India is highly vulnerable to floods. Out of the total geographical area of 329 million hectares (mha), more than 40 mha is flood prone. The 2013 floods in Uttarakhand, the 2014 floods in the Kashmir Valley, the 2015 floods in Chennai, and recent rain induced floods in Himachal Pradesh shows that the Floods are increasing in frequency and intensity.
There are multiple factors responsible for increasing frequency and intensity of Floods in India. They are:
- Extreme precipitation events: A majority of river basins in the Indian-subcontinent experienced a rise in extreme precipitation events during the last decade. The extreme precipitation caused widespread flooding. The extreme precipitation resulted in a large flooding in Uttarakhand in June 2013 claiming more than 6000 lives.
- Encroachment on floodplains: Illegal construction work in ﬂoodplains reduces the capacity of rivers to contain a high level of water within their banks. Thus, the tendency to occupy ﬂoodplains results in ﬂooding. The recent Floods in Delhi mainly occurred due to excessive encroachment on Yamuna floodplains.
- Cyclone: Cyclone generated seawaves of abnormal heights spreads the water in the adjoining coastal areas. In October 1994 Orissa cyclone generated severe floods and caused unprecedented loss of life and property.
- Interference in drainage system: Drainage congestion caused by badly planned construction of bridges, roads, railway tracks, canals etc. hampers the flow of water and the result is flood.
- Deforestation: Vegetation hampers the flow of water and forces it to percolate in the ground. As a result of deforestation, the land becomes obstruction free and water flows with greater speed into the rivers and causes floods.
- Sediment deposition: River beds become shallow due to sedimentation. The water carrying capacity of such rivers is reduced. As a result the heavy rain water overflows the
- river banks.
- Change in the course of the river: Meanders and change in the course of the river cause floods. This is one of the main reasons for floods in Assam.
Structural Measures to Tackle Flooding
- Embankments: This has been one of the major structural approaches in which the river is restricted to its existing course and prevented from overflowing the banks.
- Dams, Reservoirs and other Water Storage Mechanism: Dams, reservoirs and other water storages, both natural and man-made, are effective means for reducing the flood peaks in the rivers.
- Channel Improvements: The aim of channel improvements is to increase the area of flow or velocity of flow or both to increase carrying capacity.
- Drainage Improvement: This aims at construction of new channels or improving capacity of existing channels to decongest and prevent flooding.
- Diversion of Flood Water: This involves diverting all or part of flood water into natural or artificial constructed channels which may be within or outside the floodplain. Usually effective to prevent flooding around cities.
- Catchments Area Treatment: The aim in this approach is to provide protection to catchment areas through measures such as afforestation which minimise siltation of reservoirs and silt load in the rivers. This can be a very useful approach to control flood peaks and suddenness of run offs.
- Seawalls/Coastal Protection Works: The construction of seawalls and other such work, try to prevent flooding from sea water.
In addition to tangible losses, flooding also leads to harder-to-map cascading effects. This means that, as a consequence of flooding, there is a chance of disrupted infrastructure, overwhelmed emergency services, displaced vulnerable communities and greater public health challenges. So there is a need to take both structural and non structural measures like early warning systems, community preparedness and education etc to restrict flood damage.