Floods and landslides have killed three persons and affected more than 56,000 people across eight districts of Assam since May 14.
- Flood is an overflow of a large amount of water beyond its normal limits, especially over what is normally dry land.
- NDRF Report: 40 million hectares (10% of the land mass) in India is prone to floods.
Causes:
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Meteorological Factors
Heavy rainfall
Cloudburst: Cloud Burst occurs due to intense precipitation in a short duration which can sometimes be accompanied by hail and storm and can cause a flood
Cyclone: Cyclones occur in a low-pressure zone where winds rotate inwardly. Cyclones can be accompanied by a massive storm and lead to extreme weather conditions.
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Physical factors
Insufficient Drainage Management: Improper planning of the drainage system of an area can cause excess water due to heavy rainfall to get stuck and lead to a flood.
Catchment Area: Catchment area is an area from where the rainfall water flows into a river. This can be a lake or reservoir. During monsoon, when excess water exceeds the limit of holding capacity of the catchment area, it leads to floods.
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Human factors
Siltation: Siltation refers to the flow of silt and sediments in the riverbed. As particles remain suspended in the river and accumulated in the riverbed, it disrupts the flow of the river, causing a flood.
Collapse of Dams: Dams are built to store water and provide water to people. As dams are human-made, these can be worn out and subsequently collapse causing floods. |
Measures to control floods:
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Structural measures:
Embankments, flood walls, sea walls Dams and reservoirs Natural detention basins Channel improvement Drainage improvement Diversion of flood waters. |
Non-structural measures:
Flood forecasting and warning Floodplain zoning Flood fighting Flood proofing Flood insurance.
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Other measures:
- Flood-plain zoning measures aim at demarcating zones or areas likely to be affected by floods of different magnitude or frequencies and probability levels. It is hazard mapping to be precise.
- After demarcation it is important to specify the types of permissible developments/constructions in these zones, so that whenever floods actually occur, the damage can be minimized.
- The establishment and modernization of the flood forecasting network, including inflow forecast through automated data collection and transmission; use of satellite-based communication systems through very small aperture terminals; and improvement of forecast formulation techniques using computer-based catchment models.
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