Ice, moraine, and landslide dams in mountainous terrain

We review recent work on ice, moraine, and landslide dams in mountainous terrain, thus complementing several comprehensive summaries on glacier dams in intracontinental and Arctic areas of low relief. We discuss the roles of tectonic and climatic forcing on ice-, moraine-, and landslide-dam formation and sudden drainage, and focus on similarities and differences between their geomorphic impacts on confined valleys drained by steep bedrock and gravel-bed rivers.Despite numerous reported failures of natural dams in mountain belts throughout the world, their relevance to long-term dynamics of mountain rivers remains poorly quantified. All types of dams exert local base-level controls, thus trapping incoming sediment and inhibiting fluvial bedrock incision. Pervasive geomorphic and sedimentary evidence of outburst events is preserved even in areas of high erosion rates, suggesting that sudden dam failures are characterized by processes of catastrophic valley-floor aggradation, active-channel widening, and downstream dispersion of sediment, during which little bedrock erosion seems to be achieved.We find that, in the absence of direct evidence of former dams, a number of similarities among the geomorphic and sedimentologic characteristics of catastrophic outburst flows may give rise to ambiguous inferences on the dam-forming process. This is especially the case for tectonically active mountain belts where there is ample and comparable potential for the formation and failure of ice, moraine, landslide, and polygenetic dams concomitant with climatic oscillations or earthquake disturbance. Hence, the palaeoclimatic implications of erroneously inferring the cause of dam formation may be significant.We recommend that future research on natural dams in mountainous terrain addresses (a) climate- and earthquake-controlled systematics in the pattern of formation and failure; (b) quantification of response of mountain rivers to catastrophic outburst events and their concomitant process sequences; (c) elaboration of a comprehensive classification of natural dams in mountainous terrain with special attention to polygenetic dams; (d) physical-based modelling of dam formation, failure, and routing of water and sediment outbursts; and (e) quantitative controls on the contribution of natural dams to sediment budgets in mountainous terrain.     

一个由左右岸滑坡形成的滑坡坝成因机制分析

滑坡坝及形成的堰塞湖在世界各国特别是山区一带广泛分布。它能够形成天然水库 ,在发生溃坝和洪水漫坝的情况下 ,造成的灾害损失很大。历史上产生过许多天然滑坡坝 ,有些很快发生溃坝 ,有些存在时间很长。存在时间较长的滑坡坝 ,它周围风景秀丽 ,成为旅游热点地区 ,同时也可开发其水资源。滑坡坝的形成有滑坡堵江、崩塌堵江和泥石流堵江 3种形式 ,它的形成机制对于滑坡坝的存在时间起了重要的作用。在开发和利用滑坡坝时 ,它的成因机制需要分析评价。本文对某滑坡坝的形成机制进行了研究 ,在研究某滑坡坝时发现 ,它由左右两岸的滑坡共同作用形成 ,这种形成模式在国内外报道很少 ,对类似工程也有一定的借鉴意义     

基于河长—坡降指数的滑坡堵江事件自动识别

由于本身特征的复杂差异性和背景环境信息干扰,目前地质灾害自动识别难度较大,尚无法满足应用需求。利用算法自动提取某类地质灾害普遍具备且明显区别于周围地物的特征,是实现地质灾害自动识别的有效途径。一定规模的滑坡堵江事件常通过链式过程在山间河谷形成裂点等诸多微地貌特征,成为其遥感解译和现场调查的重要标志。本文从河流地貌演化角度出发,以河流裂点作为滑坡堵江的普遍地貌特征,提出了基于河长-坡降指数（Stream Length-gradient index,SL) 的滑坡堵江事件自动识别方法,并通过GIS程序设计和编写提供了相应功能模块。以DEM、遥感影像和区域地质图为数据源,利用该方法在西藏亚东县康布麻曲上游流域开展应用分析,得到以下结论:针对1:5万DEM数据,采样点计算间隔设定为300m比较合理,能够同时满足降低数据误差和突出地形差异的要求;研究区中不同因素按照对河流地貌的改造程度,排序为滑坡堵江>基岩变化>构造活动;经验证研究区滑坡堵江事件自动提取的正确率达85.71%,表明在高山峡谷地区,基于河长—坡降指数开展滑坡堵江事件自动识别具有可行性,效果理想。     

Volcanic natural dams: identification,stability, and secondary effects

Volcanic activity can enhance several secondary effects, including the formation of one or more natural dams. A common example is from volcanic collapse, where huge mass volumes are rapidly emplaced, obstructing the drainage around a volcano. Their duration depends on the volume of the obstructing mass, inflow rate, and on its textural characteristics. A block facies of a debris avalanche produces durable and permeable dams that consist of decimeter to meter-sized blocks without matrix, whereas a mixed facies is easily eroded after overflowing. Analysis of the sedimentological characteristics of different volcaniclastic deposits that formed natural dams indicate that a mean grain size (Md) equal to −1 phi divides the field of debris avalanche dams (Md < −1 phi) from that formed from other types of volcanic deposits. In addition, the matrix proportion of dams formed by debris avalanches are less than the 50% and the percentage of mud fraction is highly variable, up to 30%. Combining the granulometric textures with duration time of the dam shows no clear relation. Dam durability is probably more dependent on the volume of the lake and the inflow rate. Only in some cases, as mud fraction increases is the blockage also less durable because the lower permeability favors rapid infilling. The texture of the dam also determines the types of secondary flows that originate by their breakdown. These vary from cohesive debris flow to hyperconcentrated flow, representing different hazards due to their magnitude and their different behavior downstream.     

筑坝对河流生态系统影响研究进展

河流是陆地生态系统和水生态系统间物质循环的通道,筑坝人为改变河流物理、化学、生物地球化学循环模式,影响河流生态系统的结构、功能.分析了筑坝对河流水文水力特性、生源要素(氮、磷、硅等)、水生态系统结构和功能的影响以及河流生态系统恢复等研究的进展.随着水库成为陆地水分循环的一个主要组成部分,对流域生态系统健康的影响日益显著,进而对大坝的生态效应、河流生态恢复等需要进行深入的研究,减轻大坝的负面效应.     

Experimental study on cascading landslide dam failures by upstream flows

Landslide dams in mountainous areas are quite common. Typically, intense rainfalls can induce upstream flows along the sloping channel, which greatly affects the stability and failure modes of landslide dams. If a series of landslide dams are sequentially collapsed by an incoming mountain torrent (induced by intense rainfall), large debris flows can be formed in a short period of time. This also amplifies the magnitude of the debris flows along the flow direction. The catastrophic debris flows, which occurred in Zhouqu, China on August 8, 2010, were indeed caused by intense rainfall and the upstream cascading failure of landslide dams along the gullies. Experimental tests were conducted in a sloping channel to understand the dynamic process of cascading landslide dam failures and their effect on flow scale amplification. Similar to the Zhouqu conditions, the modeled landslide dams were distributed along a sloping channel and breached by different upstream flows. For each experiment, the front flows were sampled, the entrained grain sizes were analyzed, and the front discharge along the channel was measured. The results of these experiments show that landslide dams occurring along the channel can be destroyed by both high and low discharge flows, although the mechanisms are quite different for the two flow types. Regardless of flow type, the magnitude of the flows significantly increases after a cascading failure of landslide dams, resulting in an increase in both the diameter and the entrained coarse particles percentage.     

Numerical modeling the role of rubber dams on groundwater recharge and phreatic evaporation loss in riparian zones

Rubber dams have been widely built for their advantages in increase of flooding resources utilization in the north arid and semiarid plain regions of China. Rise in river water stage by the dams, particularly during the drought periods, increases lateral seepage of river water into groundwater, and thus groundwater table and phreatic evaporation loss in the riparian zones. In this study, a riparian area of the Baihe River in Nanyang of Henan Province, China was selected for investigation of influences of the river dams on the groundwater recharge and evaporation loss. A hydraulic model, HEC-RAS, was used for simulation of the river stage variations along the Baihe River, and a numerical groundwater model, MODFLOW, was applied for simulation of groundwater dynamics and estimation of river flow seepage into aquifer and evaporation loss. The results show that the dams increase river stages of 2–3 m during January 2000–December 2002. The increase in the captured groundwater recharge was 7.15–34.06 million m³/a and the increased phreatic evaporation loss occupies 10% of the increased recharge when four rubber dams were built.     

Breaching parameters of landslide dams

Landslide dams pose enormous risks to the public because of the potentially catastrophic floods generated by breaching of such dams. The need to better understand the threats of landslide dams raises questions about the proper estimation of breaching parameters (breach size, breaching duration, and peak outflow rate) of landslide dams and the feasibility of applying models for estimating the breaching parameters of man-made earthen dams to landslide dams. This paper aims to answer these two questions. In this study, a database of 1,239 landslide dams, including 257 cases formed during the 12 May 2008 Wenchuan earthquake, has been compiled. Based on records of 52 landslide dam cases with breaching information in the database, empirical models for estimating the breaching parameters of landslide dams are developed. A comparison study between landslide dams and man-made earth and rockfill dams is conducted, which shows that the models for man-made earth and rockfill dams are not suitable for estimating the breaching parameters of landslide dams. Two case studies are presented to show the application of the set of empirical models developed in this paper.     

Seismic hazard and total risk analyses for large dams in Euphrates basin,Turkey

Reservoirs constructed near urban areas pose a high-risk potential for downstream life and property. Turkey is one of the most seismically active regions in the world and has at least 1200 large dams with different types. Major earthquakes with the potential of threatening life and property occur frequently here. The Euphrates basin studied in this article is located in a seismically very active part of Turkey. The northern part of the basin is structurally cut by numerous faults. Many large dams are located on or close to these faults. In this paper we summarize the methods used for the analysis of seismic hazards and total risk, discuss the seismic hazards of thirty-two large dams constructed on the Euphrates basin on the basis of the seismic activity of the dam site and their total risk as based on physical properties and the position in the basin. The seismic hazard analyses have indicated that peak ground acceleration changes within a wide range (0.011 g and 0.564 g) for the dam sites of the basin. A seismic hazard map showing the equivalent PGA (peak ground acceleration) values was developed so as to use for the preliminary analysis of dam structures, which will be designed in the basin. The total risk analyses depending on the seismic hazard rating of dam site and risk rating of the structure have concluded that fifteen large dams have high-risk class in the basin. These dams must be analyzed with high priority and redesigned to increase the safety of the embankments and their appurtenant structures, if necessary.     

3D stability analysis of gravity dams on sloped rock foundations using the limit equilibrium method

A convenient approach to performing stability analysis of concrete gravity dams is the so-called two-dimensional “gravity method.” However, concrete gravity dams located in valleys with sloped rock foundation abutments behave as three-dimensional (3D) structures and are often able to share compressive and shear loads between adjacent monoliths, especially when shear keys are present. A general 3D limit equilibrium method was developed in this study to compute global sliding safety factors (SSF_g) by considering sequential load redistribution among adjacent monoliths when individual monoliths have mobilized their sliding strength. Two validation examples of the sliding safety assessment of existing dams are presented to illustrate the accuracy and efficiency of the proposed approach compared to that of the full 3D numerical analyses conducted using the distinct element method. It is shown that gravity dams may be formed by individual monoliths on sloped rock foundations that will slide if considered as isolated structures but will constitute a stable assembly when the load-sharing capabilities of monoliths are recognized in the analysis.     

中国喜马拉雅山地区滑坡堵江编目及空间特征分析

滑坡堵江数据获取与编目是其区域研究开展的基础。喜马拉雅山脉地处中国西南边陲,新构造运动强烈,滑坡堵江事件频发,在产生巨大经济损失的同时也造成了不良国际影响。鉴于该区区域滑坡堵江现场调查难以开展的问题,本文利用遥感技术、地理信息技术,结合野外验证获取了区内136处滑坡堵江事件的空间位置、基本属性和几何形态,建立了中国喜马拉雅山地区滑坡堵江编目。区内滑坡堵江集中分布在米林、札达、加查、错那、隆子、郎县等县,成因类型以滑坡、崩塌、泥石流为主。基于环境要素信息量计算得出该区滑坡堵江的易发程度随高程、坡度、地震加速度的增大先增大后减小,随地震点密度增大先减小后增大,随构造线密度增大逐渐增大,随与水系距离增大逐渐减小。不同坡向中,西向斜坡更容易诱发滑坡堵江,东南坡向最不容易诱发滑坡堵江。高位高山地貌类型、地层条件中的朗县构造混杂岩组和坚硬岩组,构造分区中的高喜马拉雅分区和雅鲁藏布江分区是滑坡堵江形成的有利条件。对比各环境要素不同类别的信息量取值认为影响该区滑坡堵江事件形成的主要背景因素是高程、地貌类型、地层岩组、构造分区和地震点密度。这些滑坡堵江事件几何参数的研究结果表明坝体长度-坝体面积与滑坡面积-坝体面积之间具有拟合程度较高的乘幂函数关系,而其他参数间的相关性并不突出。     

Morphological analysis and features of the landslide dams in the Cordillera Blanca,Peru

Global warming in high mountain areas has led to visible environmental changes as glacial retreat, formation and evolution of moraine dammed lakes, slope instability, and major mass movements. Landslide dams and moraine dams are rather common in the Cordillera Blanca Mountains Range, Peru, and have caused large damages and fatalities over time. The environmental changes are influencing the rivers’ and dams’ equilibrium, and the potential induced consequences, like catastrophic debris flows or outburst floods resulting from dam failures, can be major hazards in the region. The studies of past landslide dam cases are essential in forecasting induced risks, and specific works on this topic were not developed in the study region. Reflecting this research gap, a database of 51 cases and an evolution study of landslide dams in the Cordillera Blanca Mountains is presented. The main morphometric parameters and information of the landslide, the dam body, the valley, and the lake, if any, have been determined through direct and indirect survey techniques. Low variability in some of the main morphometric parameter distributions (valley width and landslide volume) has been shown, most likely due to an environmental control connected to the regional tectonic and glacial history. In order to analyze present and future landslide dam evolution, a morphological analysis was carried out using two recently developed geomorphological indexes employed on the Italian territory. The results of the Cordillera Blanca analysis have been compared with a large Italian landslide dam inventory, highlighting as much the differences as the similarities between the two datasets. The long-term geomorphological evolution changes are evaluated. Many of the stable dams are in disequilibrium with their surrounding environment and their classification result is of “uncertain determination.”     

Response of Concrete and Masonry Dams to Ground Vibration due to Blasting

The safety and stability of concrete and masonry dams is a great concern when blasting has to be conducted close to these dams in order to construct small hydro-electric projects. There is a danger of ground vibration amplification to those residential-type buildings that are built close to these dams.

Responses of three concrete and masonry dams were measured directly by conducting a number of blasts and by monitoring vibration in the ground as well as on the dams. The amplitudes and frequencies of the motions were analysed and vibration attenuation relations were derived. These relations were used to compare the vibration levels on the dams with those in the ground.

Because of close-in construction blasts that produced high frequency ground vibrations, there was no amplification of the ground vibrations by these dams. The measured amplitudes of ground vibration were comparable to those of the dams.     

Trophic status of Vondo and Albasini Dams; impacts on aquatic ecosystems and drinking water

The presence and levels of major nutrients in the water from Vondo and Albasini Dams and their water treatment plants have been assessed to determine trophic status of the dams and impacts on aquatic ecosystems and drinking water. Water quality parameters particularly phosphates and nitrates are critical in assessing the trophic status. Water quality parameters linked to eutrophication and agrochemicals were analyzed. Phosphate was undetectable in both dams. The nitrate levels in Albasini and Vondo Dams which were from 1.16 to 6.65?mg/L and 0.46 to 4.19?mg/L, respectively, were within and above the South African guideline for aquatic ecosystems of 2?mg/L. The raw water pH for Vondo and Albasini Dams were from 6.20 to 7.46 and 6.35 to 8.70, respectively, and were mostly within acceptable guidelines for aquatic ecosystems. The water transparency for Vondo and Albasini Dams were from 0.5 to 4.2?m and 0.4 to 0.9?m, respectively. The levels of all other water quality parameters investigated in both dams and their WTPs mostly indicate low, rarely high and no water quality problems in aquatic ecosystems and drinking water. The low levels of total suspended solids and water transparency, the pH range, low to high electrical conductivity, low to acceptable dissolved oxygen levels, acceptable to high biological oxygen demand and nitrate levels for both dams indicate oligotrophic to eutrophic states. Though oligotrophic state dominates, the mixture of trophic states has been attributed to increase in urbanization and intensive agriculture.     

余震作用下堰塞坝体破坏及溃决过程大型振动台试验研究

山区特大地震往往导致大量堰塞湖,例如2008年汶川地震形成了至少257个堰塞湖,并且主震后发生了大量余震,这些余震可能会影响堰塞坝体的安全状态。通过大型振动台模型试验,研究了余震及库水耦合作用下堰塞坝体的破坏及溃决机理和过程。共进行了两组不同材料的振动台模型试验,分别模拟含黏粒较多且颗粒较小（坝体Ⅰ）和基本不含黏粒且颗粒较大（坝体Ⅱ）的两种坝体。在不同水位条件下进行振动台试验。研究成果表明:（1）地震和库水耦合作用下堰塞坝体的主要溃决方式是漫顶溢流,主要溃决过程为地震力使松散的堰塞坝体发生沉陷,库水渗入使沉陷加剧,最终水位上升漫过坝顶发生溢流冲蚀破坏。（2）地震一般不会直接引起堰塞坝体的破坏。地震力对坝体稳定性的主要影响是使坝体发生沉陷变形。在地震和库水耦合作用下,坝体沉陷比单一因素作用下更为剧烈,因此地震作用会使漫顶溢流提前发生。（3）地震和库水耦合作用下坝体Ⅰ沉陷量大于坝体Ⅱ,说明现实中由大粒径岩土体组成的堰塞坝体具有更好的稳定性。     

雅砻江流域河道高程剖面上的堰塞坝印记

堰塞坝会对山区河流的纵剖面产生强烈扰动,在某些情况下,堰塞坝造成的河流纵剖面变陡很容易与构造作用下基准面下降的迁移裂点混淆.然而,在何种程度下堰塞坝会影响基于地貌测量的构造分析还没有系统的研究.因此本文选取青藏高原东缘的雅砻江流域为研究对象,利用遥感影像解译,结合数字高程模型(DEM),来研究堰塞坝对河流纵剖面的影响....     

Knickpoints along the upper Indus River,Pakistan: an exploratory survey of geomorphic processes

This article summarizes an exploratory study carried out to investigate the significance of various geomorphic features on the formation of observed knickpoints along the upper Indus River in northern Pakistan. These features include bedrock lithology, active faults, sediment flux from tributary channels, and landslide dams which have blocked the main channel. The knickpoints and their related geomorphic parameters (channel profile, concavity, drainage area and normalized steepness index, etc.) were extracted from Advanced Spaceborne Thermal Emission and Reflection (ASTER) Global Digital Elevation Models (GDEMs) with 30 m resolution using ArcGIS, River Tools, and Matlab software. A total of 251 major and minor knickpoints were extracted from the longitudinal profile along a ~ 750 km reach upstream of Tarbela Reservoir. The identified knickpoints and their respective normalized steepness index (k_sn values) were compared with bedrock lithology, mapped faults, regional landslide/rockslide inventory, and the locations of historic landslide dams. The analyses revealed that the knickpoints do not correlate with the bedrock lithology except where major unit boundaries coexist with mapped faults, especially in reaches criss-crossed by active thrust faults in the Nanga Parbat Haramosh (NPHM) region. Neither did the river’s major confluences exhibit any notable knickpoints, but the correlations between knickpoints, mapped landslides, and historic rockslide avalanche dams accounted for approximately 75% of the observed knickpoints, a surprising finding. These observations suggest that more detailed studies aided by high resolution data should be undertaken to further explore the characteristics of knickpoints triggered by tectonic uplift, local fault offset, bedrock erodibility, and landslide/rockslide dams.     

地震加速度动态分布及对高土石坝坝坡抗震稳定的影响

《水工建筑物抗震设计规范》（DL5073-1997）建议的土石坝地震加速度动态分布系数适合于150 m以下的土石坝,而前许多土石坝的设计高度已远大于150 m。与低坝相比,高坝受地基刚性的约束减弱,坝体的自振周期延长。在坝体地震反应中,高阶自振周期与地震卓越周期耦合的机率增大,高阶振型的振动易被激发放大,从而导致坝体地震加速度沿坝高的分布与低坝有所不同。据此,采用有限元法研究了高土石坝的加速度分布,提出了高于150 m土石坝的地震加速度动态分布系数图示。在此基础上,利用堆石材料的非线性强度准则,对高度超过150 m的土石坝坝坡抗震稳定性作了进一步的分析,得出随着坝体地震加速度动态分布系数的降低,坝坡临界破坏的安全系数有所提高。     

Analysis of earth dams affected by the 2001 Bhuj Earthquake

An earthquake of magnitude of 7.6 (M_w 7.6) occurred in Bhuj, India on January 26, 2001. This event inflicted damages of varying extents to a large number of small to moderate size multi-zone earth dams in the vicinity of the epicenter. Some of the distress was due to the liquefaction of saturated alluvium in foundation. Liquefaction was relatively localized for the majority of these dams because the earthquake struck in the middle of a prolonged dry season when the reservoirs behind these dams were nearly empty and shallow alluvium soils underneath the downstream portions of the dams were partly dry. Otherwise, liquefaction of foundation soils would have been more extensive and damage to these dams more significant. Six such dams have been examined in this paper. Four of these facilities, Chang, Shivlakha, Suvi, and Tapar were within the 50 km of epicenter region. These dams underwent free-field ground motion with peak ground accelerations between 0.28g to 0.52g. Of these Chang Dam underwent severe slumping, whereas Shivlakha, Suvi, and Tapar Dams were affected severely especially over the upstream sections. Fatehgadh Dam and Kaswati Dam were affected relatively less severely. Foundation conditions underneath these dams were first examined for assessing liquefaction potential. A limited amount of subsurface information available from investigations undertaken prior to the earthquake indicates that, although the foundation soils within the top 2.0 to 2.5 m underneath these dams were susceptible to liquefaction, Bhuj Earthquake did not trigger liquefaction because of lack of saturation of these layers underneath the downstream portions of these dams. These dams were then analyzed using a simple sliding block procedure using appropriate estimates of undrained soil strength parameters. The results of this analysis for these structures were found to be in general agreement with the observed deformation patterns.     

Emergency response to the Tangjiashan landslide-dammed lake resulting from the 2008 Wenchuan Earthquake, China

Natural landslide dams triggered by earthquakes are a common feature and a significant hazard in high-relief, tectonically active areas. The great Wenchuan Earthquake of May 12, 2008 created 256 natural dams, of which 34 presented significant risks to downstream areas in the event of their uncontrolled failure. Out of the 34 large landslide dams that warranted mitigation, we discuss Tangjiashan landslide dam in detail. Emergency response to the Tangjiashan landslide-dammed lake in the following weeks and months successfully reduced the risk, and the advantages and disadvantages of various countermeasures that were applied are summarized here. Successful strategies relied on accurate scientific assessments, on timely execution of the countermeasures, and on the correct design of sluiceway (spillway) channels across the landslide dams. Retrospective assessment indicates that the following improvements would be more beneficial: (1) Sluiceway channels utilizing a combination of cross-section types, rather than simply trapezoidal in shape; (2) increased channel slope, which is more than the original gradient of the river; (3) better protection of inlets and outlets to control the planned incision rates; and (4) channels lined to better control the incision rate. We discuss applications of the concept of artificially controlled failure, and we submit these observations for the benefit of those responding to future seismic catastrophes.