Dam-break Modeling in Alpine Valleys

Dam-break analysis is of great importance in mountain environment,especially where reservoirs are located upstream of densely populated areas and hydraulic hazard should be assessed for land planning purposes.Accordingly,there is a need to identify suitable operative tools which may differ from the ones used in flat flood-prone areas.This paper shows the results provided by a 1D and a 2D model based on the Shallow Water Equations(SWE) for dam-break wave propagation in alpine regions.The 1D model takes advantage of a topographic toolkit that includes an algorithm for pre-processing the Digital Elevation Model(DEM) and of a novel criterion for the automatic cross-section space refinement.The 2D model is FLO-2D,a commercial software widely used for flood routing in mountain areas.In order to verify the predictive effectiveness of these numerical models,the test case of the Cancano dam-break has been recovered from the historical study of De Marchi(1945),which provides a unique laboratory data set concerning the consequences of the potential collapse of the former Cancano dam(Northern Italy).The measured discharge hydrograph at the dam also provides the data to test a simplified method recently proposed for the characterization of the hydrograph following a sudden dam-break.

Coupled 2D Hydrodynamic and Sediment Transport Modeling of Megaflood due to Glacier Dam-break in Altai Mountains,Southern Siberia

One of the largest known megafloods on earth resulted from a glacier dam-break,which occurred during the Late Quaternary in the Altai Mountains in Southern Siberia.Computational modeling is one of the viable approaches to enhancing the understanding of the flood events.The computational domain of this flood is over 9460 km2 and about 3.784 × 106 cells are involved as a 50 m × 50 m mesh is used,which necessitates a computationally efficient model.Here the Open MP(Open Multiprocessing) technique is adopted to parallelize the code of a coupled 2D hydrodynamic and sediment transport model.It is shown that the computational efficiency is enhanced by over 80% due to the parallelization.The floods over both fixed and mobile beds are well reproduced with specified discharge hydrographs at the dam site.Qualitatively,backwater effects during the flood are resolved at the bifurcation between the Chuja and Katun rivers.Quantitatively,the computed maximum stage and thalweg are physically consistent with the field data of the bars and deposits.The effects of sediment transport and morphological evolution on the flood are considerable.Sensitivity analyses indicate that the impact of the peak discharge is significant,whilst those of the Manningroughness,medium sediment size and shape of the inlet discharge hydrograph are marginal.

Comparison of depth-averaged concentration and bed load flux sediment transport models of dam-break flow

This paper presents numerical simulations of dam-break flow over a movable bed. Two different mathematical models were compared: a fully coupled formulation of shallow water equations with erosion and deposition terms(a depth-averaged concentration flux model), and shallow water equations with a fully coupled Exner equation(a bed load flux model). Both models were discretized using the cell-centered finite volume method, and a second-order Godunov-type scheme was used to solve the equations. The numerical flux was calculated using a Harten, Lax, and van Leer approximate Riemann solver with the contact wave restored(HLLC). A novel slope source term treatment that considers the density change was introduced to the depth-averaged concentration flux model to obtain higher-order accuracy. A source term that accounts for the sediment flux was added to the bed load flux model to reflect the influence of sediment movement on the momentum of the water. In a onedimensional test case, a sensitivity study on different model parameters was carried out. For the depth-averaged concentration flux model,Manning's coefficient and sediment porosity values showed an almost linear relationship with the bottom change, and for the bed load flux model, the sediment porosity was identified as the most sensitive parameter. The capabilities and limitations of both model concepts are demonstrated in a benchmark experimental test case dealing with dam-break flow over variable bed topography.

A Dam Break Analysis Using HEC-RAS

This paper firstly described the dam break in the aspects of theories and models. Break parameters prediction, the understanding of dam break mechanics, peak outflow prediction were shown as the essential for the dam break analysis, and eventually determined the loss of the damages. Secondly, as an application example, Foster Joseph Sayers Dam break was further modeled and analyzed using USACE Hydrologic Engineering Center’s River Analysis System (HEC-RAS) model based on available geometry data. The results show that dam break is a complicated and comprehensive process involving lots of principles. Combination of mechanics and case studies, reflection of predominant mechanisms of headcut erosion, more specific categorization of dam, prudent investigation and inference of dam break process are needed in developing a satisfactory dam break simulation model. Foster Joseph Sayers Dam break due to piping elongates the time period of high water surface level, which increases the duration of risk. However, the dam break does not increase the downstream maximum water surface elevation (Max. W.S. Elev) significantly at previous design Probable Maximum Flood (PMF). Dam break has a greater impact on the downstream location where is closer to the dam in accordance with the comparison of the hydrographs at different downstream locations. Sensitivity analysis demonstrates that the changes of dam break parameters had no much influence on the downstream Max. W.S. Elev.

Optimal Evacuation Scheme Based on Dam-Break Flood Numerical Simulation

The optimal evacuation scheme is studied based on the dam-break flood numerical simulation. A threedimensional dam-break mathematical model combined with the volume of fluid (VOF) method is adopted. According to the hydraulic information obtained from numerical simulation and selecting principles of evacuation emergency scheme, evacuation route analysis model is proposed, which consists of the road right model and random degree model. The road right model is used to calculate the consumption time in roads, and the random degree model is used to judge whether the roads are blocked. Then the shortest evacuation route is obtained based on Dijstra algorithm. Gongming Reservoir located in Shenzhen is taken as a case to study. The results show that industrial area Ⅰ is flooded at 2 500 s, and after 5 500 s, most of industrial area Ⅱ is submerged. The Hushan, Loucun Forest and Chaishan are not flooded around industrial area Ⅰand Ⅱ. Based on the above analysis, the optimal evacuation scheme is determined.

均质土坝管涌溃决实验渗流分析

管涌渗漏破坏是导致土石坝溃决的主要原因之一,通过模型实验开展土石坝管涌过程渗流场变化研究,对土石坝安全预测预警具有重要意义。采用预设管涌通道模拟管涌渗漏的方式,建立了室内小尺寸均质土坝管涌溃决模型;通过布置小量程渗压计,获取土坝模型的渗流场数据,对土坝模型从蓄水到渗透破坏再到溃决全过程的渗流场变化进行了深入分析研究。分析发现,在蓄水阶段,相同轴距的管涌断面测点渗流压力小于非管涌断面测点的测值,但测值达到峰值的时间早于非管涌断面测点;在溃决阶段(出现明流和形成溃口阶段),坝体内渗流压力出现骤降,且越靠近管涌断面渗流压力骤降时间越早、骤降幅度也越大。该认识,对于土石坝管涌渗漏破坏预测预警提供借鉴。

基于GPU加速的溃坝洪水演进模拟研究

溃坝洪水演进与淹没范围快速模拟,对指导抢险救灾至关重要。为此,引入GPU加速技术,构建了一套高效高分辨率溃坝数值模型,与经典三驼峰溃坝试验对比发现,模拟结果与试验结果非常吻合,并利用该模型模拟了典型溃坝洪水演进及溃口流场、溃后水位变化情况。结果表明,模型能较好地模拟溃坝洪水演进,较好捕捉溃口发展过程及泥沙输移。t=200 s时溃决流量出现小峰值4 m3/s,t=450 s时,溃决流量出现最大峰值13.8 m3/s;随着下泄流量增大,溃口加速侵蚀和冲刷并逐渐连通,溃口由0.21 m扩大至0.40 m。GPU加速比约为CPU的10.33~13.75倍,且网格数越多,加速效果越明显。

MIKE软件技术在水库溃坝洪水数值模拟中的应用研究

当前,水库大坝受到超频率的洪水以及强震破坏,而容易导致溃决风险。针对水库大坝溃决相关问题,融合BREACH和MIKE21构建耦合模型,并用于溃坝洪水数值模拟试验。结果表明,7种方案最大下泄流量为方案1的18.39×10^(4) m^(3)/s;方案1洪峰向地点C汇入点的洪水最大流量比邢台坝址下降约44%。方案1的溃坝洪水水位始终最高,A地最高为306m。综合来看,耦合模型在水库溃坝洪水数值模拟中具备有效性,在实际的水库防洪避险中具备实用性。

泰安市果庄河流域串(并)联水库溃坝模拟分析

针对山丘区串(并)联水库群溃坝后的风险问题,选取泰安市果庄河流域内的4座小型串(并)联水库为研究对象。采用数值模拟的方法对串(并)联水库群的溃坝淹没情况及风险性进行了分析,计算了水库溃坝流量,搭建了二维水动力学模型进行水库溃坝数值模拟。通过分析不同溃坝方案下小型梯级水库群淹没要素,以淹没面积为风险评估指标进行风险性分析,分析结果可为山丘区串(并)联水库的溃坝风险评估和风险对应提供技术支撑。

清远抽水蓄能电站溃坝洪水演进及影响分析

为研究清远抽水蓄能电站溃坝对下游梯级水库和防洪保护区的影响,利用MIKEFLOOD构建一二维耦合模型对溃坝洪水演进进行模拟。研究共设置12种工况,分析不同因素对溃坝后洪水流量、淹没范围、淹没水深等演进过程的影响。结果显示,溃决形式(溃口宽度)及溃决水位、溃决历时都是影响溃坝洪水的重要因素,且梯级电站溃坝后对于距离较近且地势较低的楼心村、大楼村影响最为显著,应采取相应预防措施。

基于二维水动力模型的溃坝洪水数值模拟研究

【目的】研究水库溃坝洪水影响。【方法】以辛庄水库为例,通过建立二维水动力模型,模拟了不同溃决方案下溃坝洪水演进过程,计算了下游高速铁路处淹没水深、流速、冲刷深度等,分析了溃坝洪水对下游高速铁路的安全运行影响。【结果】水库未溃决时,溢洪道最大下泄洪水能够正常通过铁路涵洞,对下游工程影响较小;水库大坝正面溃决的影响要比侧面溃决的影响大,下游部分铁路路基顶面过水,影响铁路正常运行;大坝溃决后最大流速是未溃决时的2.15~2.48倍,涵洞处最大冲刷深度是未溃决时的1.56倍。【结论】二维水动力模型可较好的模拟溃坝洪水演进过程和淹没范围,研究成果可为水库溃坝洪水灾害预防提供参考和数据支撑。

小型水库超标准洪水溃坝模拟及风险分析

我国小型水库数目众多,承担着防洪、灌溉、供水等重要作用。为减少水库遇超标准洪水溃坝后下游风险区的生命财产损失,以南王水库为研究对象,考虑水库遇超标准洪水下瞬时溃坝与渐进式溃坝两种溃坝形式,采用DB-IWHR溃坝模型模拟溃口流量过程,利用MIKE软件构建一二维耦合模型模拟洪水演进情况并进行风险分析。结果表明,下游淹没情况符合溃坝洪水演进的一般规律,模型可较好模拟超标准洪水引起大坝溃决的溃口流量与洪水演进过程,可为小型水库超标准洪水溃坝应急预案提供参考。

堰塞体溃决离心模型试验供水系统关键技术研究

堰塞体溃决洪水洪峰流量及洪水时程曲线特征的预测是堰塞湖应急抢险及下游风险控制方案制订的重要依据。堰塞体溃决的离心模型试验,在研究堰塞体溃决机理、溃决过程及溃决洪水的历时曲线特征方面独具优势,但离心模型试验供水系统的设计,涉及到从外部静止状态到高速旋转状态的模型中连续供水,同时还要保证堰塞体溃决过程中上游水位为设定的常水头,是堰塞体溃决离心模型试验中的关键性的一大难题。本文围绕以上难题,设计了一种环形水箱以解决从静态到动态模型的连续供水问题,通过理论分析,确定了环形水箱中可提前注入的最大水量。另外在试验箱设置了竖井式溢流口,可以排出高出设定常水头的水体,保证了上游水位的稳定。通过以上设计有效地解决了供水系统中的关键难题,并在后续堰塞体溃决离心模型试验中得到了验证。

均质黏土坝漫顶缩尺模型的相似性优化试验研究

为进一步研究土石坝漫顶溃坝模型与原型之间的相似性问题,从均质黏土坝在水流冲刷作用下的起动极限状态分析入手,提出调整筑坝压实度来降低缩尺模型坝的抗冲刷能力,进而达到漫顶溃坝过程相似性优化的设想。基于黏土的抗剪强度及黏聚力会随着压实度的降低呈非线性减小,以某土石坝工程的漫顶溃坝分析为原型,开展了不同压实度和几何比尺条件下的均质黏土坝相似漫顶流槽试验。结果表明:采用与原型黏土坝相同筑坝密实度的模型坝溃决过程与原型完全不相似,模型与原型之间的差异性会随着几何比尺的增加而愈发明显;适当减小黏土模型坝的压实度能够显著提升模型坝与原型在溃坝形态、溃决时间等溃坝过程相似性。

ONE-AND TWO-DIMENSIONAL COUPLED HYDRODYNAMICS MODEL FOR DAM BREAK FLOW

1-D and 2-D mathematical models for dam break flow were established and verified with the measured data in laboratory. The 1-D and 2-D models were then coupled, and used to simulate the dam break flow from the reservoir tail to the dam site, the propagation of dam break waves in the downstream channel, and the submergence of dam break flow in the downstream town with the hydrodynamics method. As a numerical example, the presented model was employed to simulate dam break flow of a hydropower station under construction. In simulation, different dam-break durations, upstream flows and water levels in front of dam were considered, and these influencing factors of dam break flow were analyzed, which could be referenced in planning and designing hydropower stations.

土石坝水库溃坝洪水非恒定流演进计算应用研究

本文通过对老鹰嘴水库工程土石坝溃坝洪水研究,预测水库大坝溃口发生的过程(如形状、深度、宽度、溃口扩张的速度等),计算溃口出水流量,通过水库库容演算,预测水库溃口过流量的过程线;对大坝在正常蓄水位、大坝校核洪水、大漫顶三种情况下的溃坝洪水,进行了下游河段洪水非恒定流演进计算,分析最不利为大坝漫顶工况,并在大坝漫顶工况下根据不同溃决状态,分别计算出1/4溃决、1/2溃决、全溃决的下游淹没水位、影响范围人口等数据,为制定相应的应急措施提供依据。

基于改进EAHP-正态云模型的尾矿库溃坝风险评价

针对尾矿库溃坝风险专家群决策评价中的主观随意性和语言模糊性,以及传统层次分析法采用“点”数据或“刚性”数据构造判断矩阵与实际情况不符等问题,将可拓集合理论以及物元理论与之相结合,并考虑到不同专家对指标重要性赋值结果可能与专家群体综合评判结果间的离异程度较大等客观因素,提出了一种可考虑专家客观权重系数的改进可拓层次分析法,同时利用正态云模型在处理指标随机性和模糊性等方面的独特优势,构建了一种基于改进EAHP-正态云理论的尾矿库溃坝风险评价方法.实例验证表明,该工程漫顶溃决、渗流破坏和管理因素方面均处于安全状态,失稳溃决方面处于较安全状态,整体上处于安全状态,当属正常库,与工程实际相吻合,该方法可有效提升尾矿库评价指标权重群决策结果的客观性和准确性,为该工程日后安全监测的重点及除险加固方案的制定提供参考.

平原河网地区水库溃坝洪水数值模拟分析——以江西省柘林水库为例

为了克服传统一维水动力学模型在模拟平原河网地区溃坝洪水中的不足,准确模拟洪水漫溢堤防后泛洪区溃坝洪水演进过程,建立了平原河网地区水库溃坝洪水计算的一维-二维耦合模型。以江西省柘林水库为例,计算了水库不同工况下的溃坝洪水及其在下游洪泛区的演进过程,分析了溃坝洪水的淹没风险。结果表明:柘林水库遭遇可能最大洪水漫顶溃决和管涌渗透破坏溃决工况,坝址洪峰流量分别为87000 m^(3)/s和46000 m^(3)/s;修河干流柘林坝址至虬津河段两侧有山头控制,溃坝洪水可被约束在狭窄的山谷内,水位涨幅较大;虬津以下为开阔的滨湖平原,水位涨幅下降明显。研究成果可为平原河网地区溃决洪水计算提供借鉴,并为柘林水利枢纽工程突发溃坝事件应急处置提供技术支撑。

一、二维耦合模型在梯级水电站大坝溃坝分析中的应用

合理论证溃坝洪水灾害影响对大坝风险评价和应急管理具有重要意义。针对梯级水电站大坝连溃风险,建立一、二维耦合模型,对溃坝洪水演进规律及大坝下游平原洪泛区淹没影响开展分析。以W江梯级水电站为例,考虑汛期与非汛期水库不同运行情况下两种工况的溃坝影响,从典型断面洪峰流量、最高水位以及峰现时间等角度分析溃坝洪水演进规律。在此基础上,以洪泛区最大淹没水深为代表性指标,对溃坝洪水风险等级进行了划分,并绘制洪水风险图,工况1、工况2高风险区面积分别达到431.31 km^(2)和575.76 km^(2),表明溃坝洪水对下游地区影响严重。相关成果可为应急预案制定和防灾减灾提供重要参考。

尾矿坝溃坝模型研究及应用

根据多个大坝的实际溃决资料,提出尾矿坝溃坝的数学模型,该模型考虑尾矿的物理力学性质及其在流动中的变形,适合溃坝砂流下泄流量变幅大的特点。并就尾矿坝溃坝后泥石流对坝下游的影响提出预测的方法,该方法确定了泄砂总量、溃坝口平均宽度、坝址最大砂流量、坝址流量过程线等溃坝的重要参数。最后利用数学模型对某尾矿库溃坝砂流进行了预测,并指出该坝下游人员的撤离高程,为防灾减灾以及保护人民生命财产安全等起到了积极作用。