The inundation of an area by water is called a flood.
In other words, when a river over flows its banks and water spreads in the surrounding areas is a flood.
Cause of flood
 Heavy rainfall
Heavy rain in the catchment area of a river causes water to over flow its banks, which results in the flooding of nearby areas.
 Sediment deposition
River beds become shallow due to sedimentation.
The water carrying capacity of such river is reduced.
As a result the heavy rains water over flows the river banks.
Vegetation hampers the flow of water and forces it to percolate in the ground.
As a result of deforestation, the land becomes obstruction free and water flows with greater speed into the rivers and causes flood.
Cyclone generated sea waves of abnormal height spreads the water in the adjoining coastal areas.
In October 1994 Orissa cyclone generated severe floods and caused unprecedented loss of life and property.
 Interference in drainage system
Drainage congestion caused by badly planned construction of bridges, roads, railway tracks, canals etc. hampers the flow of water and the result is flood.
 Change in the course of the river
Meanders and change in the course of the river cause floods.
Large coastal areas are flooded by rising sea water, when a tsunami strikes the coast.
Flood prone areas
About 4 crore hectare area of our country is flood-prone, which is one eighth of the total area.
The most flood prone areas are the Brahmputra, Ganga and Indus basins.
Flood affected states— Uttar Pradesh, Bihar, West Bengal, Orissa, Haryana, Punjab and Andhra Pradesh.
Now a days Rajasthan and Gujarat also feel the fury of floods.
Karnataka and Maharashtra are no-longer immune to floods.