大坝防洪时变风险率研究

在时变效应基础上,分析了影响大坝防洪安全各种随机量的时变特性,进行了时变随机量定量评估方法的研究。将Bayes统计推断方法引入防洪时变随机量的评估中,有利于克服经典统计学方法的局限性,具有一定的实用性和可操作性。以大坝漫顶时变风险率分析为例,讨论了泥沙淤积、泄洪闸门事故等的时变作用,采用概率统计方法和Bayes推断的方法,进行了时变随机量的定量评估,分析了时变效应对大坝防洪安全的影响。     

基于蒙特卡罗法的缓变型防洪风险分析

针对水库大坝服役期的水文、水力不确定性因素及工程结构风险等因素的影响,在时变效应理论的基础上,构建了时变随机变量量化的函数模型,并提出缓变型防洪风险分析模型;同时运用蒙特卡罗法(Monte Carlo method)来求解风险率,进而定量的分析大坝的防洪安全。以池潭水电站为例,利用监测资料序列构建坝前最高水位与坝顶高程的缓变历程的函数关系,结果分析表明:大坝继续使用期内的防洪风险率满足现行规范设防标准,可为大坝的防洪风险评估提供科学依据,亦可将该分析方法拓展至其他服役水利工程的防洪安全评估。     

水库汛限水位动态控制的风险评估

水库汛限水位的动态控制实质上是一种风险调度.在对短期水文预报不确定性分析的基础上,提出了将洪水预报精度等级评定指标转化为人库洪水过程的随机特征值的方法,利用水库调洪演算的随机微分方程,分析了不同预报精度等级和不同预见期条件下水文预报误差的传递与演化过程,并建立了水库汛限水位动态控制的风险率计算模型,以定量评估抬高汛限水位对水库大坝和下游河道防洪安全的影响.算例分析表明,汛限水位的抬高将使水库和下游河道的防洪风险率增大,通过提高预报精度和延长预见期可以降低由汛限水位拾高所增加的风险率.     

基于蒙特卡洛法的水库汛限水位动态控制风险分析

为定量评估汛限水位动态控制对水库大坝防洪安全的影响,以基于预报预泄的水库洪水动态水位控制为研究对象,分析预报入库水量的误差、预泄采用的连续无雨天数,以及预泄采用的洪水预报预见期这三个不确定性因子给水库洪水动态水位控制带来的附加防洪风险和随机分布特征,利用蒙特卡洛随机模拟研究了汛限水位动态控制风险率的计算方法。以河口村水库为例,采用蒙特卡洛模拟方法分析了水库汛限水位动态控制的风险率,说明了该方法研究水库汛限水位动态控制风险的可行性。     

水库防洪预报调度的风险分析

本文从水文预报误差的不确定性分析出发，将短期洪水预报精度评定指标转化为入库洪水过程的随机特征值，并引入水库调洪演算随机数学模型，从而实现水文预报风险向预报调度风险的转化，为定量考察预报调度风险率、合理选择动态的汛限水位提供了科学的依据。通过这一方法论证了水文预报精度对水库防洪预报调度风险率的影响，表明提高水文预报精度将有利于降低水库调洪风险率。     

防洪预报调度方式综合特性风险率计算方法研究

水库防洪预报调度中的多种不确定性因素是风险产生的根本原因。分析水库防洪预报调度中不确定性因素的随机性、模糊性及灰色性,并在已有的防洪预报调度方式随机风险率计算方法的基础上,提出了随机-模糊、随机-灰色及综合特性风险率的计算方法,研究了水库实施防洪预报调度方式相对于常规调度方式水库风险率的变化。桓仁水库的应用研究表明,防洪预报调度方式综合特性风险率计算方法是可行的,相对于常规调度方式并未增加水库的防洪风险。     

防洪设计标准和大坝的防洪安全

防洪设计标准的选择就其本质而言是风险决策问题．本文着重分析了这一标准的内涵及其对大坝防洪安全的影响．采用事故树分析方法，逐层顺序讨论了漫坝失事事故的形成，定量给出了相应的防洪风险率，校核了现有大坝的总体设防水准．在此基础上，论证了合理选择大坝防洪设计标准的原则和方法．     

两变量防洪风险模型研究

针对传统设计洪水过程线推求方法所存在的局限性,采用Copula函数建立洪峰和洪量的两变量联合分布,对洪峰和洪量设计值进行联合随机模拟,同时根据随机模拟值与实测洪水过程特征量的相似性来选择典型洪水过程,并基于多变量重现期,建立了两变量防洪风险分析模型。以清江流域隔河岩水库为例,分析不同汛限水位对应的极限风险率和漫坝风险率。研究结果表明：① 隔河岩水库汛期运行水位可确定为193.6m,在预报长江将发生大洪水时,可将水位提前降低至192.2m,不会增加水库的防洪风险;② 当汛限水位继续抬高至194.0m时,尽管极限风险率变化不大,但漫坝风险率成倍增加。所提出的模型可以充分考虑洪水过程的随机性和不确定性,可为流域水库的防洪设计和安全运行提供参考。     

基于随机微分方程的大坝漫顶风险研究

考虑入库洪水的水文条件、出库泄流能力、库容与水位关系以及防洪起调水位等不确定性因素,基于随机微分方程对大坝的漫顶风险进行了量化分析。计算实例表明:运用随机微分方程进行水库的调洪演算中综合考虑了各种不确定性因素对库水位随机过程的影响,计算的大坝漫顶风险率更趋合理。     

汛限水位动态控制的防洪极限风险分析

综合考虑水文、水力不确定性因素对汛限水位控制下的水库防洪极限风险进行研究，采用随机模拟方法计算极限防洪风险率。应用一阶季节性自回归模型模拟多场入库洪水序列，考虑水力不确定性对泄洪能力的影响，在给定调洪规则下对不同汛限水位方案进行调洪，得到水库最高调洪水位和防洪极限风险率。实例结果表明：水文因素的随机性和防洪调度规则是水库防洪风险的主要影响因素，水力因素对防洪风险影响不大，同时得出了水库面临汛限水位所能承受的极限风险率，为决策者安全度汛提供一种参考依据。     

土石坝安全等级划分与防洪风险率评估

本文从土石坝安全等级评定和划分的有关规定出发,建立了防洪安全等级划分与风险概率的对应关系。根据风险率计算近似方法,校核率定了划分不同安全等级的风险率阈值和安全指数阈值,给出了不同安全等级土石坝的风险率区间,以实现大坝安全鉴定分级的定性评估与风险率定量计算的衔接。计算结果表明,土石坝的三种主要失事模式,包括洪水漫顶、滑坡失稳和渗流破坏,其安全等级划分的风险率阈值和安全指数阈值,大体维持在相同的水平上,略有差异。随大坝级别和安全等级的提高,风险率阈值减小,安全指数阈值相应增大。影响大坝安全的诸多不确定因素,包     

随机微分方程在泄洪风险分析中的运用

本文根据调洪过程中水库蓄洪量具有Ｗｉｅｎｅｒ过程特性的分析，建立了带有随机作用项的Ｉｔｏ随机微分方程，以描述和分析调洪过程中库水位的随机变化规律。在此基础上，给出了动态的泄风险表达，并通过Ｆｏｋｋｅｒ－Ｐｌａｎｃｋ向前方程，求解了与泄洪风险率紧密相关的库水位过程的概率密度分布。计算实例表明，运用随机微分方程进行水库的调洪演算，能够全面，正确地反映各种不确定性因素对库水位过程的影响，从而使泄洪风险分     

堰塞湖溃坝快速定量风险评估方法——以2014年鲁甸地震形成的红石岩堰塞湖为例

2014年8月3日云南昭通市鲁甸县发生6.5级地震,形成高83 m,库容2.6亿m³的红石岩大型堰塞湖,严重威胁上下游生命财产安全。由于震后地质条件恶劣,道路堵塞,环境危险,且堰塞坝寿命极短,现有方法很难在有限时间内对堰塞坝进行快速且定量风险评估。本文提出一套基于最基本的堰塞坝几何参数、河道三维地形信息和人口分布数据的快速定量风险评估方法,可以实现任何堰塞坝突发区域内的溃坝、洪水演进和生命损失分析:首先采用地理信息工具快速获取坝址、上下游河道三维地形信息;然后采用统计模型和HEC-RAS软件模拟溃坝和洪水演进过程;最后采用风险分析模型计算得到下游生命损失。本文将该方法应用于红石岩堰塞湖案例分析发现:开挖泄流槽可以降低峰值流量和生命损失,但不能防止溃坝;开挖泄洪支洞后,可以避免在非汛期情况下发生溃决;但在极端洪水情况下(如百年一遇)仍会发生溃坝,并产生较大的洪水和生命损失,因此仍需要加固坝体,做好观测,并准备好应急预警和疏散预案。本方法可针对突发堰塞湖进行快速定量的风险评估,为堰塞湖的应急管理和决策提供依据。     

模糊层次分析法在淤地坝风险评价中的应用

淤地坝是黄土高原地区治理水土流失有效的水利工程措施,其在减少入黄泥沙、淤地造田、防洪减灾、改善生态、促进经济发展等方面发挥着重要作用。但淤地坝的水毁灾害时有发生,建立淤地坝的风险评价体系迫在眉睫。经调研分析,对淤地坝风险进行识别,建立了现状风险、管理风险、失事后果的3层次9指标的淤地坝风险层次分析模型。运用模糊层次分析法对淤地坝各风险的权重进行了计算,并且对淤地坝的安全进行了综合评价。结果表明：模糊层次分析法有效地改进了层次分析法的一致性问题,并且可以简便地对淤地坝的风险进行评价,为淤地坝的风险评价提供了一种新思路。     

基于MIKE模型的南丰景观坝行洪能力影响分析

近年来洪水引发的灾害日益凸显,造成的破坏持续增多,因此进行河道行洪能力影响分析对于加强河流的洪水管理及减少洪水带来的损失具有十分重要的意义。为评价南丰景观坝的防洪安全,基于MIKE水动力软件中的MIKE11、MIKE21模块,构建盱江南丰段的一、二维数值模型,对景观坝建设前后20 a一遇设计洪峰流量进行洪水模拟,然后选取河道水位和流场等指标的变化,分析景观坝的建设对研究河段河道行洪能力影响。研究结果表明,在20 a一遇洪水情况下景观坝上游壅水里程约3 km,且最大壅高约为0.1 m,同时两岸基本无漫堤险情;河道流态无明显变化,但局部流场产生发生一定变化,其中曾巩大桥等四座大桥桥墩处流速有不同程度的减小并产生局部回流,景观坝坝址处流速略有增大。     

Flood risk control of dams and dykes in middle reach of Huaihe River简

Three stochastic mathematical models for calculation of the reservoir flood regulation process, river course flood release, and flood risk rate under flood control were established based on the theory of stochastic differential equations and features of flood control systems in the middle reach of the Huaihe River from Xixian to the Bengbu floodgate, comprehensively considering uncertain factors of hydrology, hydraulics, and engineering control. They were used to calculate the flood risk rate with flood regulation of five key reservoirs, including the Meishan, Xianghongdian, Nianyushan, Mozitan, and Foziling reservoirs in the middle reach of the Huaihe River under different flood frequencies, the flood risk rate with river course flood release under design and check floods for the trunk of the Huaihe River in conjunction with relevant flood storage areas, and the flood risk rate with operation of the Linhuaigang Project under design and check floods. The calculated results show that （l） the five reservoirs can withstand design floods, but the Xianghongdian and Foziling reservoirs will suffer overtopping accidents under check floods; （2） considering the service of flood storage areas under the design flood conditions of the Huaihe River, the mean flood risk rate with flood regulation of dykes and dams from Xixian to the Bengbu floodgate is about 0.2, and the trunk of the Huaihe River can generally withstand design floods; and （3） under a check flood with the flood return period of 1 000 years, the risk rate of overtopping accidents of the Linhuaigang Project is not larger than 0.15, indicating that it has a high flood regulation capacity. Through regulation and application of the flood control system of the Linhuigang Project, the Huaihe River Basin can withstand large floods, and the safety of the protected area can be ensured.     

Numerical Simulation of Flood Wave Propagation in Two-Dimensions in Densely Populated Urban Areas due to Dam Break

Dams are important structures having many functions such as water supply, flood control, hydroelectric power and recreation. Although dam break failures are very rare events, dams can fail with little warning and the damage at the downstream of the dam due to the flood wave can be catastrophic. During a dam failure, immense volume of water is mobilized at very high speed in a very short time. The momentum of the flood wave can turn to a very destructive impact force in residential areas. Therefore, from risk point of view, understanding the consequences of a possible dam failure is critically important. This study deals with the methodology utilized for predicting the flood wave occurring after the dam break and analyses the propagation of the flood wave downstream of the dam. The methodology used in this study includes creation of bathymetric, DEM and land use maps; routing of the flood wave along the valley using a 1D model; and two dimensional numerical modeling of the propagation and spreading of flood wave for various dam breaching scenarios in two different urban areas. Such a methodology is a vital tool for decision-making process since it takes into account the spatial heterogeneity of the basin parameters to predict flood wave propagation downstream of the dam. Proposed methodology is applied to two dams; Porsuk Dam located in Eski?ehir and Alibey Dam located in Istanbul, Turkey. Both dams are selected based on the fact that they have dense residential areas downstream and such a failure would be disastrous in both cases. Model simulations based on three different dam breaching scenarios showed that maximum flow depth can reach to 5 m at the border of the residential areas both in Eski?ehir and in Istanbul with a maximum flow velocity of 5 m/s and flood waves having 0.3 m height reach to the boundary of the residential area within 1 to 2 h. Flooded area in Eski?ehir was estimated as 127 km², whereas in Istanbul this area was 8.4 km² in total.     

Optimal Design of Check Dams in Mountainous Watersheds for Flood Mitigation

One of the measures for flood control is to construct a series of small barriers, known also as check dams, on tributaries of watershed stream network. Check dams are generally used in mountainous areas in order to control sediment transport and attenuate flood peak. In this paper, a simulation-based optimization model is developed to determine size, shape and the number of check dams for flood mitigation. HEC-HMS model is used to simulate watershed rainfall-runoff process considering various check dam designs. The model is coupled with a multi-objective evolutionary algorithm, called non-dominated sorting differential evolution (NSDE), to find the trade-off solutions considering three objective functions: 1) minimizing the investment cost, 2) minimizing the flood peak discharge and 3) maximizing the time to peak discharge. The proposed model is applied to a mountainous watershed in Iran and (near) optimal strategies, including the suitable number of check dams in each sub-watershed, and optimal dam size (e.g. optimal height, bottom width and side angles) in each sub-watershed are obtained. The results show that cost-effective designs can decrease peak discharge up to 53%, 54 and 54% corresponding to 2-yr, 5-yr and 10-yr flood return period scenarios, respectively. In addition, the check dams can also increase the time to peak for up to 88%, 81 and 77%, corresponding to 2-yr, 5-yr and 10-yr flood scenarios, respectively.