Chapter 14 — 5.3 Water Resources of India

Water is India's most precious resource because it is the one on which agriculture, industry, cities and life itself depend, and it is also the one that the monsoon makes uncertain. The country receives an average of about 118 centimetres of rain a year, which over 32.8 lakh square kilometres amounts to about 4,000 cubic kilometres of water, or 4,000 billion cubic metres. This is a large amount, more than most countries receive per person. But about half of it returns to the air by evaporation and transpiration, and of the rest about 1,869 cubic kilometres flows in the rivers as surface water and 432 cubic kilometres seeps underground as replenishable groundwater. Of the surface flow only about 690 cubic kilometres can actually be used, because much of the rest runs to the sea in a few weeks of flood, so the utilisable water of India is about 1,122 cubic kilometres a year.

Three features of the monsoon make this water hard to use. First, it is concentrated in time: three quarters of the rain falls in the four months from June to September, and in the remaining eight months the rain-fed rivers of the peninsula shrink to trickles. Second, it is uneven in space: Meghalaya gets over 1,000 centimetres and Jaisalmer under 10. Third, it is unreliable: a monsoon 20 per cent below normal brings drought to a third of the country, and one 20 per cent above brings floods. The whole problem of water in India is to store the flood of four months for the drought of eight, and to move water from where it falls to where it is needed.

The demand is rising. Irrigation takes about 80 per cent of the water used, and the area irrigated has grown from 2.3 crore hectares in 1951 to over 11 crore hectares. Domestic use in cities, industry and thermal power take the rest and are growing faster. India has 18 per cent of the world's people and 4 per cent of its fresh water, and its water availability per person, about 5,000 cubic metres a year in 1951, has fallen to about 1,500 as the population has grown and is expected to fall below the scarcity line of 1,000 cubic metres in the coming decades. Many river basins, the Indus, the Krishna and the Kaveri, are already fully used and are disputed between states.

India's water resources are therefore of four kinds, and this section takes them in turn: the surface water of the rivers, the lakes, the groundwater in the alluvium and rock, and the stored water of dams and tanks that human labour has added. Rain water harvesting and the recycling of waste water are the new sources on which the future depends.

The rivers of India are grouped by their source into the Himalayan rivers, which rise in the mountains and are fed by snow and rain, and the peninsular rivers, which rise on the plateau and are fed only by rain. The Himalayan drainage consists of three great systems, the Indus, the Ganga and the Brahmaputra, which together carry about two thirds of India's river water.

The Indus, called Sindhu in Sanskrit, the river that gave India its name, rises in Tibet near Lake Mansarovar on the northern slope of the Kailash range at about 5,180 metres. It flows north-west for 700 kilometres through Ladakh between the Ladakh and Zaskar ranges, past Leh, receiving the Zaskar, Shyok and Nubra from the Karakoram glaciers, then enters Pakistan, bends south round the western end of the Himalaya at Nanga Parbat in a gorge over 5,000 metres deep, and flows south across the plains of Punjab and Sindh for 2,000 kilometres to the Arabian Sea near Karachi. It is 2,880 kilometres long, of which about 710 are in India, and drains 11.7 lakh square kilometres.

Its five great tributaries from the east give Punjab its name and join the Indus as one stream, the Panjnad, at Mithankot. The Jhelum rises at Verinag in the Kashmir valley, flows through Srinagar and the Wular lake and joins the Chenab. The Chenab, the largest, is formed by the Chandra and Bhaga in Lahaul, Himachal Pradesh, and flows through Jammu. The Ravi rises near Rohtang Pass in the Kullu hills and flows past Chamba and Lahore. The Beas rises at Beas Kund near Rohtang and joins the Sutlej at Harike in Punjab, entirely within India. The Sutlej, the longest, rises like the Indus in Tibet, at Lake Rakas near Mansarovar, cuts through the Himalaya at the Shipki La in Himachal, and on it stands the Bhakra dam. In the west the Kabul, Swat, Kurram and Gomal join from Afghanistan.

The Indus was the cradle of the Harappan civilisation and remains the life of Pakistan. Under the Indus Waters Treaty of 1960 between India and Pakistan the waters of the three eastern rivers, the Ravi, Beas and Sutlej, were allotted to India and those of the three western rivers, the Indus, Jhelum and Chenab, to Pakistan, with India allowed limited use of the western rivers for power and irrigation in Jammu and Kashmir. On the eastern rivers India built the Bhakra-Nangal, Pong and Ranjit Sagar dams and the canals, including the Indira Gandhi Canal, that made Punjab, Haryana and Rajasthan the granary of India.

The Ganga is the largest river of India, draining a basin of 8.6 lakh square kilometres in India, a quarter of the country, and more than 40 crore people live in its valley. It rises as the Bhagirathi from the Gangotri glacier at Gaumukh in Uttarakhand, at 3,900 metres, and is joined at Devprayag by the Alaknanda, which comes from Badrinath; below the confluence the river is called the Ganga. It leaves the mountains at Haridwar, where the Upper Ganga Canal begins, and flows south-east across the plain for 2,000 kilometres through Uttar Pradesh and Bihar, past Kanpur, Allahabad or Prayagraj, Varanasi and Patna, to Farakka in West Bengal. At Farakka it divides: the main stream turns south-east into Bangladesh as the Padma, receives the Brahmaputra as the Jamuna and the Meghna, and enters the Bay of Bengal; a smaller distributary, the Bhagirathi-Hooghly, flows south through West Bengal past Murshidabad, Nabadwip and Kolkata to the sea at Sagar Island. The total length of the Ganga is 2,525 kilometres, all in India and Bangladesh, and the Ganga-Brahmaputra delta, 350 kilometres wide, is the largest in the world.

The tributaries from the Himalaya on the left bank are the largest. The Yamuna, the biggest, rises at the Yamunotri glacier, flows parallel to the Ganga past Delhi, Mathura and Agra and joins it at Prayagraj, the Sangam; its own tributaries, the Chambal, Sind, Betwa and Ken, come from the peninsula. The Ramganga joins near Kannauj; the Gomti flows through Lucknow. The Ghaghara or Karnali, the Gandak and the Kosi come from Nepal and join in Bihar; the Kosi, notorious for shifting its bed and flooding, is called the sorrow of Bihar. The Mahananda joins in West Bengal, and beyond Farakka the Tista, once a tributary of the Ganga, now joins the Brahmaputra.

From the peninsula on the right bank come the Son, rising at Amarkantak and joining near Patna, the Chambal and Betwa through the Yamuna, and the Damodar, which joins the Hooghly below Kolkata.

The Ganga is perennial, snow-fed in the dry months and rain-fed in the monsoon, and its plain is India's most fertile and crowded land. It is also the most sacred river of the Hindus and, below Kanpur and Varanasi, one of the most polluted; the Ganga Action Plan of 1985 and the Namami Gange programme of 2014 are the efforts to clean it. The Farakka barrage, completed in 1975, diverts water into the Hooghly to keep the port of Kolkata alive, and the sharing of the Ganga at Farakka with Bangladesh is governed by a treaty of 1996.

The Brahmaputra, the son of Brahma, is one of the great rivers of Asia and the only large river of India with a masculine name. It rises in the Chemayungdung glacier near Mansarovar in Tibet, at about 5,150 metres, only a few kilometres from the sources of the Indus and Sutlej, so that one small region of Tibet gives birth to three of the subcontinent's great rivers. In Tibet it is called the Tsangpo, the purifier, and flows east for 1,200 kilometres in a broad, cold, dry valley parallel to the Himalaya at a height of about 4,000 metres, receiving little water and carrying little silt. Near Namcha Barwa it turns sharply south and cuts through the eastern Himalaya in the deepest gorge on earth, 5,000 metres deep, falling 2,000 metres in 200 kilometres, and enters India in Arunachal Pradesh as the Dihang or Siang. At Sadiya it is joined by the Dibang and the Lohit and takes the name Brahmaputra. It then flows west-south-west through the whole length of the Assam valley for 720 kilometres, past Dibrugarh, Tezpur and Guwahati, turns south round the Garo hills into Bangladesh, where it is called the Jamuna, joins the Padma, that is the Ganga, at Goalundo, and the combined river, joined by the Meghna, enters the Bay of Bengal. Its length is about 2,900 kilometres, of which 916 are in India, and its basin in India is 1.9 lakh square kilometres.

In Assam the river receives many tributaries from the wet Himalaya on the north, the Subansiri, Kameng, Manas, Sankosh and the Tista, which comes from Sikkim and West Bengal, and from the hills on the south the Dhansiri, Kopili and Barak. Because its basin receives 200 to 400 centimetres of rain and its tributaries drain the steep, soft, earthquake-shaken slopes of the eastern Himalaya, the Brahmaputra carries an enormous load of silt and water, more than any other Indian river; in flood at Guwahati it may discharge 70,000 cubic metres a second. Choked with its own silt, it splits into a maze of braided channels around sandbanks and islands, up to 10 kilometres wide, and Majuli, between two of its channels, is the largest river island in the world, though it is being eroded away. Every monsoon the river floods the Assam valley, destroying crops and villages and drowning the rhinoceros grasslands of Kaziranga; its shifting banks eat away towns such as Dibrugarh, and its bed is rising. The earthquake of 1950 raised the bed by several metres and made the floods worse.

The Brahmaputra is navigable throughout Assam and is a National Waterway from Sadiya to Dhubri. Its power potential is the largest in India, and dams are being built on the Subansiri and other tributaries; China's dams on the Tsangpo upstream are a concern. Unlike the Ganga it has no large canals and no great cities, because its floods and shifting course make its banks unsafe, yet it is the river that made the plain of Assam and its tea gardens.

The rivers of the peninsula rise on the plateau, are fed only by the rain of the monsoon and flow in old, broad, shallow valleys that have almost reached their base level. Because the plateau is tilted from west to east, all the large rivers rise in the Western Ghats, within a few dozen kilometres of the Arabian Sea, and flow the whole width of the peninsula to the Bay of Bengal, building deltas at their mouths; only the Narmada and Tapi, which follow rift valleys, and a number of short streams flow west.

East-flowing rivers. The Mahanadi, the great river, rises in the Sihawa hills of Chhattisgarh, flows 858 kilometres east through Odisha, past the Hirakud dam and Cuttack, and enters the Bay of Bengal through a delta; it is the river of Odisha. The Godavari, the largest and longest peninsular river, called the Dakshina Ganga, rises at Trimbak near Nashik in the Western Ghats, only 80 kilometres from the sea, and flows 1,465 kilometres east across Maharashtra and Telangana into Andhra Pradesh, receiving the Manjra, Pranhita, Indravati and Sabari, and reaches the sea through a delta below Rajahmundry. The Krishna rises at Mahabaleshwar and flows 1,400 kilometres through Maharashtra, Karnataka and Andhra Pradesh, receiving the Bhima and the Tungabhadra, past the Nagarjunasagar dam to its delta near Vijayawada. The Kaveri or Cauvery, the sacred river of the south, rises at Talakaveri in the Brahmagiri hills of Coorg in Karnataka and flows 800 kilometres south-east through Karnataka and Tamil Nadu, over the Sivasamudram falls, past Mettur and Tiruchirappalli, to its delta at Thanjavur; because it receives both the summer and the winter monsoon it is the most perennial of the peninsular rivers and has been used for irrigation since the Grand Anicut of the second century. Smaller east-flowing rivers include the Subarnarekha, Brahmani and Baitarani of Jharkhand and Odisha, the Pennar and the Vaigai.

West-flowing rivers. The Narmada rises at Amarkantak on the Maikal hills and flows 1,312 kilometres west through the rift valley between the Vindhya and the Satpura, over the Dhuandhar falls and the marble rocks at Jabalpur, past the Sardar Sarovar dam, to the Gulf of Khambhat in a broad estuary, not a delta. The Tapi or Tapti rises at Multai in the Satpura and flows 724 kilometres west through a parallel rift valley to the Gulf of Khambhat at Surat. The Sabarmati and Mahi of Gujarat, and the swift short rivers of the Western Ghats, the Sharavati with the Jog falls, the Periyar and the Bharathapuzha of Kerala, also flow west. The west-flowing rivers form estuaries because they are short, fall steeply and the tide sweeps their silt away.

The peninsular rivers are older and their courses more fixed than those of the Himalayan rivers, and their gradient, except near the Ghats, is gentle, but their flow depends wholly on the rains and shrinks to almost nothing between January and June.

The two groups of Indian rivers differ in almost every respect, and the comparison is a standard examination question.

Three of these differences matter most. The first is perennial flow. Because the Himalayan rivers are fed by melting snow in April, May and June, precisely the months when no rain falls, they never run dry, and the plains of Punjab, Uttar Pradesh and Bengal can be irrigated by canals the whole year without a dam. The peninsular rivers, fed only by the monsoon, have to be stored behind dams if they are to give water in the dry months; that is why almost every peninsular river has a great reservoir on it.

The second is youth and change. The Himalayan rivers are still cutting down through rising mountains and still building their plains; they have deep gorges, waterfalls and rapids in the hills, and on the plain they meander, throw off ox-bow lakes, shift their beds and flood. The Kosi and the Brahmaputra are the extreme examples. The peninsular rivers flow over rock that has been stable for hundreds of millions of years; their valleys are graded, their courses fixed, and they rarely shift, though they too flood in a heavy monsoon.

The third is antecedence. The Indus, Sutlej and Brahmaputra are older than the Himalaya; they existed before the mountains rose and kept their courses by cutting down as fast as the land rose, which is why they flow through gorges thousands of metres deep across the highest range in the world. No peninsular river crosses a barrier in this way; they were guided from the start by the eastward tilt of the plateau.

Lakes are a small part of India's water but valuable for drinking water, irrigation, fishing, tourism and the balance of local climate. They are of several origins. Tectonic and glacial lakes of the Himalaya: the Wular in Kashmir, the largest fresh-water lake in India, formed by the Jhelum in a sunken basin; the Dal at Srinagar; Nainital and the other tals of Kumaon; Tsomgo in Sikkim and the great salt lake Pangong in Ladakh, half in China. Lagoons on the coasts, lakes of salt or brackish water cut off from the sea by sand bars: Chilika in Odisha, the largest brackish lagoon in Asia, 1,100 square kilometres, a wintering ground for migratory birds; Pulicat on the Andhra-Tamil Nadu border; Vembanad and the other backwaters of Kerala; and Kolleru between the Godavari and Krishna deltas. Salt lakes of the desert: Sambhar in Rajasthan, the largest inland salt lake, from which salt is produced, and Didwana and Pachpadra. Ox-bow lakes of the plains, the cut-off meanders of the Ganga and its tributaries, called bils in Bengal, such as Kanwar Tal in Bihar, the largest, and Loktak in Manipur, the largest fresh-water lake of the north-east, with its floating phumdis. Artificial lakes behind dams are now the largest lakes of the country: Govind Sagar behind Bhakra, Gobind Ballabh Pant Sagar at Rihand, Hirakud, Nagarjunasagar, Stanley reservoir at Mettur and Maithon and Panchet on the Damodar. West Bengal has no large natural lake, but the bils of the delta, the Santragachi jheel, the East Kolkata wetlands and the reservoirs of Mukutmanipur and Massanjore serve the same purposes.

Groundwater is the water held in the pores of sand and gravel and the cracks of rock below the surface, replenished by rain and by seepage from rivers and canals. India has about 432 cubic kilometres of replenishable groundwater a year, and it supplies about 60 per cent of the irrigated area, through wells and tube-wells, and 85 per cent of rural drinking water. The richest groundwater lies in the deep alluvium of the Northern Plain, where the water table is shallow and the aquifers are thick, and it is thin and patchy in the hard rock of the peninsula, where water lies only in weathered zones and fractures. The alluvium of West Bengal is one of the best aquifers in the country.

Groundwater is being over-used. Since the 1970s, with cheap electric pumps and free or subsidised power, India has become the largest user of groundwater in the world, pumping about 250 cubic kilometres a year, more than the United States and China together, and in Punjab, Haryana, Rajasthan, Gujarat and Tamil Nadu the water table is falling by a metre or more a year as more is drawn than the rain returns. Deeper pumping brings up water contaminated with fluoride, which cripples bones, and in the Ganga delta of West Bengal and Bangladesh with arsenic, a natural poison in the sediments that has affected millions of people in Murshidabad, Nadia, Malda and the 24 Parganas. The protection of groundwater by recharge and by regulating pumping is now as urgent as building dams.

Irrigation is the artificial supply of water to the land for the growing of crops, from a river, canal, well, tank or reservoir, when the rain is insufficient or ill-timed. India is one of the most irrigated countries in the world, with over 11 crore hectares, about half its cultivated area, under irrigation, and the reasons why so much effort has gone into it are the reasons why Indian agriculture cannot depend on the monsoon alone.

Uncertainty of the monsoon. The monsoon may come late, break early, fail in the middle or fail altogether, and a single dry spell of three weeks in August can destroy the rice crop. Irrigation is insurance: a farmer with a canal or a tube-well can save the crop the monsoon abandons. In West Bengal the aman rice of the plains is still largely rain-fed, and the boro rice of winter would be impossible without irrigation.

Uneven distribution of rainfall. Rajasthan, Gujarat, the Deccan interior and the rain-shadow of the Ghats receive less than 75 centimetres of rain, too little for most crops, and could not be farmed without water brought from elsewhere. Punjab and Haryana with 50 to 70 centimetres are the granary of India only because they are the most irrigated states, with over 95 per cent of their cropland watered by canals and tube-wells.

Concentration of rainfall in four months. Even in wet regions there is no rain from October to May, so a second crop in winter, the rabi of wheat, mustard, potato and boro rice, and a third in summer are possible only with irrigation. Irrigation raises the cropping intensity from one crop a year to two or three.

Water-demanding crops. Rice needs 120 to 150 centimetres of standing water, sugar-cane 200 centimetres or more, and jute, cotton and vegetables need water at exact times; the high-yielding varieties of the Green Revolution need assured water and fertiliser and give their high yields only under irrigation, which is why the revolution succeeded first in irrigated Punjab.

Soil and heat. Sandy and lateritic soils, as in western Bengal, hold little moisture and dry out in days, and the high temperature of the Indian summer evaporates water quickly, so crops need frequent watering.

Population. With 140 crore people to feed from a fixed area of land, the only ways to grow more food are higher yields and more crops a year, and both require water. Irrigation has raised India's foodgrain output from 5 crore tonnes in 1951 to over 30 crore tonnes.

Irrigation has its costs: canals without drainage waterlog the land and bring salt to the surface, as in parts of Punjab and the Indira Gandhi Canal command; over-pumping empties the aquifers; and dams drown forests and villages. The aim of modern policy is not more water but more crop per drop, through sprinkler and drip irrigation and better management.

India irrigates by three principal means, and each prevails where the relief, soil and water supply suit it.

Canal irrigation supplies about a quarter of the irrigated area. Canals are of two kinds. Inundation canals are simply channels cut from a river bank that fill when the river is in flood and dry when it falls; they were common in old Punjab and Sindh and are now rare. Perennial canals take water from a river all the year through a barrage or weir that raises the river level, or from a reservoir behind a dam, and distribute it through main canals, branches, distributaries and field channels over a command area that may be lakhs of hectares. Canals suit the Northern Plain, where the rivers are perennial, the land is flat and the soil is deep, and the great canal systems are there: the Upper and Lower Ganga canals of Uttar Pradesh, the Sirhind and Bhakra canals of Punjab, the Western and Eastern Yamuna canals of Haryana, the Indira Gandhi Canal of Rajasthan, the Sarda canal, the Sone canals of Bihar and the Damodar canals of West Bengal, and in the peninsula the delta canals of the Godavari, Krishna, Kaveri and Mahanadi. Canals are cheap per hectare once built and irrigate vast areas, but they waste water by seepage and evaporation, cause waterlogging and salinity where there is no drainage, and deliver water by a fixed schedule rather than when the crop needs it.

Well and tube-well irrigation is the largest source today, about 60 per cent of the irrigated area. The traditional dug well, lined with brick, reaches the water table a few metres down and is worked by a Persian wheel, a bullock-drawn leather bucket or a small pump; it waters one or two hectares. The tube-well, a pipe bored 30 to 200 metres into the aquifer and fitted with an electric or diesel pump, yields far more and has spread since the 1960s to more than two crore in the country, above all in Uttar Pradesh, Punjab, Haryana, Bihar and West Bengal, wherever the alluvium is thick and the water table high. Wells give water at the farmer's own command, whenever the crop needs it, are cheap to build and suit small holdings; but they fail where the rock is hard, they depend on electricity, and they are emptying the aquifers of the north-west.

Tank irrigation supplies about 5 per cent, mostly in the peninsula, in Tamil Nadu, Andhra Pradesh, Telangana and Karnataka, and in the lateritic west of Bengal. A tank is a pond made by damming a small stream or a hollow with an earthen bund to catch the monsoon rain, from which water is let into the fields below through sluices. Tanks suit the hard, undulating rock of the plateau, where wells are poor and canals impossible, and many are centuries old; Tamil Nadu has over 40,000. They are cheap and community-managed, but they hold water for only a few months, lose much by evaporation, silt up and fail in a poor monsoon, and many have been neglected since tube-wells arrived.

Modern methods use water more efficiently: sprinkler irrigation sprays water like rain and suits uneven land and sandy soil; drip irrigation delivers water through pipes drop by drop to the root of each plant, saving 40 to 60 per cent, and is spreading in the vineyards and orchards of Maharashtra and Gujarat and the vegetable gardens of Bengal. Lift irrigation, pumping river water up to fields above the river, is common along the Ganga and the Damodar.

A multipurpose river valley project is a scheme in which a large dam or a series of dams on a river and its tributaries is built to serve many purposes at once: to store the monsoon flood and release it in the dry season for irrigation; to prevent floods downstream; to generate hydro-electric power from the fall of water; to supply drinking and industrial water to cities; to make the river navigable; to develop fisheries in the reservoir; to afforest and conserve the soil of the catchment; and to provide recreation. The idea came from the Tennessee Valley Authority of the United States, set up in 1933, and Jawaharlal Nehru called the great dams of the 1950s the temples of modern India. The main projects, from north to south, are:

• Bhakra-Nangal on the Sutlej, in Himachal Pradesh and Punjab, the largest: the Bhakra dam, 226 metres, one of the highest gravity dams in the world, with the Govind Sagar reservoir, the Nangal barrage below it, 1,325 megawatts of power and canals irrigating 14 lakh hectares of Punjab, Haryana and Rajasthan. It made possible the Green Revolution.
• Damodar Valley Corporation on the Damodar in Jharkhand and West Bengal, described in the next topic.
• Hirakud on the Mahanadi in Odisha, with the longest main dam in the world, 4.8 kilometres, and a total length with dykes of 26 kilometres, controlling the floods of the Mahanadi delta, irrigating 2.5 lakh hectares and generating 350 megawatts; the aluminium plant at Hirakud runs on its power.
• Rihand on the Rihand, a tributary of the Son, in Uttar Pradesh, with the Gobind Ballabh Pant Sagar, feeding the power stations of Sonbhadra.
• Chambal projects, the Gandhi Sagar, Rana Pratap Sagar and Jawahar Sagar dams shared by Madhya Pradesh and Rajasthan.
• Sardar Sarovar on the Narmada in Gujarat, 163 metres, irrigating 18 lakh hectares of Gujarat and Rajasthan and generating 1,450 megawatts, the centre of a long controversy over the displacement of tribal villages in Madhya Pradesh and the Narmada Bachao Andolan.
• Nagarjunasagar on the Krishna in Telangana and Andhra Pradesh, the largest masonry dam in the world, irrigating 8 lakh hectares.
• Tungabhadra on the Tungabhadra in Karnataka and Andhra Pradesh; Mettur on the Kaveri in Tamil Nadu; Kosi on the Kosi in Bihar and Nepal; Tehri on the Bhagirathi in Uttarakhand, the highest dam in India at 260 metres; and the Indira Gandhi Canal project in Rajasthan.

Benefits. The projects irrigate about 4 crore hectares, generate about a quarter of India's electricity from water, have tamed the floods of the Damodar, Mahanadi and Sutlej, supply water to Delhi, Mumbai, Hyderabad and Bengaluru, and created fisheries, tourism and industries such as the aluminium of Hirakud and the fertiliser of Nangal.

Drawbacks. Reservoirs drown forests, farmland, villages and wildlife and have displaced an estimated two crore people, mostly tribal, often without proper resettlement; they silt up and lose capacity, so that Bhakra and the DVC dams hold far less than designed; they spread waterlogging and salinity in their commands; they block the silt that fertilised the deltas and the fish that migrated up the rivers; they can trigger earthquakes in the surrounding rock, as at Koyna in 1967; and their water is disputed between states. The modern view is that large dams are one tool among many, to be weighed against watershed management, small tanks and groundwater recharge.

The Damodar Valley Corporation, the DVC, was India's first multipurpose river valley project, set up on 7 July 1948 by an Act of Parliament, and it concerns West Bengal directly. The Damodar rises on the Chota Nagpur plateau in the Palamu hills of Jharkhand at about 600 metres, flows 592 kilometres east and south-east through the coalfields of Bokaro, Dhanbad and Raniganj, enters West Bengal near Asansol, crosses Bardhaman and Hooghly and joins the Hooghly about 50 kilometres below Kolkata. Its tributaries, the Barakar, Konar, Bokaro, Jamunia and Usri, drain a basin of 25,000 square kilometres, of which about 65 per cent is in Jharkhand.

Before 1948 the Damodar was the sorrow of Bengal. Its upper basin receives 130 centimetres of monsoon rain on steep, deforested slopes of hard rock, so that after a heavy storm the river rose within hours into a flood of 20,000 cubic metres a second that burst over the flat lands of Bardhaman, Hooghly and Howrah, drowning villages and crops and filling the channels with sand. There were sixteen great floods between 1730 and 1943, and the flood of 1943 in the middle of the famine turned the government to a permanent solution. The plan, drawn up on the model of the Tennessee Valley Authority, was carried out jointly by the central government, Bihar, now Jharkhand, and West Bengal.

The works are: four dams, Tilaiya on the Barakar, 1953, Konar on the Konar, 1955, Maithon on the Barakar, 1957, the largest, with India's first underground power station, and Panchet on the Damodar, 1959, all in Jharkhand near the Bengal border, with a combined flood storage of about 1.3 cubic kilometres; the Durgapur barrage on the Damodar in West Bengal, 1955, 692 metres long, which diverts water into the Damodar canals, about 2,500 kilometres of channels irrigating 5 lakh hectares in Bardhaman, Hooghly, Howrad and Bankura, and feeds the Durgapur industrial water supply; a chain of power stations, hydro-electric at the four dams and thermal at Bokaro, Chandrapura, Durgapur, Mejia and Raghunathpur, which give the DVC an installed capacity of over 6,000 megawatts, almost all of it thermal from the coal of the valley; and soil conservation works, afforestation, check dams and terracing on the upper catchment to reduce silt.

Achievements. The floods of the lower Damodar have been greatly reduced, though not ended; the canals turned the western districts of Bengal into the state's rice bowl and allowed the second crop; the DVC's power runs the steel of Durgapur and Bokaro, the coal mines, the engineering works of Asansol and the cities of the valley, and the Damodar is often called the Ruhr of India for the industries along it; the reservoirs supply water to Durgapur and Dhanbad, support fisheries and attract tourists to Maithon and Panchet.

Problems. The reservoirs have silted up faster than planned, losing a third of their capacity, because the catchment conservation was never completed; the planned eight dams became four, so flood control is partial and the release of water from Maithon and Panchet in a heavy monsoon still floods Bardhaman and Howrah, as in 2000, 2017 and 2021; the canals waterlog some land and the pollution of the river by the mines, power stations and Durgapur factories is severe; and the thermal stations that supply most of the power add ash and carbon to the air. The DVC remains, nevertheless, the model on which every later project in India was designed.

West Bengal is a land of rivers: they made its plain, they carry its trade and they decide its harvests. They fall into three groups by origin.

The rivers of the north come from the Himalaya and are snow-fed and perennial. The Tista, the largest, rises in the Tso Lhamo lake in north Sikkim, flows south through the Sikkim and Darjeeling hills in a deep gorge, enters the plain at Sevoke, crosses Jalpaiguri and Cooch Behar and enters Bangladesh to join the Brahmaputra; its tributaries are the Rangit, Rangpo and Lish. Its floods and shifting bed are a hazard, its water is shared with Bangladesh under a long-disputed agreement, and the Teesta barrage at Gajoldoba irrigates north Bengal and the Teesta hydro-electric projects in Sikkim and Darjeeling generate power. The Torsa, Jaldhaka, Raidak and Sankosh come from Bhutan across the Duars, and the Mahananda, from the Darjeeling hills, flows past Siliguri and Malda to the Ganga.

The rivers of the west rise on the Chota Nagpur plateau, are rain-fed and seasonal, flow east across the lateritic uplands in sandy beds and are the rivers of the Rarh. They are the Damodar with its DVC dams and the Durgapur barrage, the Ajay and the Mayurakshi, on which the Massanjore dam in Jharkhand and the Tilpara barrage in Birbhum irrigate Birbhum and Murshidabad, the Dwarakeswar and Shilabati, which join as the Rupnarayan, the Kangsabati or Kasai, on which the Mukutmanipur dam in Bankura, the second largest earthen dam in India, irrigates Bankura and the Medinipurs, and the Subarnarekha, which crosses the corner of Jhargram and Purba Medinipur to the sea.

The rivers of the delta are the branches of the Ganga. The Bhagirathi-Hooghly leaves the Ganga at Farakka, where the Farakka barrage, 2,245 metres long, completed in 1975, diverts 40,000 cusecs through a feeder canal to keep the river flowing and the port of Kolkata open, and runs 500 kilometres south past Murshidabad, Nabadwip, Kalyani, Kolkata and Haldia to the sea at Sagar Island. In its lower course it is called the Hooghly and is tidal from the sea to Nabadwip. Its distributaries and cross-channels, the Jalangi, Mathabhanga, Churni and Ichhamati, wander through Nadia and the 24 Parganas, many of them decaying, and the rivers of the Sundarbans, the Matla, Bidyadhari, Saptamukhi, Thakuran, Gosaba and Raimangal, are tidal creeks of salt water with no fresh source. The Rupnarayan and the Haldi, on whose junction with the Hooghly stands Haldia port, join from the west.

Irrigation in West Bengal covers about 55 per cent of the cropped area. Canals from the DVC, Mayurakshi, Kangsabati and Teesta projects and the Midnapore canal serve the west and north; shallow and deep tube-wells, over 5 lakh of them, in the alluvium of Nadia, Hooghly, Bardhaman and the 24 Parganas are the largest source and the basis of the winter boro rice; and tanks and ponds, of which the state has over 20 lakh, irrigate the lateritic west and supply fish. Lift irrigation from the rivers and the recycled sewage of the East Kolkata wetlands complete the picture. The problems are the arsenic in the shallow groundwater of the delta districts, the silting of the Hooghly, the floods of the Damodar and Tista and the dry-season shortage in the west.

India faces a growing water crisis with two faces. The first is scarcity: availability per person has fallen from 5,000 cubic metres a year in 1951 to about 1,500, and about a third of the country's districts are water-stressed; the water tables of Punjab, Rajasthan, Gujarat and Tamil Nadu fall by a metre a year, the tanks of the south are neglected, cities such as Chennai and Bengaluru run dry in bad years, and the rivers Kaveri, Krishna, Ravi-Beas and Tista are fought over by states and neighbours. The second is pollution: untreated sewage from towns, effluent from factories, pesticides and fertilisers from fields and arsenic and fluoride from over-pumped aquifers make much of the available water unfit to drink, so that water-borne diseases, diarrhoea, cholera, typhoid and hepatitis, remain the largest killers of Indian children. The Ganga, Yamuna, Damodar and Hooghly are among the most polluted rivers in the world in stretches, and about 70 per cent of India's surface water is contaminated.

Conservation of water means using less, wasting less and putting more back into the ground, and it has many means.

Rainwater harvesting is the collecting and storing of rain where it falls. On a house the roof water is led by gutters and pipes into a tank for use or into a recharge pit or dug well to feed the groundwater; a roof of 100 square metres in Kolkata, with 160 centimetres of rain, can yield over one lakh litres a year. In the countryside rain is caught in tanks, ponds, check dams and percolation pits. India's traditional systems, the tanks of Tamil Nadu, the johads of Rajasthan, the bamboo drip irrigation of Meghalaya, the kuls of Himachal, the zings of Ladakh and the tankas and baolis of the desert, are being revived, and Tamil Nadu and several cities have made rooftop harvesting compulsory in new buildings.

Watershed management treats a whole small river basin as a unit: contour bunding, terracing, planting trees and grass on the slopes, building check dams across the gullies and percolation tanks in the valley, so that the rain sinks into the soil instead of rushing off with it. The work of Ralegan Siddhi and Hiware Bazar in Maharashtra and of Tarun Bharat Sangh in Alwar, Rajasthan, which revived dead rivers by building thousands of johads, are the famous examples. Groundwater recharge through recharge wells and the desilting of tanks and ponds, as under the Jal Shakti Abhiyan and West Bengal's Jal Dharo Jal Bharo scheme, which has dug lakhs of ponds, replenishes the aquifers.

Efficient use includes drip and sprinkler irrigation, which save half the water of flood irrigation; crops suited to the rainfall instead of water-hungry rice and sugar-cane in dry regions; lining canals to stop seepage; and the metering and pricing of water and electricity for pumping. Recycling of treated sewage for industry and gardens, as in the East Kolkata wetlands, and the treatment of effluent before discharge protect the rivers. Interlinking of rivers, the proposal to carry surplus water from the Ganga and Brahmaputra to the deficit basins of the peninsula through canals such as the Ken-Betwa link, is debated as a large-scale answer.

Law and policy support these: the Water Act of 1974, the National Water Policy, the Jal Jeevan Mission for piped water to every rural home, the Atal Bhujal Yojana for groundwater, and the Namami Gange programme for the Ganga. Yet the largest saving lies with the citizen: a dripping tap wastes 20 litres a day, a bath uses 100 litres against a bucket's 20, and a household that harvests its roof water, fixes its leaks and does not pollute its pond does its share of the country's conservation.