Disasters and Disaster Management – Sendai Framework, Floods, Cyclones, etc.

Flash floods and their mitigation

Note4Students

From UPSC perspective, the following things are important :

Prelims level : Flash floods

Mains level : Flood management

This newscard is an excerpt from the original article published in the Indian Express.

What are Flash floods?

  • A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions.
  • It may be caused by heavy rain associated with a severe thunderstorm, hurricane, tropical storm, or meltwater from ice or snow flowing over ice sheets or snowfields.

Take a glimpse of the series of disasters in Uttarakhand

Chamoli example

  • Flash flood incident in Uttarakhand is another warning of the dangers that a Himalayan state like Uttarakhand faces from natural processes like landslides, snow avalanches cloudbursts or lake bursts.
  • As we saw in 2013 in the same state, such processes can trigger much bigger disasters and cause massive destruction.
  • But it is possible to work towards minimising the threat of such incidents and reduce their impact.

Role of glacial lakes

  • There are over 1,000 glaciers in Uttarakhand. Almost all of them are receding. Most of the glaciers also have debris cover.
  • When glaciers retreat due to rising temperatures, the snow melts but the debris remains. This debris aids in the formation of lakes.

Cause: Retreat of glaciers

  • Glaciers have reduced considerably in mass and surface area since the little ice age period.
  • This has led to the formation of a large number of glacial lakes all across the Himalayas.
  • Many of these high-altitude lakes are potentially dangerous, because of their potential to cause flash floods in the event of a breach.

How big is the threat?

  • Over the years, the frequency of formation of these lakes has increased.
  • But despite that, there are not many GLOF (glacial lake outburst flood) events happening in Uttarakhand.
  • Not as many as in Sikkim, for example. This is because Uttarakhand has very steep slopes, and the water manages to find a way out.

What should be done?

(a) Coherent research

  • There are a lot more glaciologists and others who are working in the area and generating data.
  • Multiple scientific groups and institutions are involved. But there is no coherent output. Lots of data are being generated but not being put to good use.
  • There has to be one agency dedicated to the job.

(b) Monitoring

  • The first step in tackling the threat from these glacial lakes is to start monitoring them and the glaciers more actively and regularly.
  • There is a need to monitor every glacier. Glaciers in one basin do not have remarkably different properties.
  • Relying only on satellites and remote sensing is not going to be enough.
  • What is required is a consolidated state of glaciers in India, with the ability to zoom in on any of them and track the changes happening year by year.

(c) Planning

  • Construction-related activities in the state might not have a direct link to Chamoli incident, but these are not entirely benign.
  • The Himalayas are very young mountain systems, and extremely fragile and a minor change in orientation of the rocks can be enough to trigger landslides.
  • It is important to include glaciers in any environment impact assessment for major projects such as the construction of dams.
  • The entire catchment areas should be made part of the impact assessment.

(d) Mitigation

  • If we monitor the glaciers regularly, it would enable us to identify the lakes that need mitigation solutions.
  • Several structural and geotechnical measures can be applied, and there are successful examples where the threat from these lakes has been reduced.
  • It is possible to construct channels for the gradual and regulated discharge of water from these lakes, which will reduce the pressure on them, and minimise the chances of a breach.
  • At the same time, it also reduces the volume of water that goes into the flash flood. Also, alarm systems can be set up at the lakes that will warn the community downstream whenever an overflow happens.

Way forward

  • It is not possible to completely prevent these kinds of incidents. But their potential to cause destruction can certainly be minimized.
  • Scientists can find a way to let the lake waters slowly drain at the nearby river at a regulated rate so that there is no flooding, and the pressure on the lake does not become unbearable.
  • Such solutions can be applied in Uttarakhand, and some work is being done.
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