Floods

• A flood occurs when a high water level overflows a stream or river’s natural banks.
• It happens when the river’s discharge exceeds the capacity of its channel, causing excess water to flow over the river banks and submerge adjacent dry land.
• Floods are commonly associated with streams or rivers and can be seasonal or flash floods.
• In India, floods and droughts are cumulative hazards that may affect different pockets of the country at the same time of year due to the peculiar nature of the monsoon.
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Causes of Floods

• Natural Causes:
  • Heavy rainfall and cloud bursts: Heavy concentrated rainfall and thunderstorms can reduce the capacity of rivers to accept more surface run-off, causing water to spill over to adjoining areas and causing extensive damage in a short span of time.
  • Heavy melting of ice and snow: Melting of ice and snow can result in increased water flow in rivers, leading to flooding.
  • Changes in river systems and large catchment areas: Alterations in river systems and catchment areas can affect the flow and capacity of rivers, potentially leading to floods.
  • Sediment deposition/Silting of river beds: Accumulation of sediment and silting of river beds can reduce the carrying capacity of rivers, resulting in floods during heavy rainfall.
  • The collapse of dams: Dam failures or collapses can cause sudden and severe flooding downstream.
  • Transgression of sea during tropical cyclones: Coastal areas can experience flooding due to the transgression of sea during tropical cyclones, which can result in storm surges and inundation.
  • Tsunami and landslides: Tsunamis and landslides can cause flooding in coastal and riverine areas.
• Man-made/Anthropogenic Causes:
  • Deforestation: Deforestation leads to soil erosion and landslides, as well as loss of vegetation and soils that act as natural sponges to absorb rainfall. This can increase the risk of floods.
  • Unscientific land utilization and farming practices: Improper land utilization and farming practices, such as leaving fields bare or ploughing in the wrong direction, can contribute to floods by allowing soil and water to flush into rivers.
  • Increased urbanization: Urbanization can reduce the ability of land to absorb rainfall due to the introduction of impermeable surfaces, resulting in increased surface run-off and potential flooding.

Consequences of Floods

• Negative impact:
  • Extensive damage to life and property: Floods cause significant damage and loss of life, making them the most damaging natural disaster.
  • Loss of crops: Floods can cause temporary loss of agricultural seasons and damage fertile soil cover, leading to crop loss and food insecurity.
  • Habitat destruction and loss of animal life: Floods can cause habitat destruction and loss of animal life due to drowning and other related factors.
  • Disruption of essential services and communication: Floods can disrupt essential services, lines of communication, and movement of people and goods.
  • Spread of water-borne and infectious diseases: Floods can lead to the spread of water-borne and infectious diseases like cholera and gastro-enteritis.
• Positive impact:
  • Fertile silt deposition: Floods deposit fertile silt over agricultural fields, which is good for crops.
  • Groundwater recharge: Floods can recharge groundwater tables, increasing access to water resources.

Flood distribution in India

• Floods cause huge losses to lives, properties, livelihood systems, infrastructure, and public utilities in India.
• 40 million hectares of India’s geographical area are prone to floods, which is 12%.
• About 27% of the flood damage in the country is in Bihar, 33% in Uttar Pradesh and Uttarakhand, and 15% by Punjab and Haryana.
• The major flood areas in India are in the Ganges – Brahmaputra – Meghna Basin which accounts for nearly 60% of the total river flow of the country.
• The middle and lower courses of North Indian rivers such as Ganga, Brahmaputra, Kosi, Damodar, Mahanadi, etc. are prone to floods due to very low gradient.
• Peninsular rivers are mature and have hard rock beds, making them prone to flooding.
• Parts of the Eastern coasts of India are particularly prone to cyclones during October – November. These cyclones are accompanied by strong winds, storm surges, tidal waves, and torrential rains.
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Flood Control Management

• The central and state governments in India have taken several steps to reduce the menace of floods, including:
  • Flood forecasting: The central water commission has established 175 flood forecasting stations on various rivers in the country. These stations issue daily flood warnings throughout the flood season from May to October, providing prior information about the occurrence of floods and enabling timely action to reduce loss of lives, livestock, and movable properties.
  • Reduction in run-off: Inducing and increasing infiltration of surface water into the ground in catchment areas through large-scale afforestation, especially in upper catchment areas, is an effective method of flood control. This helps to reduce the volume of water that runs off the surface and contributes to flooding.
  • Construction of dams: Dams and multi-purpose projects are being constructed across rivers to store surplus water in reservoirs. Many dams have been constructed during different Five-year plans to reduce run-off and store and release water under controlled conditions.
  • Channel improvements and construction of embankments: Channels of rivers that are more prone to flooding are improved by deepening and widening, and water is diverted into canals. Embankments have also been constructed along rivers like Brahmaputra, Krishna, Godavari, Gandak, Kosi, Narmada, Tapi, Son, Sutlej, and their tributaries to reduce the risk of floods.
  • Flood plain zoning: Flood plain zoning, which involves identifying flood plains and floodways in relation to land use, is an important step in controlling floods. This helps in regulating land use practices in flood-prone areas, minimizing exposure to flood risks and reducing damages caused by floods.
• These measures taken by the central and state governments in India aim to mitigate the impact of floods, protect lives and livelihoods, and reduce damages to infrastructure and public utilities caused by floods.

NDMA Guidelines for Flood Management

STRUCTURAL	NON – STRUCTURAL
Reservoirs, dams, other water storages	Flood plain zoning
Embankments/flood walls	Flood proofing
Drainage improvement	Flood management plans
Desilting/ dredging of rivers	Integrated watershed management
Diversion of flood water
Afforestation/ catchment area treatment

Government Programmes for Flood management

• Legislative measures are taken to restrict construction in flood-prone areas.
• Construction of buildings, factories, and houses near river channels should be prohibited.
• Areas occasionally flooded should be under green belts and social forestry should be encouraged.
• National Flood Control Management Programme was established in 1954.
• Three types of flood control measures were envisaged: Intermediate, short, and long term.
• National Hydrology Project was launched in 2016.
• It gathers hydro-meteorological data in real-time.
• 50% of the outlay amount was received from a World Bank loan.
• Data can be accessed by any user at the State/District/Village level.

Mitigation (Post – Flood Management)

• Rescue Operations
• Speedy restoration of the transport system
• Supply of safe drinking water
• Repair of power, telephone, and sewerage lines
• Supply of food, shelter, and clothing
• Survey to assess the loss and compensation
• Rehabilitation of properties
• Desilting and dewatering of inundated areas
• Contingency Plan for the agriculture sector