News Assam is in the grip of yet another flood, with 57 lakh people displaced, all 33 districts affected, and 36 people killed besides hundreds of animals. More in News

  • This is the first wave of floods this monsoon, and flood control experts expect at least two more
  • While floods are a regular annual feature in Assam, some years witness more destruction than others.
  • In terms of impact on human lives, the floods of 1988, 1998 and 2004 were the worst; the 2004 floods alone affected 12.4 million people and claimed 251 lives.
  • The current wave of floods has affected 57 lakh people and claimed 36 lives so far. But experts say that the worst is yet to come.
Reasons for Floods in Assam
  • Apart from incessant rainfall during the monsoon, there are many contributory factors, natural and man-made.
Natural factors Brahmaputra River
  • At the crux is the very nature of the river Brahmaputra —dynamic and unstable.
    • The Brahmaputra features among the world’s top five rivers in terms of discharge as well as the sediment it brings.
    • Its 580,000 sq km basin spreads over four countries: China, India, Bangladesh and Bhutan, with diverse environments.
Sediments deposit
  • At 19,830 cubic meters per second (cumec), it ranks fourth in discharge at the mouth, behind only the Amazon (99,150 cumec), the Congo (39,660 cumec) and the Yangtze (21,800 cumec)
  • In terms of sediment yield, two spots along the Brahmaputa’s course were at second and third places in 2008, behind the Yellow River whose annual sediment yield is 1,403 tonnes per sq km.
    • The Brahmaputra’s annual sediment yield was 1,128 tonnes per sq km at Bahadurabad of Bangladesh, and 804 tonnes per sq km at Pandu of Guwahati.
    • The vast amount of sediment comes from Tibet, where the river originates.
      • That region is cold, arid and lacks plantation. Glaciers melt, soil erodes and all of it results in a highly sedimented river
    • By the time the river enters Assam, it deposits vast amounts of this silt, leading to erosion and floods.
      • As the river comes from a high slope to a flat plain, its velocity decreases suddenly and this results in the river unloading the sediment,
Earthquake-prone nature of the region
  • Because of the earthquake-prone nature of the region, the river has not been able to acquire a stable character.
    • Following the devastating earthquake of 1950, the level of the Brahmaputra rose by two metres in Dibrugarh area in eastern Assam.
Man-made factors
  • Habitation
  • Deforestation
  • Population growth in catchment areas (including in China)
The sediment deposition creates temporary sandbars or river islands. It is common for people to settle in such places, which restricts the space the river has to flow. When rainfall is heavy, it combines with all these factors and leads to destructive floods. This happens very frequently. Measures to address the factors that cause floods
  • In its master plan on the river in 1982, the Brahmaputra Board had suggested that dams and reservoirs be built to mitigate floods.
    • The idea of dams, however, has traditionally been a double-edged sword.
    • While one of their objectives is to regulate the release of flood waters, the release when it comes can sometimes be beyond the capacity of the channels downstream.
    • In the Brahmaputra basin, locals and environmentalists protested against dam-building plans on grounds of displacement and destruction of evology, preventing the plans from moving forward.
      • The Brahmaputra Board proposed a multipurpose dam in the present Gerukamukh site where NHPC (National Hydroelectric Power Corporation) is constructing the Subansiri Lower Hydroelectric Project.
      • But the proposal was scrapped because of objections by the Arunachal government due to submergence [concerns], which included a few small towns
    • Building embankments on the river.
      • Embankments were proposed only as an interim and ad hoc measure for short-term mitigation
      • Most embankments built in the 1980s are not strong enough.
      • Since they were temporary measures, the government did not spend on high-specification embankments. These are weak and are regularly breached
    • The government also considered dredging, basically digging up the riverbed and making the river “deeper”.
      • However, experts have strongly advised against this simply because the Brahmaputra sediment yield is among the highest in the world.
  • There is a need for sustainable solution. Addressing the issues only in Assam when the flood strikes isn’t the solution.
  • There is need for national planning and measures to control flood. For that, interstate relationships, political cooperation and the role of the government are important.
Source: https://indianexpress.com/article/explained/explained-behind-assams-flood-fury-5836815/