The glacial lake holds a large amount of water, and a dam failure can possibly release millions of cubic metres of water in a very short time.
Due to the climate change, glaciers in the Himalayas are retreating, leading to an increase in glacial lakes. (Image: IE)
Uttarakhand Glacier Burst: Flash floods hit Uttarakhand’s Chamoli district on Sunday, due to a suspected glacier break. This has come months after the PM Narendra Modi-led National Disaster Management Authority (NDMA) issued guidelines detailing the measures to reduce and deal with disasters stemming from Glacial Lake Outburst Floods (GLOFs). These guidelines had been issued in October last year, according to a report in IE. But what are these GLOFs and how can these glacial bursts be reduced?
The melting of the glaciers leads to water in glacial lakes being accumulated behind natural dams made of pebbles, sand, ice and ice residue called glacial or moraine dams. When water dammed by a moraine dam or glacier gets released suddenly, it results in the occurrence of a flooding known as GLOF. The moraine dam has a weak structure and this can give way to an abrupt failure of the dam atop the glacial lake. The glacial lake holds a large amount of water, and a dam failure can possibly release millions of cubic metres of water in a very short time, leading to a disastrous flooding downstream. Among other such events that have been recorded, peak flows have gone up to a whopping 15,000 cubic metre per second.
Due to the climate change, glaciers in the Himalayas are retreating, leading to an increase in glacial lakes. This has become a potential risk for the infrastructure and life downstream. An inventory of water bodies and glacial lakes had been carried out by the National Remote Sensing Centre in the Himalayan Region of Indian River Basins between 2011 and 2015. This study found that as many as 352 water bodies and glacial lakes were present in the Indus basin, while this figure was 283 for the Ganga river basin and 1,393 for the Brahmaputra.
Risk reduction: What needs to be done
According to the guidelines issued by NDMA, the first step is to identify and map such lakes, and then taking measures to make structural improvements that would prevent these dams from sudden breaches. Moreover, for events where such a breach occurs, a mechanism would need to be put in place to save lives as well as property.
Field observations, the lakes’ and dams’ geomorphologic and geotechnical characteristics, and records of past events can help in identifying lakes that are potentially dangerous. Meanwhile, the NDMA has also suggested that changes in water bodies, like formation of new lakes, can be automatically detected with the help of Synthetic-Aperture Radar imagery. The authority also said that remote monitoring of lake bodies could also be carried out from space by putting in place methods and protocols for the same.
Moreover, pumping, siphoning out water or controlled breaching can be used to reduce the volume of water in such lakes, which would help in structural management of these water bodies. Apart from that, a tunnel can also be constructed under an ice dam or through a moraine for this.
There has been some work that has been carried out to identify such lakes. However, other aspects like establishment of a robust early warning system, as well as the framework for development of infrastructure and construction and excavation in vulnerable areas are still a work in progress. In the guidelines, the NDMA said that India did not have uniform codes for construction, excavation or grading, as against other countries. It added that an effective way to reduce risk from GLOF, a no-cost method is to restrict construction and development in vulnerable areas. Moreover, habitation in prone areas should also be prohibited, the NDMA had said.
On the other hand, even globally the number of implemented and operation early warning systems for GLOFs is very small, and in the Himalayan region, there are only three reported instances of the implementation of monitoring and sensor-based technical systems for GLOF early warning, and of these, one is in China and two are in Nepal. Meanwhile, India has a great history of successful warnings regarding Landslide Lake Outburst Floods (LLOFs), and this dates back to the 19th century.