Flood
Topic: Natural Hazards and Disaster Management in India · NCERT: Class 7, Ch 3 "Climates of India"; Class 9, Ch 3 "Atmosphere and Climate"; Class 11, Ch 6 "Natural Hazards and Disasters: Causes, Consequences and Management"
Meaning
A flood happens when land that is usually dry goes under water. This occurs when runoff (rainwater flowing over the land) is more than river channels, lakes and drains can carry. Natural causes include long spells of heavy rain, snowmelt, storm surge from cyclones, low infiltration (water not soaking into the ground) and silt filling riverbeds. Human causes make floods worse: cutting forests, poor farming, blocked drains, and building on floodplains and riverbeds. Most floods are slow and seasonal, and their causes are well known, so they can be managed. Floods destroy crops, roads and homes and spread diseases such as cholera, gastroenteritis and hepatitis. They also leave behind fertile silt.
Example
Assam floods almost every monsoon when the Brahmaputra overflows. The same floods lay new silt on Majuli, the largest riverine island, which keeps its soil fertile.
Don't confuse with
- Flash flood: sudden and short, and gives almost no warning. An ordinary river flood builds up slowly and lasts longer.