Glacial Lakes and Glacial Lake Outburst Floods in Nepal
Glacial Lakes and Glacial Lake Outburst Floods in Nepal
International Centre for Integrated Mountain Development, Kathmandu, March 2011
This report was prepared by the International Centre for Integrated Mountain Development (ICIMOD) for the Global Facility for Disaster Reduction and Recovery (GFDRR)/The World Bank.
Published by International Centre for Integrated Mountain Development
GPO Box 3226, Kathmandu, Nepal
Copyright © 2011
International Centre for Integrated Mountain Development Global Facility for Disaster Reduction and Recovery of the World Bank
All rights reserved. Published 2011
ISBN 978 92 9115 193 6 (printed)
978 92 9115 194 3 (electronic)
Photos: All photos by Sharad P Joshi,
except p 55 (top) - Achyuta Koirala;
p 59 - Pravin R Maskey, p 80 Arun B Shrestha
Isabella Khadka (Consultant editor)
Greta Rana (Consultant editor)
A Beatrice Murray (Senior editor)
Dharma R Maharjan (Layout and design)
Asha Kaji Thaku (Editorial assistant)
Printed by Hill Side Press (P) Ltd., Kathmandu, Nepal
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Citation: ICIMOD (2011) Glacial lakes and glacial lake outburst floods in Nepal. Kathmandu: ICIMOD
The Hindu Kush-Himalayan region contains the world’s largest volume of glacier ice and perennial snow outside the polar regions. Its meltwater contributes to the major rivers that supply freshwater to almost a quarter of humanity residing in the downstream areas. Glaciers are sensitive indicators of increased air temperature. They have been studied extensively in many parts of the world as part of an international effort to improve understanding of the current pattern of global warming. Following the culmination of glacier advance during the Little Ice Age more than a hundred years ago, with short periods of reversal, glaciers have been thinning and retreating in many parts of the world. This process, in large part due to anthropogenic changes in the Earth’s atmosphere, appears to have accelerated during the last few decades. The Hindu Kush-
Himalayan region is no exception to the trend. The Himalayan range extends for approximately 2,400 km within the 3,500 km length of the Hindu Kush-Himalayan ranges, and has about 33,000 sq.km of the estimated 110,000 sq.km of glaciated area. The Nepal Himalayas occupy 800 km of the central section of the Himalayan range. Glacier thinning and retreat in the Himalayas has resulted in the formation of new glacial lakes and the enlargement of existing ones due to the accumulation of meltwater behind loosely consolidated end moraine dams that had formed when the glaciers attained their Little Ice Age maxima. Because such lakes are inherently unstable and subject to catastrophic drainage they are potential sources of danger to people and property in the valleys below them. The torrent of water and associated
debris that sudden lake discharges produce is known as a glacial lake outburst flood (GLOF). Recent surveys have shown that many glacial lakes in Nepal are expanding at a considerable rate so that the danger they pose appears to be increasing. Nepal has experienced 24 GLOF events in the recent past, several of which have caused considerable damage and loss of life, for example, the Bhote Koshi Sun Koshi GLOFs of 1964 and 1981 and the Dig Tsho GLOF of 1985. The 1981 event damaged the only road link to China and disrupted transportation for several months, while the Dig Tsho GLOF destroyed the nearly completed Namche Small Hydroelectric Project, in addition to causing other damage farther downstream. The source of the former event was inside the Tibet Autonomous Region of China, indicating the necessity for international regional cooperation to address the dimension of the problem. Glacial lakes, however, are not only sources of potential danger, they are also an important potential natural resource, which has yet to be effectively investigated. Monitoring glacier and water hazards, promoting community resilience and preparedness for disaster risk reduction, and ensuring the sharing of upstream-downstream benefits are priority areas in ICIMOD’s programme. As glaciers and glacial lakes are related to both water resources and to water-related natural hazards, they need to be mapped and monitored to assess both their potential hazard and their resource value. ICIMOD has been involved in this type of endeavour since 1986. The work reported here has received financial support from the World Bank. It is a systematic and comprehensive study of the status of glacial lakes in Nepal and an assessment of the hazard they pose and of the vulnerability of downstream people and property. It begins with the actual mapping of glacial lakes. This is followed by a hazard assessment. Next the problem of determining the most dangerous of the lakes is addressed, accompanied by analysis of the degree of downstream vulnerability. The report concludes by proposing some preliminary steps for development of a national strategy for response to the hazard, and emphasising the need for applying the experience obtained towards initiation of a region-wide international response. In this regard, on behalf of ICIMOD, I would like to thank the World Bank for its vital financial contribution. I would also like to thank the Swedish International Development Cooperation Agency (Sida) and the Norwegian Ministry of Foreign Affairs for additional financial support.
Director General, ICIMOD
Executive Summary vii
Section 1: Introduction to the Study 1
1 Introduction 3
2 Glacial Lake Outburst Floods in Nepal 9
3 Defining Risk 13
4 Mapping of Glaciers and Glacial Lakes 17
5 Prioritisation of Critical Lakes 29
Section 2: Field Investigations and Risk Assessment 33
6 Field Investigations 35
7 Results of the Field Investigations 39
8 GLOF Modelling 63
9 Vulnerability Assessment 73
Section 3: Discussion, Recommendations and Conclusion 79
10 Monitoring, Early Warning and Mitigation 81
11 Guidelines for GLOF Risk Management and Strategy in Nepal 83
12 Conclusions and Recommendations 89
Acronyms and Abbreviations 96
Additional Material – DVD in back pocket
For as long as historic records have been available, evidence has been documented that glaciers and glacial lakes have been a hazard to people and property located downstream. During the so-called ‘Little Ice Age’ (about AD 1500 – 1900), glaciers thickened and advanced and, in many instances, blocked side valleys causing river and meltwater to accumulate against an ice barrier. In some instances, as these glacial lakes grew, increasing hydrostatic pressure eventually caused the ice dam to lift or burst. In other instances, the lake level simply rose to overtop the ice dam. In either case, when the lake drained, either partially or entirely, the water which was released suddenly was destructive to anything in its path. This phenomenon was repeated at intervals as the glacier dam re-formed following the outbreak. In regions such as the European Alps, Scandinavia, and Iceland such catastrophic events have been recorded for several hundred years, often in great detail. Comparable disasters have doubtlessly occurred in other mountain areas where they were either not recorded, or took place in areas that were uninhabited. Such hitherto unrecorded major events are now being detected by modern geo-scientific research.
The sudden drainage of ice-dammed lakes attracted scientific interest from the mid-19th century as the natural sciences developed rapidly. Some of the earliest attempts to relate such events to atmospheric warming and sea-level rise (post-Little Ice Age) were undertaken by Swedish and Icelandic scientists and this gave rise to the colloquial Icelandic term ‘jökulhlaup’ (glacier leap) entering the scientific literature (Thorarinsson 1939; Ahlmann 1948). Another, even more dramatic, form of glacier outburst which results from sub-glacial volcanic activity is also common in Iceland (Thorarinsson 1953; Björnsson 2009a, 2009b). Individual historic events (for example, the 1727 eruption of Öraefajökull), in conjunction with peak glacial activity during the Little Ice Age, were sufficiently catastrophic to threaten the very existence of Iceland.
After the mid-19th century, the world climate began to change. The maximum advance of glaciers occurred at different times in different parts of the world, ranging from the early 19th century to as recently as 1905. After this time, mountain glaciers globally began to experience overall thinning and retreat, with several decadal reversals and regional contrasts. This behaviour of glaciers so intrigued scientists that in the first half of the 20th century individual glaciers were selected for continuous annual mass balance and climatological study: included were several glaciers in Europe such as the Kårsa glacier in Arctic Sweden (Wallén 1949); somew hat later, the Peyto glacier in the Canadian Rockies (Østrem 1966, 2006; Østrem and Brugman 1991); and others in the Canadian High Arctic (Axel Heiberg Island, Fritz Müller). Fritz Müller’s world glaciological vision led to the establishment of the International Inventory of Glaciers (Müller et al. 1977). Many studies which systematically record glacier terminal positions have been carried out annually without a break until the present day. This large and growing bank of data provides vital information for critical determination of the impacts of current climate change. It is universally recognised by glaciologists and climatologists, however, that the number of ’indicator’ glaciers is very small and that many mountain ranges have no adequate representative data sets. Furthermore, observations that are restricted to an annual recording of the position of glacier termini provide a very limited tool. As a result of the fact that the world’s glaciers are at present thinning and retreating, associated meltwater lakes are increasing in size and new lakes continue to be created. These lakes differ from the ice-dammed lakes which attracted scientific attention earlier, because they are predominantly supra-glacial and moraine-dammed rather than dammed by
advancing glaciers. This type of lake is characteristic of many of the glacial lakes found in the Himalayas and they constitute the major topic of this report.
Objectives of the Study
The present study had two main objectives:
1. to develop recommendations for adaptation to, and mitigation of, GLOF hazards in Nepal, concentrating on a small number of lakes perceived as especially critical, and
2. to assist the Government of Nepal in developing an overall strategy to address possible risks from GLOFs in the future.
This two-fold objective requires both an assessment of the extent to which specific glacial lakes are unstable, and an analysis of the degree to which people and property downstream are vulnerable. The overall approach requires strengthening of partnerships among key stakeholders including local people, major private and community corporations, government agencies, non-government organisations (NGOs), and tourist-oriented businesses, among others. This work will contribute to the development of an overall strategy for GLOF risk management which will include a more precise identification of the hazard as well as early warning and mitigation measures. As the physical attributes of glacial lakes are similar throughout the Hindu Kush-Himalayas, it is hoped that the results of this work can also be applied to other parts of the region.
GLOF Risk Assessment Methodology.
A step by step approach has been developed and applied for GLOF risk assessment. A schematic representation of the methodology of this approach is shown in Figure1.1. It begins with the mapping of glacial lakes and the study of the existing inventory. Once the glacial lakes are mapped, they are then identified as either potentially dangerous or not, based on a set of defined criteria. The labelling of the lakes at this step does not include categorising the vulnerability of the downstream areas. The next step involves ranking of the potentially dangerous lakes and setting of priorities for further detailed investigation. For this, the physical condition of a lake related to its stability is assessed by taking into consideration its area, the characteristics of the associated glacier, any changes in boundary conditions, and the stability of the surrounding terrain. Downstream socioeconomic parameters must also be obtained (Figure 1.1).
Socioeconomic parameters include settlements, the number and type of bridges and roads, number and capacity of
hydropower projects and the distances to these, the area of agricultural land, location of other important infrastructure, and any other activities of economic value. Repeated observation from low-flying aircraft is a rapid reconnaissance tool which provides an overview of changes and assists in the identification of vulnerable settlements and infrastructure to help assign priority to areas at the hydrological basin level. Thus, aerial observation is an important step in the ranking of potentially dangerous lakes. After ranking, typically only a few lakes will be given high priority for detailed follow-up investigation through either deskbased or field studies. Glacial Lakes and Glacial Lake Outburst Floods in Nepal 6 Existing inventory of glacial lakes (Desk-based study)
Mapping of glacial lakes
(Desk-based study, GIS/RS tools)
Identification of potentially dangerous lakes
(Use of GIS/RS tools)
Ranking of potential dangerous lakes
Selection of high priority lakes for further detailed investigation
Detailed desk based thematic studies of selected lakes for field investigations
Detailed field investigation of selected lakes in the defined thematic areas
Data analysis, interpretation and report preparation
Glacial lake database
List of potentially dangerous lakes
Final findings and results: Report
Categories (1, 2, 3) of potentially dangerous lakes
List of priority lakes requiring detailed field investigation
Thematic information and database of studied lakes
Satellite images, maps, reports
Criteria for identification of potential dangerous lake
Ranking criteria (area, distance to glacier, moraine condition, surrounding environment, socio-economic parameters (economic activities in downstream river valley, settlements, infrastructure)
List of category I (high priority) lakes
Thematic areas of study
• Assessment of the stability of the natural moraine dams
• Estimation of the lake storage volume
• Potential external GLOF triggering factors
• Hydro-meteorological data analysis
• Dam-break modelling and downstream vulnerability assessment
The next step in the risk assessment is the desk-based study of the high-priority lakes selected in order to identify the data gaps and any specific characteristics to be emphasised during the following field study.The detailed field investigation should focus mainly on the following aspects: estimation of the stability of natural moraine dams; determination of a lake’s storage capacity; potential external triggering factors; hydrometeorological data analysis; modelling a potential dam outburst; and carrying out a downstream vulnerability assessment. For overall GLOF risk management, the magnitude of the hazard is directly related to the downstream vulnerability appraisal (Figure 1.1). Analysis and interpretation of the results obtained from these studies should lead to improved understanding of the overall physical and socioeconomic risks from a GLOF. This will enable recommendations to be formulated for GLOF hazard management and risk mitigation measures.
Design of the Nepal Study
In order to fulfil the objectives outlined above, the step-by-step methodology was applied systematically in collaboration with partners including institutes of the Government of Nepal, academic institutions, international organisations, and other key stakeholders. A Steering Committee was formed on 5 November 2008 to provide overall guidance and support for the project with representatives from Nepal’s Department of Hydrology and Meteorology (DHM), Department of Water Induced Disaster Prevention (DWIDP), the Ministry of Home Affairs (MoHA), the Water and Energy Commission Secretariat (WECS), and ICIMOD. An inception workshop was held on 12 November 2008 to formulate the detailed project activity plan. The workshop was attended by representatives of government organisations, academic institutions, international NGOs (INGOs), and private institutes.
As an integral part of the investigation, several workshops and consultative meetings were organised at ICIMOD in Kathmandu. This ensured guidance for project implementation, field planning, and acquisition of equipment, as well as for dissemination of the findings from the field investigations. It also provided guidance for development of a strategy for GLOF risk management. Three workshops were held in the corresponding districts of the three lakes selected for intensive study in order to share information derived from the field investigations. This proved an effective arrangement for obtaining feedback from local communities and stakeholders. Similarly, two national workshops were organised at ICIMOD in order to facilitate dissemination of information on the project progress. The open discussions that ensued served to enhance project performance. Feedback was also obtained from various experts. Specialised members from partner institutions participated in the field investigations and contributed to the preparation of the technical reports. This helped to reinforce the capacities of the Nepalese institutions. Dissemination of the experience and information gathered during the field investigations to stakeholders, partner institutions, and local communities through a series of workshops and seminars helped to create awareness not only at the grass roots level but also among local government organisations and other stakeholders. Interaction with local communities and local government organisations, such as the district development committees, also helped to create an awareness of the project’s findings and draw attention to the fact that glacial lakes also constitute a potential natural resource that should be incorporated into local land-use planning. The present report was prepared as the final step, summarising different aspects of the findings of the project and the wider implications for dissemination to a broad audience. The report contains a summary of the information on mapping of glacial lakes, databases, field-based investigation information, and issues related to GLOF monitoring, early warning, and mitigation. It also includes general guidelines for the formulation of a strategy with regards to GLOF risk management. With the involvement of the appropriate regional partners, it is hoped that the methodology developed and applied in this project can be extended to similar GLOF-prone areas in other parts of the Hindu Kush-Himalayan region...