On an average, every year India gets 4,000 billion cubic meters of water mostly through rainfall and some snowfall. However, this is the average, over a large number of years. In any given year, the rainfall, and hence the river flow, may vary from this average, on the lower side, or on the higher side. Such rainfall instances, very low or very high, are called hydrologic extremes. Floods and droughts, both are a result of hydrologic extremes. This short article explains the phenomenon of floods, and droughts, why these occur, and how
to manage them.


The term ‘floor’ is commonly used to describe any inundation by water. But here are two distinct mechanisms that can cause inundation. A rainfall takes place somewhere in the upstream catchment, and consequent high flow in the river may spill out in to the habitation are some where downstream. This is called flood. In India, 33.5 m.Ha (million Hectares)
of area is floor prone, and out of this, on an average, some or 7.5 m.Ha is affected by floods every year. The floods are most common in Ganga and Brahmaputra river basins.

Causes of Floods

• A very heavy rainfall in the upstream catchment causes a very large river flow. The width of the river through the city downstream is not adequate to carry that flow, and the water spills over, beyond the usual river banks.
• Nature lake Burst: A landslide takes place in the river and acts like a dam.Water accumulates behind it, creating a lake.
• Breach of Embankments: Embankments are constructed along both banks of the river to protect human habitation. If the embankment breaches, the river flow enters the habitation.
• Dam Break: This is very rare, but a man made dam many burst releasing a large quantity of water and causing a flood.

 Managing Floods

 Floods can’t be entirely prevented. The approach to flood management is a combination of protection from floods of less severity, reducing the damage by flood forecasting and disaster relief in case of floods of larger severity. Flood management options are typically divided in two types, structural – i.e. comprising some construction of embankments, and flood control reservoirs; and non-structural,,comprising flood forecasting, flood plain zoning, and disaster relief.

Embankments are low bunds constructed along the river bank, to “contain” the river flow and prevent it from spilling in to the areas of human activity.

Finally, if a flood does occur, relief operations are needed to rescue marooned people and provide them with shelter, food and water, and medical help.

Draining Congestion

Inundation in cities is usually due to the inability to drain out the rain water fast enough. Construction of buildings impends the flow of water over the land; solid waste may choke the storm water drains, which are in any case not adequate, and in coastal cities, the problem is compounded if a heavy rainfall coincides with high tide. Mumbai was inundated on 29th August 2017. And at the same time, the city of Houston in USA was also inundated, for worse than Mumbai, due to the same mechanisms. It may sound harsh, but short duration inundation due to drainage congestion, is a problem the cities many have to live with.


Like floods, droughts are also a hydrologic extreme. But drought neither have a clearly defined beginning, nor a clearly defined end. At times, it may not be even possible to say with certainty that a droughts has set in. drought I a phenomenon that extends over a long duration. Droughts are divided in three types.

Meteorological drought is when the rainfall is deficient.
Hydrological drought is when there is inadequate water in the rivers and or aquifers.
Agriculture drought is when there is inadequate water supply to crops start wilting.

About 153 mha area of the country is drought prone. Till about 1900, drought meant famine and widespread deaths. As many as 11 famines were recorded between 1769 and 1901 with an estimated 20 million deaths. However, not it is possible to transport large quantities of food grains to drought affected area, and to some extent also transport water, and the famine deaths are avoided. Nevertheless, drought brings serve distress to rural people even in this age.

Inter Basin Water Transfer (IBWT)

The geographical area from which the rainfall accumulates and drains out through a river, is called its river basin. By an ingenious design of canals, and at times by pumping, it is possible to take water from a surplus basin to a deficit basin. Such water transfer is called inter basin transfer of water. The earliest plan to construct canals to link certain rivers, was in the year 1858 by Sir Arthus Cotton, a British engineer. However, the purpose of his plan was inland water transport, and not water distribution. Around the same time, railway
as a means of transport became feasible, and his plan of interconnecting the rivers was set aside.

• Irrigation to an additional area of 35 mHa;
• Generate 34,000 MW of hydro power;
• Provide drinking water to a large number of villages and towns;
• Drought mitigation in Andhra Pradesh, Karnataka, Tamil Nadu,M.P., W.B., Bihar, U.P., Haryana, Rajasthan, Jharkhand and Gujarat.
• Flood control in Ganga, Brahmaputra, Mahanadi and Godavari basins;
• Facilitate inland navigation;
• Development of fisheries;
• Infrastructure development;
• Employment generation
• Improve aquatic environment by improving EFR, during lean season.

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Courtesy : Kurukshetra