Chapter 9: Water Resources
In the middle of New Delhi, between office blocks and parked cars, a flight of stone steps drops straight into the ground. This is Agrasen ki Baoli, a step-well whose present form is believed to have been built in the 14th century. It is not a tank that somebody filled. It is a staircase cut down to meet water that was already there, held in the soil and rock beneath the city. Go down in the months after the rains and the water waits only a few steps below your feet. Come back at the end of a long dry summer and you must walk much further down before you reach it. Nobody empties the baoli in between. The water itself moves, rising when rain soaks into the ground and falling when it is taken out faster than it comes back. The steps were built long enough to follow it either way. That rise and fall is the quiet subject of this chapter. The ground under Delhi is now being asked for far more water than the rain returns to it, and the level has fallen sharply. The builders of those steps had no instrument to measure groundwater. They could simply see it.
Diagram
Fig. 9.A1 Caption: In a step-well the water table is not hidden underground — it stands on the steps where anyone can read it. Brief: Cut-away view of a step-well with a long descending stair; show two water lines on the steps, one high just after the rains and one much lower after summer, each labelled with the season, and label the surrounding soil and rock as the store the water sits in.
9.1 Sources Of Water
A water resource is any of the natural waters occurring on the earth that living beings could put to use. The term is wider than the water that comes out of a tap. It covers the water standing in the oceans, the water moving down rivers, the water held in lakes, and the water hidden below the ground.
Of all these, the ones most readily available for use are the waters of the oceans, the rivers and the lakes. The other available water resources are groundwater, deep sub-surface waters, and glaciers and permanent snowfields — the ice that stays frozen all year in high mountains and polar regions.
How Little Of It We Can Use
The word ‘plentiful’ is misleading here, because most of the earth’s water cannot be drunk, poured on a field or fed into a boiler. The earth’s water sorts itself into four stores, and only the last two are of use to us. (a) About 97 per cent of the earth’s water supply lies in the ocean, and its high salt content makes it unfit for human consumption and for most other uses. (b) Of the remaining 3 per cent, 2.3 per cent is locked in the polar ice caps, frozen solid and far from where people live. (c) The balance is 0.7 per cent, available as freshwater, and of this 0.66 per cent is groundwater sitting below the surface. (d) The rest, 0.03 per cent, is available to us as freshwater in rivers, lakes and streams.
That last figure is worth pausing on. Every river you have crossed, every lake you have seen and every stream that fills after rain belongs to three-hundredths of one per cent of the earth’s water.
Flowchart
Fig. 9.A2 Caption: Each split leaves a smaller store, and the two we actually use are the last and the smallest. Nodes: all the water on the earth → 97 per cent in the oceans, unfit for use because of high salt content; remaining 3 per cent → 2.3 per cent locked in the polar ice caps; balance 0.7 per cent available as freshwater → 0.66 per cent as groundwater; 0.03 per cent as freshwater in rivers, lakes and streams
Water On The Surface
Surface water is the water standing or flowing on land. It is the result of precipitation, or of seepage from underground. Precipitation is water reaching the ground from the atmosphere, as rain, snow or hail.
This water gathers into streams, lakes, rivers and ponds, flows across the land and finally joins the sea. Surface water is the part of the resource you can see, and therefore the part that has always been used first.
Water Under The Ground
The water from precipitation, that is from rain or snow, first flows on the surface. Some of it evaporates and the rest sinks into the soil. The water which seeps through the cracks and crevices under the surface of the land is known as groundwater.
Groundwater does not sit in underground lakes. It remains in the soil, in the subsoil, or in the bedrock — the solid rock lying below the loose material — filling the spaces between grains and the cracks inside the rock. Most of this water ultimately reaches the sea, moving slowly underground until it does. Groundwater constitutes 0.66 per cent of usable water on the earth.
An underground water stream that is saturated with water and transmits water readily is known as an aquifer. The two conditions in that sentence both matter: the rock must be full of water, and it must let that water move through it easily enough to be drawn out.
What India Has
Nature has endowed India with plentiful water resources. These resources account for four per cent of the world’s water resources. They reach us in three forms. (a) Surface water, that is water from rivers, lakes, ponds and tanks. (b) Groundwater resources, drawn from below the surface. (c) A vast coastline, with indented coasts in some states, where the sea works its way into the land rather than meeting it in a straight line.
Odisha, Kerala and West Bengal have vast surface water resources in the form of lagoons and lakes. A lagoon is a shallow body of water lying along the coast, cut off from the open sea by a bar of sand or a strip of land. The water in these bodies is brackish — slightly salty, because sea water and fresh water mix in them.
Brackish water cannot be drunk or used for most crops, but it is not wasted. It is utilised for fishing and for the irrigation of certain crops like paddy and coconut, which tolerate it.
9.2 Need To Conserve Water
Water is a natural resource which satisfies a basic human need. Nothing else stands in for it: a household without water cannot cook, wash or drink, and a field without water grows nothing.
Demand has risen on three fronts at once. The population has increased, irrigation has spread, and industrialisation has put water to work in factories. Each of these draws on the same limited store.
A Falling Water Table
This rising demand has led to a decline in groundwater levels in various parts of the country. According to a report by the Central Ground Water Board (CGWB), in recent years, Delhi, Haryana, Chandigarh, Himachal Pradesh and Uttarakhand have recorded a sharp fall in the groundwater levels, ranging from 70 to 80 per cent.
The level being spoken of here is the water table — the upper surface of the groundwater, the depth below which the soil and rock are saturated. It is not fixed. It rises when rain soaks in, and it sinks when water is pumped out faster than it is replaced.
If this trend continues, there will be a critical shortage of water of suitable quality to meet future needs. Notice the phrase ‘of suitable quality’. A shortage is not only about how much water is left, but about how much of it is fit to use.
Flowchart
Fig. 9.A3 Caption: Three separate demands pull on one store, and the level falls when they take out more than the rain puts back. Nodes: increase in population + spread of irrigation + industrialisation → demand for water rises → more water withdrawn from the ground → withdrawal exceeds what rain returns → decline in groundwater levels → water table falls → critical shortage of water of suitable quality
Why Conservation Cannot Wait
We need to conserve water for the following reasons. (a) The overexploitation of groundwater often results in the lowering of the water table, so wells and pumps must reach deeper each year to find the same water. (b) The loss of vegetation causes drought and a reduction of rainfall and a lowering of the water table, because bare ground holds neither moisture nor the rain that falls on it. (c) Irrigation utilises more than 90 per cent of the total freshwater, which means that how we water our fields decides most of the question. (d) The increase in population results in water scarcity, since the same supply is being divided among more people every year. (e) Our water resources like the groundwater, rivers and lakes are polluted, and their water can hardly be used without adequate treatment.
The last reason is the one students most often miss. Pollution does not remove a single litre of water from a river, but it takes that water out of use just as surely as evaporation would. Treatment can bring some of it back, and treatment costs money, energy and time.
9.3 Conservation Practices
Freshwater is becoming less available while demand keeps rising, so we need to conserve water and manage our water resources. Quick steps are needed: proper policies and laws must be made, and effective measures adopted for conservation.
Five practices carry most of that work in India. (a) Rainwater harvesting, which catches rain where it falls instead of letting it run away. (b) Adopting water saving technologies, so that the same task is done with less water. (c) Encouraging watershed development, which treats a whole drainage area as one unit. (d) Water recycling, so that used water is treated and put to work again. (e) Preventing the pollution of water, which keeps the supply we already have fit for use.
9.3.1 Rainwater Harvesting
Rainwater harvesting is the process of increasing the recharge of groundwater by capturing and storing rainwater locally in sub-surface water reservoirs. To recharge groundwater is to add water back to the store below the surface, replacing what has been drawn out.
It includes activities aimed at the following. (a) Harvesting surface water and groundwater together, so that both stores are used and refilled. (b) Prevention of losses through evaporation and seepage, which take water away before it can be used. (c) All other hydrological studies and engineering interventions aimed at conservation and efficient utilisation of the limited water endowment of an area such as a watershed.
Rain Is The Primary Source
According to the hydrological cycle — the endless circulation of water between the sea, the air and the land that you met in earlier classes — rain is the primary source of water. Rivers, lakes and groundwater are all secondary sources: each of them is only rain that has arrived by a longer route.
We depend entirely on these secondary sources, and most of the time we forget the value of the rainwater itself. Water harvesting means understanding the value of rain and making optimum use of rainwater at the place where it falls. It is the activity of direct collection of rainwater, which can then be stored for direct use or used to recharge groundwater.
What Our Ancestors Built
Water has been harvested in India from ancient times, and our ancestors had perfected the art of water management. Many water harvesting structures and water conserving mechanisms were followed in each region of the country. Three methods were common. (a) People harvested rainwater by collecting water from the rooftops and storing it in tanks built in their courtyards, and from open community lands they collected the rainwater and stored it in artificial wells. (b) They harvested rainwater runoff by capturing water from swollen streams during the monsoon season and storing it in water bodies. (c) They harvested water from flooded rivers.
The storing mechanism, or the water receptacle, was known by different names in different areas. They were called Khatri or Kuhl in the Western Himalayas, Baolis or Dighis in the Gangetic plains, Johads in Central India, Bhandaras or Kere in the Deccan Plateau, Surangam in the Western Ghats, Korambu in the Eastern Ghats and Zing in Ladakh. The names differ because the problem differs: a mountain valley, a flood plain and a dry plateau each hold their rain in a different way.
9.3.2 Objectives Of Rainwater Harvesting
The main objectives of rainwater harvesting are the following. (a) Meeting the ever increasing demand for water. (b) Reducing the run-off which chokes drains. (c) Avoiding the flooding of roads. (d) Augmenting the groundwater storage and raising the water table. (e) Reducing groundwater pollution. (f) Improving the quality of groundwater. (g) Reducing soil erosion. (h) Supplementing the domestic water requirement during summer and drought.
Read that list again and notice that it solves two opposite problems with one action. Water that is caught on the way down does not race into the drains and flood the road, and the same water, sent into the ground, is waiting there in the dry months.
Diagram
Fig. 9.1 Caption: Modern rainwater harvesting collects rain from the roof, carries it down a pipe and puts it back into the ground. Brief: Redraw the printed figure — a house with a sloping roof as the catchment, rain falling on it, a water pipe or conduit leading down, an underground path to a filtration point, and a hand pump drawing from below; label rainwater, catchment, water pipe (conduit), hand pump, water table, and the note that water is available for use, with arrows running from roof to conduit to ground.
9.3.3 Need Of Water Harvesting
In India we have an acute shortage of water during the year. Part of the reason is simply that we have not cared to conserve water or rationalised its use.
The rest of the reason is in the way the rain arrives. The annual rainfall in India is 1,170mm (46 inches), which is higher than the world average of 800mm (32 inches). By that figure alone India looks well supplied.
Graph
Fig. 9.A4 Caption: India receives more rain in a year than the world average, and Cherrapunji receives many times either figure. Brief: Vertical bar chart; x-axis three bars — world average, India, Cherrapunji; y-axis annual rainfall in mm from 0 to 12,000; values 800mm, 1,170mm and about 11,000mm; data from the figures printed in this section.
Why The Wettest Place Can Still Go Thirsty
Ironically, even Cherrapunji, in the hills of Meghalaya in north-eastern India, which receives about 11,000mm of rainfall annually, suffers from an acute shortage of drinking water. A place that gets nearly ten times the national figure should not be short of anything.
The explanation is intensity. Rainfall in India occurs in short spells of high intensity. When heavy rain falls fast and stops soon, the ground cannot take it in quickly enough, and most of the rain falling on the surface tends to flow away rapidly.
What flows away is lost twice over. It is not stored on the surface, and it leaves very little behind for the recharge of groundwater. This is why most parts of India experience a lack of water even for domestic uses.
9.3.4 Water Harvesting Mechanism
Any harvesting system, from a village rooftop to a city building, is built from the same four elements. (a) Catchments — the catchment of a water harvesting system is the surface which receives the rainfall directly. It can be a paved area like a terrace or courtyard of a building, or an unpaved area like a lawn or an open ground, and temporary structures like sloping sheds can also act as catchments. (b) Conduits — conduits are the pipelines or drains that carry rainwater from the catchment or rooftop to the harvesting system, and may be of any material, like Polyvinyl chloride (PVC), asbestos or Galvanised Iron (GI), or any other material that is commonly available. (c) Storage facility — rainwater can be stored in any commonly used storage container, such as an RCC, masonry or plastic water tank. (d) Recharge facility — as an alternative to storing, rainwater can be used to recharge groundwater aquifers through suitable structures like dugwells, borewells, recharge trenches and recharge pits.
The last two elements are a choice, not a sequence. Water that goes into a tank is water you will use yourself in the next few weeks. Water that goes into the ground is water the whole neighbourhood’s wells will draw on for much longer.
Flowchart
Fig. 9.A5 Caption: The rain follows the same path to the conduit, and then the system chooses between a tank and the ground. Nodes: rain falls on the catchment (terrace, courtyard, lawn, open ground or sloping shed) → conduit of PVC, asbestos or GI carries it away → branch one: storage facility, an RCC, masonry or plastic tank → water available for direct use; branch two: recharge facility of dugwells, borewells, recharge trenches or recharge pits → water percolates into the ground → aquifer recharged → water table rises
Structures That Send Water Underground
Various kinds of recharge structures are possible, and each one is designed to make sure that rainwater percolates into the ground instead of draining away from the surface. Some of these are the following. (a) Borewells and dugwells are used to raise the underground water table by collecting rainwater on the rooftop of a building, which is then diverted by drainpipes to a filtration tank, and from there it flows into the borewell or dugwell. (b) A recharge pit is excavated into the ground and lined with a brick or stone wall having openings at regular intervals, so that water can pass out through the sides into the soil. (c) A percolation pit, also called a soakaway, is a bored hole of up to 30cm diameter drilled in the ground to a depth of 3 to 10m. (d) Recharge trenches are excavated on the ground and refilled with porous media like pebbles, boulders or brickbats, which hold the surface runoff long enough for it to sink in. (e) Permeable surfaces, like a patch of grass, retain a large proportion of the rainwater falling on them, yielding only 10-15 per cent as runoff. (f) Porous tiles are laid on pavements and footpaths, letting rain pass through a surface that would otherwise shed all of it.
The last two are worth noticing because they cost almost nothing and are invisible once laid. A city that paves every open surface with concrete has decided, without saying so, that its rain will leave by the drain.
9.3.5 Storing Water For Direct Use
Where the water is meant for use rather than for recharge, it has to be held in a tank. An underground RCC (Reinforced Cement Concrete) tank or a masonry tank can be used for storage of the rainwater. The tank can be installed inside the basement of a building or outside the building, and prefabricated tanks such as PVC can be installed above the ground.
Each tank must have an overflow system for situations when excess water enters the tank, and the overflow can be connected to the drainage system. Without it, a heavy spell would simply push water back up the pipe it came down.
Keeping The Stored Water Clean
Generally, runoff from only paved surfaces is used for storing, since it is relatively free of bacteriological contamination. Rooftop rainwater harvesting is the process of water harvesting in which rainwater falling on a roof is diverted through drain-pipes to the storage container.
Three simple guards keep that water usable. (a) Mesh filters are provided at the mouth of the drain-pipe to prevent leaves and debris from entering the system. (b) A first-flush device is provided in the conduit before it connects to the storage container, so that the first dirty wash off the roof is let go. (c) A sand filter is provided if the stored water is to be used for drinking purposes.
Water quality improves over time during storage in the tank, because impurities settle down in the tank if the water is not disturbed. Even pathogenic organisms — the harmful ones that cause disease — gradually die out due to storage.
Biological contamination can be further removed by disinfecting the water, and many simple methods of disinfection are available which can be carried out at the domestic level. Storage, in other words, is not merely a holding step. Left still and left long enough, the tank does part of the cleaning itself.
9.4 Irrigation
Irrigation refers to the process of watering agricultural plants through artificial means, from wells, tanks, tubewells, canals and other sources. The word ‘artificial’ is doing the work in that definition: irrigation is what a farmer does when the rain has not done it for him.
From the point of view of sustained agricultural production and all-round development, water is the most precious resource we have. Presently about 92 per cent of water is used for agriculture, 2 per cent for industries, and 6 per cent for drinking and domestic purposes.
Graph
Fig. 9.A6 Caption: Nearly all the water a country uses goes on to its fields, not into its taps or its factories. Brief: Pie chart in three slices — agriculture 92 per cent, drinking and domestic purposes 6 per cent, industries 2 per cent; label each slice with its use and its percentage; data from the figures printed in this section.
For farmers, rainfall is still the most important source of water. About 55 per cent of the net sown area in the country — the land actually sown with crops in a year — depends on rainfall to sustain crop production. On such land, success in dry farming depends on moisture conservation practices and the judicious use of whatever water is available for irrigation.
Irrigation Is Older Than The Machines
Under this situation it becomes imperative to use artificial means to raise crops, and in India this is nothing new. Irrigation has been practised here from ancient times. A number of the artificial lakes and canals that dot the country are centuries old, and some of them have served for more than a thousand years.
The notable examples are the two big tanks in Chingleput district of Tamil Nadu, in the far south-east of the peninsula, constructed in the 8th and 9th centuries AD, and the Grand Anicut built across the Cauveri river during the second century AD. The irrigation canals built by various rulers from time to time testify to the importance of irrigation in the development of agriculture in India.
What makes this case worth studying is not its age but the problem it answers, which has not changed. A river with a short, violent season and a long dry one is useless to a farmer unless its water can be held or diverted at the right moment. Every barrage and canal built since is a newer answer to the same question the builders of the second century AD were facing.
Why Irrigation Became A Priority
After India attained independence and began planned development, the increase in irrigation potential was regarded as one of the prerequisites for agricultural development in the country. There were six reasons for treating it that way. (a) Uncertainty of rainfall — the rainfall in India is highly irregular in place and in time, so that normal rainfall is marked by wide fluctuations in different parts of the country. The monsoon sometimes arrives early and at times comes late, and not only are its arrival and withdrawal uncertain but so are its continuity, its rhythm and its intensity. (b) Uneven distribution of rainfall — most parts of the country receive 80 per cent of the annual rainfall from June to September from the South-west monsoon, and the amounts differ sharply from region to region. (c) Crop requirements — different crops require different quantities of water for their growth, and the demand shifts with the stage of growth and with the season. (i) Most of the crops do not require water when they are maturing, but grain crops require more water during the time the ear heads are formed. (ii) India has three cropping seasons, kharif, rabi and zaid, and each stands in a different relation to irrigation. (iii) High yielding varieties requiring higher quantities of chemical fertilizers need more moisture, which could be supplied only through irrigation. (iv) Commercial crops like sugarcane need a higher quantity of water because they require frequent watering, which could be managed through an efficient irrigation system. (d) Nature of the soil — the water requirement of different crops depends on the nature of the soil they grow in, because some soils hold moisture and others let it go. (e) To utilise river water effectively — many rivers in India are not perennial, meaning they do not flow all year round, and they carry insignificant flows during the rabi season. (f) To maximise production — to obtain maximum production irrigation is a must, and according to agricultural scientists the production of irrigated crops is more than that of unirrigated crops in the same area.
How Unevenly The Rain Falls
The second reason deserves the figures behind it. The Western Ghats, the range running down the western edge of the peninsula, and north eastern India receive more than 250cm of annual rainfall. The northern plains and the eastern Peninsula receive between 100 and 200cm.
At the other end, the Kutch region of Gujarat, parts of Punjab and Haryana, and the western half of Rajasthan lie in the arid zones. An arid zone is one where rainfall is so low that it cannot meet the needs of crops, and here the amount of rainfall is low and there is a constant scarcity of water. This inadequacy of rainfall has to be met by irrigation.
The Three Cropping Seasons
The three seasons named above divide the farming year, and irrigation matters differently in each. Kharif crops, which occupy the largest area in the country, are dependent on the monsoon rains, and where irrigation facilities are not developed these crops are grown as rainfed crops.
Rabi crops are grown on the soil moisture which is left after the harvest of kharif crops, or over the area where an assured supply of irrigation is available. Zaid or summer crops are exclusively irrigated crops, because nothing else is falling from the sky at that time of year.
Further, the rapidly growing population has forced farmers to raise two or three successive crops in a single year on the same land. This cannot be done without the help of irrigation.
What The Soil Does With The Water
The fourth reason works below the surface. Clayey soils have a higher moisture holding capacity and therefore require less irrigation, because the water they receive stays within reach of the roots.
Sandy loams have less moisture retentive capacity and need frequent watering, and this is why drip irrigation is suitable in dry regions. Relief matters in the same way: level and lowland areas require less water than sloping and highland areas, where water drains away downslope instead of standing where it fell.
Rivers That Are Not There All Year
The fifth reason is best read with a map of the country’s rivers in front of you. There is a wide disparity in the water flow from year to year, and the rivers of central and southern India have water for the four months of monsoon rains and remain largely dry during the eight months of the year. Therefore, to effectively utilise the water of these rivers, means of irrigation have to be used.
Map
Map 9.1 Caption: Rivers in India. Brief: Political outline of India showing the full extent of India as officially defined, drawn at the printed scale of 1:20,000,000; show and name the river courses as printed, including the Indus, Jhelum, Chenab, Ravi, Beas, Satluj, Ganga, Yamuna, Ghaghra, Gomti, Gandak, Kosi, Chambal, Betwa, Son, Damodar, Brahmaputra, Luni, Sabarmati, Mahi, Narmada, Tapti, Mahanadi, Godavari, Krishna, Bhima, Penganga, Pennar, Cauveri, Vaigai and Periyar, together with the reservoirs and lakes labelled on the printed map, the Tropic of Cancer, the Arabian Sea, the Bay of Bengal, the Andaman Sea and the Indian Ocean, and the scale bar in kilometres.
9.5 Means Of Irrigation
No single means of irrigation suits the whole country. Based on the availability of surface water from rivers and streams, the availability of groundwater, the relief, the soils and the climatic conditions, different means of irrigation are utilised in different parts of India.
Two contrasting examples make the point. In the crystalline soil areas of the Deccan Plateau, the hard-rock upland that fills most of peninsular India, tanks form the major source of irrigation. The alluvial tracts of the Gangetic and Coastal plains, where the soil is deep and soft, are best suited for canals and well irrigation.
The means themselves divide into two groups. The conventional means of irrigation include wells, tanks and inundation canals, and here irrigation is usually done manually, with the farmer himself pulling water out of wells, tanks and canals, or using animals to draw it. The modern means include tubewells, perennial canals and drip irrigation.
Flowchart
Fig. 9.A7 Caption: The means of irrigation divide by the effort that lifts the water and by the source it is taken from. Nodes: means of irrigation → conventional means, worked by hand or by animals → wells; tanks; inundation canals. means of irrigation → modern means, worked by power → tubewells; perennial canals; drip irrigation
9.5.1 Wells
A well is a small hole dug in the surface of the earth to obtain water from the water table, for irrigation and for other purposes. Wells are usually of two types. Lined wells are man-made, artificially constructed by digging into the ground and supporting the walls with bricks laid in a circular pattern. Unlined wells are formed by different natural phenomena and are normally not protected by any lining of their walls.
Well irrigation is a cheap, simple and dependable source of irrigation. It is practised in areas where plenty of groundwater is available and the depth of the water table does not exceed 15m, which is about the height of a four-storeyed building.
Where Wells Are Dug
Well irrigation is confined mainly to the alluvial plains, where the soft nature of the soil lets wells be dug easily and the yield of crops from the land after irrigation is considerably high. Wells are dug in the middle of the area to be irrigated, and at a place which is relatively at a high level, so that the lifted water can run down to the fields on its own.
The presence of perennial rivers ensures that the water table is recharged. A river that flows all year keeps seeping into the ground beside it, and the wells nearby are refilled from that seepage.
The areas where well irrigation is practised include Punjab, Uttar Pradesh, Goa, Haryana, Bihar, Rajasthan, Gujarat, Maharashtra, Madhya Pradesh, Andhra Pradesh, Karnataka and Tamil Nadu.
Lifting The Water
Digging the well is only half the task, because the water still has to be raised to the surface. The water from the wells is lifted for irrigation in a number of ways. (a) The Persian wheel method is used mainly in Punjab, Haryana and Western Rajasthan. It is a partly submerged vertical wheel with buckets attached to the rim, and as the wheel is turned by draught animals rotating a geared horizontal wheel, the buckets are filled and emptied into a trough above, which carries the water to the crop-sown fields. (b) The lever method is used in Bihar and Andhra Pradesh, and is an economical and efficient method of lifting water from shallow wells to a height of 3.5 to 4.5m. (c) The inclined plane method, also known as mhote, uses a pair of bullocks that walk down a slope specially constructed from the wall of the well, pulling a bucket or a leather bag up from behind.
Diagram
Fig. 9.2 Caption: A Persian wheel lifts water from a well as draught animals turn the horizontal wheel. Brief: Reproduce the printed photograph of a Persian wheel in use; label the vertical wheel with buckets on its rim, the geared horizontal wheel, the draught animal turning it, and the trough that carries the water away, with an arrow showing the direction the wheel turns.
The lever method repays a closer look, because it works on a principle the student already knows. The lift consists of a strong log laid across a fulcrum, with a bucket attached to the long arm by means of a bamboo or a rope, and a heavy weight attached to the other side of the log.
When the bucket is full, one person gently releases the rope and the bucket comes up as the stone goes down. The bucket is then emptied into the field channel and lowered into the well again. The weight, not the worker, does most of the lifting.
Diagram
Fig. 9.3 Caption: A lined well, with its walls supported in a circular pattern and a bucket lowered from above. Brief: Reproduce the printed photograph of a well; label the lined wall, the frame above the mouth, the rope and pulley, and the bucket.
The inclined plane method uses animals in the same way but over a longer stroke. In this type, a pair of bullocks move down from the slope, or inclined plane, specially constructed from the wall of the well, pulling a bucket or a leather bag from behind, and the load is discharged into the connecting channel. The rope goes through a pulley in this process.
After discharging the water, the bullocks walk up the slope until they reach the top, by which time the bucket has reached the surface of the water and has filled again. The process is repeated again and again to irrigate the fields.
Diagram
Fig. 9.4 Caption: In the inclined plane method a pair of bullocks walk down a ramp to raise the bucket. Brief: Reproduce the printed photograph of the inclined plane method; label the bullock pair, the constructed slope, the rope running over the pulley, and the connecting channel, with an arrow showing the direction the animals walk.
9.5.2 Advantages Of Well Irrigation
Well irrigation has stayed in use for a very long time because it asks little of the farmer who owns it. (a) Wells can be dug at a very low cost, which is well within the means of poor farmers. (b) Oxen which are kept for ploughing the land can be utilised for drawing water from the wells at no extra cost to the farmers. (c) By the use of pumps and tubewells, water can be lifted even from great depths.
9.5.3 Disadvantages Of Well Irrigation
Against that, a well is only as good as the ground beneath it. (a) Wells depend on underground water resources whose distribution varies from region to region, so a method that works in one district may fail in the next. (b) It is difficult to dig wells or bore tubewells in the hilly regions of the north and the stony areas of the Peninsula, where the rock resists the digging. (c) The traditional wells dry up due to the over-withdrawal of groundwater and the lowering of the water table. (d) The availability of electricity and diesel to operate tubewells causes many problems and is costly for farmers.
9.5.4 Tubewells
A tubewell is a deeper well, at a depth of 20-30m, from which water is lifted up with the help of power driven pumps. It is also known as the ‘lift method’. The difference from an ordinary well is not only depth but power: no animal can raise water from thirty metres at a useful rate.
The ideal conditions for the drilling of tubewells are the following. (a) The availability of plentiful water at great depths, so that the pump has something worth reaching. (b) Level land and soft soil for the tubewells to be set up. (c) A large fertile area in its surrounding area to be irrigated, so that the cost is spread over a good yield. (d) The availability of regular cheap electricity to run the tubewells.
Tubewells are used in the northern plains, in the States of Punjab, Haryana, Uttar Pradesh, Bihar, West Bengal, Rajasthan, Madhya Pradesh and Gujarat.
Diagram
Fig. 9.5 Caption: A tubewell discharges into a field channel, lifted by a power driven pump. Brief: Reproduce the printed photograph of a tubewell; label the delivery pipe, the outlet into the channel, and the field beyond, with an arrow showing the direction of flow.
9.5.5 Advantages Of Tubewell Irrigation
A tubewell gives the farmer something no rain-fed system can — water on demand. (a) It is an independent source of irrigation, not tied to a canal schedule or a monsoon. (b) It brings up clean water. (c) It can irrigate a large area of agricultural land. (d) It is easier to bring up a large amount of water in a short time period. (e) It is a perennial means of irrigation, as it is drilled up to the permanent water table, and it can be switched off when not required.
9.5.6 Disadvantages Of Tubewell Irrigation
The same qualities create the difficulties. (a) Excessive use of tubewell water can lead to depletion of groundwater, because a pump can take out far more than the rain puts back. (b) It is useless if the water is brackish. (c) It is expensive, as it requires a continuous supply of electricity.
9.5.7 Canals
India has one of the world’s largest canal systems, stretching over more than one lakh kilometres, which is one hundred thousand kilometres of channel. The irrigation canals are of two types, and the difference between them is whether anything has been built across the river. (a) Inundation canals are taken out directly from the rivers without constructing any barrage or dam, and they use the excess water of rivers at the time of floods, remaining operational during the rainy season. (b) Perennial canals are taken out from perennial rivers by constructing barrages or dams to regulate the flow of water, so they can draw water throughout the year and irrigate large areas.
The beds of inundation canals lie at a level higher than those of the rivers, so they get a supply of water only when the rivers are in flood. This is why these canals have limited use: they carry water in the season when the fields need it least. Most of the canals in India belong to the perennial category.
Canal irrigation is in practice in Uttar Pradesh, Madhya Pradesh, Andhra Pradesh, Rajasthan, Haryana, Jammu and Kashmir, Assam and Tripura. Canals also supply water to a sizeable part of the irrigated area in Bihar, Odisha, Karnataka, Tamil Nadu and West Bengal. Mizoram, the least irrigated State, is solely dependent on canals. The Northern Plains have an elaborate system of canals.
Diagram
Fig. 9.6 Caption: A perennial canal carries a regulated flow past cultivated land. Brief: Reproduce the printed photograph of a canal; show the lined bank, the level of water in the channel, and the fields and hills beyond.
9.5.8 Advantages Of Canal Irrigation
A canal moves water from where there is a surplus to where there is a shortage, and that single fact explains most of its advantages. (a) The rainfall deficiency in some areas is made up by canals taken out from the perennial rivers. (b) In arid areas like Rajasthan, canals have proved to be a boon, as a result of which sandy patches are yielding good agricultural harvests. (c) Canal irrigation has enabled Punjab and Haryana to be called the ‘granary of the country’ and the nucleus of the Green Revolution. (d) Major parts of Tamil Nadu enjoy rainfall during the winter season while the summer remains dry, so irrigation is needed in summer to make up the lack of rainfall, and canal irrigation provides a solution to this problem.
9.5.9 Disadvantages Of Canal Irrigation
The trouble with a canal is that it does not stop giving water when the soil has had enough. (a) At some places, where perennial unlined canals flow at the ground level and between raised high banks, the water table may reach the surface and make the once cultivable soil completely waterlogged, and complete saturation of the soil with water may give rise to swamps. (b) In canal irrigation, where the water table is a few feet below the ground, the alkaline salts come to the surface, mix with the soil and make it unproductive. (c) Due to waterlogging, the capacity of the soil to absorb water decreases, so a few centimetres of rainfall in excess of the normal covers the land with a sheet of rainwater, which in the absence of proper drainage ruins the standing crops, houses and even stored food grains and fodder.
Read those three together and notice the sequence. Water seeping steadily from an unlined canal raises the water table; a high water table brings salt up with it; and soil that is already saturated has no room left for the next spell of rain. One cause has produced three separate kinds of damage.
9.5.10 Tanks
A tank refers to a small bund of earth or stones built across a stream to impound water, which is then led through narrow channels to the cultivated fields. To impound is simply to hold water back; the tank is the pond that forms behind the bund.
Tank irrigation is in practice in Peninsular India including Maharashtra and Gujarat. Tanks constitute a special feature of irrigation in the Deccan for four reasons. (a) The rivers of the Deccan are not snow-fed and are mainly dependent on the rainwater, so they carry water only when it rains. (b) There are many streams which become torrential during the rainy season but dry up when the rain ceases. (c) The hard rocks in the area do not absorb water, so wells also cannot be made there. (d) The terrain of the Deccan Plateau is uneven, with many natural depressions where tanks can be easily built.
The third reason turns into the solution. Because the rock will not take the water in, tanks can be easily made by making dams in hollow spaces, in which rainwater is stored in large quantities for distributing a regular supply of water through the channels to the arable lands in the dry seasons.
Tank irrigation has reached its highest perfection in the south, specially in Andhra Pradesh, Telangana and Tamil Nadu. In Tamil Nadu it is significant in the districts of Chingleput, North Arcot and South Arcot, in Nellore in Andhra Pradesh, and in Warangal in Telangana.
States of West Bengal and Rajasthan too have some irrigation tanks, particularly in their southern and south-eastern regions respectively. Some irrigation tanks do exist in the Bundelkhand area in Uttar Pradesh and in South Bihar.
Diagram
Fig. 9.7 Caption: An irrigation tank holds rainwater behind a bund in the middle of a settled area. Brief: Reproduce the printed photograph of an irrigation tank; show the water body, the built embankment enclosing it, and the surrounding settlement.
9.5.11 Advantages Of Tank Irrigation
Where the rock is hard and the rain is seasonal, a tank does what nothing else can. (a) In the uneven rocky plateau of Peninsular India, where rainfall is highly seasonal, tank irrigation is useful. (b) In the large stretches of the Indian plateau, hard rocky terrain makes wells and canals difficult to construct, so only tank irrigation is feasible. (c) Tank irrigation is highly significant in storing the abundant rainwater that would otherwise flow out and go waste.
9.5.12 Disadvantages Of Tank Irrigation
Tanks are shallow, open and dependent on the same rain that fills the streams, and every one of their weaknesses follows from that. (a) Tanks get silted up soon, and regular desilting is required to make them suitable for irrigation. (b) When the monsoons fail these tanks go dry, and therefore they are not a dependable source of irrigation. (c) Most of the tanks are non-perennial and become dry during the winter and summer seasons, when water is urgently required for rabi and zaid crops. (d) Due to the large area they cover and their shallow depth, a huge quantity of stored water either evaporates or sinks underground without being used in irrigation. (e) Tanks occupy a large fertile area which otherwise could have been utilised for growing crops. (f) The lifting of water from the tanks and bringing it to the fields is a strenuous and costly task.
But even then, tanks are an effective means of collecting rainwater, and their use should be popularised for irrigation, aquaculture, drinking water and water sports.
9.5.13 Drawbacks Of Conventional Methods Of Irrigation
The conventional irrigation systems suffer from a number of constraints leading to the improper utilisation of water. (a) In the conventional system of irrigation, a large quantity of water is not properly utilised. (b) Crops are usually subjected to cyclic changes of flooding and water stress, by providing heavy irrigation at one time and leaving the fields to dry up for about 10 to 15 days, so the moisture availability to the crops keeps on changing and this results in poor yields. (c) The fields situated in low areas always get excess water causing prolonged waterlogging, so crops are subjected to waterlogging resulting in poor yields. (d) In the fields, about 10-15 per cent of the land is utilised for preparing channels and distributions, which decreases the effective area of cultivation. (e) Extensive areas of land in the arid and semi-arid regions of India are no longer used for cultivation due to the accumulation of salts.
The last of these deserves its own sentence. Excessive irrigation and poor water management are the main reasons for waterlogging and the gradual build up of excessive salts, and this progressive build up of soil salinity — the amount of salt held in the soil — has made the soils unsuitable for cultivation. Land is being lost by the act of watering it.
9.5.14 Modern Irrigation Methods
All these constraints have led to the utilisation of modern irrigation methods, which are highly scientific. What makes them scientific is that they control where the water goes, how fast it arrives and how long it runs, instead of simply letting a field fill.
9.5.15 Furrow Irrigation
Furrow irrigation is a type of flood irrigation in which the water poured on the field is directed to flow through narrow channels dug between the rows of crops, instead of being evenly distributed throughout the whole field.
The furrows must have equal dimensions, in order to guarantee that the water is distributed evenly. If one channel is deeper than the next it will take more than its share, and the crop rows beside it will be watered unequally. Furrow irrigation is useful in areas where water is easily available.
Diagram
Fig. 9.8 Caption: Water runs down narrow furrows dug between the rows of a crop. Brief: Reproduce the printed photograph of furrow irrigation; show the parallel furrows holding water between planted rows, with an arrow indicating the direction the water flows down the field.
9.5.16 Drip Irrigation
Drip irrigation, sometimes called trickle irrigation, involves dripping water at very low rates, of 2-20 litres per hour, from a system of small diameter plastic pipes fitted with outlets called emitters or drippers.
Water is dripped onto the soil in such a way that only part of the soil, the part in which the roots grow, is wetted. This is unlike surface and sprinkler irrigation, which involves wetting the whole soil profile. Applications are more frequent, but water usage and power consumption are lower.
A drip system consists of a network of mainlines and smaller lateral lines, which have emitters or drippers spaced along them. Water is applied at a low pressure, allowing it to drip slowly and steadily from the emitters directly onto or just below the soil surface at the base of the plants.
The result is that the plant’s water and nutrient uptake is consistently replenished without overwatering. The system can be automated with a filter, a pressure regulator and a timer to control the flow and the duration of watering.
Diagram
Fig. 9.9 Caption: Drip lines run along the crop rows, wetting only the soil at the base of each plant. Brief: Reproduce the printed photograph of drip irrigation; show the thin lateral pipes lying along the planted rows and the darker wetted patches of soil at the plant bases.
9.5.17 Advantages
The advantages of drip irrigation follow from the fact that the water is placed rather than poured. (a) Water conservation — by delivering water directly to the roots, drip irrigation significantly reduces water loss from evaporation and runoff compared to sprinklers or flood irrigation. (b) Improved plant health — it keeps the soil moisture at an optimal level, preventing over-watering or under-watering and reducing plant stress, and it keeps the foliage dry, making plants less susceptible to fungal diseases. (c) Nutrient delivery — the system can be used to deliver water-soluble fertilizers directly to the root zone along with the water. (d) Increased efficiency — it provides water more efficiently to plants, increasing water use efficiency and potentially leading to higher crop yields, and it reduces energy consumption because the system works on low pressure. (e) Versatility — it can be used on various crops, in different soil types, and even with poor quality water like saline water.
That last advantage is worth unfolding, because versatility here means four separate things. (a) Crops — it is most suitable for row crops such as vegetables and soft fruit, and for tree and vine crops where one or more emitters can be provided for each plant, and generally only high value crops are considered because of the high capital costs of installing a drip system. (b) Soil — on clay soils the water must be applied slowly to avoid surface water ponding and runoff, while on sandy soils higher emitter discharge rates will be needed to ensure adequate lateral wetting of the soil. (c) Elevation — it is adaptable to any farmable slope, and normally the crop would be planted along contour lines with the water supply pipes, called laterals, laid along the contour also, which is done to minimize changes in emitter discharge as a result of land elevation changes. (d) Reduced weeds — because only the area around the plant roots is watered, there is less water available for weeds to grow, which reduces competition and labour.
There is one more gain, and it is about risk rather than water. A drip system means less dependency on weather, and therefore greater stability and lower risks of failure for the farmer who installs it.
9.5.18 Disadvantages
A drip irrigation system is expensive, but it is permanent and can easily be automated. That automation is very useful when labour is scarce or expensive to hire, though training users, updating and maintaining the systems adds to the cost.
There is also a quieter risk. As crops are used to being watered each day, they may only develop shallow roots, and if the system breaks down the crop may begin to suffer very quickly. A plant that has never had to search for water has not learned to.
9.5.19 Sprinkler Irrigation System
The sprinkler irrigation system allows the application of water similar to rainfall, through nozzles fitted to a system of pipes, with the help of a pump. The water is well distributed and uniformly irrigates most of the soil.
A sprinkler system consists of a network of mainlines and smaller lateral lines which have small diameter nozzles placed in them. A good clean supply of water, free of suspended sediments, is required to avoid sprinkler nozzle blockage and to avoid spoiling the crop by coating it with sediment.
Diagram
Fig. 9.10 Caption: Sprinklers throw water over a field in a spray that imitates rainfall. Brief: Reproduce the printed photograph of sprinkler irrigation; show the line of sprinklers in operation, the arcs of spray, and the crop beneath them.
9.5.20 Advantages
Sprinklers suit fields where the whole surface must be wetted evenly. (a) Sprinkler irrigation is suited for most row, field and tree crops, and the water can be sprayed over or under the crop canopy, with the best results obtained where the plant population per unit area is very high. (b) It is adaptable to any farmable slope, whether uniform or undulating, and the lateral pipes supplying water to the sprinklers should always be laid out along the land contour whenever possible, which minimizes the pressure changes at the sprinklers and provides a uniform irrigation. (c) It saves land, as no bunds are required to hold the water in. (d) Sprinklers are best suited to sandy soils with high infiltration rates, although they are adaptable to most soils, and they are not suitable for soils which easily form a crust. (e) It reduces water consumption by 30-50 per cent as compared to traditional methods. (f) Water soluble nutrients can be added to the water, which increases yield and reduces labour costs.
Where sprinkler irrigation is the only method available for a soil that crusts, light fine sprays should be used, and the larger sprinklers producing larger water droplets are to be avoided. A heavy drop lands hard enough to seal the surface it falls on.
9.5.21 Disadvantages
Throwing water into the air has its own price. (a) Besides being expensive, there is a loss of water due to evaporation before the spray reaches the ground. (b) In case of over-watering, the crop gets damaged due to pestilence. (c) The water quality needs to be good, or the sprinkler will get blocked. (d) Large sprinklers are not recommended for the irrigation of delicate crops such as lettuce, because the large water drops produced by the sprinklers may damage the crop. (e) Power consumption is high, because the water must be pushed through the nozzles under pressure.
9.6 Summary
- A water resource is any of the natural waters occurring on the earth that living beings can put to use, including oceans, rivers, lakes, groundwater, deep sub-surface waters, and glaciers and permanent snowfields.
- Only a small part of the earth’s water is usable, and it is divided in a fixed way.
- About 97 per cent lies in the ocean and is unfit for use because of its high salt content.
- Of the remaining 3 per cent, 2.3 per cent is locked in the polar ice caps.
- The balance of 0.7 per cent is freshwater, of which 0.66 per cent is groundwater.
- Only 0.03 per cent is available to us as freshwater in rivers, lakes and streams.
- Surface water is water on land, formed by precipitation or by seepage from underground, which gathers into streams, lakes, rivers and ponds and finally joins the sea.
- Groundwater is the water that seeps through the cracks and crevices under the surface and remains in the soil, subsoil or bedrock, and an aquifer is an underground water stream saturated with water that transmits it readily.
- India holds four per cent of the world’s water resources, in the form of surface water, groundwater and a vast coastline with indented coasts, and the brackish lagoons and lakes of Odisha, Kerala and West Bengal are used for fishing and for crops like paddy and coconut.
- Demand for water has risen with population, irrigation and industrialisation, and the CGWB has reported a sharp fall in groundwater levels of 70 to 80 per cent in Delhi, Haryana, Chandigarh, Himachal Pradesh and Uttarakhand.
- Water must be conserved for five reasons: overexploitation lowers the water table, loss of vegetation causes drought and lowers it further, irrigation uses more than 90 per cent of the total freshwater, a rising population creates scarcity, and pollution makes water unusable without treatment.
- Conservation is carried out through rainwater harvesting, water saving technologies, watershed development, water recycling and the prevention of water pollution.
- Rainwater harvesting is the process of increasing the recharge of groundwater by capturing and storing rainwater locally in sub-surface water reservoirs, and India has practised it since ancient times under many regional names.
- India’s annual rainfall of 1,170mm is above the world average of 800mm, yet shortage is common, because rainfall arrives in short spells of high intensity and flows away before it can recharge the ground — which is why even Cherrapunji, with about 11,000mm a year, is short of drinking water.
- Every harvesting system is built from four elements, and the last two are a choice.
- The catchment, which is the surface receiving the rainfall directly.
- The conduits, which carry the water from the catchment to the system.
- The storage facility, a tank holding water for direct use.
- The recharge facility, which sends water into the aquifer through dugwells, borewells, recharge trenches and recharge pits.
- Irrigation is the watering of agricultural plants through artificial means, and about 92 per cent of India’s water goes to agriculture, against 6 per cent for drinking and domestic use and 2 per cent for industries.
- Irrigation was made a priority after independence for six reasons: the uncertainty of rainfall, its uneven distribution, the differing requirements of crops and cropping seasons, the nature of the soil, the need to use the water of non-perennial rivers, and the higher production of irrigated crops.
- The means of irrigation are chosen to fit the surface water, groundwater, relief, soil and climate of a place.
- Wells are cheap and dependable where the water table lies within 15m, and are worked by the Persian wheel, lever and inclined plane methods.
- Tubewells reach 20-30m with power driven pumps and suit the level, soft, fertile northern plains.
- Canals are inundation or perennial, and most Indian canals are perennial, drawn from rivers regulated by barrages or dams.
- Tanks suit the Deccan, where rock will not absorb water and the uneven terrain offers natural hollows.
- Every conventional means carries a cost: wells and tubewells lower the water table, canals cause waterlogging and bring alkaline salts to the surface, and tanks silt up, go dry and lose water to evaporation.
- Conventional irrigation also wastes water, swings crops between flooding and stress, loses 10-15 per cent of the field to channels, and builds up soil salinity that has taken land in arid and semi-arid regions out of cultivation.
- Modern methods control where the water goes and how fast it arrives.
- Furrow irrigation directs water down narrow channels between crop rows and needs furrows of equal dimensions.
- Drip irrigation delivers 2-20 litres per hour to the root zone, wetting only part of the soil, and is efficient but expensive.
- Sprinkler irrigation applies water like rainfall through nozzles, reducing water consumption by 30-50 per cent, but loses water to evaporation and uses much power.
Flowchart
Fig. 9.A8 Caption: The rain that runs away is lost twice, and every practice in this chapter is an attempt to keep it in the store a little longer. Nodes: rain falls → branch one: runs off rapidly over hard or paved ground → joins streams and rivers → reaches the sea, with little left behind; branch two: soaks in through soil, recharge pits, trenches and permeable surfaces → groundwater store rises → water table rises → drawn by wells, tubewells, canals and tanks → used for irrigation, industry and domestic supply → withdrawal greater than recharge? yes → water table falls and shortage follows; no → store holds → conserved by harvesting, recharge and efficient irrigation → back to the groundwater store
What This Chapter Cannot Tell You
The chapter works with national and world figures, and a national average hides almost everything a farmer needs to know. An annual rainfall of 1,170mm says nothing about the district that received it in four days, and a country-wide split of 92, 6 and 2 per cent says nothing about which state, crop or season the water actually went to.
The lists of advantages and disadvantages are also written for the method, not for the field. Whether drip irrigation is worth its cost, or a canal will waterlog a particular tract, depends on the soil, the slope, the depth of the water table and the price of power at that place — none of which a general list can settle. ## 9.7 Check Your Concepts
- Look at Table 9.1.
- Name the canals listed for Rajasthan and for Bihar.
- The table lists canals state by state. State one thing the table does not tell you about any of these canals.
- This chapter states that 0.7 per cent of the earth’s water is available as freshwater, that 0.66 per cent of it is groundwater, and that 0.03 per cent lies in rivers, lakes and streams. Using only these figures, work out what share of the earth’s freshwater is groundwater, showing each step of your working, and say what that share means for a country trying to plan its water supply.
- Rain falls on the roof of a building fitted with a rooftop rainwater harvesting system. Describe, in order, the path that water takes from the roof to the point where it is used or stored, naming the elements it passes through and the two different destinations it may reach.
- Cherrapunji receives about 11,000mm of rainfall a year, and India’s annual rainfall of 1,170mm is well above the world average of 800mm. Explain why neither figure guarantees a supply of water, and state what a rainfall total does not tell you about the rain.
- Give two points of difference between ‘surface water’ and ‘groundwater’.
- Give a geographical reason for each of the following.
- Inundation canals are being converted to perennial canals.
- Tank irrigation is preferred over other means of irrigation in Peninsular India.
- Briefly explain why groundwater levels are dropping rapidly in India.
- Given a choice, which modern method of irrigation would you use to irrigate your farm? Give reasons to support your answer.
9.8 Case-Based Questions
- Canals are a channel for the supply of water from rivers to the farm fields. The perennial canals are not only an advantage but can be disadvantageous too. They are functional in the state of Punjab because of the favourable situations available there.
- What conditions favour the development of canal irrigation in the mentioned area?
- State two disadvantages of it.
- Fig. 9.9 shows drip irrigation in a field. List its advantages.