45 million hectares (13.6 %) of India geographical is prone to floods (2012). The flood prone areas of India are well scattered in different parts of the country, ranging from the heavy rainfall areas to the scanty rainfall areas.
The flood prone areas of India are as under:
- The Ganga River Basin
- The Brahmaputra River Basin
- The Punjab Haryana Flood Plain
- Flood Prone Areas of the Coastal Plains.
The Ganga River Basin
The Ganga and its tributaries drain the states of Uttarakhand, Himachal Pradesh, Haryana, Uttar Pradesh, Bihar, West Bengal, Jharkhand, Chhattisgarh, Madhya Pradesh, and Rajasthan. Its large left hand tributaries Sharda, Kali, Gomati, Ghagra, Gandak, Kosi, and Mahananda; and the right hand tributaries, the Yamuna, Chambal, Sind, Betwa, Ken, Son, and Damodar play havoc in the alluvial plain as well as the terai. Due to heavy rains in the rainy season and melting of snow in the spring season, this river system causes heavy floods in the middle and lower reaches of their catchments.
The Brahmaputra River Basin
The Assam Valley is considered to be one of the worst flood affected areas of India with ritualistic annual nature. The main cause of floods in the Brahmaputra basin are:
- (i) heavy and torrential rainfall—during the rainy season over 200 cm of rainfall is recorded over greater parts of its middle and lower reaches,
- (ii) silting of the river course due to heavy soil erosion,
- (iii) landslides,
- (iv) heavy pressure of population, and
- (v) shifting cultivation on the surrounding hilly areas.
All the districts of Assam are inundated almost every year. The worst affected areas in Assam are ‘Majuli’—India’s largest river island, Dhubri, Kokrajhar, Barpeta, Guwahati, Mangaldoi, Sibsagar, Jorhat, Dibrugarh, and Tezpur.
The Punjab Haryana Flood Plain
Though area falls under the scanty rainfall, due to water-logging and ill- drainage, Punjab and Haryana are adversely affected by floods. The rivers, Satluj, Beas, Ghaggar, Jhelam record floods almost annually. The main reasons of floods in Punjab and Haryana are:
- (i) deforestation in the Lower Himalayas and the Siwalik,
- (ii) increase in soil erosion in the upper reaches of the rivers leading to silting of river beds,
- (iii) construction of structures in the Bet (Khadar) areas of the rivers,
- (iv) unscientific land use, cropping patterns and rotation of crops, and
- (v) obstruction of natural drainage by the construction of roads, railways and human establishments.
Flood Prone Areas of the Coastal Plains
The coastal areas of Odisha, Andhra Pradesh, Tamil Nadu, Kerala, Maharashtra and Gujarat are prone to floods in lower reaches of the Mahanadi, Godavari, Krishna, and Kaveri. The beds of these rivers are shallow which inundate after a heavy downpour in their catchments. The main causes of floods are
- i. Indiscriminate felling of trees in the catchment areas
- ii. the accelerated soil erosion and silting of river beds
- iii. occurrence of spring tides leads to floods in estuaries of Narmada and Tapi.
- iv. The coastal areas also submerge due to the surge of sea water at the time of tropical cyclones in the Bay of Bengal and the Arabia Sea.
- v. The occurrence of Tsunamis also may lead to floods.
