The Brahmaputra Valley that encompasses the Northeast part of India witnesses floods almost every year, leaving behind a tale of death and destruction. 

• In recent years, however, the extent of devastation due to floods has increased significantly. 

About Flood

• A flood is an overflow of water that submerges land that is usually dry. 
• In the sense of “flowing water”, the word may also be applied to the inflow of the tide. 
• There are three common type of floods: 
• Flash Floods:
  • Flash Floods are caused by rapid and extensive rainfalls.
• River Floods:
  • Caused when consistent rain or snow melt forces a river to exceed capacity. 
• Coastal Floods:
  • Caused by storm surges associated with tropical cyclones and tsunami.

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Why Assam Gets Flooded Every Year? 

The Brahmaputra Factor

• Location: Assam is situated at the foothills of the Himalayas and comprises two valleys namely Brahmaputra and Barak.
• Huge Coverage: It flows through Assam over a length of around 650 km with an average width of 5.46 km, making it the principal river that crisscrosses the floodplains. 
• Sedimentation: Coming from the Kailash range (high elevation), the river gets highly sedimented by the time it enters Assam (low elevation). 
  • Due to this flattening of the slope, there is a sudden drop in velocity and the river deposits huge quantities of sediment and other debris collected from hilly terrains on the riverbed, raising its level. 
  • During summers, the sedimentation increases as soil erodes with the melting of glaciers. 

The Monsoon Factor

• Intense Monsoon: According to the State Disaster Management Authority, annual rainfall averages around 2900 mm with maximum precipitation in June and  July. 
  • The Water Resources Ministry of Assam states that 85% of the annual rainfall in the Brahmaputra basin takes place during the monsoon months. 
  • Besides, the valley gets a good amount of rainfall in April and May due to thunderstorm activities which account for flooding during heavy rain in June, when the soil is already saturated. 

Riverbank Erosion

• Need: As sedimented rivers move through the state along with their tributaries, they take with them soil and sediment from banks. 
  • Soil erodes and rivers expand as it gets more area and this results in flooding. 
  • This erosion of the land alongside rivers has emerged as a serious problem for Assam.
  • A major cause of the displacement of people due to the disappearance of villages.
    • The width of Brahmaputra has increased up to 15 km due to bank erosion at some places in Assam. 

Human intervention

• Construction of Embankments: 
  • Embankments are constructed to confine the course of a river. This solution, however, has evolved to be an added challenge over time in Assam.
    • Construction of embankments first started in Assam in the 1960s to control floods. 
    • Six decades later, most of these embankments have either outlived their utility or are in bad condition. Many others were washed away. 
    • Every year, as floods follow monsoon, river water breaches these barriers and inundated houses and land. 
• Population Boom: 
  • Population boom in the State has put more pressure on the State’s ecology.
    • The population density of Brahmaputra valley has highly increased as per the 2011 census, according to a report by the Brahmaputra Board. 
  • The board under the Ministry of Jai Shakti monitors the Brahmaputra and Barak Valley and covers States under the Brahmaputra basin. 

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Climate Change

• A Report by the State government: It states that extreme rainfall events will increase by 38%. 
• Factors: Heavy rainfall replacing continuous low or normal rainfall during monsoon combined with the melting of glaciers due to rising temperatures will mean: 
  • Rivers from the Himalayas will be carrying more water and sediment even before they enter Assam where smaller rivers are swelled up due to incessant rainfall. 
  • This increases the possibility of frequent flash floods in low-lying areas. 

Other Factors Worsened the Flood Situation: Deforestation, Hill Cutting, Encroachments, Destruction of Wetlands, Lack of Drainage System in the State, Unplanned Urban Growth, Construction of Dams, Hydro Projects, Irrigation Projects, etc.

Adverse Effect of Assam Floods

• Kaziranga National Park: 
  • More than 15% of the Kaziranga National Park has been inundated  with the Brahmaputra flowing above the danger level, an official statement noted. 
  • At least five animals, including a leopard, have been killed in floods in the national park so far this year.
  • However, large frequent floods have started creating problems for the national park.
    • NH-37: When the flood water hits a certain level, the animal moves towards safer, higher ground in the Karbi Anglong hills. However, they have to cross NH-37 which cuts across the park, which leads to the killing of animals in road accidents.
• Effects on Infrastructure:
  • Train services got disrupted as water affected railway tracks at several places.
  • All modes of transport went on halt except Boats, which charged as much as ₹100 per 100 m in some areas to make up for their inability to fish or ferry people to rivers for a living. 
    • Food and potable water is not easily available.
  • Roads and bridges have suffered serious damage. 
• Effects on Animals:
  • Killing by Poachers: Animals are also killed by poachers who take advantage of their vulnerability.
  • Human-animal Conflict: Animals also move towards villages in floods, this leads to human-animal conflict. 

Advantages of Floods in the Northeast Region

• Raising of Lowlands: Every year, the Brahmaputra and its tributaries transport billions of tonnes of sediment, mainly from the Eastern Himalayas. This raised the lowlands and regularly adjusted river beds. 
• Rejuvenation of Ecosystem: Floods cause disruption and damage but they also generate a bounty of fish and rejuvenate flood-plain ecosystems all along the Brahmaputra, including in the Kaziranga. 
• Shaping of the State: The entire Assam landscape has been shaped over millions of years with the help of an active monsoonal environment and mighty rivers that carry sediments weathered from the still-rising Himalayas. 

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Measures Need to be Taken

• Information Communications: It should be ensured that more credible information is made available so that preparedness can be improved and residents can be alerted. 
  • Experts have indicated that the region needs more institutionalized and technologically advanced systems to allow for credible and fast warning systems. 
• Protecting Kaziranga: Emphasis needs to be put on securing animal corridors and ensuring a safe passage to the Karbi hills. 
  • Need for a landscape-scale conservation approach that recognises the value of the Karbi Anglong hills. 
  • The highlands of Karbi Anglong, where the animals take refuge, are the lifeline of the park during the floods. 
• Constructing Sluice Gates: Sluice Gates should be constructed on tributaries of Brahmaputra and other rivers. It would prove to be an effective step.
  • Sluice Gate’s valves are designed to seal in one direction and commonly are used to control water levels and flow rates in rivers and canals.
  • They also are used in wastewater treatment plants. 
• Other Measures: A Centre for Disaster Management should be established in Assam to carry out studies for effective implementation of measures.