FLASH FLOODS

2. What is a Flood

• Flood is an overflow of a large amount of water beyond its normal limits, especially over what is normally dry land.
• Flooding is an overflowing of water onto land that is normally dry. 
• Floods can happen during heavy rains, when ocean waves come on shore, when the snow melts quickly, or when dams or levees break. 
• Damaging flooding may happen with only a few inches of water, or it may cover a house to the rooftop. 
• Floods can occur within minutes or over a long period, and may last days, weeks, or longer. 
• Floods are the most widespread of all weather-related natural disasters.

3. Common causes of floods can be divided into the factors triggering them.

These factors include -

• Meteorological factors

• Physical factors

• Human factors

 3.1 Meteorological Factors

The natural causes of floods are discussed below -

• Heavy Rainfall: The season of monsoon
• Cloud Burst: Cloud Burst occurs due to intense precipitation in a short duration which can sometimes be accompanied by hail and storms and can cause a flood.

• Climate Change: According to the International Panel for Climate Change, the rainfall intensity, duration and frequency are going to increase in the future.
• Skewed Rainfall Pattern: 80% of the precipitation takes place in the monsoon months
• Trans-National Rivers: The fact that some of the rivers (like the Brahmaputra, many tributaries of Ganga) causing damage in India to originate in neighbouring countries, adds another complex dimension to the problem
• Cyclone & Heavy rainfall

3.2. 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 limited holding capacity of the catchment area, it leads to floods.

3.3. Human Factor

• 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.

• Improper Agricultural Practices: If farmers are not cautious of the effects of farming practices meaning if they leave the waste material in the river or cannot handle water management properly, it can lead to a flood. 

• Deforestation: Deforestation is one of the major human causes of floods. Trees act like a sponge that helps to hold soil and water and prevent flooding. As trees are being cut down at a fast pace to make way for urbanisation to grow, more water runs towards a river during heavy rainfall. As a result, a flood occurs.

• 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. Also, if heavy rainfall sustains for a long time, State Governments often declare to open dam gates which can lead to a dangerous flood.- Temples of Modern India to Water Bombs

• Unplanned Development

• Neglect of Pre-Disaster Planning

 4.Types of Flood

• Coastal Floods: Coastal floods occur when strong winds or storms move towards the coast during high tide.

• Flash Floods: Flash floods usually occur in hilly areas in limited space. Here the sudden heavy rainfall or snow thaws are the causes of flooding. The fast-moving torrent of Flash floods can sweep large objects such as cars, rocks and everything that comes in their path.

• River Floods: River floods occur due to the inflow of water from heavy rainfall, snowmelt or powerful storms.

• Pluvial Floods: Pluvial floods occur in areas that cannot hold rainwater and end up forming puddles and ponds. eg- rural areas.

• Urban Floods: When the drainage system of urban areas fails to absorb rainwater.

The impacts of floods affect both individuals and communities and have social-environmental consequences. 

• Human Loss and Property Loss: Every year, millions of people become homeless and washed away due to floods.

• Spread of Communicable Diseases: Waterborne diseases like cholera, typhoid fever, hepatitis, and leptospirosis spread in flood-affected areas. Floods also lead to vector-borne diseases, transmitted through parasites and pathogens such as a mosquito. As a result, the health of flood victims deteriorates.

• Destruction of Crops: Every year, floods destroy a large number of crops.

• Loss of Livestock: Like humans, livestock also get displaced during floods and dies due to the loss of their habitats.

• Disruption of Communication Link and Transportation: Flood causes damage to transportation links such as bridges, rail, power plants etc., thus causing communication disruption in those areas.

• Economic and Social Disruption: The economy comes to a standstill as people are forced to move to another place, and revival of this situation takes time.

Approaches to dealing with floods may be any one or a combination of the following available options:

• Attempts to modify the flood
• Attempts to modify the susceptibility to flooding damage
• Attempts to modify the loss burden
• Bearing the loss.
• The main thrust of the flood protection programme undertaken in India so far has been an attempt to modify the flood in the form of physical (structural) measures to prevent the floodwaters from reaching potential damage centres and modify susceptibility to flooding damage through early warning systems.

6.1 Structural measures

The following structural measures are generally adopted for flood protection:

• Embankments, flood walls, sea walls
• Dams and reservoirs
• Natural detention basins
• Channel improvement
• Drainage improvement
• Diversion of flood waters.

6.2 Non-structural measures

Non-structural measures include:

• Flood forecasting and warning
• Floodplain zoning
• Flood fighting
• Floodproofing
• Flood insurance.

7.What are Flash Floods

• Flash floods are the most dangerous kind of floods because they combine the destructive power of a flood with incredible speed. 
• Flash floods occur when heavy rainfall exceeds the ability of the ground to absorb it. They also occur when water fills normally dry creeks or streams or enough water accumulates for streams to overtop their banks, causing rapid rises of water in a short amount of time. 
• They can happen within minutes of the causative rainfall, limiting the time available to warn and protect the public.

 8. Status of Floods in India

8.1 NDRF Report

• 40 million hectares (10% of the land mass) in India are prone to floods.
• On average every year, 5 million hectares of land are affected, 1600 lives are lost and more than Rs. 1,800 crores is incurred.

8.2 Statistics

• Between 1970 and 2004, 3 floods occurred per year on average. However, between 2005 and 2019, the yearly average rose to 11. 19 districts were affected annually on an average until 2005. After 2005, the number jumped to 55.
• 2017 analysis suggests that 4.48 million Indians are exposed to riverine floods, the highest in the world.

9. What areas are at risk from flash floods?

• Densely populated areas are at high risk for flash floods. The construction of buildings, highways, driveways, and parking lots increases runoff by reducing the amount of rain absorbed by the ground. This runoff increases the flash flood potential.
• Areas near rivers are at risk from floods. Embankments, known as levees, are often built along rivers and are used to prevent high water from flooding bordering land. 
• Dam failures can send a sudden destructive surge of water downstream. 
• Mountains and steep hills produce rapid runoff, which causes streams to rise quickly. 
• Saturated soils can also lead to rapid flash flooding. 
• Sometimes the thunderstorms that produce heavy rainfall may happen well upstream from the impacted area, making it harder to recognize a dangerous situation.
• Very intense rainfall can produce flooding even on dry soil.
• Additional high-risk locations include recent burn areas in mountains and urban areas from pavement and roofs which enhance runoff.
• Ice jams and snowmelt can help cause flash floods. A deep snowpack increases runoff produced by melting snow. Heavy spring rains falling on melting snowpacks can produce flash flooding.

10. The impact of floods in India

11. Impact of flood on wildlife

12. Government actions regarding flood management

12.1.The National Flood Management Commission

• Launched in 1954
• Different structural and non-structural methods have been applied by various states under it.

• To evolve a scientific, integrated and coordinated approach to flood control
• It recommended Flood plain zoning and management to regulate human activities.

• It was set up to review the impact of the recommendations of Rashtriya Barh Aayog.
• It recommended large flood moderation projects, following up the enactment of flood plain zoning.

12.4.National Water Policy, 2002

• It recommended
• Basin-wise plan for flood control and management.
• Flood control to be given overriding consideration in reservoir regulation policy.
• More emphasis on non-structural measures.
• Strict regulation of settlements and economic activities in flood plains.

12.5. K. Mittal Committee, 2003
Its main recommendations were

• Afforestation and treatment of catchment area, right land-use practices and others.
• In the river itself a construction of suitable hydraulic structures that may trap silt.
• Embankment along the aggrading river should be constructed, only after proper studies are made on its behaviour especially due to sedimentation load and resultant morphological changes.