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Reviewing Scientific Assessment Data On Imja Glacial Lake And GLOF For The Activity Of Component I Of Community Based Flood And Glacial Lake Outburst Risk Reduction Project (CFGORRP)

Final Report

ADAPT NEPAL February 2014

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----------------------------------------------------------------------------------------------------------------------------- ---------------------------Association For The Development of Environment and People in Transition (ADAPT-Nepal), January 2014

Reviewing Scientific Assessment Data On Imja Glacial Lake And

GLOF For The Act iv i ty Of Component I Of Community Based

Flood And Glacial Lake Outburst Risk Reduction Project (CFGORRP)

Final Report

Submitted to:

Department of Hydrology and Meteorology

Ministry of Science, Technology and Environment

Government of Nepal

Submitted by:

ADAPT-Nepal

February 2014

Acknowledgement

ADAPT-Nepal wishes to thank the Director-Genral of the Department of Hydrology and

Meteorology (DHM), Dr. Rishi Ram Sharma for entrusting us to carry out such an important study.

We are indebted to Community Based Flood and Glacial Lake Outburst Risk Reduction Project

(CFGORRP), specifically to Mr. Top Bahadur Khatri and Mr. Pravin Raj Maskey for their

guidance and support in preparing this report.

We also acknowledge the service of Dr. Rijan Bhakta Kayastha and Mr. Nitesh Shrestha for their

hard labour and their appreciable efforts in completing the study in such a short time.

ADAPT-Nepal

February 2014

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Executive Summary

Himalayan glaciers cover about three million hectares or 17% of the mountain area as compared to

2.2% in the Swiss Alps. They form the largest body of ice outside the polar caps and are the source of

water for the innumerable rivers that flow across the Indo-Gangetic plains. Himalayan glacial

snowfields store about 12,000 km3 of freshwater. About 15,000 Himalayan glaciers form a unique

reservoir which supports perennial rivers such as the Indus, Ganga and Brahmaputra which, in turn,

are the lifeline of millions of people in South Asian countries (Pakistan, Nepal, Bhutan, India and

Bangladesh) (IPCC WGII AR4).

Glaciers are highly sensitive to climate change due to their relatively quick response. Climate cooling

results in glacier advancement and warming leads to glacier retreat; so they are excellent indicators of

climate change. Hence, recent glacial retreat and concomitant glacial lake formations/expansions in

mountain areas serve as an example and infallible testimony of climate change. As glaciers retreat,

lakes commonly form behind the newly exposed terminal moraine. The rapid accumulation of water

in these lakes can lead to a sudden breach of the moraine dam. The resultant rapid discharge of huge

amount of water and debris is known as a glacial lake outburst flood (GLOF). These GLOF events

may result into catastrophic damage to the downstream areas.

In Nepal there are 3,808 glaciers with a total area of 4,212 sq.km and 1,466 glacial lakes. Nine lakes

were mapped in the Nepalese part of the Mahakali River basin with a total area of 0.137 sq.km; 742

lakes were mapped in the Karnali basin with a total area of 29.147 sq.km — the largest number and

greatest lake area in any one basin; 116 glacial lakes were mapped in the Gandaki basin with a total

area of 9.538 sq.km — the largest average size in any basin (0.082 sq.km); and 599 lakes were mapped

in the Koshi basin with a total area of 25.958 sq.km. Similarly, the majority of lakes are moraine-

dammed (975 lakes occupying 72% of the total lake area); supra-glacial lakes are mostly small with an

average size of 0.009 sq.km and these represent only 1.5 % of the total glacial lake area; erosion lakes

represent 17% of the total lake area; and other glacial lakes represent 9.5%.

This report on Imja Glacial Lake is based upon information gathered through personal

communication and published reports from different organizations working on glacial lake issues such

as International Centre for Integrated Mountain Development (ICIMOD), Water and Energy

Commission Secretariat (WECS), Department of Hydrology and Meteorology (DHM), United

Nations Development Program (UNDP), World Bank and Kathmandu University. It also reviewed

and analyzed almost all studies carried out on Imja and Tsho Rolpa Glacial Lakes of Nepal. It also

gathered information of Raphstreng, Luggye and Thorthormi Glacial Lakes of Bhutan and few glacial

lakes of Cordillera Blanca, Peru. Almost all glacial lakes in Nepal and Bhutan are formed in 1950s and

then gradually grown up along with warming climate in this region.

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The Dudh Koshi sub-basin of Nepal contains twelve potentially dangerous glacial lakes, among them

Imja Lake is one of the fastest growing lake in Nepal. Because of the risk associated with Imja Lake,

implementation of mitigation and safety measures is really essential. This situation, together with

realization of increase of melt water stored in the Imja Glacial Lake in Solukhumbu district in Nepal,

has prompted the Community based GLOF risk reduction project to lower down the lake water level

by 3 m.

Imja Glacial Lake is located in the eastern part of the Sagarmatha region in Solukhumbu district,

Nepal. Lhotse Shar, Imja and Ampulapcha Glaciers are the parent glaciers of Imja Glacier and Imja

Glacial Lake. Till 1950, there was no lake at that location but a couple of ponds as seen on the

topographical map known as the ‘Schneider Map’, Khumbu Himal (1:50,000), which was based on

terrestrial photo-grammetry and field work carried out during 1956 to 1963.

The Lake was just 0.03 km2 in 1963 but increased to 1.06 km2 in 2009 and now is identified as one of

the fastest growing lakes in the entire Himalayan region. The GLOF event if occurred will have severe

impact on the 35 VDCs adjoining Imja/Dudhkoshi River affecting total population of 96,767.

Realizing the potential threat of Imja Lake, various studies on Imja Glacial Lake have been carried out

in the past by various researchers. From 1991, several study team conducted topographic and

bathymetric investigation to find out the lake area, depth, volume of water stored and stability of end

and lateral moraine. However, the study conducted so far is not sufficient to understand the risk

associated with Imja Lake, thus further research activities along with mitigation strategies are essential

to lower the lake water level to safer level.

Tsho Rolpa Glacial Lake is another rapidly expanding glacial lakes in the Himalayas. The lake area

increased from 0.23 km2 in 1958 to 1.55 km2 in 1999. Because of its growing rate, it is considered as

potentially most dangerous glacial Lake in Nepal. Tsho Rolpa Glacial Lake is extensively studied by

many researchers and institutions on various aspects of the lake and associated hazards. Based upon

the past studies, adaptation and mitigation works have been carried out on Tsho Rolpa Glacial Lake.

The lake-water-level is lowered by 3 meters and Lake Outflow is channelized through a controlled

gated waterway. Tsho Rolpa Glacial Lake is the only glacial lake in Nepal where installation of a

modern GLOF early warning system and GLOF risk reduction work has been carried out.

Among different glacial lakes in Bhutan, Raphstreng and Thorthormi Lakes are largely emphasized

because of their potential threat and associated risk. The Raphstreng Lake is suffering from weakening

of the Lake barrier and threatening downstream areas. In response to this, the Government of Bhutan

investigated the status of stability of the Lake and implemented three phase of mitigation works from

1996 to 1995 to lower the water level by 4 m. Thorthormi is a supra glacial lake that is 65 m higher

than Raphstreng Lake.

Various mitigation and safety measures in the lakes of Peru have also been carried out. For example

in the Safuna Alta Lake two tunnel of 47 m and 159 m were built to drain out the lake water. Similarly,

in Jancarurish Lake a V-shaped channel was constructed by cutting the end moraine. Safety works in

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Hatun Cocha Lake was implemented in early 1960 along with installation of two outlet pipes to drain

out the lake water. In case of Paron Lake, various safety measures have been implemented by placing

sand bags and earthen dam to enhance the stability of end moraine.

Based upon the review of past literatures and with the experiences of recent GLOF risk reduction

activities carried out in Nepal, Bhutan and Peru, it is recommended to lower the lake level using

modern equipment, however, extreme care is required during excavation and channelization process.

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Abbreviations and Acronyms ACO Austrian Coordination Office

ADB Asian Development Bank

ADAPT-Nepal Association for Development of environment And People in Transition-

Nepal

AWS Automatic Weather Station

BCPR Bureau for Crisis Prevention and Recovery

BPC Butwal Power Company

BYS Balaju Yantra Shala

CBEWs Community-based Early Warning Systems

CCRD Climate Change Resilient Development

CDRMP Comprehensive Disaster Risk Management Program

CFGORRP Community Based Flood and Glacial Lake Outburst Risk Reduction Project

CRM-TASP Climate Risk Management Technical Assistance Support Project

DHM Department of Hydrology and Meteorology

DFID Department for International Development

DPnet Disaster Preparedness Network

DRM Disaster Risk Management

DRR Disaster Risk Reduction

DWIDP Department of Water Induced Disaster and Preparedness

ECHO European Commission’s Humanitarian Aid office

ELA Equilibrium Line Altitude

EWS Early Warning System

FWS Flood Warning Section

GEF Global Environment Facility

GEN Japanese Glaciological Expedition of Nepal

GLOF Glacial Lake Outburst Flood

GoN Government of Nepal

GPS Global Positioning System

GPR Ground Penetrating Radar

HKKH Hindu Kush Karakorum Himalaya

HMGWP High Mountain Glacial Watershed Program

ICIMOD International Centre for Integrated Mountain Development

IFRC International Federation of Red Cross and Red Crescent Societies

IFC International Finance Corporation

IPCC International Panel on Climate Change

JICA Japan International Cooperation Agency

KU Kathmandu University

LDCF Least Developed Countries Fund

LIA Little Ice Age

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LPG Liquefied Petroleum Gas

MFSC Ministry of Forests and Soil Conservation

MoFALD Ministry of Federal Affairs and Local Development

MoHA Ministry of Home Affairs

MoSTE Ministry of Science, Technology and Environment

NRRC Nepal Risk Reduction Consortium

NAPA National Adaptation Program of Action

NeDA Netherlands Development Assistance

NEOC National Emergency Operation Centre

NRRC Nepal Risk Reduction Consortium

PEB Project Executive Board

PMU/DHM Project Management Unit/ Department of Hydrology and Meteorology

RCRRP Regional Climate Risk Reduction Project in the Himalayas

RGLOFRRP Regional GLOF Risk Reduction Project

RGoB Royal Government of Bhutan

RGSL Reynold Geoscience Limited

RIMES Regional Multi-Hazard Early Warning System

SPCR Strategic Program for Climate Resilience

SNP Sagarmatha National Park

TMI The Mountain Institute

TOR Terms of Reference

TRGRRP Tsho Rolpa GLOF Risk Reduction Project

TU Tribhuvan University

UNEP-RRCAP United Nations Environment Program-Regional Resource Centre For Asia

and Pacific

UNDP United Nations Development Program

USAID U.S. Agency for International Development

VDC Village Development Committee

WB World Bank

WECS Water and Energy Commission Secretariat

WWF World Wildlife Fund

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Table of Contents Acknowledgement ............................................................................................................................

Executive Summary .......................................................................................................................... I

Abbreviations and Acronyms ......................................................................................................... IV

Chapter I Introduction ..................................................................................................................... 1

1.1. Glacier Retreat and Climate Change .................................................................................. 1

1.2. Glacier and Glacial Lakes in Nepal .................................................................................... 3

1.3. Glacial Lake Outburst Floods ............................................................................................ 4

1.4. Objective of the Study ....................................................................................................... 6

1.5. Scope of Work .................................................................................................................. 7

1.6. Methodology ..................................................................................................................... 8

Chapter II Understanding the Glaciers and Glacial-Lake phenomenon: Nepal and other countries 10

2.1. General............................................................................................................................ 10

2.2. Tsho Rolpa GLOF Risk Reduction Project ..................................................................... 10

2.2.1 Adaptation and mitigation works carried out on Tsho Rolpa Glacial Lake .................. 12

2.3. Case of Bhutan ................................................................................................................ 16

2.3.1 Pho Chu basin ............................................................................................................... 17

2.3.2 Luggye Lake................................................................................................................... 18

2.3.3 Raphstreng Lake ........................................................................................................... 19

2.3.4 Thorthormi Lake ........................................................................................................... 19

2.3.5 Adaptation and mitigation works on glacial lakes in Bhutan ....................................... 21

2.4 Case of Peru ......................................................................................................................... 25

2.4.1 Primary natural disasters in Peru ................................................................................. 26

2.4.2 Safety measures adopted for glacial lakes in the Cordillera Blanca, Peru ................... 27

2.4.3 Methodology for implementing safety measures in the Cordillera Blanca ................. 28

2.4.4 Mitigation and safety measures in the lakes of Peru ................................................... 28

2.5 National Disaster Preparedness on Glacial Lake and GLOF: A Review of Current Status of

Nepal ......................................................................................................................................... 33

2.5.1 Comprehensive Disaster Risk Management Program (CDRMP) .................................. 33

2.5.2 Regional Climate Risk Reduction Project in the Himalayas (RCRRP) – Nepal

Component ............................................................................................................................ 33

2.5.3 Regional GLOF Risk Reduction Project (RGLOFRRP) - Nepal Component .................... 34

2.5.4 Climate Risk Management Technical Assistance Support Project (CRM-TASP) ........... 34

2.5.5 Strategic Program for Climate Resilience (SPCR) ......................................................... 35

2.5.6 4th Flagship Program (FS4) of the Nepal Risk Reduction Consortium (NRRC) ............. 35

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2.5.7 The High Mountain Glacial Watershed Programme, ADAPT-Asia and other USAID- .. 35

Chapter III Study Area: Imja Glacial Lake ...................................................................................... 37

3.1 General ................................................................................................................................ 37

3.2 Baseline socio-economic information of downstream of Imja Glacial Lake ....................... 39

3.2.1 Social Sector.................................................................................................................. 39

3.2.2 Infrastructure ................................................................................................................ 40

3.3 Previous studies on Imja Glacial Lake and surroundings .................................................... 42

3.3.1 Topographic Survey ...................................................................................................... 42

3.3.2 Bathymetric Investigation ............................................................................................ 49

3.3.4 Geophysical Investigation ............................................................................................. 51

3.3.5 Glacier observations ..................................................................................................... 53

3.3.6 GLOF Modeling study of Imja Lake ............................................................................... 53

Chapter IV Lessons Learnt: Mitigation Measures and Gap Analysis ............................................... 57

4.1 GLOF Risk Reduction Activities .......................................................................................... 57

4.2 Lessons Learned ................................................................................................................... 57

Chapter V Recommendations ....................................................................................................... 60

Planning Phase .......................................................................................................................... 60

Execution Phase ........................................................................................................................ 61

Monitoring Phase ...................................................................................................................... 62

References .................................................................................................................................... 63

List of Figures

Figure 1 Location map of Tsho Rolpa Glacial Lake in Dolakha district, Nepal .............................. 10

Figure 2 Tsho Rolpa Glacial Lake and its development stages in different years ......................... 12

Figure 3 . Water coming out from test siphon from Tsho Rolpa Glacier Lake ............................. 13

Figure 4 . Schematic diagram and information of the Early Warning System established on Tsho

Rolpa Glacial lake and its downstream in 1998. ........................................................................... 14

Figure 5 Open channel constructed at Tsho Rolpa ....................................................................... 15

Figure 6 Map of Bhutan with glacier and glacial lakes ................................................................. 16

Figure 7 Raphstreng, Thorthormi and Luggye Glacial Lakes in Bhutan ........................................ 17

Figure 8 Luggye lake and Jamlhari Peak (left) and expansion of Luggye Lake (1956-2004) ......... 18

Figure 9 Raphstreng Lake with glacier snout and outlet canal (left) and expansion of Raphstreng

Lake (1956-2004) .......................................................................................................................... 19

Figure 10 A glacial lake located in the Thorthormi glacier near the inlet of Luggye Lake (left) and

expansion of Thorthormi Lake (1956-2004) ................................................................................. 20

Figure 11 Location of Thorthormi Lake and Subsidiary Lake I and II ............................................ 21

Figure 12 Excavation works at Raphstreng Lake, Bhutan ............................................................. 22

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Figure 13 Excavation works at Thorthormi Lake, Bhutan ............................................................. 23

Figure 14 Early warning system at Lunana region, Bhutan .......................................................... 24

Figure 15 Location map of Cordillera Blanca in Peru .................................................................... 26

Figure 16 Two tunnels built to prevent water level from rising in Safuna Alta Lakes .................. 29

Figure 17 V-shaped cut into Jancarurish Lake's moraine in 1951 ................................................ 30

Figure 18 Safety wirk in Hatuncoche Lake .................................................................................... 31

Figure 19 Paron Lake is surrounded by eight snow-covered peaks: Huandoy, Pisco, Chacraraju,

Pirámide, Paria, Artesonraju, Nevados de Caraz, and Aguja Nevada ........................................... 32

Figure 20 Location map of Imja Lake ............................................................................................ 37

Figure 21 TerraSAR-X image of Imja Glacial Lake on 1 May 2008. Resolution: 1 m and Scene size:

10 km width and 5 km length. ...................................................................................................... 38

Figure 22 Map of Imja Lake development .................................................................................... 38

Figure 23 Topographical map of dead ice and end moraine of Imja Glacier and bathymetric map

of Imja Glacier. Contour of moraine and dead ice area was at 5-m intervals. Depth contour of

the lake is expressed as relative height to water surface level (5009 m a.s.l. ............................. 43

Figure 24 Topographic map of Imja Lake outlet ........................................................................... 44

Figure 25 Key Plan of Imja Lake Outlet-main and Diversion canals ............................................. 46

Figure 26 Bathymetries of Imja Glacial Lake measured in (a) March 1992 (Yamada, 1998) and (b)

April 2002. ..................................................................................................................................... 49

Figure 27 Bathymetric and topographic map of Imja Lake showing the longitudinal profile and

cross-section along the deepest point .......................................................................................... 50

Figure 28 Bathymetric survey results from Imja Lake in September 2012. Dashed contours

indicate region of interpolated data ............................................................................................. 51

Figure 29 GPR transect at Imja glacier at Imja Lake crossing from north to south on September

25, 2012 using a 10 MHz antenna assuming a velocity in ice of 167 x 106 m/s .......................... 52

Figure 30 Peak flood and flood height in the downstream of Imja Glacial Lake. ......................... 54

Figure 31 Modelled flood inundation map along Dudh Koshi valley downstream of Imja Glacial

Lake ............................................................................................................................................... 55

Figure 32 VDCs exposed to potential GLOF from Imja Glacial Lake. ............................................ 56

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List of Tables Table 1 GLOF events recorded in Nepal ......................................................................................... 5

Table 2 List of potentially critical glacial lakes in Nepal identified in the 2010 study and their

priority category ............................................................................................................................. 6

Table 3 Area change of major glacial lakes in Pho Chu sub-basin from 2001 to 2006 ................. 17

Table 4 Natural disasters in the Cordillera Blanca ........................................................................ 26

Table 5 Number of adjoining VDCs and population exposed to potential Imja GLOF risk and by

distance from the lake .................................................................................................................. 39

Table 6 Population and district exposed to potential Imja GLOF risk .......................................... 39

Table 7 Details of Main Canal Dimensions ................................................................................... 47

Table 8 Details of Main Canal Dimensions ................................................................................... 48

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Chapter I Introduction

Himalayan glaciers cover about three million hectares or 17% of the mountain area as compared to

2.2% in the Swiss Alps. They form the largest body of ice outside the polar caps and are the source of

water for the innumerable rivers that flow across the Indo-Gangetic plains. Himalayan glacial

snowfields store about 12,000 km3 of freshwater. About 15,000 Himalayan glaciers form a unique

reservoir which supports perennial rivers such as the Indus, Ganga and Brahmaputra which, in turn,

are the lifeline of millions of people in South Asian countries (Pakistan, Nepal, Bhutan, India and

Bangladesh) (IPCC WGII AR4).

1.1. Glacier Retreat and Climate Change

The Himalayan glaciers are a water tower for fresh water supply as well as good indicator for exploring

past and present climate changes as they remain sensitive to global temperature conditions (IPCC

2001, Oerlemans, 1994). In recent times, the issue of concern for glaciologists and climate scientists

has been the rate of retreat which has accelerated in the past few decades (Dyurgerov and Meier,

2005). Glacier retreat provides a clear indication of a global climate that has been warming since the

Little Ice Age (LIA), which occurred from approximately 1650 to 1850 (Oerlemans 2005). Throughout

the world, including the Himalayan region, evidence left by glacier moraines shows the maximum

extent of these glaciers during the LIA and quantifies the fact that glaciers have been retreating since

this period in response to a warmer climate. There is now clear evidence that the retreat of glaciers in

many locations of the world has accelerated in recent decades (Zemp et al. 2008). The rate of upward

shift of ELA in east Nepal (Kanchanjunga, Khumbu, Rolawaling, Langtang) between the Little Ice

Age (1815) and 1959 was 0.38 m per year and between 1959 and 1992 was 0.76 m per year (Kayastha

and Harrison, 2008). The higher rate of shifting of ELA in the recent past was mainly due to increase

in air temperature in the recent decades.

According to the Fourth Assessment Report of the IPCC (2007), climate change brought about by

anthropogenic activities has resulted in the average surface temperature increasing by 0.74°C in the

last 150 years. This warming has directly impacted the temperature sensitive snow and ice cover,

resulting in rapid glacial melt, which in turn has caused variations in flow and discharge of the rivers

downstream and also a rise in sea levels (Bates et al., 2008). In the 2007 Intergovernmental Panel on

Climate Change (IPCC) Working Group II Report (Cruz et al., 2007) it was mentioned that the

Himalayan glaciers are receding faster than in other parts of the world. Some intermittent glaciological

studies since 1970s revealed that Nepalese glaciers are showing this trend to some extent. There is

high confidence that over the last two decades, the Greenland and Antarctic ice sheets have been

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losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern

Hemisphere (IPCC WGI AR5).

Increasing number of potentially dangerous glacier lakes with numerous GLOF events in last few

decades can be used as a metaphor to the evidences of climate change. Till late 1950s, there were no

or small sized glacier lakes found in the Himalayas through satellite observation. Studies show that

Nepal's glaciers are retreating faster than the world average (Dyurgerov and Meier, 2005), and the

number and size of glacier lakes are increasing along with increase in temperature. Increasing

temperatures reduce the proportion of snow to rain that causes the reduction in the glacier

accumulation and a decrease in the surface albedo, which result in an increased glacier ablation (Ageta

et al., 2001, p.45). Therefore, reduced snowfall simultaneously decreases accumulation and increases

ablation, which ultimately results in accelerated glacier retreat. One of the widely studied glacier AX010

in the eastern Nepal Himalayas retreated by 160 m in 1978- 1999 and has shrunk by 26% in 21 years,

from 0.57 km2 in 1978 to 0.42 km2 in 1999 (Fujita et al., 2001a). Similarly, the Rikha Samba glacier in

the western Nepal Himalayas retreated by 300 m during 1974-1999 (Fujita et al., 2001b). Moreover,

the rate of glacier retreat was found to be increasing in recent years. For example, the glacier AX010

retreated by 30 m yr-1between 1978-1989, whereas it retreated by 51 m yr-1 during 1998-1999 (Fujita

et al., 2001a). All of the observed glaciers in the Himalayas have been retreating during recent decades

(Ageta et al., 2001) at a higher rate than any other mountain glaciers in the world (Nakawo et al., 1997).

A comparison of the 1992 glaciers with those of 1958 in Gunsa Khola basin of Kanchanjunga area,

east Nepal revealed that out of 57 glaciers, 50 % of them have retreated in the period from 1958 to

1992. Also, 30 % of the glaciers are under stationary conditions and 12 % are advancing(Asahi et al.;

(2000).

Glacier AX010 in the Shorong Himal (27o 42’ N, 86o 34’ E) is one of the most studied glaciers in

Nepal. Changes in glacier terminus have been monitored since 1978 to 2004. The aerial extent of the

glacier was measured intermittently in 1978, 1996 and 1999 by topographic survey (Fujita, 2001). The

terminus retreat from 1978 to 1989 was 30 m (-2.7 m a-1), which is equivalent to 12 m thinning of the

glacier surface. Similarly, the terminus retreat rates from 1989 to 1995, 1996 to 1999 and 1999 to 2004

were -6.7 m a-1, -30 m a-1 and -14 m a-1, respectively.

Khumbu Glacier is a large debris-covered valley glacier in the Khumbu Region, about 15 km long,

which drains mainly from the West Cwm between Mt. Everest and Lhotse. The bare ice zones (ice

pinnacles) in the glacier are gradually shrinking (Seko et al., 1998). The surface of the glacier lowered

about 10 m throughout the debris-covered ablation area in the period 1978-1995 (Kadota et al.,

2000).Yamada et al. (1992) reviewed terminus fluctuations of seven clean type glaciers in Khumbu for

the period 1970s-1989. Majority of glaciers have retreated in the range of 30 to 60 m in the observed

period. An expedition organized in 2004 found the majority of glaciers in Khumbu Region continuing

to shrink at a fast rate while some smaller glaciers have begun to disappear.

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Yala Glacier in the Langtang Valley, Rasuwa district surveyed in September 1994, May and October

1996 and found that the retreat rate and surface lowering has accelerated in recent years(Fujita et al.,

1998 and 2001). Rikha Samba Glacier in Hidden Valley, Mukut Himal, Mustang has retreated by about

200 m from 1974 to 1994(Fujita et al., 1997). The areal average of the amount of surface lowering and

the volume loss of the glacier was estimated to be 12.6 m ice equivalent and 13% of the total mass,

respectively. The annual mass balance of – 0.55 m-1 water equivalent was obtained as an average for

20 years, which is one of the largest negative values amongst small glaciers of the world.

1.2. Glacier and Glacial Lakes in Nepal

A comprehensive inventory of glaciers and glacial lakes in Nepal dates back to 1999/2000. ICIMOD

with support from UNEP-RRCAP prepared a report (ICIMOD/UNEP (2001) encompassing Nepal

and Bhutan glaciers and glacial lakes. The inventory was based mainly on topographic maps published

between 1960 and 1982; for areas where no maps were available, satellite images dating from 1999

and 2000 were used (Mool et al. 2001a). The inventory identified 3252 glaciers and 2323 glacial lakes

in Nepal.

Later in 2009/10, ICIMOD produced a new inventory for Nepal based on Landsat images taken in

2005 and 2006. In both inventories, glaciers and glacial lakes were mapped and numbered according

to river basins and sub-basins. For this, the Nepal Himalayas were divided into four major river basins

from east to west: the Koshi basin; the Gandaki basin; the Karnali basin; and the Mahakali basin. Each

was divided further into sub-basins (ICIMOD 2011). This new inventory identified 3,808 glaciers with

a total area of 4 212 sq.km and 1,466 glacial lakes in Nepal. Nine lakes were mapped in the Nepalese

part of the Mahakali river basin with a total area of 0.137 sq.km; 742 lakes were mapped in the Karnali

basin with a total area of 29.147 sq.km — the largest number and greatest lake area in any one basin;

116 glacial lakes were mapped in the Gandaki basin with a total area of 9.538 sq.km — the largest

average size in any basin (0.082 sq.km); and 599 lakes were mapped in the Koshi basin with a total

area of 25.958 sq.km. Similarly, the majority of lakes are moraine-dammed (975 lakes occupying 72%

of the total lake area); supra-glacial lakes are mostly small with an average size of 0.009 sq.km and

these represent only 1.5 % of the total glacial lake area; erosion lakes represent 17% of the total lake

area; and other glacial lakes represent 9.5%.

The decrease in number of glacial lakes is attributed to some extent to different sources of data and

different methodologies. Nonetheless, some of the changes identified do appear to be the result of

very small supra-glacial lakes coalescing to form fewer but larger glacial lakes.

The recent increase in number of glaciers is mainly due to disintegration of large glaciers due to loss

of ice on those glaciers. However, the drastic decrease in the area of glaciers is also due to high quality

data compared to 2001 inventory data. Although such an inventory of glaciers have started since 2001

in Nepal, there are no continuous scientific studies of Nepalese glaciers. Only terminus retreat data of

few glaciers are available but not glacier mass balance data. The most studied glaciers of Nepal are

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Glacier AX010 in Shorong Himal, Yala Glacier in Langtang Valley, Rikha Samba Glacier in Hidden

Valley and Khumbu Glacier in Khumbu region.

Out of 1466 glacial lakes in Nepal (ICIMOD, 2011), the most studied glacial lakes of Nepal showed

increasing in their size. Imja Glacial Lake in Solukhumbu district increased its size to 0.4 sq. km. in

1984 from only few small ponds in 1960 and then to its area 1.01 sq. km in 2009. Similarly, Tsho

Rolpa Glacial Lake in Dolakha district increased its size from 0.23 sq. km. in 1957-59 to 1.54 sq. km.

in 2009. Thulagi Glacial Lake in Gorkha district increased its size from 0.22 sq. km. in 1958 to 0.94

sq. km. in 2009.

1.3. Glacial Lake Outburst Floods

The ongoing climatic changes and changes those are projected to occur in the near future are likely to

have severe impact on water resources. The vast water resources potential of Nepal has considerable

importance in the economic development of the country. However, Nepalese river basins are spread

over such diverse and extreme geographic and climatic conditions that the potential benefits of water

are accompanied by risk. Besides, rising temperatures have caused glaciers to melt and retreat faster.

Receding glaciers which are attached with glacial lakes are helping to expand the existing glacial lake

area and increasing the risk of the sudden flooding following glacial lake outbursts.

Results based on the studies using satellite data have tried to correlate the change in the size of existing

glaciers with fluctuations in temperature show that recession rates have increased with rising

temperatures. The altitudinal-increment of temperature possesses further melting of our freshwater

reserves and thereby resulting into constructive formation of larger glacial lakes.

Meltwater lakes are potentially unstable; the sudden catastrophic release of water from such a lake is

known as a glacial lake outburst flood (GLOF). In Nepal, until the sudden outburst of Dig Tsho Lake

on 4th August, 1984 occurred, very little attention was given on this phenomena. The event caused

death of three persons with destruction of one hydropower plant (worth US$ 1.5 million), 14 bridges

and 35 houses. The outbreak of Dig Tsho caused more than three million dollars’ worth of damage

and disrupted the downstream community of Khumbu for several months. The alarm bells sounded

by this outburst event put in motion a plethora of scientific investigations, including, surveys, research,

and preliminary estimates of downstream vulnerability among others (ICIMOD 2011). The Water and

Energy Commission Secretariat (WECS) of then-His Majesty’s Government, the International Centre

for Integrated Mountain Development (ICIMOD), and the United Nations University (UNU)

collaborated in the work that eventually produced the first detailed assessment of a GLOF event in

Nepal (WECS internal report 1987; Ives 1986; Vuichard and Zimmermann 1986, 1987).

A number of GLOFs have been reported in the region in the last few decades, particularly from the

eastern region (Mool and others, 2001; Yamada, 1998; Richardson & Reynolds, 2000). Altogether

Nepal has experienced at least 24 GLOF events in the past. Of these, 14 are believed to have occurred

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in Nepal itself, and 10 were the result of flood surge overspills across the China-Nepal border. Risk

of damage and loss of life continues as the flood surges downstream across the river valleys displacing

human settlements and investments. Regarding the glacial lake outburst floods that occurred in Nepal,

there were altogether 14 GLOF events that had occurred in Nepal. The detail information of these

GLOF events is shown in Table 1.

Table 1 GLOF events recorded in Nepal(after Mool et al., 1995, 2001; Yamada, 1998; Bajracharya et

al., 2008; Ives et al., 2010)

No. Date River basin Lake Cause Losses

1 450 yearsago SetiKhola Machhapuchchhre Moraine

collapse

Pokhara valley covered

by 50–60m deep debris

2 3 Sep 1977 Dudh Koshi Nare Moraine

collapse

Human lives, bridges,

others

3 23 Jun 1980 Tamor NagmaPokhari Moraine

collapse

Villages destroyed 71

km from source

4 4 Aug 1985 Dudh Koshi Dig Tsho Ice avalanche Human lives,

hydropower station, 14

bridges, etc

5 12 Jul 1991 Tama Koshi Chubung Moraine

collapse

Houses, farmland, etc

6 3 Sep 1998 Dudh Koshi Tam Pokhari Ice avalanche Human lives and more

than NRs 156 million

7 15 Aug 2003 Madi River Kabache Lake Moraine

collapse

Not known

8 8 Aug 2004 Madi River Kabache Lake Moraine

collapse

Not known

9 Unknown Arun BarunKhola Moraine

collapse

Not known

10 Unknown Arun BarunKhola Moraine

collapse

Not known

11 Unknown Dudh Koshi Chokarma Cho Moraine

collapse

Not known

12 Unknown Kali Gandaki Unnamed

(Mustang)

Moraine

collapse

Not known

13 Unknown Kali Gandaki Unnamed

(Mustang)

Moraine

collapse

Not known

14 Unknown Mugu Karnali Unnamed (Mugu

Karnali)

Moraine

collapse

Not known

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Evaluation of the possibility of catastrophic drainage is based on the characteristics of a lake, its dam,

associated glaciers, and other topographic features (Mool et al. 2001a). The factors taken into account

include the size; rate at which the lake is expanding; position with respect to the associated glacier;

height of the moraine dam; overtopping height (free board); origin of the lake (supra, cirque, moraine

dammed); physical condition of the surroundings, such as the existence of hanging glaciers or potential

rock and debris fall or slides; and the volume of water that could drain out. Based on these criteria,

ICIMOD 2010 has identified 21 potentially critical glacial lakes and prioritized the lakes as high

priority, medium priority and low priority based on socio-economic and physical characteristics.

Table 2List of potentially critical glacial lakes in Nepal identified in the 2010 study and their priority category

The socioeconomic and physical parameters were considered together and the critical lakes were

categorized into: 1) high priority lakes – requiring extensive field investigation and mapping; 2)

medium priority lakes – that require close monitoring and reconnaissance field surveys; and 3) low

priority lakes – that warrant periodic observation. Of the 21 lakes reviewed, 6 were classed as Category

1, 4 as Category 2, and 11 as Category 3.

1.4. Community Based Flood and Glacial Lake Outburst Risk Reduction

Project (CFGORRP)

Community Based Flood and Glacial Lake Outburst Risk Reduction Project (CFGORRP) is a joint

undertaking of the GoN, GEF and UNDP. The project is being implemented by DHM under the

MoSTE as the lead implementing agency. The project working areas include Solukhumbu in the high

mountains and Mahottari, Siraha, Saptari and Udaipur districts in the Terai.

S. No.

Lake ID Number (2009)

Lake Name Category S. No.

Lake ID Number (2009)

Lake Name Category

1 kotak_gl_0009 Tsho Rolpa I 12 gakal_gl_0004

– III

2 koaru_gl_0009 Lower Barun I 13 koaru_gl_0012 Barun III

3 kodud_gl_0184 Imja Tsho I 14 kodud_gl_0238 – III

4 kodud_gl_0036 Lumding I 15 gabud_gl_0009 – III

5 kodud_gl_0242 West Chamjang I 16 kodud_gl_0220 – III

6 gamar_gl_0018 Thulagi (Dona) I 17 koaru_gl_0016 – III

7 kotam_gl_0133 Nagma II 18 gakal_gl_0008 – III

8 kodud_gl_0241 Hungu II 19 kotam_gl_0111 – III

9 kodud_gl_0193 Tam Pokhari II 20 kodud_gl_0239 East Hungu 2

III

10 kodud_gl_0229 Hungu II 21 gakal_gl_0022 Kaligandaki III

11 kotam_gl_0191 – III

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1.5. Objective of the Study

The objective of CFGORRP is:–To reduce human and material losses from GLOF in Solukhumbu

district and catastrophic flooding events in the Tarai and Churia Range. For achieving this objective,

the Project has been streamlined into two main Components. Component I is specifically aligned

towards reducing GLOF risks arising from Imja Lake whereas Component II aims to reduce human

and material losses from recurrent flooding events in the four flood prone districts of Terai.

The main objective of this study is to carry out scientific assessment of Imja Glacial Lake based on

secondary data (mostly past studies) and recommend suitable option with design to lower down the

lake water level by 3 m.

1.6. Scope of Work

The scope of the work includes the following:

The Consultant/Service Provider will undertake a thorough desk study and review available scientific information and data on Imja Lake and its surroundings.

Consult with key stakeholders to collect, collate and update information through discussion, consultative meetings with government-WECS, DWIDP, SNP, MFSC, DGM research institutions KU, TU, and other development partners UNDP, ICIMOD, DP net, WWF, for GLOF related information and particularly works related to Imja lake and surrounding areas.

Collate and update baseline data of GLOF impact downstream from Imja Lake based on field investigation reports of ICIMOD, DHM, WECS, KU, HMGWP and other organizations.

Undertake a gap analysis on technical, socio–economic, practical issues for implementing a cost effective, workable structural and non-structural mitigation measures.

Identify any other pertinent scope of works that needs to be carried out before GLOF mitigation activities commence during the implementation of the Project.

Information on activities within the study area that are relevant to project work undertaken by government, development partners, community based organizations and other stakeholders.

Review of information, data and reports on Imja Glacial Lake and surrounding focusing particularly on but not limited to discharges at Lake Outlet, stability of moraine dam, lake storage volume, glacier conditions, input- output of lake, buried ice in the end moraine complex, expansion of the lake and triggering factors for the GLOF hazard and recommend cost effective structural and non-structural mitigation measures.

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Review of GLOF Risk reduction initiatives in Tsho Rolpa Glacial Lake in Nepal, Thorthormi / Raphstreng Tsho Lake in Bhutan, Community GLOF risk reduction in Pakistan and elsewhere in HKH region and Andes, how their lessons learned can be incorporated into the Project.

Review hydro-meteorological data availability for Imja Lake and the surroundings and recommend ways for improvements.

Based on the above assessment, prepare a draft report to present the findings to PMU/DHM, PEB and partners for further comments.

Finalize the report incorporating all the comments and feedbacks and submit final report to PMU for acceptance.

1.7. Methodology

General Approach

As per the TOR, thorough review of available literature is conducted which includes review of

information, data and reports on Imja Glacial Lake and surrounding through various field

investigation reports prepared by various organizations like ICIMOD, DHM, WECS, KU, HMGWP

and other organizations to collate and update baseline data of GLOF impact downstream from Imja

Lake. Similarly, Review of GLOF Risk reduction initiatives in Tsho Rolpa Glacial Lake in Nepal,

Thorthormi / Raphstreng Tsho Lake in Bhutan, Community GLOF risk reduction in Pakistan and

elsewhere in HKH region and Andes, how their lessons learned were undertaken.

Participatory Approach

The consultant worked in close consultation with WECS, DWIDP, SNP, MFSC, DGM research

institutions KU, TU, and other development partners like UNDP, ICIMOD, DP net, WWF, etc for

GLOF related information and particularly worked to collect, collate and update information related

to Imia lake and surrounding areas.

The methodological details include the gap analysis on technical , socio–economic, practical issues for

implementing a cost effective, workable structural and non-structural mitigation measures based on

the information, hydro-meteorological data and reports on Imja Glacial Lake.

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Desk Work: Literature review

Various national and international reports, journals and text books were collected and reviewed. All

published and unpublished documents relevant to the glacier and glacial lakes, and GLOF mitigation

measures were thoroughly reviewed. Primarily the various activities in line with the glacier inventory,

and GLOF risk assessment reports published by various agencies were considered here. Similarly

websites of different international agencies working in glaciers and glacial lakes were studied. Besides

the government publications on the village information, demographic profiles and socio-economic

activities were also considered in this study.

Likewise informal questionnaires were prepared for conducting technical review of Imja glacial lake

and others. This included Key Informant’s interview.

Office work: data entry, expert consultation, analysis and report preparation

Primary data collected based on the consultation with relevant experts was reviewed; quality check

was performed and analyzed. The outcome of the analysis was discussed with the experts/ concerned

authorities and verified. Based on these findings, lesson learnt, gap analysis and recommendations

have been prepared in line with the GLOF risk arising from Imja Lake.

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Chapter II Understanding the Glaciers and Glacial-Lake phenomenon: Nepal and

other countries

2.1. General

Despite the fact that glacier and glacial lakes are fresh water reserves of the world, they also possess

imminent threat to the downstream population and properties as the lake water is likely to breach any

moment depending on its geo-physical condition. Under the changing climatic conditions, glaciers are

highly sensitive due to their relatively quick response. Climate cooling results in glacier advancement

whereas warming leads to glacier retreat; so they are excellent indicators of climate change. Hence,

recent glacial retreat and concomitant glacial lake formations/expansions in mountain areas serve as

an example and infallible testimony of climate change. As glaciers retreat, lakes commonly form

behind the newly exposed terminal moraine. The rapid accumulation of water in these lakes can lead

to a sudden breach of the moraine dam.

2.2. Tsho Rolpa GLOF Risk Reduction Project

Tsho Rolpa is located in the Rolwaling Valley, Dolakha district in the central Nepal Himalayas at

27°52’ N latitude and 86 ° 28’ E longitude, at an altitude of 4546 m asl and forms the headwaters of

Rolwaling Khola, a tributary of the Tama Koshi River (Fig. 1). The lake had been rapidly expanding

on the terminal part of the debris-covered Trakarding Glacier at least since 1958 (surface area 0.23

km2) when the Survey of India performed a topographic survey to late 1990s (surface area 1.55 km2

in 1999) before carrying out mitigation works (Chikita et al., 1999; ICIMOD, 2011). The Tsho Rolpa

Glacial Lake and its development stages in different years are shown in figure 2. The lake was

considered potentially most dangerous glacial lake in Nepal especially before carrying out engineering

works in 2000 to lower the lake water level to reduce the level of risk from a potential GLOF.

Figure 1. Location map of Tsho Rolpa Glacial Lake in Dolakha district, Nepal

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According to ICIMOD (2011), maximum and average depth of the lake were 133.5 m and 56.4 m,

respectively with surface area 1.54 km2 and estimated volume of water stored 85.96 x 106 m3 whereas

the lake was 3.45 km long as of 2009. Owing to an accelerated growth of the lake, rapid degradation

of damming moraines (terminal and lateral), melting of dead-ice inside the moraine, presence of

seepage of the lake from the end moraine, and rapid ice calving from the active glacier-terminus were

attributed for the high GLOF hazard at the lake (Rana et al., 2000) (Fig. 15). As a result of perceived

high GLOF hazard at the lake, mitigation measures including the lake water level lowering and early

warning system were recommended and implemented. Despite of some reduced hazard level of a

potential GLOF at the lake following the mitigation works, Tsho Rolpa is even now regarded as one

of the most critical glacial lakes in Nepal and the lake is being continuously monitored by the DHM.

Tsho Rolpa was extensively studied by many researchers and institutions on various aspects of the

lake and associated hazards (Damen, 1992; Meizer and Smith, 1992; WECS/JICA 1993, 1994,

1995a/b/c/d, 1996; Yamada 1993; RGSL 1994, 1996, 1997, 2000; Modder and Olden 1995; Mool

1995; Sakai 1995; Budhathoki et al., 1996; Chikita, 1997; Yamada 1998; Chikita, 1999; Reynolds, 1999;

DHM 2002a/b, 2003a/b, 2004; Shrestha, 2004; ICIMOD, 2011). The first scientific study of Tsho

Rolpa was undertaken by Damen (1992), who recommended for taking measures to lower the lake

water level and monitoring the lake area changes over time for disaster risk management from the

potential GLOF at Tsho Rolpa. Following his study, a series of preliminary studies were carried out

by WECS with assistance from JICA on many aspects of the lake (bathymetric survey, geophysical

surveys) since 1993 to 1997. Geophysical survey with electrical resistivity probe conducted by WECS

initially detected presence of dead-ice beneath debris cover at the end moraine area (WECS, 1995b).

Subsequent geophysical surveys found that the dead-ice considerably melted out resulting in increasing

depth of top of the dead-ice surface from the debris surface (Renold Geoscience, 2000; ICIMOD,

2011). Trakarding Glacier, the feeding glacier of Tsho Rolpa, retreated 72.3 m yr-1 between 1960 and

2009 while the lake extended by 17-20 m year-1 since 1993 (ICIMOD, 2011). Recurrent bathymetric

surveys undertaken (WECS, 1993 and 1994; Shrestha et al., 2004; ICIMOD, 2010) found that lake

was over 120 m deep and the lake has been progressively deepened with an average rate of about 0.43

m yr-1 (ICIMOD, 2011). Extremely dynamic end moraine area rendered by rapid melting of dead-ice,

existence of hanging glaciers, and terminus of active Trakarding Glacier which is up to 50 m high that

can calve into the lake producing huge waves are some major sources of potential triggers to GLOF

hazards at the lake (Rana et al., 2000)

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Figure 2. Tsho Rolpa Glacial Lake and its development stages in different years

Yamada (1998) carried out one of the most comprehensive study on Tsho Rolpa incorporating various

aspects of the lake and its surroundings: geomorphological features of Tsho Rolpa; interior dead ice

sounding in the end moraine area; meteorological conditions; seasonal variation of the lake level and

the amount of discharge; mass balance of the lake water; limnological studies of the lake such as water

temperature, suspended particles, its sedimentation and density stratification; chemical composition

of lake water and chemical background around the lake; processes and rate of the lake expansion;

condition of the supra-glacial pond on the Trakarding Glacier as an embryo of a glacial lake．

2.2.1 Adaptation and mitigation works carried out on Tsho Rolpa Glacial Lake

Tsho Rolpa is the only glacial lake in Nepal, where installation of a modern GLOF early warning

system and GLOF risk reduction work was carried out through lake level lowering. In May 1995, test

siphons were installed in the southwestern part of the end moraine after a company called WAVIN

Overseas B.V. donated specially-designed siphon pipes and couplers to see if they could be used to

reduce the level of the lake (Fig. 3). The work was undertaken through the Nepal-Netherlands

Friendship Association (Rana et al., 2000). In June 1997, the Nepalese government installed five locally

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manufactured siphons (two with double inlets and three with single inlets) to augment the siphons

installed by WAVIN Overseas B.V in 1995. Its capacity was too low as compared to the discharge

into the lake (18000 liter/second) which was not enough to reduce the risk. It was found during

inspection that the system was not working in its full capacity. The discharge was only 117 liter sec-1.

Figure 3. Water coming out from test siphon from Tsho Rolpa Glacier Lake

Later, the Ministry of Home Affairs initiated siphoning with proposed capacity of 600 liters/second.

The test siphons worked satisfactorily with some maintenance. The test showed that if funds were

available, siphoning out the lake water could be an option to lower the water. However, the siphon

option was later dropped due to the requirement of a large number of pipes, the lack of space to install

them, and the maintenance required. In June 1997, the Government of Nepal established an early

warning system at Tsho Rolpa and its downstream (Fig. 17), by building a temporary Nepalese Army

post at the lake, as well as police posts downstream. These posts were equipped with satellite phones

and radios so that inhabitants of downstream locations, as well as the Khimti Hydropower Project,

could be informed on a timely basis of a potential glacial lake outburst flood through Nepal’s main

radio station.

A year later (before the monsoon of 1998), the DHM established the meteor burst Early Warning

System to provide the inhabitants of the Rolwaling and Tama Koshi Valleys with early information

about a glacial lake outburst flood, thereby allowing them time to reach a safe location and save lives

and properties. The meteor burst system consisted of a glacial lake outburst flood sensing system

located just downstream of the end moraine. When a flood is sensed, a warning is relayed to 19 stations

located downstream, equipped with audible alarms (Fig. 4). The system consisted of 19 automatic

sirens at 18 villages covering major settlement at GLOF risk along Rolwaling/ Tamakosi valley to

Rajagaon located some 100 km downstream from the lake. Beside of these automatic siren stations, 3

relay stations (Simigaun-2, Bhirkot-1) were also installed. This automated early warning system was

established with financial support from the World Bank. Instruction booklets on how to save lives

from the flood both in English and Nepali have been prepared and distributed. The early warning

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system was working for 4 years till 2003. But during the Maoist insurgency in the country, the battery

and solar panel from almost all the stations were taken away and stopped functioning. Therefore,

community involvement since beginning to continuously in the system is a must to have a good

success in such a project.

Figure 4. Schematic diagram and information of the Early Warning System established on Tsho Rolpa Glacial lake

and its downstream in 1998.

The government of Nepal had commissioned a project Formulation Mission to assess the risk and

make recommendations on the best possible method to mitigate the risk from potential GLOF. A

team comprising experts from the Department of Hydrology and Meteorology, Butwal Power

Company (BPC) and Reynold Geoscience Limited (RGSL), UK was formed; the team recommended

a Tsho Rolpa GLOF Risk Reduction Project (TRGRRP) to be executed on two phase. The first phase

was proposed for lowering lake level by 3 m by excavating a channel through the western lateral

moraine while the second phase of the project would lower the lake water level by a further 17 m

(giving a total lowering of 20 m). An agreement for the Tsho Rolpa GLOF Risk Reduction Project

(TRGRRP), Nepal, was signed between Ministry of Finance of His Majesty's Government of Nepal

and the Netherlands Minister for Development Cooperation on 3rd August 1998 (DHM, 2003b).

Netherland Development Assistance (Neda) and DHM was appointed executive authority of

Netherland and Nepal, respectively for implementing the project. This project was aimed at reducing

The system consisted of:

- 2 sensing stations

- Meteoburst and ELOS transmission

- 19 warning stations (17 villages)

- 2 Data Management Center

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the water level in Tsho Rolpa by a minimum of 3 m below the datum to immediately and tangibly

reduce the risk of a breach forming in the natural moraine dam and subsequently reduce the risk of a

GLOF occurring downstream in the Rolwaling and Tamakoshi valley (Rana et al., 2000; Khanal, 2009).

The lowering of lake level was to be achieved by means of construction of an open channel (new

outlet) at the western terminal moraine in a very controlled manner regulated by the gate structure

(Rana et al., 2000; Khanal, 2009) (Fig. 5). The engineering works for channel construction to lower

the water level from the lake began in June 1999 and lowering of 3 meters lake level from the datum

level was started from June 2000 after a successful completion of the construction works (Fig. 5).

Figure 5. Open channel constructed at Tsho Rolpa

Later, TRGRRP, DHM set up an evaluation team of independent experts, to conduct final evaluation

of the project (14 May - 3 June 2002). According to Khanal (2009), major evaluation points by the

team on technical and hazard/risk aspects were: (i) the construction of channel through the moraine

of the Tsho Rolpa and subsequent lowering of lake level by 3 m has reduced the GLOF risk

significantly by (a) increasing the freeboard (b) reducing the hydrostatic pressure acting against the

moraine dam (c) reducing the volume of a potential outburst flood, and (d) reducing the hydrostatic

gradient along the expected groundwater paths to potential seepage and (ii) on the need for further

lowering of Tsho Rolpa (Phase II), the evaluation team strongly recommended conducting further

investigation to collect necessary data on geo-physical, geo-technical, hydro-geological, geo-

morphological and other relevant disciplines in the lake surroundings.

As per the recommendation of project evaluation team (Final Evaluation Report: 3 June 2002), further

research and study work in and around Tsho Rolpa area were carried out under DHM's project

proposal "Strengthening of the Ongoing Tsho Rolpa Glacier Lake Outburst Flood Risk Reduction

Project (September 2001)" (Khanal, 2009). Later, the Netherlands government agreed to fund for it

and termed as "Additional Services" to TRGRRP. Substantial portion of this fund was to be used for

establishing micro-hydro power plant at the project site to meet the daily power requirement of project

personnel stationed at the site and illumination of the project area. Balaju Yantra Shala (Pvt.) (BYS)

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undertook construction of a 15 kW micro-hydropower as per an agreement between DHM and BYS

on 18 April 2003. By the end of September 2003, BYS completed all civil and electromechanical works

relating to the establishment of power plant including power distribution network in the site. The

hydropower plant was running with its full capacity during the two-month period of its test

commissioning. However, due to partial damage of penstock pipe currently its capacity is only 8 kW

(Khanal, 2009).

2.3. Case of Bhutan

The glacier inventory in Bhutan was undertaken in 2001 (Mool et al., 2001). From the inventory a total

of 677 individual glaciers were indentified with approximate area of 1,317 km2. Similarly, a total of

2,674 glacial lakes have also been indentified, of which 25 are classified as potentially dangerous (Fig.

6). On 7 October 1994, a GLOF occurred from Luggye Lake (Fig. 7) in the watershed 90 km upstream

of Punakha Dzong in Bhutan. Since then the Royal Government of Bhutan started conducting

different monitoring and awareness campaigns in order to mitigate the adverse impact of GLOF. In

1998, the Japan-Bhutan joint research project updated the inventory of major glacial lakes and

prepared an assessment of GLOF including ranking of potentially dangerous lakes. A study of 66

glaciers in Bhutan Himalaya revealed an average retreat of 8.1 % from 1963 to 1993 (Karma et al.,

2003). In 1963, the area covered by glaciers was 146.9 km2; by 1993, this had been reduced to 134.9

km2. Later Karma et al. (2008) concluded that the growing Thorthormi Glacial Lake had a potential

for outburst in the near future. At present, there are 25 lakes in Bhutan identified as potentially

dangerous and warranting further investigation.

Figure 6. Map of Bhutan with glacier and glacial lakes

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Figure 7. Raphstreng, Thorthormi and Luggye Glacial Lakes in Bhutan

(acquired on 28 October 2009)

2.3.1 Pho Chu basin

Pho Chu is a sub-basin of the Puna Tsang Chu basin and one of the largest sub-basins in Bhutan.

Mool et al. (2001) mapped 549 lakes in the Pho Chu sub-basin from topographic maps of 1960s in

the Bhutan Himalaya. In the 1960s, the lakes in Pho Chu basin covered an area of 23.49 km2; by 2001

the lake area increased to about 25.45 km2 (Bajracharya et al., 2007).

Table 3 shows the distribution of glacial lakes in the Pho Chu sub-basin. In the 1960s, lakes covered

an area of 23.49 km2; by 2001 the overall area covered by lakes in this sub-basin increased to about

25.45 km2, growth of about 8 %. over the past 40 years, a total of 175 lakes have either dried up or

become so small that they cannot be mapped. Some 82 new lakes have been formed and are numbered

serially for pho_gl_550 to pho_gl_631.

Table 3Area change of major glacial lakes in Pho Chu sub-basin from 2001 to 2006

Lake ID Area in 2001

(m2)

Area in 2006

(m2)

Area change

(%)

Remarks

Pho_gl_84 214,078 743,187 247.2 Increased

Pho_gl_148 454,510 635,180 39.7

Pho_gl_163 369,572 241,808 34.5 Decreased

Pho_gl_164 (Tarina Tso) 280,550 439,103 56.5 Increased

Pho_gl_172 33,552 38,139 13.7 Increased

Pho_gl_206 44,194 0 Vanished

Pho_gl_207 15,463 0 Vanished

Pho_gl_209 (Raphstreng

Tso)

145,949 1,240,131 749.7 Greatly increased

Pho_gl_2010 (Luggye Tso) 769,800 1086411 41.1 Increased

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2.3.2 Luggye Lake

Luggye Lake is an end moraine-dammed lake in the Pho Chu basin of the Lunana region. Early to the

1950, there were no indications of any lakes being associated with Luggye glacier. However, in 1976

the first supraglacial lake appeared. The Luggye Lake suffered an outburst event on 7th October 1994

causing severe damage to downstream valley. After this event the lake continued to grow in size along

with continuous retreat of the glacier (Fig. 8). In 2001 the lake area increased to 1.12 km2 from 0.02

km2 in 1968. The risk assessment of the Luggye GLOF by Leber and Hausler (2002) concluded that

the blockage of the outlet of the moraine by a landslide from the left lateral moraine should be

considered as major risk. They further recommended that the active sliding zone on the left lateral

moraine be stabilized at the outlet to allow free flow of lake because of its wide outlet channel.

Figure 8. Luggye lake and Jamlhari Peak (left) and expansion of Luggye Lake (1956-2004) (right) (Bajracharya et al.,

2007)

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2.3.3 Raphstreng Lake

Raphstreng Lake appeared as a supra glacial lake in 1958 situated at an altitude of 4360 m. The

measured area of Raphstreng Lake in 1960 was 0.15 km2 later in 1986 its dimension increased

significantly (Fig. 9). In 1986, it was 1.65 km long, 0.96 km wide and 80 m deep (Sharma et al., 1986).

Nine years later, the Indo-Bhutan expedition of 1995 measured a maximum length of 1.94 km, width

of 1.13 km, and depth of 107 m. Because of weakening of lake barrier and its potential threat to the

downstream areas, the Government of Bhutan investigates the status of stability of the lake in 1995

and three phases of mitigation work were carried out from 1996 to 1998 in order to lower the water

level by 4 m. Similarly, a channel of 78.5 m in length and 36 m wide at the outlet was manually widened

and deepened to drain out the water from the lake; however, the lake is still potentially dangerous due

to massive storage of water.

Figure 9. Raphstreng Lake with glacier snout and outlet canal (left) and expansion of Raphstreng Lake (1956-2004)

(Bajracharya et al., 2007)

2.3.4 Thorthormi Lake

Thorthormi glacier consists of various supra glacial lakes and many of which are merging and growing

in size. The largest of the lakes is Thorthormi Lake. The Thorthormi terminal moraine having width

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of 30 m acts as a dam between Thorthormi Lake and Lake Raphstreng. Lake Thorthormi is a supra

glacial lake that is 65 m higher than Raphstreng Lake and lies directly above it. It is separated from the

Pho Chu by a thin, continuously eroding, left lateral moraine. Since Thorthormi Lake is at a higher

elevation than Raphstreng Lake, and since the terminal and left lateral moraine are narrow and

unstable, this lake and glacier is now under continuous monitoring. The continuous expansion of all

these supra glacial lakes has a potential for an outburst in the near future for several reasons. First,

accelerated melting of the ice has been observed; second, there is only a gentle gradient at the snout

region; third, the left lateral moraine ridge is being eroded by discharge water from the upstream

Luggye Lake; and finally, considerable seepage is seen from the left lateral moraine. Past research has

pointed out the Thorthormi Lake is continuously growing in size (Fig 10). Data from various

researches show significant change in lake area of 0.02 km2 in 1968 to 1.28 km2 in 2001. As a result

the Thorthormi Lake is listed as potentially dangerous lakes in Bhutan (Leber et al., 2002).

Figure 10. glacial lake located in the Thorthormi glacier near the inlet of Luggye Lake (left) and expansion of

Thorthormi Lake (1956-2004) (Bajracharya et al., 2007)

Realizing the potential threat of the Thorthormi Lake, the government of Bhutan implemented a

project entitled "Reducing Climate Change-induced Risks and Vulnerabilities from Glacial Lake

Outburst Floods in the Punakha-Wangdi and Chamkhar Valleys" from 2008. The main project

objectives are to raise awareness on disaster risk management, artificial lowering of potentially

dangerous Thorthormi Glacial Lake and expansion of early warning mechanisms in the Punakha

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Wangdue valley. The project, to reduce the lake water level in Thorthormi Lake is the major

component of the project financed by Least Developed Countries Fund (LDCF) managed by GEF

and facilitated by UNDP Bhutan, ACO, WWF and RGoB. The project started from 2008 and

completed in 2012.

The main objective of the 2008 phase was to re-assess the excavation site by incorporating a detailed

engineering design for excavation work and also to come up with the necessary safety measures.

Similarly, study on geological conditions, sub-surface information through geophysical methods was

done in the Thorthormi Glacier. Further, survey was conducted to finalize the excavation site and

method for spill way channel. From the field survey they identified two subsidiary lakes (subsidiary

lake I and II) near the main glacier lake (Fig. 11).

Figure 11. Location of Thorthormi Lake and Subsidiary Lake I and II

2.3.5 Adaptation and mitigation works on glacial lakes in Bhutan

2.3.5.1 Artificial lowering of Raphstreng Lake

The artificial lowering of Raphstreng Lake to reduce risk of GLOF was done from 1996 to 1998 by

the Ministry of Home and Cultural Affairs, Bhutan with the financial support from Government of

India. The total volume of materials to be excavated based on the best fit design adopting 2% channel

gradient is 34209.77 m3 in three years of the project with four working months per year. As per the

design, they achieved total excavation of 7273.90 m3 in the first year, 15463.57 m3in the second year

and 11472.34 m3 in the final year. The pictorial glimpses of excavation work at Raphstreng Lake are

presented in figure 12.

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Figure 12. Excavation works at Raphstreng Lake, Bhutan

2.3.5.2 Artificial lowering of Thorthormi Lake

Similar excavation works have been carried out in the Thorthormi Lake from 2008 to 2012. The

artificial lowering project on Thorthormi Lake was implemented by UNDP/GEF with funding from

LDCF and co-financing from Government of Austria, UNDF, WWF Bhutan and RFoB. The

methodology for the excavation work is similar to the one that was implemented on Rapstreng Lake

earlier. Most of the excavation works were manual with simple working tools without involving heavy

machineries. For disposing bigger boulders silent explosives were recommended which may require a

portable drilling machine (pionjor machine) for breaking down into smaller pieces and for pulling the

bigger boulders a max puller was used.

To provide water free working environment and sufficient working space for the workers, a 10m final

base width for the channel was proposed. In this way, the water was diverted through half of the

channel while the workers excavated the other half and vice-versa. Temporary sand bags were used

for water diversion. To avoid any major erosion activity along the excavation site and also to reduce

risk, maximum down cutting was restricted to 1.67 m per working season.

From the engineering safety point of view the following conditions are recommended for a stable spill

way channel:

o The excavation should be carried out in step of 1.67 m down cutting from the

centerline of the channel till the lake water level is lowered by 5 m at each point.

o The spillway channel bed slope should not exceed 2% (1:50) and the excavation should

be carried out as per the design details at Annexure 2

o The maximum side slope of the proposed channel must not exceed 1:1.5 (V:H) at any

phase.

o The channel bed width shall be 10 m wide to provide sufficient working space for the

workers as well as for diverting the discharge from the lake (base flow only) through

its half width during the execution of the work. The water shall be diverted through

the half width of the excavated channel using boulders and bags barrier.

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o Large boulders from the waterway channel shall be broken into manageable sizes using

silent explosives and placed at the bottom of the side slopes to enhance the stability

of the side slopes.

o The steeper sections of the outlet immediately downstream of the second subsidiary

lake need slope treatment works. If the walls/check dams are constructed along the

watercourse at regular interval, the water velocity will be reduced and the scouring will

be minimized. Either gabion check dams or boulder wall have to be constructed

depending upon the feasibility of transporting the gabion wire mesh (2 m x 1 m boxes)

to the site on head load. The location of the proposed check dams are indicated in the

drawing.

The mitigation work is to be carried out in very fragile geological environment. There could be

possibility that the mitigation work may itself trigger minor GLOF. Therefore it was suggested to

establish a reliable communication facility (satellite telephones) to warn the community living

downstream incase if GLOF occur during the excavation time. The slope stabilization and erosion

control works recommended above was carried out after the completion of the entire excavation work

depending on the real need at the site.

From 2009 every year a scientific team visited the lake an excavated the glacier debris till 2012 to lower

the water level from the lakes. From 2009 to 2012, the total material excavated from main Lake,

Subsidiary Lake I and Subsidiary Lake II are 9549, 5660 and 4988 m3, respectively. The excavation of

glacier materials from main lake has lowered the lake by 5.04 m from 2009 to 2012. Similarly, the

lowering of water level in Subsidiary Lake I and II is 3.66 and 5.08 m, respectively. The pictorial

highlights of excavation works is presented in figure 13.

Figure 13. Excavation works at Thorthormi Lake, Bhutan

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2.3.5.3 Early warning system in the Lunana region, Bhutan

The earliest awareness of glacial lakes in Bhutan dates from the 1960. After the Luggye Lake GLOF

event of 7 October 1994 in Punakha Wangdue Valley, emphasis was given on GLOF risk mitigation.

As a result a manually operated early warning system has been developed in the Lunana region by the

Flood Warning Section (FWS) of the Department of Energy. Two staff members from the FWS are

stationed in the Lunana Lake area. They are equipped with wireless sets and satellite telephones to

report lake water levels on a regular basis and to issue warnings to downstream inhabitants. Several

gauges have also been installed along the main river as well as at the lakes. These are monitored at

various stations at different times depending on the distance from the station and base camp. The

station is in regular contact with other wireless stations in the downstream areas along the Puna Tsang

Chu, including the village and towns of Punakha, Wangduephodrang, Sunkosh, Khalikhola, and

Thimpu (Bajracharya, 2007) (Fig. 14 )

Figure 14. Early warning system at Lunana region, Bhutan

Engineering and safety plan for Thorthormi Lake

The engineering and safety plan at Thorthormi Lake was carried out from August-October 2008.

According to the plan following engineering and safety study has been planned;

Topographic survey of the Thorthormi Lake

Mapping of slide, stability assessment of moraine dam

Sample collection to determine cohesion, fraction angle, soil classification and the permeability

Geophysical investigation by seismic refraction and electrical resistivity methods

Civil engineering works including identification of appropriate location for the outlet channel

excavation, engineering design for the mitigation work, estimation of volume of materials to

be excavated

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Bathymetric survey to measure the depth of the lake

Communication setup, appropriate safety gears, onsite medical facility and emergency

arrangements for safety measures.

2.4 Case of Peru

The glaciers on the Cordillera Blanca (Fig. 15) were formed as a consequence of changes in climate

over the past 700,000 years. Glaciological research indicates that seven cooling events have occurred

on earth over the last 650,000 to 680,000 years. Glacial masses in mountainous areas and in other

continental regions of the planet extended and receded intermittently during this time. The last cooling

event is estimated to have peaked 18,000 years ago, leading to an interglacial period that lasted for

approximately 6,000 years. It is from this point forward that higher temperatures and decreased

snowfall have resulted in gradual ice melt and glacial recession.

An updated glacier and glacial lake inventory indicates that there are 830 glacial lakes in the Cordillera

Blanca, with 514 draining into the Río Santa watershed and the larger Pacific watershed. All 514 have

areas greater than 5,000 m2and volumes between 100,000 m3and 79 million m3. Many of these glacial

lakes have caused natural disasters in the past while others currently pose significant threats. On the

snow-covered slopes moraine dam failures have been more periodic than erratic. Over the last three

decades, increased climate variability has modified glacier stability and created conditions different

from those studied prior to the 1970s. Prevention measures need to include new criteria and disaster

risk analyses.

The analysis of glacier stability or risk assessment for glacial lakes has, from a pragmatic perspective,

directed us toward a safety measure implemented over the last 60 years. Reducing the volume of the

glacial lake is a less radical and more analytical solution than the complete lake drainage originally

proposed.

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Figure 15. Location map of Cordillera Blanca in Peru

Naturally, the process of reducing lake volume has been gradually improved over the years due to the

increasing availability of financial resources and new technology such as mechanical equipment. In the

present context of climate change and its impact on water resources, the treatment given to dangerous

lakes must also take into account the management of water resources. Outburst floods and avalanches

have caused the majority of natural disasters in the Cordillera Blanca, making research and assessments

of these events extremely important. Knowledge of the conditions that cause these events and their

characteristics can provide insights for initial preventive measures.

2.4.1 Primary natural disasters in Peru

Peru has a long and fairly well documented history of natural disasters (Table 4). However, it is

possible that significant glacial retreats during the medieval warming period (800 to 1200 A.D.) also

produced avalanches whose traces are visible on many slopes around the Cordillera Blanca, in areas

such as Caraz, Marcará, and Callejón de Huaylas.

Table 4. Natural disasters in the Cordillera Blanca

Year Event

1725 Outburst flood buries town of Ancash

1725 Avalanches and outburst floods in Huaraz

1883 Outburst flood in Macashca, close to Huaraz

1869 Outburst flood in Monterrey - Huaraz

1917 Outburst flood from Nevado Huascarán over Ranrahirca

1938 Outburst flood in the Ulta - Carhuaz ravine

1941 Outburst flood in Pativilca watershed

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1941 Outburst flood in Huaraz (4,000 – 5,000 dead)

1945 Outburst flood over the Chavín de Huantar ruins

1950 Outburst flood in Jancarurish reservoir. Hydropower plant destroyed

1951 First outburst flood in Artesoncocha Lake – Parón Lake

1951 Second outburst flood in the Artesoncocha Lake – Parón Lake

1952 Outburst flood in Millhuacocha Lake – Quebrada Ishinca

1953, 1959 Outburst flood in Tullparaju Lake – Huaraz

1962 Outburst flood in Ranrahirca, in Nevado Huascarán (4,000 dead)

1965 Outburst flood in the Tumarina Lagoon – Carhuascancha

1989 Outburst flood in Huancayo, from an outburst of Chuspicocha Lake

1970 Outburst flood in Yungay and Ranrahirca (15,000 dead)

1998 Outburst flood in Machupicchu. Hydropower plant destroyed

2.4.2 Safety measures adopted for glacial lakes in the Cordillera Blanca, Peru

The safety measures adopted for glacial lakes in the Cordillera Blanca have two primary objectives;

a) Decrease the volume of the lake, build structures to maintain the volume at desirable levels, and

contain potential GLOFs resulting from falling ice.

b) Utilize the structures to regulate the lake as a reservoir, in light of potential future water shortages.

The following procedures will reduce risk from dangerous glacial lakes:

Cutting the open face of the moraine into a V shape: This process will gradually lower the

water level parallel to the face. This measure has been widely implemented in glacial lakes with

moraine dams, but it is a daring procedure that has been successful most of the time only because

no avalanches occurred during construction. In Los Cedros in 1951, an avalanche of ice fell into

Lake Jancarurish during the building of drainage works, resulting in an uncontrollable surge and

the Jancarurish outburst flood. It is therefore recommended to lower the level of the lake by

pumping or siphoning prior to the process of cutting the moraine edge, essentially creating an

edge that can buffer potential surges.

Construction of drainage tunnels. Drainage tunnels can be cut in glacial lakes with natural

rock dams and, in some cases, also in lakes with loose moraine dams. Several procedures have

been used to construct these tunnels, and the connection to the lake has varied from case to

case. The most important example is in Lake Parón, where a 1,300 meter (4,265 feet) tunnel was

connected to the lake with two 60 cm diameter holes. The lake was drained through the tunnel

and subsequent geotechnical studies evaluated its use and suitability as a reservoir.

Filtration. This has also been used with moraine dams, such as the procedure in Lake

Yanarraju in the eastern region of the Cordillera Blanca.

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2.4.3 Methodology for implementing safety measures in the Cordillera Blanca

The methodology that has been systematically followed in the Cordillera Blanca Glacial Lake includes

following steps;

Carry out an initial assessment of the characteristics of the lake and surrounding glacier. In

this phase, preliminary studies are carried out to include the study area in the inventory of glacial

lakes.

Carry out a more in-depth study. If the initial assessment finds characteristics that indicate

there is a risk downstream, further study is warranted. This includes cartographic and

bathymetric studies of the glacial lake and surrounding terrain, glaciological studies of the glacier,

geological studies, and analyses of the soil mechanics of the terrain. These studies should already

begin to address the potential implementation of safety measures.

Analyze the hydrology of the watershed. This is equally important to determine safe discharge

levels for the design of overflow canals, allowing for safe removal of excess lake volume.

Implement the safety measures based on information collected from the in-depth studies.

Safety measures include volume reductions, hydraulic infrastructure such as open canals, and

the drainage tunnel or channel that will be covered by the rebuilt dam to contain potential surges

caused by falling ice.

2.4.4 Mitigation and safety measures in the lakes of Peru

2.4.4.1 Safuna Alta Lake

Safuna Alta Lake is situated at 4360 m asl in Quitaracza River basin, in the Pomabamba province of

Ancash (Fig. 16). Due to the conditions of the surrounding glaciers, the moraines’ structure is highly

unstable. A recommendation was made therefore in the early 1960s to build a 47-meter tunnel to

prevent the lake’s water level from rising. A month before the earthquake of May 1970, a tunnel was

completed that reduced the water level by 38 meters (Ames and Francou). The tunnel was above the

lake’s water level. The tunnel was severely damaged by the earthquake. A new tunnel had to be built

159 meters long that, like the previous tunnel, would be excavated entirely through moraine material.

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Figure 16. Two tunnels built to prevent water level from rising in Safuna Alta Lakes

The water level from the lake continued to decrease then after. In 1974 when the team of researcher

visited the lake, the level of water was down just over 10 meters and continued to decline further in

subsequent years. It should be mentioned that the depth of the lake has changed markedly since 1967,

when it reached a depth of 154 meters. In 1973 the depth was 98 m; in 2001, 119 m; in 2002, 81.5 m,

and in 2010, 84 m.

2.4.4.2 Jancarurish Lake

Jancarurish Lake is located in the western part of Alpamayo and, like many other lakes in the Cordillera

Blanca, is a dangerous lake because of the Alpamayo glaciers. To drain Jancarurish Lake, Control

Commission cut and open V-shaped channel to lower the water level. The water was contained using

sandbags that stemmed the flow of water and allow digging on dry ground (Fig. 17). Depending on

the amount of water reaching the lake, the water level may rise from 20 to 50 cm per day. At the end

of the day in the afternoon the dam is opened to let the water flow and carry the fine material

downstream. Opening of the sluice can pose a risk because if a hanging glacier causes an avalanche,

the path to a violent flow of water is open and, under certain random circumstances, a GLOF or

avalanche may occur.

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Figure 17. V-shaped cut into Jancarurish Lake's moraine in 1951

2.4.4.3 Hatun Cocha (Big) Lake

Hatuncocha Lake is located in Santa Cruz ravine, in the northern Cordillera Blanca, in the province

of Huaylas. It is one of the most popular local tourist spots because of its variety and diversity of

landscapes. Several paths to climb the Alpamayo, Santa Cruz, Pucahirca, and other snow capped

mountains begin near the lake. Safety works in Hatuncocha Lake were built in the early 1960s and

included the installation of two steel pipes 1.20 meters in diameter. The lake water is then drained out

through the pipe system as shown in figure 18.

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Figure 18. Safety work in Hatuncoche Lake

2.4.4.4. Paron Lake

Paron Lake is the most emblematic case of glacial lake management in the Cordillera Blanca and at

the national level. Located on the western slope of the Cordillera Blanca, Paron Lake is the headwater

source for the Río Parón-Llullán River watershed, one of the principal basins draining into the Santa

River. The watershed has an area of 42 km2 (16 square miles) at the edge of the lake, and a total area

of 146 km2 (56 square miles). The coordinates at the center of the lake are 8° 59’ 40” south, and 77°

40’ 19” west. At outburst level, the elevation at the surface of the lake is 4,200 meters (13,779 feet). It

is 3,600 meters (11,811 feet) long at its maximum length and 750 meters (2,461 feet) wide at its

maximum width, with an average depth of 69.5 meters (228 feet) and an outburst volume of 79 million

m3 (2.79 billion cubic feet). It is the largest lake in the Río Santa watershed (Fig. 19).

After the outburst flood from Lake Artesoncocha in 1951, some safety measures (e.g. placing sand

bags over the natural dam) were implemented and topographical studies began to examine the

characteristics of the lake for future drainage projects. The Peruvian Santa Corporation, as the entity

that led the development of the Ancash department through 1967, contracted the services of several

recognized experts to analyze glaciers and glacial lakes in the Cordillera Blanca. They included Dr.

Louis Lliboutry (glaciology), André Pautre (geology), and Georges Post (soil mechanics). They reached

several important conclusions about potential events that could lead to GLOFs:

Seismic activity, which can affect the Hatunraju moraine or alluvial cone along the right side of the lake, through a process of liquefaction.

A karst network in the ice of the Hatunraju Glacier, causing ice below the Lake Paron water level to melt. The hollows left by the melting ice could then lead to a violent discharge from the lake.

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An excessively rapid discharge from the lake.

An outburst flood resulting from blocked infiltration networks, calving from the glacier, or increased volumes from outburst floods from secondary glacial lakes above.

Figure 19. Paron Lake is surrounded by eight snow-covered peaks: Huandoy, Pisco, Chacraraju, Pirámide, Paria,

Artesonraju, Nevados de Caraz, and Aguja Nevada

The potential for GLOFs from many different events and the high level of risk associated with Lake

Paron led to the radical recommendation of draining the lake. The experts concluded that “taking into

account the unknown and dreadful consequences that a rupture of the Lake Paron dam would have,

the most sensible course of action is to drain the lake as much as possible.”

The corporation analyzed the followed alternatives:

• An open face cut in the moraine. This alternative was rejected on the grounds that it would

destabilize the slopes of both the lateral moraine on the left side of the lake and the alluvial

cone on the right side.

• Pump water out of the lake. This would be a temporary and expensive solution.

• Bore a tunnel or sluice along the rocky right side of the lake, digging through the bottom of

the lake in the thinnest stratum of detritus. This was accepted as the safest technical alternative.

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2.5 National Disaster Preparedness on Glacial Lake and GLOF: A Review of

Current Status of Nepal

2.5.1 Comprehensive Disaster Risk Management Program (CDRMP)

Project duration: 2011-2015; Financial scope: 20 million USD (Donors: UNDP, BCPR, DFID, EC-

DIPECHO and WB)

The CRDMP was assigned to UNDP by the inter-agency Nepal Risk Reduction Consortium (NRRC)

and addresses the NRRC’s Flagship Program 5 (see Section 2.3.2). The CDRMP aims to strengthen

the institutional and legislative aspects of DRM in Nepal, by building the capacities of MoHA, other

ministries, and local and emergency preparedness and response. A particular strength of the CDRMP

lies in the broad array of institutional partnerships it can mobilize to support an effective and

coordinated GLOF and flood risk management effort under the current LDCF project. Three of the

planned project target areas are also directly covered by the CDRMP, namely Solukhumbu where Imja

Lake is located, and two of the four districts targeted by the project in the Terai and Churia Range,

Mahottari and Saptari (see Section 2.3.5). CDRMP’s engagement in these areas will provide

complementary investment to support capacity development and institutionalization of GLOF and

flood risk management skills, including support to the development of Community-based Early

Warning Systems (CBEWs).

2.5.2 Regional Climate Risk Reduction Project in the Himalayas (RCRRP) – Nepal Component

Project duration: 2010; Financial scope: USD 200,000

The RCRRP was supported by the European Commission’s Humanitarian Aid office (ECHO) and

was implemented by UNDP’s Bureau for Crisis Prevention and Recovery (BCPR). The aim of the

project was to develop and implement comprehensive risk management strategies to address climate-

induced hydro-meteorological hazards in the Himalayan region. In the implementation process,

feasible measures to reduce the risks faced by mountain communities and to mitigate impacts of

hydro-meteorological/climatic hazards were identified and implemented at community and local

administration level. The RCRRP supported capacity development for disaster risk reduction on a

small-scale with a focus on Dolakha District through the following actions: delivering community-

based disaster risk management training for communities and government agencies; conducting

hazard vulnerability and risk assessments; preparing feasibility studies for low cost early warning

systems; delivering school-based training in disaster risk reduction; developing school manuals for

disaster risk reduction; and supporting the preparation of community disaster preparedness and

response plans.

While its limited financial scope was restricting the outreach of the RCRRP, the project responded to

the rising GLOF threat from Tsho Rolpa Glacial Lake through establishing a community-based, low-

tech Early Warning System (EWS) in 3 downstream communities. The initiative was an important

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starting point for GLOF risk reduction, but of insufficient scale to incorporate other communities

downstream of Tsho Rolpa (such as Beding, Syalu, SuriDovan, Bhorle, Singati, Nagdhaha, Khimti,

and others as far as 100 kilometers down the projected GLOF Impact Zone).

2.5.3 Regional GLOF Risk Reduction Project (RGLOFRRP) - Nepal Component

Project Duration: 2008/2009; Financial scope: USD 295,000; Funding agency: DIPECHO/ECHO

This project was designed to address the problem of GLOFs in the Himalayan region and enable

comparative analysis of GLOF threats and risk mitigation efforts in Nepal, Bhutan, India and Pakistan.

This comparative analysis found that a coordinated approach combining structural with sociological

and community-based methods is necessary to prepare vulnerable communities against the threat of

GLOFs and glacier melts in the targeted sub-region. The project has provided a community-based

risk assessment of GLOF risk from Imja Lake and Dig Tsho. The project assessment report highlights

that while implementing disaster risk reduction programs in the Imja valley, it is important to combine

structural programs with non-structural activities.

2.5.4 Climate Risk Management Technical Assistance Support Project (CRM-TASP)

Project Duration: 2008-2012 Financial scope: USD 525,000

The CRM-TASP project, a UNDP BCPR-supported initiative, analyzes risks to development that are

associated with climate variability and change, and prioritizes measures that will assist countries in

better managing those risks in both the short and longer terms. It advocates managing risks at all time

scales (weather, climate, extremes, changing climate) and integrates the analysis of climate-related risks

with analysis of the institutional, decision and policy landscape; consensus-based identification and

prioritization of risk management actions (in alignment with the NAPA); development of decision-

support tools; and the mainstreaming of climate risk management into local and national development

processes.

In the context of this project, the CRM-TASP project provides connectivity with a Regional Multi-

Hazard Early Warning System (RIMES), which is coordinated by the Asian Disaster Preparedness

Center in Bangkok. RIMES provides flood and storm early warning information to a number of Asian

Countries, which can then be transmitted from Hydro-met Departments (such as DHM) to regional

and local partners.

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2.5.5 Strategic Program for Climate Resilience (SPCR)

Project Duration: 5 years from 2012; Funding scope: Approximately $40 million as a combination of

grant and loan from the Climate Investment Funds managed by ADB and WB

The Strategic Program for Climate Resilience (SPCR) was developed by the GoN, in partnership with

World Bank, IFC, ADB and was approved by the Pilot Program for Climate Resilience (PPCR) sub-

committee on June 28, 2011. The SPCR will be providing valuable complementary parallel financing.

Component 2 of the SPCR (‘Building Resilience to Climate-Related Hazards’), focuses on

strengthening hydro-meteorological infrastructure, weather and flood forecast and information

systems, and community hazard warning systems and will complement several outputs and activities

planned under this project. This component is designed to build resilience in vulnerable communities

by establishing multi-hazard early warning systems and improving access to financial instruments such

as micro-insurance/finance that reduce the adverse impacts of climate induced shocks. The main

objective of the SPCR Component 2 is to diminish the impacts of extreme climate related events,

protect lives and assets, and support agricultural livelihoods by establishing multi-hazard information

and early warning systems, upgrading the existing hydro-met and agricultural information management

systems, and improving the accuracy and timeliness of weather and flood forecasts and warning. This

includes strengthening the capacity of DHM. In particular, SPCR-supported activities under this

component will complement project activities related to the establishment of the community-based

Early Warning Systems in Imja GLOF Impact Zone and in the Terai and Churia Range.

2.5.6 4th Flagship Program (FS4) of the Nepal Risk Reduction Consortium (NRRC)

Project Duration: 2010-2015; Funding scope: 2.8 million

The project will also coordinate with the NRCC’s Flagship 4 (FS4) Program, which focuses on

integrated community based disaster risk reduction/management. The NRRC Flagship 4 (FS4), led

by the International Federation of Red Cross and Red Crescent Societies (IFRC) and Ministry of

Federal Affairs and Local Development (MoFALD), is taking the lead in reducing vulnerability to

natural disasters through community-based Disaster Risk Reduction (DRR) / Disaster Risk

Management (DRM).

2.5.7 The High Mountain Glacial Watershed Programme, ADAPT-Asia and other USAID-funding

initiatives & Programmes

HMGWP: Project Duration: 2012-2015; Funding scope: NA

Adapt-Asia: Project Duration: 2012; Funding scope: USD 152,000

The High Mountain Glacial Watershed Program (HMGWP) is an initiative of TMI funded by the

USAID through its CCRD Project. HMGWP also receives financial support from the U. S.

Department of State. HMGWP’s goal is to increase awareness of the critical importance of high

mountain watersheds in the context of climate change, highland-lowland interactions and ecosystem

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services. It seeks to achieve this goal by combining international and national scientific experience

with local knowledge and resources to develop innovative tools and practices for facilitating adaptation

to climate change in high-altitude mountain ecosystems and increasing local resilience to the impacts

of climate change. TMI and the HMGWP have already started working in one of the key Project

Target Areas around Imja Lake and have provided useful inputs for the design of Component 1.

HMGWP will be implementing a number of complementary activities in support of achieving Project

Outcome 1, particularly in relation to Outputs 1.3 and 1.4 on establishing a CBEWS in the Imja GLOF

Impact Zone and strengthening local individual and institutional capacity for GLOF risk management.

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Chapter III Study Area: Imja Glacial Lake

3.1 General

Imja Glacial Lake is located in the easternmost part of the Sagarmatha region in Solukhumbu district,

Nepal (Fig. 20). Lhotse Shar, Imja and Ampulapcha Glaciers are the parent glaciers of Imja Glacier

and Imja Glacial Lake (Fig. 21). The Imja Glacial Lake at the toe of the Imja Glacier is located at

latitude 27° 59’ N and longitude 86° 56’ E in the Nepalese Himalayas. No lake can be seen on the

photographs taken in 1956 by Muller (Swiss Everest/Lhotse Expedition of 1956), in 1963 by Bishop

and probably in 1971 by Yamada (1998). No lake but a couple of ponds can be found on the

topographical map known as the ‘Schneider Map’, Khumbu Himal (1:50,000), which was based on

terrestrial photo-grammetry and field work done from 1956 to 1963. The map shows only a couple of

small ponds on the glacier tongue with a total area of 0.03 km2 as shown in the map of Imja Glacial

Lake development (Fig.22). The lake was first recognized in the terrestrial oblique photographs taken

in 1975 by a Japanese glaciological research team (Japanese Glaciological Expedition of Nepal, GEN).

The aerial oblique photographs taken in 1975 and 1978 by GEN show a large lake with islands and

peninsulas. The size of the lake was estimated to be around 0.40 sq. km in 1984. The islands and

peninsulas disappeared, probably by melting. According to the result of the field survey made in early

April 1992 area of the lake expanded to 0.60 km2 (Yamada, 1992). The age of the lake as of 2010 may

be estimated to be about 55 years. Imja Glacial lake with an area of 1.06 km2 as of May 2009 (ICIMOD,

2011), was recorded as one of the fastest-growing lakes in the entire Himalaya.

Figure 20. Location map of Imja Lake

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Figure 21. TerraSAR-X image of Imja Glacial Lake on 1 May 2008. Resolution: 1 m and Scene size: 10 km width

and 5 km length.

Figure 22. Map of Imja Lake development

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3.2 Baseline socio-economic information of downstream of Imja Glacial Lake

The baseline socio-economic information of downstream of Imja Glacial Lake adopted mostly from

the final report of "GLOF risk assessment of the Imja, Tsho Rolpa and Thulagi Glacial Lakes in Nepal

prepared by Narendra Raj Khanal and his team in 2009" (Khanal, 2009) with some latest data.

3.2.1 Social Sector

3.2.1.1 Demographics of vulnerable population

There are total 35 VDCs adjoining Imja/Dudhkoshi River along a distance of 120 km from Imja

Glacial Lake to the confluence of Imja/Dudhkoshi with Sunkoshi with a total population of 93,145

as per Population Census, 2011. Among them five VDCs with 12,690 population are located within

50 km distance from the lake site, nine VDCs with 30,474 population within 50-75 km distance, 14

VDCs with 32,904 population are within 75-100 km distance and 7 VDCs with 17,077 population

within 100-120 km downstream (Table 5). The VDCs likely to be affected are located in three districts

– Solukhumbu, Khotang and Okhaldhunga. Nearly 52 % population is in Solukhumbu, 24% in

Khotang and 24% in Okhaldhunga district (Table 6).

Table 5Number of adjoining VDCs and population exposed to potential Imja GLOF risk and by distance from the

lake

Distance from the lake No of VDCs Population

Within 50 km 5 12690

50-75 km 9 30474

75-100 km 14 32904

100-120 km 7 17077

Total 35 93145

(Source: CBS, 2011)

Table 6Population and district exposed to potential Imja GLOF risk

District Population %

Solukhumbu 48403 52

Khotang 22496 24

Okhaldhunga 22246 24

Total 93145 100

(Source: CBS, 2011)

There are more than 50 ethnic groups living in the adjoining VDCs along the river. The dominant

ethnic/caste groups in terms of the size of population within 50 km distance are Sherpa (60 %) and

Rai (19 %) whereas it is Rai, Chhetri and Tamang within 50-75 km distance. Similarly, Rai, Bahun,

Chhetri and Magar are the major caste/ethnic groups within 75-100 km distance from the lake site.

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3.2.1.2 Housing and human settlements

The most vulnerable settlements in the downstream of Imja Glacial Lake are Chhukung with 8 houses

comprising hotels and lodges by backwater effect, Dingboche with altogether 85 building and farm

land in which 21 are lodges; 10 permanent houses and 54 traditional houses/Goths; Pangboche with

one house and one goth; Churo with one hotel and one goth; Orso with one hotel and 4 goths;

Syomare with 12 houses by secondary landslide effect. Besides these settlements Jorsalle, Tawa,

Chhamuwa, Bengkar, Toktok, Gumela, Rakding, Phakding, Dukdingma, Chhermading and Ghat are

at also risk. These settlements with many hotels, lodges, tea shops and shops are growing as business

centers serving to the tourists.

3.2.1.3 Education and culture

There is a Khumjung Secondary School at Khumjung Village in Khumjung VDC just above Namche.

Khumjung School has been very fortunate to receive help from many international friends and donors

to ensure it can offer students a quality education even in its remote location. Since the school’s

construction in 1961, Sir Edmund Hillary and the Himalayan Trust have supported the school with

many projects and funds. Except this school there are few other primary level schools at Namche and

near Pangboche. There are few other schools below Namche too. Since most of the people are Sherpa

in the Namche and Khumjung VDCs they perform Sherpa culture. Only in the lower Chaurikharka

VDC there are some Rai, Chhetri and Tamang and they enjoy their respective culture. There is no

cultural problem in the region. All ethnic groups are staying together.

3.2.1.4 Health

There is a Khunde Hospital at Khunde Village above Namche and adjacent to Khumjung Village

which is serving as a main health center in the Khumbu region. The hospital also run by the Himalayan

Trust with good health treatment facility with reasonable price to locals as well as foreigners. The

government health post is situated at Namche and a Dental Clinic is also available at Namche. At

Pheriche there is a health center which serves to the uppermost people residing at Dingboche,

Pangboche and nearby settlements.

3.2.1.5 Vulnerable, marginalized and disadvantaged groups

Rai, Chhetri and Magar who are living downstream of Imja Glacial Lake are the most vulnerable

groups in terms of their livelihood in the case of GLOF event. Their earnings are solely depend on

the tourism through small riverside business or labor work as porter to incoming tourists to Khumbu

region.

3.2.2 Infrastructure

3.2.2.1 Energy

Khumbu Bijuli Company is the main hydropower producer and distributor in the Khumbu region. It

has installed capacity of 650 kW which is serving mainly to Namche, Khunde, Khumjung and few

surrounding villages. Besides this there are few other micro-hydropower plants at Tengboche, Toktok,

Bam Khola and Lukla. The total potential capacity to generate hydropower from the downstream of

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Imja Glacial Lake area is about 1500 MW. The development of these power plants is also very

dependent on any adaptation or mitigation works that has planned to be taken place. The main energy

source for cooking and heating purpose is firewood, kerosene and LPG gas in the settlements where

electricity is not distributed by Khumbu Bijuli Company.

3.2.2.2 Drinking water and sanitation

Drinking water and sanitation situation is good in most parts of the region. Namche village has piped

drinking water supply system and sewerage system. Therefore, most of the lodges has flush type toilets.

3.2.2.3 Transportation, healthcare and communications

There is no road access to those three VDCs; Chaurikharka, Namche and Khumjung in the Khumbu

region. Lukla has year-round running airport which serves as a main gateway to the Khumbu region.

Syangboche (3860 m) just above Namche has also an airport suitable for Pilatus Porter aircraft which

is not used now. It was closed since last one decade. Regarding the communication, mobile network

is available now in the most of the Khumbu region. Also, internet service is available now.

3.2.2.4 Disaster Risk Management-related structures/measures

Many research, few training have been carried out before but no construction of shelter and

establishment of early warning system have been done yet to prevent the potential hazards. Disaster

risk management activities are gradually taking place in the downstream area of Imja Glacial Lake

through the HMGWP.

3.2.3 Economic and Livelihood Sectors

3.2.3.1 Agriculture

Due to its high Himalayan topography agriculture practices are very limited in this region. Potatoes

are grown in Pangboche, Dingboche and in other areas including some green vegetables and cabbage,

cauliflowers, radish and carrot.

3.2.3.2 Trade and industry

Sherpa is the wealthiest ethnic group in the region from the economic point of view and they are less

vulnerable to impact of possible GLOF event. Other ethnic groups and tourists are the most

vulnerable in the case of possible GLOF event in this region. The main income source is the tourism

and mountaineering in the region to all ethnic groups. Sherpa are in the foremost compare to other

ethnic group. The other income source is agriculture (farming and livestock).

3.2.3.3 Migration

Migration is negligible from this region because they are having great benefit from tourism industry.

Many men are engaged in mountaineering and trekking most of the time. Most women and elderly

men handle their business. Some business people who has house in Kathmandu also moved to

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Kathmandu and other places to escape to cold weather and off season in the upper Khumbu region.

But again they return to their places in March or April.

3.3 Previous studies on Imja Glacial Lake and surroundings

3.3.1 Topographic Survey

The first topographic survey of Imja Glacial Lake was done in April 1992 by Yamada (1992). At that

time the length and width of the lake were 1.3 km and 0.5 km, respectively. The average depth of the

lake was 47 m and the maximum depth was 99 m. The lake occupied an area of 0.6 km2 and the

accumulation of water was estimated at about 28 million m3.

A topographical survey was carried out at the end moraine and the dead ice area of the Imja Lake in

October 2001 and in April 2002 by the team of Akiko Sakai (Sakai et al., 2007). The survey was carried

out by using a digital theodolite with a laser distance meter and differential Global Positioning System

(d-GPS). The topographic map of dead ice and end moraine is given in figure 23. They observed a

significant change in spillway on the dead ice area as compared with the research done by Watanabe

et al. (1995). They observed the spillway along the southern side the cone as opposed to its northern

side in 1994. They also concluded no possibility of GLOF by collapse at the right moraine, however

if the end moraine or dead ice to melt or collapse, a GLOF would occur. Similarly, if the left side of

the moraine and dead ice area were to completely collapse, the lake water up to 30 m depth would

flow away.

The topographic survey of Imja Lake was undertaken from 4 May to 2 June 2009 by a team from

ICIMOD with the help of various Nepalese academic and governmental organizations. The

topography survey includes survey of end moraines along with the overflow channels, lateral moraines,

the lake shorelines, and the glacier terminus. The topographic survey of 2009 concluded a further

increase of 0.012 km2 of lake area.

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Figure 23. Topographical map of dead ice and end moraine of Imja Glacier and bathymetric map of Imja Glacier.

Contour of moraine and dead ice area was at 5-m intervals. Depth contour of the lake is expressed as relative

height to water surface level (5009 m a.s.l.

3.3.1.1. Preliminary topographic survey for lowering the lake water level by 3 m

3.3.1.1.1 Project background

In support of UNDP/Nepal’s Community Based GLOF and Flood Risk Reduction Project, ADAPT

Asia-Pacific under the Prime Contract and Task Order AID 486-C-11-00005, has acquired the services

of Kathmandu University (KU) to conduct a topographic survey and engineering design of the outlet

channel at the end-moraine of Imja Glacial Lake and pre-feasibility study of a mini-hydropower

generation facility from drained water near Dingboche. The main objective of the project was to

present detailed topographical survey and other relevant field data needed to design the outlet channel

for controlled release of the Imja Lake water to reduce any GLOF risk.

3.3.1.1.2 Topographic survey of outlet area

Field investigation of the study area was done during 15 May to 4 June 2012 to carry out the

topographic survey at the end-moraine and outlet portion of Imja Lake. The study team observed

numerous hummocks of moraine complex along the lateral and end-moraine. Small traces of

biological growth were also seen on the exterior face of the end moraine. The topographical survey

comprises of traversing and contouring surveying. The traverse loop was referenced to control point

(BM4) established by ICIMOD while bearing was derived from the local north using precise compass.

The traverse loop consisted of seven control points including BM4. Similarly, detailed contour survey

of Imja outlet was carried out based on the control points established through the traverse survey.

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The topographic data recorded included features, such as existing outlet river channel, and the lake

boundary along with other depicting spot height necessary for site layout planning purposes. The

survey work was carried out using both total station and GPS instruments (Fig. 24).

Figure 24. Topographic map of Imja Lake outlet

3.3.1.1.3 Pre-feasibility study to lower the lake water level

The initial idea of lowering the lake water level proposed by ADAPT Asia-Pacific, the water level of

Imja Lake is needed to be lowered by one meter each year for three years, and a design of an

appropriate system and channel to drain out the water systematically and in a controlled manner is the

purpose of this study. During several discussions with concerned stakeholders, there were two schools

of thoughts in lowering the Imja water level:

First, the Imja water level should be lowered by one meter per year by stage-wise excavation and

strengthening of the currently existing natural channel so as to create little additional disturbance to

the environment. This is also seen to be the most acceptable option to the local communities. A

hydraulic gate should also be placed in the canal.

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Second, total excavation required to reduce the lake level by 3 meters should be completed in the first

year. However, a hydraulic gate should be installed which will then be used to gradually reduce the

water level by a meter a year to a total of 3 m in three years. This option will enable the construction

work to be completed in a shorter duration and with possibly less cost. However, there will need to

be close

As per requirement, the amount of water to be drained out in one year, taking into account the current

area and volume expansion rate is 1.59 million cubic meters, which will result in an additional discharge

of 0.05 m3 s-1, which is not much significant compared to current 1.026 m3 s-1 discharges from the

outlet. Based on field survey and considering the previous studies about geomorphology of the outlet

region, two alternatives for lowering the lake level are proposed that correlate with the above

mentioned schools of thought.

Alternative 1: This alternative consists of strengthening natural spillway in three stages to drain out 3

m of water in three years. The outlet will be excavated one meter each year for three years, each time

strengthening the area influenced by the added hydraulics. After each stage of excavation, the river

bed and the region influenced will be reinforced and in the third year, the outlet channel with a flow

control mechanism will be constructed. However, using this alternative without the discharge control

mechanism in the first two years may result in high river discharge, which will cause high erosion.

Since the excavation work will be done during the dry season, when the lake water level will be lower,

that will naturally control the discharge. Furthermore this alternative will allow observation during the

first year of the influence of limited additional flow on the natural channel and in the worst case; it

will be easy to shift to alternative 2 if required.

Alternative 2: In this alternative, the main outlet will be constructed to its full depth of three meters

in the first year. However, a drainage canal will be constructed with a hydraulic gate to regulate the

flow so that the lake lowering is controlled to a meter a year for three years. The canal will be lined

and adequately protected as was done for a similar structure in the TRGRRP.

.

In both alternatives, the design consists of 30 m long canal with 3 meter depth and a vertical steel gate

to regulate the discharge and a diversion canal to divert flow of water during construction of the main

channel (Fig. 25). The area of the diversion canal and other influenced area will be stabilized by

grouting. Based on the experience in TRGRRP, the canal will be lined with geo-textile material and

geo-membrane to prevent any seepage.

The Imja Lake outlet channel system will consist of a main channel, a diversion channel, an abutment

for accommodating the control gate, a race floor for confining hydraulic jump, a control building and

a workshop. Both channels will have iron gates to control the flow. The level and timing of the lake

lowering is to be determined after a careful study of the fresh observed survey data of the lake.

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Figure 25. Key Plan of Imja Lake Outlet-main and Diversion canals

3.3.1.1.4 Diversion Channel Alternatives

A diversion canal will need to be constructed to divert water from the main channel during

construction. Diversion channel requires over 100 m excavation of the moraine, Also this diversion

channel will be located at the depression closely parallel to the main canal which will make it easier for

operation and maintenance.

The diversion channel will be a gated structure for controlled flow of the water through it. The

diversion canal is generally refilled after construction of the main canal. However, in this case, the

diversion canal can be used in future to reduce the strain on the main canal during high flows. In these

conditions, both the diversion channel and the main outlet channel can be used to release the water

in a controlled manner. The amount of water to be released through each channel will be calculated

based on geotechnical and engineering studies that will be done prior to construction. This engineering

study will then be used as a TOR for the design-build contractor, who will have to do further soil and

geotechnical studies to validate assumptions made in the present study.

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3.3.1.1.5 Civil Components

The civil components of the Imja outlet main channel system consists the following structures: Main

canal, Cofferdam, Diversion canal, Abutments, stilling basin race floor, buildings, workshops, gabion

wall lining with geo-membrane seepage protection system.

1. Main Canal

Considering the type of earthwork material available on the site, a trapezoidal canal shape has been

chosen. For smooth transition of flow from mouth to main canal at chainage 0+000, the top and the

bottom of the canal get gradually reduced to 6 m and 2 m respectively till chainage 0+010. Then the

canal is made straight up to chainage 0+030. Refer Drawings A-1, A-2, A-3 and A-4 in Part A for

details. The designed canal dimensions are given in Table 7.

Table 7. Details of Main Canal Dimensions

Description Dimension

At ch. 0+000 At ch. 0+010 At ch. 0+030

Base width 4 m 2 m 2 m

Top width 8 m 6 m 6 m

Side slope (m) 2 2 2

Normal depth of water 1 m 1 m 1 m

Free Board 0.5 m 0.5 m 0.5 m

The axis of sluice gate that is proposed to control the flow downstream is located at change 0+020.

Gabion mattresses are considered for canal lining purposes. In order to cope with any seepage the

geo-textile and geo-membrane floor lining is proposed as done in Tsho Rolpa GLOF Risk Reduction

Project (TRGRRP). Three typical cross-sections for unlined, lined canals upstream and downstream

of control gate are selected to comply with the design suggested in TRGRRP.

2. Cofferdam

A 2 m high 15 m long cofferdam with base and top widths of 6 m and 2 m respectively is proposed

to divert the water during construction of main canal. After the completion of both main and diversion

canals, the cofferdam will be removed. Materials for the cofferdam will be the moraine boulders,

gravels and pebbles excavated from the bottom of the diversion canal.

3. Diversion Canal

The diversion canal will be a gated diversion canal of trapezoidal shape and will be located at the

natural valley on southern side of the main channel is proposed. The proposed dimensions are

presented in Table 8.

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Table 8Details of Main Canal Dimensions

Description Dimension

Length 100 m

Base width 3 m

Top width 7 m

Side slope (m) 2

Normal depth of water 1 m

Free board 0.5 m

The purpose of this canal is to drain water during construction of the main outlet channel. However,

it is proposed to maintain this canal after full functioning of the main canal to serve as an additional

outlet during emergency. A typical cross-section is presented in drawing A-6 in Part A.

4. Abutments

Two rectangular abutments of length 3 m, width of 2 m and height of 3.5m has been proposed to

hold a steel gate of 2.2 tonnes (approx). Abutments comprise of RCC structure.

5. Race floor for hydraulic jump

A 10 m long Race floor for confining the hydraulic jump after the sluice gate is proposed. It consists

of trapezoidal structure with top width 6 m and bed width 2 m. It starts from change 0+020.

6. Control Buildings

Construction of two control buildings; one at main outlet channel and other at diversion channel is

proposed. The control buildings comprise of electronic mechanism to control the steel gates. The

dimension of these buildings will be tentatively 10 m x 6 m x 3 m.

7. Workshop

A workshop of dimension approximately 7 m x 4 m x 3 m would be built on the site for maintenance

of the equipments necessary for operation of the project.

3.3.1.1.6 Mechanical Components

1. Gate on main channel:

A vertical steel gate of rectangular shape with width 2 m and height 3 m is proposed to be installed at

the outlet channel. The gate weighs around 2.2 tons and will be located at chainage of 0+020 m.

2. Gate on diversion channel:

A vertical steel gate of rectangular shape with width 1m and height 3m is proposed for installation at

diversion canal.

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3.3.1.1.7 Pre-feasibility study of mini-hydropower

The pre-feasibility study of mini-hydropower project was also carried out. According to the study a

mini-hydropower project of 585 kW capacity from Imja River is feasible to generate sufficient energy

supply for four nearby villages namely Chhukung, Dingboche, Pheriche and Lobuche. The proposed

power house is at Dingboche region and the designed to be implemented in two phase. The total cost

estimated to construct the power plant of full capacity is $ 2,761,400 resulting on pre unit cost of $

4720.

3.3.2 Bathymetric Investigation

The bathymetric survey of Imja Lake was conducted by WECS in 1991 (WECS, 1991). During the

survey the study team observed 99 m of maximum depth of Imja Lake. Further they calculated the

melting rate at the bottom of the lake which was estimated to be 3.3 m year-1. Later, in 1992 Yamada

and his team performed bathymetric investigation on Imja Lake (Yamada and Sharma 1993). Later on

April of 1992 and 2002 group of Koji Fujita conducted a bathymetric survey and compared the results

with the survey done in 1992 by Yamada (Yamada 1998) (Fig. 26). In 1992, the depth measurements

were made by a tape measure lowered through boreholes made with a fisherman's drill at 61 points

(Yamada and Sharma, 1993). Measurements points only along a longitudinal line were surveyed by a

dGPS in 2002. Shoreline of the lake was measured during both observations by a compass and a laser-

distance meter from each depth measurement point near the shoreline was also used. The comparison

of two bathymetric surveys revealed no significant lowering of lake bottom due to the insulation effect

of thick debris on the ice beneath the lake and a continuous supply of debris. However, a drastic

expansion of the lake was observed due to retreat of the upstream glacier.

Figure 26. Bathymetries of Imja Glacial Lake measured in (a) March 1992 (Yamada, 1998) and (b) April 2002.

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The bathymetric survey by a team of ICIMOD was carried out from 4 May 2009 to 2 June 2009 with

a help of inflatable boat with an outboard motor. The observations were used to estimate lake storage

volume; to evaluate the lake bottom condition near the outlets; and to assess stability of the end

moraines below the lake surface. The positions (X and Y coordinates or grid) of the bathymetric

observation points were recorded using a GPS. Bathymetric maps were then prepared and the surface

area and storage volume of the lakes were calculated (Fig. 27).

Figure 27. Bathymetric and topographic map of Imja Lake showing the longitudinal profile and cross-section along

the deepest point (ICIMOD, 2011)

A bathymetric survey conducted by a team of Somos-Valenzuela between September 22 and 24, 2012

using a Biosonic EchoSounder MX sonar unit mounted on an inflatable raft (Somos-Valenzuela et al.,

2013). Several transects were measured across the lake, as well as the lake outlet complex of the former

glacier tongue of the lake (Fig. 28). According to the survey the maximum depth has increased from

98 m to 116 m since 2002, and that its estimated volume has grown from 35 million m3 to 63.8 million

m3. Most of the expansion of the lake in recent years has taken place in the glacier terminus/lake

interface to the east, now losing more than 200 m of glacial ice per year compared to estimates of 34

m yr-1 in 2007.

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Figure 28. Bathymetric survey results from Imja Lake in September 2012. Dashed contours indicate region of

interpolated data (Somos- Valenzuela, 2013)

3.3.3 Hydro-meteorological Investigation

Field expedition organized by ICIMOD from 4 May 2009 to 2 June 2009 in Khumbu region installed

a DAVIS Automatic Weather station near the Imja Lake. Data from 11 to 28 May 2009 was collected

from the station. Similarly, data from nearest hydro-meteorological station at Dingboche village was

also collected and from 1987 to 2004. The average annual mean temperature for this period was -

0.8°C; with an average annual increase of 0.07°C. Hydrological measurements were also carried out

during the same field expedition by using trace and salt dilution methods. The measurement showed

discharge of 0.4 m3 s-1 in May 2009.

A team of researcher from School of Engineering, Kathmandu University conducted a hydrological

survey of Imja Lake outlet in August 2012. Flow measurement of Imja outlet was done by using the

salt dilution method. After injecting the salt solution the discharge was measured at 200 m downstream

of the existing outlet. The discharge during August 2012 was 1.026 m3 s-1.

3.3.4 Geophysical Investigation

Engineering geological studies were carried out during the May - June expedition of 2009 by a team

of ICIMOD to evaluate the geological settings of the glacial lakes, glaciers, moraines, and the

surrounding area. The composition of rocks as well as geological and geomorphological processes and

landforms were evaluated. Various landforms and processes were also analyzed. Similarly, Geophysical

investigations were carried out for detection of buried ice both within the moraines and below the

lakes. A RAMAC GPR instrument with a 100 MHz antenna was used for the GPR surveys. In the

rough and unstable field conditions of Tsho Rolpa, wide angle reflection and refraction survey lines

were selected. Due to malfunctioning of the GPR equipment and bad weather, only a few

measurements were made at Imja Lake. The geophysical investigations showed the existence of dead-

ice blocks within the end moraine, together with multiple thermokarst features. In places the ice was

visible at the surface. Limited radarogram analysis based on a ground penetrating radar survey along

the shoreline of Imja Lake showed that the moraine contains patches of unconsolidated materials

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made up of big boulders that create large voids. They recommended that further detailed GPR

investigations are required around the end and lateral moraines as there are many exposed thermokarst

features along the channel which will play a role in determining the stability of the moraine.

Somos-Valenzuela and his team from HMGW Program conducted an observation of the structure of

the terminal moraine at Imja Lake. Detailed ground penetrating radar (GPR) surveys were conducted

(Somos-Valenzuela et al., 2012). The GPR survey showed extensive presence of ice in the core of the

terminal moraine complex (Fig. 29). The thickest areas of ice are in the moraine near the western end

of the lake on the northern side of the lake outlet. The ice of this region is several tens of meters thick

and up to fifty meters thick in some places. Along the northern and southern sides of the lake outlet,

the ice is between ten and twenty-five meters thick. In some portions of the moraine on the southern

side of the outlet the ice thickness is up to 40 m.

Figure 29. GPR transect at Imja glacier at Imja Lake crossing from north to south on September 25, 2012 using a

10 MHz antenna assuming a velocity in ice of 167 x 106 m/s (Somos-Valenzuela et al., 2013)

Extensive seepage of water from the terminal moraine was observed in two locations during visits to

the lake in September 2011, May 2012, and September 2012. GPR transects above and below the site

of seepage show the presence of ice above the seep and much less ice below the seep. Seepage of

water through the terminal moriane is an indication of potential weakness in the moraine and a

possible site of future moraine failure. They pointed out the presence of ice in the moraine in the

vicinity of excavations site must be considered for the construction of a diversion channel on the

southern side of the outlet as planned by United Nations Development Programme to develop an

Imja Lake Risk Reduction Program. Further, excavation activities that encounter ice in the moraine

material may cause weakening of the ice resulting in increased water seepage and erosion of the

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moraine. Therefore, detail GPR surveys should be conducted in this area to indentify the presence of

ice in the moraine as well as degree of water saturation of the moraine material for excavation works.

3.3.5 Glacier observations

Surface lowering in the dead-ice area of the Imja Glacier was examined for a shorter period, from

1989 to 1994 by Watanabe et al. (1995), and from 2001 to 2007 by Fujita et al. (2009). Watanabe

estimated the rates of the dead ice in from of the Imja Lake varying from 0.1 to 2.7 m year-1 during

the period 1989-1994. A maximum in excess of 5 m year-1 occurred where the ice surface had been

submerged by lake water before 1994. During the same period, the lake level fell from 5,022 m a.s.l.

in1984 to about 5,017 m a.s.l. in 1994. Such decrease in lake level is attributed by the melting of dead

ice along the outflow, thus reducing the risk of collapse of lateral moraine.

The average lowering rate for dead-ice area west of the lake was calculated as 0.4 m year-1 for, whereas

the respective lowering of 1.1 m year-1 and 2.2 m year-1 has been observed for the up-glacier area east

of the lake, and for the lake surface (Lamsal et al., 2011). The rate of surface lowering in the up-glacier

area was approximately three times higher than that in the dead-ice area.

Considerable amount of researches have been conducted in the dead-ice area (Watanabe et al., 1994,

1995, 2009; Sakai et al., 2007; Fujita et al., 2009; and Lamsal et al., 2011). Low slope areas (flat and

gentle) outside the moraine boundary act as receptacles to retain potential ice/glacier/rock falls into

the lake, while the steeper surfaces are the potential source of triggers for a GLOF. About 300 m of

glacier surface in the area melted out or retreated from 2006 to 2010. Thus, the glacial lake can expand

into steeper glacier surface area irrespective of surface gradient of the glaciers unless the lake water

level is lower than the bottom of the glacier ice, or unless the lake water level contacts with the bedrock

beneath the ice. It appears that the lake expansion is largely dictated by ice-calving into the lake which

is largely a climate independent glacier-disintegration mechanism as suggested by Purdie and Fitzharris

(1999), and Dykes et al. (2011).

The glacier observations during the May-June expedition of 2009 by ICIMOD (ICIMOD, 2011)

observed numerous crevasses and collapse features. The collapse features are thought to be related to

the high melting rate of glacier tongue due to strong solar radiation. They also observed presence of

supra-glacial melt-ponds and very slow flow rate of the glacier. At the opposite end of the lake, the

melting of ice blocks within the end moraine is thought to be slow because of the existence of isolated

ponds.

3.3.6 GLOF Modeling study of Imja Lake

The main objective of GLOF modeling was to simulate moraine dam failure of the lake and assess

potential GLOF impacts downstream. The specific objectives were i) to develop a glacial lake breach

model, ii) to develop a model of flood propagation in the valley downstream, iii) to develop a model

of inundation in the river valley, iv) to forecast flood arrival time and velocity of flow, and v) to assess

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downstream GLOF impact. The study was in three stages: i) modeling outbursts; ii) modeling flood

propagation downstream and flood mapping; and iii) downstream GLOF impact assessment.

The breach height for the lake was derived as 20 m with breaching times of 2.69 hours and peak flows

at the time of flow as 5,817 m3 s-1 for Imja Glacial Lake. Dingboche, Pangboche, Benkar, Ghat, and

Rabuwa located at 7.97, 15.72, 29.18, 37.34, and 100.2 km from the Imja Glacial Lake outlet, can

expect flood arrival times of 3.124, 3.39, 3.8, 4.2, and 7.44 hours, respectively. Because of the wide

crest width of Imja moraine dam, breaching takes about three hours as obtained from the National

Weather Service (NWS) breach model; the data about the flood reaching downstream corresponds to

the time breaching commences. The peak flood from Imja Glacial Lake decreases sharply within the

initial 10 km stretch, with a further gradual decrease beyond 20 km (Fig. 30). Dingboche, Orse, Ghat,

Bupsa, Lap, Phapare, and Kuwapani would receive moderate impacts.

Figure 30. Peak flood and flood height in the downstream of Imja Glacial Lake.

Figure 31 show the flood inundation map of potential Imja GLOF. The continuous expansion of the

lake poses a great threat to downstream settlements, livelihoods, infrastructure and socio-economic

development. It is estimated that a total area of 1009.9 hectares up to 120 km km downstream of Imja

Glacial Lake is exposed to GLOF risk. 56% (567.00 ha) of flood inundation is projected to occur

along the river course itself; the remaining 44% of flooding will affect agricultural land, forest, grass,

and bush land. Among these, about 88 ha of agricultural land, 207 ha of forest, 24 ha of bush land, 54

ha of grass land, and about 36 ha of barren land are exposed to the GLOF risk (ICIMOD, 2011).

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Figure 31. Modelled flood inundation map along Dudh Koshi valley downstream of Imja Glacial Lake (ICIMOD,

2011)

There are more than 50 ethnic groups living in the adjoining VDCs along the river. The dominant

ethnic/caste groups in terms of the size of population within 50 km distance are Sherpa (60%) and

Rai (19%) whereas it is Rai, Chhetri and Tamang within 50-75 km distance. Similarly, Rai, Bahun,

Chhetri and Magar are the major caste/ethnic groups within 75-100 km distance from the lake site.

The VDC and district wise population exposed to potential Imja GLOF risk is presented in Table 5

and 6.

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Figure 32. VDCs exposed to potential GLOF from Imja Glacial Lake.

Sherpa is the wealthiest ethnic group in the region from the economic point of view and they are less

vulnerable to impact of possible GLOF event due to higher adaptive capacity, yet their exposure to

the associated risks cannot be neglected. Other ethnic groups and tourists are the most vulnerable in

the case of possible GLOF event in this region. The main income source is the tourism and

mountaineering in the region to all ethnic groups. Sherpa are in the foremost compare to other ethnic

group. The other income source is agriculture (farming and livestock).

There are several planned and licensed hydropower schemes downstream of Imja lake. These account

to a total of 1500 MW up to Dudh Koshi at Rabuwa Bazar (Khanal, 2009). The development of these

power plants is also very dependent on the GLOF risk from Imja Lake, and hence, to protect the

people and properties downstream, the government is involved in the planning of structural mitigation

measures and takes an active interest in monitoring the lake level.

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Chapter IV Lessons Learned and Gap Analysis

4.1 GLOF Risk Reduction Activities

The following activities were carried out on Tsho Rolpa Glacial Lakes for adaptation measures to

overcome the impacts of climate change in the Nepalese Himalayas.

Test Siphon: A test siphon system at Tsho Rolpa Glaial lake was provided by the Wavin Overseas

Company of the Netherlands through the efforts of the Netherlands–Nepal Association of

Amsterdam. The system was installed at the site in 1995 to test the operation of siphon in high

mountain environment. However, due to ice-clogging in the winter, low discharge rate due to

insufficient numbers of pipes, regular maintaining of alignment of the pipes, the test siphon

mechanism to reduce the GLOF risk was not found suitable as discussed above in 2.2.1 Adaptation

and mitigation works carried out on Tsho Rolpa Glacial Lake . In Imja lake also the same case

applies and hence siphon system would not be successful.

Implementation of an Early Warning System: Following panic of potential GLOF event from

Tsho Rolpa, the GoN initiated an early warning system in June 1997 to provide timely GLOF warning

to the people living downstream with the support of World Bank.. The first flood warning system was

installed in May 1998. The DHM implemented the project and the technical design of the system was

by BC Hydro International Limited, Canada (a government agency). The system consisted of 19

automated sirens at 17 villages along Rolwaling and Tama Koshi Valleys. However, the early warning

system did not last long mainly due to lack of local community involvement in the early warning

system and political situation of the Nepal at that time.

Lowering the Lake Water Level: In addition to the establishment of early warning system, the lake

water level in the Tsho Rolpa Glacial Lake was also lowered by 3 m in order to reduce risk of potential

dam outburst. It was achieved by constructing a dam with a gated canal opening with the funding

from the Government of The Netherlands. From the spill-out water of the lake, hydropower was

developed of 15 Kw. capacity to make the Watchman’s house warm and for cooking food and other

purposes. This project is one of the best examples of risk reduction and adaptation activities in case

of GLOF.

4.2 Lessons Learned

Although the studies on GLOF related cases in Nepal are inadequate to clearly spell out suitable

mitigation measures on GLOF risk reduction, some of the lessons learned can be described as follows:

Combination of structural and non-structural measures: As a GLOF risk reduction activity, structural

and non-structural measures should be integral parts of risk reduction. Relief and recovery

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activities are to be carried out only as a response to aftermath of GLOF impact to the people

living downstream. Non-structural measures are to be focused on community awareness,

enhancement of response capacity and preparedness.

Building ownership and enhancing local capacity: The GLOF risk reduction system needs to be

developed in line with the CFGORRP project formulation on community-based system. The

community needs to be involved right from the beginning of project formulation for the

ownership as well as transfer responsibility to operate the system. Essentially, the involvement

of local communities at risk is critical for the sustainability of the system. Tsho Rolpa EWS,

is a living example, which failed partly due to lack of ownership of local community and partly

due to insurgency and armed-conflict. Unless affected people are involved –in determining

their needs, participation in project design and management of the system, the long-term

sustainability of the interventions such as EWS is less likely to be successful.

Sustainability: The capacity building in the form of technical training and a mechanism of

financial resources generation is necessary for long-term sustainability of systems such as

EWS. Even the best performing communities will require a minimum financial resources and

follow-up activities for sustainability and capacity enhancement.

Socio economic considerations: Technical considerations should not preclude socio-economic

considerations (WMO, 2003). One of the key reasons why projects go wrong is that they are

approved on the basis of technical information alone, rather than based on both technical

information and local wisdom (ActionAid, 2005). The CFGORRP should focus on local

income generation activities of vulnerable communities to bring socio-economic changes in

the project area.

Strengthening coping capacity: The GLOF risk reduction initiatives can only be successful when

the local coping capacity is strengthened through knowledge on GLOF hazard, awareness

raising of the community and preparedness to cope with GLOF. Programmes that directly

support local communities and their organisations reinforces coping and resilience capacities.

Community preparedness against GLOF disasters: Creating functional groups, developing

organisational capacities and enabling them to link with the national disaster management

mechanisms are effective ways of strengthening preparedness at the community level. In any

disaster of given magnitude, the first line of defence is still awareness and preparedness of the

communities at risk (Espinueva, 2012). The CFGORRP should focus on building

preparedness at local level through awareness program, building institutions and mechanism

to respond to disaster and capacity enhancement.

Regular Monitoring of potential disaster events: Broad and regular discussion about the existing

hazards, possible protection measures and strategies for GLOF risk management must be

developed to prepare for coming events (Petrow et al, 2006). The frequency of occurrence of

GLOF event is very low, but the monitoring of Imja Lake on GLOF triggering factors such

as possibilities of seepages or any unusual phenomenon could enhance local preparedness and

reduce GLOF impacts in the local community. The CFGORRP should focus on such

monitoring activities to enhance local preparedness to reduce GLOF impacts.

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Institutional lessons

Accountability: Although DWIDP is responsible for water induced disasters in Nepal. The

GLOF related disasters are not within the purview of DWIDP so far. DHM has the mandate

of conducting study on glacial lakes and GLOF, but lacks technical capability to undertake

civil engineering works. MoHA is responsible for coordinating all disaster related activities but

is more focused on relief and recovery. There is need for demarcation of responsibility of key

organization such as DWIDP for engineering work, DHM for early warning system and

MoHA for relief and rescue as well as coordination of all disaster related activities among line

agencies. It is absolutely necessary to clarify 1) who is primarily accountable for monitoring of

conditions of glacial lakes, repair and maintenance of the facilities in Glacial Lakes, regularly

maintaining the instruments fixed at the lake for disaster risks monitoring, 2) who is

accountable for structures such as EWS in the downstream and 3) dissemination of

information timely, awareness raising and capacity enhancement through periodic trainings.

Task-force/Committee: At each villages a Task-force/committee needs to be formed for

preparedness of GLOF. Trainings are needed for capacity enhancement of these institutions.

For smooth operation of the task force/committee, financial resource generation at local

community levels through micro-financing / insurance or other appropriate ways are needed

for the sustainability of these institutions and to reduce disaster risks.

Preparedness and Response Mechanism: The community response and preparedness mechanism

such as team formation, setting-up of early warning system, training of human resources in

rescue, first aid kits, creation of emergency fund, stocking of rescue materials, evacuation

zones, relief centers etc. are required for effectively responding to GLOF and other disasters.

The CFGORRP needs to streamline these processes.

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Chapter V Recommendations

After careful review of activities on GLOF mitigation practices in Bhutan and Nepal in recent past, it

is recommended to carry out different activities in 3 phases: i) Planning ii) Execution and iii)

Monitoring.

Planning Phase

Carry out topographic, bathymetric and geophysical field survey of the lake and the

surroundings to identify suitable open channel alignment that has no or least buried ice.

Based on results of these surveys, design structural components of open channel that are

flexible, cost effective by using locally available materials but without compromising the safety

and incorporating non-structural works.

In the structural part:

Design appropriate open channel by estimating its appropriate capacity so that the lake

water level is lowered by 3 meters. Due to lack of long term data on Imja Lake outlet,

the efficient open channel capacity needs to be ascertained during design.

The open channel design should be non-scouring and non-silting with energy

dissipation at natural falls to minimize concrete structures. The out flows from open

channel sections should be controlled by impermeable geo-membranes.

The open channel design should also include generation of micro-hydro to address

energy needs of local settlements such as Chhukung, Dingboche and Pheriche as these

tourist destinations have high demand for electricity. Encourage locals to seek funding

from public-private partnership, local contribution, Buffer zone funding, or through

different funding agencies.

The heavy equipment used in Tsho Rolpa and lying in the site needs to be evaluated

for its usability in Imja Lake to save scarce resources for the procurement of heavy

equipment for Imja Lake.

The excavation of open channel should be carefully done to use heavy equipment as

in Tsho Rolpa over the one working season as far as possible. The regular geophysical

investigation of subsurface is required to avoid buried ice along the open channel as

far as possible.

Due to lack of reliable long term hydro-meteorology data, installation of AWS and

water level sensor with recording facility and real time data transmission facility to

DHM is essential. The proper record keeping and dissemination of data is essential for

monitoring of Imja Lake and scientific research.

Ensuring effective participation of local people during planning and design of the

project activity to build ownership of local community.

The mitigation of GLOF hazard in Nepal and HKH-K region are very limited, so the

national and regional experts may not be available for design. Therefore, the

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international expertise for design or backstopping by international experts and getting

services of national consultant that had design experience in Tsho Rolpa may be

required.

A temporary GLOF EWS should be established near the project site for the safety of

people working in the project site.

In the non-structural part:

Building community ownership and ensuring the involvement of local government

units such as VDC and at community level with consultation, awareness raising

program, capacity enhancement trainings, mock drills etc. for GLOF at risk

management at local level.

Building local level Imja Lake Monitoring Group, GLOF risk management committee

and GLOF risk management committee GRMC at Namche, with the mandate to

collect information on GLOF events from Imja and other glacial lakes and disseminate

information to other vulnerable committed at downstream of Namche and to

NEOC/MoHA and DHM.

The capacity buildings of community organization, GRMC, DHM and other

stakeholders by providing appropriate trainings. Building capacity of DHM staff

through relevant training programs.

Ensuring sustainability by committed financing mechanism and follow-up programs.

Execution Phase

Establishment of GLOF EWS at the construction site for the safety of people at

construction site with appropriate relay stations at Chhukung or Dingboche and

Namche to warn local community on any disaster event during project construction

phase. If possible, the EWS network should also be connected to national level

institutes like NEOC, MoHA and DHM.

Construct the open channel as per approved design and drawings with extra caution

by conducting geophysical investigations to identify buried ice and other instabilities.

Transport the heavy equipment and accessories from Tsho Rolpa to Imja Lake if the

heavy equipment are in good conditions and it can be used.

Ensure maximum participation of the local work force in the construction work with

logistic support including personnel gears such as down jacket, boot, etc.

Provide training to the work force on health hazards and safety measures to be taken

in high mountain environment.

Ensure safety measures for the work force at the project site including the

establishment of appropriate medical facility and accommodation. Providing proper

health insurance and provision of accidental/life insurance for all project staff and

construction work force.

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Ensuring emergency evacuation plans, provide emergency evacuation zones, stockpile

emergency materials such as medicines, equipment etc.

Providing trainings to the project staff on working in high altitude environment.

Monitoring Phase

The remoteness, harsh topographical condition at High Mountain Environment calls

for close monitoring of activities and achieving the deadlines. So there is a need for

developing monitoring framework for design, construction and post construction

phases with clearly defied roles and responsibilities.

Develop the mechanism of regular monitoring of lake by local community, regional

GRMC, and at centre by DHM, NEOC/MoHA.

Build a strong technical team at the centre to monitor performance and impacts of

extreme weather condition on built infrastructure and monitor it from time to time.

Develop check list for monitoring key features such as seepages, triggers from

avalanche, debris /rock falls, slope failures etc. to monitor changes and design

appropriate action plans for the safety of Imja Lake. Build regular monitoring and

reporting mechanism on overall surroundings of the lake and the condition of newly

constructed open channel in particular.

Collect regular data from AWS and EWS and monitor changes through periodic

analysis of data and information and its impact on Imja Lake, moraine dam Imja glacier

terminus etc.

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