ADVERTISEMENTS:
The peculiar nature of India’s climate, dominated by monsoons, causes situations where drought and floods may affect different pockets at the same time of year.
Reasons for Floods:
The main reasons for floods in India are listed below.
Heavy Concentrated Rainfall:
India receives a high average rainfall for a country of its size. Sometimes, upto 15 cm rainfall may hit a place in a single day.
ADVERTISEMENTS:
Interestingly, the monsoon rains come at a time when the summer season is well set and snow-fed rivers of the Himalayas already have an excess of water due to greater melting of snow in the mountains. This situation reduces the capacity of rivers to accept any more surface run- off due to rains.
As a result, the plains in the north, where river velocity is already reduced, are particularly vulnerable to flooding. Heavy rains lead to a rise in volume of the river load, which causes change in river course. As a result of this, water spills over into adjoining areas which are not able to drain this water out and thus get flooded.
North Indian Rivers such as Damodar, Kosi, and Brahmaputra are known for their proneness to floods. The middle and lower courses of the Brahmaputra are especially flood-prone because of a very gradual gradient which is not able to take the increased load during monsoons.
The peninsular rivers have different reasons for getting flooded, which are related to the nature of topography through which these rivers flow. The peninsular rivers are mature and flow over very hard beds and because of their inability to erode very deep into their beds, they have shallow basins. This makes them prone to flooding in case of heavy concentrated rainfall.
Cyclone and Strong Winds:
Parts of the eastern coast of India are particularly prone to cyclones during October-November. Such cyclones develop as low pressure depressions, in the Bay of Bengal and get ‘sucked in’ at the deltas along the east coast in Orissa and Andhra Pradesh. These cyclones come with strong winds and heavy rains which cause extensive damage in a short span of time.
ADVERTISEMENTS:
Inadequate Drainage:
The intensively cultivated areas of Punjab and Haryana get easily flooded in case of heavily concentrated rains because of bad drainage.
The vulnerability of flood-prone areas is aggravated by three factors:
(i) Indiscriminate deforestation in catchment areas and upper reaches results in soil erosion and consequent silting of river courses, which, again reduces their capacity to absorb more water.
ADVERTISEMENTS:
This factor is a major cause of worry as far as flooding in the Himalayan Rivers is concerned. The Brahmaputra is particularly affected by silting of its tributaries, the Dihang and Lohit.
(ii) Overgrazing, especially in the foothills, leaves the soil without cover. The type of soil cover is easily dislodged by the surface run-off during heavy rains and becomes the cause of silting of river courses. Overgrazing in the hills of Himachal Pradesh, Punjab and Uttarakhand has made long stretches of the Himalayan Rivers in their lower reaches prone to flooding.
(iii) Unscientific farming practices like shifting cultivation result in loss of vegetation cover and consequent soil erosion. This mode of silting of rivers is evident in north-eastern India where silting of tributaries of the Brahmaputra is a major cause of flooding of the Brahmaputra River.
Distribution of Flood-Prone Areas:
Among the severely affected areas of the country are the Brahmaputra valleys, north Bihar (Kosi River and north Gangetic plain) and lower West Bengal.
Apart from these, floods affect large areas in the following belts:
(i) The lower courses of rivers in the north Indian plains get silted and change their courses. These areas lie in the states of Punjab, Haryana, Himachal Pradesh, Delhi, Rajasthan, Uttar Pradesh, Bihar and West Bengal (Fig. 13.25).
(ii) The tributaries of the Indus—the Jhelum, Satluj, Beas, Ravi and Chenab—cause floods in Jammu and Kashmir, Punjab, Haryana, western Uttar Pradesh and Himachal Pradesh. Inadequate drainage in parts of Haryana and Punjab is the main cause of inundation.
(iii) Certain areas in central India and the peninsula get flooded by the Narmada, Tapti, Chambal, Godavari, Krishna, Cauveri and Pennar.
(iv) Certain areas along the east coast get flooded due to cyclonic storms.
ADVERTISEMENTS:
The total area affected by floods in India is between 7.5 million hectares and 10 million heactares. Uttar Pradesh is the worst affected state.
Consequences of Floods:
The most damaging aspect of floods is the huge loss of human lives. In economic terms, the immediate effect of floods is seen in temporary loss of fertile lands (since most of the flood- affected area is also the most cultivable area). The sowing season, the rainy season and the monsoons coincide in India.
Although floods bring fertile silt along with them each time, they also cause extensive soil erosion resulting in loss of precious soil cover. The Brahmaputra is particularly notorious for erosion of its banks during the monsoons. Areas with poor drainage, like Punjab and Haryana, which are also intensively cultivated with a high level of assured irrigation and use of chemical fertilisers and pesticides, are vulnerable to salination once the flood waters evaporate during the warm season that follows the rains.
The underground salts which have percolated down to lower levels with flood water come out during the warm season through capillary action and give the topsoil a fluorescent appearance, while seriously depleting its fertility.
Sometimes, river courses are permanently shifted because of floods. This has a long-term effect on land use along river courses. The indirect impact of floods is seen in disruption of rail and road communication, and of essential services.
Flood Control Measures and Related Problems:
The Indian government has taken various steps to check or minimise the damage caused by floods.
Storage reservoirs have been built as part of multi-purpose projects over several flood-prone rivers. Some of these reservoirs are Konar, Panchet, Maithan and Tilaiya on Damodar River, Hirakud on Mahanadi, Bhakra on Satluj, Pong on Beas, Ukai on Tapti, Nagarjuna Sagar on Krishna.
Embankments and drainage channels have been constructed to protect towns and land in flood-prone areas.
Certain long-term measures include collection of hydrological data and installation of flood warning systems. These measures, however, have their share of drawbacks and do not, in themselves, provide a comprehensive solution to the menace of flood.
Mere construction of storage reservoirs is not enough.
Extensive soil conservation measures, upstream of the reservoir and around it, are required to prevent silting of reservoirs through soil erosion. Silting reduces water holding capacity of reservoirs, thus reducing their efficiency in absorbing the overflow of flood water. According to a study, the rate of sedimentation of reservoirs in India is three times the estimated rate (i.e., estimated when they were built).
This has reduced the life of reservoirs in India to one-third. Also, in case the floods are caused by heavy rains in the downstream areas, the reservoirs are not effective. For instance, in Punjab in recent years, the Bhakra and Pong reservoirs have hardly been filled to capacity, while torrential rains caused, floods down streams, affecting nearly half the state’s population.
Embankments are not a scientific solution:
Embankments are an .unnatural way to check the flow of water. Often, the river level is above the surrounding surface in case of an embanked stream, because silt gets accumulated in the riverbed, instead of spiffing over onto the flood plain. The flood plain, as a result, is deprived of fertile silt, year after year.
Also, in case a breach occurs in a part of the embankment, the water will gush out at a very high speed and cause more damage than a slowly rising unbanked river in flood. The siltation results in floods even if there is moderate rainfall in the catchment areas. The protection provided by embankments is unstable.
Flood-Plain Zoning is a reliable and scientific method:
Compared to reservoirs and embankments, this is a ‘non-structural’ measure. This method is based on the principle that, “where the river has the right of way, stays out of its way”. Flood plain is the boundary or extent of the river movement about its mean course. Topographically, it is lower than the surrounding areas and is more prone to flooding.
Flood-plain zoning means demarcating such zones and preventing indiscriminate development and human settlement in such areas. In 1957, the Central Flood Control Board had mooted the idea of demarcating flood zones and the measures to prevent indiscriminate development and settlement in such areas. In 1975, the central government circulated a model bill containing such provisions.
It also provided for setting up of flood zoning authorities in all the states to take up surveys and demarcation of flood zones or plains. It recommended legislative support to prohibit the use of flood plains and removal of unauthorised constructions.
But most states are yet to take the desired steps under pressure from influential builders, developers and other vested interests. States, on the other hand, ask for huge funds for relief measures and not much is done for long- term protection of the flood-prone areas.