Hydrodynamic Characteristics of Undular Tidal Bores in the Qiantang River Based on Field Observations

Understanding the undular tidal bores in the Qiantang River is essential for effective river management and maintenance.While breaking tidal bores have been studied extensively, reports on undular tidal bores in the Qiantang Riverremain limited. Furthermore, observed data on undular tidal bores fulfilling the requirements of short measurementtime intervals, and spring, medium, and neap tide coverage, and providing detailed data for the global vertical stratificationof flow velocity are quite limited. Based on field observations at Qige in the Qiantang estuary, we analyzedthe characteristics of undular tidal bores. The results showed that the flooding amplitude (a) of the first wave isalways larger than its ebbing amplitude (b). Moreover, the vertical distribution of the maximum flood velocity exhibitesthree shapes, influenced by the tidal range, while that of the maximum ebb velocity exhibites a single shape. Duringthe initial phase of the flood tide in the spring and medium tides, the upper water body experiences multiple oscillatingchanges along the flow direction, corresponding to the alternating process of the crest and trough of the tide levelupon the arrival of the tidal bore. The tidal range is a crucial parameter in tidal bore hydrodynamics. By establishingthe relationship between hydrodynamic parameters and tidal range, other hydrodynamic parameters, such as the tidalbore height, maximum flood depth–averaged velocity, maximum flood stratified velocity at the measurement points,and duration of the flood tide current, can be effectively predicted, thereby providing an important reference for rivermanagement and maintenance.

Tidal Bore Dynamics Around the Similar Right-Angle Shoreline in the Qiantang Estuary,China

Tidal bores are a unique hydrodynamic phenomenon during flood tide in the Qiantang Estuary.The tidal bore propagation around the similar right-angle shoreline is rarely documented in tidal estuaries.To investigate tidal bores around this shoreline,a hydrodynamic model combined with a theoretical method is employed to reveal the characteristics of the bore propagation.The theoretical solution of the tidal bore intensity is deduced to illustrate the relationship of the incident tidal bores and the back-flow bores during the propagation.The hydrodynamic model based on shallow water equation is employed to perform the simulation of tidal bores in the estuary.Model results with respect to the bore height and the propagation speed of tidal bores have a favourable agreement with field data.The tidal bore dynamics in the neighborhood of the similar right-angle shoreline are elucidated.The characteristics of tidal bores in terms of water surface,velocity,bore steepness and the intensity are illustrated and the back-flow bore is analyzed by numerical and theoretical methods around the similar right-angle shoreline.The height of the back-flow bore relative to the incident tidal bore ranges from 1.05 to 1.77.Model result reveals that the ambient water depth and the shape of the similar right-angle shoreline are contributed to the back-flow bore formation.

Flume Experiment Investigation on Propagation Characteristics of Tidal Bore in A Curved Channel

Tidal bore is a special and intensive form of flow movement induced by tidal effect in estuary areas, which has complex characteristics of profile, propagation and flow velocity. Although it has been widely studied for the generation mechanism, propagation features and influencing factors, the curved channel will complicate the characteristics of tidal bore propagation, which need further investigation compared with straight channel. In this study, the flume experiments for both undular and breaking bores’ propagation in curved channel are performed to measure the freesurface elevation and flow velocity by ultrasonic sensors and ADV respectively. The propagation characteristics,including tidal bore height, cross-section surface gradient, tidal bore propagation celerity, and flow velocity are obtained for both sides of the curved channel. And three bore intensities are set for each type of tidal bores. The freesurface gradients are consistently enlarged in high-curvature section for undular and breaking bores, but have distinct behaviors in low-curvature section. The spatial distributions of tidal bore propagation celerity and flow velocity are compared between concave and convex banks. This work will provide experimental reference for engineering design of beach and seawall protection, erosion reduction and siltation promotion in estuary areas with the existence of tidal bores.

Experimental hydrodynamic study of the Qiantang River tidal bore

To study the hydrodynamics of tidal bore, a physical modeling study is carried out in a rectangular flume with considera- tions of the tidal bore heights, the propagation speeds, the tidal current velocities, the front steepness, and the bore shapes. After the validation with the field observations, the experimental results are analyzed, and it is shown that： （1） the greater initial ebb velocity or the larger initial water depth impedes the tidal bore propagation, （2） the maximum bore height appears at an initial ebb velocity in the range of 0.5 m/s-l.5 m/s. （3） when the Froude number exceeds 1.2, an undular bore appears, atter it exceeds 1.3, a breaking bore occurs, and after it exceeds 1.7, the bore is broken.

A preliminary study of the turbulence features of the tidal bore in the Qiantang River,China

In this paper, the turbulence characteristics of the tidal flow in the Qiantang River, China, the world-famous Qiantang bore, are studied. A detailed field observation at the Yanguan section of the Qiantang River was carried out during the spring tide in October 2010 with a continuous collection of high frequency turbulence data. The data analysis shows that the hydrodynamic processes are characterized by a strong tidal bore. Statistics of the turbulence such as the probability distributions of the turbulent components, the variance terms and the covariance terms are found consistent with those of previous studies of estuaries without the tidal bore. However, along the vertical profile, the distributions of all variables become more scattered downwards. The horizontal turbulence fluctuations are of a similar magnitude while the vertical turbulence has a fluctuation magnitffde about 1/3 of that of the horizontal turbulences. The fluctuation strengths and the Reynolds stresses are much larger than those of other estuaries when the bore arrives. The bottom shear stress varies periodically with the tides, less than 0.44 N/m2 during the ebb but is increased drastically at the bore arrival, with the maximum being 0.92 N/m2. A good linear relationship is found between the bottom shear stress and the bottom suspended sediment concentration.

Effect of dike line adjustment on the tidal bore in the Qiantang Estuary,China

In this paper,the effect of the dike line adjustment on the Qiantang Tidal Bore（QTB）is studied by physcial experiments.A lab-scale physical model of the Qiantang Estuary is built and the tidal bore is generated.With this model,the formation and pro-pagation processes of the tidal bore are simulated with or without the dike line adjustment.It is shown that the adjusted dike line changes the direction of the reflected tidal bore.The height of the tidal bore increases in the upstream region where the dike line is contracted.In the tested bent and forking regimes,the bore height at the upstream station is increased by 0.10 m and 0.04 m,respectively.Furthermore,the crossing bore still exists near the Daquekou station and the location slightly moves by about 3 km to the downstream region.

Sedimentation processes and sedimentary characteristics of tidal bores along the north bank of the Qiantang Estuary

A tidal bore is a unique Earth surface process, characterized by its highly destructive energy, predictable periodicities and magni-tudes, and the production of characteristic sedimentary features. Tidal bores and associated rapid flood flows are highly turbulent flows of the upper-flow regime with a velocity over several meters per second. Reynolds (Re) and Froude (Fr) numbers, respectively, are larger than 104 and 1.0, making them significantly different from regular tidal flows but analogous to turbidity currents. Until now, understanding of tidal-bore depositional processes and products has been limited because of the difficulty and hazards involved with gauging tidal bores directly. The Qiantang bore is known as the largest breaking bore in the world. Field surveys were carried out in May 2010, along the north bank of the Qiantang Estuary to observe the occurrence of peak bores, including regular observations of current, water level and turbidity at the main channel. Several short cores were sampled on the intertidal flats to study the characteristic sedimentary features of tidal bores. Hydrodynamic and sedimentological studies show that the processes of sediment resuspension, transport and deposition are controlled primarily by the tidal bores, and the subsequent abruptly accelerated and decelerated flood flows, which only account for one tenth of each semidiurnal tidal cycle in the estuary. Tidal-bore deposits are generally poorly sorted because of rapid sedimentation after highly mixed suspension by intense turbulence. This behavior is characteristic of the absence of tractive-current depositional components in a C-M diagram. It also goes along with well-developed massive bedding, graded bedding, basal erosion structures, convolute bedding and dewatering structures. Together, these sedimentary features can constitute fingerprinting of turbidites, widely distributed in the deep-water environment. However, a tidal bore is triggered by intensely deformed tidal waves propagating into a shallow-water environment, which returns to regular tidal flows rapidly after the passage of the bore head. The tidal-bore deposits are usually bounded by the intertidal-flat deposits with typical tidal beddings at the top and on both flanks. The difference between tidal-bore deposits (TBD) and tidal sandy/muddy deposits (TSD/TMD) is evident not only in sedimentary structures, but also in the grain-size composition. They can be clearly distinguished in grain-size bivariate plots, typically the plot of mean grain size vs. standard deviation (or sorting). Some trend variations generally exist in mean grain size with TBD>TSD>TMD, sorting with TMD>TBD>TSD (larger value indicating poorer sorting), and both skewness and kurtosis with TSD>TBD>TMD. These findings will undoubtedly shed new light on our understanding of tidal-bore sedimentology, ancient tidal-bore sedimentary facies and environments, and related oil-and-gas field prospecting.

强涌潮区管袋围堰施工安全风险仿真研究

强涌潮区的水域环境复杂多变,这极大增加了管袋围堰施工安全管理的难度。为确定强涌潮区管袋围堰施工从清基到维护阶段的安全管控重点,首先利用系统理论过程分析法(STPA)对施工安全风险因素进行定性分析,从人员、物资、管理、技术、环境5个维度构建了强涌潮区管袋围堰施工安全风险指标体系;然后建立系统动力学(SD)演化模型,并运用网络层次分析法(ANP)确定各指标权重;最后结合工程实例进行模拟仿真。结果表明:随着工程推进以及对安全投入的逐步增加,管袋围堰施工安全风险水平呈现出先大幅上升,后逐步下降,最终趋于平缓的趋势;人员、物资是清基和吹填期影响施工安全的主要因素,而在排水和维护期,环境、管理是主要影响因素;人员、管理和环境这三因素对安全投入变化更为敏感。建议在施工过程中重视不同阶段之间的管控重点差异,及时转换管理策略并采取针对性措施以有效降低施工安全风险。

强涌潮水流条件下直立圆柱体的涌潮作用力试验研究

为厘清强涌潮河口直立式圆柱体受到的涌潮作用力与涌潮水流条件、圆柱直径的关系,通过涌潮水槽模型试验研究了三种直径直立圆柱在不同潮前水深、涌潮高度条件下的涌潮作用力。结果表明,强涌潮的涌潮作用力为直立圆柱受到冲击力叠加该时刻的水流绕流阻力、圆柱前后水位压差力。通过数据回归分析,得到了一个无量纲涌潮作用力计算公式。该公式表明,涌潮作用力分析计算除了要考虑涌潮高度、圆柱直径外,潮前水深也是关键因素,且涌潮作用力与圆柱直径之间存在显著的非线性关系。

风对波状涌潮海塘越浪水动力特性影响的数值研究

文章基于二维不可压缩两相流数值模型,首先通过对比数值计算结果与试验数据,验证了该两相流涌潮计算模型模拟波状涌潮与海塘相互作用的可靠性;然后通过设置合理的计算工况,系统分析了风速、涌潮高度、潮前水深和斜坡坡度对波状涌潮在海塘上的越浪水动力特性的影响。计算结果表明:向岸风速会显著影响波状涌潮的海塘越浪量,风速越大,涌潮的越浪量越大,且挡浪墙所受荷载也越大;随着涌潮高度和潮前水深的增大,涌潮越浪量和挡浪墙所受涌潮荷载也随之增大;当增大海塘斜坡坡度时,涌潮越浪量和挡浪墙所受涌潮荷载均呈现先增大后减小的趋势。

径流与涌潮对钱塘江尖山潮滩演变的影响分析

潮滩湿地具有生态系统服务、海岸防护等重要功能,认识其在涌潮与径流作用下的潮滩演变特征,对保护钱塘江涌潮区域湿地至关重要。基于钱塘江尖山潮滩151张地形及径流、水位、泥沙和遥感数据,探究潮滩演变特征与驱动机制。结果表明:(1)尖山潮滩呈动态平衡,在观测区,枯季淤积速率为0.01 m/d,坡度降至1‰后稳定;洪季崩岸速率达3 m/d,崩退宽度达113 m,但洪季后以0.05 m/d的速率恢复。(2)洪季潮滩处的涌潮略强于枯季,洪水促进河势分汊,而涌潮主要通过南汊输沙,减少了北汊潮滩处泥沙输送。(3)钱塘江流量是控制潮滩年内季节性冲淤变化的关键因素,潮滩变化速率与流量、初始高程及潮差呈多元线性关系。(4)洪水改变河势,潮滩泥沙供应减少,含径流的退潮流冲刷增强使其崩岸退缩,但当水流冲刷减小、涌潮与涨潮流输沙占优时,潮滩迅速淤积。

卷积神经网络方法在涌潮水动力特性演变中的应用研究

该文基于开源软件OpenFOAM求解雷诺平均的Navier-Stokes方程,实现了对于波状涌潮(Fr=1.2~1.3)的数值模拟,并与物理实验数据比较,验证了数值模拟的准确性。使用CONV1D卷积神经网络模型对数值模拟数据进行了学习,预测出在具有斜坡地形上的涌潮水动力发展过程。对比涌潮到达x=30.0 m测点处的用时和该测点的最高水位的模型预测结果与数值模拟结果可知:到达用时的平均相对误差为2.28%,最高水位的平均相对误差为3.73%。较小的相对误差证明了CONV1D模型的准确性。该文对于涌潮的水动力过程模拟、与涌潮相关的灾害预警以及初生涌潮未来发展趋势研究都具有一定意义。

钱塘江河口治江缩窄对涌潮的影响

20世纪60年代后期以来,钱塘江河口进行了大规模的治江缩窄,显著改变了河口的水沙、地貌及其相互作用过程,而对于涌潮在高强度人类活动扰动下的响应认知尚不全面。基于实测资料,结合涌潮数学模型分析大规模治江缩窄对钱塘江河口潮汐、河床以及涌潮的影响。结果表明:治江缩窄后,滩槽分布基本稳定;山潮水比增大,大致以盐官为界,涌潮河段下游段淤积,上游段冲刷,沙坎下移;高潮位沿程抬升,涌潮起潮点附近及闸口—仓前河段潮差增大,仓前—盐官河段潮差减小;涌潮起潮点和最大涌潮位置下移,观潮位置固定,潮景丰富稳定,潮到时间稳定,涌潮高度变幅减小,仓前—盐官河段涌潮高度减小。为保护涌潮,需要在涌潮河段维持较大的潮差和适宜的水深,不宜开展大规模的缩窄。

多因子影响下的钱塘江通航保证率研究

钱塘江闻堰—八堡段为钱塘江河流河口段,河床冲淤剧烈,水深受地形影响变化较大,直接影响船舶通航,此外受上游径流及涌潮影响,航道通航保证率计算较为复杂。为此,利用2007年以来历年的水下地形,综合考虑涌潮、径流、水深等因子对钱塘江闻堰—八堡段的实际通航保证率进行分析。结果表明,2007—2020年满足3.8 m水深条件的通航保证率为60.1%~79.8%,满足3.5 m水深条件的通航保证率为71.9%~87.5%,满足3.2 m水深条件的通航保证率为81.1%~97.0%,与实际较为吻合。研究方法对河床冲淤变幅较大且动力条件较为复杂的河口区通航保证率分析具有参考意义。

特征构筑物涌潮景观形态多样性塑造研究

丰富涌潮景观形态的多样性能增加人们的观潮热情,促进旅游事业发展。结合钱塘江河口海塘安澜工程建设,在对钱塘江河口涌潮景观形态整理分析的基础上,发现海塘塘脚及其护塘丁坝位置,不同类型构筑物与涌潮相互作用可形成多样性的涌潮景观形态。通过室内涌潮水槽和现场试验研究,发现海塘塘脚、丁坝坝面布置的不同构筑物在涌潮水流条件下可塑造冲天、散射等多样性的涌潮景观形态。从特征构筑物激起的水体最大高度及潮景持续时间角度可知,四脚空心块、U型块体、V字型块体等特征构筑物塑造涌潮景观形态的多样性效果较佳。

强涌潮区海塘整治提升工程管袋围堰施工关键技术研究

海宁市百里钱塘综合整治提升工程二期处于钱塘江强涌潮区,工程规模大,环境条件复杂,实施管袋围堰施工存在巨大的技术难度和安全风险。为此,文章结合工程地质和潮汐水文特征,从围堰施工材料、施工流程及重点防范措施等方面提出强涌潮区海塘整治提升管袋围堰施工关键技术。实践表明,海宁市百里钱塘综合整治提升工程二期(尖山段海塘)采取的一系列工艺与技术,能有效解决强涌潮区海塘提标加固施工中的难题、降低安全风险、缩短工期、节约成本,可供强涌潮区同类工程借鉴。

钱塘江河口泥沙特性及河床冲淤研究

简要介绍了钱塘江河口含沙量、泥沙粒径的分布特性,建立了钱塘江河口泥沙起动流速和挟沙能力公式,分析了河床大冲大淤、大冲以后大淤、上游段洪冲潮淤、下游段洪淤潮冲等河床演变特性,研究了河床冲淤对洪水和潮汐的巨大反作用.分析研究表明,涌潮到达时,水流激烈冲刷河床,引起含沙量剧增,大多在涌潮过后的20 min内达到极值,形成大含沙量区.在平水期和枯水期,涨潮输沙量明显大于落潮,加剧了河口上游的淤积,涌潮是钱塘江河口大冲大淤的机理之一.

涌潮的水槽模拟及验证

在涌潮玻璃水槽中,通过调节水槽两端变频器的频率控制潮前水深的稳定,使水体具有一定的潮前落潮流速,并以此为工况,增加下游变频器不同的运行频率模拟各种强度的涌潮,测试涌潮的传播速度、涌潮高度、流速垂向分布等水动力学特征参数,捕捉涌潮形态.在此基础上,选用2010年10月钱塘江河口盐官河段的现场实测资料对试验结果进行比较分析,结果表明涌潮水槽试验结果与盐官河段实地观测资料匹配良好.这说明涌潮玻璃水槽物理模型能成功模拟涌潮,适用于涌潮的测试研究。

钱塘江河口涌潮传播速度研究

为分析钱塘江河口涌潮传播速度的时空规律及其影响因素,应用从一维连续方程和动量方程出发推导的涌潮传播速度计算公式分析涌潮传播速度的影响因素,并将其应用于钱塘江河口涌潮的计算,结果表明与实际情况吻合良好.利用实测资料分析了钱塘江涌潮传播速度的变化规律及影响因素,与计算公式的分析结果相一致.影响涌潮传播速度的因素主要有下游潮差、江道地形和径流流量,其月内变化主要受下游潮差变化的影响,此外在一定程度上还受到上游径流量的影响.在年际尺度上,则主要取决于河床地形的冲淤变化.应用解析算法和常规水文资料建立的涌潮传播速度计算方法简单易行,可较好地应用于涌潮到达时间的预报.

钱塘江涌潮特性及其数值模拟

在钱塘江涌潮实测资料的基础上,分析了钱塘江涌潮高度、涌潮传播速度、涌潮流速、涌潮形态及景观、涌潮压力等涌潮特性.同时,应用基于KFVS(kinetic flux vector splitting)格式的二维涌潮数值模型模拟了钱塘江涌潮的形成、发展和衰减的全过程,复演了"交叉潮"、"一线潮"、"回头潮"等现象.通过对计算结果的比较分析,对涌潮特性有了进一步的认识.