The analysis on reservoir sediment deposition and downstream river channel scouring after impoundment and operation of TGP

According to the measured data after impoundment and operation of the Three Gorges Reservoir,the reservoir sediment deposition and downstream river channel scouring are described briefly and compared with the research results achieved in the demonstration stage.It is indicated through analysis that the reservoir sediment deposition and downstream river channel scouring during 8-year impoundment and operation are still within the original forecast,so the original forecasting results are feasible.The further observation and comparison should be conducted because the comparison between the observed data and the original forecast is not so sufficient in time and the prototype observation and related research work should be strengthened in the future.

Bed Load Transport Rate in Scouring and Armoring Process of Non-uniform Sediment River Bed

Flume experiments were carried out to study bed load transport rate during rive bed scouring and ar- moring.A theoretical differential equation linking the transport rate to the probability of incipient motion of non-uniform sediment is solved.The transport rate is shown to decrease exponentially with time,according to the theory,which is in good agreement with the experiment data.

水库拦沙对黄河下游河床演变的影响

为充分认识水库拦沙对其下游河道河床演变及防洪的影响,基于三门峡水库和小浪底水库拦沙期水沙及断面观测资料,研究了黄河下游河槽冲淤、洪水冲刷效率、河槽几何特征、排洪能力等规律。结果表明:水库拦沙期,黄河下游沿程河槽均发生了不均衡冲刷;河床粗化明显,粗化后床沙中值粒径最大值为冲刷前的2.1~2.5倍;高村以上河段同水位过洪能力增加明显,冲刷后较大的河槽容积可为小浪底水库排沙提供暂时的滞沙;河床粗化后细泥沙和中泥沙补给能力不足,河槽冲刷效率随冲刷历时的增加衰减明显。由于水库多年调节水沙过程及下游相对完善的河道整治工程约束,小浪底水库拦沙期黄河下游河槽冲刷重心下移,河床粗化程度增加,冲刷效率明显降低。研究成果可为水库水沙调控技术指标的选取提供科学依据。

万家寨水库排沙效果及影响因素分析

降水冲刷是恢复水库库容的有效手段。2011年以来万家寨水库在排沙期多次开展降水冲刷运用,取得了较好的排沙效果。基于实测资料,分析了2011年以来万家寨水库排沙效果及其影响因素。结果表明:2011—2021年(不含2016年)万家寨水库累计排沙7.173亿t;排沙主要集中在排沙期;2018—2020年来水较丰,水库降水冲刷历时长,3 a累计排沙4.840亿t;水库排沙影响因素众多,长历时大流量洪水过程有利于水库排沙;运用水位降低时,蓄水量减小,沿程冲刷距离长,壅水输沙距离缩短,有利于提高水库的排沙效果。通过回归分析,建立了不同水位下出库输沙率与主要影响因素的关系。

长江流域平原河网地区合流制排水系统溢流污染特征研究

在平原河网地区丹金溧漕河金坛段选取3个典型合流制溢流排口及管道检查井进行溢流污染监测,分析溢流水质水量变化。以合流制管道沉积物为试验材料进行冲刷模拟试验,探究沉积物冲刷规律。结果表明,累积降雨量≥2 mm就会产生溢流现象;溢流水量变化主要受降雨等级、降雨强度及居民用水量影响,且溢流量峰值较降雨强度峰值滞后;溢流污染物浓度与前期干旱天数、排口性质、降雨等级和降雨强度有直接联系,其变化基本均呈先上升后下降趋势,且无论哪种降雨等级溢流口在产生径流后约20~30 min后污染物浓度会较高。沉积物对溢流污染贡献占比较大,管道冲刷过程中沉积颗粒物呈阶段交替式运动,各污染指标在降雨形成径流一段时间后出现峰值。

基于MIKE21的黄河三角洲泥沙冲淤数值模拟预测

在人类活动影响与全球气候变化等因素持续影响下,黄河三角洲海岸始终处于动态调整状态。探究三角洲海岸线调整规律以及未来发展趋势,对三角洲地区经济发展和生态环境保护具有重要工程意义。本文基于MIKE21数学模型,建立2015年和2023年两个年份岸线条件下的泥沙冲淤模型,对比验证了刁口附近海域2015—2023年冲淤变化,验证了黄河泥沙模型设置的准确性;并在此基础上,设置了3组径流和泥沙工况,预测了现行河口附近海域2023—2030年的冲淤变化。结果显示:在2015—2023年间黄河2016年最小径流量下的输沙量工况下,现行河口处有少量冲刷,孤东近岸海域基本冲淤平衡,废黄河口处少量冲刷;在2015—2023多年平均径流量和输沙量工况下,孤东近岸海域东岸向有3 m左右淤积,现行河口和废弃河口处持续冲刷,最严重处达3 m左右;在黄河多年平均径流和输沙量的85%工况下,现行河口和废弃河口处持续冲刷,最严重处达3 m左右,孤东近岸海域东岸淤积可以达到1.5 m。研究结果可以更好地理解黄河三角洲海岸线的变化,为未来黄河口海岸带开发治理和可持续发展提供科学指导。

黄河泥沙固化材料抗冲特性分析

为了分析黄河泥沙基坝体材料的抗冲刷性能及影响因素,试验研究了固化剂掺量和冲刷时长对黄河泥沙基坝体材料抗冲刷性能的影响规律,并设置了不同固化剂掺量及不同冲刷时长的对照组。本次试验对比不同固化剂掺量及冲刷时长对试块抗冲刷性能的影响,对试验数据进行函数拟合。从拟合后的函数图像分析,随着固化剂掺量的增加,试块的抗冲刷性能提升,但考虑到建设成本问题,固化剂掺量为30%最为符合工程需求。

金沙江向家坝水电站下游河道2020年淤积成因分析

向家坝下游河道泥沙冲淤变化对岸坡稳定及通航具有重要影响,向家坝水电站运行后坝下游河床一直呈冲刷状态,但2020年首次出现淤积。采用输沙法和断面法计算向家坝出库沙量和下游河段泥沙冲淤量,结合气象、水动力及实勘资料,分析向家坝下游2020年淤积成因。研究结果表明:向家坝蓄水后出库年径流量变化不大,出库沙量受上游电站拦沙作用大幅减少,但2020年向家坝下游支流降雨偏丰,支流输沙量大幅增加,产生区域强输沙过程;该年下游各控制站最高水位较历史平均水位均偏高,汛期比降变化不大,水流挟沙能力不足以输送显著增多的泥沙;加上采砂减少和采砂造成的下切幅度较大部位发生回淤。这些原因导致2020年向家坝下游河道产生淤积。

长江中游武汉河段江心洲的差异化冲刷规律

近20 a长江中游分汊河段的江心洲经历了冲刷并发生蚀退,但对微弯河段和顺直河段的江心洲差异化冲刷尚未有清晰认识。选取长江中游武汉河段的白沙洲和天兴洲作为研究对象,采用遥感影像、水文资料及野外调查,分析了白沙洲与天兴洲形态变化及差异化冲刷的原因。结果表明:1989—2020年,白沙洲洲体萎缩将近43.83%,天兴洲洲头浅滩变化较大,整体出露面积相对稳定;白沙洲与天兴洲的归一化植被指数(NDVI)整体较小,洲体植被覆盖空间差异性减小;这2个江心洲枯水期出露面积的变化主要体现在洲头浅滩;位于顺直河段的白沙洲洲头及侧向洲体遭遇冲刷,左侧洲体出现窝崩现象,其主要原因是白沙洲大桥桥墩的壅水与阻流作用;位于微弯河段的天兴洲自三峡工程蓄水后洲头遭受冲刷,2004年洲头守护工程实施和人工抛石有效地抑制了冲刷并实现了促淤作用。因此,江心洲的冲刷差异性主要体现在河段形态、主支汊相对位置和有无守护工程。

海床破坏下的海底管道路由区水动力冲淤特性研究与应用

针对某海底管道路由区人为作业形成的海床破坏区域在水动力作用下发生海底冲淤侵蚀变化问题,在路由区水动力参数观测和海底取样的基础上,研究提出了基于水动力数值模拟分析软件与模型的路由区冲淤特征的分析方法,设计了基于这一工程实际的二维水流-泥沙数学模型,利用管道路由区域实测的水文、地质数据确定了模型的边界条件,有效模拟了不同模型尺度下管道路由区的冲淤状况,经现场实测验证了该方法的正确性与有效性,可为海底管道的保护与运维评估提供技术支持。

床沙级配调整对黄河下游洪水演进的影响

小浪底水库运行以来,进入黄河下游的水沙条件出现了较大变化,受水库清水下泄影响,黄河下游床沙粒径出现了明显的粗化。为了探讨床沙级配粗化对黄河下游洪水演进的影响,本文首先建立了适用于黄河下游的一维水沙耦合数学模型,然后采用花园口至孙口河段2020年4—10月的实测洪水过程对模型进行了验证;其次根据河段床沙粗化特点,并以花园口床沙粗化过程为代表,设计了4组床沙级配作为模拟计算的初始床沙条件;最后采用验证后的模型进行了模拟计算,分析了床沙级配调整对洪水演进的影响。结果表明:床沙级配调整对黄河下游的流量、水位、含沙量、洪水演进时间以及河段冲淤量均有影响,但是对流量影响较小,而水位、含沙量、洪水演进时间与河段冲淤量对床沙级配的改变响应较为敏感。床沙中值粒径d_(50)由0.076 mm(级配1)增至0.242mm(级配4)时,夹河滩断面水位增高0.89 m,花园口至孙口河段冲淤量由冲刷0.679亿m^(3)转变为淤积0.059亿m^(3),冲刷量减幅为109%。研究结果可为新水沙情势下黄河下游河道治理提供借鉴与参考。

Prediction of Scour Depth around Offshore Pipelines in the South China Sea

搜索深度预言近海管道具有到海底的管道工程的设计和构造的大意义。在这份报纸，基于 CFD 软件，流畅的包裹和用户定义功能(UDF ) ，一个 Eulerian 二阶段的模型，包括为水和沉积的联合模型分阶段执行的 Euler-Euler，和为液体的一个狂暴的模型分阶段执行，被采用在管道附近预言 scour 深度。模型被从实验室实验获得的观察数据验证。根据模拟，包括早期的速度的效果，影响 scour 深度的因素等等输送直径和沉积粒子尺寸，被调查。根据各种各样的沉积的早期的速度的公式，同时接近计算在上理论搜索深度在华南海为七个车站的管道被开发，在设计申请的地方，信息是可得到的。

三峡水库蓄水后长江中游嘉鱼河段河床演变特性分析

嘉鱼河段是长江中游典型的碍航河段之一,需重点关注河床演变特性。根据1970~2021年实测水下地形资料,全面分析了该河段的冲淤、岸线、河床形态、洲滩深槽等变化,研究该河段自2003年三峡水库蓄水运用及2006年实施航道整治工程以来河床演变特性。结果表明:自三峡水库蓄水运用以来,该河段岸线基本稳定,河床冲刷部位主要在枯水河槽;近些年断面形态逐渐趋于稳定,岸线变化不大;河段内洲滩平面位置保持相对稳定的状态,仅在复兴洲尾部左缘、燕窝镇对面江中形成了一个新的江心洲;深槽平面位置较为稳定。研究成果可为该河段防洪调度、河道治理等提供参考。

Numerical Simulation of Local Scour Around A Large Circular Cylinder Under Wave Action

A horizontal two-dimensional numerical model is developed for estimation of sediment transport and sea bed change around it large circular cylinder tinder wave action, The wave model is based on an elliptic mild slope equation. The wave-induced current by the gradient of radiation stress is considered and a depth integrated shallow water equation is applied to the calculation of the current. The mass transport velocity and the bed shear stress due to streaming are considered, which are important factors affecting the sediment transport around a structure due to waves, especially in reflective areas. Wave-current interaction is taken into account in the model for computing the bed shear stress. The model is implemented by it finite element method, The results of this model are compared with those from other methods and agree well with experimental data.

Experimental Study of Sediment Incipience Under Complex Flows

Sediment incipience under flows passing a backward-facing step was studied. A series of experiments were conducted to measure scouring depth, probability of sediment incipience, and instantaneous flow velocity field downstream of a backward-facing step. Instantaneous flow velocity fields were measured by using Particle Image Velocimetry (PIV), and an image processing method for determining probability of sediment incipience was employed to analyze the experimental data. The experimental results showed that the probability of sediment incipience was the highest near the reattachment point, even though the near-wall instantaneous flow velocity and the Reynolds stress were both much higher further downstream of the backward-facing step. The possible me- chanisms are discussed for the sediment incipience near the reattachment point.

Bed Load Transport Rates during Scouring and Armoring Processes

Dambreak-induced bed scouring may undermine the foundation of bridge piers and other structures,and that destruction can pose a serious threat.Consequently,this paper aims at exploring the mechanisms of scouring and armoring.Firstly,the incipient velocity for nonuniform sediment particles was studied,and a formula was derived based on the angle of repose of nonuniform sediment.The results showed that the mechanism of incipient motion for sand and fine gravel differed from that for coarse gravel and cobbles.Also,comparison between experimental and field data shows that the results from the proposed formula agree well with those observed for all conditions.Secondly,a birth-death,immigration-emigration Markov process was developed to describe the bed load transport rate associated with scouring and armoring.The comparison between experimental data and computed results shows that our model can predict the bed load transport rate,although there may be some limitations,the chief of which is that there are many variables in the model to be determined through experiment.This makes its application in river engineering inconvenient.

Scour depth beneath a pipeline undergoing forced vibration

This paper studies the coupling effect of the pipeline vibration on the seabed scour. A vertical two- dimensional model is applied to numerically investigate the local scour below a vibrating pipeline with different amplitudes and periods. Using the scour underneath a fixed pipeline as a reference, this paper focuses on the impact of the pipeline vibration on the equilibrium scour depth. Generic relationships are established between the non-dimensional scour depth and the non-dimensional vibrating parameters, i.e., amplitude and frequency. The normalization process takes into account the influences of such parameters as the incoming flow velocity, pipe diameter, and Shields parameter. An empirical formula is proposed to quantify these relationships.

CFD prediction of local scour hole around bridge piers

In order to predict the local scour hole and its evaluation around a cylindrical bridge pier,the computational fluid dynamics(CFD) and theories of sediment movement and transport were employed to carry out numerical simulations.In the numerical method,the time-averaged Reynolds Navier-Stokes equations and the standard k-ε model were first used to simulate the three-dimensional flow field around a bridge pier fixed on river bed.The transient shear stress on river bed was treated as a crucial hydrodynamic mechanism when handling sediment incipience and transport.Then,river-bed volumetric sediment transport was calculated,followed by the modification of the river bed altitude and configuration.Boundary adaptive mesh technique was employed to modify the grid system with changed river-bed boundary.The evolution of local scour around a cylindrical bridge pier was presented.The numerical results represent the flow pattern and mechanism during the pier scouring,with a good prediction of the maximum scour hole depth compared with test results.

荆江河段泥沙冲淤对三峡水库汛期排沙的响应

三峡水库汛期排沙研究大多关注库区的减淤效应,对坝下游河道的冲淤影响尚需进一步研究,对优化水库调度和河道保护利用具有重要意义。以三峡水库下游荆江河段为对象,建立了荆江长河段二维水沙数学模型,并结合实测资料分析,基于三峡水库2018年7月排沙调度,通过设置不同的排沙比(7%~100%),计算分析了荆江河段冲淤对三峡水库排沙比的响应。结果表明:虽然荆江河段全年总体冲刷,但排沙比较大时汛期仍可能淤积,上荆江河段受排沙调度影响相对较大;总体而言,2018年汛期水沙条件下,30%左右的排沙比是荆江河段洪季冲淤的临界点;排沙比提高后,汛期淤积部位大部分为边滩等缓流区,以及弯曲河段凹岸等,主槽仍冲刷,对维护滩槽高差具有积极意义。

Local scour at submarine pipelines

The rapid development of offshore oilfields has increased the number of submarine pipelines being constructed for the transport of crude oil to onshore refineries.Interactions between the pipeline and an erodible bed under the influence of current and waves often lead to local scouring around the structure.When this occurs, the pipeline may be suspended on the seabed resulting in the formation of a span.If the free span is long enough, the pipe may experience resonant flow-induced oscillations,leading to structural failure.This study examines the complex flow-structure-sediment interaction leading to the development of local scour holes around submarine pipelines.It reviews published literature in this area,which primarily is confined to the development of 2- dimensional scour holes.Despite the abundance of such research studies,pipeline-scour in the field essentially is 3-dimensional in nature.Hence,most of these studies have overlooked the importance of the transverse dimension of the scour hole,while emphasizing on its vertical dimension.This clearly is an issue that must be re-examined in light of the potential hazard and environmental disaster that one faces in the event of a pipeline failure.Recent studies have begun to recognize this shortcoming,and attempts have been made to overcome the deficiency.The study presents the state-of-the-art knowledge on local scour at submarine pipelines,both from a 2-dimensional as well as the 3-dimensional perspective.