Context

• Recently,  the Department of Water Resources, River Development and Ganga Rejuvenation released the Glacial Lake Atlas of Ganga River Basin.

About Glacial Lake Atlas of Ganga River Basin 

• The present glacial lake atlas of ganga river basin is based on the inventoried glacial lakes in part of Ganga River basin from its origin to foothills of Himalayas.

  

• The study portion of Ganga River basin covers part of India and transboundary region.
• The Atlas is available on Bhuvan portal of NRSC, ISRO, India WRIS Portal and NHP web site.
• For the present study, glacial lakes with water spread area greater than 0.25 ha were mapped using Resourcesat-2 (RS-2) Linear Imaging Self Scanning Sensor-IV (LISS-IV) satellite data. Based on its process of lake formation, location, and type of damming material, glacial lakes are identified in nine different types, majorly grouped into four categories.
• Possible uses of the Glacial Lake Atlas for the water resources professionals, researchers, disaster management authorities and other stakeholders for managing the glacial lakes as well as to mitigate the possible adverse impacts of Glacial Lake Outburst Floods (GLOF) and climate change.
• National Remote Sensing Centre (NRSC), Indian Space Research Organization (ISRO), Hyderabad as one of the Implementing Agency under the National Hydrology Project (NHP), is carrying out hydrological studies using satellite data and geospatial techniques.
• As a part of the responsibilities entrusted to NRSC under NHP, detailed glacial lake inventory, prioritization for Glacial Lake Outburst Flood (GLOF) risk, and simulation of GLOF for selected lakes have been taken up for all the catchments of Indian Himalayan Rivers.

The expected utility of Glacial Lake Atlas of Ganga River Basin is:

• The atlas provides a comprehensive and systematic glacial lake database for Ganga River basin with size > 0.25 ha
• In the context of climate change impact analysis, the atlas can be used as reference data for carrying out change analysis, both with respect to historical and future time periods
• The atlas also provides authentic database for regular or periodic monitoring changes in spatial extent (expansion/shrinkage), and formation of new lakes
• The atlas can also be used in conjunction with glacier information for their retreat and climate impact studies.
• The information on glacial lakes like their type, hydrological, topographical, and associated glaciers are useful in identifying the potential critical glacial lakes and consequent GLOF risk.
• Central and State Disaster Management Authorities can make use of the atlas for disaster mitigation planning and related program.

Back to Basics

What are GLOFs and how vulnerable are the Himalayas?

• When glaciers melt, the water in glacial lakes accumulates behind loose, natural “glacial/moraine dams” made of ice, sand, pebbles and ice residue.
• A GLOF refers to the flooding that occurs when the water dammed by a glacier or a moraine is released suddenly.
• According to NDMA, glacial retreat due to climate change occurring in most parts of the Hindu Kush Himalaya has given rise to the formation of numerous new glacial lakes, which are the major cause of GLOFs. Since glaciers in the Himalayas are in a retreating phase, glacial lakes are growing and pose a potentially large risk to downstream infrastructure and life.

How can the risk be reduced?

• The NDMA guidelines say that risk reduction has to begin with identifying and mapping such lakes, taking structural measures to prevent their sudden breach, and establishing mechanism to save lives and property in times of a breach.
• Potentially dangerous lakes can be identified based on field observations, records of past events, geomorphologic and geotechnical characteristics of the lake/dam and surroundings, and other physical conditions.
• NDMA has recommended use of Synthetic-Aperture Radar imagery to automatically detect changes in water bodies, including new lake formations, during the monsoon months. It has said methods and protocols could also be developed to allow remote monitoring of lake bodies from space.
• To manage lakes structurally, the NDMA recommends reducing the volume of water with methods such as controlled breaching, pumping or siphoning out water, and making a tunnel through the moraine barrier or under an ice dam.

Source: PIB

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