小浪底水库“腾库迎洪”期异重流形成分析

小浪底水库异重流的形成与运行规律是关系黄河调水调沙方案拟定的重要指标。基于现场调研、理论探讨与预测分析结合等手段,明晰了2018年“腾库迎洪”期小浪底水库来水来沙过程,根据水库调度与库区淤积形态等边界条件,观测了异重流的形成与运行,采用基于流速分布的水库异重流潜入点预测公式进行了计算分析。结果表明:2018年7月库区产生的剧烈冲刷,在潜入点处发生大量淤积,水深大幅减小,引起潜入点下移;潜入点位置随入库水沙增大、坝前水位降低及库区淤积的推进向坝前移动,计算与实测结果反映了该变化过程。     

小浪底水库“腾库迎洪”期异重流形成分析

小浪底水库异重流的形成与运行规律是关系黄河调水调沙方案拟定的重要指标。基于现场调研、理论探讨与预测分析结合等手段,明晰了2018年"腾库迎洪"期小浪底水库来水来沙过程,根据水库调度与库区淤积形态等边界条件,观测了异重流的形成与运行,采用基于流速分布的水库异重流潜入点预测公式进行了计算分析。结果表明:2018年7月库区产生的剧烈冲刷,在潜入点处发生大量淤积,水深大幅减小,引起潜入点下移;潜入点位置随入库水沙增大、坝前水位降低及库区淤积的推进向坝前移动,计算与实测结果反映了该变化过程。     

水库异重流一维水沙耦合模型

建立了基于库区不规则断面的一维非恒定异重流数学模型,并采用明流与异重流水沙输移模型交替运算的两步模式,即用潜入条件动态判别异重流计算的上游边界位置,将潜入点上游的明流浑水段与下游异重流段计算连接起来。水流运动、泥沙输移与河床变形过程完全耦合,采用TVD(Total Variation Diminishing)形式的MUSCL-Hancock格式进行数值求解。将该模型应用于恒定流量与释放定量悬沙两种条件下的异重流水槽实验模拟,比较了有无水面梯度项对模拟精度的影响,计算结果表明该模型能较为准确地预测异重流的厚度、含沙量分布及传播过程。     

浊流和泥石流的异重流初期潜入点的实验研究

潜入点的水流泥沙条件是异重流的发生条件和持续条件,受到了国内外学者的广泛关注。初期潜入点Fr代表异重流的发生条件,而稳定潜入点Fr则代表异重流的持续条件。通过一系列的低浓度浊流和高浓度浊流及泥石流的异重流潜入点的实验研究,分析对比低浓度浊流和高浓度浊流及泥石流的异重流的关系,得到在均匀顺直水槽中的异重流初期的潜入点Fr规律。提出在一定的水槽宽度、泥沙浓度条件下,异重流的初期潜入点Fr与头部流速成正比。与其它文献不同研究条件的实验结果对比有很好的一致性,说明该研究结论有很好的可靠性。该研究结论的适用范围为初期潜入点,不适用于稳定潜入点和初期潜入点与稳定潜入点之间的过渡阶段。但高浓度浊流和泥石流的异重流初期潜入点Fr与其稳定潜入点Fr很接近,粘性泥石流的异重流更接近。     

黄河万家寨水库库区冲淤变化分析

介绍了黄河万家寨水库运行及库区水文泥沙动态监测的基本情况，并对水库容淤积、库区淤积物分布、泥沙组成及水库淤积形态等方面的问题进行了分析探讨。     

深水库区细颗粒淤积物重力驱动流动数值模拟——以三峡水库为例

针对三峡水库近坝区细颗粒泥沙淤积特征,从过程机理出发,提出了深水库区细颗粒泥沙淤积过程的物理图形。采用临界坡度作为细颗粒淤积物失稳流动的判别标准,借鉴浅水流动模式,描述失稳后细颗粒淤积物重力驱动流动过程,通过耦合三维水沙数学模型,建立了细颗粒淤积物重力驱动流动的数值模拟方法,在此基础上对三峡水库近坝区细颗粒泥沙淤积形态进行了模拟研究。研究结果表明:水库蓄水运行初期近坝区细颗粒泥沙主要淤积在断面深槽内,且呈水平状,考虑重力驱动流动后的模拟结果与实测结果吻合较好,从而为进一步深入研究深水库区细颗粒泥沙运动特征提供了技术支撑。     

复杂边界作用下三峡水库泥沙淤积特征与趋势

受上游水沙条件和水库调度过程等影响,三峡水库实际淤积过程较为复杂。本文基于一维泥沙数学模型,分析上下游边界条件变化对三峡水库淤积特征的综合影响,建立入库沙量和汛期坝前水位与库区淤积的经验关系,讨论了其贡献及未来淤积趋势。结果表明：上游干支流入库沙量和汛期坝前水位是影响三峡水库淤积的主要因素,其变化均将造成库区淤积重心的偏移,变动回水区下段及常年回水区上段的泥沙分选及冲淤情况受影响最为明显;2013—2020年,干流来沙对三峡库区淤积的贡献减小(由65%减小至42%),支流来沙贡献逐步增大(由32%增大至56%);汛期坝前水位变化对该时段库区淤积较2003—2012年期间的影响已经较小(1.6%～1.8%);当遭遇平常水文年水沙过程,未来三峡水库泥沙淤积量约在0.5亿t/a左右;当遭遇不利洪水组合水文年,尤其是支流发生大规模强降雨使岷江和嘉陵江洪峰流量大于30 000 m³/s时,三峡水库泥沙淤积量约在1.6亿t/a左右。     

柘溪水库拦门沙淤积及治理对策九五优秀科研成果介绍

柘溪水库拦门沙淤积及治理对策研究课题是应电站和库区管理部门的邀请和委托于 1 995年至1 996年间由长沙中南机电技术研究所进行和完成的 ,并以我国优秀科研成果入选《中国九五科学研究成果》丛书 (该成果研究论文在本刊 1 996年第 2期刊出 )。该研究成果首先明确了泥沙淤积是水库运行中五大环境工程地质课题之一 (其他 4个课题为水库渗漏 ,诱发地震 ,库岸变形和矿产淹没 ) ,同时明确了将库尾和各支流入库口的泥沙淤积称为拦门沙 ,提出了对库区泥沙淤积的研究方向。拦河筑坝建立水库 ,使库区的河道落差集中到坝址 ,改变了原来河道的水沙流态和流速 ,引起了河道自然环境变化和河床演变。     

溪洛渡库区支流拦门沙形成机理

水库蓄水后，水深增加使得河道干支流水动力条件发生改变，干流泥沙倒灌造成支流淤积，影响水库有效库容和航运安全。以溪洛渡水库为例，基于实测资料和三维水沙数学模型，研究库区干流和支流的水沙输移规律，分析支流河口段泥沙淤积特性及拦门沙形成机理。结果表明：(1)库区支流河道淤积泥沙来自支流上游和干流倒灌，其中，支流上游来沙是库区支流河道淤积的主要来源。(2)干流倒灌库区支流河口形成对流和环流区，泥沙易于淤积，西溪河和牛栏江坡度较缓，存在形成拦门沙的风险较大；美姑河坡度较大，存在形成拦门沙的风险较小。(3)对于西溪河、牛栏江和美姑河，干流倒灌的距离随着流量的增加而增加，高水位运行时，水位对干流倒灌的距离影响不明显；而对于金阳河和西苏角河，干流倒灌的距离随着流量的增加基本不变，干流倒灌的距离随着水位的增加而增加。研究成果为新水沙情势下库区支流拦门沙风险防控提供依据。     

三峡水库135m运行阶段永久船闸下引航道泥沙淤积分析

通过实测三峡水库135m运行阶段永久船闸下引航道及口门区泥沙淤积与水沙因子变化,计算分析了下引航道及口门区的淤积量及分布、拦门沙淤积形态、淤积机理及清淤时机,建立了口门含沙量与长江含沙量、口门斜流流速与长江流量、拦门沙淤积高度与来沙量等关系;并结合倒灌异重流理论,计算验证了下引航道及口门区异重流、环流淤积。结果表明,下引航道及口门区主要集中在主汛期(7~9月)淤积,汛末(10~12月)进行一次清淤即可满足航深要求。     

The Research Progress of Turbidity Currents and Related Deep-water Bedforms

Since turbidity current was reported in the 19th century, its flow dynamics, depositional processes and products have drawn much attention of geoscience community. In the last decades, with the help of rapid development of geophysical technology in deep-water areas, superficial bedforms formed by turbidity currents like cyclic steps have been widely documented on the seafloor, and they have been interpreted to be closely related to turbidite facies defined by the Bouma sequence. However, there is still a lack of direct observation on turbidity currents due to difficulties in the design and deployment of flow-measuring instruments under the sea. Such difficulties also result in much uncertainties in the explanations for the formation of bedforms and related flow processes. This paper summarized and discussed current research status of turbidity-currents classification, the formation and evolution of bedforms. Examples of supercritical-bedform studies using various methods such as experiments, numerical simulation, bathymetric data and seismic data, were shown in this paper. As one of main supercritical flow bedforms, cyclic steps were described in detail in this paper, including its formation, evolution and relationship with Bouma sequence. The variations in initial bed morphology and hydrodynamic parameters are responsible for the changes in the shapes of bedforms. Turbidites formed under different hydrodynamic conditions correspond to different units of Bouma sequence. Not all turbidity events can form a complete Bouma sequence. Therefore, traditional Bouma sequence cannot be applied to all turbidite studies. A more complete turbidite facies model must be established through studies from modern deep-sea sediments, outcrops, physical and numerical simulations. Additionally, turbidity currents and related supercritical bedforms are receiving more and more attention. They are important components of understanding the dynamic evolution of deep-water continental slope. The study of cyclic steps and other bedforms related to turbidity currents not only helps to characterize flow dynamics, but also provides a theoretical basis for the research of turbidite reservoirs. Finally, we proposed future research directions of turbidity currents and their related supercritical bedforms.     

小浪底水库淤积形态数值模拟

水库淤积形态是影响库容分布、水库排沙的一项重要因素。小浪底水库近坝段淤积泥沙粒径极细,具有流动性,针对其细颗粒泥沙淤积特点,揭示了水库细颗粒淤积物的流变特性与流型特征;通过引入水、淤积物、床面之间的界面受力分析,构建了细颗粒淤积物失稳流动描述模式,并与水沙输移模型相耦合,建立了考虑细颗粒淤积物流动特性的水库淤积形态模拟方法,在此基础上对小浪底水库淤积形态进行了验证分析。研究结果表明:低密度细颗粒淤积物为宾汉型流体,淤积平衡坡降较小,当其密度大于1.25 g/cm 3后,流动性快速减弱;考虑细颗粒淤积物流动特征的水库淤积形态模拟结果与实测结果吻合较好。研究成果可为水库淤积形态形成机理及其对水沙调控的响应研究提供技术支撑。     

小浪底水库淤积形态数值模拟

水库淤积形态是影响库容分布、水库排沙的一项重要因素。小浪底水库近坝段淤积泥沙粒径极细,具有流动性,针对其细颗粒泥沙淤积特点,揭示了水库细颗粒淤积物的流变特性与流型特征;通过引入水、淤积物、床面之间的界面受力分析,构建了细颗粒淤积物失稳流动描述模式,并与水沙输移模型相耦合,建立了考虑细颗粒淤积物流动特性的水库淤积形态模拟方法,在此基础上对小浪底水库淤积形态进行了验证分析。研究结果表明:低密度细颗粒淤积物为宾汉型流体,淤积平衡坡降较小,当其密度大于1.25 g/cm³后,流动性快速减弱;考虑细颗粒淤积物流动特征的水库淤积形态模拟结果与实测结果吻合较好。研究成果可为水库淤积形态形成机理及其对水沙调控的响应研究提供技术支撑。     

A comparison of an autosuspension criterion to field observations of five turbidity currents

An autosuspension criterion that has been developed directly from the fluid dynamical equations, by taking into account the vertical structure of turbidity currents, is compared to field observations of five turbidity currents. It is found that the criterion is consistent with the motion of all five currents, which suggests that the criterion may, at least under certain circumstances, be a reasonable guide in estimating the conditions necessary for a turbidity current to be self-sustaining.     

浊流沉积研究的新进展:鲍马序列、海底扇的重新审视

本文在总结前人对浊流沉积研究的基础上,分析前人对浊流与浊积岩、浊流沉积与浊流相模式的对应关系之间的认识,并对鲍马序列进行重新审视。在海底扇研究过程中,鲍马序列已经不能充分反映浊流沉积的全过程。鲍马序列所反应的沉积模式其实是由碎屑流、浊流、底流等多种形式流体组合和改造后的结果,海底扇沉积模式不能笼统归结为浊流沉积作用的结果。在完善重力流、底流等沉积作用的同时,建立一个与沉积作用相互联系的深海沉积系统,以对深海研究提供更好地指导和预测。     

黄河泥沙冲淤数学模型研究

应用作者提出的动床阻力、非均匀沙挟沙力、床沙交换调正及滩槽水沙交换等关系与新的不平衡输沙等初步经验关系,建立了黄河下游及水库河床变形计算一维数学模型。经1960年～1988年共28年实测水沙资料的验证计算,结果与实际基本符合。该模型的特点是可预报各种水流及河床边界条件下的动床阻力;可同时计算确定混合沙中各粒径组的推移质、悬移质挟沙力、含沙浓度垂线分布及上滩水流含沙量;能较好地反映浑水上滩淤积减沙使主槽减淤增冲的实际情况;能够基本反映泥沙多来多排及高含沙水流的冲淤特性;能综合反映出来水流量、含沙量及级配的调节变化产生的输沙冲淤差别。应用该模型计算黄河小浪底水库库区及下游河道的冲淤,成果比较合理。     

Patterns of deposition from experimental turbidity currents with reversing buoyancy

Turbidity currents are turbulent, sediment‐laden gravity currents which can be generated in relatively shallow shelf settings and travel downslope before spreading out across deep‐water abyssal plains. Because of the natural stratification of the oceans and/or fresh water river inputs to the source area, the interstitial fluid within which the particles are suspended will often be less dense than the deep‐water ambient fluid. Consequently, a turbidity current may initially be denser than the ambient sea water and propagate as a ground‐hugging flow, but later reverse in buoyancy as its bulk density decreases through sedimentation to become lower than that of the ambient sea water. When this occurs, all or part of the turbidity current lofts to form a buoyant sediment‐laden cloud from which further deposition occurs. Deposition from such lofting turbidity currents, containing a mixture of fine and coarse sediment suspended in light interstitial fluid, is explored through analogue laboratory experiments complemented by theoretical analysis using a ‘box and cloud’ model. Particular attention is paid to the overall deposit geometry and to the distributions of fine and coarse material within the deposit. A range of beds can be deposited by bimodal lofting turbidity currents. Lofting may encourage the formation of tabular beds with a rapid pinch‐out rather than the gradually tapering beds more typical of waning turbidity currents. Lofting may also decouple the fates of the finer and coarser sediment: depending on the initial flow composition, the coarse fraction can be deposited prior to or during buoyancy reversal, while the fine fraction can be swept upwards and away by the lofting cloud. An important feature of the results is the non‐uniqueness of the deposit architecture: different initial current compositions can generate deposits with very similar bed profiles and grading characteristics, highlighting the difficulty of reconstructing the nature of the parent flow from field data. It is proposed that deposit emplacement by lofting turbidity currents is common in the geological record and may explain a range of features observed in deep‐water massive sands, thinly bedded turbidite sequences and linked debrites, depending on the parent flow and its subsequent development. For example, a lofting flow may lead to a well sorted, largely ungraded or weakly graded bed if the fines are transported away by the cloud. However, a poorly sorted, largely ungraded region may form if, during buoyancy reversal, high local concentrations and associated hindered settling effects develop at the base of the cloud.