GLACIAL LAKE OUTBURST FLOOD AND ASSOCIATED GEOHAZARDS IN

HIMACHAL HIMALAYA ,

ABSTRACT SUBMITTED TO UNIVERSITY OF DELHI

FOR THE AWARD OF DOCTOR OF PHILOSOPHY

IN GEOGRAPHY

By PANKAJ KUMAR

Under the Supervision of Dr. R.B. SINGH

DEPARTMENT OF GEOGRAPHY DELHI SCHOOL OF ECONOMICS

UNIVERSITY OF DELHI DELHI – 110007

SEPTEMBER 2012

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INTRODUCTION

Himalayan glaciers cover about 3 million hectares or 17 per cent of the mountain area. They form the largest body of ice outside the polar caps. About 15,000 Himalayan glaciers form a unique reservoir which supports mighty perennial rivers such as the Ganga, the Indus and the Brahmaputra which, in turn, are the lifeline of millions of people. The Ganga basin alone is home to 500 million people, about 10 per cent of the total human population. In the last 100 years alone, the global mean temperature has increased by about 0.5 to 1° C and the rapid receding of glaciers, to a major extent, is a consequence of global warming.

The glaciers in the western Himalaya are fed by both winter and summer precipitation. But those in the eastern and central Himalaya get their nourishment only from summer precipitation. The global climatic change during the first half of the 20th century has brought a tremendous impact on the high mountainous glacial environment. Many of the glaciers melted rapidly and gave birth to the origin of a large number of glacial lakes. Due to the faster rate of snow and ice melting, possibly caused by the global warming, the accumulation of water in these glacial lakes has been increasing rapidly and resulting into sudden discharge of large volume of water and debris and causing flooding in the downstream. Glacial Lake Outburst Flood (GLOF) causes disasters to life and property in the downstream regions. As the glacier continues to shrink, landslides, ice avalanches and floods will increase. But some of the most devastating effects of glacial meltdown occur when glacial lakes overflow. For decades glacier ice and debris have acted like natural dams to contain the growing lakes. But when melting glaciers feed the lakes faster than water can drain, violent torrent of liquid and debris often escapes as pressure in the burgeoning lake causes it to literally push past the glacier, ice or debris that holds it back. Due to rapid glacial melting, these “glacial lake outburst floods”- once a rarity-have become frequent occurrence one such GLOF example is Parichu lake burst of Himachal Himalaya, sighted in findings of a report connected with the Bhakra Nangal Project, that the devastating flood in June 2006, which gained momentum as it passed down the river from the heights of Kinnaur district destroyed almost everything on its way including the costly infrastructures thus pushing back the clock of development by

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several decades. It resulted in a loss of lots of life and property, disrupting services such as power, water supply and telecommunication in the flood-affected areas of Kinnaur, Shimla and Mandi district of Himachal Pradesh. More than 150 people were swept away, several were buried under the huge mass of rubble and the area had remained inaccessible for several days. About 50 bridges from Khab to Sunni and about 50 km of Hindustan-Tibet Road, the lifeline of the Lahaul-Spiti district, were washed away. The damage to the highway had a tremendous impact on the economy of the area with apple, peas and other cash crops could not be exported outside. An inquiry into the accident had concluded, that the probable cause was “Glacial Lake Outburst Flow” and a cloud burst at the same time in the catchment area of the Parichu in Tibet.

A Glacial Lake Outburst Flood (GLOF), is technically a sudden and often catastrophic flood that occurs during a volcanic eruption, but is also to describe other sorts of glacial flooding, can occur when a lake contained by a glacier or a terminal moraine dam fails. This can happen due to erosion, a building of water pressure, an avalanche of rock or heavy snow, an earthquake or cryoseism, or if large enough portion of a glacier breaks off and massively displaces the water in glacial lake at its base. Glacial lakes come in various sizes, but may hold millions to hundreds of millions of cubic meters of water. THE RESEARCH PROBLEM

Glacier lakes are the most visible and probably the most dramatic consequence of climate change in the mountains. The possible outburst of such lakes is a direct threat to downstream populations and infrastructure. The dynamic development of glacial lakes and the dramatic consequences in case of outburst has to be seen in the wider context: glacial lakes are the tip of the iceberg of climate change. It can mean the gradual receding of the storage capacity of water in glaciers for the dry season, a quicker runoff of water during monsoon season, and extended days with little water. The long term consequences affect the availability of water downstream for food production and have direct implications for food security.

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The Himalaya is considered to be highly sensitive to Climate Change, and is one of the youngest mountain ranges on earth. It is characterized by a high energy environment due to high relief, steep slopes, complex geological structures with active tectonic process and continued seismic activities. Furthermore, the region has a climatic system with great seasonality in rainfall. In combination, they make natural hazards, especially the water induced disasters a common phenomenon in the region.

GLOFs are severe geomorphological hazards and their floodwaters can wreak havoc on all human structures located along their path. Much of the damage created during GLOF events is associated with large amounts of debris that accompany the floodwaters. GLOF events have resulted in many deaths, as well as the destruction of houses, bridges, entire fields, forests, and roads. Unrecoverable damage to settlements and farmland can take place at great distances from the outburst source. In most of the events livelihoods are disturbed for long periods. The lakes at risk, however, are situated in remote and often inaccessible areas. When they burst, the devastation to local communities could be tremendous, while those living in far away cities downstream may be unaware of the catastrophe. Many glacial lakes are known to have formed in the Himalaya in the last half century, and a number of GLOF events have been reported in the region in the last few decades.

There is need to apply a particular approach to glacier hazards research known as multiple hazards research to deal with glacier melting in the mountainous area. Multiple hazards research attempts a comprehensive study of a wide range of glacial hazard operating in an area rather than singling out one type of hazard. Generally, it is accepted that the occurrence of hazardous processes in mountainous areas is increasing but least attention is paid on such a serious issue. Glacial hazard zone mapping is a good technique which involves a critical assessment and analysis of the past occurrences of the hazards -their locations, frequencies and magnitude in relation to various geo-environmental factors that influence several types of hazards. The factors that affect GLOFs are numerous and varied and interact in complex ways therefore an evaluation of the terrain in relation to hazards must include the geology, structure, slope, hydrology, climate, land use, relative relief and evidence of past and present occurrences.

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A proper information system with sound techniques need to be developed and therefore research work must be taken up to identify the regions which are at risk due to glacial lake outburst floods. The present study attains significance in the light of the fact that very little work has been done till date on this topic in India and more particularly in Himachal Pradesh. AIMS AND OBJECTIVES

The study includes following objectives: 1. To assess Spatio-temporal extent of Glacier and Glacial Lakes in Himachal

Himalaya. 2. To establish relationship between climate change and Glacial Lake Outburst. 3. To identify and map potential GLOF sites and associated geo-hazards in the

region. HYPOTHESIS

Glacial Lake Outburst Floods are the outcome of physical and climate change driving forces. THE STUDY AREA

Himachal Pradesh, situated in the lap of Western Himalaya, has majestic mountains, fertile valleys, perennial rivers, precious forests, invaluable flora and fauna, tremendous wealth of resources, minerals, very rich culture and diverse customs and manners. The state of Himachal Pradesh is situated between 30° 22’ 44” and 33° 12’ 40” N latitude, and 75° 45’55” to 79°04’20” E longitude, and occupies an area of 5.57 million ha. Himachal Pradesh is a hilly state with a general increase in elevation from west to east and south to north ranging from 350 m to 7,000 m. Its one-third area remains snow covered for about seven months in a year. This snowy part of the State is the source of three major rivers – the Beas, the Ravi, and the Chenab while the Satluj and the Yamuna rivers originate from Tibet and Yamunotri, respectively. Its climatic conditions vary from extremely hot to severe cold regions like Chamba,

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Kinnaur and Lahaul Spiti. Dharamsala and Palampur in Kangra district receive the highest precipitation only next to Chirapunji (highest rainfall in the world); while areas like Spiti almost have no rainfall during the winter season. RESEARCH METHODOLOGY

The study focuses on the delimitation of the spatial extent of glacier, glacial lakes and identification of potentially dangerous glacial lakes in Himachal Himalaya. Since the study is both spatial and temporal, data has been collected through both primary and secondary sources but the secondary data plays a much greater role.

To get a better understanding of the study area various maps such as administrative, physiographic, geology, drainage, altitude, relief, soil, forest cover, land use pattern, slope, aspect, agro-ecological zones etc has been scanned, digitized and prepared by using various GIS software.

The Survey of India toposheet of Scale 1:250000 has also been used. This map has been converted to the scale of 1:50,000 with the help of GIS software. Along with this, Shuttle Radar Topographic Mission (SRTM) DEM (Digital Elevation Model) of the study area having 90 meter resolution has been taken from Global Land Cover Facility (GLCF) website. All these digital data have been incorporated in further study to fulfill objectives.

For the mapping and inventory of glaciers and glacial lakes, the methodology used is based on rationing of the Landsat TM band. The past and the present state of dotting of glacial lakes on the landscape of Himachal Himalaya have been obtained.

The basic materials required for the compilation of an inventory of glaciers and glacial lakes are large scale topographic maps and aerial photographs. Topographic maps on a scale of 1:50,000 published by the Survey of India during the period from the 1960s to the 1990s are used. Remote sensing data from Land Observation Satellite (Landsat), Thematic Mapper (TM) of different time framework was obtained from Global Land Cover Facility (GLCF), Earth Explorer and was used to demarcate the areal extent of glaciers, glacier lakes and potential dangerous glacier lakes. Normalized Difference Snow Index (NDSI) is used to mask the glaciated region.

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(Green-SWIR)NDSI = (Green + SWIR)

Where, SWIR = Short Wave Infra Red

As far as glacial lakes are concerned Normalized Difference Water index (NDWI= (TM4-TM5) / (TM4+TM5)) and Normalised Difference Pond Index (NDPI) has been applied to identify and to see the change in the nature of these lakes. The combination of digital satellite data and the Digital Elevation Model (DEM) of the area is also used for better and more accurate results for the inventory of glaciers and glacial lakes. Ground truthing were done to rectify the errors while identifying the exact location of glaciers and glacial lakes.

To find out the relationship between climate change and nature of glacier, glacial lake and glacial lake outburst floods, meteorological data for a period of 30 year has been collected from India Meteorological Department, Pune. There are 14 meteorological stations in Himachal Pradesh. These are Shimla, Bhuntar, Sundarnagar, Mandi, Manali, Dharamsala, Nahan, Solan, Una, Kalpa, Kothi, Koksar, Gondla, and Dhararmpur. Out of these 14, meteorological data of only four station Shimla, Bhuntar, Manali, and Kalpa stations has been analyzed in this study. Mean monthly temperature and rainfall trend of these stations has been depicted through line graph along with this, data of number of days with snow and sleet has been analyzed to find results. Along with this, research findings of other scholars and researchers has been consulted and collaborated in the study to examine the relationship at various levels. As far as the potential lake outburst is concerned different triggering mechanism of GLOFs events, which depends on the nature of the damming materials, the position of the lake, the volume of the water, the nature and position of the associated mother glacier, physical and topographic condition, and other physical condition has been analyzed with the help of satellite image and also by personal visit to selected glacial lakes of the study area. To identify and map potential GLOF in the area Clague and Mathew’s formula has been taken into consideration. Paree Chu lake outburst has been taken as case study to see the impact of GLOF in the area and also to map geohazards caused by outburst along the Spiti and the Satluj river. The administrative

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boundary of the three northern Himalayan districts Kinnaur, Lahaul and Spiti and Chamba has been taken for the purpose of detailed study of snow area and glacial lakes.

In this study, primary data collection involved a visit to the area and getting questionnaire filled by the people experiencing the relationship between change in micro climate of the area and occurrence of these geohazards. To explain the history, physical layout and the growth of glacial lakes in the state, and to support the secondary data findings with the help of empirical findings, it would be very important to interview the local population and gather information regarding the impacts of various outburst floods in the past.

The processing and analysis of the data has been done by using various remote sensing and GIS software like ERDAS Imagine 9, Arc View 3.2, Arc GIS 10 and other social science software like SPSS, Microsoft Excel, etc. The presentation of the data has been done by statistical and cartographic methods such as, bar diagrams, line graph, choropleth, dot maps as and when required. FINDINGS The study reveals the fact that, out of the total geographical area in 2011, snow cover comprises 5,250 sq km (9 per cent) area was snow covered. However, snow cover was 9,451 sq km in the year 1989. Therefore, a reduction of 4,201 sq km area in snow cover has been noticed in a time span of 20 years. In percentage term the loss is around 8 per cent. The rate of loss per year comes out to be 210 sq km. The change in the area of snow cover reveals the fact that the change is prominent in the north-eastern part of the Himachal Pradesh.

The mean snow line altitude for the year 2011 is 4,479 m while the estimated result for the year 1989 is 4,245 m. During this 20 year time span a gap of 234 m has been noticed which indicate the shift of snow line altitude from lower to higher altitude. The shift in the snow line height is prominent in western and central part of Himachal Himalaya.

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Snow cover inventory of Chamba district shows a general decrease in the area from year 1989 to 2011. Non-snow area increased from 88 per cent in the year 1989 to 95 per cent in 2011. Around 16 per cent snow area has been deglaciated during 20 year time span. Coarse granular snow area has been noticed absent in the year 2011. Normalised Difference Snow Index (NDSI) depicts a picture of overall decrease in snow cover during 1989 to 2011 in the Lahaul and Spiti district. Fine Granular snow has shown maximum decrease of 10 per cent area. The total snow cover area during the year 1989 use to be 4,414 sq km which has come down to only 2,085 sq km. The total loss in the area is around 17 per cent during 20 years of time span. The rate of loss calculated is 116 sq km per year. The Kinnaur district is repeating the same story of decrease in the snow cover. The total loss in the snow area is 36 per cent which is around 2,271 sq km area. The rate of decrease is 114 sq km per year. Frost and Granular snow has shown 19 per cent and 17 per cent decrease respectively.

Reflectance ratio of water body in NIR and SWIR is much lower than in visible band. So stacked image of indices Normalised Difference Water Index (NDWI) and Normalised Difference Pond Index (NDPI) is used in glacial lake inventory of three upper district of Chamba, Lahaul and Spiti and Kinnaur district. The isolated lakes above 3,500 masl are assumed to be remnants of the glacial lakes left due to the retreat of the glaciers.

The Samples of lake pixels were taken from the known glacial lakes and water body such as Chandratal lake, Surajtal lake, Samudratapu glacial lake etc. from the NDWI and NDPI images separately which range between +1 to -1. From the collected samples mean value has been calculated for water body. The calculated mean value has been taken as threshold to demarcate glacial lake features from the other features. The gray scale threshold is used to segment an input into two classes – one for those pixels having values below an analyst defined gray level and one for those above this value. The calculated threshold value for NDWI and NDPI combine indices is -0.69. On screen digitisation were performed on reclassified image to extract the areal extent of each and every glacial lake lying in these three upper districts of Chamba, Lahaul and Spiti and Kinnaur district.

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A total of 17 glacial lakes have been identified in the Chamba district lying above 3500 m in altitude. The total area of the lakes in the district is around 0.237 sq km. Cha_gl_14 which is an erosion lake is the largest among all comprising 43,030.97 sq m of area while Cha_gl_3 is the smallest one. The average length of the glacial lake in the district is 162 m. The average altitude of a glacier lake in the region comes out to be 4,745 m from sea level. Almost all lake identified in the district are above altitudinal height of 4,000 m. The average distance of a glacial lake from the adjacent glacier is around 350 m and the range varies from 10 m in case of Cha_gl_3 to 800 m for Cha_gl_15. The orientation of the glacial lake in the region varies considerably. The glacial lakes in the region are small in size all together comprise only 0.023 per cent of the total geographical area of the district. In the district most of the glacial lakes are found to be associated with glaciers.

The Lahaul and Spiti district is the part of Greater Himalayan region having dry cold desert type of climatic condition. Most of the area of the district lies above 4,000 m altitude. Two major glacial lakes which attract tourists from all over the world such as Chandratal and Surajtal are located here. A total of 30 glacial lakes have been identified in the district lying above 3500 m in altitude. Among the three districts it has highest number of glacial lake. The total area of the lakes in the district is around 3.318 sq km. L&S_gl_17 which is known as Samudratapu glacial lake is the largest among all comprising 11,69,571.64 sq m. The average length of the glacial lake in the district is 429 m. and the maximum and the minimum length are of L&S_gl_17 (1873 m) and L&S_gl_4 (86 m) respectively. The average altitude of a glacier lake in the region comes out to be 4,869 m from sea level. Almost all the lake identified in the district are above altitudinal height of 4,000 m. Out of the total 12 glacial lake are above the height of 5,000 m. The glacial lakes in the region are small in size and all together comprise only 0.0040 per cent of the total geographical area of the district. In the district most of the glacial lakes are found to be associated with glaciers.

Considering their size two major glacial lake viz Samudratapu glacial lake and Geepanggath glacial lakes have been identified for case study. The inventory of these two lakes has been conducted separately using satellite image Landsat TM of year 1976, 1989 and 2011.

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Geepang Gath glacier is located in Chandra basin of Lahaul and Spiti district of Himachal Himalaya. It is situated at 77°13'11"E longitude and 32°31'38"N latitude. The formation of glacial lake at the snout position of Geepang Gath glacier has been noticed in the year 1976. The present result shows that from year 1976 to 2011, the lake area has increased more than 2.5 times which is around 176 per cent increase. The increase in the area in the decade 1990 to 2000 is around 31 per cent while it is rapid during last decade which is around 60 per cent. Thus, there is an overall 0.884 sq km increase in its area within a time span of 35 years.

Samudratapu glacial lake located at lat/long 32° 29´80’’N and 77° 33´44’’ E at an elevation of 4,200 m msl near the glacial terminus has formed due to the retreat of the snout of Samudra Tapu glacier. Areal extent shows increasing of the lake area from 0.39 sq km in 1976 to 0.97 sq km in 2011. The total increase in the area in per cent is 147.

In the district Kinnaur, a total of 18 glacial lakes have been identified lying above 3,500 m in altitude. The total area of the lakes in the district is around 5, 85,720 sq m (0.585 sq km). The average area of the lake comes out to be 0.032. The average length of the glacial lake in the district is 269 m while average altitude of a glacier lake comes out to be 4,967 m from mean sea level. Almost all the lake identified in the district are above altitudinal height of 4,000 m. Out of the total 10 glacial lake are above the height of 5,000 m. The average distance of a glacial lake from the adjacent glacier is around 603 m and the range varies from 0 meter to 1,800 m. The glacial lakes in the region are small in size and all together comprise only 0.093 per cent of the total geographical area of the district.

The result of primary survey depicts a picture that more than 60 per cent of people have knowledge of glacial lake formation in the area. Sites wise survey analysis of finding reveals that people living away from the glaciated region such as Pangi and Gramphu have poor knowledge about any such lake. Almost all the respondents of village Leo have noticed formation of glacial lake in the nearby area. Out of the total 100 respondents, 39 are in favour that melting of glaciers is the major reason of formation of these lakes. Around 60 per cent of respondents have accepted that they have come across the news that few lakes are increasing their areal coverage and the increase is of moderate magnitude.

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The second objective of the study focuses on finding relationship between climate change and glacial lake outburst floods. To qualify this objective primarily meteorological data of temperature and rainfall of Bhuntar, Manali, Dharamsala and Mandi for a period of 30 years ranging from 1977 to 2007 has been obtained. A land surface temperature map has been derived using Landsat TM thermal band-6 to show surface temperature and change during year 1989 and 2011. A retreating trend of glaciers in Himalaya and Himachal Himalaya has been analyzed from research article and reports published by various organizations such as Geological Survey of India, International Centre for Integrated Mountain Development (ICIMOD), Snow and Avalanche Establishment (SASE). Primary survey was also conducted to know the people perception regarding climate change impact on glaciers and livelihood in the region.

Long-term mean annual temperature records from 1901 to 1982 over India detected an increasing trend in mean surface air temperatures. It was observed that about 0.4°C warming has taken place over India during the last eight decades mainly due to rise in mean maximum temperatures. Analysis of data for the period 1901-2009 suggests that annual mean temperature for the country as a whole has risen by 0.56°C. The all India annual and monsoon rainfall for the period 1901-2009 do not show any significant trend. Similarly rainfall for the country as whole for the same period for individual monsoon months also does not show any significant trend.

Annual temperature trend of Bhuntar meteorological station is showing substantial increase of around 2°C from 1977 to 2007. In the year 1977 the mean maximum temperature was 25.31°C while it was 26.65°C in 2007. The range of maximum temperature for the same period is 2.46°C. The highest maximum temperature for the station has been recorded 31.36°C in the year 2007. At Dharamsala about 2°C increase in the mean maximum temperature has been calculated. The trend line plotted shows that in the year 1972 the initial point of trend line was around 23.1°C while in the year 2007 it is at around 24.2°C. Mean maximum annual temperature for the station Manali is of around 0.6°C.

Mean minimum temperatures of all stations are showing increasing trend with varying degree ranging from 0.1ºC at Dharamsala to 2ºC at Mandi. At Bhuntar meteorological

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station trend line projects an increase of around 0.3ºC in a time span of 30 years. Mandi and Manali has shown comparatively higher increase in annual mean minimum temperature.

The present study of annual mean temperature for three meteorological stations of Himachal is showing an increase in the mean temperature at all location. Among these three, mean temperature increase is maximum at Bhunter which is of 1.2°C in a period of 30 years. At Manali station annual mean maximum temperature trend is showing decreasing trend while annual mean temperature trend is projecting an increase.

The study revealing the fact that land surface temperature has shown an increase and the increase is not only vertical but also horizontal in nature. The increase is looking more pronounced in the Spiti valley, Kinnaur and in the northeast Chamba. In the Spiti valley, maximum surface temperature increase has been noticed between the heights of 4,000 to 5,000 m. Land surface temperature in the region is primarily ranging between -10 to +35 ° C. The range of the magnitude of land surface temperature in the region is ranging from -1.5 to 3.5°C. Most of the area is showing an increase in the land surface temperature.

The total annual rainfall for the state is 149 cm and the total annual number of rainy days is 65. Kangra district receives the maximum amount of rainfall (185cm) in a year, whereas Una receives the minimum amount of rainfall (121cm) in a year. Annual mean rainfall trend plotted for Manali, Dharamsala, Bhuntar and Mandi is not showing any clear picture of either decreasing or increasing trend. At all four meteorological stations, annual mean of heaviest rainfall in 24 hours is showing a decreasing trend but with varying degree. Manali station has shown a sharp decrease of around 17 mm in a time span of 32 year ranging from 1974 to 2007. Among these four meteorological stations annual average number of snow days data is available only for Bhuntar station. Analysis of the data reveals the fact that average day with snow in a year is also decreasing. The decrease is of around 3.4 days in a period of 23 years.

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In the Himalayan region, glaciers and snow cover have been thinning since the end of 19th century in line with the global trends. With significant snout fluctuations, most of the glaciers in the Himalayan mountain ranges have been retreating at accelerated rates in the last three decades and their rate of retreat is much faster than that of glaciers in other parts of the world. These changes correspond to the rising surface temperature trends in the Himalaya which have been reported to be higher than the global average warming.

Almost all the glaciers of Himalaya and Karakoram are receding with varying rate. Some glaciers like Kichik Kumdan and Yengutsa in Karakoram range is receding at alarming rate of more than 100 m per year. The largest glacier, Siachin, is also wasting with about 30 m per year. For Gangotri glacier, average rate of retreat is about 25 metres per year since 1935.

Studies on selected glaciers of Himachal Himalaya indicate that most of the glaciers are retreating discontinuously since post-glacial time. Of these, Geological Survey of India studied the Gara, Gor Garang, Shaune Garang, Nagpo Tokpo Glaciers of the Satluj river basin and observed an average retreat of 4.22 - 6.8 m/year. The Bara Shigri, Chhota Shigri, Miyar, Hamtah, Nagpo Tokpo, Triloknath and Sonapani Glaciers in the Chenab river basin retreated at the rate of 6.81 to 29.78 m/year. The highest and lowest retreat was in the Bara Shigri Glacier and Chhota Shigri Glacier respectively. During the period 1963 -1997, Kulkarni and others found the retreat of Janapa Glacier by 696 m, Jorya Garang by 425 m, Naradu Garang by 550 m, Bilare Bange by 90 m, Karu Garang by 800 m and Baspa Bamak by 380 m. They further observed a massive glacial retreat of 6.8 km (178 m/year) in Parbati Glacier in Kullu district during 1962 to 2000.

A good chunk of village people of Pangi, Leo and Gramphu (around 70 per cent) are having knowledge of effect of climate change in the area in the form of their altered agricultural practices. During the primary survey some of the respondents of Leo and Pangi mentioned very strongly, its negative impact on water availability from glacier and apple and pea harvesting. According to them due to rapid glacier melt, small

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streams from which they divert channel to get drinking water are vanishing very fast in the summer period.

Glacial lakes are a common feature at altitudes of 4,500 to 5,500 m in many river basins of the Himalaya. Most of the glacial lakes in the Himalayan region are known to have formed within the last 5 decades, and a number of Glacial Lake Outburst Flood (GLOF) events have been reported in this region. At least one GLOF event was recorded in Himalayan region in 3 to 10 years. In the Himachal Himalaya few incidence of GLOF has been noticed by the people residing in the remote area but has not been documented. Parechu lake outburst in the Spiti river in June 2005 has been covered widely by print and electronic media. As GLOFs pose severe threats to humans, man-made structures, agricultural fields, and natural vegetation it is important to make accurate estimates of the likely magnitude of future floods.

To qualify the third objective of ‘ Identification of Potential GLOFs’ the present study uses technique adopted by Clague and Mathews (1973) to estimate maximum instantaneous discharge from a lake at the time of outburst. The maximum instantaneous discharge can be estimated by using the volume as an input. Estimation of lake volume has been done by using data of lake area and average depth of lake extracted from the Google Earth. The lake area has been digitized from NDWI, NDPI combine image of Landsat TM. A district wise inventory of potential GLOFs has been prepared and mapped. For identification of potentially dangerous glacial lakes, the glacial lakes with an area larger than 20,000 m2 have been considered and they have been defined as major glacial lakes.

A total of 17 glacial lakes have been identified in Chamba district lying above 3,500 m in altitude. Out of the total 17 glacial lake only three glacial lake has areal coverage more than 20,000 sq m. The peak discharge can be estimated as 43, 67 and 56 m3/s respectively for Cha_gl_4, Cha_gl_14 and Cha_gl_17. Taking the Mean Daily Discharge of 50 m3/s as threshold for deciding a lake as potential threat, lake no. 14 and 17 of Chamba district can pose danger to the downstream population and has been termed as potential GLOFs. In the district Lahaul and Spiti out of the total 30 glacial lake in the district, 22 qualified the criteria of 20,000 sq m of areal coverage

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for further investigation of GLOF threat potential. Analysis of the results reveals the fact that out of total 30 glacial lakes in the district 16 have been identified as potential GLOFs which area lake no.8, 9, 10, 11, 13, 14, 15, 16, 17, 18, 20, 21, 25, 28, 29 and 30. In the district Kinnaur, a total of 18 glacial lakes have been identified in the district lying above 3,500 m in altitude. Glacial lake no. 4, 5, 7, 8 and 17 has been termed as potential GLOFs in the district.

The example of Glacial Lake Outburst Flood (26th June, 2005) of Paree Chu lake of Tibet Himalaya has been taken for detailed study of its impact on the downstream population living in the Spiti and the Satluj river valley of Himachal Pradesh. Paree Chu lake is situated at an elevation of 3875 meter in the Tibet Himalaya. The position of the lake is lying at 32°19'37'' N and 78°43'13'' E. The river travel around 42 km in the Tibetan territory and inter the Himachal Pradesh state of Indian territory at 78°40'14.512"E and 32°4'24.463"N location.

A Glacial Lake Outburst Flood (GLOF) of huge magnitude due to sudden rise/breach of Paree Chu river in the Chinese territory struck the Spiti and Satluj valley on 26th June, 2005. The major cause of the Paree Chu lake outburst was the failure/breach of dam formed of moraine and rockfall debris near the mouth of Paree Chu lake. The formation of the blockage due to rockfall at the mouth of Paree Chu lake take place roughly during the month of July 2003.

The areal coverage of water in the lake was 0.20 sq km on 16 April 2004. The length and width and the depth of lake started increasing and reached to 1.25 sq km on 26th July, 2004. On 14th August 2004 the lake area was 1.26 sq km. In the month of September 2004, the lake was about 2,100 m long, 1,100 m wide and about 40 m deep storing about 64 million cubic meters of water. After the breach and releasing of water, on 6th September, 2006 areal coverage of lake drastically reduced to 0.50 sq km. The lake is again showing some sign of increase in its area in the year 2007.

The average daily discharge during June 2005 increased continuously from 112 m3/s to 270 m3/s up to mid-June. From mid June onward the discharge increased exponentially causing a flash flood in the entire Satluj valley on 26th June. The Glacial Lake Outburst Flood starting from Paree Chu traversed the Spiti River and reached

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the Satluj River at Khab at about 11:35 am. The discharge measured at Khab on 26th at 10 am was 834 m3/s. At 11:35 am, the water level rose to about 20 m at Khab and Kharo and washed away the discharge site located at Khab. It is calculated that discharge during this GLOF was about 2,000 m3/s.

The Qmax calculated by taking the areal coverage of Paree Chu lake on 14th August, 2004 which was 12,69,898 sq m and the depth of 40 m calculated by Gupta and Sah for the month of September 2004. The cross-sectional profile generated by Google Earth has been taken to calculate the average depth of lake. The average depth comes out to be 38 m taking the maximum depth of 40 m marked in the center of the lake. The result for the Lake volume and Qmax has been derived as 4,82,56,124 m3 and 1007 m3/s respectively. This amount of instantaneous discharge of water is very high in comparison to the maximum discharge recorded normally during the peak discharge month making potential threat to the areas downstream.

The damage caused by the Paree Chu GLOF in the year 2005 is restricted only along the course of the Satluj and the Spiti river. The maximum damage was reported in the zones between Paree Chu and Khab and Morang and Wangtu because of the presence of the Quaternary materials in the form of debris fans and terrace materials at a number of places like Leo, Morang, Ribba, Purbani, Kilba, Tapri and Wangtu.

Paree Chu tributary joins the Spiti River at Sumdoh and from Sumdoh to Khab, the river flows with a gradient of 15.0 m/km. A 5 km stretch of road between Sumdoh and Shailkher was completely washed away and the military check post colony remained cut off from the rest of the area. A bridge near the meeting point of Paree Chu and Spiti river at Sumdoh was also washed away. An alternative track was developed by the local to reach Shailkher. At Shailkher inundation of crop land lying close to the river channel has been noticed. The erosion of toe of the river bank slope was prominent between Sumdoh and Leo as the mountains along the river channel are made of soft rock. At Leo village, 16 houses and 16 ha of horticultural land were completely lost while some other houses developed cracks during the 2005 GLOF. The approach road and bridge were completely destroyed leading to the isolation of the village. The GLOF has also resulted into the valley widening and river course straightening near Leo village.

Abstract

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The Satluj River from Khab to Shipki La follows a spectacular gorge with a gradient of 20.5 m/km, and is confined by rocky cliffs, thus no damage was reported in this section. Another reason of no damage to the settlement in this section is that the villages are situated more than 100 m above the river bed. A bridge on the confluence of the Spiti and the Satluj and the water discharge station washed away. The villagers were unable to access the market and the seasonal pea was fully damaged.

In a total stretch of 45 km between Khab and Morang GLOF generated flash flood washed away around 3 km and partially damaged around 5 km length of National Highway 22. An evidence of Landslide Lake Outburst Flood (LLOF) has been noticed near Spello in the Satluj river channel. Roads and bridges were also destroyed in the 2005 flood around Raksham village, near the confluence of the Sutlej and the Baspa rivers.

Between Morang and Jhakri, the river flows with a gradient of 13.52 m/km and at number of places like, Akpa, Ribba, near Urni and Kilba, Quaternary deposits are noted to occur. Most of the damage occurred in this section. In a total length of 50 km, about 5 km length of road in various sections was completely destroyed in full width, while about 5 km was partially damaged. The complete road section between Akpa and Kharo was washed away, endangering the entire Ribba village, which is located on Quaternary deposits.

High silt content in the river resulted in the temporary shutdown of hydroelectric projects in the area. The washing away of bridges on the Spiti and the Satluj rivers affected the day-to-day activities of the 2,400 people living in 23 villages in the area. The affected area is the main apple-growing region of Himachal Pradesh. The economy of the local people depends on the export of the apples. The damage to the road communication affected the overall economy of the region.