Theory:

A flood is an event in which a part of the earth’s surface gets inundated. Heavy rainfall and large waves in seas are the common causes of floods.
 
Floods can be defined as high stream flows, which brim over natural or artificial banks of the river or a stream. Here, the flow is higher than the usual flow, as well as the inundation of low land. (Or) A flood is an overflow of water that usually submerges dry land.
 
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The major causes of floods are:
A. Meteorological factors
i) Heavy rainfall
ii) Tropical cyclones
iii) Cloud burst
iv) Extreme monsoonal rainfall
 
B. Physical factors
i) Large catchment area
ii) Inadequate drainage arrangement
iii) Drainage clogging
 
C. Human factors
i) Deforestation
ii) Siltation
iii) Faulty agricultural practices
iv) Faulty irrigation practices
v) Collapse of dams
vi) Accelerated urbanisation
vii) Residential areas in marshlands
 
 
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The major flood-prone areas in India are shown on the map.
 
Major flood-prone areas in the north and northeast India are Gangetic plains covering the states of Punjab, Haryana, Uttar Pradesh, North Bihar, West Bengal and Brahmaputra valley. Other regions that are prone to frequent floods are Coastal Andhra Pradesh, Odisha and southern Gujarat.