Dam Breach Analysis Using HEC-RAS and HEC-GeoRAS: The Case of Kesem Kebena Dam

Ethiopia has been booming with active construction of dams within the past few decades for different infrastructural needs, but has never experienced demolition or failure of dams in its history;hence little attention is being given to possible breach scenarios of dams and the resulting floodings. This paper makes analysis of the possible breach of kesem dam and the resulting flood inundation. In this study, the dam has been checked for both overtopping and piping failure modes using one dimensional river analysis model called HEC-RAS. Empirical equations were used to predict dam breach parameters of the two failure modes for use in this model. PMF inflow with a peak 9237.77 m3/s is used as an input to the reservoir to check if overtopping failure was possible. The spill way has proven to have adequate capacity for the flood due to the PMF. Therefore, breaching of the embankment was not possible. Piping failure was also simulated in HEC-RAS and the resulting breach due to piping failure, was analyzed and flood hydrograph was obtained at different cross sections along the river. These are flood hydrographs at 20 km, 40 km and 60 km at the downstream. The resulting flood plain was also mapped using HEC-GeoRas to show the extent of flooding.

Numerical modeling of earthen dam breach due to piping failure

Based on model tests of earthen dam breach due to piping failure, a numerical model was developed.A key difference from previous research is the assumption that the cross-section of the pipe channel is an arch, with a rectangle at the bottom and a semicircle at the top before the collapse of the pipe roof, rather than a rectangular or circular cross-section.A shear stress-based erosion rate formula was utilized, and the arched pipe tunnel was assumed to enlarge along its length and width until the overlying soil could no longer maintain stability.Orifice flow and open channel flow were adopted to calculate the breach flow discharge for pressure and free surface flows, respectively.The collapse of the pipe roof was determined by comparing the weight of the overlying soil and the cohesion of the soil on the two sidewalls of the pipe.After the collapse, overtopping failure dominated, and the limit equilibrium method was adopted to estimate the stability of the breach slope when the water flow overtopped.In addition, incomplete and base erosion, as well as one-and two-sided breaches were taken into account.The USDAARS-HERU model test P1, with detailed measured data, was used as a case study, and two artificially filled earthen dam failure cases were studied to verify the model.Feedback analysis demonstrates that the proposed model can provide satisfactory results for modeling the breach flow discharge and breach development process.Sensitivity analysis shows that the soil erodibility and initial piping position significantly affect the prediction of the breach flow discharge.Furthermore, a comparison with a well-known numerical model shows that the proposed model performs better than the NWS BREACH model.

Breaches of the Baige Barrier Lake: Emergency response and dam breach flood

This paper documents the emergency response to the breaches of the Baige Barrier Lake. The lake was successively formed by landslides that occurred on October 10 and November 3, 2018 at the provincial border between Sichuan and Tibet in China. The barrier lake created by the "10.10" landslide breached on October 12 and triggered a flood with a peak discharge around 10000 m^3/s. The residual landslide barrier was enhanced by a second landslide on November 3, resulting in a higher barrier with larger flood potential. An overflow channel was excavated in the crest of the barrier to prompt the breach to be triggered at a lower water level. The second breach happened on November 12 with a measured peak discharge of 31000 m^3/s. Nearly 75000 people were evacuated before the two breaches. In order to prevent the downstream dams from possible over-topping, nearly 3.27×10~8 m^3 of the stored volume was released from the Liyuan reservoir 688 km downstream of Baige Barrier Lake. This paper presents the measured hydrographs and the back-analysis results for the "11.03" barrier lake. It is shown that the modern models of dam breach hydraulics can reasonably reproduce the barrier breach hydrographs;however, further studies are needed to define the key parameters which highly influence the calculated results. Knowledge acquired during the emergency response to the case can be shared with experts working on breaches of embankment dams and can be referenced to promote both the theory study and the engineering practice to mitigate the potential risks caused by this type of catastrophic events.

基于GeoDam-BREACH与Graham法的溃坝生命损失估算

应用GeoDam-BREACH工具包模拟了超标准洪水状况下小井沟水库下游的溃坝洪水演进过程,得到水库溃坝下游淹没范围与淹没区水深分布,然后采用Graham法对溃坝导致的生命损失风险进行分析。分析结果表明,小井沟水库发生漫顶破坏时,溃坝洪水对下游产生严重影响,下游村镇有受淹风险;下游溃坝淹没区域的风险人口死亡率较高,并且随着警报时间的减小而增大,从而得出警报时间和风险人口对溃坝洪水严重性的理解程度是生命损失的重要影响因素、应当加强水库大坝的日常巡查工作和预警系统的结论。研究成果为小井沟水库的防洪调度和应急预案编制提供了有效支持,对于同类水库的防洪和安全管理亦具有参考价值。

Physical modeling into outflow hydrographs and breach characteristics of homogeneous earthfill dams failure due to overtopping

The main objective of the present study is to introduce new empirical equations for the determination of breach geometrical dimensions and peak outflow discharge(Q_(p)).Therefore,a historic failure database of 109 embankments was collected and examined.The most important factors that affect the breach evolution,including grading size,hydraulic,and outflow characteristics are also studied.Some of the parameters used for the determination of Q_(p) and average breach width(Bave)have a significant effect on the erosion process,but they are less reflected in the technical literature.To study the behavior of noncohesive soils during overtopping,15 physical tests were performed at the laboratory,and the effects of interfering parameters were investigated.The experimental output hydrograph was used to simulate the hydrographs resulting from the failure of real dams,and recent artificial intelligence techniques along with linear and nonlinear regression models were employed.The area-time analysis of the laboratory hydrographs shows that the soil particle size and the characteristics of reservoir-basin significantly affect the rate of breach formation and outflow discharge.New relationships are introduced,based on the breach characteristics,by a combination of historical and experimental data,as well as case studies conducted on the hypothetical failure of 10 operational dams.The mathematical model is also used to simulate the process of breach evaluation.Based on statistical indices,comparison of the results,and sensitivity analysis,the developed equations can better express the susceptibility of materials to erosion and their application can minimize downstream vulnerabilities.

Simulation of dam breach development for emergency treatment of the Tangjiashan Quake Lake in China

The Tangjiashan Quake Lake is the largest quake lake triggered by the 5.12 Wenchuan Earthquake that happened on May 12,2008 in China,posing high risk of catastrophic flash flood hazards to downstream human life and properties.A physics-based numerical simulation approach is proposed for real-time prediction of dam breach development of the Tangjiashan Quake Lake in the case of emergency treatment.Bed erosion and lateral development of the dam breach are represented through accounting for the underlying physics including selective sediment transport and gravitational collapse.Conceptualized breach erosion model that involves few parameters enables quick calibration based on the monitored hydrological data in emergency analysis where fully geotechnical information about the barrier dam is not available.The process of dam breach development is found to be nonlinear in cascades due to the combined effects of headcutting and bank collapse.The agreement between the simulation results and the observed data shows the applicability of the present approach for emergency analysis of quake lakes.Limitations will arise in the situation where the soil composition of barrier dam is significantly inhomogeneous.Incorporation of circular arc failure for cohesive soil and lateral seepage in bank slope will also enhance its applicability to complex situations.

An approach to quick and easy evaluation of the dam breach flood

In the context of an impending dam failure, quick evaluation of dam breach flood is necessary. Previous studies provided an approach to calculate the dam breach hydrograph using an Excel spreadsheet based on the improved soil erosion model and numerical algorithm. However, calculation of the breach lateral enlargement requires the modeling of the successive collapse of the breach banks. It is time-consuming with special training, which is difficult to provide during an emergency. This study proposes that the lateral enlargement process can be modeled using a hyperbolic relationship with sufficient accuracy. Consequently, field engineers can perform the dam breach analysis along with the sensitive study for a target case within 1 h in an Excel spreadsheet which is self-tutorial. This paper presents this easy and quick approach based on only fifteen input parameters that can be determined based on the experience. This approach can also be used for the preliminary study when a dam safety planning work is undertaken.

Cascading dam breach process simulation using a coupled modeling platform

This study evaluates the possibility of a cascade failure by developing a coupled breach-modeling platform based on onedimensional flow modeling of the river channel, flood propagation, regulation process of reservoir fluctuation, overtopping with breaching, and wave damping downstream. A hyperbolic model of the DB-IWHR was embedded into the platform to simulate the dam breaching process. Five breach models and software were used to calculate the Tangjiashan barrier lake breaching. The results of a sensitivity study were then compared with the measured data. The peak flow and the time of occurrence were confirmed to be predictable with a reasonable accuracy if the input values were within ranges appropriate for the model. The approach was applied to a case involving two layout planning schemes for a cascade of rock-filled dams under extreme operating conditions. The probability of the failure of a key control cascade downstream caused by a continuous cascade breach upstream was simulated. Moreover, measures to prevent the transmission of risk by advance warnings were investigated. The proposed methodology and the discharge capacity measures provide guidelines to assess the risk to a cascade of dams under extreme operating conditions and offer support for the design criteria of unusual discharge structures for very large dams.

A simplified physically-based breach model for a high concrete-faced rockfill dam:A case study

A simplified physically-based model was developed to simulate the breaching process of the Gouhou concrete-faced rockfill dam(CFRD),which is the only breach case of a high CFRD in the world. Considering the dam height, a hydraulic method was chosen to simulate the initial scour position on the downstream slope, with the steepening of the downstream slope taken into account; a headcut erosion formula was adopted to simulate the backward erosion as well. The moment equilibrium method was utilized to calculate the ultimate length of a concrete slab under its self-weight and water loads. The calculated results of the Gouhou CFRD breach case show that the proposed model provides reasonable peak breach flow, final breach width, and failure time, with relative errors less than 15% as compared with the measured data. Sensitivity studies show that the outputs of the proposed model are more or less sensitive to different parameters. Three typical parametric models were compared with the proposed model, and the comparison demonstrates that the proposed physically-based breach model performs better and provides more detailed results than the parametric models.

考虑人体与水流相互作用的溃坝洪水生命损失评估模型

溃坝洪水会给下游人民群众造成巨大的生命损失,开展溃坝洪水造成的生命损失风险定量评估对应急抢险救灾具有重要的现实意义。本文在已有生命损失贝叶斯网络HURAM1.0模型基础上,引入了人体稳定性物理模型,考虑人体与水流相互作用关系,对处于洪水中的人先进行稳定性判定,并进行溺水判定,运用蒙特卡洛模拟方法,综合了水深和水流速对生命损失的影响,建立HURAM2.0模型;并将该模型应用于唐家山堰塞坝溃坝洪水生命损失分析。结果表明:HURAM2.0模型建立了水流流速对生命损失影响的定量关系,更精确地刻画了人体在水流中的稳定性和求生能力,相比HURAM1.0模型对较强洪水强度条件下的生命损失预测结果更准确。同时,在本文建立的模型中,除水深度、洪水严重程度变化不大,其余变量的敏感性均有所上升,其中居民区住宅层数、在建筑物中庇护情况和溃坝时长等变量对模型计算结果的最大影响程度分别增加142%、95%和93%,加强了模型在低、中、高3类洪水强度下的解释性,与HURAM1.0相比在贝叶斯反演分析中更占优势。在唐家山堰塞坝溃坝风险分析中,HURAM2.0能区分出不同水流速条件下的生命损失,更符合实际情况,即开挖泄流槽前风险大、死亡率高,在现场勘测和开挖泄流槽后风险及死亡人数大大降低,建议结合预警疏散以降低生命损失风险。

考虑超标准洪水作用的沥青心墙坝溃决生命损失评估模型

抗冲刷能力更强的沥青心墙坝一旦遭遇超标准洪水,将面临溃决风险,对下游人民造成严重威胁。现有针对沥青心墙坝的溃决生命损失研究尚属匮乏,亟需开展生命损失评估。本文分析超标准洪水作用下沥青心墙坝的溃决特征,考虑生命损失影响因素之间的相互作用过程,基于溃决洪水致灾机制构建生命损失定量评估模型,实现溃决生命损失的快速定量分析;通过方法对比和敏感性分析,明晰不同影响因素对溃决生命损失的作用规律。将模型应用于新疆射月沟溃决案例发现:溃决洪峰流量为3320 m^(3)/s,溃决历时3.35 h,与实际结果相符;生命损失定量模型分析结果为31人,与实际误差在11%以内,优于其他损失模型;风险人口的敏感性指数I_(max)和I_(min)值最大,分别为1.436、0.486,是射月沟溃决生命损失最重要的影响因素,其他依次为洪水严重性、是否撤离、警报时间、淹没范围。

堰塞坝溃决参数及其寿命预测

堰塞坝溃决洪水对下游影响区域的人民生命财产、基础设施以及生态环境构成严重威胁,提高堰塞坝溃决参数及其寿命预测的准确度是应急处置的迫切需求。本文对全球1957组堰塞坝案例分别进行地理、统计学分析,在得到溃决参数主要影响因素的基础上,选取数据库中拥有完整信息的48组案例,利用非线性回归方法分别建立了洪峰流量、破坏深度、溃口顶宽、溃口底宽和溃决时长的预测模型,其均具有较高的拟合程度。之后分析了堰塞坝溃决参数的敏感性,结果显示坝高对溃决过程有显著影响。此外,基于19组寿命信息充分的案例,使用不同自变量和算法分别建立了蓄水阶段持续时间、溢流阶段持续时间的预测模型,并采用加权融合法提出了相应的融合模型。该成果可为量化评估堰塞坝溃决过程参数和寿命预测提供参考。

梯级水库群溃坝洪水风险分析——以澜沧江上游为例

梯级水库的建设是开发利用我国丰富水能资源、保障国家能源安全、实现减排目标的重要途径.但是由于部分水库结构老化、地势险峻以及近几年极端天气频发等原因,极有可能造成单坝溃决,继而引起梯级连溃,最终使整条流域系统瘫痪,为下游城镇带来不可估量的经济和生命损失.为准确预测梯级连溃发生后的危险程度及影响范围,基于心墙坝漫顶溃坝数学模型和HEC-RAS软件提出了梯级连溃地貌特征演变及洪水演进计算方法,并应用于澜沧江流域梯级水库RM-XW水电站大尺度连溃分析.结果表明,在遭遇1.4倍超标准洪水的情况下,RM水电站发生漫顶溃决,溃决过程中,心墙发生四次折断,并伴随溃口迅速扩张以及溃决流量激增,最高峰值流量达699986.5 m^(3)/s,溃决洪水演进至下游,使WNL-XW水电站相继发生漫顶.河道距离、坝型特征和坝体物理参数是影响梯级连溃过程中溃决流量大小的重要因素.

基于NWS BREACH的唐家山堰塞坝泄流过程模拟

NWS BREACH模型是目前国内外模拟土石坝或堰塞坝漫顶及管涌破坏最常用的数学模型。基于唐家山堰塞坝的实测资料,建立了唐家山堰塞坝漫顶泄流过程数学模型,并通过现场监测得到的流量过程和库水位变化资料验证了所建立模型的合理性。对模型中的重要参数进行了敏感性分析,研究了坝料平均粒径、冲蚀率、下游坝坡坡比3个参数对模型计算结果的影响,表明坝料冲蚀率和下游坝坡坡比对泄流过程影响显著。研究成果对堰塞坝除险和洪水风险评估具有指导意义。

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。

Sequential Damming Induced Winter Season Flash Flood in Uttarakhand Province of India

204 persons were killed while two hydropower projects located in close proximity at Rishiganga(13.2 MW),and Tapoban(520 MW)were damaged in Dhauliganga flood of February 7,2021 in the Indian Himalaya.This incidence occurred during the winter season when the discharge of the glacier fed rivers is minimal,and no rain was experienced in the region around the time of the flood.Despite discharge of the main river,Rishiganga,not involved in the flood due to damming upstream of its confluence with Raunthi Gadhera,based on field evidences massive volume of around 6 million cu m water involved in this flood is attributed to sequential intermittent damming at three different places;(i)Raunthi Gadhera was dammed first in its upper reaches,(ii)Rishiganga river was then dammed to the north of Murunna,and(iii)finally Dhauliganga river was dammed around Rini village to the upstream of its confluence with Rishiganga river.Lacking warning system only enhanced the flood-induced devastation.Legally binding disaster risk assessment regime,together with robust warning generation,and dissemination infrastructure are therefore recommended for all major infrastructure projects.

BREACH模型与MIKE21模型在溃坝风险中的耦合分析

BREACH模型常用来模拟水库大坝漫顶及管涌溃坝模式并获取溃口流量与时间关系,MIKE21模型常用来模拟湖泊、河口、海湾等二维水动力学并获取洪泛区内洪水风险信息要素,两大模型耦合分析在保障水库大坝安全运行及风险管理方面发挥了积极作用。以BREACH模型模拟溃口流量动态数据过程与溃口演变尺寸为基础,通过Arc GIS预处理地形文件、工程建筑物参数与水文数据,构建MIKE21二维水动力学模型并计算网格差值空间,利用Flow Model模块生成溃坝洪水模拟文件,采用判别溃口流量差值是否满足精度要求的迭代法来耦合两大模型,最终结合所要分析水库大坝的工程概况,计算不同风险情况下的水库大坝溃坝洪水淹没水深与范围,进而模拟溃坝洪水演进过程。该方法已成功应用于郑州常庄水库风险分析,结果表明,该方法能客观反映溃坝洪水行洪情况,使用方便,为水库大坝运行管理与应急处置提供了一定的技术支持。

Breach模型与River2D模型在土石坝溃坝中的耦合分析

Breach是一个用于对土石坝进行溃坝分析以获取时间和流量关系的模型,River2D是一个用于模拟下游洪泛区内溃坝洪水演进以获取全要素风险信息的模型。两个模型的耦合分析在保护水库的安全及管理水库的运行方面有着预防的作用。

A framework of numerical simulation on moraine-dammed glacial lake outburst floods

Glacial outburst floods(GLOFs) in alpine regions tend to be relatively complicated, multi-stage catastrophes, capable of causing significant geomorphologic changes in channel surroundings and posing severe threats to infrastructure and the safety and livelihoods of human communities. GLOF disasters have been observed and potential hazards can be foreseen due to the newly formed glacial lakes or the expansion of existing ones in the Poiqu River Basin in Tibet, China. Here we presented a synthesis of GLOF-related studies including triggering mechanism(s), dam breach modeling, and flood routing simulation that have been employed to reconstruct or forecast GLOF hydrographs. We provided a framework for probability-based GLOFs simulation and hazard mapping in the Poiqu River Basin according to available knowledge. We also discussed the uncertainties and challenges in the model chains, which may form the basis for further research.

基于DL Breach模型的尾矿库溃坝影响数值分析

尾矿库溃坝事故危险性大,尚缺乏有效的溃坝沙流预测机制。基于DL Breach模型,提出一种尾矿库溃坝沙流的计算方法,依据尾矿下泄沙流的性质,结合尾矿库溃坝的工程经验及规范,建立溃坝沙流运动模型,计算溃坝过程中的主要影响参数,分析下泄沙流的淹没范围、淹没深度的演变规律。结果表明,溃坝下泄沙流的堆积深度总体上先增大后减小,下泄沙流在钻天道沟谷内淹没深度较大,淤积较多,最大堆积深度达2.48 m;随着与初期坝的距离逐渐变大,下游的3#桥处的最大淹没深度不超过1 m,整体安全风险可控。利用该模型进行尾矿库溃坝数值模拟,可以预测尾矿坝溃决可能引起的灾害,对尾矿库的安全运行具有指导意义。