WATER RESOURCES ENGINEERING I (S5 CIVIL)
MODULE I
IRRIGATION
Irrigation is the process by which water is brought to dry land through artificial means, such as pipes,
hoses or ditches. The land that is being irrigated usually contains crops, grass or vegetation that would not
usually receive enough water from rainfall or other natural sources. Sometimes the reason to irrigate a
portion of land is that it happens to be a dry season, with less-than-average amounts of rainfall, or it might
be necessary to do so because that land never would receive enough water on its own to be fertile.
The water that is used for irrigation might be taken from nearby lakes, reservoirs, rivers or wells. The
amount of water that is to be used for irrigation depends on the type of crop that is being farmed as well
as the amount of rainfall in the region. There are some countries where water is used for irrigating land
more than it is used for other purposes.
Necessity of Irrigation
India is basically an agricultural country, and all its resources depend on the agricultural output.
Water is evidently the most vital element in the plant life. Water is normally supplied to the
plants by nature through rains. However, the total rainfall in a particular area may be either
insufficient, or ill-timed. In order to get the maximum yield, it is essential to supply the optimum
quantity of water, and to maintain correct timing of water. This is possible only through a
systematic irrigation system-by collecting water during the periods of excess rainfall and
releasing it to the crop as and when it is needed. Thus, the necessity of irrigation can be
summarized in the following four points:
1. Less Rainfall
When the total rainfall is less than needed for the crop, artificial supply is necessary. In such a
case, irrigation work may be constructed at a place where more water is available, and then to
convey the water to the area where there is deficiency of water.
2. Non-uniform Rainfall
The rainfall in a particular area may not be uniform over the crop period. During the early
periods of the crop, rains may be there, but no water may be available at the end, with the result
that either the yield may be less, or the crop may die altogether. By the collection of water during
the excess-rainfall period, water may be supplied to the crop during the period when there may
be no rainfall. Most of the irrigation projects in India are based on this premise. The rainfall
during the winter is very scanty, and hence rabi crops need artificial supply of water through the
irrigation works.
3. Commercial Crops with Additional water
The rainfall in a particular area may be sufficient to raise the usual crops, but more water may be
necessary for raising commercial and cash crops.
4. Controlled Water supply
By the construction of proper distribution system, the yield of the crop may be increased.
Purposes of Irrigation

Providing insurance against short duration droughts

Reducing the hazard of frost (increase the temperature of the plant)

Reducing the temperature during hot spells

Washing or diluting salts in the soil Softening tillage pans and clods

Delaying bud formation by evaporative cooling

Promoting the function of some micro organisms
Objectives of irrigation

To Supply Water Partially or Totally for Crop Need

To Cool both the Soil and the Plant

To Leach Excess Salts

To improve Groundwater storage

To Facilitate continuous cropping

To Enhance Fertilizer Application- Fertigation
Benefits of Irrigation
1. Increase in Crop Yield
2. Protection from femine
3. Cultivation of superior crops
4. Elimination of mixed cropping:
5. Economic development
6. Hydro power generation
7. Domestic and industrial water supply
The harmful effects of excessive irrigation
Water is very important for the growth of plants but excessive irrigation of field leads to water
logging of soil. Too much water is harmful for crop production as discussed under:
1. Too much water is the soil inhibits the process of germination of seeds. It is due to the reason
that under these conditions the seeds do not get sufficient air to respire. Is due to the reason that
under these conditions the seeds do not get sufficient air to respire .our might have observed that
the seeds fail to germinate, if it rains soon after sowing. This is due to excessive water in the
field, which affects the soil aeration.
2. Roots do not grow properly in a waterlogged field. We can see that potted plants do not grow
well if they are given excess water. This is due to the reason that excess water affects soil
aeration and hence plants roots do not grow properly.
3. Excessive water in the field increases the amount of salt on the surface of soil due to
evaporation. The accumulation of salts damages the soil fertility, except rice; almost all crops
receive as ever set back in their growth when excess water stagnates. Damage caused by excess
water and consequent development of salt problem can be minimized by removing standing
water from the fields through proper drainage system.
4. The excessive irrigation may lead to lodging of the crop, may fall on the ground under the
effect of strong winds. Due to excess water the roots of the plant may not be able to provide
necessary anchorage in the wet soil.
Thus, excessive watering may damage the crop and reduce the quantity and quality of the
produce. This also results in wasting of expensive water.
So the ill effects of irrigation are
 Water logging
 Breeding place of mosquitoes
 Ground water table is increased
 Complete saturation of root zone causes efflorescence.
Techniques adopted for carrying water from its source to the crop are called methods or modes of
application. These are:
1. flooding -wetting all the land surface;
2. furrows -wetting only certain part of ground level;
3. sprinkler -in which the soil is wetted in much the same way as rains;
4. sub-surface irrigation -in which surface is wetted very lightly, but the sub soil is fully saturated; and
5. localized irrigation -in which water is applied at each individual plant at. a near daily rate.
Characteristics of an Efficient Irrigation Method
An efficient method of irrigation should fulfill five major objectives viz. (1) distribution of water
uniformly over the field according to crop need, (2) storage of maximum fraction of water in the root
zone for plant use, (3) crop growth should not be adversely affected, (4) soil transport or loss is
negligible, and (5) the technique used is economically sound and adoptable at the farm.
Factors Affecting Suitability of Irrigation Method
The selection of a suitable irrigation method for a particular farm location depends upon the
following factors.
1. Soil
Textural, crusting, cracking and infiltration characteristics of surface soil; nature and depth of
relatively impermeable layers in sub-soil, if any; water storage capacity of root zone; nature and extent of
land slope; size of field; surface drainage; nature and extent of salts in surface and sub-soil are the salient
soil factors influencing between of an irrigation method.
2. Water
Nature of water supply (continuous or rational). source (pump or canal), size of water delivery,
quality of irrigation water, and quantity of water supply (adequate or limited) are a few factors that must
be taken into consideration while deciding the method of irrigation.
3. Crops
Nature of crops, area under different crops and their rooting behaviour, optimum depth and
timing of irrigation, sensitivity of crops to excessive soil moisture, cultural operations required, etc. must
be considered at the time of selection of irrigation method for a crop.
4. Others
There are other factors influencing irrigation method like outlook, managerial efficiency and financial
resources of the farmer; nature of the farm machinery used; availability and cost of labour; wear and tear
maintenance facilities and costs of irrigation equipments; and availability of power supply. As far as
possible, an irrigation method should not only provide a high level of water application efficiency, but
also ensure its economic viability, sustained soil productivity and wide' adaptability to prevalent feature
of the farm. Generally, irrigation methods followed in India lack in an economic use of irrigation water.
Methods of Irrigation
Methods of irrigation, generally adopted in India, can be represented in the flow chart.
Methods of Irrigation
Surface irrigation
In this method, water from an irrigation channel is allowed to reach a part or whole of the field
and spread by the gravitational flow incidental to the slope of the land. Water may be distributed to the
crops in border strips, check basins or furrows. The important requirements to obtain high efficiency in
surface method are (1) properly constructed water distribution systems to provide adequate flow of water
to the fields; and (2) proper grading and leveling of land to achieve uniform distribution of water.
1. Border strip method
The border method of irrigation makes use of parallel ridges to guide a sheet of flowing water as
it moves down the slope. The land is divided into a number of long parallel strips called borders that are
separated by low ridges. The border strip has little or no cross slope but has a uniform gentle slope in the
direction of irrigation. The essential feature of border irrigation is to provide an even surface over which
the water can flow down the slope with a nearly uniform depth. Each strip is irrigated independently by
turning into a stream of water at the upper end. The water spreads and flows down the strip in a sheet
confined by the border ridges. The irrigation stream must be large enough to spread over the entire width
between the border ridges without over topping them. When the advancing water front either reaches the
lower end, or a few minutes before or after that, the stream is turned off. The water temporarily stored in
the border moves down the strip and infiltrates into the soil, thus completing the irrigation. It is adapted to
most soils where depth and topography permit, 1 the required land leveling at a reasonable cost and
without any permanent reduction in soil fertility. It is, however, more suitable to soils having moderately
low to moderately high infiltration rates. It is generally not used in coarse sandy soils that have very high
infiltration rates. It is also not well suited to soils having a very low infiltration rate. This method is
suitable to irrigate all close growing crops like wheat, barley, fodder crops and legumes. It is, however,
not suitable for crops like rice which requires standing water during most part of its growing season.
Advantages
i. It is easy to construct border ridges even with some simple farm implements like a bullock drawn Aframe ridge or tractor-drawn disc ridger.
ii. Labour requirement in irrigation is greatly reduced as compared to the conventional check basin
method of irrigation.
iii. Uniform distribution and high water application efficiencies are possible if the system is properly
designed.
iv. Large irrigation streams can be efficiently used.
v. Operation of the system is simple and easy.
vi. Adequate surface drainage is provided if outlets are available.
Disadvantages
i. It requires an extensive land grading which is too expensive.
ii. It is mainly suitable for deep soils with the availability of large flow of water.
iii. Drainage may be essential.
iv. Water wastage is frequently observed.
Straight and contour borders
If the borders are constructed along the general slope of the field, they are known as straight
borders or slope borders, and if they are constructed across the general slope of the field they are called
contour borders. When fields can be leveled to desirable land slopes economically and without affecting
its productivity, graded borders are easier to construct and operate. In case where land slope exceeds safe
limit, fields are undulating and leveling is not feasible, borders may be laid across the slope. The design
of a contour border is the same as that of a straight border. Each contour border is level crosswise and has
a uniform longitudinal gradient as in a straight border. The width and length of a contour border are
identical to that of a straight border for a particular set of conditions.
In laying contour borders, the field is divided into a series of strips on the approximate contour,
and each strip is leveled as an independent area. Thus, a series of strips are formed in successive
elevations around the slope. The vertical interval between the adjacent benches should, as far as possible,
be limited to 30 cm, but should not exceed 60 cm. The height of ridge should be sufficient to check both
the normal irrigation stream and run-off.
2. Check basin irrigation
Check basin irrigation is the most common method of irrigation in India and in many other
countries. This is the simplest in principle of all methods of irrigation. There are many systems in its use,
but all involve dividing the field into smaller units so that each has a nearly level surface. Ridges-areconstructed around the areas forming basins within which the irrigation water can be controlled. The
basins are filled to the desired depth and the water is retained until it infiltrates into the soil. The depth of
water may be maintained for considerable periods of time by allowing the water to continue to flow into
the basins.
The distinguishing features of various uses of check basin method of irrigation involve the size
and shape of the basins and “whether irrigation is accomplished by intermittent or continuous" collection
of water in the basins. The ridges or bunds may be temporary for a single irrigation as in the pre-sowing
irrigation of seasonal crops. They may be semi-permanently constructed for the repeated use in the case
of paddy fields. The size of ridge will depend on the depth of water to be impounded as well as on the
stability of the soil when wet.
Water is conveyed to the field by a system of supply channels and lateral field channels. The
supply channel is aligned on the upper side of the area and there is usually one lateral channel for every
two rows of check basins. Water from the laterals is turned into the beds and is cut off when sufficient
water has been administered into the basin. Water is retained in the basin until it soaks into the soil. The
size of the irrigation stream is not critical as long as it is sufficient to provide a coverage of the entire strip
in a relatively short time span required to apply the desired amount of water into the soil. As the
infiltration rate of soil increases, stream size must be increased or the size of the basins reduced in order
to cover the area within a short period of time. A large size irrigation stream will permit a comparatively
larger size of the basin.
The size of check basin may vary from one square metre, used for growing vegetables and other
intensive cultivation, to as large as two hectares or more, used for growing rice under wet land conditions.
When the land can be graded economically into nearly level fields, the basins are rectangular in shape. In
rolling topography the ridges follow the contours of the land surface. The contour ridges are connected by
cross ridges at intervals. The vertical interval between contour ridges usually varies from 6 to 12 cm. in
case of upland irrigated crops like wheat and 15 to 30 cm in case of low land irrigated crops .like rice.
In irrigating orchards, square to contour basins may be used as in other crops. When the plants are
widely spaced the ring method of basin irrigation is adopted. The rings are circular basins formed around
each tree. The ring basins are small when the plant is young. The size is increased as the plant grows.
Check basin irrigation is suited to smooth, gentle and uniform land slopes and for soils having
moderate to slow infiltration rates. Steep slopes require complex layouts and heavy land leveling. Both
row crops as well as close growing crops are adapted to basins as long as the crop is not affected by
temporary inundation. The method is especially adopted for, irrigation of grain and fodder crops in heavy
, soils where water is absorbed very slowly. It is also suitable in very permeable soils which must be
covered with water rapidly to prevent i excessive deep percolation loss of water at the upstream end.
Advantages
i. Since in this method the entire area is not flooded, it ensures -high water use efficiency.
ii. Excessive seepage loss can be avoided by adopting this practice
iii. Damage to plants and loss of soil nutrients do not occur in this practice:..
Disadvantages
i. The major disadvantage of check basin method of irrigation is that the ridges interfere with the
movement of animal drawn or tractor drawn implements for inter culture operations or harvesting of
crops.
ii. Considerable land is occupied by ridges and lateral field channels and crop yields are substantially
reduced.
iii. The method impedes surface drainage.
iv. Precise land grading and shaping are required.
v. Labour requirement in land preparation and irrigation are much higher.
3. Furrow irrigation
The furrow method of irrigation is used in irrigation of row crops with furrows developed
between the crop rows in the planting and cultivating processes. The size and shape of the furrow depends
on the crop grown, equipment used and spacing between crop rows. Water is applied by running small
streams in furrows between the crop rows. Water infiltrates into the soil and spreads laterally to irrigate
the areas between the furrows. The length of time water takes to flow in the furrows depends on the
amount of water required to replenish root zone and the infiltration rate of the soil. Both large and small
irrigation streams can be used by adjusting the number of furrows irrigated at anyone time to suit the
available flow. In areas where surface drainage is necessary, the furrows can be used to dispose of the
run-off from rainfall rapidly.
Furrow irrigation can be used to irrigate all cultivated crops planted in rows, including orchards
and vegetables. Among the common cultivated crops of India, the method is suitable for irrigating maize,
sorghum, sugarcane, cotton, tobacco, groundnut, potato and other vegetables. Furrows are particularly
well adapted to irrigating crops which are subject to injury from accumulated surface water or susceptible
to fungal root rot. Furrow irrigation is suitable to most soils except sands that have a very high infiltration
rate and provide poor lateral distribution of water between furrows.
Furrows are small, parallel channels, made to carry water in order to irrigate the crop. The crop is usually
grown on the ridges between the furrows.
Furrow irrigation is suitable for many crops, especially row crops. Crops that would be damaged if water
covered their stem or crown should be irrigated by furrows. Furrow irrigation is also suited to the growing
of tree crops. In the early stages of tree planting, one furrow alongside the tree row may be sufficient but
as the trees develop then two or more furrows can be constructed to provide sufficient water. Sometimes a
special zig-zag system is used to improve the spread of water.
Uniform flat or gentle slopes are preferred for furrow irrigation. These should not exceed 0.5%. Usually a
gentle furrow slope is provided up to 0.05% to assist drainage following irrigation or excessive rainfall
with high intensity.
Furrows can be used on most soil types. However, as with all surface irrigation methods, very coarse
sands are not recommended as percolation losses can be high. Soils that crust easily are especially suited
to furrow irrigation because the water does not flow over the ridge, and so the soil in which the plants
grow remains friable.
This section deals with the shape, length and spacing of furrows. Generally, the shape, length
and spacing are determined by the natural circumstances, i.e. slope, soil type and available
stream size. However, other factors may influence the design of a furrow system, such as the
irrigation depth, farming practice and the field length.
Furrow length
Furrows must be on consonance with the slope, the soil type, the stream size, the irrigation depth,
the cultivation practice and the field length. The impact of these factors on the furrow length is
discussed below.
Slope
Although furrows can be longer when the land slope is steeper, the maximum recommended
furrow slope is 0.5% to avoid soil erosion. Furrows can also be level and are thus very similar to
long narrow basins. However a minimum grade of 0.05% is recommended so that effective
drainage can occur following irrigation or excessive rainfall. If the land slope is steeper than
0.5% then furrows can be set at an angle to the main slope or even along the contour to keep
furrow slopes within the recommended limits. Furrows can be set in this way when the main land
slope does not exceed 3%. Beyond this there is a major risk of soil erosion following a breach in
the furrow system. On steep land, terraces can also be constructed (see Basin Irrigation) and
furrows cultivated along the terraces.
Soil type
In sandy soils water infiltrates rapidly. Furrows should be short (less than 110 a), so that water
will reach the downstream end without excessive percolation losses.
In clay soils, the infiltration rate is much lower than in sandy soils. Furrows can be much longer
on clayey than on sandy soils.
Stream size
Normally stream sizes up to 0.5 l/sec will provide an adequate irrigation provided the furrows are
not too long. When larger stream sizes are available, water will move rapidly down the furrows
and so generally furrows can be longer. The maximum stream size that will not cause erosion
will obviously depend on the furrow slope; in any case, it is advised not to use stream sizes
larger than 3.0 l/sec.
Irrigation depth
Applying larger irrigation depths usually means that furrows can be longer as there is more time
available for water to flow down the furrows and infiltrate.
Cultivation practice
When the farming is mechanized, furrows should be made as long as possible to facilitate the
work. Short furrows require a lot of attention as the flow must be changed frequently from one
furrow to the next. However, short furrows can usually be irrigated more efficiently than long
ones as it is much easier to keep the percolation losses low.
Field length
It may be more practical to make the furrow length equal to the length of the field, instead of the
ideal length, when this would result In a small piece of land left over. Equally the length of field
may be much less than the maximum furrow length. This is not usually a problem and furrow
lengths are made to fit the field boundaries.
Advantages
i. Water in the furrows contacts only one half to one fifth of the land surface, thereby reducing puddling
and crusting of the soil, and evaporation losses.
ii. Early sowing is possible which a distinct advantage in heavy soils is.
iii. It can be safely adopted on the sloppy lands by opening the furrows across the slope.
iv. This .method reduces labour requirement in land preparation and Irrigation.
v. Compared to check basin method, there is no wastage of land in field ditches.
Disadvantages
i. It requires skilled labourers to operate.
ii. It may cause serious erosion, if excess water flows over the ridges.
iii. Difficult to carry on mechanical operations.
Irrigation furrows may be classified into two general types is based on their alignment. They are
(i) straight furrows, (ii) contour furrows. Based on their size and spacing furrows, may be classified as
deep furrows and corrugation.
a. Deep furrows
As mentioned above, deep furrows are of two type’s i.e. straight furrows and contour furrows.
i. Straight furrows
Straight furrows, like borders, are laid down across the prevailing land slope. They are best suited to sites
where the land slope does not exceed 0.75 per cent. In areas of intense rainfall, however, the furrow grade
should not exceed 0.5 % so as to minimize the erosion hazard.
ii. Contour furrows
Contour furrow method is similar to the graded furrow method in that the irrigation water is
applied in furrows, but the furrows carry water across the sloping field rather than down the slope.
Contour furrows are curved to fit the topography of the land. The furrows are given gentle slope along its
length as in the case of graded furrows. Field supply channels rundown the land slope to feed the
individual furrows and are provided with erosion control structures.
b. Corrugation irrigation
Corrugation irrigation consists of running water in small I: furrows, called corrugatio'1s which
direct the flow down the slope. It is commonly used for irrigating non-cultivated close growing crops
such as small grains and for pasture growing on steep slopes. Corrugation may be used in conjunction
with border irrigation on lands with relatively flat slopes in order to get uniform coverage with water. The
water is applied to small furrows and the crop rows are I not necessarily related to the irrigation furrows.
In this method the soil may be prepared and the crop plan without regard for irrigation layout
after the seed is sown, but before the germination has taken place, a corrugation is used making small
furrows or corrugation to aid in controlling irrigation water. The corrugation may be used with a simple
bamboo corrugators or cultivators equipped with small furrowers or other similar implements.
Corrugations are V -shaped or U shaped channels about 6 to 10 cm deep. They are spaced 40 to 75 cm
apart. The entire soil surface is wetted slowly by the capillary movement of the water which flows in the
corrugations.
This method of irrigation is the most suitable in loamy soils in which the lateral movement of
water occurs readily. Clay soil having poor infiltration capacity is quite unsuitable for irrigation by
corrugations. This method is also not suitable for irrigation in deep sandy soils due to excessive loss of
water by deep percolation before the entire soil surface is wetted.
Saline or alkaline soils or irrigation water having salt content is not suitable for this method
because of the danger of salt accumulation on surface soils due to capillary movement of water.
Advantages
i. Corrugation irrigation minimizes the crusting effect on the surface soil which may occur when the
entire surface is flooded.
ii. High water use efficiency is ensured.
iii. It can be used for germinating seeds which are drilled or broadcast in the soil.
Disadvantages
i. Not suitable for a wide range of soils.
ii. This is a labour intensive method.
iii. If the corrugations are placed across the land slope, the over flow of water may move down into the
lower corrugations and may cause severe soil erosion.
B. Sub-surface irrigation
In this method of irrigation water is applied below the ground surface by maintaining an artificial
water table at some depth depending upon the soil texture and the depth of the plant roots. Water reaches
the plant roots through capillary action. Water may be introduced through open ditches or underground
pipelines such as tile drains or mole drains. The depth of open ditches varies from 30 to l00cm and they
are spaced about 15 to 30 metres apart. This water application system consists of field supply channels,
ditches or trenches and drainage ditches for the disposal of excess water. The irrigation ditches should be
suitably spaced to cover the whole field adequately.
This method is suited to soils having reasonably uniform texture and is permeable enough for
water to move rapidly both vertically as well horizontally within and for some distance below the crop
root zone. The soil profile must control a barrier against excessive loss through deep percolation.
Topography must be smooth and nearly level or slight slopes very gentle and uniform.
Advantages
1. In soils having low water capacity and a high infiltration rates.: where surface methods cannot be used
and sprinkler system : is very expensive, sub-surface irrigation method can be used effectively.
ii. Evaporation loss from ground surface is minimum.
iii. In this method, it is possible to maintain the water level at optimum depths for crops required at
different growth stages.
Disadvantages
i. It is quite expensive and labour intensive in the beginning.
ii. The method requires an unusual combination of natural conditions; therefore its scope is limited.
iii. Frequent removal of accumulated soil and other materials from channels is necessary.
In India, this i1rigation is practiced to a limited extent for growing vegetable crops around Dal
Lake in Kashmir and for irrigation of coconut palms in the organic soils of Kuttanad area in Kerala.
C. Sprinkler irrigation
In the sprinkler method of irrigation, water is applied above the ground surface as spray. The
spray is developed by flow of water under pressure through small orifices or nozzles. The pressure is
obtained by pumping with careful selection of nozzle sizes, operating pressures and sprinkler spacing.
High efficiency in water application/distribution can be obtained with sprinkler system.
Sprinkler systems are of generally two major types viz. (i) rotating head system, and (ii)
perforated pipe system.
In case of rotating head system small nozzles are placed on riser pipes and these riser pipes are
fixed at an even interval along the length of lateral pipes which are placed on the ground surface.
However, they can be mounted on posts exceeding the crop height and made rotating through 90 degree.
In rotating sprinkler, the most, important device to rotate the sprinkler head is a small hammer activated
by the trust of water striking the vane connected to it.
In case of perforated pipe system, holes are perforated in lateral irrigation pipes which are
especially designed to distribute water with a good deal of uniformity. This system is usually designed for
low operating pressures (i.e. 0.5 to 2.5 kg/sq cm). Due to this low pressure, the system is attached to an
overhead tank to achieve the requisite pressure head. The sprays are directed on both sides of the pipe
which cover a strip of land from 6 to 15 metres wide.
Nearly all cultivable soils can be sprinkler irrigated. It is, however, not suitable in very high
textured soils where the infiltration rates are very low (i.e. less than 4 mm per hour). Most crops
excepting rice and jute can be sprinkler irrigated. The flexibility of sprinkler equipment and efficient
control of its application make this method adaptable to most of the topographic conditions. However,
extremely high temperature and wind velocity markedly reduce the uniformity of water distribution and
irrigation efficiency. This I system of irrigation is especially useful to the soils that have steep slopes or
irregular topography and soils which are too shallow to level
Advantages
i. This technique enables judicious utilization of even small water flows and permits efficient irrigation of
undulated lands, and soils with shallow depths.
ii. It saves 10to 16% land that is used in construction of channels and ridges in other methods.
iii. Highly permeable as well as relatively less permeable soils can be easily irrigated by sprinkler method
without any risk of run-off and erosion, inundation and seepage losses.
iv. Fertilizers, pesticides and weedicides can be applied along with water spray, thus, saving extra labour.
Disadvantages
i. High initial cost of equipments.
ii. Operating costs are generally higher than irrigation by surface methods.
iii. Winds disturb the sprinkler pattern giving uneven distribution of the irrigation water.
iv. Sprinkling with water containing an appreciable amount of salts may result in bum or death of the
plants.
v. Under certain climatic conditions diseases may be encouraged. The problem of fruit rotting in tomato
and strawberry gets aggravated especially in moist soil condition.
D. Localized irrigation
Drip irrigation
As the name signifies, drip irrigation, also termed as trickle irrigation, involves the slow
application of water to the root zone of a crop. The method was initiated in Israel and is now being tried
in other countries. In this method, water can be used very economically, since loss due to deep percolation
and surface evaporation are reduced to the minimum. This method, therefore, is highly suitable to arid
regions and orchard crops. The successful raising of orchards even on saline soils has been made possible
by the drip system of irrigation. The system can also be used for applying fertilizers in solutions.
In this system, water is applied more frequently, close to the stems of plants through suitably
spaced drippers (emitters) attached to plastic or metallic pipes spread above or below soils along crop
rows. The pipes are hooked to source of water supply through a storage tank or pressure device which
provides necessary hydraulic head or pressure for movement of water to the drippers. A pumping unit
creates a pressure of about 2.5kg/sq cm. In this case only a part of soil in the vicinity of plant roots is
wetted and kept close to field capacity. The amount of water dripping from nozzles can be regulated as
desired by varying the pressure at the nozzles and the size of the orifice of the nozzles. The initial high
cost of the equipment and its maintenance are the major limitations in this system. It may, however, work
out to be cheaper than the sprinkler system especially for the orchards and other widely spaced crops.
Drip and Sprinkler Irrigation in India: Constraints
India ranks first in respect of total irrigated area existing in the world. It has got approximately 80
million hectares of irrigated land. But the methods of irrigations employed are still very primitive and
inefficient. Recent achievements in the field of irrigation for instance drip and sprinkler irrigations are yet
not sufficiently popular in India.
More than 10 million hectare is irrigated by sprinkler method and I million hectare by drip
irrigation in the world. But in India, it is only about 0.7 m. ha under sprinkler irrigation and less than
20,000 ha with drip irrigation. Therefore, it is necessary to popularize these advanced methods of
irrigation especially in those areas where water is a scarce resource.
India is blessed with abundant water resources. However, the available water, particularly for
irrigation is tending to diminish and at the same time its demand is gravely felt due to population
explosion. The emerging challenge is to tap all the available resources of water.
Technological innovations are to be exploited to achieve the twin objectives of higher
productivity and better water use efficiency. For this, we will have to popularize drip and sprinkler
irrigation methods. On account of certain financial, technical and institutional constraints, these methods
have not got their due place in India and consequently, the area benefited is negligible. Therefore, the
question arises as to what are the constraints and problems holding up progress.
The following are the major constraints faced by the farmers in adopting the drip and sprinkler
systems of irrigation.
1. High initial cost.
2. Inadequate subsidy amount.
3. Difficulty in getting subsidy amount
4. Lack of availability of technical input and after sale services.
5. Clogging of dripper and cracking of laterals.
6. Damages due to rats and squirrels.
7. High cost of spares and components.
8. Discrimination in subsidy distribution among different categories of farmers.
To exploit the full potential of these two innovations, the constraints are to be overcome by
appropriate policy instruments. Financial support and technical guidance. These calls for an integrated
approach and endeavor on the part of government. Implementing agencies, rnanufacturing cornpanies,
voluntary organizations and the ultimate users of the systems i.e. the farmers.
Adverse Effect of Improper Irrigation
As water is a limited resource with no substitute. Its efficient and judicious utilization is of utmost
importance in sustaining and increasing agricultural production. If irrigational water is used inefficiently
and unscientifically, it may cause certain adverse effects, rather than being useful, to the crop and soil.
Seepage from main and branch canals, distributaries, and field channels along with the deep
drainage loss from the base and cropped fields due to heavy rains and over irrigation add to the ground
water and cause rise of water table. If not checked, the water table may rise close to the surface and cause
water logging of soil. If here is a salty layer in the soil, the salts may get dissolved in the rising water table
and come up on the surface soil thereby rendering the soil less productive due to salinity. Soil aeration is
also badly affected.
Rising of water table beyond the threshold depth can be prevented by providing requisite subsurface drainage. Alternatively, in areas with good quality ground water, radial drainage with shallow
pumps and recycling the water for irrigation can be practiced with advantage to keep down the water
tables and stretch the irrigation supplies.
Another aspect associated with injudicious irrigation is leaching of the mobile nutrients like
nitrate below the root zone of crops, which decreases the nutrient use efficiency by crops. In order to
minimize this loss through leaching, it becomes necessary to regulate irrigation and fertilizer applications.
Crop water requirement
General
Crop water requirement may be defined as the quantity of water, regardless of its source, required by
crop or diversified pattern of crops in a given period of time for its normal growth under field
conditions at a place. It includes the loss due to evapo-transpirtation (ET) or consumptive use (CU)
plus the losses during the application of irrigation water and the quantity of water required for special
operations such as land preparation, transplanting, leaching etc. it may those be formulated as:
CWR=ET or CU + application losses +conveyance losses+ special needs.
In other words crop water requirement can be defined as the total amount of water and the way in
which a crop requires water from the time it is sown to the time it is harvested. It is clear that the
water required will vary with the crop as well as the place. Different crops will have different water
requirement and the same crops may have different water requirement at different place depending
upon climate, type of soil method of cultivation and useful rainfall etc.
Crop water requirement serves as the basis for the design of the capacity of reservoir and canal,
irrigation scheduling and management.
Crop period and base period
Crop period:
It is a period elapsed from the instant of its sowing to the instant of harvesting.
Base period:
It is the time between the first watering of a crop at the time of its sowing to its last water before
harvesting.
Crop period is slightly more than the base period but for all particular purpose, they are taken as one
and the same thing, and generally expressed in days.
Duty and delta of a crop
Duty (D)
The duty of water is the relationship between the volume of water and the area of the crop it matures.
This volume of water is generally expressed by a unit discharge flowing for a time equal to the base
period of the crop called Base of Duty. Duty represents the irrigation capacity of unit water (ha/m3/s).
𝑄
𝐴
Where A command area and Q continuous discharge required for the base period.
If 3m3/s of water is required for a crop sown in area of 5100ha continuously, the duty of irrigation
water will be
𝑄
5100
𝐷= =
= 1700ha/m3 /s
𝐷=
𝐴
3
and a discharge of 3m3/s is required throughout the base period.
Duty is generally represented by D.
In a large canals irrigation system, the water from its source, first of all flows into the main
canal, then it flows into primary canal; from the primary it flows into secondary canals and from
secondary to tertiary canals and finally in to the field. During the passage of water from those
irrigation channels, the water is lost due to evaporation and percolation. Those losses are called
transit loss or transmission or conveyance losses.
Duty of water for a crop is the number of hectares of land which the water can irrigate. Therefore, if
the water requirement of the crop is more, less amount of hectares of land it will irrigate. Hence, if
water consumed is more, duty will be less. Therefore it’s clear that the duty of water at the head of
the water course will be less than the duty of water on the field; because when water flows from the
head of the water course and reaches the field, some water is lost as transit losses. Duty of water,
therefore, varies from one place to another and increases as we move downstream from the head of
the main canal towards the head of branches or water courses.
Delta (Δ)
Each crop requires certain amount of water depending up on the area to be cultivated. If the area to
be cultivated is large, the amount of water required will be more; on the other hand if area is small
the amount of water required will be less. The total quantity of water required by the crop for its full
growth may be expresses in ha-m. Thus the total depth of water (in cm) required by a crop to come to
maturity is called Delta.
Suppose certain amount of water is applied to a crop from a time of sowing till the crop matures and
if the applied water is not lost or used up by any means then there will be a thick layer of water
standing all over the field. The depth or height of this water layer is known as delta for the crop.
V
Δ=
A
where V is total volume of water required for the base period and A is command area.
Problem
If rice required about 8cm depth of water at an average interval of about 12days, and the crop period
for rice is 120days. Find out the delta of rice.
Solution
8cm of water at an average of 12 days
Water requirement = 8cm/12days = 0.6667cm/day
For 120 days [email protected]/day
Delta (Δ) =80cm.
The average values of delta for certain crops are shown below. Those values represent the total
water requirement of the crop on the field, actually can be less depending upon the useful
rainfall.
Crop
Delta on field cm
Sugarcane 120
120
Rice
120
Tobacco
75
Rice
120
Tobacco
75 60
Garden fruit
Tobacco
75
Garden
fruit
Cotton
Garden 50
fruit 60
60
Cotton 50 45
Vegetables
Cotton
50
Vegetables
Wheat 40 45
Vegetables
45
Wheat30
40
Barly
Wheat
40
Barly 30
Maize
25
Barly
30
Maize
Fodder25
22.5
Maize
25
Fodder
Peas
1522.5
Fodder
22.5
Peas 15
Peas
15
Relation between Duty and Delta
Assume a crop of base period B in days, D duty of water in hectare per cubic meters per second and
Δ be the delta or depth of water for a crop in meter.
From the definition of delta, duty and base period 1m3/s flowing continuously for B days mature D
hectares of land under the crop or 1m3/s continuously for B days gives a depth Δ over D hectares of
land.
The total amount of water applied to this crop during B days. By definition of duty:
𝑉 = [1 × 60 × 60 × 24 × 𝐵] m3
𝑉 = 86400𝐵 × 𝑀3
The depth of water applied on this land 1ha = 104 m2
∆=
𝑉
𝐴
=
86400𝐵
𝐷104
m=
8.64𝐵
𝐷
m
Where: B in days, Δ delta in m and D in ha/m3/s
Surface Irrigation
Definition
Surface irrigation has evolved into an extensive array of configurations which can be broadly
classified as:
(1) Basin irrigation; (2) border irrigation; (3) furrow irrigation; and (4) uncontrolled flooding.
There are two features that distinguish a surface irrigation system:
(a) The flow has a free surface responding to the gravitational gradient; and (b) the on-field
means of conveyance and distribution is the field surface itself.
Surface methods are classified by the slope, the size and shape of the field, the end conditions,
and how water flows into and over the field.
Each surface system has unique advantages and disadvantages depending on such factors as were
listed earlier like: (1) initial cost; (2) size and shape of fields; (3) soil characteristics; (4) nature
and availability of the water supply; (5) climate; (6) cropping patterns; (7) social preferences and
structures; (8) historical experiences; and (9) influences external to the surface irrigation system.