Reviewing Scientific Assessment Data on Imja Glacial Lake and GLOF
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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 ………………………………………………………………………………………………………………………………………………………… 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 Submitted to: Department of Hydrology and Meteorology Ministry of Science, Technology and Environment Government of Nepal Submitted by: ADAPT-Nepal February 2014 P a g e | I -------------------------------------------------------------------------------------------------------------------------------------------------------- Association For The Development of Environment and People in Transition (ADAPT-Nepal), January 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 ………………………………………………………………………………………………………………………………………………………… 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. P a g e | I -------------------------------------------------------------------------------------------------------------------------------------------------------- Association For The Development of Environment and People in Transition (ADAPT-Nepal), January 2014 ………………………………………………………………………………………………………………………………………………………… 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 P a g e | II -------------------------------------------------------------------------------------------------------------------------------------------------------- Association For The Development of Environment and People in Transition (ADAPT-Nepal), January 2014 ………………………………………………………………………………………………………………………………………………………… 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. P a g e | III -------------------------------------------------------------------------------------------------------------------------------------------------------- Association For The Development of Environment and People in Transition (ADAPT-Nepal), January 2014 …………………………………………………………………………………………………………………………………………………………