Water transport at subtidal frequencies in the Marsdiep inlet

Long-term time series of subtidal water transport in the 4-km wide Marsdiep tidal inlet in the western Dutch Wadden Sea have been analysed. Velocity data were obtained between 1998 and the end of 2002 with an acoustic Doppler current profiler that was mounted under the hull of the ferry ‘Schulpengat’. Velocities were integrated over the cross-section and low-pass filtered to yield subtidal water transport. A simple analytical model of the connected Marsdiep and Vlie tidal basins was extended to include wind stress and water-level and density gradients and applied to the time series of subtidal water transport. In accordance with the observations, the model calculates a mean throughflow from the Vlie to the Marsdiep basin. The mean water transport through the Marsdiep inlet consists of an export due to tidal stresses and freshwater discharge and an import due to southwesterly winds. In contrast, the variability in the subtidal water transport is mainly governed by wind stress. In particular, southwesterly winds that blow along the main axis of the Marsdiep basin force a throughflow from the Marsdiep to the Vlie basin, whereas northwesterly winds that blow along the main axis of the Vlie basin force a smaller mean water transport in the opposite direction. The contribution of remote sea-level change to the water transport, or coastal sea-level pumping, has been found to be much smaller than the contribution of local wind stress.     

Three-dimensional numerical simulation for tide and tidal current in the Beibu Gulf

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浙江省滩涂围垦与区域经济的可持续发展

滩涂围垦是浙江省扩大土地资源的主要出路.通过对浙江省经济社会发展战略与土地利用状况、建设用地与滩涂围垦关系等的论述与分析,指出了浙江省经济社会的发展,需要以建设用地的增长为基础;土地供求矛盾,需要以滩涂围垦来缓解;从而阐明了浙江省滩涂围垦与区域经济可持续发展若干关系.并对浙江省滩涂资源的4个方面特性进行了分析,提出了浙江省沿海滩涂资源开发利用的5项保障措施,以利于促进浙江省滩涂围垦和区域经济的可持续发展.     

Sediment transport on an estuarine intertidal flat: Measurements and conceptual model of waves, rainfall and exchanges with a tidal creek

Sediment (silt) transport on a wave-dominated estuarine intertidal flat dissected by a tidal creek that connects to the watershed freshwater network is investigated by analysing field data from Waikopua, New Zealand, and by applying simple models. The intention is to expand understanding beyond the case of the idealised, two-dimensional wave-dominated flat. During fairweather (no waves), there is a continuous exchange of silt between the bed of the tidal creek and the upper flat, and that exchange is controlled by the elevation of the flat with respect to the creek bed. Rainfall in the watershed does not fundamentally alter the way the intertidal flat and the creek interact, but it does increase silt loads in the creek, which in turn increases the amount of silt exchanged with the upper flat. Waves on the flat are fetch-limited, and frictional dissipation causes waves to reduce in height at the edge of the water body. Under some circumstances, a frictional-dissipation zone may occupy the entire middle-plus-upper flat. There is a maximum in wave-orbital speed at the bed (U_sigb) in the middle reaches of the flat, which arises from the particular balance between down-fetch wave growth, wave dissipation by bottom friction, and attenuation through the water column of wave-orbital motions under the short-period waves. There is a progressive decoupling of suspended-silt concentration (SSC) from U_sigb moving from the bottom to the top of the flat, such that SSC is highest towards the top of the flat, where U_sigb is virtually zero. We suggest that this is due to wave activity retarding the settling of suspended silt, and explore that idea with a simple model that is capable of reproducing the essential features of the data set. The results are assimilated in a conceptual model of the system, which shows the balances that control net silt transport in the creek and on the different parts of the flat, three different silt sources, and the role of waves and rainfall. The conceptual model also points at the feedbacks between sediment-transport processes and morphology that are inherent in the system. Implications of those feedbacks to long-term morphodynamics are essentially unexplored.     

伶仃洋洪季潮波传播变形及不对称性规律分析

珠江河口伶仃洋水域潮波传播变形及其不对称性关系对河口动力环境和物质输运产生影响。研究根据珠江口伶仃洋及东四口门19个潮位站2011年6月实测逐时潮位, 利用收缩河型沿程潮幅解析理论, 阐释伶仃洋从桂山岛上行沿程潮汐传播规律特征; 在调和分析基础上, 应用偏度理论和分潮组合分析方法, 阐明了伶仃洋东西岸及洪奇门、蕉门内潮汐不对称性分布特征, 对照数值研究结果, 指出伶仃洋至虎门之间水域导致潮汐不对称性的主控因素及响应规律。研究表明, 河口平面形态呈近似指数收缩特征的伶仃洋, 沿程潮幅的变化符合指数收缩型河口波幅解析变化规律, 东岸潮幅高于西岸的主要原因是东岸水深大于西岸, 其次是科氏力影响; 行进潮波虽受地形摩擦耗能及非线性作用下不同频率分潮间能量迁移的影响, 但收缩河口能量汇聚效应可以保证收缩段天文分潮潮幅减缓衰减甚至增加, 半日分潮能量汇聚效果强于全日分潮, 各非线性项作用促使浅水分潮产生并持续增能, 保证一定距离内沿程潮幅的增大; 潮汐不对称性的偏度由湾口落潮占优向湾顶涨潮占优发展, 在伶仃洋中部赤湾至金星港一线转为涨潮占优, 产生该现象的原因是自湾口向湾顶不同频率间天文分潮K₁-O₁-M₂的相互作用, 导致表现为落潮优势潮的不对称性减弱, 而天文分潮M₂和其对应的浅水分潮倍潮M₄组合作用使涨潮优势偏度值的不对称性增强; 收缩河口形态属性要素中, 水深是影响潮不对称性的最主要因素。     

台湾海峡潮汐潮流的有限元模拟

本文采用三维有限元(QUODDY)模型模拟了台湾海峡的潮汐和潮流特征。模拟结果表明,有限元模型可以得到较好的模拟结果:M2,S2,O1,K1的潮位调和常数的平均绝对偏差分别为(4.18cm,7.0°),(4.68cm,11.4°),(3.52cm,7.1°)和(3.86cm,4.5°);东、北分量潮流的平均偏差M2为(10.1cm/s,29.8°)和(12.2cm/s,30.2°),而K1为(5.3cm/s,47.7°)和(5.7cm/s,49.8°)。海峡内半日潮波系统中占主导地位的是自海峡北边界传入的半日潮波。潮汐类型为正规半日潮和不正规半日潮的海区约占整个计算区域的92%以上。海峡内由四个主要分潮引起的理论最大潮差平均值为320cm,其中最大理论潮差可达681cm,出现在海峡西北部的海坛岛至兴化湾一带。     

A Vertical Two-Dimensional Model to Simulate Tidal Hydrodynamics in A Branched Estuary

A vertical (laterally averaged) two-dimensional hydrodynamic model is developed for tides, tidal current, and salinity in a branched estuarine system. The goveming equations are solved with the hydrostatic pressure distribution assumption and the Boussinesq approximation. An explicit scheme is employed to solve the continuity equations. The momentum and mass balance equations are solved implicitly in the Cartesian coordinate system. The tributaries are govemed by the same dynamic equations. A control volume at the junctions is designed to conserve mass and volume transport in the finite difference schemes, based on the physical principle of continuum medium of fluid. Predictions by the developed model are compared with the analytic solutions of steady wind-driven circulatory flow and tidal flow. The model results for the velocities and water surface elevations coincide with analytic results. The model is then applied to the Tanshui River estuarine system. Detailed model calibration and verification have been conducted with measured water surface elevations,tidal current, and salinity distributions. The overall performance of the model is in qualitative agreement with the available field data. The calibrated and verified numerical model has been used to quantify the tidal prism and flushing rate in the Tanshui River-Tahan Stream, Hsintien Stream, and Keelung River.     

海岸河口三维潮流数学模型

本文采用有限元法建立了适用于海岸河口浅水地区的三维潮流数学模型，垂向采用绝对分层坐标系统，将整个水柱分成若干层，在每层内通过垂向积分平均，将三维问题简化为多个平面二维问题。在求解有限元方程中，引入集中质量矩阵技术，在时间上采用两步ＬａｘＷｅｎｄｒｏｆｆ格式，使有限元方程直接以显式解出，不需联立求解，节省了大量的计算时间和计算内存，通过模拟表面切应力作用在矩形水地上而引起的水流，计算结果与分析解比较一致，并将本模型应用到香港维多利亚水道中，计算结果与实测值亦符合较好，证明本模型是一个实用而有效的三维潮流数学模型。     

青岛海湾大桥对胶州湾潮汐、潮流及余环流的影响预测——Ⅰ.胶州湾及邻近海域的潮流

根据崂山头、朝连岛、灵山岛一个月的潮位资料,采用三角形网格的分步杂交方法,建立了胶州湾及邻近海域的二维变边界潮流数值模型。并模拟了大、中、小潮三种潮汛条件下的潮流场,水位场及余流场。得出了胶州湾高潮水域面积、潮间带面积,湾口累积流通量等有关参数。     

长江河口最大浑浊带含沙量垂线分布状态的分析

计算表明,潮泵效应在长江河口最大浑浊带悬沙输移中起着重要的作用。含沙量垂线分布的潮周期变化反映悬沙与床沙之间存在双向交换。据此讨论了最大浑浊带与拦门沙的关系。