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.

Numerical Simulation of Dam-Break Flooding of Cascade Reservoirs

Previous studies at home and abroad have mainly focused on single dam-break, and little attention has been paid so far to the dam-break of cascade reservoirs.Multi-source flooding, which can lead to three-dimensional turbulent phenomena and superposition effects, is the main difference between the dam-break of cascade and single reservoirs. Detailed descriptions of the coupled numerical simulation of multi-source flooding have little been reported, and the initial wet riverbed is rarely considered in current models. Therefore, in this paper, a method based on the three-dimensional k-ε turbulence model coupled with the volume-of-fluid method is proposed to simulate the dam-break flooding of cascade reservoirs. The upstream river, reservoir, and downstream river are connected by the internal boundary method, and the initial conditions,including river flow and reservoir water, are determined according to the results of the numerical simulation. Coupled numerical simulation of different dam-break flooding is then achieved. The present work solves the challenges presented by the enhancement and superposition of natural river flow, upstream flooding, and downstream flooding.This paper provides a theoretical basis for future studies on the dam-break flood routing of cascade reservoirs.

Life Loss Estimation Based on Dam-Break Flood Uncertainties and Lack of Information in Mountainous Regions of Western China

Compared with urban floods, dam-break floods are associated with greater uncertainties, including variable dam-break modes and hydrological characteristics, so conventional flood estimation methods cannot be directly applied in the estimation of dam-break flood loss. In particular, there is scant information regarding the conditions of affected area and hydrological characteristics in southwest China. In this paper, we introduce an integrated model for estimating flood loss that is adapted to the mountainous regions of southwestern China in light of the relative lack of available information. This model has three major components: a basic information model, a dam-routed flood propagation simulation model, and a loss estimation model. We established the basic information model despite the relative lack of available information using 3S technology [remote sensing(RS); geographical information system(GIS); global positioning system(GPS)], data mining technology, and statistical analysis techniques. Our dam-routed flood propagation simulation model consists of major hydrologic processes and their governing equations for flow propagation, which we solve using finite-difference schemes. In this model, the flood propagation area is divided into grids and each grid is determined by the characteristic parameters obtained from the propagationsimulation. We present a case study of the Lianghekou hydropower station in Sichuan Province, China to illustrate the practical application of this integrated model for life loss estimation.

The Two Main Mechanisms of Glacier Lake Outburst Flood in Tibet,China

With the global warming,the disasters of Glacier Lake Outburst Flood(GLOF) have taken place frequently in Tibet in recent years and attracted more and more attention.A systematic survey was conducted on the 19 GLOFs in Tibet to study their two main mechanisms.Investigations indicated that all the events occurred in end-moraine lakes,and the outburst occurred partially and instantly.And the breach had the shape of an arc or a trapezoid in overflow outburst and its top width was 3-5 times more than the height.The two main mechanisms of GLOFs in Tibetan end-moraine Lake were overflow and piping,and the overflow mechanism caused by iceberg collapse was dominated in most cases.A formula was proposed to calculate the critical thickness of iceberg tongue that determines the collapse.Granular analysis of the moraine materials revealed that seepage deformation is crucial in the outburst process.Finally,we conducted a case study of the Guangxiecuo Lake to show its possible process of outburst and estimated the peak discharge of the resulted flood.

Modelling Chorabari Lake outburst flood, Kedarnath, India

In this study, the Glacier Lake Outburst Flood(GLOF) that occurred over Kedarnath in June 2013 was modeled using integrated observations from the field and Remote Sensing(RS). The lake breach parameters such as area, depth, breach, and height have been estimated from the field observations and Remote Sensing(RS) data. A number of modelling approaches, including Snow Melt Runoff Model(SRM), Modified Single Flow model(MSF), Watershed Management System(WMS), Simplified Dam Breach Model(SMPDBK) and BREACH were used to model the GLOF. Estimations from SRM produced a runoff of about 22.7 m3 during 16–17, June 2013 over Chorabari Lake. Bathymetry data reported that the lake got filled to its maximum capacity(3822.7 m3) due to excess discharge. Hydrograph obtained from the BREACH model revealed a peak discharge of about 1699 m3/s during an intense water flow episode that lasted for 10–15 minutes on 17 th June 2013. Excess discharge from heavy rainfall and snowmelt into the lake increased its hydrostatic pressure and the lake breached cataclysmically.

PRELIMINARY STUDY ON FLASH FLOODS IN TARIM RIVER BASIN

Flash floods are the important events of the hydrological regime of rivers in arid areas. In the Tarim River, northwestern china, flash flood are being monitored. The observed data and investigation demonstrate the difference in time, place, fraquency and intensity of their occurrences. In this paper two main flash fled are put forward, they are rainstorm flash flood (RFF) and glacier lake outburst flood(GLOF). Two cases of flash flood in the two tributaries of the Tarim River presented in this paper. It analyses and compares the causes and the development of the two kinds of flash floods.Through further discussion about influence of flash floods on the main channel of the Tarirn River, conclusion can be drawn that the greatest flood in record of the main channel come from the GLOF of the upper reaches of the Kunmalik River, especially augmented by great ablation flood. Finally the advantages and disadvantages from flash floods to the environment of the catchment are demonstrated in the paper.

Overview of an early warning system for Glacial Lake outburst flood risk mitigation in Dudh-Koshi Basin, Nepal

Natural disasters inflict severe damage on almost the entire spectrum of social and natural habitats. This ranges from housing and shelter, water, food, health, sanitation to information and communication networks, supply of power and energy,transportation infrastructure, and others. Nepal is a risk prone country for Glacial Lake Outburst Flood(GLOF). GLOFs exist as major challenges as they repeatedly cause a heavy toll of life and property. During such a disaster, major challenges are indeed the protection of life, property and vital life-supporting infrastructure. Any delay or laxity in disaster relief can escalate the magnitude of distress for the victims. Thus, rather than trying to take curative measures, it is better to minimize the impacts of GLOF. These measures subsequently help in reducing the magnitude of death and casualties due to a GLOF event. This reduction of impact is often achieved by optimizing preventive measures. For applying necessary deterrent measures, it is essential to disseminate information about the danger beforehand. Early Warning System(EWS) is an important step for such information dissemination for GLOF disaster management and helps to anticipate the risk of disaster and disseminate information to lives at risk. It is impossible and impractical to reduce all GLOF risks, but it is possible to reduce several impacts of a GLOF through the implementation of the EWS. This paper presents the design and implementation of an EWS for monitoring potential outbursts of a glacier lake in the Dudh-Koshi Basin, Nepal.

Identifying hot spots of long-duration extreme climate events in the northwest arid region of China and implications for glaciers and runoff

China’s Northwest Arid Region(NAR),with dry and cold climate conditions and glaciers widely developed in the high mountains,provides vital water resources for Asia.The consecutive cold,warm,dry and wet days have much higher impacts on the water cycle process in this region than extreme temperature and precipitation events with short durations but high intensities.Parametric and nonparametric trend analysis methods widely used in climatology and hydrology are employed to identify the temporal and spatial features of the changes in the consecutive cold,warm,dry and wet days in the NAR based on China’s 0.5°×0.5°meteorological grid datasets of daily temperature and precipitation from 1961 to 2018.This study found that(1)the consecutive cold days(Cold Spell Duration Indicator,CSDI),and the consecutive dry days(CDD)decreased,while the consecutive warm days(Warm Spell Duration Indicator,WSDI),and the consecutive wet days(CWD)increased from 1961 to 2018,(2)and the eastern Kunlun Mountains were the hot spots where all of these consecutive climate indices changed significantly,(3)and the changes in these consecutive climate indices were highly correlated with the rise in the Global Mean Land/Ocean Temperature Index.The results indicated that winters tended to warmer and dryer and summer became hotter and wetter during 1961–2018 in the NAR under the global warming,which can lead to the sustained glacier retreat and the increase in summer runoff in this region,and the eastern Kunlun Mountains are the area where could face high risks of water scarcity and floods if the changes in these climate indices continue in the future.Given the vulnerability of the socio-economic systems in the NAR to a water shortage and floods,it is most crucial to improve the strategies of water resources management,disaster prevention and risk management for this region under climate change.

青藏高原冰湖溃决灾害隐患识别、发育规律及危险性评价

青藏高原是全球冰湖溃决灾害发生最频繁的区域之一,冰湖溃决对人类及工程建设安全造成严重威胁。以2015-2018年Landsat 8 OLI_TIRS等遥感影像及数据为基础,对青藏高原40000余条冰川10 km范围内且面积大于900 m^(2)的冰湖进行了遥感解译,分析了冰湖分布与发育特征,建立了冰湖溃决隐患的识别指标体系,利用突变级数法(CPM)对隐患点进行了危险性分级评价。结果表明:①青藏高原发育冰湖16481处,海拔分布在5000~5500 m之间的冰湖占总量的43.69%;面积集中在100~500 km^(2)之间的占总量的47.40%;行政分布上主要分布在西藏自治区,有12664个,占总量的76.84%;流域上主要分布在雅鲁藏布江流域,有8321个,占总量的50.49%。②识别出冰湖灾害隐患点369个,其中低危险点126个,中危险点177个,高危险点66个。③冰湖溃决隐患点面积多为0.1~0.2 km^(2);海拔主要分布在5000~5500 m之间;与母冰川距离大多小于100 m;冰碛坝宽度一般小于300 m,背水坡坡度大多小于50°;冰湖溃决隐患点的母冰川冰舌端坡度分布在10°~20°之间;绝大多数冰湖溃决的方向朝向北方。

西藏冰湖溃决频次与径流峰值流量相关性分析

冰湖溃决事件频繁发生,严重阻碍西藏自治区区域社会经济发展,影响社会稳定。随着气候变暖,冰川减薄后退,冰川径流量增大,冰湖溃决风险上升。基于西藏自治区东南地区的嘎隆拉冰川径流观测资料,分析了2017—2019年消融期间5—9月冰川径流变化特征,探讨了西藏1931—2020年冰湖溃决事件发生的频次与径流峰值流量的关系。结果表明:在1931—2020年,西藏地区共发生冰湖溃决事件32次,集中在5—9月发生;在旬变化上,极大值频次呈单峰结构,在7月上旬频次最高;冰湖溃决频次与径流峰值流量显著相关,相关系数为0.673,随着径流增大,冰湖溃决发生的频次逐渐增大。在气候变暖的背景下,冰川融化引发的冰湖溃决灾害应引起重视,要加强冰川消融径流观测及冰湖水位的监测,进行冰湖溃决洪水预报。

Preventing the Deluge: Climate Change, the Four Spheres, Interactions, and Causalities

Climate change means water change, and the impacts of climate change cause not only global sea levels to rise, but also elicit dangerous levels of coastal and mainland flooding. This study relates the effects of climate-change-induced sea level risings to several harmful, and sometimes preventable, factors causing floods. One topic discussed here will be the ocean’s current (more specifically, “The Atlantic Meridional Overturning Current”) as it continues to warm with increasing temperatures. In addition to discussing the effects of the AMOC, it also relates the increasing causes that are contributing to flooding, plus the proliferation of melt from ice sheets, ice caps, and glaciers, which inevitably contributes to the devastating effects of flooding on coastal communities, destroying habitats and contributing to the extinction of both aquatic and land animals, and even impacting human infrastructure and livelihoods. This examination additionally presents the serious implications that climate change and flooding have had on the planet’s freshwater resources and reserves, which are being further destroyed by the added influx of salt water, causing water to then be treated with aquifers, an energy-intensive and highly expensive process. Lastly, this paper provides several suggested possibilities for curbing some of the harmful effects humans have already had on contributing to climate change, as well as the environmental factors that have further caused dangerous levels of flooding.

溃坝洪水研究进展

溃坝洪水研究的目的是计算溃决坝址的流量、水位过程线,并向下游作洪水演进得到沿程的流量、流速、水位、波前与洪峰的到达时间,评估下游洪水淹没损失情况,以便于采取措施,降低洪水风险。从溃坝水流理论研究、溃坝问题的试验研究、溃坝模拟及洪水在下游演进这3个方面对溃坝洪水研究进行了综述,回顾和总结了国内外溃坝洪水研究的发展历程、已取得的成果和近些年的进展,提出了将来要研究的重点,并对研究前景进行了展望。目前溃坝理论的数值求解发展迅速,由试验提出了溃坝机理,研究不断模型化;但高强输沙理论未建立,溃口冲刷过程未能准确表达,对梯级溃坝和冰湖溃决洪水研究较少。今后应加强溃坝水流理论研究,开展大尺度、多库溃坝模型试验研究,积极做好梯级溃坝和冰湖溃决洪水模拟,进一步建立快捷可靠的区域溃坝洪水预报系统。

西藏年楚河冰川终碛湖溃决条件及洪水估算

利用遥感卫片和航片资料查清了西藏年楚河上游冰川终碛湖的数量、大小和分布，并对其中最大的３个冰湖进行了分析，确认其中的白湖为一典型危险冰湖，只要有合适的气候条件就可能发生溃决。通过冰湖实地考察，验证了室内分析成果，补充收集计算所需的资料，采用美国天气局的ＢＲＥＡＣＨ模型和计算机程序。

百年来天山阿克苏河流域麦茨巴赫冰湖演化与冰川洪水灾害

阿克苏河源区的冰川融水和冰湖溃决洪水,对我国境内阿克苏河乃至整个塔里木河的径流补给及下游的防洪安全都有着举足轻重的作用.萨雷扎兹-库玛拉克河的麦茨巴赫冰川湖(Merzbacher Lake)为众多冰川湖中最大的一个,同时又是频繁发生突发性溃决洪水的冰湖,在1932-2008年的67a内发生溃决突发性洪水62次,其频率高达92.5%以上.随着气温的变暖,冰川减薄后退,冰川融水增多、冰湖库容增加,洪水总量在不断增大.冰川洪水的总量已经由1960-1970年代的1×108m3左右,增加到1990年以来的3×108～4×108m3,最高达5×108m3多;年最大流量1990年代较1950年代增多37%,洪水频率也在不断增加.库玛拉克河流域冰川物质平衡变化也对冰湖溃决洪水影响很大,冰川消融的越多,产生的冰川洪水洪峰也越大.随着全球气候进一步变暖,将会加大下游的防洪压力.所以,要加强冰川消融观测及冰湖水位的监测,建立预警系统,进行冰湖溃决洪水预报,为下游的防洪安全和水电安全运行提供科技支持.

近20a来西藏朋曲流域冰湖变化及潜在溃决冰湖分析

全球气候变暖,青藏高原冰川普遍处于退缩趋势,由此引发的冰湖溃决洪水的灾害也随之增加.通过对2000/2001年度卫星遥感数据解译结果和1987年国际联合考察的朋曲流域冰湖溃决洪水结果的分析,研究了近20a来朋曲流域内冰湖的变化.结果显示,该流域中的冰湖数量有减少,但冰湖的面积却在增加,这是同期全球气候变暖的结果.在提供了冰湖编目数据的基础上,识别了有潜在危险的冰湖,为冰湖溃决洪水早期预警系统提供了科学依据.

新疆叶尔羌河冰川湖突发洪水对气候变化的响应

利用1961—2008年的气象-水文资料,探讨了气候变化与叶尔羌河流域冰川湖突发洪水的关系.采用非参数Wilcoxon统计检验和Kendall的τ关联检验分析温度、降水变化与洪峰流量量变化的关联性和一致性;用Mann-Kendall法对气温、降水和洪峰流量>4000 m3.s-1突发性洪水的0℃层高度进行突变检验和趋势分析.结果表明:流域气温在1995年发生突变,且对冰川湖突发洪水发生起主导作用;降水突变不明显,对冰川湖突发洪水发生只起促进作用.自1880年以来,冰川湖突发洪水发生频率增加,与流域气温变化一致.1994年以来气温呈直线上升,洪水频率也呈显著增加趋势;冰川湖突发洪水发生频率与降水变化关系不明显;突发性洪水发生与其前8 d的0℃层高度显著上升密切相关.

基于遥感与GIS的朋曲流域冰川及冰湖变化研究

由于全球变暖,冰川正逐年退缩,随之引发的冰湖溃决洪水已不容忽视,但静态和孤立地研究冰湖已不能满足人们对冰湖信息的需求,本文基于20世纪70年代的地形图数据和2000年以来的ASTER遥感影像数据,使用GIS手段矢量化朋曲流域20世纪70年代和近期的冰川及冰湖的空间分布,并进行编目。对于获得的空间数据分析结果表明,在过去30年里该区冰川面积减少近9％,冰湖面积则增加了13％,在此基础上比较二者的联系和变化,识别出了24个可能发生溃决的冰湖,这为朋曲流域建立一套冰湖溃决预警系统提供依据;同时,对于研究其他类似地区的冰湖溃决现象也具有指导意义。

西藏年楚河冰川湖考察

年楚河流域地处喜玛拉雅山北坡,满拉水利枢纽位于年楚河中上游,控制流域内分布有众多的冰川终碛湖,经分析其中的白湖为危险冰湖,具有溃决的可能.为进行白湖溃决洪水的估算,解决计算模型的有关参数,对白湖、桑旺湖、黄湖的水文气象特性和地理、地貌特征等进行实地考察,直观的认识了冰川终碛湖,并取得了有价值的资料.

冰湖溃决灾害风险研究进展及其展望

系统回顾了国内外冰湖溃决灾害风险研究现状,结果显示,以往冰湖溃决灾害风险评估研究过多集中于冰湖溃决致灾诱因、特征,溃决危险性评价和溃决概率预测以及溃决洪峰流量及其演进模拟研究等自然风险方面,而承灾区经济社会系统脆弱性、暴露性和适应性风险研究却较为缺乏。因此,开展冰湖溃决灾害综合风险研究,不仅对冰湖溃决危险性评价意义重大,而且对于下游承灾区防灾减灾和预警体系建立也具有重要的理论参考价值。

希夏邦马峰东坡冰川与冰川湖泊变化遥感监测

1977—2003年的遥感影像显示,希夏邦马峰东坡的冰川在迅速退缩,而其相应的冰川湖泊在迅速增大.南部的吉葱普冰川每年的退缩速度57 099 m2,冰舌退缩48 m.a-1,相应的卢姆池米冰湖面积增加速度大约为79 048 m2.a-1;北面的热强冰川退缩速度在63 224 m2.a-1,冰舌退缩71 m.a-1,相应的扛西错冰湖面积增加约73 425 m2.a-1.从这两个冰湖的类型和变化分析,认为其具有发生冰川湖泊溃决洪水的潜在危险.