FLOODS

What is a Flood?

A flood is an overflow of water that submerges land that is usually dry. This is the most frequent natural disaster. ‘Flood’ can mean anything from a few inches of water to several feet. Floods are an area of study of the discipline hydrology and are of significant concern in agriculture, civil engineering and public health. Floods can cause widespread devastation, resulting in loss of life and damages to personal property and critical public health infrastructure.

Between 1998-2017, floods affected more than 2 billion people worldwide. People, who live in floodplains or non-resistant buildings, or lack warning systems and awareness of flooding hazards, are most vulnerable to floods. Floods are also increasing in frequency and intensity, and the frequency and intensity of extreme precipitation is expected to continue to increase due to climate change.

Causes of Flood

Flood occurs naturally as well as due to man-made sources.

Heavy rainfall:

Sustained heavy rainfall can lead to sudden increase in water levels. This is the main reason for flooding of roads and houses. Heavy rainfall also causes rivers to overflow, which further leads to flooding.

Overflowing of rivers:

While dams help in controlling large amounts of rainfall and preventing floods, it may not always be the case. At times the water level increases to a point where it overflows into residential areas, causing floods.

Poor Drainage System:

Poor drainage systems lack the ability to contain water. Due to this, these basins fill up and flood low-lying areas, especially in urban regions. These drainage systems are made of concrete which leaves no space for the water to sink into.

Lack of vegetation:

Widespread vegetation helps prevent flooding by slowing down the water runoff. While it is not common, lack of vegetation increases the chances of it.

Melting of Snow:

Abrupt increase in temperature causes snow on mountains and hilly areas to melt. This melts snow flows in rivers and overflows it and causes floods.

Poor Build Dams:

Dams play a crucial role in controlling water level in rivers. When these are built poorly, it can be very disastrous- rivers overflow and result in flooding.

Types of Flood:

1. Flash floods:

In areas with steep slopes, heavy rain can cause a riverbed that held very little or no water at first, to suddenly brim with fast flowing water. This type of flood occurs very fast.

2. Coastal floods:

This is simply a coastal region being flooded by the sea. The cause of such a surge is a severe storm. The storm wind pushes the water up and creates high waves. Very characteristic of a coastal flood is that the water level drops and rises with the tide.

3. Urban floods:

Flooding in urban areas can be caused by flash floods, or coastal floods, or river floods, but there is also a specific flood type that is called urban flooding. It is specifically caused by a lack of drainage in an urban area. When the sewage system is unable to contain water during heavy rain, floods occur.

4. River (or fluvial) floods:

This type of flooding occurs from rivers overtopping their banks or breaking through dikes (river flooding). When heavy rain is sustained, it can cause rivers and banks to overflow.

5. Ponding (or pluvial flooding):

Ponding is a type of flooding that can happen in relatively flat areas. When more rainwater enters a water system than can be stored, or can leave the system, flooding occurs.

“Know More” In ponding, rain is the source of the flood: not water coming from a river, but water on its way to the river. That's why it is also called "pluvial flood".

Floods are differentiated by various attributes and factors, such as:

1. Triggering factors

Sometimes floods are caused due to prolonged rainfall, sometimes torrential rains or storms cause flooding. In the summer season, high average temperature can result in increased melting of the snow hence, high discharge downstream. Tidal surges due to attraction forces of the sun and moon can also cause localized flooding on sea costs.

2. Duration of the event

Duration of the event means the time span between the start and end of the flooding or the event that caused the flood. It can also be defined as the time duration through which the flood lasted.

3. Time of onset

It is the time span between the start of the event causing the flooding and the time when the flood has actually occurred.

4. Frequency

Frequency of flood events mean how often the flooding occur in a given time period for example, a year. It allows scientists/researchers to understand when a flood of certain magnitude and intensity will occur in a given area.

5. Magnitude

Magnitude refers to the energy released during the event.

6. Intensity

Intensity of floods is the damage caused by it.

Effects

Floods impact on both individuals and communities, and have social, economic, and environmental consequences.

The immediate impacts of flooding include loss of life, damage to property, destruction of crops, loss of livestock, and deterioration of health conditions owing to waterborne diseases. As communication links and infrastructure such as power plants, roads and bridges are damaged and disrupted, some economic activities may come to a standstill, people are forced to leave their homes and normal life is disrupted.

Floods also impact the economy. During a flood, everything stops including business and economic processes. Businesses are unwilling to invest in a flood prone area. Economy of these areas will be on stand still.

Safety Measures to be taken:

Before:-

Floods can occur slowly, or with very fast speed. If you live in a flood prone are, pay attention to changing weather and flood conditions, and be prepared to move to higher ground.

Look out for IMD (Indian Met Department) warning.

During:-

· Move towards higher grounds.

· Evacuate immediately, if told to evacuate.

· Do not walk, swim or drive through flood waters.

· If in a car,

o Do not drive on bridges.

o Stay in the car if trapped in rapidly moving water.

o If water is rising inside, get on the roof.

After:-

· Pay attention to authorities for information and instructions.

· Avoid driving except in emergencies.

· Be aware of the risk of electrocution. Do not touch electrical equipment if it is wet or if you are standing in water. Turn off the electricity to prevent electric shock if it is safe to do so.

· Use generators at least 20 feet from any doors, windows, or vents.

· The initial damage caused by a flood is not the only risk. Standing flood water can also spread infectious diseases, bring chemical hazards, and cause injuries.

Most flood prone areas in India:-