectively to the relatively high wave-energy levels affecting Merlimont beach, and to the cross-shore increase in wave height hinged on tidal modulation of water depths. These two large quasi-permanent bars probably originated as essentially breakpoint bars and are different from a small bar formed by swash and surf processes in the course of the experiment at the mean high water neap tide level, which is characterised by a certain degree of tidal stationarity and larger high-tide waves.     

舟山本岛南部附近海域潮汐潮流特征分析

文章基于沈家门长期潮位站、长峙岛临时潮位站的观测资料和对舟山本岛南部海域多个站位实测的潮流基础数据,采用调和分析法对潮汐潮流进行特征分析。舟山本岛南部附近海域潮汐类型属于规则半日潮,潮差变化和日不等现象明显,有一定的潮汐浅海作用。潮流类型属于以往复流为主的规则半日浅海潮流,实测潮流中涨落潮流速不等、历时不等现象显著,最大流速、平均流速均是大潮大于小潮,涨潮流历时长于落潮流历时,潮流变化主要受协振波所控制,流向在涨落潮方向波动。     

Applications of EMD to analyses of high-frequency beachface responses to Storm Bebinca in the Qing'an Bay,Guangdong Province,China

On average, five to six storms occur in the Qiongzhou Strait every year, causing significant damage to coastal geomorphology and several property losses. Tropical Storm Bebinca is the most unusual and complex storm event that has occurred in this region over the last 10 years. To detect the high-frequency beachface responses to the storm, a pressure sensor was deployed in the surf zone to record the free sea surface height, and the heights of grid pile points on the beachface were measured manua...     

南海东沙岛西南大陆坡内潮特征

2008年4月-10月,在南海东沙岛西南大陆坡底部布放了1套全剖面锚系,同时沿大陆坡底部布放了3套近底锚系,应用谱分析和调和分析方法分析温度和海流连续观测资料,进而研究该海域的内潮特征.结果表明,东沙岛西南大陆坡存在强内潮现象,大陆坡底部温度变化受到内潮波的影响,上层海洋存在强日潮周期的内潮波振动;正压潮和斜压潮均以O...     

潮汐影响下海滩前滨波浪传播耗能过程分析

文章基于长乐海滩前滨剖面的实测波浪数据, 通过统计分析以及谱分析的方法, 探讨了潮汐过程中长乐海滩波浪参数及耗能过程的变化规律。结果表明, 观测期间内波浪以混合浪为主, 各测点谱型较宽, 存在多峰振荡现象。向岸传播过程中, 波能耗散的形式为窄频域向宽频域转变, 能量分布趋于分散, 高频波能减小, 低频波能反而有所上升, 波浪破碎后生成长重力波。破波带内的能量衰减与波浪传播距离具有良好的相关性, 破碎波能在破波带内大约衰减了98.3%。潮汐水位对波浪具有明显的调制作用。入射波能随潮汐水位的增加而有所增加, 且水位越高, 入射波能分布越分散。破波带内的有效波高和潮汐水位具有显著的正相关关系。潮汐过程中固定测点的波谱变化与波浪沿剖面的波谱变化具有明显的相似性。     

Tidal-cycle changes in oscillation ripples on the inner part of an estuarine sand flat

Oscillation ripples form on subaqueous sand beds when wave-generated, near-bottom water motions are strong enough to move sand grains. The threshold of grain motion is the lower bound of the regime of oscillation ripples and the onset of sheet flow is the upper bound. Based on the relation between ripple spacing and orbital diameter, three types of symmetrical ripples occur within the ripple regime. In the lower part of the ripple regime (orbital ripples), spacing is proportional to orbital diameter; in the upper part (anorbital ripples) spacing is independent of orbital diameter. Between these regions occurs a transitional region (suborbital ripples).

Oscillation ripples develop on a sandy tidal flat in Willapa Bay, Washington, as a result of waves traversing the area when it is submerged. Because wave energy is usually low within the bay, the ripples are primarily orbital in type. This means that their spacing should respond in a systematic way to changes in wave conditions. During the high-water parts of some tidal cycles, ripples near the beach decrease in spacing during the latter stage of the ebb tide while ripples farther offshore do not change. Observations made over several tidal cycles show that the zone of active ripples shifts on- or offshore in response to different wave conditions.

Detailed bed profiles and current measurements taken during the high-water part of spring tides show the manner in which the oscillation ripples change with changes in orbital diameter. Changes in ripple spacing at the study site could be correlated with changes in orbital diameter in the manner suggested by the criterion for orbital ripples. However, there appeared to be a lag time between a decrease in orbital diameter and the corresponding decrease in ripple spacing. Absence of change during a tidal cycle could be attributed to orbital velocities below the threshold for grain motion that negated the effects of changes in orbital diameter.

Because changes in sand-flat ripples depend both upon changes in orbital diameter and upon the magnitude of the orbital velocity, exposed ripples were not necessarily produced during the preceding high tide. In fact, some ripples may have been just produced, while others, farther offshore, may have been produced an unknown number of tides earlier. Therefore, when interpreting past wave conditions over tidal flats from low-tide ripples, one must remember that wave periods have to be short enough to produce velocities greater than the threshold velocity for the orbital diameters calculated from the observed ripple spacings.