Exploration of the Mechanisms for the Low Sensitivity of Deposition Flux to Upstream Sediment Reduction in the North Passage, Yangtze Estuary

Deltas are densely populated industrialized regions,and home to important ports and navigation channels.Due to human interferences,the Yangtze Estuary has experienced a significant reduction in sediment load caused by the Three Gorges Dam(TGD),as well as adjustment to local morphodynamics by the Deep-water Navigation Channel(DNC).While the dramatic reduction in sediment triggers the increased channel erosion,the deposition flux of the DNC located at the estuary mouth has little change.To explore the physical mechanism of this phenomenon,a two-dimensional model is used to establish the relationship between sediment load and the sediment budget of channels based on the bathymetry in 2016.Model results show that the tidal reach and the inner estuary have a negative sediment budget.And the seasonal characteristics of water and sediment fluxes become less obvious downstream.Sensitivity analysis shows that the influence of upstream sediment load on deposition flux decreases along the channel,with a transition from deposition to erosion occurring in the tidal reach.For the last-level bifurcation,the annual siltation of sediment in the North Passage(NP)decreases by 4.5%with low sensitivity.This is attributed to the reduction of sediment load partially mitigated by riverbed erosion and cascade bifurcations.In addition,the lateral sediment supply,which accounts for 68%of the sediment input in the NP,is stable.Overall,this study strengthens the understanding of the relationship between sediment load and artificially deepened systems,thus allowing for better management of estuarine sediment and navigation channel.

Calculation of Diversion Ratio of the North Channel in the Yangtze Estuary

The circumfluence around the Jiuduan Sandbank is thoroughly studied by means of the principle of least resistance in fluid dynamics. The diversion ratio of the North Channel for 1998 is calculated, which is almost the same as the field survey data. The normal and minimum diversion ratios of the North Channel after stages I , II and III regulation works as well as the future phase are obtained. The numerical results and predicted value are accurate.

Fractal Characteristics and Prediction of Backsilting Quantity in Yangtze Estuary Deepwater Channel

Fractal interpolation has been an important method applied to engineering in recent years. It can not only be used to fit smooth curve and stationary data but also show its unique superiorities in the fatting of non-smooth curve and non-stationary data. Through analyzing such characteristic values as average value, standard deviations, skewness and kurtosis of measured backsilting quantities in the Yangtze Estuary 12.5 m Deepwater Channel during2011–2017, the fractal interpolation method can be used to study the backsilting quantity distribution with time.According to the fractal interpolation made on the channel backsilting quantities from January 2011 to December2017, there was a good corresponding relationship between the annual(monthly) siltation quantities and the vertical scaling factor. On this basis, a calculation formula for prediction of the backsilting quantity in the Yangtze Estuary Deepwater Channel was constructed. With the relationship between the predicted annual backsilting quantities and the vertical scaling factor, the monthly backsilting quantities can be obtained. Thus, it provides a new method for estimating the backsilting quantity of the Yangtze Estuary Deepwater Channel.

Morphodynamic Characteristics and Medium-Term Simulation of the North-South Passage Under the Impact of the Yangtze Estuary Deepwater Navigation Channel Project

The morphological evolution characteristics of the North-South Passage area since the construction of the Yangtze Estuary Deepwater Navigation Channel Project(DNCP)are analyzed on the basis of the measured data.A twodimensional morphodynamics numerical model of the Yangtze Estuary is established to verify the morphological evolution of the North-South Passage under the influence of the DNCP and to predict the future evolution in the next 40 years.Data analysis shows that the North Passage has experienced rapid adjustment stages and adaptive stages after the construction of the DNCP.Slow erosion occurred along the main channel,and slow siltation could be observed in the area between the groins.The South Passage showed a state of upper section erosion and down section deposition.At present,the whole South Passage is in a slight erosion state.According to the numerical model,the eroding and silting speed of the North Passage will slow down in the future.The present state that erosion occurs in the main channel and siltation occurs between the groins will continue.The South Passage will still maintain upper section erosion and down section deposition in the future.Due to the main channel erosion of the North Passage and siltation of the South Passage,the sediment division ratio of the North Passage will increase in the future but still be smaller than 50%.After morphological evolution of 40 years,the direction of residual sediment transport caused by M2 and M4 tidal components in the North Passage has not changed,but the transport rate will decrease.It is considered that the morphological evolution of the North-South Passage could reach a relatively stable state after 40 years.

长江口深水航道浮泥运移规律及精细化维护疏浚

基于2016—2019年长江口深水航道施工区段月度测图和2016—2020年北槽深水航道洪枯季常态天气条件下的浮泥观测资料,研究浮泥输移特征及回淤、高频水深等变化特征,提出航道精细化疏浚维护方案。结果表明,常态天气条件下洪季的高低频水深差幅度大于枯季,北槽航道中段洪季的浮泥厚度要远大于枯季,航道回淤量具有随高低频水深差的增加而增加的特征。建议优先在洪季实施精细化维护疏浚方案,试应用后能有效减小浮泥、高低频水深差等变化过程对航道考核测量和航道维护疏浚的干扰,提高航道维护疏浚的精细化管理水平。

Comprehensive analysis on the sediment siltation in the upper reach of the deepwater navigation channel in the Yangtze Estuary

The results from both the field measurements and numerical simulation were reported to comprehensively analyze the sediment siltation in the upper reach of the Deepwater Navigation Channel Project in the Yangtze Estuary after the project has been implemented. In this research, firstly some basic information about the river evolution in the Yangtze Estuary is analyzed, including the variations of water depths in the Hengsha Passage and the inlet cross-sections of the North Passage and the South Passage, and changes of diversion ratios of ebb flow and sediment flux in the North Passage and the South Passage, Then the Delfl3D-FLOW model is applied to simulate the hydrodynamics and sediment transport in the Yangtze Estuary. This model has been calibrated and the simulated results agree well with the measured data of the tidal levels, flow velocities and suspended sediment concentration （SSC）, indicating that the model can well simulate the hydrodynamics and sediment transport of the Yangtze Estuary caused by the Deepwater Navigation Channel Project. The research results show that the development of the Hengsha Passage and decrease of diversion ratio of ebb flow and sediment flux in the North Passage are the main reasons of sediment siltation in the upper reach of the Deepwater Navigation Channel in the Yangtze Estuary.

长江口白茆沙河段南强北弱格局变化特征研究

近年来白茆沙汊道“南强北弱”态势持续增强,南水道主槽和近岸河床冲刷明显,日益威胁水下岸坡稳定与附近码头安全。通过对白茆沙汊道演变态势与分流比变化特征展开分析,进而对白茆沙汊道“南强北弱”分流格局变化及原因进行了系统研究。研究认为:白茆沙汊道“南强北弱”格局增强的态势是白茆沙汊道历年来周期性演变中某一阶段的表现形式;鉴于不同方法计算的汊道分流比存在差异,故用分流比表征汊道强弱时,应选用同一类型的值进行比较;深水航道一期整治工程实施遏制了白茆沙冲刷后退的态势,改变了该河段周期性演变的模式,有利于河势稳定;在现有水情、工情及河势条件下,白茆沙汊道“南强北弱”的格局变化将趋缓。

径流变化下长江口多分汊系统冲淤分布差异及动力机制

为探究水库调平径流过程下长江口多分汊系统冲淤规律,根据1950—2021年水沙、地形和工程资料,拟定径流强度指标(Da,60 000 m^(3)/s以上流量多年平均持续天数)、追踪滞流点位置和按航道疏浚还原北槽冲淤量辨析长江口冲淤分布差异和动力机制。结果表明:Da越大,越利于北部和南部汊道落潮分流比增大和减小,促进北部汊道冲刷加剧、淤积减缓和南部汊道淤积加剧、冲刷减缓,且利于北部和南部汊道淤积重心向下游和上游移动;冲淤差异受水流惯性和南岸节点挑流驱动,径流流量变化使得落潮主流北偏或南偏,形成南北汊道横向和纵向冲淤的联动机制;随着径流过程持续坦化,长江口北部汊道整体和上段将维持淤积加剧或冲刷减缓趋势、下段将维持冲刷加剧或淤积减缓趋势,南部汊道冲淤趋势相反;北槽滞流点在上下段间迁移的临界径流流量为35 000 m^(3)/s,未来上段淤积可能增强,建议适时调整航道维护区段。

长江口南港沙洲演变对河口治理工程的响应

为研究河口治理工程对南港沙洲形态的演变及其对航道安全的影响,在近10年海图和近期水动力条件以及微地貌数据的基础上,分析了新浏河沙、瑞丰沙及中央沙南沙的演变过程。研究结果表明:南港上段2010-2013年间的总体净淤积量约为1.96亿m^(3),新宝山水道北侧河道冲刷剧烈,深泓线北偏;2013-2019年总体净冲刷量约为2.58亿m^(3)。其间,新浏河沙及瑞丰沙洲0 m等深线以上沙体面积整体增长了2.54 km^(2),中央沙南沙面积增长了1.38 km^(2),沙洲体的质心上移,-5 m至0 m等深线以内的面积不断减小。河口治理工程的实施,是导致南港沙洲0 m以上面积增大和沙洲形态变化的重要原因,这对南港深水航道运输安全有着严重威胁,不利于长江口河势稳定与航道航行安全,亟待综合整治。

Morphological evolution of mouth bars on the Yangtze estuarine waterways in the last 100 years

The mouth bar in the Yangtze estuarine waterways has a significant influence on navigational transport within the estuary, flood discharge and construction of the Shanghai Port. In this paper the morphological evolution and mechanisms of mouth bar formation of the Yangtze estuarine waterways are studied by analyzing hundreds of years of historical data and the latest profile maps of some or the main mouth bar channels in the Yangtze Estuary. The results are shown as follows： The mouth bars in the North Branch have moved gradually from outside the mouth to the inside and formed a huge sand bar. In the North Channel, the head of the mouth bar has migrated about 30 kilometers downstream, and a channel bar has been developing since 2001. Two mouth bar tops, which always existed in the North Passage disappeared in 2010. The head of the mouth bar in the South Passage has migrated downstream about 14 km and the number of tops increased at first but is reduced to only one now. According to the results, we can conclude that the evolution of the mouth bars differs depending on their location. In the North Branch it is directly related to large-scale reclamation in Chongming Island, but in the North Passage it has a close relationship with regulation of the Yangtze Estuary Deepwater Channel. However, the evolution of mouth bars in the North Channel and South Passage is not only connected with the Yangtze Estuary Deepwater Channel Regulation Project, but also with the reclamation in the East Hengsha Shoal and the closure of the Qingcaosha Reservoir.

长江口新河势下横沙浅滩发展分析

从长江口新河势的基本特征出发,按时间线阐述新河势下横沙浅滩侵蚀作用的发展过程,并预测未来趋势。基于自然和人工等2个因素分析侵蚀的成因,以期为后期固沙保滩、航道整治等工程的方案设计提供理论依据。

长江口规划生态航道建设方向研究

针对长江口北港、南槽生态航道的建设问题,通过分析区域环境特点和航道发展需求,梳理已建的长江口深水航道生态化建设情况,提出长江口生态航道建设的核心和模式。结果显示:1)南槽和北港生态航道的建设需以确保河势格局稳定为基础;2)需与滩涂保护、生态功能区域保护形成联动布局;3)需积极研发和应用生态结构,构筑“人工生态礁体”群,优化河口综合环境;4)需结合滩涂泥沙资源需求和航道建设自身筑堤用沙需求,实现航道疏浚土的资源化、生态化利用;5)需强化建设运营中科学的管控体系、生态补偿体系等。

径流和潮流共同作用下的福姜沙河段分流分沙不平衡性

分流分沙比是研究分汊河段的一个重要指标。通过收集和分析2012—2019年长江口福姜沙河段实测水文资料,并采用了三维潮流泥沙数学模型ECOM-Sed对分流分沙进行计算研究。结果表明:上游径流增加或下游潮差减小均会导致福北水道的分流分沙不平衡度增加,航道的维护量和分流分沙不平衡度呈正相关性。福北水道仅有约30%的流量难以输移40%沙量,这种分流分沙比的不平衡性会导致福北水道航道严重淤积。根据研究成果,可在福姜沙目前的三座丁坝上实施加长或加高等工程措施,以降低福北水道的分流分沙不平衡性来减少福北航道的淤积量。

新水沙环境下青草沙水库外侧滩地形态调整特征及保护措施

采用青草沙水库周边2014-2019年实测水下地形数据,定量分析了各堤段滩地形态调整特征,基于MIKE21数值模型对护滩措施的效果进行了模拟。结果表明:2014年后青草沙水库外侧滩地基本未出现明显的淤积外延发展,且局部沙体逐渐萎缩,其中北堤中段外侧滩地头部大幅度冲退,最大距离近900 m(-5 m及-10 m等深线),沙体形态呈扁平化调整,须适时进行保护;新桥通道进、出口落潮主流略有偏转,向水库大堤侧靠近,影响滩地的冲淤过程;在青草沙外侧滩地头部沙体实施潜堤护滩措施后,北堤中段外沙体滩面流速整体明显减小,且对周边区域的水动力过程影响较小。

长江口深水航道回淤量随水文条件变化的特征分析

文章以流量、潮位、潮差、水温、水深和波能为影响因子,建立了长江口深水航道回淤预测的神经网络模型,并利用该模型的预测结果分析了回淤量随单一影响因子的变化规律。结果表明:全航道回淤总量随流量呈一定的非单线性变化特征;波能、水温、潮位和潮差对回淤量的影响基本呈单线性变化特征,回淤量随各水文要素的增大而增大;洪季条件下对回淤量影响较大的水文条件分别为流量、波能和潮位,而潮差和水温变化的影响相对较小。本文的研究成果为长江口深水航道的维护以及回淤机制的研究提供可靠的理论依据和明确的参考指标,具有重要的工程实践意义。

2021年洪季长江口北槽盐度变化分析

盐水入侵是河口地区普遍存在的自然现象,对水生生物、工业生产和居民生活用水带来不利影响。有效应对盐水入侵,对保护长江河口地区重要的生态环境价值和社会经济价值具有重要意义。整理分析了2021年洪季长江口北槽定点盐度和潮流量等实测资料,分析盐度的沿程、潮周期以及分层系数的变化特性。结果表明:①盐度的时空分布呈自上游至河口盐度沿程显著增加规律,大潮期涨潮和落潮期平均增加幅度为16.14‰和14.42‰;小潮期涨潮和落潮期平均增加幅度为15.14‰和14.40‰。②盐度在时间上具有明显的涨落潮变化特征,在涨潮时增大,落潮时减小。③北槽中上游盐度分层系数在一个潮周期内随着涨落潮流的变化而不断发生变化,呈现出由小变大再由大变小的周期性规律变化;中下游盐度分层系数变化周期性不明显。

长江口深水航道治理一期工程实施对北槽拦门沙的影响

介绍了长江口拦门沙发育及其特点和北槽航道拦门沙形成机理,利用长江口深水航道治理一期工程实施后的地形资料分析治理工程对北槽航道拦门沙影响。结果表明:治理工程建成后,增加了主槽流速,减少了航道回淤,打通北槽航道拦门沙,增加了航道水深,治理工程效果明显。

长江口南港航道沙波群研究

本文利用Ｉｎｎｅｒｓｐａｃｅ４４９热敏式双频测深仪和ＧＰＳ（全球定位系统）在长江口南港和南北槽主航道走航观测结果，确认南港（吴淞口以下）上段航道在洪季正常风况下存在尺度较大的沙波群，并对沙波的几何特征、形成条件、迁移速率以及台风后的变化做了初步分析。结果表明：（１）在统计的６５２个沙波中，平均和最大波长分别为２１ｍ和１０５ｍ。平均和最大波高分别为０．８ｍ和２．７ｍ，波高和波长间具有明显的正相关关系；沙波中７２％为单一沙波，复合沙波的波长和沙波指数较大；单一沙波最大、最小和平均沙波指数分别为３６．５、１１．２和２１．８（复合沙波最大可达６９．３）；随着沙波度的增大，沙波指数呈增大趋势；绝大多数沙波（波高＜１ｍ）是对称或近于对称的，但波高＞１ｍ的沙波通常向海倾斜。（２）沙波沉积物为分选好的细沙，Φ５０为２．７０。（３）沙波现场水流费劳德数Ｆｒ小于０．２，与某些理论相符而与某些水槽实验结果相冲突。（４）大潮和寻常潮一个涨（落）潮过程沙波来回迁移的距离约为１～５ｍ；小潮期间沙波的迁移距离接近０；落潮迁移距离总是大于涨潮。（５）台风后沙波有被掩埋的迹象。结果包括：①沙质床底是形成沙波的重要基础。南北槽虽具有沙波形成的?

长江口南港水道溢油数值模拟

使用FVCOM建立了长江口水动力模型,然后基于拉格朗日粒子追踪法及自由走动理论建立了长江口溢油模型,研究长江口南港水道处溢油污染的问题。模拟了溢油在东南风、东北风、西北风下涨憩、落憩时24 h内的扩散漂移轨迹以及分布情况,对不同情景进行了分析。研究表明风向对溢油的走势有较大的影响:东南风落憩的溢油可能会污染到青草沙水库、崇明东滩及中华鲟保护区,涨憩时主要污染为九段沙湿地;东北风涨憩和落憩时主要污染上海岸线;西北风落憩时主要污染长兴岛南岸以及九段沙湿地,涨憩时污染九段沙湿地,研究结果可为潜在的溢油应急响应决策提供参考。

近期(2000-2008年)长江口南港河槽的冲淤变化——兼议外高桥新港区岸段强烈淤积的原因

长江口南港是上海外高桥新港区所在岸段,其冲淤变化对该港区水深的维护具有重要影响。本文利用ArcGIS对2000-2008年长江口南港海图资料进行数字化,建立不同时期此河槽的数字高程模型,定量计算南港河槽尤其是主槽的冲淤变化,分析其演变规律。结果表明:(1)2000-2004年南港河槽整体上冲刷21.9×106m3(平均冲刷速率为3.5cm/a);(2)2004-2008年南港河槽整体上转为淤积,河床共淤积26.0×106m3(平均淤积速率为4.1cm/a);(3)2004-2008年外高桥新港区净淤积73cm,其中2006年7月-2007年7月1年淤积57cm。结论包括:(1)南港复式河槽中间沙脊的大量采砂导致的过水断面调整可能是近期沙脊两侧深槽出现淤浅趋势的重要原因;(2)2006年7月-2007年7月南港主槽(包括外高桥新港区)的强烈淤积可能还与该水文年长江径流量特低有关。(3)南港作为长江入海水沙的过境通道,其冲淤变化与河流来沙量变化的关系不大,而流域极端气候事件导致的径流量变异、河口人类活动以及河槽的自适应调整可能是该河槽年际冲淤变化的更重要诱因。