The Rashtriya Barh Ayog (RBA) made an assessment of the extent of the country exposed to the possibility of floods.
The maximum area affected due to flood in a state in any one of the years is taken as the area liable to flood in that state.
The total of such maxima of the various states is considered to be the area liable to floods in the country.
On the above basis and using the figures available for the period from 1953 to 1978, Rashtriya Barh Ayog (RBA) assessed the flood-prone area in the country as 40 m. ha. The states are to work out area prone to floods in a more systematic and scientific manner by marking out the area inundated on maps and working out the flood- prone area on sub-basin and basin-wise.
In India, about one-eighth part of the area (about four crore hectares) is affected by flood. The following are the flood-affected areas of India:
Eastern Region:
This area extends from east of Ghaghra river to Dibrugarh and beyond. Eastern Uttar Pradesh, North Bihar and West Bengal, Manipur, Arunachal Pradesh and Assam are included in this region. Yamuna, Ganga, Damodar, Brahmaputra, Dihang and Lohit are important rivers of this region.
Brahmaputra is the main river of the eastern region where devastating floods are caused every year. Important rivers of Brahmaputra area are Brahmaputra, Barak, Lohit and Dihang. Heavy rainfall up to 600 cm. per annum occurs in this region. Hilly portions are unconsolidated here, hence soil erosion is fast. Deforestation on a large scale has been caused due to mining activities in Meghalaya.
Deforestation has also occurred due to ‘Jhum’ (shifting) cultivation system prevalent in these areas. Rivers of this region flow through narrow valleys, due to which problem of discharge of water exists. Sediment is being deposited in Brahmaputra river.
Two rivers Torsa and Jaldhaka of Brahmaputra drainage area flow through areas of West Bengal bringing sediment in large quantity every year. Because of their changing route, they also cause floods. Thus water dispersal, obstacles in discharge of water, landslides and change in flow route of rivers are the main problems of the Brahmaputra area.
Brahmaputra River originates in friable and is susceptible to erosion and thereby causes exceptionally high silt charge in the river. In addition, the region is subject to severe and frequent earthquakes which causes numerous landslides in the hills and upsets the regime of the rivers.
The predominant problems in this region are flooding caused by the spilling of rivers over their banks, drainage congestion and tendency of some of the rivers to change their courses. In recent years, the erosion along the banks of the Brahmaputra has assumed serious proportions.
Considering the individual states in the region, the main problems in Assam are inundation caused by spilling of the Brahmaputra and the Barak and their tributaries and erosion along the Brahmaputra River. In northern parts of West Bengal, the rivers Teesta Torsa and Jaldakha are in flood every year and inundate large areas.
These rivers also carry considerable amount of silt and have a tendency to change their courses. The rivers in Manipur spill over their banks frequently. The lakes in the territory get filled up during the monsoon and spread to large marginal areas. In Tripura, there is the problem of spilling and erosion by rivers.
Northern Region:
Rivers Jhelum Ravi, Beas, Chenab, Sutlej, Yamuna and Indus of Jammu & Kashmir, Himachal Pradesh, Punjab, Haryana Uttaranchal and Western Uttar Pradesh, are included in this region. In Haryana, flood is caused in areas adjoining river banks. Flood also occurs in Sahibi and Nazafgarh nallas. Water disposal is the main problem in south-western districts of Haryana and eastern districts of Uttar Pradesh. In mountainous parts of Himachal Pradesh, average annual rainfall is 175 centimetres.
Flood is mainly caused in river Jhelum in Srinagar city and valley, whereas soil erosion takes place in Jammu due to rivers Chenab and Ravi. Problem of flood is comparatively lesser in Punjab, Himachal Pradesh, Haryana and Rajasthan, as compared to Ganga and Brahmaputra.
The flooding and erosion problem is serious in the states of Uttar Pradesh, Bihar and West Bengal. In Rajasthan and Madhya Pradesh, the problem is not so serious but in some of the recent years these states have also experienced some incidents of heavy floods.
In Bihar, the floods are largely confined to the rivers of North Bihar and are more or less an annual feature. The rivers such as the Burhi Gandak, the Bagmati, the Kamla Balan, other smaller rivers of the Adhwra Group, the Kosi in the lower reaches and the Mahananda at the eastern end spill over their banks causing considerable damage to crops and dislocation of traffic. High floods occur in the Ganga in some years causing considerable inundation of the marginal areas in Bihar.
In Uttar Pradesh and Uttaranchal, the flooding is frequent in the eastern districts, mainly due to spilling of the Rapti, the Sarada, the Ghaghra and the Gandak. The problem of drainage congestion exists in the western and north-western areas of Uttar Pradesh, particularly in Agra, Mathura and Meerut districts. Erosion is experienced in some places on the left bank of Ganga, on the right bank of the Ghaghra, and on the right bank of the Gandak.
In Haryana, flooding takes place in the marginal areas along the Yamuna and the problem of poor drainage exists in some of the south western districts. In Delhi, a small area along the banks of the Yamuna is subject to flooding by river spills. In addition local drainage congestion is experienced in some of the developing colonies during heavy rains.
Southern and Central Region:
In this part of the peninsula, Narmada, Tapti, Godavari, Krishna, Kaveri and Pennar are main rivers which cause losses due to flood in delta areas. These rivers have mostly well defined stable courses. They have adequate capacity within the natural banks to carry the flood discharge except in their lower reaches and in the delta area. The lower reaches of the important rivers on the East Coast have been embanked, thus largely eliminating the flood problem.
This region covers all the southern states, namely, Andhra Pradesh, Chhattisgarh, Karnataka, Tamil Nadu and Kerala, and the central states of Orissa, Maharashtra, Gujarat and parts of Madhya Pradesh. The region does not have very serious problems except for some of the rivers of Orissa, namely, the Brahmini, the Baitarni, and the Subarnarekha. The Delta areas of the Mahanadi, Godavari and the Krishna rivers on the east coast periodically face flood and drainage problems in the wake of cyclonic storms.
The Tapti and the Narmada are occasionally in high floods affecting areas in the lower reaches of Gujarat.
The flood problem in Andhra Pradesh is confined to spilling by the smaller rivers and the submergence of marginal areas along the Kolleru Lake. The most important coastal problem is presented by the Kolleru lake and the numerous rivers that rise in the ghats and flow into the lake.
Rivers like Budameru and the Thammileru not only overflow their banks along their course to Kolleru Lake but also cause a rise in the level resulting in inundation of adjoining lands. The problem is being tackled systematically since 1969 on the basis of the recommendations of an expert committee of engineers known as the Mitra Committee. The execution of drainage improvement programme is being coordinated by Krishna Godavari Pennar Delta Drainage Board.
Orissa Region:
Mahanadi, Brahmani, Baitarni and Subarnarekha are the main rivers of this region. Flood is a grave problem at the origin of these rivers. Mahanadi is called “Sorrow of Orissa”, but the construction of Hirakud dam over it has given some relief from floods.
In Orissa, damage due to floods is caused by the Mahanadi, the Brahmani and the Baitarni, which have a common delta where the flood waters intermingle and when in spate simultaneously cause considerable havoc. The deltaic districts are densely populated and receive heavy precipitation in the eastern ghat region, and this creates problems in one or more of these rivers.
The problem is accentuated when the flood synchronizes with high tides. The silt deposited constantly by these rivers in the delta area raises the flood level and the rivers often overflow their banks or break through new channels causing heavy damage. The lower reaches of the Subarnarekha are affected by floods and drainage congestion.
Problem of flood is caused in India due to quantity of rainfall and meteorological variations during monsoon season. During this period, 90 per cent rainfall occurs in India. The form and intensity of the problem of floods depends on the nature of different catchment areas. The most complex problem is faced in Brahmaputra and Ganga basins. Every year, during floods, 77.5 lakh hectare lands is waterlogged and thousands of cattle and hundreds of people lose their lives in the country.
Soil erosion is being caused at a very fast speed by rivers at the points of their origin on high mountainous places as well as in lower areas due to deforestation. As a result, of which burden of sediment is increasing day by day, thereby reducing water carrying capacity of the rivers. Flood is caused every year due to this reason.
Flood losses are caused every year in the north-eastern states. In Meghalaya, Cherapunji gets highest rain of the world on Funnel Shaped hills where there are limestone rocks. Due to mining of limestone, reckless deforestation has taken place, due to which most of the rain water flows away causing flood situation. Cherapunji faces drought during summer.
Devastating floods are caused in Uttar Pradesh due to rivers Ganga, Yamuna, Ramganga, Ghaghra, Gomti, ctc Rivers. Due to flood in Yamuna River, nearby areas of Delhi, Mathura, Agra and other towns are affected. River Ganga affects areas in Allahabad, Varanasi, Gazipur, Balia, Patna etc. Gomti River causes Hood losses every year in Jaunpur and Lucknow. In Lucknow, floods occurred during 1923, 1960, 1971 and 1980, while in Jaunpur floods occurred in the years 1974, 1830, 1871, 1894, 1903, 1915, 1922, 1936, 1949, 1955, 1960, 1971 and 1980.
Damodar River, called as “Sorrow of Bengal”, is considered as a wild monster from the point of view of destruction. There is maximum effect of cyclonic rainfall here. During 26 to 29 September, 1978 there was rainfall of 600 millimetres. Its tributaries have been lontrolled by construction of dams over them like Panchet Dam, Maithan Dam, Konar Dam and Tilaiya Dam.
In Bihar, 193 persons died in floods during 1999. Kosi (Sorrow of Bihar), Bagmati, Kamla, Balaan, Puppun and Gandak are the main rivers which have completely destroyed the kharif crop in this state in an area of 3.75 lakh hectares. During this period, flood also caused losses in Assam, Gujarat and Himachal Pradesh. About 3 lakh persons were affected by floods in Assam.
In the famous ‘Kajiranga National Park’ of Assam, many wild bears and rhinoceroses died in the flood. Landslide happened in Himachal Pradesh due to heavy rains. Water level of Beas, Ravi and Sutlej crossed danger marks whereas, 34 persons died in Gujarat due to floods.