announcement

Share facts or photos of intriguing scientific phenomena.

What Causes Floods?

What Causes Floods?

Water is important to sustain life. But what happens when there's an overflow of water and it hampers life? You must be well acquainted with the phrase, 'water, water everywhere but not a drop to drink', well that's exactly what a flood is all about.
Cheryl Mascarenhas
Last Updated: Dec 10, 2017
Floods are the most common and widespread natural disasters that affect millions of people the world over. A flood, simply defined, is the inundation of relatively dry or low-lying areas by excess water. Often spelling danger to both life and property, floods or deluges are referred to as hazards or catastrophes affecting mankind. A steady rise in the level of water bodies due to persistent rain is considered to be the root cause of floods.
Flooding takes place when the volume of water exceeds the normal amount that a water body can usually contain. Flooding on the banks is considered to be a seasonal phenomenon. However, a significant flood is one that wreaks havoc in the surrounding areas, thus endangering life and other inhabited areas.
Floods, that affect places experiencing heavy rainfall are called natural floods. Flooding occurs due to the displacement of a huge amount of water as a result of natural reasons. However, rain is not the only cause of a flood. They can also be caused due to significant and unexpected events like breakage of dams. These are termed as catastrophic floods.
The main causes for the occurrence of floods include:


Natural Causes
Rain
Rainwater that is essential to sustain life, is often the very cause of mass destruction. Incessant heavy rains cause water-logging in the streets and also contribute to an increase in the water level in the water bodies. This sudden increase results in a runoff or overflow of water in the adjoining low-lying areas, thus submerging the land and affecting life in that particular area. Coastal regions and regions receiving heavy rainfall are more prone to such flooding. Areas that experience water-logging due to the presence of an underlying impermeable rock or have improper draining systems are prone to floods during the rains.
Melting Snow
Another source of freshwater supply to many areas around the world is through surface runoff produced from melting snow. Come summer, and the accumulated snow begins to melt, leading to an automatic rise in the water levels in the surrounding water bodies. The Red River flood of 1997 is an example of flooding that occurred due to snow melt. Another factor that can be considered as a cause of floods is global warming. Rapid increase in overall temperatures is causing the glaciers and icebergs in snow-clad regions to melt at an alarming rate. This surface runoff ends up in the oceans leading to flooding in the coastal areas.
Tidal Waves
Tidal waves or tsunamis are a series of huge waves caused due to disturbances caused by underwater earthquakes or volcanoes. These waves generally travel inland at whopping speeds, destroying anything and everything that comes in their way. Tidal waves lead to water logging in the surrounding areas thus causing floods.
Turbulent Wind
Hurricanes are a common feature known to cause floods owing to the high winds and heavy rain that they bring along. Hurricanes in particular cause storm surges in the coastal areas and inland flooding. Cyclones and tropical storms are another cause for the rise in ocean water, leading it to surge inland, thus flooding the coastal areas.
Cloudbursts
Flooding can also occur as a result of a cloudburst, also known as torrential rain. Cloudbursts are sudden aggressive rainstorms that last for a brief spell over a small geographical area. Cloudbursts are often accompanied with thunder and hail storms, often causing water logging and flash floods. Cloudbursts are a common feature in the Indian sub-continent.
Excessive Silting/Sedimentation
Rivers bring along sediment and silt on their way to the sea and deposit it all along their banks. Over a period of time, the accumulated sediment eat up the river bed thus causing the river to overflow, especially during the monsoons. The areas along the banks are prone to regular floods caused due to this excessive silting.
Man-made Causes
Deforestation
Trees, vegetation and forests help absorb excessive water. Besides, they also helps break the flow of water. Thanks to the ever-increasing demands of survival, be it basic demands like food and shelter or larger demands for space, man conveniently resorts to cutting down forests. This ceaseless cutting of forests results in soil erosion, ultimately finding its way into the rivers leading to flooding of the surrounding areas. Deforestation and extreme exploitation of the land often causes devastating flash floods.
Improper Water Management
The major cause of floods these days is the construction of bridges, buildings and roads along the river banks. Construction often comes at the cost of leaving unwanted debris along the banks of the river and at times the river bed, resulting in a rise in the water level causing flooding in nearby areas. Another factor contributing to constant floods, is the closure of storm drains that serve the purpose of draining storm water into the nearby rivers.
Reclamation of Land
Again we come down to man's need for expansion and the need to acquire space. River banks and coastal areas are filled with sand and concrete walls are built to restrict the flow of the river. Owing to the constricted space of the river, the river overflows its boundaries thus submerging the surrounding areas.
Construction of Dams and Reservoirs
Ever thought of how a dam can cause floods? Dams act as reservoirs storing water for a later period of time. When it rains, the dams often get swollen with water, causing a significant rise in the storage level. This results in releasing excessive water causing floods in the surrounding areas.
Unexpected Causes
Dam Bursts
Imagine seeing tons of water bursting out of a wall, rushing madly towards you at an unfathomable speed. That's exactly what happens when a dam bursts owing to faulty construction or improper maintenance of the reservoir. Nothing short of a catastrophe, the bursting of a dam can cause major floods and large amount of destruction of both life and property. Dams can burst as a result of tremors felt due to earthquakes or volcanic eruptions or the tectonic movement of plates over an extended period of time. Fault lines are generally found below such huge water bodies exposing the reservoir to tremors. This ultimately results in bursting or breaking of the dam. The Great Flood of 1889 or the Johnstown flood, that claimed nearly 2209 lives and wrecked damage amounting to US$17 million was one of the worst catastrophes affecting America.


Floods bring untold misery and destruction in their wake and the aftermath often stretches for days and weeks. Thanks to modern technology, it is now possible to predict the occurrence of floods, thus allowing people to be prepared to handle a crisis and escape to safety even before they are close to an impending disaster.