台湾浅滩多尺度沙波地貌的地形傅里叶分解

海底沙波在全球广泛分布、成因复杂，但往往多种尺度的沙波叠加在一起形成复杂的沙波地貌体系，导致难以进行量化研究。针对该问题，本文提出一种实用的傅里叶分析方法，设计了巴特沃斯滤波器，将水深数据变换到频率域，进而将复杂沙波地貌分解成不同频率的单一类型沙波。并以台湾浅滩复杂的沙波地貌体系为例进行了分析研究，分解量化出3种空间尺度的沙波:巨型沙波(波长>100 m，波高>5 m)、中型沙波(波长5～100 m，波高0.4～5 m)和沙波纹(波长<5 m，波高<0.4 m)。本文提出的海底沙波地貌量化分析方法，有助于研究不同尺度海底沙波的成因与机理，对沙波区海洋工程的安全评估也具有实用价值。     

两相流模型在南海内孤立波与沙波相互作用中的应用

为研究内孤立波与沙波的相互作用,本文对基于OpenFOAM的SedWaveFoam求解器进行改进,建立了内孤立波-泥沙运动欧拉两相流模型。在利用试验资料对模型进行验证的基础上,在南海北部典型代表性条件下,模拟分析了500 m水深位置沙波床面上内孤立波作用下的水动力变化和泥沙运动。结果表明,内孤立波逐渐离开沙波时,海底沙波背流面处出现与内孤立波背景流速反向的流速,在内孤立波导致的流场作用下,沙波床面上的泥沙悬起并运动到床面以上的水体中。振幅100 m的内孤立波可以导致床面以上14 m高的位置处出现约0.07 kg/m³的悬沙浓度。     

厦门湾口外近岸陆架区海底沙波发育特征

利用2014–2017年在台湾海峡西部采集的多波束、单道地震剖面、沉积物粒度样品及海流监测资料,在厦门湾近岸陆架区识别出一系列海底沙波,并对沙波的形态特征、分布规律和沉积物组成特征进行分析,探讨水动力条件及其对沙波发育的影响。结果表明沙波发育区水深一般为10~60 m,地形较平缓开阔,坡度一般为0°~1°;平面上沙波区呈一系列NW-SE向条带状坡地,波脊呈线性或新月形,波脊轴线为SW-NE方向,沙波波长为120~800 m,波高2~12 m,沙波指数较大(>30)。地震剖面显示,波形形态主要分为三类:近对称性沙波、非对称性沙波及叠合沙波。近对称性沙纹的波高较大,沙波指数小;非对称性沙波的波长较长,沙波指数大;稳定沙波经后期水流“改造、激活”形成叠合沙波。砂含量较高,沉积物类型以砂、粉砂质砂及砂质粉砂为主,多为细砂—中砂。厦门湾口外的近岸陆架区水动力较强,流系复杂,总体受浙闽沿岸流、南海表层流和黑潮分支的影响。本区为不正规半日潮,流速为0.3~0.7 m/s,落潮流以S向为主,涨潮流向以NNE向为主,潮流作用对沙波的发育和改造起重要影响。     

胶州湾口海底沙波的类型、特征及发育影响因素

采用多波束资料对胶州湾口的海底沙波类型、特征进行了研究,发现研究区主要有线性沙波(二维)、沙丘(三维)2种沙波类型。结合水流流速、海底构造和表层沉积物综合分析发现:海底沙波缓坡朝向与优势流向不完全一致,为强流作用的产物,在涨、落潮作用下均可形成;沉积物的多寡是研究区海底沙波类型分布的决定因素,海底松散沉积物较为丰富的地区形成二维沙波。在水动力强大的胶州湾口,沉积物多分布在构造低洼地带,使二维线性沙波的分布与海底断裂延伸方向一致。     

胶州湾湾口海底沙波地形地貌特征及其活动性研究

利用多波束、侧扫声纳以及单道地震资料对胶州湾湾口潮流作用下形成的典型海底沙波地貌的平面形态、剖面特征和分布特点进行了分析研究。根据实测的水文资料计算了不同潮流流速下沙波的瞬时移动速度,推测了直脊型沙波和新月型沙波的形成]化过程:区内新月型沙波在西向优势流的作用下大约以50m/a的速度向西迁移,直脊型沙波则在两端方向不一致的优势流长期作用下,发生逆时针旋转,同时在往复流的作用下以一个平衡位置左右摆动;就地貌形态而言,新月型沙波是不稳定的,直脊型沙波达到相对平衡状态。     

海南东方岸外海底沙波活动性研究

对海南东方岸外 2 0～ 50 m水深海底沙波形成的动力环境、形态特征、剖面结构及其分布特征进行了描述和分析。根据环境参数 ,对其活动性进行了计算 ,并将计算结果与发育环境相类似的 Surtainville沙波进行了类比。认为研究区沙波主要系在潮流作用下形成。研究区沙波迁移速率为每年数米。东区 (水深 2 0～ 40 m)是沙波发育的主体 ,受落潮流作用 ,沙波自北向南迁移 ;西区 (水深 36～ 52 m)沙波受涨潮流控制自南向北迁移 ;中区为过渡区 ,沙波相对稳定     

长江口沙波统计特征及输移规律

利用多波束测深系统对长江口南港、北槽、横沙通道和北港水下地貌进行测量,对沙波波高、波长、迎流倾角、背流倾角、水深和沉积物特征进行统计,并根据流速、沉积物粒径及水深估算其潮周期内净位移。结果表明:长江口沙波基本都为大型沙波,且沙波大小与其所在区域沉积物粒径呈正比关系;长江口各个区域沙波的对称性不同,涨、落潮优势流越明显,则沙波对称性越差,净位移越大;沙波对称性能反映此区域水动力强弱及潮周期内沙波净位移大小。     

空间互相关方法在分析海底沙波迁移规律中的应用

海底沙波具有显著的活动性并能够对海底工程设施造成潜在威胁，因此对海底沙波活动性的评估一直以来受到广泛关注。目前大多数研究者仍利用平面剖面对比来分析海底沙波的迁移特征。然而，该方法难以全面高效地获取海底沙波二维平面迁移矢量。本文基于2007年和2009年的高分辨率多波束测深数据，详细阐述了空间互相关方法在分析北部湾东南海域海底沙波迁移规律中的应用过程。利用实测数据进行对比分析，获得了研究区海底沙波的活动特征，并进一步讨论了空间互相关算法中不同参数的选取对结果的影响。结果显示，利用空间互相关分析方法能够有效获取海底沙波二维迁移矢量，获得的海底沙波迁移速率和迁移方向与前人研究成果吻合，表明了该方法的可行性和可靠性。但在对实际DTM数据进行空间互相关分析时，需根据海底沙波形态、数据质量等因素选取合适的参数及矢量获取方法。本研究实验了一种确定海底沙波迁移规律的新方法，该方法将有效提升获得海底地形变化规律的效率和准确度，可获得更加精细的海底地形动力过程。     

潮流及单向流作用下海底沙波形成和运移试验

基于量纲分析理论进行水槽试验,研究了潮流以及单向流作用下海底沙波的形成和发展过程。通过分析 海床地形数据,对海底沙波的特征尺度和发展过程进行定量描述,得出了潮流流速、周期、水深以及叠加单向流等因素对沙波特征尺度的影响。结果表明,潮流作用产生的海底地貌由大尺度的沙波和小尺度的沙纹共同组成,大尺度沙波在地貌形态塑造中占主导地位。从平坦海床开始,沙波波高和波长随水流作用逐渐增大,增长速度越来越慢,最终达到动态平衡。沙波特征波高和特征波长随流速和水深增大而增大,同时随往复流周期的增大而增大,并不断趋近于单向水流的情况。进一步对小尺度的沙纹地貌进行分析,得出了沙纹特征尺度随水流条件的变化规律。     

沙脊沙波泥沙数学模型的研究

在剪切水流条件下,基于水沙两相流动量方程,推导出描述海底沙脊沙波内在演变规律的基本方程。将此方程与二维浅水环流方程、波浪折射-绕射方程进行耦合,建立大范围海区平面二维波、流、泥沙数学模型,并结合海区实际观测水文地质、潮汐、波浪、泥沙资料进行模型验证。通过对比分析发现,数值模拟值与实测站位观测值二者吻合较好,表明了模型的可靠性。应用此模型对东方1-1气田穿越的大范围海底沙脊沙波在相应海动力条件下的移动规律及演变趋势进行定量预测,结果显示,随着时间的推移,沙脊沙波移动距离逐年递增,但发展变化趋势基本稳定。     

Coastline sand waves on a low-energy beach at “El Puntal” spit, Spain

Coastline sand waves have been observed at “El Puntal” spit, located on the north coast of Spain. The spit has been monitored by an Argus video system since 2003 and the formation and destruction of sand waves has been observed. Coastline data from the video images are analyzed by means of principal components analysis, obtaining a mean sand wave length of 125–150 m and a maximum amplitude of ≈ 15 m. It is also observed that sand waves reach their maximum amplitude at about 15 days. No propagation of these sand waves is noticed during the approximately two-month-long events analyzed. Sand wave formation and evolution are examined in relation with the prevailing local wave conditions during that period. Incident waves at the west end of the spit approach from the east–northeast, with a very high angle with respect to the shoreline. Field observations suggest that sand waves may result from an instability in alongshore sediment transport caused by moderate-energy waves with a high-angle incidence.     

海南岛西部岸外沙波的高分辨率形态特征

利用SIMRAD-EM3000多波束探测系统和DGPS定位系统,对海南岛东方岸外的沙波沙脊区进行了高精度探测,分析结果表明:从海岸到陆架底形具有明显的分带性,依次出现弱侵蚀底形段、沙波沙脊底形段和平坦底形段。沙波仅发育于沙波沙脊段,介于水深20~50 m之间,沙波形态有二维与三维两种,沙波波高多为0.7~2.5 m,波长20~70 m,沙波指数(L/H)为20~60,对称指数为1~3;沙波沙脊区沉积物的搬运方向有明显的规律性,在沙脊的西侧,沉积物主要向北搬运;在沙脊的东侧,沉积物主要向南搬运;沙波的形成和发育主要受潮流场控制,热带风暴对其有改造作用。     

Sand wave deposition in the Taiwan Shoal of China

The Taiwan Shoal is the convex terrain in the southern Taiwan Strait, the largest strait in China. In 2006 and 2007, 21 samples and more than 200-km sub-bottom data as well as 80-km near shore side-scan sonar data were gotten, which gave an initial image of the boundaries of the Taiwan Shoal and revealed the internal structure of the sand waves in this area. The results showed that the major component of the sediment samples was sand, and sand waves occurred everywhere in this area, which closely followed the range of the Taiwan Shoal as we know. The western boundary of the Taiwan Shoal thus reaches the 30 m isobaths near the shore, and as a result, its area potentially covers approximately 12 800-14 770 km². The sand waves have different shapes under the complex ocean dynamics, and the height of sand waves in the near shore is usually smaller than that in the Taiwan Shoal. The number of sand waves ranged from 1-5 per kilometer, with more waves in the isobath-intensive area, suggesting the importance of topography for the formation of sand waves. The stratigraphic structure under the seabed has parallel bedding or cross bedding, and large dipping groove bedding can be seen locally in different parts, which may be the result of terrestrial deposition since the Late Pleistocene.     

基于近底原位观测的小尺度海底沙波地形小波分解

浅海海床发育着不同尺度的活动性砂体,在大型活动性砂体上常叠加发育着大量小尺度沙波(纹),分析这些小尺度沙波(纹)有助于揭示活动性砂体的成因机制。但它们的尺度较小,常规分析方法往往将其作为高频噪声滤除,难以对该尺度海底沙波(纹)进行分离量化研究。为了解决这个问题,本文设计并实现了一种基于小波分析的小尺度海底沙波地形分解方法,并以台湾浅滩典型区域的高精度近底原位观测数据为例,实现了小尺度海底沙波地形的分解和定量分析,分解出背景地形、小型沙波和沙波纹(波长小于0.6 m)3种地貌类型。本文提出的小尺度海底沙波地形分解量化方法,可广泛应用于浅海高活动性地貌发育演化和海底边界层沉积动力过程研究,对评估海洋工程的稳定性也具有一定的实用价值。     

南海东沙群岛以北海底沙波稳定性分析

利用在南海东沙群岛北部至西北海域为工程目的所采集的海底地形测量、底质取样、海底底流测量资料,以及以往的区域地质、地球物理资料,采用沉积学、构造学和海洋水动力学综合研究方法,对该区海底沙波形成及稳定性进行了综合分析。认为该区海底沙波是在目前水动力环境下所形成,为今生,海底表层沉积物为晚更新世地层受到冲刷改造的再沉积。沙波形成主要受潮流底流的水动力作用控制,并与构造抬升有关。沙波具有一定的活动性,主要由SE向NW方向移动,且活动性逐渐减弱。北区段海底沙波稳定,中区段海底沙波较稳定,它们对海底工程建设不会造成影响;而南区段海底沙波较为活动,当沙波发生较大规模移动时,对海底工程建设会造成一定影响。     

The brightness reversal of submarine sand waves in “HJ-1A/B” CCD sun glitter images

The brightness reversal of submarine sand waves appearing in the small satellite constellation for environment and disaster monitoring and forecasting("HJ-1A/B") CCD sun glitter images can affect the observation and depth inversion of sand wave topography. The simulations of the normalized sun glitter radiance on the submarine sand waves confirm that the reversal would happen at a specific sensor viewing angle, defined as the critical angle. The difference between the calculated critical angle position and the reversal position in the image is about 1, which is excellent in agreement. Both the simulation and actual image show that sand wave crests would be indistinct at the reversal position, which may cause problems when using these sun glitter images to analyze spatial characteristics and migration of sand waves. When using the sun glitter image to obtain the depth inversion, one should take the advantage of image properties of sand waves and choose the location in between the reversal position and the brightest position. It is also necessary to pay attention to the brightness reversal when using "HJ-1A/B" CCD images to analyze other oceanic features, such as internal waves, oil slicks, eddies, and ship wakes.     

Regeneration of sand waves after dredging

Sand waves are large bed waves on the seabed, being a few metres high and lying hundreds of metres apart. In some cases, these sand waves occur in navigation channels. If these sand waves reduce the water depth to an unacceptable level and hinder navigation, they need to be dredged. It has been observed in the Bisanseto Channel in Japan that the sand waves tend to regain their shape after dredging. In this paper, we address modelling of this regeneration of sand waves, aiming to predict this process. For this purpose, we combine a very simple, yet effective, amplitude-evolution model based on the Landau equation, with measurements in the Bisanseto Channel. The model parameters are tuned to the measured data using a genetic algorithm, a stochastic optimization routine. The results are good. The tuned model accurately reproduces the measured growth of the sand waves. The differences between the measured weave heights and the model results are smaller than the measurement noise. Furthermore, the resulting parameters are surprisingly consistent, given the large variations in the sediment characteristics, the water depth and the flow field. This approach was tested on its predictive capacity using a synthetic test case. The model was tuned based on constructed predredging data and the amplitude evolution as measured for over 2 years. After tuning, the predictions were accurate for about 10 years. Thus, it is shown that the approach could be a useful tool in the optimization of dredging strategies in case of dredging of sand waves.     

Fluid expulsion features associated with sand waves on Australia’s central North West Shelf

Multibeam swath bathymetric data collected in 95–120 m water depth on Australia’s North West Shelf revealed two distinct populations of sand waves: a laterally extensive, low-amplitude composite form comprising superimposed dunes and ripples, and a laterally restricted form which has unusually high bedform heights and slopes. These large subaqueous sand waves comprise bioclastic ooid/peloid sand. Significantly, evidence of seabed fluid flow was detected in association with the high-amplitude sand waves. This evidence includes seabed pockmarks approximately 2–15 m in diameter imaged with side-scan sonar, tubular and massive carbonate concretions dredged from the seabed, and potential active venting of a fluid plume from the seabed observed during an underwater camera tow. Molecular and isotopic analyses of carbonate concretions collected from within pockmarks associated with the high-amplitude sand waves indicate that the fluids from which they precipitated comprise modern seawater and are not related to thermogenic fluids or microbial gases. The fluid flow is interpreted to be driven by macrotidal currents flowing over the relatively steep slopes of the high-amplitude sand waves. Pockmarks and carbonate concretions then develop where the interstitial flows are confined and focused by subsurface ‘mounds’ in a shallow seismic reflector.     

海底沙波特征线的最优方向剖面自动识别方法

海底沙波是发育在近海陆架上的一种常见海底地貌类型,海底沙波特征与运动规律的研究具有重要的科学意义与工程应用价值,沙波脊线与谷线是表征海底沙波的最基本特征,也是精确描述沙波运动的基本参量。本文提出了一种基于复合数字水深模型的沙波特征线自动识别方法——最优方向剖面法,基于水深曲面归算得到最优剖面方向,再依据最优剖面方向求导并判定极值,自动提取沙波形态特征点,最终形成沙波脊线和谷线。以台湾浅滩复合型沙波为例进行对比实验研究,结果表明,该方法能基于不同分辨率的数字水深模型自动准确地提取海底沙波脊线与谷线,勿需设置阈值,地形自动化识别程度得到进一步提升,具有重要的实际应用价值。     

From and migration of sand waves in a large estuary,Long Island Sound

Sand waves occur in eastern Long Island Sound with heights up to 4 m and lengths to 100 m. The waves do not form if either more than 10% mud or 12% coarse sand is present in the sediment. Mud suppresses wave formation by increasing the cohesion of the sediment. Sand-wave shape is independent of the water depth, d, provided the sand-wave height, H, is smaller than 0.86 d^1.19. Both symmetric and asymmetric wave forms are present. Observation of the migration of sand waves by repeated bathymetric surveys indicates a net sand flux greater than 0.01 cm³ cm^?1 sec^?1 in the direction faced by the steep slopes of the waves (i.e. westward, into the Sound). Under this sand flux, waves more than 30 cm high will not be measurably altered by a reversal of the semidiurnal tidal current.