Forces of Nature: Floods
Flood is the overflowing of water onto land that is normally dry. The word is also applied to suggest the inflow of tide.
One of the most common causes of floods is heavy rainfall that comes with tropical storms. Such storms are full of moisture as they form over the warm waters of the tropics. When right conditions form, these giant storms come towards the land and cause heavy downpour. The streams and rivers often cannot cope up with the increased precipitation and cause the water to overflow or floods.
Hurricanes often cause coastal flooding. Powerful winds create huge waves that crash on beaches. Hurricanes can be destructive in combination with high tide.
Monsoon rainfalls cause seasonal or periodic floods on many rivers. This often forms an area known as the ‘floodplain’. Riverine floods occur only in winter as a result of heavy rain in combination with melting of snow and glaciers in spring.
Long, low sea waves caused by volcanoes, landslides, earthquakes, or explosions can also cause floods. These waves are Tsunamis.
Tsunamis are extremely dangerous because of their high speeds, and deeper water means faster-travelling waves. When the sea floor is several miles below, waves can travel more than 600 miles an hour! Wait! This isn’t all. They slow down as they come close to shallow water, but build in height. Some tsunamis can be 50 to 100 feet high when they hit the shore!
Tsunamis can travel thousands of miles without weakening. They can pass through islands or coral reefs without stopping, but usually die or bounce back after hitting a large land mass.
A flood may also occur when volcanic eruptions melt a large amount of ice and snow quickly. Undersea earthquakes, eruptions of island volcanoes that form a large crater called Caldera (such as Thera or Krakatau), and marine landslips on continental shelves may all engender tsunamis.
Standing alone in chaos. The aftermath is far worse and long-lasting than the actual overflow....
Under some rare conditions associated with heat waves, flash floods from quickly melting mountain snow have caused loss of property and life.
There is one major cause apart from geology or weather: Human. The distribution of human populations near water is a major cause for concern. We have built cities and communities by the sea and rivers for easy access to cheap transportation and for food sources and trade. The fertile soil has attracted agriculture and other developments throughout the ages. But, this fertile soil in a river delta is subject to regular flooding due to variation in precipitation or rainfall. Floods happen when soil and vegetation cannot absorb all the water.
Even the extensive and elaborate protection systems fail to prevent floods. They may result in much greater flooding downstream and in locations where they break, as they increase the difference between the water level during flood and the surface of the inland.
Dikes and Levees: Earthen dams, such as dikes, dunes or buffs, are embankments of earth and rock built across rivers to dam them up. Levees are made alongside rivers to keep them from overflowing. However, both can fail because of heavy rainfall, earthquake, internal erosion, engineering and construction faults, or avalanches.
Concrete dams: Concrete dams holdback water in man-made lakes called reservoirs. The water is released through floodgates at a regular pace so it doesn’t overflow the rivers below the dams. But, engineering and construction faults, and the location of the dam may result in failures. Say, building a dam in an area that experiences frequent earth movements may cause disasters.
Rushing water is extremely powerful. Imagine gallons of water crashing through the streets at 80 miles per hour! The water also carries along mud, earth, boulders, and other debris… actually, anything not firmly attached to the ground. In 1955, a flood in the US carried away a wooden, four-story hotel!!! The water sometimes mixes with oil and sewage, destroying buildings and objects. Roads, railroads and bridges are often broken or washed away.
Communication is difficult. Even after the water drains away, a lot of destruction is left behind. In 1887 in China, more than a million residents starved to death because a flood ruined crops, leaving no other source of food! Floodwater is also polluted, spreading diseases such as typhoid fever, cholera, hepatitis-A, malaria, dengue and yellow fever.
Floods are the most frequent type of disaster worldwide. Floods are already wreaking havoc in many states of India. Nowadays, strategies to deal with floods also include evacuation strategies. Although nature is generally blamed, most often it is the direct or indirect effect of human action that triggers a flood. Can we then prevent this catastrophe? Think about it and tell us ‘how’?