Chapter 13: Water Resources and Types of Irrigation
On the southern rim of the Meghalaya plateau sits Mawsynram, a small town that catches the monsoon before almost anywhere else in India. As the rain-laden winds sweep in off the Bay of Bengal, they slam into the plateau’s steep wall and are forced upward, wringing out their moisture. The result is staggering: Mawsynram receives, on average, well over 11,000 millimetres of rain a year — roughly fifteen times what Delhi gets, and among the highest totals measured anywhere on Earth. Cherrapunji, close by, is nearly as drenched.
You would think such a place could never run short of water. Yet every winter it does. Once the monsoon withdraws, four or five dry months follow. Streams thin, springs weaken, and people must walk down the hillsides to reach water far below.
The reason is the quiet theme of this whole chapter. The rain does not fall evenly through the year — it arrives in a violent monsoon burst and then stops. And it does not stay where it lands: the plateau’s steep slopes shed it almost at once, sending it cascading down into the plains of Bangladesh before anyone can hold it back.
Rain, in other words, is not the same as water security. A land can be soaked and still be thirsty. Storing that water, keeping it clean, and delivering it to fields and cities is the work this chapter is about.
Diagram
Fig. 13.0-1 Caption: The monsoon empties itself on the plateau’s steep edge, and the water runs straight off — plenty of rain, little of it kept. Brief: Schematic cross-section (not to scale) of the south-facing escarpment of the Meghalaya plateau. Lower-left: the low Bangladesh plain with the Bay of Bengal beyond; rising to the upper-right: a steep escarpment up to the flat plateau top, with Mawsynram / Cherrapunji marked on the upper slope near the crest. Draw moist monsoon air as broad arrows entering from the sea at lower-left and moving up-and-right along the slope (rising). Draw heavy rainfall from clouds over the upper slope and crest. Draw runoff as arrows racing back down the steep face from upper-right toward the plain at lower-left. Label: Bay of Bengal, plain (Bangladesh), steep escarpment, plateau top (Mawsynram), rising moist air, heavy rainfall, rapid runoff. Emphasise the contrast — heavy rain arriving, most of it running straight off, little stored. No India outline or boundaries; cross-section only.
13.1 Water Resources of India
Water is the one resource nothing living can do without, and India — for all its rivers and rain — does not have a great deal of it to spare. The country holds about 2.45 per cent of the world’s land and roughly 17 per cent of its people, yet only about 4 per cent of the world’s fresh water.
Fresh water is water with little dissolved salt, fit to drink and to grow crops. It is a thin slice of all the water on Earth. Oceans cover most of the planet, but their salt water is of little direct use; fresh water makes up barely 3 per cent of the total, and most of that is frozen in ice sheets and glaciers.
So the real question for India is not just how much water falls from the sky, but how much can be caught, held and used — and in what forms it is stored. Water reaches us in two forms. Surface water flows and stands in the open, in rivers, lakes and tanks. Groundwater soaks down into the soil and rock below. The rest of this section follows India’s water from the cloud into these two stores.
13.1.1 India’s Place in the World’s Water Budget
A country’s water budget is a simple piece of book-keeping: rain and snow come in, some is lost, and what is left is what there is to work with. For India the incomings are large. In an average year the country receives about 4,000 billion cubic metres (BCM) of water as rain and snow. One BCM is a thousand million cubic metres — picture a cube of water a kilometre on every side.
But most of that water never reaches a tap or a field. A large share evaporates straight back into the air or is soaked up by the soil. What drains away over the surface and collects in streams is called runoff, and India’s average annual runoff is about 1,869 BCM — less than half of what fell.
Even that is not all available. Much of the runoff arrives as monsoon floods that rush to the sea before anything can be done with them, or flows through country too rough to dam. The part that can actually be stored and drawn on is the utilizable water, and here the figure shrinks again, to roughly 690 BCM of surface water. To this we can add about 430 BCM of groundwater that refills each year, giving a usable total of a little over 1,120 BCM.
Set the two ends of the chain side by side: about 4,000 BCM falls, but only around 1,120 BCM can be used. Little more than a quarter of India’s rain ends up as water the country can command. That single gap — between what arrives and what can be held — is why a well-watered country still worries about water.
Flowchart
Fig. 13.1-1 Caption: Of all the rain that falls on India, only a little more than a quarter can finally be put to use. Nodes: Rain and snow over India (~4,000 BCM a year) → most lost to evaporation and soaked into the soil → what drains off becomes river flow: natural runoff (~1,869 BCM) → only part can be captured and stored: utilizable surface water (~690 BCM); the rest escapes as flood or reaches the sea unused → add water that sinks underground and refills yearly: replenishable groundwater (~430 BCM) → total water India can actually use (~1,120 BCM)
13.1.2 Surface Water
Surface water is the water we can see — in rivers, lakes, ponds and tanks. Rivers are by far the most important source, fed either by rainfall or by the melting of Himalayan snow. India has been estimated to have more than ten thousand rivers and sizeable tributaries, together carrying an enormous flow.
Yet, as the water budget showed, only about 690 BCM — roughly a third of all river flow — can actually be used. The rest is lost to the difficulties of terrain, timing and distance.
This surface water is also shared very unequally between the rivers. The three great rivers of the north — the Ganga, the Brahmaputra and the Indus — together carry close to 60 per cent of India’s total surface flow. The Ganga and the Brahmaputra are among the largest rivers in the world by the sheer volume of water they move.
But a large flow is not the same as a large supply, and no river shows this better than the Brahmaputra.
The Brahmaputra makes the chapter’s key point about surface water: the size of a river’s flow is not the size of its usefulness. What can actually be used depends on when the water comes, whether it can be stored, and whether it is near the people who need it — not on the raw volume. This is exactly why India can be rich in river flow and still short of water.
Lagoons and Backwaters
Along its long coast India also holds surface water in lagoons — shallow water bodies cut off from the open sea by a bar or spit of sand — and in the connected channels called backwaters. These are well developed on the indented coasts of Kerala, Odisha and West Bengal. Their water is usually brackish, meaning saltier than fresh water but less salty than the sea, so it is used mainly for fishing and for irrigating salt-tolerant crops such as coconut and certain varieties of paddy.
13.1.3 Groundwater
Not all rain runs off. A part of it seeps downward through joints and cracks in the soil and rock — a process called percolation — and gathers below the surface as groundwater. About 60 per cent of it stays within the upper layers of the soil, close enough to be reached by wells and useful to crops; the rest sinks deeper. A body of permeable rock or sediment that holds and passes on this water is an aquifer.
Only the water that is recharged each year can be drawn on without emptying the store. This replenishable groundwater — the yearly refill — is estimated at about 430 BCM for the whole country.
An Uneven Underground Store
Where this groundwater lies is decided far more by rock than by rainfall. It depends on the structure of the rock, the shape of the surface, and how readily water can sink in.
The northern plains are the country’s great reservoir. They are built of soft, porous alluvium — sediment laid down by the Himalayan rivers — through which water percolates easily into deep, generous aquifers. More than two-fifths of India’s groundwater potential lies beneath these plains, and Uttar Pradesh alone holds close to a fifth of the national total.
The peninsular plateau is the opposite. It is made of old, hard, crystalline rock that water cannot penetrate — such rock is described as impervious, meaning it does not let water pass. So the plateau stores little groundwater, holding it only in shallow weathered cracks. Even here, though, the largest states — Maharashtra, Madhya Pradesh and Tamil Nadu — have a fair volume simply because of their size.
We can see this pattern on a map of groundwater availability.
Map
Map 13.1 Caption: Groundwater is generous where the plains are soft and scarce where the plateau is hard. Brief: Map of India showing the general availability of groundwater by region, shaded from high (darkest) to low (palest): high across the northern plains (Punjab, Haryana, Uttar Pradesh, Bihar, the Brahmaputra valley), low across most of the peninsular plateau, moderate in coastal and delta strips. Include a simple key with three or four high-to-low classes and label the major regions named. This is a general pattern map, not a per-state data map. The map must show the full extent of India as officially defined by the Government of India, including Jammu and Kashmir and Ladakh, and must mark no boundary as disputed.
Most groundwater — about three-quarters of it — is used for irrigation, the rest for homes and industry. But how far each region has drawn on its store varies enormously. Some states have barely tapped their potential, while Punjab has developed almost all of its own, pumping so hard that its water table — the upper level of the water-saturated ground — is now falling year after year — a danger we return to later in the chapter.
13.2 Water Demand and Utilisation
Knowing how much usable water India has is only half the story. The other half is who uses it, and for what. A fixed supply put to one use is not available for another, so the pattern of demand decides where the pressure falls.
India is still a farming country. About half of its workforce depends on agriculture, and agriculture is thirsty work. It is by far the largest user of water — of both the surface water in rivers and canals and the groundwater drawn up by wells. The other users, homes and industry, take only a small share.
The figures make the imbalance plain.
Read the table and one fact dominates: whether the water comes from a river or from underground, roughly nine parts in ten go to farming. Homes and factories together share what is left. There is a small but telling difference lower down. Homes draw more of their water from the surface — piped from reservoirs and rivers — while industry draws relatively more from the ground.
Why does agriculture swallow so much? India has to feed a very large population, and a great part of its cropland is watered by irrigation rather than by rain alone. Many of its main crops — rice, sugarcane and the high-yielding wheat of the plains — need generous and regular moisture. The bulk of India’s water, in short, is spread across its fields.
That balance will not stay fixed. As the population grows and cities and industry expand, the demand from homes and factories is bound to rise, and agriculture’s share is likely to slip. But the total demand keeps climbing against a supply that cannot be enlarged — and that is where competition and scarcity begin.
A fixed supply, a rising demand, and a large share already committed to the fields: this is the setting for the problems that follow — the fouling of the water that does exist, and the search for ways to conserve it.
13.3 Water Quality and the Conservation of Water Resources
Water in India is not only scarce; much of what exists is being spoiled or wasted. Conservation therefore has two tasks — to keep the water we have clean, and to hold on to more of it. This section looks first at how India’s water is being fouled, and then at the main ways of conserving it.
13.3.1 Deterioration of Water Quality
Water quality means the purity of water — water free of unwanted foreign substances. Water is polluted when micro-organisms, chemicals or wastes are added to it in amounts that make it unfit for use.
India’s water is fouled from three main directions. The first is sewage. Cities and towns produce vast quantities of it, and most is emptied into rivers untreated, turning the water downstream unfit even for bathing. A large share of India’s surface water — by some estimates around three-quarters — is polluted, and many river stretches now run as little more than drains. The Yamuna, along its worst stretches, is among the most polluted rivers in the country.
The second direction is industry. Factories discharge chemical and organic waste straight into water bodies; the leather factories of Kanpur, for instance, pour millions of litres of waste into the Ganga every day.
The third is farming. The heavy use of chemical fertilisers and pesticides leaves residues that wash off the fields into rivers and soak into the ground, raising the levels of nitrates and other chemicals. Groundwater suffers too: in different parts of the country it carries harmful amounts of fluoride, arsenic or nitrates, which are far harder to remove than surface pollution.
13.3.2 Preventing Water Pollution
Cleaning water begins with knowing how dirty it is. The Central Pollution Control Board (CPCB), working with the State Pollution Control Boards, monitors water quality at a national network of stations. Their surveys show that organic and bacterial contamination — largely from sewage — is the leading cause of river pollution.
India has also built a legal framework. The Water (Prevention and Control of Pollution) Act of 1974, the Water Cess Act of 1977, and the Environment (Protection) Act of 1986 all aim to check pollution, while the National Water Policy sets an order of priority for water use, placing drinking water first.
The laws exist; the difficulty has been in enforcing them. Many polluting units have continued to operate on the banks of rivers, and the treating of waste has lagged. This is why so much effort now goes into raising public awareness — because a law that people do not support is hard to make work.
13.3.3 Recycling and Reuse of Water
Not every use of water needs clean water. This simple idea is the basis of recycling and reuse. Waste water of poorer quality can be treated and used again for tasks that do not require it to be pure — cooling and fire-fighting in industry, or washing and gardening in towns.
Every litre reused for such tasks is a litre of good water freed for drinking. The practice is still at an early stage in India, but its potential is large, and it will grow as clean water becomes dearer.
13.3.4 Watershed Management
A watershed is an area of land that drains all its rainwater to a single common outlet — a stream or a point at its lowest edge. Because the whole area shares one drainage, it makes an ideal unit for conserving soil and water together: what is done on the upper slopes decides what reaches the bottom.
Watershed development treats the whole area as one, from the ridge down to the valley. Trees and bunds on the upper slopes slow the runoff and hold the soil; fields in the middle are bunded to catch water; and check dams near the outlet store what remains and let it soak into the ground. The work covers both farmed and unfarmed land, weaving in horticulture, agro-forestry and the growing of forests. Governments and voluntary organisations run such schemes, among them the centrally-sponsored Hariyali programme.
Diagram
Fig. 13.3-1 Caption: A watershed is all the land that funnels its rainwater to one outlet, so treating it whole conserves both soil and water. Brief: Perspective/block diagram of a small watershed — a bowl of land ringed by a ridge line, sloping inward and downward to a single stream outlet at the lowest point. From ridge to valley show: tree cover and contour bunds on the upper slopes (slowing runoff, checking erosion); bunded fields on the middle slopes (catching water); and a check dam with a small storage pond near the outlet (storing water, recharging the ground). Arrows show rainwater moving downslope from ridge toward the outlet, slowed and captured at each step. Label: ridge line (watershed boundary), upper slope with trees and contour bunds, bunded fields, check dam and storage, stream outlet. Emphasise water moving ridge-to-valley and being held on the way down.
13.3.5 Rainwater Harvesting
The opening story of this chapter — a place drowned in summer rain and thirsty by winter — describes the very problem that rainwater harvesting sets out to solve. Rainwater harvesting is the technique of capturing rain where it falls and storing it, either in tanks above ground or by letting it soak down to refill the aquifer. This refilling of groundwater is called recharge.
Its aims are several at once: to meet rising demand, to raise a falling water table, to cut the runoff that floods roads and chokes drains, to reduce soil erosion, and to keep a store for the dry months.
The methods are mostly simple and cheap. Rain from a rooftop can be piped into a storage tank or a recharge pit. Pits and trenches filled with gravel let surface water soak down to the water table. A check dam or an earthen bund across a small stream ponds the water long enough for it to percolate. Rain can even be led into an abandoned well or around a handpump to recharge the ground.
Diagram
Fig. 13.3-2 Caption: Rainwater harvesting catches the monsoon before it escapes — into storage above ground, or down into the aquifer below. Brief: Composite diagram showing three or four simple rainwater-harvesting and recharge methods side by side: (1) rooftop harvesting — rain from a house roof led by a pipe into a storage tank and into a recharge pit; (2) a gravel-filled recharge pit or trench beside a building, water soaking down to the water table; (3) a check dam or earthen bund across a small stream, ponding water that percolates into the ground; (4) recharge through a dug well or handpump. Arrows show rainwater flowing from roof and surface into storage and downward into the ground toward the water table (mark the water table as a dashed line). Label each method, the storage tank, the recharge pit, the check dam, the well, and the water table. Emphasise the downward arrows of water recharging groundwater.
An Old Indian Skill, Revived
None of this is new to India. For centuries people have stored rain in tanks and stepwells, and in the dry north-west they led rooftop and catchment water into underground stores called kunds — small covered tanks that hold rainwater through the dry season. In the deserts of Rajasthan, villages have revived the old earthen check dams known as johads; in the Alwar district the Arvari Pani Sansad has organised this work across many villages, and streams that had gone dry began to flow again. Andhra Pradesh runs a state-wide harvesting drive called Neeru-Meeru (Water and You), and Tamil Nadu has made rooftop rainwater harvesting compulsory for new buildings.
13.4 Irrigation: Meaning, Importance and Need in India
Most of the water India uses goes to its fields, so the largest single question about the country’s water is really a question about irrigation. Irrigation is the supplying of water to crops by artificial means — through canals, wells, tube-wells or tanks — drawing on sources such as rivers, ponds and underground water. It is what a farmer does when the rain will not do the job by itself.
And in India, very often, the rain will not. Farming that depends on rain alone is called rain-fed farming, and across much of the country rain-fed farming is a gamble. To see why, look at how India’s rain actually behaves — for it is unreliable in three separate ways: in where it falls, in when it falls, and in how much falls.
An Unreliable Rain
First, the rain is uneven in space. Some regions are soaked while others go short. The arid north-west and the dry interior of the peninsula, which lies in the rain-shadow of the Western Ghats, receive far too little to grow a dependable crop. These deficit regions must irrigate simply to farm at all.
Second, the rain is uneven in time. It does not fall steadily through the year but arrives in a burst — about three-quarters of India’s rain comes in the four monsoon months, from June to September. For the rest of the year the land is largely dry. Any crop grown in those dry months, such as the winter wheat of the plains, must be watered by hand of man rather than by cloud.
Third, the amount is uncertain from year to year. This year-to-year swing is called rainfall variability, and it is high over large parts of India. Nor is it only the dry areas that suffer it; even well-watered regions can have a poor year. Worse, the monsoon’s own timing is uncertain — its onset, its mid-season breaks and its withdrawal all shift unpredictably, and droughts recur. Without stored water to fall back on, a single weak monsoon can mean a failed harvest.
Why Even Good Rain Is Not Enough
Suppose the rain is generous and well timed. Even then, irrigation is often needed. Some of India’s most important crops are water-hungry: rice, sugarcane and jute need far more water than the monsoon alone reliably delivers.
The high-yielding varieties of seed that drove the Green Revolution add to the demand. These varieties give their extra yield only with regular, assured moisture; a dry spell at the wrong moment costs the whole gain. So irrigation becomes necessary even where rainfall would otherwise be thought sufficient.
Irrigation also unlocks the calendar. India’s long growing season could, in principle, yield two or three crops a year from the same land — multiple cropping — but only if water is assured between the rains. Assured water turns one crop a year into two or three.
The reward for all this is real. Irrigated land is markedly more productive than rain-fed land, and its yields swing far less from year to year. Extending irrigation therefore does two things at once: it raises output, and it steadies it against the moods of the monsoon.
Flowchart
Fig. 13.4-1 Caption: Why India cannot leave its fields to the rain alone. Nodes: India’s rainfall is uneven in space, crammed into time, and unreliable in amount → rain alone cannot water the crops through the whole year → many crops (rice, sugarcane) and high-yielding varieties need more, and more regular, water than rain gives → so water must be supplied artificially: irrigation → assured water allows dry-season and multiple cropping, and steadier, higher yields
13.5 Primitive Methods of Irrigation
Which source a farmer turns to for water depends on the land around him — its slope, its soil, its rainfall, whether there is a river or groundwater to draw on, and what the crop demands. Out of these choices India’s many irrigation methods have grown, and they fall into two broad families.
The primitive methods — wells, tanks and inundation canals — have been used since ancient times. They are simple and cheap, but small in reach and often unreliable. The modern methods — tube-wells, perennial canals, and sprinkler and drip systems — are later improvements that water much larger areas far more dependably. Over time the modern methods have overtaken the primitive ones, which now survive only in certain regions. The following table shows where the country’s irrigated land gets its water today.
This section takes the three primitive methods in turn; the next takes the modern ones.
13.5.1 Well Irrigation
A well is a hole dug into the ground to reach the water held in the soil below. An ordinary well is about three to five metres deep, though deeper ones are sunk to fifteen metres or more. The water is raised by the Persian wheel and other traditional lifting devices, and used for irrigation as well as for drinking and washing.
Wells work only where there is enough sweet — that is, fresh — groundwater within reach. They are common across the Great Plains, in the deltaic tracts of the peninsular rivers, and in the weathered upper layers of the Deccan lavas, where water gathers in the cracked rock. They fail where the rock is hard and impervious, as over much of the peninsula, and where the groundwater is brackish, as in large dry tracts of the north-west. About 18 per cent of India’s irrigated area is watered by wells, and the largest concentration is in the drier states of Uttar Pradesh, Rajasthan and Madhya Pradesh, which lean on their groundwater precisely because their surface water is short.
Well irrigation has genuine strengths. It is the simplest and cheapest source, within reach of a poor farmer. It is independent: the farmer can draw water exactly when the crop needs it, whereas canal water is released by an outside agency on its own schedule. A well can be dug wherever it is convenient, and there is no recurring charge for its water. The salts dissolved in well water can even add a little to the soil’s fertility.
Its weaknesses are equally clear. A single well waters only a small patch, perhaps one or two hectares. It can be emptied if over-drawn, and in a drought — just when it is needed most — the falling water table can leave it dry. And where the groundwater is brackish, a well is of no use at all.
13.5.2 Tank Irrigation
A tank is a body of stored water, made by throwing a small bund — an embankment of earth or stone — across a stream or around a natural hollow, so that rainwater collects behind it. The stored water is then led out to the fields. Most tanks are small and are built and owned by individual farmers or village groups.
Tank irrigation belongs above all to the peninsular plateau, where Andhra Pradesh and Karnataka are among the leading states. The reasons it thrives there, and hardly anywhere else, are worth setting out.
The peninsula’s undulating, rocky ground makes canals and wells hard to build; its hard rock lets little water percolate underground; and its rivers are seasonal, drying up in summer, so they cannot feed canals through the year. The monsoon streams that do run come down in torrents, and the only way to keep that water is to dam it into a tank. Scattered fields and villages suit such small, local stores.
Diagram
Fig. 13.5-1 Caption: An earthen bund across the valley traps the monsoon stream, and a sluice lets the stored water down to the fields. Brief: Schematic oblique view of a tank. Show a shallow valley with a low earthen bund thrown across its lower end, impounding a body of water behind it. A monsoon stream feeds in from the upper side (arrow of water flowing in). A sluice or outlet through the bund releases water to terraced fields below it (arrow of water flowing out to the fields). Label: catchment stream, earthen bund, stored water (tank), sluice/outlet, irrigated fields. Keep schematic; arrows show water in from the catchment and out through the sluice to the fields.
Tanks have their merits. Many use natural hollows and so cost little to build; even a single farmer can own one; built on rocky beds, they last long; and fish reared in them add food and income for the farmer. But their drawbacks are serious. Many tanks dry up in the dry season and fail just when water is wanted. Silt collects on the bed and must be dug out to keep the capacity up. Being wide and shallow, a tank loses much water to evaporation, and it locks up a large area of otherwise cultivable land.
For all these reasons tank irrigation has been shrinking. Tanks now water only about 3 to 4 per cent of India’s irrigated area, down from around a seventh in the early 1960s, as canals, wells and tube-wells have spread.
13.5.3 Inundation Canals
An inundation canal is a channel cut straight from a river, with no barrage or regulating structure at its head to control the flow. Because there is nothing to hold water back, the canal fills only when the river itself is high.
So its working is entirely seasonal. During the rains the river swells and spills into the canal, watering the fields; once the rains end and the river level drops below the canal head, the canal simply dries up. Irrigation from it is therefore uncertain, tied to the flood and gone with it. Such canals were once taken from rivers like the Satluj.
Because that uncertainty made them unreliable, most inundation canals have been rebuilt as perennial canals — canals fed through a barrage across the river so that they carry water all year round. With that step we cross from the primitive methods into the modern ones, which the next section takes up.
13.6 Modern Methods of Irrigation
The modern methods of irrigation are, in the main, improvements on the primitive ones. They are easier to run, they water much larger areas, and they deliver water more regularly. A tube-well waters many times the area of an ordinary well; a perennial canal, unlike an inundation canal, carries water the whole year round. These methods now dominate India’s fields, but they do not spread evenly — each region leans on the source its land allows.
Map
Map 13.2 Caption: Each part of India leans on the source its land allows — canals and tube-wells in the plains, tanks in the peninsula. Brief: Map of India showing the dominant source of irrigation by region, with a key distinguishing areas irrigated mainly by canals, mainly by tube-wells, mainly by wells, and mainly by tanks. Show canals and tube-wells dominant across the northern plains (Punjab, Haryana, western Uttar Pradesh); tube-wells and wells across the drier plains and parts of the peninsula; tanks across the peninsular plateau (Andhra Pradesh, Karnataka, Tamil Nadu); some canal irrigation in the coastal deltas of the south. Include a clear four-class key. The map must show the full extent of India as officially defined by the Government of India, including Jammu and Kashmir and Ladakh, and must mark no boundary as disputed.
13.6.1 Tube-Well Irrigation
A tube-well is a deep well — generally more than fifteen metres deep — from which water is lifted by a pumping set driven by an electric motor or a diesel engine. The pump is what sets it apart from an ordinary well: it can raise water from far greater depths, and in far greater quantity, so a single tube-well can irrigate many times the area an ordinary well can.
A tube-well cannot be sunk just anywhere. It needs a good store of groundwater, and a water table that is not too deep — beyond about fifty metres, pumping the water up costs more than it is worth. It needs a steady supply of cheap power, electric or diesel, and fertile soil nearby to make the outlay worthwhile. These conditions are met most fully in the northern plains, and it is there that tube-wells cluster. Tube-wells are today the single largest source of irrigation in India, watering nearly half the irrigated area, and Uttar Pradesh has the largest area under them.
Their advantages follow from the pump. A tube-well waters a large area, draws from deep down, and can be used whenever the crop needs water, without waiting on any agency. It is the natural choice where canals do not reach.
But the same pump is the source of their gravest problem. Because a tube-well can draw water so fast and in such volume, an area crowded with tube-wells can pull groundwater out faster than the rain refills it. In Punjab and Haryana, where thirsty rice has spread across the plains, the water table has fallen critically as a result — a warning the chapter returns to at its close. Tube-wells also carry recurring fuel or power costs, and they are of no use where the groundwater is brackish.
13.6.2 Canal Irrigation
A perennial canal draws its water through a barrage — a low dam built across a river to raise the water level and turn part of the flow into the canal — so that it can supply water all year, not only in flood. From the barrage the water fans out down a branching ladder of ever-smaller channels to the fields.
Flowchart
Fig. 13.6-1 Caption: A perennial canal spreads a river’s water down a branching ladder of channels to the fields. Nodes: River → barrage (holds the water back and raises its level) → main canal → branch canals → distributaries → field channels → the farmer’s field
The area a canal system is designed to water is called its command area. Canals work best where that command area is wide and level, the soil deep and fertile, and the river dependable — and no part of India suits them better than the northern plains.
Canal irrigation is heavily concentrated in the plains of Punjab, Haryana, Uttar Pradesh, Rajasthan and Bihar. The rocky, uneven peninsula, where canals are hard and costly to dig, has very few — though the flat coastal deltas of the south do carry some.
Canals bring solid advantages. They give a perennial, dependable supply; they carry silt that renews the fertility of the fields; and many are part of multipurpose projects, so their water comes cheaply alongside power and flood control. Their large first cost is spread thin over many years of use.
Their disadvantages are just as real, and they gather around one theme — too much water in the wrong place. Water soaks out of the canals into the surrounding land, waterlogging it; the rising water table brings salts to the surface and can poison the soil; marshy stretches breed mosquitoes and malaria; and in heavy rain canals may overflow and flood nearby fields. These troubles of over-watering are serious enough to need a section of their own, which follows.
13.6.3 Sprinkler Irrigation
Sprinkler irrigation is an overhead method: water is pumped through pipes and sprayed over the field, falling on the crop like artificial rain. Because the water travels in closed pipes rather than open channels, almost none is lost to seepage on the way, and it can be spread evenly across the ground.
Its strengths make it valuable where older methods struggle. It saves water by cutting seepage losses; it works on uneven and sandy land where canals cannot be cut; and it suits the arid and semi-arid regions that receive scanty rainfall. Its weaknesses are the cost of the equipment and the pumping it needs, and the fact that some of the sprayed water is still lost to wind and to evaporation in the air before it reaches the soil. It is comparatively new to Indian farming and is spreading only slowly.
13.6.4 Drip Irrigation
Drip irrigation, also called trickle irrigation, is the most sparing method of all. Instead of flooding the ground or spraying it, water is delivered slowly, drop by drop, straight to the base of each plant through a network of pipes fitted with small outlets called emitters.
Diagram
Fig. 13.6-2 Caption: Water travels by pipe to each plant and drips out at the root, so almost none is lost on the way. Brief: Schematic of a drip irrigation layout on a field or orchard row. Show a water source or tank with a filter, a main pipe leading to lateral pipes running along the rows of plants, and small emitters on the laterals releasing water (small drop symbols) directly at the base of each plant, wetting only a small zone around the roots. Label: water source, filter, main pipe, lateral pipe, emitter (dripper), root zone wetted. Show clearly that only the root zone is wet, not the whole field. Drops and arrows show water moving from the source through the pipes to each plant’s base.
Because the water goes straight to the roots, drip loses almost nothing to evaporation, seepage or runoff, which makes it the most water-efficient method known. It can also carry dissolved fertilizer directly to the plant, a practice called fertigation, and because only the root zone is wetted, fewer weeds grow between the plants. These qualities make drip well suited to the arid and water-scarce parts of the country, and to widely spaced crops such as fruit trees, vegetables, cotton and sugarcane.
Its drawbacks keep it from spreading faster. The pipes and emitters cost a good deal to install; the fine emitters can clog and so need clean, filtered water and regular care; and the method does not suit every crop — densely sown crops such as paddy gain little from it. Still, as water grows scarcer, drip is the method whose careful economy the country increasingly needs.
13.7 The Misuse of Water: Over-Watering and Its Dangers
Irrigation is meant to feed the land. Yet water, like any powerful tool, can do harm when it is misused — and one of its commonest misuses is simply giving the land too much of it. Over-watering is the application of far more irrigation water than the crop and the soil can actually take. Done year after year, it can ruin the very fields it was supposed to enrich.
Why Fields Are Over-Watered
Farmers over-water for understandable reasons. Wanting a bumper crop, they flood their fields, on the belief that more water must mean more yield. The habit is strongest in canal-irrigated areas: having paid for canal water, a farmer wants the fullest return on it, and when water arrives cheap and abundant it is used carelessly. Where fields are poorly drained, the excess has nowhere to go.
How Over-Watering Ruins the Soil
The damage comes in a clear chain, and it is worth following step by step. The first stage is waterlogging — the raising of the water table by all that excess water until the soil is saturated, choking the roots, which can no longer get the air they need.
The second stage is worse and follows from the first. Once the water table rises to within about two metres of the surface, the soil begins to draw water upward through its fine pores — a movement called capillary action. That water reaches the surface and evaporates in the heat, but the salts dissolved in it cannot evaporate; they are left behind, gathering as a whitish crust on the field. This build-up of salts is called salinity; where the salts are those of sodium, the soil also turns alkaline. Farmers know the salt crust by local names such as reh and kallar. Salted in this way, once-fertile land becomes unfit to grow anything.
Diagram
Fig. 13.7-1 Caption: Too much irrigation lifts the water table; the water creeps up, evaporates, and leaves its salt as a crust on the field. Brief: Cross-section of an over-irrigated field. Show the field surface with a thin crop; below it soil layers, and a water table drawn as a dashed line that has risen to within about two metres of the surface (mark the ~2 m depth). Draw upward arrows of capillary rise carrying water from the water table toward the surface; at the surface, evaporation arrows leaving upward into the air, and a whitish salt crust left on the soil (labelled salt crust / reh). Include a small inset showing a normal, deeper water table for contrast. Label: crop, soil, risen water table (~2 m), capillary rise (arrows up), evaporation (arrows up into the air), salt crust at surface. Arrows: water rising through the soil, water vapour leaving at the surface, salt staying behind.
Where It Has Struck
Over-watering has done real harm to India’s most heavily irrigated land. The canal-fed plains of Punjab, Haryana and Uttar Pradesh suffer widely from reh, and large tracts of the Nira valley in Maharashtra have been rendered useless by salt drawn up through canal irrigation. Misuse in fact wears two opposite faces — too much water laid on the surface, which waterlogs and salts the land, and too much water drawn from below, which, as we saw with the tube-wells of Punjab and Haryana, empties the aquifer. Both come from treating water as if it were limitless.
Can the Damage Be Undone?
Salted land is not always lost for good. Reclamation — restoring the soil to use — is possible, though it is slow and costly. Gypsum spread on the field helps drive out the sodium; leaching, the flushing of salt down and out of the topsoil with clean water, carries the salt away, provided there is proper drainage to take it; and green manure and farmyard manure rebuild the soil. Government schemes have reclaimed alkali land in the worst-affected states along these lines. But it is far cheaper to water carefully in the first place than to heal a salted field afterwards.
This is the chapter’s hardest lesson. Water is not simply a good to be poured on in greater and greater amounts; it is a resource to be measured and managed. Too little starves the crop, and too much salts the soil — which is why the careful methods of conservation and efficient irrigation, met earlier in this chapter, matter as much as the water itself.
13.8 Summary
India holds about 2.45 per cent of the world’s land and roughly 17 per cent of its people, but only about 4 per cent of its fresh water. Of the roughly 4,000 BCM of rain and snow it receives each year, only a little over 1,120 BCM can actually be used — barely a quarter. The gap between what falls and what can be held is the root of India’s water problem.
Usable water comes in two forms. Surface water, mostly in rivers, is dominated by the Ganga, the Brahmaputra and the Indus, which carry close to 60 per cent of the flow — but the Brahmaputra shows that a large flow is not a large usable supply. Groundwater is generous beneath the soft northern plains and scarce under the hard peninsula, because structure, not rainfall, decides where it waits; about three-quarters of it is used for irrigation.
Farming is by far the largest user of water, taking about nine parts in ten of both surface and groundwater, with homes and industry sharing the rest. As cities and industry grow, their demand rises against a supply that cannot be enlarged, so competition sharpens.
Much of India’s surface water has been fouled by untreated sewage, industrial effluent and farm chemicals. Conservation runs along three lines — preventing pollution, recycling and reusing water, and capturing more through watershed management, conjunctive use and rainwater harvesting. Rainwater harvesting, an old Indian art of tanks, kunds and johads, catches rain where it falls and sends it back into the ground.
Irrigation is the supplying of water to crops by artificial means, and India needs it because the monsoon is unreliable — uneven in space, crammed into a few months, and uncertain in amount. Water-hungry crops and high-yielding varieties need assured moisture, and irrigation raises yields, steadies them, and makes multiple cropping possible.
The primitive methods are wells, tanks and inundation canals. Wells are cheap and independent but small, and fail in hard rock, brackish water or drought. Tanks suit the hard-rocked, seasonal-streamed peninsula but are declining. Inundation canals fill only when the river floods, and most have been rebuilt as perennial canals.
The modern methods water far more land far more reliably. Tube-wells are now the largest source, but heavy pumping drops the water table. Perennial canals spread a river’s water across the level northern plains through a barrage and a branching command area, bringing silt and multipurpose benefits but risking waterlogging. Sprinkler irrigation sprays piped water and saves seepage; drip irrigation delivers it drop by drop to the root and is the most efficient of all, though costly.
Water misused turns destructive. Over-watering raises the water table, and capillary rise followed by evaporation leaves salts as a crust — the reh that has spoilt canal-fed land in Punjab, Haryana, Uttar Pradesh and the Nira valley of Maharashtra. Reclamation by gypsum, leaching and drainage is possible but slow and costly, so careful management matters as much as the water itself.
Flowchart
Fig. 13.8-1 Caption: The chapter in one line — rain arrives, little can be held, most goes to the fields, and careless use must give way to careful management. Nodes: Rain and snow over India (~4,000 BCM) → most lost; only ~1,120 BCM usable, as surface water (~690 BCM) and groundwater (~430 BCM) → both spread unevenly, and much surface water is polluted → the largest user by far is irrigation, needed because the monsoon is uneven and unreliable → water is applied by many methods: primitive (wells, tanks, inundation canals) and modern (tube-wells, canals, sprinkler, drip) → misused, water waterlogs and salts the land, or empties the aquifer → the remedy is to conserve and manage: prevent pollution, recycle, harvest rainwater, and irrigate efficiently
What This Chapter Cannot Tell You
A national figure such as 1,120 BCM of usable water hides the two facts that matter most — that the water is often in the wrong place and the wrong season; a country total says nothing about the district that runs dry in April.
The area a source irrigates does not tell you whether the water arrives when the crop needs it, or how much a single farmer at the tail of a canal actually receives.
The numbers here are snapshots from particular years. The shares shift as cities grow, tube-wells multiply, and the climate that delivers the rain itself changes.
13.9 Key Terms
Alluvium — sediment of silt, sand and clay laid down by a river, forming soft, porous, fertile ground.
Aquifer — a body of permeable rock or sediment that holds groundwater and lets it pass through.
Barrage — a low dam across a river that raises the water level and turns part of the flow into a canal.
Billion cubic metres (BCM) — a unit for very large water volumes; one BCM is a thousand million cubic metres, a cube of water a kilometre on each side.
Brackish — water saltier than fresh water but less salty than sea water.
Capillary action — the upward creep of water through the fine pores of the soil.
Command area — the area of land a canal system is designed to irrigate.
Conjunctive use — the planned use of surface water and groundwater together, in turn, so that both stores last longer.
Drip irrigation — a method that delivers water slowly, drop by drop, to the base of each plant through pipes and emitters.
Effluent — the liquid waste discharged by industry into water bodies.
Fertigation — supplying dissolved fertilizer to crops through the irrigation water, especially in drip systems.
Fresh water — water with little dissolved salt, fit to drink and to grow crops.
Groundwater — water that has soaked below the surface and gathered in the soil and rock.
Inundation canal — a canal cut straight from a river without a regulating structure, so it carries water only when the river is in flood.
Irrigation — the supplying of water to crops by artificial means, from sources such as rivers, tanks or underground water.
Lagoon — a shallow water body cut off from the open sea by a bar or spit of sand.
Leaching — flushing salts down and out of the topsoil with water so that they are carried away through drainage.
Modern methods of irrigation — the later, more reliable methods — tube-wells, perennial canals, sprinkler and drip — that water large areas dependably.
Multiple cropping — growing more than one crop on the same land in a single year.
Over-watering — applying far more irrigation water than the crop and the soil can take.
Percolation — the downward seeping of water through soil and rock.
Perennial canal — a canal fed through a barrage so that it carries water all year round.
Primitive methods of irrigation — the old, simple methods — wells, tanks and inundation canals — small in reach and often unreliable.
Rainfall variability — the swing in rainfall from one year to the next.
Rain-fed farming — farming that depends on rain alone, without irrigation.
Rainwater harvesting — capturing rainwater where it falls and storing it or using it to recharge groundwater.
Reclamation — restoring salt-damaged or degraded land to productive use.
Replenishable groundwater — the part of the groundwater store that is refilled each year and can be drawn on without emptying it.
Runoff — rainwater that flows off the surface and collects in streams and rivers.
Salinity — the build-up of salts in the soil, which can make it unfit for crops.
Sprinkler irrigation — an overhead method that pumps water through pipes and sprays it over the field like rain.
Surface water — water that flows or stands in the open, in rivers, lakes, tanks and ponds.
Tank — a store of water made by throwing a small bund across a stream or hollow to hold rainwater.
Tube-well — a deep well, generally over fifteen metres, from which water is lifted by a motor- or diesel-driven pump.
Utilizable water — the part of the runoff and groundwater that can actually be stored and used.
Water table — the upper level of the water-saturated ground.
Waterlogging — the saturation of the soil when the water table rises too close to the surface, choking the roots.
Watershed — an area of land that drains to one common point, and so a natural unit for managing soil and water.
Well — a hole dug into the ground to reach the water held in the soil below.
13.10 Points to Ponder
Mawsynram receives more rain than almost anywhere on Earth, yet it runs short of water every winter. Is a place’s water wealth better measured by how much rain falls on it, or by how much of that rain it can actually hold?
India can be rich in river flow and still short of water, as the Brahmaputra shows. If a river carries an enormous flow that no one can store or reach, is it a water resource at all — or does flow only become a resource once it can be held and delivered?
Groundwater beneath the plains is refilled slowly by the rain but can be pumped out quickly by a motor. When many farmers each draw from the same hidden aquifer, whose water are they using — and what happens to them all when each one decides to pump a little more?
Over-watering can turn a well-irrigated field into a salt-crusted waste. Can the same act that swells this year’s harvest quietly destroy the harvests of the next generation — and how should a farmer weigh a gain he can see against a loss he cannot yet see?
Tanks once watered about a seventh of India’s irrigated land and now water only a small fraction, replaced by tube-wells and canals. Was that switch a plain gain — or did the country give up something valuable in trading a store that fills itself from the rain for the work of pumping the ground and hauling river water across long distances?
13.11 Objective Questions
- Roughly what share of the world’s fresh water does India hold? [1 mark]
- 2.45 per cent
- 4 per cent
- 17 per cent
- 24 per cent
- Which of the following is the most water-efficient method of irrigation? [1 mark]
- Inundation canals
- Tank irrigation
- Sprinkler irrigation
- Drip irrigation
- A canal taken straight from a river with no regulating structure at its head, which carries water only when the river is in flood, is called — [1 mark]
- a perennial canal
- an inundation canal
- a distributary
- a barrage
- The single largest source of irrigation in India today is — [1 mark]
- canals
- tanks
- wells
- tube-wells
- Assertion (A): Over-watering can leave a whitish crust of salt on the surface of a field. [1 mark] Reason (R): When the water table rises close to the surface, water creeps up by capillary action and evaporates, leaving its dissolved salts behind.
- Both A and R are true, and R is the correct explanation of A.
- Both A and R are true, but R is not the correct explanation of A.
- A is true, but R is false.
- A is false, but R is true.
- Match each item in Column A with the correct description in Column B. [1 mark]
| Column A | Column B |
|---|---|
| a. Tank irrigation | i. Restoring salt-damaged land to use |
| b. Fertigation | ii. Common on the peninsular plateau |
| c. Conjunctive use | iii. Using surface water and groundwater together, in turn |
| d. Reclamation | iv. Supplying fertilizer through the irrigation water |
- Fill in the blank: Of the roughly 4,000 BCM of water India receives as precipitation each year, only about ______ BCM can actually be used. [1 mark]
13.12 Check Your Concepts
Define irrigation, and name any two sources from which irrigation water is drawn. [2 marks]
State any two objectives of rainwater harvesting. [2 marks]
Differentiate between surface water and groundwater. [3 marks]
Give reasons why tank irrigation is common on the peninsular plateau. [3 marks]
Explain the mechanism by which over-watering turns fertile land saline. [4 marks]
Describe the advantages and disadvantages of well irrigation. [4 marks]
‘A large river flow is not the same as a large usable water supply.’ Evaluate this claim with reference to an Indian river. [4 marks]
Explain why irrigation is essential for farming in India, with reference to the behaviour of the monsoon. [6 marks]
Describe the modern methods of irrigation used in India, giving one advantage and one limitation of each. [6 marks]
13.13 Map, Diagram & Data Interpretation
- Study Table 13.2 (Area Irrigated by Different Sources in India, 2015–16). [4 marks]
- Calculate the percentage of the total irrigated area watered by tube-wells. Show your working.
- Which source waters the smallest area, and roughly what share of the total does it hold?
- State one thing this table does not tell you about how well each source serves a farmer.
- Study Fig. 13.7-1 (the cross-section of an over-irrigated field). [4 marks]
- Name the process by which water moves upward through the soil towards the surface.
- Explain, step by step, how a rising water table leaves a crust of salt on the field.
- Suggest one measure that could reduce this damage.
- Study Map 13.1 (groundwater availability in India). [4 marks]
- Describe the general contrast in groundwater availability between the northern plains and the peninsular plateau.
- Give the geographical reason for this contrast.
- State one thing that a map shaded by broad regions cannot show.
- India receives about 4,000 BCM of water as precipitation each year, of which about 1,120 BCM is usable. [3 marks]
- What percentage of the precipitation is usable? Show your working.
- Give two reasons why the rest of the water cannot be used.