Flash Floods in Uttarakhand

In News: Recently, a glacial burst on Nanda Devi has triggered an avalanche and caused flash floods in the Rishiganga and Dhauliganga rivers in the Chamoli district of Uttarakhand.

Major Points:

• It washed away at least two hydroelectric power projects, the 13.2 MW Rishiganga hydroelectric power project and the 520 MW NTPC Tapovan-Vishnugad project (also known as Rishi Ganga Project) on the Dhauliganga river, a tributary of the Alakananda.
• Possible Causes:
  • A part of the Nanda Devi glacier, which broke off and collapsed in the lake, surprisingly occurred at the edge of the winter season.
    • Satellite and Google Earth images do not show a glacial lake near the region, but there is a possibility that there may be a water pocket in the region.
      • Water pockets are lakes inside the glaciers, which may have erupted leading to this event.
  • Environmental experts have attributed the glacial melt to global warming and climate change.
    • Climate change has driven erratic weather patterns like increased snowfall and rainfall, warmer winters have led to the melting of a lot of snow.
    • The thermal profile of ice has been increasing. Earlier, the temperature of ice ranged from -6°C to -20°C and now it is -2°C, making it more susceptible to melting.
  • The average temperature in the northwestern Himalaya has risen by 0.66°C since 1991 (an increase much higher than the global average).
    • The higher Himalaya became even warmer on average in the same period.

(Image Courtesy: The Wire)

• Concerns:
  • According to the UN Intergovernmental Panel on Climate Change (IPCC), glacier retreat and permafrost thaw are projected to decrease the stability of mountain slopes and increase the number and area of glacier lakes.
  • Also, the number and area of glacier lakes will continue to increase in most regions in the coming decades.
    • 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.
  • Environmentalists have always warned against the construction of dams as there is always a chance of flooding in the eco-sensitive Himalayan region.
    • 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 moraine is materials, mainly soil and rock, left behind by a moving glacier. Glaciers transport all sorts of dirt and boulders that build up to form moraines.

Glacial Burst:

• These are also known as the Glacial Lake Outburst Flood (GLOF).
• When glaciers retreat, they leave a space which becomes a glacial lake being filled with water. When such a lake breaches, it is known as GLOF.
• It can occur for a number of reasons like erosion, a build-up of water pressure, an avalanche of snow or rocks, and also an earthquake under the ice. It can also be triggered by the massive displacement of water in a glacial lake when a large portion of an adjacent glacier collapses into it.
• GLOFs have three main features:
  • Involve sudden (and sometimes cyclic) releases of water.
  • Tend to be rapid events, lasting hours to days.
  • Result in large downstream river discharges (which often increase by an order of magnitude).
• Risk Reduction Measures:
  • The National Disaster Management Authority (NDMA) has issued detailed guidelines on how to reduce and deal with GLOFs.
  • Identification of potentially dangerous lakes based on field observations, records of past events, geomorphologic and geotechnical characteristics of the lake/dam, etc.
  • Use of Synthetic-Aperture Radar imagery to automatically detect changes in water bodies, including new lake formations, during the monsoon months.
  • Development of methods and protocols to allow remote monitoring of lake bodies from space.
  • Reduction of the volume of water with methods such as controlled breathing, pumping or siphoning out water, and making a tunnel through the moraine barrier or under an ice dam.
  • Prohibition of construction of any habitation in the high hazard zone and relocation of existing buildings are to be relocated to a safer nearby region. New infrastructures in the medium hazard zone have to be accompanied by specific protection measures.
• India’s Preparedness:
  • Some work on the identification of such lakes has been done by the Central Water Commission (CWC).
  • Work in progress: A robust early warning system, 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.
  • For land-use planning in the GLOF/LLOF prone areas, there are no widely accepted procedures or regulation in India.
  • The number of implemented and operational GLOF Early Warning Systems (EWS) is still very small, even at the global scale.
• Rescue Guidelines Suggestions:
  • Apart from specialised forces such as the National Disaster Response Force (NDRF), Indo-Tibetan Border Police (ITBP) and the Army, there is a need for trained local manpower.
    • Over 80 per cent of search and rescue is carried out by the local community before the intervention of the state machinery and specialised search and rescue teams.
    • Local teams 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.
  • There is a need for comprehensive alarm systems.
    • Besides classical alarming infrastructure consisting of acoustic alarms by sirens, modern communication technology including cell and smartphones can help or replace the existing structure.
  • NDMA 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.
    • NDMA recommends innovative methods using locally available natural resources, which are more suitable to be carried in the mountains in a disassembled form.
  • For emergency medical response, Quick Reaction Medical Teams, mobile field hospitals, Accident Relief Medical Vans, and heli-ambulances in areas inaccessible by roads, can be deployed.
    • The guidelines also call for psychological counselling of victims, apart from the dissemination of accurate information through press conferences and mass media.

Source: TH