2018年雅鲁藏布江米林县加拉堰塞湖考证

加拉堰塞湖威胁其上下游的人口安全、城镇设施及生态环境。加拉堰塞体地处无人区,没有对外交通,调研困难,因此形成机制研究甚少。作者于2019年3月调研了堰塞湖现场,通过对残留堰塞体地形实测,堰塞体岩性及结构、沿途堰塞湖水毁现象调查,结合堰塞体粒度特征,查明了加拉堰塞体的物质组成、堰塞湖形成过程及湖区灾损机制。调查发现雅鲁藏布江下游左岸色东浦沟冰碛物3次活动堵塞河道形成堰塞湖,并于10月19日、31日两次溃决,溃口流量分别达到32000m3 ·s-1和19000m3 ·s-1。前两次活动入江体积达6500×104m3,堰塞体高度88m,蓄水至6.0×108m3后发生第1次溃决。第3次活动入江体积约1000×104m3,堰塞体垭口高度约67m,蓄水至3.26×108m3后发生第2次溃决,体现了源于冰碛物堆积、混杂大量冰块、含水率极高的类似泥石流堆积堰塞体的独特溃决机理和洪水特征。雅鲁藏布江大峡谷河段堰塞湖堵江事件频发,通过加拉堰塞湖形成过程、溃决机理研究,可以为本区域堰塞湖灾害应对提供参考。     

红石河堰塞湖漫顶溃坝风险评估

四川省青川县红石河堰塞湖是2008年5月12日汶川大地震形成的34座大型堰塞湖之一,是由东河口滑坡堵塞红石河形成的。该堰塞体高度约50 m、宽度约250 m、顺河向长度约500 m、形成的最大库容约400万m3。本文作者对红石河堰塞体做了较详尽的现场试验,包括土的冲蚀试验、土的基本物性试验等。基于现场试验数据,对土的冲蚀性和漫顶溃坝风险做了详细的分析。结果显示,从土的抗冲蚀性角度考虑,只要有水溢出就会有土体被冲蚀,这说明红石河堰塞体的漫顶溃决可能性较高。本文还提出经验公式来预测红石河堰塞体漫顶的溃决时间,大约为4.5d,如果考虑到大石块对抗冲蚀稳定性的有利影响,这一数值会增大。此外,还研究了溃决深度随时间的变化规律。     

雅鲁藏布江色东普沟冰崩—堵江—溃决灾害数值模拟

为了揭示雅鲁藏布江色东普沟2018年10月17日冰崩—堵江—溃决灾害链的动力演化过程,基于Massflow数值模拟仿真平台,使用Fortran编程语言,根据研究区域地质条件特征对程序进行二次开发以优化Voellmy模型,模拟冰崩—泥石流动力过程;将模拟泥石流得到的堰塞坝体嵌入地形中,运用ArcGIS计算堰塞湖范围及体积,通过Manning模型模拟堰塞湖溃决洪水动力过程。采用分段模拟法再现冰崩—泥石流—堵江—堰塞湖—溃坝的完整动力过程,对泥石流运动过程中的流速、流深,坝体高度,溃决洪水的流深、流速等参数进行定量化研究,为色东普流域的防灾减灾工作提供有效支撑。为了揭示雅鲁藏布江色东普沟2018年10月17日冰崩-堵江-溃决灾害链的动力演化过程,采用Massflow数值模拟仿真平台,以Fortran语言为编程手段,根据研究区域地质条件特征对程序进行二次开发优化Voellmy模型,模拟冰崩-泥石流动力过程;将模拟泥石流所得到的堰塞坝体嵌入地形中,采用ArcGIS计算堰塞湖范围及体积,通过曼宁模型模拟堰塞湖溃决洪水动力过程。采用分段模拟法再现冰崩-泥石流-堵江-堰塞湖-溃坝的完整动力过程,对泥石流运动过程中的流速、流深,坝体高度,溃决洪水的流深、流速等参数进行定量化研究,为色东普流域的防灾减工作提供有效支撑。     

易贡滑坡堰塞湖溃坝洪水分析

滑坡堰塞坝体主要由块石、碎石土等松散材料组成,随着上游水位的不断上升,极易失稳,一旦决口将对给下游人民的生命财产安全造成极大的威胁。因此,研究堰塞坝溃坝问题具有重要的学术意义和应用价值。2000 年 4 月 9 日,西藏林芝地区波密县易贡藏布河扎木弄沟发生大规模山体滑坡堵塞易贡藏布江,形成坝高60m,长约2500m,库容可达288108m3,体积约28108～30108m3的滑坡堰塞湖, 2000年6月10日堰塞坝溃决。本文以易贡堰塞湖溃坝为例,从连续性方程及Navier Stokes方程出发,结合标准型湍流模型,并采用VOF方法进行自由面处理,基于流体计算软件Fluent模拟分析了溃坝洪水在下游弯曲河道的演进过程及不同位置的流速变化。数值模拟结果与实测资料记录基本一致,表明该模型能够模拟溃坝洪水在地形复杂弯曲河道中的演进过程。     

堰塞坝堆积演化过程及开发利用研究进展

堰塞坝险情的形成演化与综合开发治理是防灾减灾领域研究的焦点问题,因坝体形成过程特殊、内部结构复杂、组成材料不均且堆积形态迥异,导致其与人工坝体差异较大,目前仍缺乏有效的安全性评估方法及科学的开发治理措施。本文列举了国内外典型的堰塞坝事件,从堰塞坝的形成、类型和结构特征等方面,总结了已有的研究成果,阐述了堰塞坝的形成机理,重点分析了崩塌、滑坡、泥石流堰塞坝的堆积演化过程研究。归纳了目前堰塞坝应急处置和综合治理的工程措施与非工程措施,列举了堰塞坝蓄水发电、引水灌溉、环境旅游等开发利用的成功案例。通过文献和案例汇编,建立了堰塞坝事件研究的文献资料库。鉴于堰塞坝较高的溃决风险和开发潜能,提出当前研究存在的主要问题和继续努力的研究方向,为堰塞坝的风险预测及开发利用提供有益参考。     

金沙江上游雪隆囊古滑坡堰塞湖溃坝堆积体的发现及其环境与灾害意义

西藏芒康县金沙江上游雪隆囊河谷史前时期(全新世晚期)发生了一次明显的堰塞事件,形成了一个湖水体积约3.1×108 m3的大型堰塞湖。该堰塞湖形成后期发生溃决并引发异常大洪水,这一溃决事件发生在大约1 117 A.D.。地震诱发山体滑坡可能是金沙江发生堰塞的直接原因。在雪隆囊古堰塞坝体的下游一侧到其下游3.5 km的范围内,发现大量由砾石、砂和少量黏土组成的混杂堆积体,判定其为滑坡堰塞湖的溃坝堆积,是滑坡坝体及上游河床物质在坝体溃决后快速堆积形成。整套溃坝堆积体具有支撑-叠置构造、叠瓦构造和杂基构造等沉积特征,还具有一种特殊的沉积构造:即在垂向剖面上发育粗砾石层与细砂砾层的韵律互层,但剖面中缺少砾或砂的透镜体。这种沉积构造("互层构造")是溃坝堆积相区别于冲-洪积相、泥石流相等的一种重要判别标志。采用水力学模型反演确定雪隆囊古滑坡堰塞湖溃决洪水的平均流速为7.48 m/s,最大洪峰流量为10 786 m3/s。雪隆囊溃坝堆积体沉积特征及其环境的研究,不但有助于揭示古洪水事件发生的过程和机制,同时对于认识金沙江上游地区的环境演变也具有重要意义。     

易贡滑坡-碎屑流-堰塞坝溃坝链生灾害全过程模拟与动态特征分析

为研究易贡滑坡-堰塞坝溃坝链生灾害的动力学特征,基于遥感影像数据建立三维数值模型,运用DAN3D和FLOW3D对易贡滑坡-碎屑流-堰塞坝溃坝全过程进行模拟研究。运用DAN3D模拟滑坡-碎屑流过程,得到滑坡碎屑堆积分布特征及速度变化规律,滑坡持续时间300 s,平均速度35 m/s。基于DAN3D获得的滑坡碎屑堆积分布建立等比例堰塞坝模型,运用FLOW3D模拟溃坝后洪水演进过程,得到洪水演进过程水流特征变化规律,通麦大桥处洪峰流量130 000 m3/s与实测值接近。对易贡滑坡灾害链全过程的模拟和动态特征分析可为高山峡谷区类似的滑坡-堰塞坝溃坝链生灾害风险评价提供参考。     

堰塞湖应急处置实践与认识

堰塞湖是由于山体滑坡、崩塌、泥石流等堵塞河道形成的没有经过专门设计、没有专门的泄水设施的湖泊,一旦溃决,容易给下游造成巨大的灾难。分析了堰塞湖的成因、溃决机理与风险判断,提出堰塞湖应急处置的原则、理念、阶段与处置方法,总结了堰塞湖应急处置中的一些经验和认识。以四川省汶川特大地震形成的堰塞湖应急处置为例,从可能溃决方式、溃坝洪水、应急除险总体方案、开渠引流方案和除险效果等方面,介绍了唐家山堰塞湖的应急处置实践,并简要介绍了其它一些堰塞湖应急处置。     

新疆伊宁县皮里青河滑坡成灾机理分析

2017年3月24日,受冰雪消融影响,新疆伊犁哈萨克自治州伊宁县喀拉亚尕奇乡喀拉亚尕奇村发生滑坡灾害,滑坡堵塞皮里青河,形成堰塞湖,未造成人员伤亡。通过现场调查分析和数值模拟,结果表明:(1)皮里青河滑坡成灾过程为:河流冲刷坡脚,前缘局部滑动→发生蠕滑-拉裂,坡体强烈变形→在冰雪融水入渗作用下发生整体滑动→堵塞河道,形成堰塞湖→堰塞体溃决;(2)因气温升高,冰雪消融入渗是滑坡形成的直接诱因,雪水入渗后并转化为地下水,黄土含水达到饱和,孔隙水压力增高,滑坡稳定性系数降低,在重力作用下发生整体高速下滑;(3)分析了新疆地区冰雪消融引起滑坡灾害链的成灾模式,为进一步科学地指导防灾减灾提供技术支撑。     

堰塞坝形成机理及稳定性分析

滑坡、崩塌和泥石流是形成堰塞坝的三种主要方式,其形成堰塞坝的条件非常复杂,涉及因素广泛。另一方面,堰塞坝完全堵江形成堰塞湖在世界各国山区广泛分布,时有发生,造成严重灾害。因此,有必要对堰塞坝形成机理及安全性状评估进行研究。本文主要针对滑坡、崩塌、泥石流和碎屑流形成堰塞坝机理进行介绍并探讨了堰塞坝的破坏机制。同时,通过渗透稳定性、抗滑稳定性和抗冲刷稳定性3个方面评估了堰塞坝稳定性分析,以期为堰塞湖的防治与治理提供科学依据。     

The 12 May Wenchuan earthquake-induced landslide lakes: distribution and preliminary risk evaluation

The Wenchuan earthquake, measured at M _s 8.0 according to the China Earthquake Administration, occurred at 14:28 on 12 May 2008 in the Sichuan Province of China. It brought overwhelming destruction to eight provinces and cities. Landslides and rock avalanches triggered by the earthquake produced 257 landslide lakes which were distributed along the fault rupture zone and river channels. The authors traveled to the disaster zone immediately after the earthquake to examine some of the features of the debris dams and performed a quick evaluation of the potential for outburst of earthquake-induced landslide lakes for the purpose of disaster relief. The preliminary analysis indicated that the landslide lakes could be classified as those exhibiting extremely high risk, medium risk, and low risk according to field observations and remote sensing, to determine material composition, dam structure, dam height, maximum water storage capacity, and size of the population potentially affected area. The failure risk of 21 debris dams were evaluated as follows: one dam with an extremely high danger risk, seven dams with a high danger, five dams with a medium danger, and eight dams of low danger. More concern was given to the Tangjiashan Lake and different scenarios for the potential sudden failure of its dam were assessed. The risk evaluation result was accepted in full, by the earthquake disaster relief office. A successful emergency dam treatment for risk reduction was planned, based on our assessments, and these measures were quickly carried out. According to this research, the earthquake destabilized the surrounding mountains, resulting in a prolonged geohazard for the area. Landslides and debris flows will continue to develop for at least 5 to 10 years after the Wenchuan earthquake and will produce additional dammed lakes. Recommendations and plans for earthquake–landslide lake mitigation were proposed, based on past successful practices.     

Logistic regression model for predicting the failure probability of a landslide dam

Landslides may obstruct river flow and result in landslide dams; they occur in many regions of the world. The formation and disappearance of natural lakes involve a complex earth–surface process. According to the lessons learned from many historical cases, landslide dams usually break down rapidly soon after the formation of the lake. Regarding hazard mitigation, prompt evaluation of the stability of the landslide dam is crucial. Based on a Japanese dataset, this study utilized the logistic regression method and the jack-knife technique to identify the important geomorphic variables, including peak flow (or catchment area), dam height, width and length in sequence, affecting the stability of landslide dams. The resulting high overall prediction power demonstrates the robustness of the proposed logistic regression models. Accordingly, the failure probability of a landslide dam can also be evaluated based on this approach. Ten landslide dams (formed after the 1999 Chi-Chi Earthquake, the 2008 Wenchuan Earthquake and 2009 Typhoon Morakot) with complete dam geometry records were adopted as examples of evaluating the failure probability. The stable Tsao-Ling landslide dam, which was induced by the Chi-Chi earthquake, has a failure probability of 27.68% using a model incorporating the catchment area and dam geometry. On the contrary, the Tangjiashan landslide dam, which was artificially breached soon after its formation during the Wenchuan earthquake, has a failure probability as high as 99.54%. Typhoon Morakot induced the Siaolin landslide dam, which was breached within one hour after its formation and has a failure probability of 71.09%. Notably, the failure probability of the earthquake induced cases is reduced if the catchment area in the prediction model is replaced by the peak flow of the dammed stream for these cases. In contrast, the predicted failure probability of the heavy rainfall-induced case increases if the high flow rate of the dammed stream is incorporated into the prediction model. Consequently, it is suggested that the prediction model using the peak flow as causative factor should be used to evaluate the stability of a landslide dam if the peak flow is available. Together with an estimation of the impact of an outburst flood from a landslide-dammed lake, the failure probability of the landslide dam predicted by the proposed logistic regression model could be useful for evaluating the related risk.     

青藏高原东北缘黄河上游滑坡与堰塞湖研究进展

随着黄河流域生态保护与高质量发展上升为国家战略,滑坡灾害防治成为迫切需要攻克的基础性问题。另外,黄河上游地区因地形高差大、古地震及强降雨事件频繁,诱发的滑坡及滑坡堰塞湖数量多、分布广、危害重,是近年来滑坡发育和演化机制以及滑坡堰塞湖溃决效应研究的热点。本文在综合整理该地区已有研究工作的基础上,结合笔者研究团队近20年来所获得的滑坡调查评价、测试分析和防灾减灾研究成果,系统归纳了黄河上游地区滑坡调查与风险评价、滑坡时空展布规律及主控因素研究、典型滑坡堰塞湖的续存时长及溃决危害、古滑坡堆积体开发利用及防灾减灾等方面的研究进展和成果,提出了未来在该地区研究古滑坡、堰塞湖沉积与河流阶地以及堰塞湖溃决效应等应关注的4个科学问题。研究结果对于揭示黄河上游地质历史时期滑坡发育和堰塞湖形成的主控因素,探讨滑坡发育的动力机制对地震和降雨的响应过程,拓展第四纪地质学在古滑坡形成演变方面的应用研究等具有重要参考价值。     

A procedure for making objective preliminary assessments of outburst flood hazard from moraine-dammed lakes in southwestern British Columbia

Existing methods of evaluating the hazard posed by moraine-dammed lakes are unsystematic, subjective, and depend on the expertise and biases of the geoscientist. In this paper, we provide a framework for making objective preliminary assessments of outburst flood hazard in southwestern British Columbia. Our procedure relies on remote sensing methods and requires only limited knowledge of glacial processes so that evaluations of outburst flood hazard can be incorporated into routine hazard assessments of glaciated regions. We describe objective approaches, which incorporate existing empirical relations applicable to the study region, for estimating outburst peak discharge, maximum volume, maximum travel distance, maximum area of inundation, and probability. Outburst flood hazard is greatest for moderately large lakes that are impounded by large, narrow, ice-free moraine dams composed of sedimentary rock debris and drain into steep, sediment-filled gullies above major river valleys. We demonstrate the application of the procedure using three case studies and show that flood hazard varies, especially with major changes in lake level. Our assessment scheme yields reproducible results and enables engineers and geoscientists to prioritize potentially hazardous lakes for more detailed field investigation.     

冰碛湖溃决泥石流流量计算方法

冰碛湖溃决泥石流是高山高寒地区一种常见的灾害类型,虽爆发频率低,但造成的危害极大,该类型的泥石流防治是区域开发建设中必须要面对的问题,而流量计算又是其核心问题之一。以西藏地区近100 a以来的冰碛湖溃决实例为基础,探讨了溃口深度的计算方法;以逐渐溃决模型和配方法为基础,分析了冰碛湖溃决泥石流的容重峰值流量与洪峰演进计算方法的适用性与流程;通过案例的对比研究,探讨了计算模型参数率定与误差来源。结果表明：瞬间溃决模型高估了冰碛湖溃决泥石流的峰值流量,泥石流的预测值偏保守;而逐渐溃决模型更接近于冰碛湖溃决的物理机制,在冰川U型谷内,可不考虑泥石流的堵塞作用,泥石流的峰值流量预测值与实测值较吻合;在冰川U型谷外或近沟口段则需考虑泥石流的堵塞作用。文中提出的计算模型作为冰碛湖溃决泥石流防治工程参数设计的依据是可行的。     

Formation process of a large paleolandslide-dammed lake at Xuelongnang in the upper Jinsha River,SE Tibetan Plateau: constraints from OSL and <Superscript>14</Superscript>C dating

A large number of the landslide dams located on the major rivers at the southeastern margin of the Tibetan Plateau have been previously identified through remote sensing analysis and field investigations. The Xuelongnang paleolake was one of the lakes formed by these landslide dams in the upper Jinsha River, where the association of a relict landslide dam, lacustrine sediment, and outburst sediment is well preserved. This preservation provides an opportunity to better understand the formation, evolution, and longevity of a large landslide-dammed lake in the upper Jinsha River. It was inferred that the Xuelongnang dammed lake may have been formed by an earthquake-induced paleoavalanche. The surface area of the lake at its peak was estimated at 7.0?×?10⁶ m², and the corresponding volume was approximately 3.1?×?10⁸ m³. Two outburst flood events were determined to have occurred during the life span of the lake. Based on the 18 ages obtained from optically stimulated luminescence (OSL) and carbon-14 (¹⁴C) dating combined with stratigraphic sequences observed in the field, the paleolandslide-dammed lake was formed at approximately 2.1 ka and subsequently breached locally. The dammed lake was sustained for a period of some 900 years based on the chronological constraining. This study confirms that a major landslide-dammed lake can be sustained for at least hundreds of years and breached by several dam breaks in multiple periods, which contributed to the preservation of the knickpoints at millennial scale along the major rivers in the study area.     

Predictive uncertainty of peak outflow relations for landslides dam breach

Risk assessment development considering the failure of landslide dams often requires the estimation of peak outflow through the breach. The empirical equations based on data from case studies tend to be the first direct approach. This paper conducted an uncertainty analysis when these empirical relations were utilized to predict the peak outflow of a breached landslide dam. The results suggest that the relations derived from manmade dams or embankments typically overestimate the peak outflow about 1/5 to 3/4 of an order of magnitude; and the relations derived from the database of landslide dams have much smaller mean prediction errors and also exhibit broad uncertainty bands. Application of the uncertainly analysis was illustrated by the Tangjiashan landslide dammed lake, formed during 2008 Wenchuan earthquake. In addition, the predicted results from Eq. 1 deduced herein were considered to be the reliable estimate of peak outflow through the breach of landslide dam.     

西藏终碛湖溃决形式研究

西藏终碛湖众多,一旦发生溃决,将造成巨大损失。冰湖溃决机制的研究对冰湖溃决预测和溃后灾害评估是十分必要的。将冰湖终碛堤视为天然堆石坝,用水力学和土力学理论研究冰湖溃决的力学机制。重点研究溢流型溃决形式和管涌型溃决形式,根据野外观测数据和前人的研究,发现溢流型溃决的溃口多呈梯形或圆弧状形,对比真实数据发现溃口顶宽与坝高的关系,并且所有冰川终碛堤都表现为局部溃决。通过实地考察、取样分析,判断光谢措终碛堤的可能渗透破坏形式。     

Characteristics of glacier outburst flood in the Yarkant river,Karakorum mountains

Conclusions 1. The drainage of the Kyagar glacier dammed lake and the Tram Kangri glacier dammed lake at the upper Shaksgam is the main reason for glacier outburst floods in the Yarkant river. The Kyagar glacier dammed lake is characterized by subglacial drainage, while the Tram Kangri glacier dammed lake by mainly lateral drainage and, secondly, by subglacial drainage. 2. The drainage mechanism of the Tram Kangri ice dam determines the main characteristics of flood hydrography of the Kagun station, while the Kyagar glacier dammed lake plays an important role in the formation of floods. 3. Glacier outburst floods in the Yarkant river are characterized mainly by high peak discharge, big rising rate, small total volume and short duration. The floods happen mostly from late summer to early autumn. A period of 6 to 10 years in occurrence of large scale glacier outburst floods exist. The periodicity depends mainly on large scale drainage in the Kyagar ice-dammed lake. 4. Formation and dimensions of glacier dams at the upper Shaksgam were determined by long-term variations of the regional climate, whereas the changes of storage capacity in the lake reflect cold and warm changes of alpine region. Therefore, frequent glacier outburst floods indicate glacier advance and climatic variations.