Chapter – 6 Water Resources

Earth is known as the blue planet because about 71% of the earth’s surface is covered with water.

The constant movement of water in our environment makes up the hydrological cycle or water cycle.

When the water table (top of the aquifer) is so high, that the ground is saturated, the water flows on the surface
which is known as runoff. This is why a river can keep flowing even when there has been no precipitation.

Types of water available on Earth :-

Surface water :
The visible bodies of water present on the ground are referred to as surface water. This includes the water held in
oceans rivers stream lakes wetlands and reservoirs. Surface water is easier to reach and thus is the most common
source of portable water.

Groundwater :
Groundwater is defined as the water that is found beneath the surface of the earth. Groundwater exist in aquifers
or underground layers of permeable rocks. Aquifers are underground reservoirs of water. Majority of freshwater is
found underground as soil moisture and in aquifers.

Importance of irrigation in India :

India is an agricultural country adequate availability of water is essential for successful agriculture. What a good
agriculture and produce sufficient quantity of water is needed. Thus irrigation has to be done because of the
following reasons :

• Uneven distribution of rain - Not all places in our country receive the same amount of rainfall. Thus irrigation is
required in the dry parts of the country.

• Seasonal rainfall - Rainfall is concentrated in India over a 4 - month period from June to September while the rest
of the year is relatively dry. Thus irrigation is required for year long crop production.

• Uncertainty of monsoon - Indian monsoons are very uncertain. 10 education provide security to agriculture from
irregularities of rainfall.

• Different water requirements of crops - All crops do not have the same water requirement. Sufficient amount of
water supplied by irrigation can meet the excess water requirement of crops.

• HYV seeds - The main element of green revolution in India is the use of high yielding variety seeds. To make the
Green revolution successful irrigation is necessary.

• Extension of agriculture - Irrigation is necessary to extend cultivation into semi arid regions. These regions
remain uncultivated due to lack of water. This irrigation is important to bring these lands under cultivation.

Primitive methods :-

Wells :
A well is dug in a manner such that its bottom reaches a fair depth below the water table to enable water from the
surrounding aquifer to accumulate in the well.

Types of Wells –
Persian wheel, rehat, charas, mohte, picottah and dhenkali

Prerequisites –
• Sufficient groundwater has to be available.
• Groundwater level must not be very deep.
• Soil has to be soft enough to allow the digging of wells.

Advantages –
• Wells are the simplest method of irrigation.
• It is the cheapest source of irrigation.
• It can be dug at any convenient place.
• It is an independent source of irrigation.

Disadvantages –
• The dry up during the hot summers and fail to provide water when it is needed the most.
• It can only water a limited amount of land.
• It is a time consuming method of providing water to crops.
• Well water is found to be brackish or saline.

Distribution –
Northern plains of India :
Punjab, Haryana, Rajasthan, Uttar Pradesh and Bihar.

Well irrigation is concentrated in the states of the northern plains because of :

• The high underground water table.
• The soft soil that facilitates irrigation through wells.

Tank irrigation :
Tanks are made by collecting rainwater in hollow depressions of varying sizes. During the rainy season rainwater
collects in the reservoir and is used later when needed, especially in the dry season.

Prerequisites –
• The ground should be rocky and lined with impervious rocks to prevent percolation of water.
• A rugged, uneven topography facilitates tank irrigation.

Advantages –
• Tanks are simple and easy to build.
• It is not an expensive means of irrigation.
• It allows the surplus water during monsoon to be stored and used later.

Disadvantages –
• Tanks occupy large surface area.
• Tanks dry up during the dry season and fail to provide water when it is needed the most.
• Silting of tanks is a problem.

Distribution –
Peninsular plateau of India :
Andhra Pradesh and Tamil Nadu

Tank irrigation is popular in peninsular India because of :

• The hard impermeable rocks of Deccan do not allow percolation of water.
• The undulating surface forms natural depressions to hold rainwater.
• Most peninsular rivers and streams are seasonal. Tanks enable people to store rainwater which would otherwise
have flowed away wastefully.

Inundation canals :
Inundation canal is a primitive method of irrigation. They are also known as flood water canals. They have water
only when the river is flooded during the rainy season. These canals are taken out from rivers without any
regulating systems like weirs at their head. Inundation canals and now converted into perennial canals to
ensure a study supply of water throughout the year and increase the area under agricultural productivity.
Prerequisites –
High level of flooding during the rainy season.

Disadvantages –
• They are solely dependent on rainfall for water supply.
• They fail to provide water to fields in the dry season.

Distribution –
Found near the river Sutlej which experiences high level of flooding during the rainy season.

Modern methods :-
Modern methods of irrigation are preferred over primitive methods because :
• They are more reliable and provide irrigation whenever needed throughout the year.
• They are easy to operate and less time consuming.
• They irrigate much larger area as compared to primitive methods.

Tube wells :

Prerequisites –
• Groundwater must be available in plenty and has to be fairly close to the surface.
• There should be a regular supply of cheap electricity.
• The region must be fertile and productive so that the cost of installation and operation of the tube well may be
recovered from the abundant farm production.

Advantages –
• It can irrigate a much larger area of about 400 hectares.
• It is more reliable as it can provide water even during periods of drought since it draws water from deep
underneath.

Disadvantages –
• It is an expensive means of irrigation.
• It requires excessive exploitation of groundwater leading to gradual depletion.

Distribution –
Uttar Pradesh, Bihar, Punjab, Haryana, Rajasthan

Perennial canals :
A canal is an artificial channel that is constructed to carry water to the fields to perform irrigation
A weir or dam is built across a river so that the flow of water can be regulated with the help of sluice gates and
stored in reservoirs specially built for this purpose.
Canals are lined to prevent seepage and loss of water.

Advantages – (Why are inundation canal now converted into perennial canals ?)
• They provide water for irrigation whenever required.
• Canal water is rich in sediments which add fertility to the fields.
• Initial costs are high yet they are quite cheap in the long run.

Disadvantages –
• Canal water seeps into the soil which may lead to waterlogging and erosion.
• It leads to Salt effervescence which reduces the soil fertility and makes the soil unproductive.

Distribution –
Northern plains of India :
Uttar Pradesh, Bihar, Punjab, Haryana, Rajasthan

It is concentrated in the Northern plains of India because it can be conveniently dug in areas of :
Flat level land and soft soil.
Canals are absent in the peninsular plateau because :
Digging of canals in rocky and uneven areas is difficult.

Sprinklers :
It is a type of overhead irrigation in which a device consisting of a system of pipes is fitted with a nozzle and set up
vertically in the field. With the help of a pumping system water is spread directly to all parts of the field.

Advantages –
• Does not involve any loss of water by seepage because water is sprayed as droplets.
• No water is lost by evaporation because water is supplied directly onto the fields leading to minimum wastage.
• Water reaches every part of the field uniformly.

Disadvantages –
• Quite expensive and not affordable.
• In the absence of clean water supply, the sprinkler nozzle may get regularly blocked or the crops may get coated
with sediments.

Distribution –
Arid and semi arid areas, hilly areas or areas of uneven topography.
Rajasthan and Haryana.

Drip irrigation :
It is a type of micro irrigation that allows water to reach the roots of plants in drops.

Advantages –
• Since the water reaches the roots of crops in drops it soaks into the soil before it can evaporate or get wasted as
run off.
It is not expensive.
• Since water trickles into the essential root zone it minimises the possibility of leaching of soil.

Disadvantages –
• Clogging up of pipes may occur if water is not filtered properly.
• Setting up of drip irrigation has high initial costs.

Distribution –
Maharashtra, Karnataka and Tamil Nadu

Need for conservation of water :-

Water is a vital natural resource which forms the basis of all life and is a key resource for all economic activities
ranging from agriculture to industry. Does water should we used judiciously. Conservation of water resources is
essential due to :

• Increased demand for water has resulted in its short supply.

• Large scale pollution of surface water also lessons its supply.
• Overexploitation of groundwater reserves has led to lowering of the water table.
• Wastage of water is also causing dwindling supply.

Measures for conservation of water :-

Prevention of water pollution -

The central pollution control board (CPCB) is collaborating with state pollution control boards to monitor the quality
of water resource and identifies the major cause of pollution of river waters. It also ensures conservation of water
in India. The Government of India has made legislative provisions for preventing water pollution like :
Water Act 1974
Environment Protection Act 1986
Water Cess Act 1977

Reuse and recycling of water –

Water of inferior quality can be reused for fire fighting and cooling.
In urban areas water after washing cars and be used for gardening.
Treated industrial and municipal wastewater can be recycled and reused for gardening, irrigation and other
purposes.

Rainwater harvesting -
It involves the collection and storing of rainwater for future use especially during dry seasons. It may be put to
direct use or can be utilized for recharging underground water reserves.

Objectives –
• Meets the increasing demand for water
• Reduces surface runoff
• Avoids flooding of roads
• Reduces soil erosion
• Helps to raise the groundwater table by adding to groundwater reserves
• Reduces groundwater pollution
• Supplements household requirement of water especially in hot summers

Methods –
•Water can be collected from rooftops known as rooftop rainwater harvesting.
• The water collected from rooftops can be recharged through hand pumps to the underground water reserves.
• The water collected from rooftops can also recharge the groundwater reserves through abandoned dug wells.
• In this way rainwater which would otherwise flow away wastefully is harvested for future use and is also used to
recharge groundwater reserves.

Water harvesting in India :–

Hariyali is a watershed development project sponsored by the central government and executed by the gram
panchayats. The main objectives of this project includes harvesting every drop of rainwater for purposes of
irrigation, plantations, pastoral development, fisheries and creation of sustainable sources of income for the village
community as well as securing drinking water supplies.

Johad has been traditionally used in Rajasthan for harvesting water. It is a crescent shaped bund which is built
across a sloping catchment to capture the surface runoff. Water accumulating in the johad percolates in the soil to
augment the groundwater.

The Government of Andhra Pradesh has set up a water conservation mission in the name of Neeru - Meeru. Despite
deficit rainfall all districts of the state registered rise in groundwater levels with the help of sustained rainwater
harvesting amongst other measures.