What are the factors that causes flood?

Monsoon rainfall, which is in the form of heavy downpour, often causes devastating floods in the country. Deforestation, silting of the river beds, faulty land use practices, unplanned settlement ac­tivities in the flood plains, obstruction of the natural drainage by development activities, and rise of water table due to excessive irrigation are some of the other factors which have directly or indirectly helped in aggravating menace of floods in the country.

About 25 million hectares of country’s area is prone to floods; of which about 7.4 million hectares suffer from floods every year, out of which 3.1 million hectares are cropped areas. Nearly 60 per cent of the flood damage in the country occurs from river floods and reaming 40 per cent by cy­clones and heavy rainfall. In the Himalayan river basins about 66 per cent of damage is due to floods while cyclones are rampant along the coasts of the Peninsula.

About 33% of the flood damage in the country is accounted for by Uttar Pradesh, followed by Bihar (27%), and Punjab-Haryana (15%). Every year about 1.6 million people and 30,000 cattle are adversely affected by the floods. In 1973 the floods caused damage of5000 million rupees, in 1979 of5970 million rupees and in 1982 about 1140 million rupees.

Following are some of the areas generally affected by floods in the country.

1. Ganga-Brahmaputra Basin-this is the worst flood affected region of the country accounting for 60 per cent of floods of the country. Here Assam, West Bengal, Bihar and Uttar Pradesh are the most flood-hit states of India where floods are recurrent phenomena every year.

The worst offenders are the Brahmaputra, Damodar, Kosi, Gandak, Ghaghara, Ramganga, Ganga, and Yamuna etc. which have been notorious for devastating large areas. Here gentle slope of the plain, deforestation in the Himalayan and the plain regions, silting of the river beds and human interference due to fast growing population are some of the causes for ravaging floods causing colossal loss to life and property. Assam valley is considered to be worst flood-affected areas of India. Here floods mostly occur due to heavy rains, sluggish nature of the streams and silting of the river-beds.

In the Punjab and Haryana plains flood and water logging are caused due to lack of suitable drainage which has been obstructed by canals, trans­port routes and settlements. In the Kashmir valley, the Jhelum is not able to carry the flood discharge properly.

2. Central and Peninsular India-this occu­pies parts of Madhya Pradesh Orissa, Andhra Pradesh, Maharashtra and Gujarat and deltaic tracts of Tamil Nadu. Here floods do not occur every year and these are also of short duration. The costal tracts of the East and the West Coasts are at times hit by strong tropical cyclones which cause sudden flooding and loss of property (damage to field crops and life in these areas. Along the Orissa coast water logging and flooding are constant problem in deltaic tracts of Mahanadi and Brahmani due to defective drainage and blockage of the main channel.

3. Rajasthan Plains-In Rajasthan due to sandy nature of the ground and dry climatic conditions rivers has not been able to carve out ideal drainage channel. Hence in the event of sudden rainfall rain water gets accumulated causing floods and water logging.

Flood Control: Programmes and Strategies

In 1954 after country-wide devastating floods, the National Flood Control Programme was launched. The programme comprises following three phases:

(a) Immediate Phase-this phase extends over a period of 2 years and includes collection of basic hydrological data and execution of immediate flood protection measures like construction of embank­ments, improvement of river channels and rising of villages above flood level.

(b) Short-term Phase-this phase lasts next 4 to 5 years and takes such measures like improvement of surface drainage, establishment of effective flood warning system, shifting or raising of villages over flood level, construction of diversion channels, pro­tective embankments and raised platforms to be used during the times of flood emergency.

(c) Long-term Phase-this includes long-term measures for flood control like construction of dams and storage reservoirs, digging larger diversion chan­nels and taking suitable steps for land use improve­ment and soil conservation.

To develop long-term strategy on control and management of floods, the Government of India has set up a Rashtriya Barh Ayog (National Flood Com­mission) in 1976. The Ayog in its report submitted to the Government of India in March, 1980 has dealt with the flood problem in a comprehensive manner and has made several recommendations.

Since the beginning of the National Flood Control Programme in 1954 about 15,467 km of embankments, 31,883 km long drainage channels, 857 town protection schemes and 4,705 village ground-level raising schemes have been completed up to 1991. Many multi-purpose projects like Bhakra-Nangal, Damodar Valley Corporation, Hirakud, Nagarjun Sagar, Pong, Ukai etc. have also taken effective flood control measures. Recently a Brahmaputra River Board has been constituted to control floods in the Brahmaputra Valley and harness its water for hide generation and irrigation. Up to the end of the Seventh Five Year Plan about Rs. 2,710 crores have been spent on flood control programmes which have provided reason­able protection to about 13.2 million of area (about 39% of the flood prone area).

The Central Flood Forecasting Organisation monitors the floods all over the country and issues warnings. It has nine flood forecasting centers lo­cated at Surat (Tapi), Bharuch (Narmada), Varanasi, Buxar, Patna, Hthidah and Azambad (Ganga),

Dibrugarh and Guwahati (Brahmaputra), Jalpaiguri (Tista), Delhi (Yamuna), Lucknow (Gomti), Bhubaneshwar (Subarnarekha, Burtha Balang, Brahmani and Baitarni), Sahibi (for Rajasthan), and Gandhi Sagar (Chambal). Besides there are 157 flood forecasting stations in operation from which about 5,500 flood forecasts are issued every year.

Following additional measures are suggested for flood control:

1. Restriction on indiscriminate cutting of trees in hilt region and along the river banks.

2. Protecting 1 km tract along the major rivers for massive a forestation wherein agriculture and house construction should be prohibited.

3. Regular dredging of river beds.

4. Formation of National Water Grid through which flood water could be diverted to dry areas through diversion channels or could be stored in huge storage tanks and underground reservoirs for use in lean season.

5. Creating suitable drainage in water logged areas. Here care should be taken for opening and repairing old drains.

6. Regular monitoring of floods and issue of warnings.

7. Basin wise master plan should be prepared which should include construction of embankments, improvement of drainage channels, diversion chan­nels, construction of storage reservoirs in upper reaches, a forestation, and soil conservation etc…

8. Effective measures should be taken for protecting coastal areas from sea erosion.