Glacial burst
Source: By Deeptiman Tiwary: The Indian Express
A glacier break is suspected to have caused the flash floods in Uttarakhand’s Chamoli on 7 February 2021. Last October, the National Disaster Management Authority (NDMA), which is headed by PM Narendra Modi, had issued detailed guidelines on how to reduce and deal with disasters caused by what is scientifically called Glacial Lake Outburst Floods (GLOFs).
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.
Unlike earthen dams, the weak structure of the moraine dam leads to the abrupt failure of the dam on top of the glacial lake, which holds a large volume of water. A failure of the dam has the potential of releasing millions of cubic metres of water in a short period, causing catastrophic flooding downstream. Peak flows as high as 15,000 cubic metre per second have been recorded in such events.
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.
An “Inventory and Monitoring of Glacial Lakes / Water Bodies in the Himalayan Region of Indian River Basins”, sponsored by Climate Change Directorate, Central Water Commission, and done by National Remote Sensing Centre during 2011-15, found that there are 352, 283 and 1,393 glacial lakes and water bodies in the Indus, Ganga and Brahmaputra basins respectively.
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 mechanisms 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.
A landslide occurred along the Phuktal (tributary to Zanskar river) on December 31, 2014 in Kargil district of Ladakh, leading to a potential flood situation on May 7, 2015. The NDMA created an Expert Task Force which, along with the Army, used explosives to channel water from the river using controlled blasting and manual excavation of debris.
While some work on identification of such lakes has been done by CWC, other aspects are still a work in progress: a robust early warning system, and a broad framework for infrastructure development, construction and excavation in vulnerable zones.
“In contrast to other countries, there are no uniform codes for excavation, construction and grading codes in India. Restricting constructions and development in GLOF/LLOF prone areas is a very efficient means to reduce risks at no cost,” the NDMA guidelines say.
The guidelines say construction of any habitation should be prohibited in the high hazard zone. “Existing buildings are to be relocated to a safer nearby region and all the resources for the relocation have to be managed by Central/State governments. New infrastructures in the medium hazard zone have to be accompanied by specific protection measures.”
The guidelines emphasise the importance of land use planning: “There are no widely accepted procedures or regulation in India for land use planning in the GLOF/LLOF prone areas. Such regulations need to be developed… There should be monitoring systems prior to, during, and after construction of infrastructure and settlements in the downstream area.”
The number of implemented and operational GLOF EWS is still very small, even at the global scale. In the Himalayan region, there are at three reported instances (two in Nepal and one in China) of implementation of sensor- and monitoring-based technical systems for GLOF early warning.
India, though, has a remarkable history of successful warnings in relation to Landslide Lake Outburst Floods (LLOFs), dating back to the 19th century. In 1894, a landslide in Gohna, Uttarakhand dammed the main river. On July 5 that year, the engineer in charge estimated the lake would overflow the dam in mid-August, which eventually happened.
Despite the devastating impact of the flood, including washing away of most buildings along the river and severe destruction in Srinagar, no victims were reported, thanks to the precise prediction and the early warning to the population. This was made possible by the installation of a telephone line between the lake and the downstream towns of Chamoli, Srinagar etc.
Apart from pressing specialised forces such as NDRF, ITBP and the Army, NDMA has emphasised the need for trained local manpower.
“Experience has shown that over 80 percent of search and rescue is carried out by the local community before the intervention of the state machinery and specialised search and rescue teams. Thus, trained and equipped teams consisting of local people must be set up in GLOF and LLOF prone areas,” NDMA has said. These local teams, it has said, will also assist in planning and setting up emergency shelters, distributing relief packages, identifying missing people, and addressing the needs for food, healthcare, water supply etc.
It has also called for a comprehensive alarm systems. “Besides classical alarming infrastructure consisting of acoustic alarms by sirens, modern communication technology using cell and smartphones can complement or even replace traditional alarming infrastructure,” NDMA has said.
It has asked for provision of heavy earthmoving and search and rescue equipment, as well as motor launches, country boats, inflatable rubber boats, life jackets etc. Acknowledging that a disaster spot in the Himalayas can at times be inaccessible to earthmovers, NDMA has recommended “innovative methods using locally available natural resources”. “It is important to innovate and design lighter machinery, which are more suitable to be carried in the mountains in a disassembled form,” it has said, suggesting these parts can be carried in a helicopter.
For emergency medical response, NDMA has called for Quick Reaction Medical Teams, mobile field hospitals, Accident Relief Medical Vans, and heli-ambulances in areas inaccessible by roads. The guidelines also call for psychological counselling of victims, apart from dissemination of accurate information through press conferences and mass media.
