Remember me and also my parents in your pray friends

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Assala mu alykum My Name is saqib imran and I am the
student of b.tech (civil) in sarhad univeristy of
science and technology peshawer.
I have written this notes by different websites and
some by self and prepare it for the student and also
for engineer who work on field to get some knowledge
from it.
I hope you all students may like it.
Remember me in your pray, allah bless me and all of
you friends.
If u have any confusion in this notes contact me on my
gmail id: Saqibimran43@gmail.com
or text me on 0341-7549889.
Saqib imran.

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Water Resources and Irrigation Engineering
Lectures & Notes for Civil Engineers
Water Resource Engineering is a specific kind of civil engineering that involves the
design of new systems and equipment that help manage human water resources. Some
of the areas Water Resource Engineers touch on are water treatment facilities,
underground wells, and natural springs. Water Resources Engineering focuses on the
use and management of land and water resources in rural and urban watersheds.
Definition:
Irrigation is the controlled application of water to croplands. Its primary objective is to
create an optimal soil moisture regime for maximizing crop production and quality while
at the same time minimizing the environmental degradation inherent in irrigation of
agricultural lands. OR Irrigation is the application of water to the soil to supplement
natural precipitation and provide an environment that is optimum for crop production.
Well Irrigated crops produce more food.
Introduction & History of Irrigation Engineering
History of Irrigation Engineering
1. Ancient civilizations rose over irrigated areas
2. Egypt claims having the world's oldest dam, 108m long, 12m high, built 5,000 years ago

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3. 6,000 years ago, Mesopotamia supported as many as 25 million people.
4. The same land today with similar population depends on imported wheat for food
Introduction to Irrigation Engineering
Irrigation is the controlled application of water to croplands. Its primary objective is to create an
optimal soil moisture regime for maximizing crop production and quality while at the same time
minimizing the environmental degradation inherent in irrigation of agricultural lands. Irrigation is
thus critical for food security in semi-arid and arid areas.
Irrigation has two primary objectives:
1. To supply the essential moisture for plant growth; &
2. To leach or dilute salts from the soil.
Irrigation water management deals with the frequency of irrigation, depth of water to be applied,
and measures to increase the uniformity of applications. Irrigation management should be a set of
practices designed to maximize efficiencies and minimize the labor and capital requirements of a
particular irrigation system.
Role of Civil Engineers in Irrigation Engineering
Irrigation is a cross cutting sector that involves civil engineers, hydrologists, environmental
experts, land surveyors, agricultural scientists and others, civil and irrigation engineers were
important for successful irrigation schemes
 The supply of water at farm turnout
 Water storage in Dams
 Water conveyance
 Flood control
 Supplying water WHEN needed and by the QUANTITY needed – irrigation scheduling
e.g in Weirs, Barrages
 Hydraulic Structures - Headworks, Cross Drainage works
Types of Canal Lining

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There are varieties of linings that are available today but we will be discussing the following three:
1. Plain Cement Concrete Lining
2. Reinforced Cement Concrete Lining
3. Brick Lining
1. Plain Cement Concrete Lining
This lining is recommended for the canal in full banking. The cement concrete lining is widely
accepted. It can resist the effect of scouring and erosion very efficiently. The velocity of flow may
be kept above 2.5 m/s. It can eliminate completely growth of weeds. The lining is done by the
following steps:
(a) Preparation of sub-grade
The sub grade is prepared by ramming the surface properly with a layer of sand (about 15 cm).
Then slurry of cement and sand (1:3) is spread uniformly over the prepared bed.
(b) Laying of concrete
The cement concrete of grade M15 is spread uniformly according to the desired thickness,
(generally the thickness varies from 100mm to 150 mm). After laying, the concrete is tapped gently
until the slurry comes on the top. The curing is done for two weeks. As the concrete is liable to get
damaged by the change of temperature, the expansion joints are provided at appropriate places.
2. Brick Lining
This lining is prepared by the double layer brick flat soling laid with cement mortar (1:6) over the
compacted sub-grade. The first class bricks should be recommended for the work. The surface of
the lining is finished with cement plaster (1:3). The curing should be done perfectly.
This lining is always preferred for the following reasons:
 This lining is economical.
 Work can be done very quickly.
 Expansion joints are not required.
 Repair works can be done easily.
Bricks can be manufactured from the excavated earth near the site. However this lining has certain
disadvantages:
 It is not completely impervious.
 It has low resistance against erosion.
 It is not so much durable.

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3. Reinforced Cement Concrete Lining
Sometimes reinforcement is required to increase the resistance against cracks and shrinkage
cracks. The reduction in the cracks results in less seepage losses. However this reinforcement does
not increase the structural strength of the lining. This reinforcement adds 10 to 15 percent to the
cost and for this reason steel reinforcement is usually omitted except for very particular situations.
Irrigation Efficiency - Definition and Its Types
Definition
The ratio of the amount of water available (output) to the amount of water supplied (input) is
known as Irrigation Efficiency. It is expressed in percentage.
Types of Irrigation Efficiency
The following are the various types of irrigation efficiencies:
(a) Water Conveyance Efficiency (ηc):
It is the ratio of the amount of water applied, to the land to the amount of water supplied from the
reservoir. It is obtained by the expression,
ηc = Wl Wr × 100 Where, ηc = Water conveyance efficiency Wl = Amount of water applied to
land Wr = Amount of water supplied from reservoir
(b) Water Application Efficiency (ηa):
It is the ratio of the water stored in root zone of plants to the water applied to the land. It is obtained
by the expression,
ηa = Wz Wl × 100 Where, ηa = Water application efficiency Wz = Amount of water stored in root
zone Wl = Amount of water applied to land
(c) Water Use Efficiency (ηu):
It is the ratio of the amount of water used to the amount of water applied. It is obtained by the
expression,
ηu = Wu Wl × 100 Where, ηu = Water use efficiency Wu = Amount of water used Wl = Amount
of water applied to land

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(d) Consumptive use Efficiency (ηcu):
It is the ration of the consumptive use of water to the amount of water depleted from the root zone.
It is obtained by the expression, ηcu = Cu Wp × 100 Where,
ηcu = Consumptive use efficiency Cu = Consumptive use of water Wp = Amount of water depleted
from root zone
Methods of Improving and Factors Affecting
Duty of Water
Factors Affecting Duty of Water
The Factors Affecting Duty of Water in Irrigation are described below:
1. Soil Characteristics:
If the soil of the canal bed is porous and coarse grained, it leads to more seepage loss and
consequently low duty. If it consists of alluvial soil, the percolation loss will be less and the soil
retains the moisture for longer period and consequently the duty will be high.

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2. Climatic Condition:
When the temperature of the command area is high the evaporation loss is more and the duty
becomes low and vice versa.
3. Rainfall:
If rainfall is sufficient during the crop period, the duty will be more and vice versa.
4. Base Period:
When the base period is longer, the water requirement will be more and the duty will be low and
vice versa.
5. Type of Crop:
The water requirement for various crops is different. So the duty varies from crop to crop.
6. Topography of Agricultural Land:
If the land is uneven the duty will be low. As the ground slope increases the duty decreases because
there is wastage of water.
7. Method of Ploughing:
Proper deep ploughing which is done by tractors requires overall less quantity of water and hence
the duty is high.
8. Methods of Irrigation:
The duty of water is high in case of perennial irrigation system as compared to that in inundation
irrigation system.
9. Water Tax:
If some tax is imposed the farmer will use the water economically thus increasing the duty.
Methods of Improving Duty:
Various methods of improving duty are:
(1) Proper Ploughing:
Ploughing should be done properly and deeply so that the moisture retaining capacity of soil is
increased.

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(2) Methods of supplying water:
The method of supplying water to the agriculture land should be decided according to the field and
soil conditions. For example,
 Furrow method For crops sown ion rows
 Contour method For hilly areas
 Basin For orchards
 Flooding For plain lands
(3) Canal Lining:
It is provided to reduce percolation loss and evaporation loss due to high velocity.
(4) Minimum idle length of irrigation Canals:
The canal should be nearest to the command area so that idle length of the canal is minimum and
hence reduced transmission losses.
(5) Quality of water:
Good quality of water should be used for irrigation. Pollution en route the canal should be avoided.
(6) Crop rotation:
The principle of crop rotation should be adopted to increase the moisture retaining capacity and
fertility of the soil.
(7) Method of Assessment of water:
Particularly, the volumetric assessment would encourage the farmer to use the water carefully.
(8) Implementation of Tax:
The water tax should be imposed on the basis of volume of water consumption.

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Advantages and Disadvantages of Canal Lining
Advantages of Canal Lining
1. It reduces the loss of water due to seepage and hence the duty is enhanced.
2. It controls the water logging and hence the bad effects of water-logging are eliminated.
3. It provides smooth surface and hence the velocity of flow can be increased.
4. Due to the increased velocity the discharge capacity of a canal is also increased.
5. Due to the increased velocity, the evaporation loss also can be reduced.
6. It eliminates the effect of scouring in the canal bed
7. The increased velocity eliminates the possibility of silting in the canal bed.
8. It controls the growth of weeds along the canal sides and bed.
9. It provides the stable section of the canal.
10. It reduces the requirements of land width for the canal, because smaller section of the canal
can be used to produce greater discharge.
11. It prevents the sub-soil salt to come in contact with the canal water. 12. It reduces the
maintenance cost for the canals.
Disadvantages of Canal Lining
1. The initial cost of the canal lining is very high. So, it makes the project very expensive with
respect to the output.
2. It involves many difficulties for repairing the damaged section of lining.
3. It takes too much time to complete the project work.

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4. It becomes difficult, if the outlets are required to be shifted or new outlets are required to
be provided, because the dismantling of the lined section is difficult.
Sources of Irrigation Water - Ground Water &
Surface Water
The main source of irrigation water are:
Surface water:
It is found on the surface of the land. These include spring water, River water, lake water, etc. This
can be supplied to the field by weir (check dam) by gravity or by using pump. Check dam /wier/
system is used only when the source of water is from river, or spring water that starts from up
stream.
Where the slop of the source of water is greater than the slop of the field to be irrigated. Pumps
are used where the source of water for the field is at down stream (at lower altitude.) Here mostly
centrifugal type pumps are used.
Ground water:
Where these is shortage of surface water ground water is used for irrigation. This is supplied only
by using pumps.

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Definition, Types & Comparison of Open & Pipe
Flow
Definition:
It is usually the flow in an Open Channels
Surface Flow:
The flow which is above the ground level is called surface flow.
Ground Flow:
The flow which is below the surface of the earth is called ground flow.
Hydraulics:
Deals with the study of surface water only
Ground Flow:
Deals with the surface as well as ground water water.

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Differences between open and pipe flow
1. Open channel flow has a free water surface
2. Open channel flow is subjected to atmospheric pressure while pipe flow is not (when pipe
is full).
3. Open channel flow is not completely enclosed by boundaries, unlike pipe flow.
4. Open channel is always under the action of gravity, while pipe can be under gravity or may
flow due to some external pressure.
Partially filled pipes flow:partially filled pipes have flow which is not enclosed on all sides and
air is present above it so is under atmospheric pressure.
Open Channel flow (Free Gravity flow):
Open Chanel flow is that type of flow which is neither completely enclosed by the boundaries
nor is under any external pressure but gravity. It is subjected to atmospheric pressure. e.g. Rivers,
natural and artificial canals, streams, channels etc. Partially filled pipes flow is also an example
of open channel flow.
Types of open channel flow
Steady Flow:
For open channel, the flow is steady if the depth of flow does not change with respect to time at a
particular location or section.
Unsteady flow:
For open channel, the flow is unsteady if the depth of flow changes with respect to time at a
particular location or section.
Uniform flow:
For open channel flow, the flow is uniform if the depth of flow remains constant along a certain
length of the channel.
Non Uniform flow:
For open channel flow, the flow is non uniform if the depth of flow does not remains constant
along a certain length of the channel.

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Gradually Varied flow:
If the depth of flow changes over a relatively long distance along the length of a channel, then
the flow is called gradually varied flow.
Rapidly Varied flow:
If the depth of flow changes over a relatively short distance along the length of a channel, then
the flow is called rapidly varied flow.
Why to study open channel flow: For construction of successful hydraulic
structures.
Open channel flow is difficult to deal with because:
 Difficult to secure reliable experimental data
 Are of different and irregular X-sections and shapes
Friction co-efficient is choiced by great uncertainty
Shapes, Types & Properties of Open Channels

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Open channel can be said to be as the deep hollow surface having usually the top surface open to
atmosphere. Open channel flow can be said to be as the flow of fluid (water) over the deep
hollow surface (channel) with the cover of atmosphere on the top. Examples of open channels
flow are river, streams, flumes, sewers, ditches and lakes etc. we can be said to be as open
channel is a way for flow of fluid having pressure equal to the atmospheric pressure. While on
the other hand flow under pressure is said to be as pipe flow e.g. flow of fluid through the sewer
pipes.
Open-channel flow is usually categorized on the basis of steadiness. Flow is said to be steady
when the velocity at any point of observation does not change with time; if it changes from time
to time, flow is said to be unsteady. At every instant, if the velocity is the same at all points along
the channel, flow is said to be uniform; if it is not the same, flow is said to be non-uniform. Non-
uniform flow which is also steady is called as varied flow; non-uniform flow which is unsteady
is called as variable flow. Flow occurs from a higher to a lower concentration by aid of gravity.
Shapes of open channels
Usually the man made and artificial open channels don't have rectangular cross section. The most
common shapes of open channels are circular and trapezoidal.
Types of open channel
Open Channels are classified as:
1. Rigid boundary open channels
2. Loose boundary open channels
3. Prismatic open channels
Rigid boundary open channels can be said to be as the open channels with the non-changeable
boundaries. While on the other hand if open channel has the boundaries which changes due to
scouring action or deposition of sediments, such channels are said to be as loose boundary open
channels. The open channels in which shape, size of cross section and slope of the bed remain
constant are said to be as the prismatic channels. Opposite o these channels are non-prismatic
channels. Natural channels are the example of non-prismatic channels while man made open
channels are the example of prismatic channels.
Properties of Open Channels:

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In open channels flow usually occur due to the slope of channel bottom and the slope of liquid
surface. The main difference in the open channel flow and pipe flow is that in pipe flow usually
the cross section of channel is fixed and confined while on the other hand open channel flow is
unconfined. Open channels flow is difficult to analyze than the pipe flow. That's why in open
channel flow measurement empirical approach is adopted. The velocity of flow in open channel
can be computed by help of Manning's formula:
V = 1/n x R0.66 x S0.5
In pipe flow the conduit (pipe for movement of fluid) usually completely fills with water for the
development of pipe pressure, while in the conduit which is partially filled can have open
channel flow. There is no restriction for the conduit in case of open channel flow to be
completely filled.
Factors influencing the flow in open channels:
1. Channel shape
2. Fluid depth
3. Fluid velocity
4. Slope of channel
Flow measurement in open channel
The most common method which is used for the measurement of flow in open channel is to
measure the height of the liquid as it passes over an obstruction (a flume or weir) in the open
channel. This is usually done by constructing hydraulic structures like weirs, notches and flumes
etc Manning approach can be used for flow measurement in open channels.

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Management of Water Logging & Salinity in
Pakistan
Water logging and Salinity:
The irrigation system in Pakistan has brought great benefits to many people. Dependence on the
natural hydrological system has been minimized and new settlements in canal irrigated areas have
been established. However, the canal system has been accompanied by problems, which are
increasingly difficult to overcome.
Water logging and salinity are two of the outcomes of canal irrigation in Pakistan. When only
inundation canals were used, water for crops was only available during the summer season. A
balance was maintained between the precipitation and evapo-transpiration that kept the water-table
low. With the introduction of perennial canals, water was available throughout the year resulting
in a rise of the water-table. Salts in the soil also rise to the surface with the water-table.
The water on reaching the surface evaporates and the salts are deposited on the surface, rendering
the land unsuitable for farming. The rise of the water-table to the surface level is called water
logging and the appearance of salty patches is called salinity.
Management of Water Resources:

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Ther is a scarce resource in Pakistan. Its storage, ibution and use have to be carefully managed in
order me Water Accord was not followed resulting in disputes between the provinces and a
decrease in the agricultural output. As Pakistan is predominancy an agricultural country, the
scarcity of water resources may affect Pakistan's economy negatively. order to conserve the scarce
water resources, the following steps should be taken; National priorities such as the maximisation
of agricultural production should be considered with regard to the distribution of water between
the provinces.
Sites for small dams should be developed to store surplus flow during the monsoon season. Small
dams are more cost effective and produce quick results compared with large dams because they
are constructed in a shorter period of time are cheaper to build and easy to maintain. In order to
avoid water loss from unlined canals, a crash program should be launched to line the canals with
cement. Fresh water sources like rivers and lakes should not be used as dumping sites of solid and
liquid waste. Natural fresh water lakes should be conserved to develop local water sources.
In Sindh, the Manchar, Kinjhar and Haleji lakes are the worst affected by pollution. Ground water
contamination should be prevented as far as possible by controlling the seepage of toxic waste into
the ground. A public education and information programme should be launched to influence the
attitudes of the people towards the need to conserve water because it is a diminishing natural
resource. The media, NGOs and educational institutions should take part in this programme.
Methods of Estimation of Consumptive Use of
Water

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Consumptive water use is water removed from available supplies without return to a water
resource system (e.g., water used in manufacturing, agriculture, and food preparation that is not
returned to a stream, river, or water treatment plant).
To measure or estimation the consumptive use there are three main methods:
1. Direct Methods/Field Methods
2. Empirical Methods
3. Pan evaporation method
1. Direct Methods:
In this method field observations are made and physical model is used for this purpose. This
includes,
i. Vapour Transfer Method/Soil Moisture Studies
ii. Field Plot Method
iii. Tanks and Lysimeter
iv. Integration Method/Summation Method
v. Irrigation Method
vi. Inflow Outflow Method
1.1 Vapour Transfer Method:
In this method of estimation of water consumptive use, soil moisture measurements are taken
before and after each irrigation. The quantity of water extracted per day from soil is computed for
each period. A curve is drawn by plotting the rate of use against time and from this curve, the
seasonal use can be estimated. This method is suitable in those areas where soil is fairly uniform
and ground water is deep enough so that it does not affect the fluctuations in the soil moisture
within the root zone of the soil.
It is expressed in terms of volume i.e. Acre-feet or Hectare-meter
1.2 Field Plot Method:
We select a representative plot of area and the accuracy depends upon the representativeness of
plot (cropping intensity, exposure etc).It replicates the conditions of an actual sample field (field
plot). Less seepage should be there.
Inflow + Rain + Outflow = Evapotranspiration
The drawback in this method is that lateral movement of water takes place although more
representative to field condition. Also some correction has to be applied for deep percolation as it
cannot be ascertained in the field.

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1.3 Tanks and Lysimeter:
In this method of measurement of consumptive use of water, a watertight tank of cylindrical shape
having diameter 2m and depth about 3m is placed vertically on the ground. The tank is filled with
sample of soil. The bottom of the tank consists of a sand layer and a pan for collecting the surplus
water. The plants grown in the Lysimeter should be the same as in the surrounding field. The
consumptive use of water is estimated by measuring the amount of water required for the
satisfactory growth of the plants within the tanks. Consumptive use of water is given by,
Cu = Wa - Wd
Where,
Cu = Consuptive use of water
Wa = Water Applied
Wd = Water drained off
Lysimeter studies are time consuming and expensive. Methods 1 and 2 are the more reliable
methods as compare to this method.
1.4 Integration Method:
In this method, it is necessary to know the division of total area, i.e. under irrigated crops, natural
native vegetation area, water surface area and bare land area. In this method, annual consumptive
use for the whole area is found in terms of volume. It is expressed in Acre feet or Hectare meter.
Mathematically,
Total Evapotranspiration = Total consumptive usex
Total Area Annual Consumptive Use = Total Evapotranspiration = A+B+C+D Where,
A = Unit consumptive use for each cropxits area
B = Unit consumptive use of native vegetation xits area
C = Water surface evaporationxits area
D = Bare land evaporationxits area
1.5 Irrigation Method:
In this method, unit consumption is multiplied by some factor. The multiplication values depend
upon the type of crops in certain area. This method requires an Engineer judgment as these factors
are to be investigated by the Engineers of certain area.
1.6 Inflow Outflow Method:
In this method annual consumptive use is found for large areas. If U is the valley consumptive use
its value is given by,

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U = (I+P) + (Gs - Ge) - R
Where,
U = Valley consumptive use (in acre feet or hectare meter)
I = Total inflow during a year
P = Yearly precipitation on valley floor
Gs = Ground Storage at the beginning of the year
Ge = Ground Storage at the end of the year
R = Yearly Outflow
All the above volumes are measured in acre-feet or hectare-meter.
2. Empirical Methods:
Empirical equations are given for the estimation of water requirement. These are,
2.1 Lowry Johnson Method:
The equation for this method is,
U = 0.0015 H + 0.9 (Over specified)
U = Consumptive Use
H = Accumulated degree days during the growing season computed from maximum temperature
above 32 °F
2.2 Penman Equation:
According to this method,
U = ET = AH + 0.27 EaA - 0.27
ET = Evapotranspiration or consumptive use in mm Ea = Evaporation (mm/day)
H = Daily head budget at surface (mm/day)
H is a function of radiation, sunshine hours, wind speed, vapour pressure and other climatic
factors.
A = Slope of saturated vapour pressure curve of air at absolute temperature in °F
2.3 Hargreave’s Method:
It is a very simple method. According to this method,
Cu = KEp

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Where,
Cu = Consumptive Use coefficient (varies from crop to crop)
Ep = Evapotranspiration K = Coefficient
Design of Precast Parabolic Channels in
Peshawar
Introduction to Project of Precast Parabolic Channels
 Canal irrigation system of Pakistan represents one of the largest system.
 Discrepancy feature is the conveyance losses (35 to 50%)
 Irrigation system of KPK (Province of Pakistan) is facing severe Operational problems
including water scarcity, water logging, and salinity.
 Reason was due to the traditional brick lining.
Steps to design Precast Parabolic Channels
The following steps are involved in the design of our selected water channel.
 Collection of field data.
 Using design software
 Obtaining the final design parameters
Site Selection
 Site selected was Syphon (Badabher, Peshawar, Pakistan)
 Selected channel was off taking from Warsak canal at RD 96+000 feet

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 Name of channel Badabher Akkundi BalaKhel
 CCA 2000 Gareb (Full channel)
 Selected watercourse was earthen
 Wheat and maize were the prime crops of the area
Collection of field data
Instruments
 Common survey equipments
Methodology
 Measurement of Full supply level of the channel (FSL)
 Measurement of Bed level of channel
 Measurement of Full Supply Level at crest
 Measurement of Crest level of channel
 Measurement of FSL at RD 0+00
 Measurement of Bed level at 0+00
In addition to above following data was collected at each 30 meter interval of channel. FSL of
channel
 Bed level of channel
 Left bank (L/B) and Right bank (R/B) of channel
 Highest field elevation
 RD's of Nuccas recorded along the channel.
Using Design Software
 Super Calc 5
 DOS version
 Renowned software for designing channels
 INPUTS
 Bed reduced level
 HFL
 CCA
 Discharge (Q)
Conclusions
 Super Calc provides excellent graphical presentation
 MS Excel spreadsheet used for both Brick lining and PCPS
 PCPL much cheaper than brick lining
 9 drops provided

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Construction of Open Wells
How to construct water wells?

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A water well is a lot more than a drilled hole, but for many people, the above ground part of the
drilling process is the only part they see. A water well is a specially engineered hole in the ground;
For ground water monitoring, or for scientific research purposes, wells may be drilled in a way
that allows the specialists to closely examine the rock formations and take frequent water samples.
Augured wells and diamond core drilling are drilling techniques often used for scientific purposes.
Most home wells are drilled to 8 or 6 inches in diameter. Municipal or irrigation wells are likely
to be drilled at larger diameters, sometimes as much as 24 inches or more. The important tasks for
preparing a planning report of a water resources project would include the following:
1. Analysis of basic data like maps, remote sensing images, geological data, hydrologic
data, and requirement of water use data, etc.
2. Selection of alternative sites based on economic aspects generally, but keeping in mind
environmental degradation aspects.
o Studies for dam, reservoir, diversion structure, conveyance structure, etc.
o Selection of capacity.
o Selection of type of dam and spillway.
o Layout of structures.
o Analysis of foundation of structures.
o Development of construction plan.
o Cost estimates of structures, foundation strengthening measures, etc.
3. Studies for local protective works – levees, riverbank revetment, etc.
4. Formulation of optimal combination of structural and non-structural components (for
projects with flood control component).
5. Economic and financial analyses, taking into account environmental degradation, if any,
as a cost.
6. Environmental and sociological impact assessment.

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What is Consumptive Use of Water and Factors
Affecting it
Definition:
It is the quantity of water used by the vegetation growth of a given area. It is the amount of water
required by a crop for its vegetated growth to evapotranspiration and building of plant tissues
plus evaporation from soils and intercepted precipitation. It is expressed in terms of depth of
water. Consumptive use varies with temperature, humidity, wind speed, topography, sunlight
hours, method of irrigation, moisture availability.
Mathematically,
Consumptive Use = Evapotranspiration = Evaporation + transpiration It is expressed in terms of
depth of water.
Factors Affecting the Consumptive Use of Water

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Consumptive use of water varies with:
1. Evaporation which depends on humidity
2. Mean Monthly temperature
3. Growing season of crops and cropping pattern
4. Monthly precipitation in area
5. Wind velocity in locality
6. Soil and topography
7. Irrigation practices and method of irrigation
8. Sunlight hours
Types of Consumptive Water Use
Following are the types of consumptive use,
1. Optimum Consumptive Use
2. Potential Consumptive Use
3. Seasonal Consumptive Use
1. Optimum Consumptive Use:
It is the consumptive use which produces a maximum crop yield.
2. Potential Consumptive Use:
If sufficient moisture is always available to completely meet the needs of vegetation fully
covering the entire area then resulting evapotranspiration is known as Potential Consumptive
Use.
3. Seasonal Consumptive Use:
The total amount of water used in the evapo-transpiration by a cropped area during the entire
growing season.

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Definition and Types of Cross Drainage Works
Definition:
A cross drainage work is a structure carrying the discharge from a natural stream across a canal
intercepting the stream. Canal comes across obstructions like rivers, natural drains and other
canals. The various types of structures that are built to carry the canal water across the above
mentioned obstructions or vice versa are called cross drainage works. It is generally a very costly
item and should be avoided by:
 Diverting one stream into another.
 Changing the alignment of the canal so that it crosses below the junction of two streams.
Types of cross drainage works
Depending upon levels and discharge, it may be of the following types:
Cross drainage works carrying canal across the drainage:

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the structures that fall under this type are:
1. An Aqueduct
2. Siphon Aqueduct
Aqueduct:
When the HFL of the drain is sufficiently below the bottom of the canal such that the drainage
water flows freely under gravity, the structure is known as Aqueduct.
 In this, canal water is carried across the drainage in a trough supported on piers.
 Bridge carrying water
 Provided when sufficient level difference is available between the canal and natural and canal bed
is sufficiently higher than HFL.

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Siphon Aqueduct:
In case of the siphon Aqueduct, the HFL of the drain is much higher above the canal bed, and
water runs under siphonic action through the Aqueduct barrels.
The drain bed is generally depressed and provided with pucci floors, on the upstream side, the
drainage bed may be joined to the pucca floor either by a vertical drop or by glacis of 3:1. The
downstream rising slope should not be steeper than 5:1. When the canal is passed over the drain,
the canal remains open for inspection throughout and the damage caused by flood is rare. However
during heavy floods, the foundations are susceptible to scour or the waterway of drain may get
choked due to debris, tress etc.

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Cross drainage works carrying drainage over canal.
The structures that fall under this type are:
 Super passage
 Canal siphon or called syphon only
Super passage:
 The hydraulic structure in which the drainage is passing over the irrigation canal is known
as super passage. This structure is suitable when the bed level of drainage is above the
flood surface level of the canal. The water of the canal passes clearly below the drainage
 A super passage is similar to an aqueduct, except in this case the drain is over the canal.
 The FSL of the canal is lower than the underside of the trough carrying drainage water.
Thus, the canal water runs under the gravity.
 Reverse of an aqueduct
Canal Syphon:
 If two canals cross each other and one of the canals is siphoned under the other, then the
hydraulic structure at crossing is called “canal siphon”. For example, lower Jhelum canal
is siphoned under the Rasul-Qadirabad (Punjab, Pakistan) link canal and the crossing
structure is called “L.J.C siphon”
 In case of siphon the FSL of the canal is much above the bed level of the drainage trough,
so that the canal runs under the siphonic action.
 The canal bed is lowered and a ramp is provided at the exit so that the trouble of silting is
minimized.
 Reverse of an aqueduct siphon
 In the above two types, the inspection road cannot be provided along the canal and a
separate bridge is required for roadway. For economy, the canal may be flumed but the
drainage trough is never flumed.

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Classification of aqueduct and
siphon aqueduct
Depending upon the nature of the sides of the aqueduct or siphon aqueduct it may be classified
under three headings:
Type I:
Sides of the aqueduct in earthen banks with complete earthen slopes. The length of culvert should
be sufficient to accommodate both, water section of canal, as well as earthen banks of canal with
aqueduct slope. Sides of the aqueduct in earthen banks, with other slopes supported by masonry
wall. In this case, canal continues in its earthen section over the drainage but the outer slopes of
the canal banks are replaced by retaining wall, reducing the length of drainage culvert.
Type II:
Sides of the aqueduct made of concrete or masonry. Its earthen section of the canal is discontinued
and canal water is carried in masonry or concrete trough, canal is generally flumed in this section.

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Water Resources of Pakistan and Hydraulic
Structures in Pakistan
Water Budget of Pakistan
According to the United Nations' "UN World Water Development Report", the total actual
renewable water resources decreased from 2,961 m³ per capita in 2000 to 1,420 m³ per capita in
2005. A more recent study indicates an available supply of water of little more than 1,000 m³ per
person, which puts Pakistan in the category of a high stress country. In view of growing population,
urbanization and increased industrialization, the situation is likely to get worse.
In addition, increasing pollution and saltwater intrusion threaten the country's water resources.
About 36% of the groundwater is classified as highly saline.
In urban areas, most water is supplied from groundwater except for the cities of Karachi,
Hyderabad and a part of Islamabad, where mainly surface water is used. In most rural areas,
groundwater is used. In rural areas with saline groundwater, irrigation canals serve as the main
source of domestic water. Out of the 169,384 billion m³ of water which were withdrawn in 2000,
96% were used for agricultural purposes, leaving 2% for domestic and another 2% for industrial
use. This shows the significance of agriculture in the country. Pakistan still has the world's largest

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interconnected & Continous irrigation system. In 1999-2000, the total irrigated area in Pakistan
was 181,000 km². Pakistan has one of the world’s largest gravity-flow irrigation systems, with:
1. Three reservoirs
2. 19 barrages
3. 12 river interlinking canals and
4. 59,200 kilometers of distribution canals.
More than 160,000 watercourses comprise the distribution network that takes water directly to the
farms. More than half of these watercourses are in Punjab—the largest of the country’s four
provinces and the biggest agricultural producer. The system commands a land area of 14.3 million
hectares, making it the backbone of Pakistan’s agriculture and contributes one-fourth of country’s
total gross domestic product (GDP). About 29% of water is generated through hydropower.
Major Barrages of Pakistan
Key facts
Barrage
Year of
Completion
Max. Design
Discharge
(cusecs)
No. of
Bays
Max. Flood
level from
floor(ft)
Total Design
Withdrawals for
Canal (cusecs)
Chashma 1971 1,100,000 52 37 26,700
Guddu 1962 1,200,000 64 26 -
Jinnah 1946 950,000 42 28 7,500
Kotri 1955 875,000 44 43.1 -
Sukkur 1932 1,500,000 54 30 47,530
Taunsa 1959 750,000 53 26 36,501

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Crop Water Requirement in Irrigation and
Evaluation of Water Losses
It is defined as, "The quantity of water required by a crop in a given period of time for normal
growth under field conditions." It includes evaporation and other unavoidable wastes. Usually
water requirement for crop is expressed in water depth per unit area.
IRRIGATION WATER NEED = Crop water need — available rain fall
The first thing you need to consider when planning your garden is what growing zone you live in.
This is based on both the temperature range of your climate and the amount of precipitation. Take
a close look at the area in which you are going to plant your garden. If the ground tends to be very
moist, choose plants that can tolerate constantly wet soil, and even standing water.
If you live in an area that suffers from frequent droughts, however, select plants that can tolerate
going long periods without water, especially in light of the frequent watering restrictions imposed
on such areas. If you are lucky enough to live in an area that has a balanced climate, you have a
wider range of choices for your plants.
Low Water Requirement Plants
Plants that require low levels of water are often called drought tolerant. Drought-tolerant plants
can thrive in hot, dry conditions with very little water. They include both perennials and annuals.
Most drought-tolerant plants only have to be hand-watered when they are planted and while they
are establishing themselves. After that, they can be left to the natural cycle of the elements. Popular

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drought tolerant trees include the red cedar. live oak, crape myrtle, and the windmill and saw
palmetto palm trees. All citrus trees are also drought tolerant. Many homeowners in areas prone to
drought, such as parts of the southern United States, use shrubs and ground covering vines as part
of their landscaping. These include Texas sage, orange jasmine and Chinese fountain grass. There
are not many perennial drought-tolerant plants, but amaryllis is one that is very popular, along with
the African iris. Popular drought-tolerant annuals include marigold, cosmos and the Dahlberg
daisy.
Mid-Level Water Requirement Crops
Most plants land in this range when it comes to water requirements. These plants do not need to
be watered every day, but they need to be watered when the soil has been dry for over a week or
two. Sometimes these plants are classified as plants lying in the "occasional water zone". These
include popular plants such as geraniums, most roses, wisteria, clematis and other vine plants,
sunflowers, spring flowering bulbs, and most flowering perennial shrubs. Note that flowering
annuals planted in containers will need watering at least once or twice a week, while annuals
planted in the ground will need watering less often.
High Water Requirement Plants
Some plants require large amounts of water. These plants typically grow in marshy areas or bogs,
or along the banks of rivers, streams and lakes. The soil for these plants should always be kept
moist. Standing water is not a concern for these plants, so you don't have to worry about root rot.
Perennials are especially good for wet areas because they don't have to be replanted year after year,
which can be difficult in marshy areas. Popular perennials for wet soil include iris plants, cannas,
bee balms, ferns, and bog salvia. Aquatic mint is a pleasant ground cover that likes wet soil. The
red osier dogwood does very well in wet conditions. Most annual flowering plants also do well in
constantly moist soil.

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Water Requirement of Different Crops
Amount of water required by a crop in its whole production period is called water requirement.
The amount of water taken by crops vary considerably. What crops use more water and which
ones less.......
Crop Water Requirement
(mm)
Rice 900-2500
Wheat 450-650
Sorghum 450-650
Maize 500-800
Sugarcane 1500-2500
Groundnut 500-700
Cotton 700-1300
Soybean 450-700
Tobacco 400-600
Tomato 600-800
Potato 500-700
Onion 350-550
Chillies 500
Sunflower 350-500
Castor 500
Bean 300-500
Cabbage 380-500
Pea 350-500
Banana 1200-2200
Citrus 900-1200
Pineapple 700-1000
Gingelly 350-400
Ragi 400-450
Grape 500-1200
Irrigation Crop Water Requirement
This case study shows how to calculate the total water requirement for a command area (irrigation
blocks) under various crops, soil textures and conveyance loss conditions. In order to evaluate the
required irrigation gift for the entire command area a simple water balance has to be set-up. The
total water demand for each irrigation block and the crops in each block are calculated by summing
the following components:
 infiltration (percolation loss) through the soil (I)
 seepage (conveyance loss) through the channel (S)
 maximum evapo-transpiration of the crop (ETm)

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In this exercise, the irrigation water requirement is calculated for a 10-day period during the harvest
stage.
Evaluation of Percolation loss (I)
The command area is divided in irrigation blocks. First, these irrigation blocks are crossed with
the soil texture map to determine the area of each soil texture class in each block. Percolation
losses differ per soil texture class so a table with the following percolation data is created:
Texture Percolation loss (mm/day)
Clay 4
Loam 12
Sandy clay 14
Clay loam 7
The percolation table is joined with the cross table to get the percolation for each soil texture class
in each block. The amount of water loss for each soil texture class per block is calculated with
a tabcalc statement. In order to get the total percolation loss per block the results of the previous
operation are aggregated.
Evaluation of Conveyance loss (S)
Conveyance losses are calculated in about the same way as the percolation losses. First, the map
with the irrigation blocks is crossedwith the channel distribution map. The conveyance loss per
meter channel length differs per channel type and is 0.2 m³ per day for clay channels and 0.01 m³
per day for concrete channels. A new table indicating water loss per channel type is created
and joined to the cross table. The amount of water loss for each type of channel per block is
calculated with a simple tabcalc formula. Finally the results are aggregated to evaluate the total
conveyance loss per irrigation block.
Evaluation of maximum evapo-transpiration (ETm)
Crop water requirements are normally expressed by the rate of evapotranspiration (ET). The
evaporative demand can be expressed as the reference crop evapotranspiration (ETo) which
predicts the effect of climate on the level of crop evapotranspiration. In this case study the ETo is
8 mm/day. Empirically-determined crop coefficients (kc) can be used to relate ETo to maximum
crop evapotranspiration (ETm) when water supply fully meets the water requirement of the crop.
The value of kc varies with crop and development stage. The kc values for each crop and
development stage are available in a table.
For a given climate, crop and crop development stage, the maximum evapotranspiration (ETm) in
mm/day of the period considered is:
ETm = kc * ETo

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Maximum evapo-transpiration refers to conditions when water is adequate for unrestricted growth
and development under optimum agronomic and irrigation management. Maximum
evapotranspiration is calculated in this case study by crossing the irrigation block map with the
map that shows the different crop types in the command area, joining the cross table with the kc
table and by applying the maximum evapotranspiration formula with a tabcalc statement.
Water balance calculation (S+I+ETm)
The required irrigation gift for the entire command area is equal to the sum of water losses due to
infiltration through the soil (I), seepage through the channel (S) and maximum evapotranspiration
(ETm) for each block. The total amount of water requirement in harvest period for each block
is reclassified in irrigation classes using the following table:
Upper boundary Irrigation class
4000 1
6000 2
8000 3
10000 4
12000 5
14000 6
Finally, you will create a script to automate the calculation procedure. With the script, you can
easily calculate the water requirements for other growing stages.

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Importance of Irrigation Engineering - Purposes,
Objectives and Benefits
 In the next 35-45- years, world food production will need to double to meet the demands
of increased population.
 90% of this increased food production will have to come from existing lands.
 70% of this increased food production will have to come from irrigated land
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

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 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 famine
3. Cultivation of superior crops
4. Elimination of mixed cropping:
5. Economic development
6. Hydro power generation
7. Domestic and industrial water supply:

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Evapotranspiration Measurement by Blaney
Criddle & Hargreaves
Blaney-Criddle Formula
The estimation of potential evapotranspiration is achieved by adopting empirical approaches,
such as the Thornthwaite equation, the Blaney-Criddle formula and the Hargreaves method, all
having as a requirement the availability of temperature data. The data set is made up of temperature
time series, obtained from gauging stations.
The potential evapotranspiration estimated for each station using the above-mentioned methods is
spatially integrated, in order to obtain the areal potential evapo-transpiration. The methods adopted
for the spatial integration of the point estimates are the Kriging method, the method of Inverse
Distance Weighting, the Spline method and the Thiessen method, using applications in a
Geographic Information System (GIS) with a spatial resolution of 200x200m2
.
u k (k ) (t x p) / 100
TR = kc kt) u = monthly consumptive use (inches)

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kt = climatic coefficient
= 0.173 * t - 0.314
kc = crop growth stage coefficient
t = mean monthly air temperature (°F)
p = monthly percentage of annual daylight hours
Hargreaves Method of measurement of
Evapotranspiration
Originally developed in 1975
 solar radiation and temperature data inputs
 Updated in 1982 and 1985
 solar radiation estimated from extraterrestrial radiation, RA
 Grass reference ET
 May be used to compute daily estimates, but more accurate over longer time steps: 10-
days, monthly
ETo ? 0.0023(Tmax ? Tmin T ?17.8) R
ETo = grass reference ET (mm/day)
Tmax = maximum daily air temperature (°C)
Tmin = minimum daily air temperature (°C)
Tmean = mean daily air temperature = (Tmax + Tmin) / 2
Ra = extraterrestrial radiation (mm/day)
Ra (mm/day) = Ra (MJ/m2/day) / 2.45
 Simple, easy to use
 Data required—maximum and minimum air temperature
 Better predictive accuracy in arid climates than modified Blaney-Criddle
 Max-min temperature difference
 Extra-terrestrial radiation
 Underpredictal in windy or high advection conditions—requires local calibration

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Methods & Techniques of Irrigation
There are three broad classes of irrigation systems:
1. Pressurized distribution
2. Gravity flow distribution
3. Drainage flow distribution.
1. Pressurized Distribution
The pressurized systems include sprinkler, trickle, and the array of similar systems in which water
is conveyed to and distributed over the farmland through pressurized pipe networks. There are
many individual system configurations identified by unique features (centre-pivot sprinkler
systems).
2. Gravity Flow Irrigation System
Gravity flow systems convey and distribute water at the field level by a free surface, overland flow
regime. These surface irrigation methods are also subdivided according to configuration and
operational characteristics.

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3. Control of drainage flow irrigation System
Irrigation by control of the drainage system, sub-irrigation, is not common but is interesting
conceptually. Relatively large volumes of applied irrigation water percolate through the root zone
and become a drainage or groundwater flow. By controlling the flow at critical points, it is possible
to raise the level of the groundwater to within reach of the crop roots. These individual irrigation
systems have a variety of advantages and particular applications.
Irrigation systems are often designed to maximize efficiencies and minimize labour and capital
requirements. The most effective management practices are dependent on the type of irrigation
system and its design. For example, management can be influenced by the use of automation, the
control of or the capture and reuse of runoff, field soil and topographical variations and the
existence and location of flow measurement and water control structures.
Questions that are common to all irrigation systems are when to irrigate, how much to apply, and
can the efficiency be improved. A large number of considerations must be taken into account in
the selection of an irrigation system. These will vary from location to location, crop to crop, year
to year, and farmer to farmer.
Compatibility of the irrigation systems:
The irrigation system for a field or a farm must be compatible with the other existing farm
operations, such as land preparation, cultivation, and harvest.
 Level of Mechanization
 Size of Fields
 Cultivation
 Pest Control
 Topographic Limitations.

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Restrictions on irrigation system selection due to topography include:
1. groundwater levels
2. the location and relative elevation of the water source,
3. field boundaries,
4. acreage in each field,
5. the location of roads
6. power and water lines and other obstructions,
7. the shape and slope of the field
Methods of Irrigation
Under gravity irrigation, water is distributed by means of open canals and conducts with out
pressure. Gravity irrigation methods are less expensive, but requires more skill and experience to
achieve re-scannable efficiency. This method also requires that the land to be irrigated should
have a flatter slope, other wise the cost of land leveling and preparation at times be come very
high. Gravity irrigation method. Includes furrow, boarder, basin, wild- flooding and corrugation.
1. Furrow irrigation
In this method of surface irrigation, water is applied to the field by furrow which are small canals
having a continuous our nearly uniform slope in the direction of irrigation. Water flowing in the
furrow into the soil spreads laterally to irrigate the area between furrows. The rate of lateral spread
of water in the soil depends on soil type.i.e. For a given time, water will infiltrate more vertically
and less laterally in relatively sandy soils than in clay soil.
Where the land grade is less than 1% in the direction of furrow, striate graded furrows may be
adapted. The grade can be as much as 2 to 3% depending on the soil type and the rainfall intensity,
which affects erosion. When field sloped is too steep to align the furrows down the slope, control
furrows which run along curved routed may be used. Spacing of furrows depends on the crop type
and the type of machinery used for cultivation and planting. Length of furrows depends largely on
permeability of the soil, the available labor and skill, and experiences of the irrigation. Flow
rates are related to the infiltration to the rate of the soil.
Longitudinal slope of furrow depends up on the soil type, especially its errodability and the
velocity of flow. Slope may be related to discharge as follows.
slope % 0.25 0.5 0.75 1.0 1.5 2.0
Qmax (m3/hr) 9.0 4.5 3.0 2.2 1.5 1.1

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2. Boarder - strip Irrigation
The farms are divided into number of strips of 5 to 20 meters wide and 100 to 400 meters long.
Parallel earth bunds or levees are provided in order to guide the advancing sheet of water.
Recommended safe limits of longitudinal slope also depends on the soil texture:
Sandy loam to sandy soils 0.25 - 0.6%
Medium loam soils 0.2 - 0.4%
Clay to clay loam soils 0.05 - 0.2%
3. Basin irrigation
Large stream of water is applied to almost level and smaller unit of fields which are surrounded
by levees or bunds. The applied water is retained in the basin until it filtrates. Soil type, stream
size and irrigation depth are the important factors in determining the basin area.
Method of irrigation Type of Crop suited
Border strip method Wheat, Leafy vegetables, Fodders
Furrow method Cotton, Sugarcane, Potatoes
Basin method Orchard trees
4. Wild flooding
Water is applied all over the field especially, before plowing for soil that can't be plowed when
dry. Under closed conduit- there are two types of irrigation
1. Sprinkler
2. Drip irrigation

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1. Sprinkler irrigation:
It is mostly used for young growth, to humid the atmosphere, for soil compaction( specially for
sandy loam soils before planting, for land having up and down slope and used to wash out plant
leaves especially in dusty area.
Sprinkler irrigation offers a means of irrigating areas which are so irregular that they prevent use
of any surface irrigation methods. By using a low supply rate, deep percolation or surface runoff
and erosion can be minimized. Offsetting these advantages is the relatively high cost of the
sprinkling equipment and the permanent installations necessary to supply water to the sprinkler
lines. Very low delivery rates may also result in fairly high evaporation from the spray and the
wetted vegetation. It is impossible to get completely uniform distribution of water around a
sprinkler head and spacing of the heads must be planned to overlap spray areas so that distribution
is essentially uniform
Advantages
 Economical to labour & uniform distribution.
2. Drip irrigation
This is used especially where there is shortage of water and salt problem. The drip method of
irrigation, also called trickle irrigation. The method is one of the most recent developments in
irrigation. It involves slow and frequent application of water to the plant root zone and enables the
application of water and fertilizer at optimum rates to the root system.
It minimizes the loss of water by deep percolation below the root zone or by evaporation from the
soil surface. Drip irrigation is not only economical in water use but also gives higher yields with
poor quality water.
Advantages
 No loss. of water because all water drops at root zone.
 No water logging and rise of water table at result salinity problems caused by this
irrigation type is almost nil.
 Uniform distribution of water.
 Good water management.
 Economical use of labour.
Choice and Selection of Irrigation Methods
Following are some reasons and factors which affect the selection of an irrigation system for a
specific area:
1. Compatibility of the irrigation system
2. Topographical characteristics of area
3. Economics and cost of the irrigation method
4. Soils

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5. Water supply
6. Crops to be irrigated
7. Social influences on the selection of irrigation method
8. External influences
1. Compatibility of the irrigation system
The irrigation system for a field or a farm must be compatible with the other existing farm
operations, such as land preparation, cultivation, and harvest.
 Level of Mechanization
 Size of Fields
 Cultivation
 Pest Control
The use of the large mechanized equipment requires longer and wider fields. The irrigation systems
must not interfere with these operations and may need to be portable or function primarily outside
the crop boundaries (i.e. surface irrigation systems). Smaller equipment or animal-powered
cultivating equipment is more suitable for small fields and more permanent irrigation facilities.
2. Topographical characteristics of area
Topography is a major factor affecting irrigation, particularly surface irrigation. Of general
concern are the location and elevation of the water supply relative to the field boundaries, the area
and configuration of the fields, and access by roads, utility lines (gas, electricity, water, etc.), and
migrating herds whether wild or domestic
.
Field slope and its uniformity are two of the most important topographical factors. Surface
systems, for instance, require uniform grades in the 0-5 percent range.
Restrictions on irrigation system selection due to topography include:
 Groundwater levels
 the location and relative elevation of the water source
 field boundaries
 acreage in each field
 the location of roads

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 power and water lines and other obstructions
 the shape and slope of the field
3. Economics and cost of the irrigation method
The type of irrigation system selected is an important economic decision. Some types of
pressurized systems have high capital and operating costs but may utilize minimal labour and
conserve water. Their use tends toward high value cropping patterns. Other systems are relatively
less expensive to construct and operate but have high labour requirements. Some systems are
limited by the type of soil or the topography found on a field. The costs of maintenance and
expected life of the rehabilitation along with an array of annual costs like energy, water,
depreciation, land preparation, maintenance, labour and taxes should be included in the selection
of an irrigation system.
Main costs include:
 Energy
 Water
 Land Preparation
 Maintenance
 Labor
 taxes
4. Soils
The soil's moisture-holding capacity, intake rate and depth are the principal criteria affecting the
type of system selected. Sandy soils typically have high intake rates and low soil moisture storage
capacities and may require an entirely different irrigation strategy than the deep clay soil with low
infiltration rates but high moisture-storage capacities. Sandy soil requires more frequent, smaller
applications of water whereas clay soils can be irrigated less frequently and to a larger depth. Other
important soil properties influence the type of irrigation system to use.
The physical, biological and chemical interactions of soil and water influence the hydraulic
characteristics and filth. The mix of silt in a soil influences crusting and erodibility and should be
considered in each design. The soil influences crusting and erodibility and should be considered

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in each design. The distribution of soils may vary widely over a field and may be an important
limitation on some methods of applying irrigation water.
The soil type usually defines:
 Soil moisture-holding capacity
 The intake rate
 Effective soil depth
5. Water supply
The quality and quantity of the source of water can have a significant impact on the irrigation
practices. Crop water demands are continuous during the growing season. The soil moisture
reservoir transforms this continuous demand into a periodic one which the irrigation system can
service. A water supply with a relatively small discharge is best utilized in an irrigation system
which incorporates frequent applications. The depths applied per irrigation would tend to be
smaller under these systems than under systems having a large discharge which is available less
frequently. The quality of water affects decisions similarly. Salinity is generally the most
significant problem but other elements like boron or selenium can be important. A poor quality
water supply must be utilized more frequently and in larger amounts than one of good quality.
6. Crops to be irrigated
The yields of many crops may be as much affected by how water is applied as the quantity
delivered. Irrigation systems create different environmental conditions such as humidity,
temperature, and soil aeration. They affect the plant differently by wetting different parts of the
plant thereby introducing various undesirable consequences like leaf burn, fruit spotting and
deformation, crown rot, etc. Rice, on the other hand, thrives under ponded conditions.
Some crops have high economic value and allow the application of more capital-intensive
practices, these are called "cash crops" or Cash crop farming. Deep-rooted crops are more
amenable to low-frequency, high-application rate systems than shallow-rooted crops.
Cash Crop Water Requirement
Crop characteristics that influence the choice of irrigation system are:

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 The tolerance of the crop during germination, development and maturation to soil salinity,
aeration, and various substances, such as boron
 The magnitude and temporal distribution of water needs for maximum production
 The economic value of the crop
7. Social influences on the selection of irrigation
method
Beyond the confines of the individual field, irrigation is a community enterprise. Individuals,
groups of individuals, and often the state must join together to construct, operate and maintain the
irrigation system as a whole. Within a typical irrigation system there are three levels of community
organization. There is the individual or small informal group of individuals participating in the
system at the field and tertiary level of conveyance and distribution. There are the farmer
collectives which form in structures as simple as informal organizations or as complex as irrigation
districts. These assume, in addition to operation and maintenance, responsibility for allocation and
conflict resolution. And then there is the state organization responsible for the water distribution
and use at the project level.
Irrigation system designers should be aware that perhaps the most important goal of the irrigation
community at all levels is the assurance of equity among its members. Thus the operation, if not
always the structure, of the irrigation system will tend to mirror the community view of sharing
and allocation.
Irrigation often means a technological intervention in the agricultural system even if irrigation has
been practiced locally for generations. New technologies mean new operation and maintenance
practices. If the community is not sufficiently adaptable to change, some irrigation systems will
not succeed.
8. External influences
Conditions outside the sphere of agriculture affect and even dictate the type of system selected.
For example, national policies regarding foreign exchange, strengthening specific sectors of the
local economy, or sufficiency in particular industries may lead to specific irrigation systems being
utilized. Key components in the manufacture or importation of system elements may not be
available or cannot be efficiently serviced. Since many irrigation projects are financed by outside
donors and lenders, specific system configurations may be precluded because of international
policies and attitudes.

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Types of Tube Wells and Design of Strainer for
Tube Wells
1. Strainer type
2. Cavity type
3. Slotted type
Design of strainer or well screen for Tube Wells
In design, find its length, slot size, opening area, diameter and material requirements
a. Corrosion resistant
b. Strong enough to prevent collapse
c. Prevent excessive movement of sand into well
d. Minimum resistance to flow of water into the well
Materials used for Tube Well Construction
1. Zinc free brass

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2. Stainless steel
3. Low carbon steel
4. High copper alloy
Advantages and Disadvantages of Surface
Irrigation Methods
Definition:
Surface irrigation is the introduction and distribution of water in a field by the gravity flow of
water over the soil surface. The soil acts as the growing medium in which water is stored and the
conveyance medium over which water flows as it spreads and infiltrates. Common surface
irrigation systems used are rill irrigation, furrow or border irrigation.
The term 'surface irrigation' refers to a broad class of irrigation methods in which water is
distributed over the field by overland flow. A flow is introduced at one edge of the field and covers
the field gradually.
The rate of coverage (advancement) is dependent on:
 the differences between the discharge onto the field and the accumulating infiltration into the soil.
Secondary factors include

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1. field slope
2. surface roughness
3. geometry or shape of the flow cross-section.
The practice of surface irrigation is thousands of years old. It represents about 95 % of common
irrigation activity today. The first water supplies were developed from stream or river flows onto
the adjacent flood plain through simple check-dams and a canal to distribute water to various
locations. The low-lying soils served by these diversions were typically high in clay and silt content
(alluvium) and tended to be most fertile. With the advent of modern equipment for moving earth
and pumping water, surface irrigation systems were extended to upland areas and lands quite
separate from the flood plain of local rivers and streams.
Advantages of Surface Irrigation Methods
Surface irrigation offers a number of important advantages at both the farm and project level. The
gravity flow system is a highly flexible, relatively easily-managed method of irrigation.
1. Because it is so widely utilized, local irrigators generally have at least minimal
understanding of how to operate and maintain the system.
2. In addition, surface systems are often more acceptable to agriculturalists who appreciate
the effects of water shortage on crop yields since it appears easier to apply the depths
required to refill the root zone.
3. The second advantage of surface irrigation is that these systems can be developed at the
farm level with minimal capital investment. The control and regulation structures are
simple, durable and easily constructed with inexpensive and readily-available materials
like wood, concrete, brick and mortar, etc.
4. Further, the essential structural elements are located at the edges of the fields which
facilitates operation and maintenance activities.
5. Energy requirements for surface irrigation systems come from gravity. This is a significant
advantage in today's economy.
6. They are less affected by climatic and water quality characteristics. Like sediments & other
debris reduce the effectiveness of trickle systems and wind affects the sprinkler systems.
7. Salinity is less of a problem under surface irrigation than either of these pressurized
systems.
8. Surface systems are better able to utilize water supplies that are available less frequently,
more uncertain, and more variable in rate and duration.
Disadvantages of Surface Irrigation Methods
There is one disadvantage of surface irrigation that confronts every designer and irrigator. The soil
which must be used to convey the water over the field has properties that are highly varied both
spatially and temporally. They become almost undefinable except immediately preceding the
watering or during it. This creates an engineering problem in which at least two of the primary
design variables, discharge and time of application, must be estimated not only at the field layout
stage but also judged by the irrigator prior to the initiation of every surface irrigation event. Thus
while it is possible for the new generation of surface irrigation methods to be attractive alternatives

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to sprinkler and trickle systems, their associated design and management practices are much more
difficult to define and implement.
Although they need not be, surface irrigation systems are typically less efficient in applying water
than either sprinkler or trickle systems. Many are situated on lower lands with heavier soils and,
therefore, tend to be more affected by water logging and soil salinity if adequate drainage is not
provided. The need to use the field surface as a conveyance and distribution facility requires that
fields be well graded if possible. Land levelling costs can be high so the surface irrigation practice
tends to be limited to land already having small, even slopes.
Surface systems tend to be labour-intensive. This labour need not be overly skilled. But to achieve
high efficiencies the irrigation practices imposed by the irrigator must be carefully implemented.
The progress of the water over the field must be monitored in larger fields and good judgement is
required to terminate the inflow at the appropriate time. A consequence of poor judgement or
design is poor efficiency.
One sometimes important disadvantage of surface irrigation methods is the difficulty in applying
light, frequent irrigation early and late in the growing season of several crops. For example, in
heavy calcareous soils where crust formation after the first irrigation and prior to the germination
of crops, a light irrigation to soften the crust would improve yields substantially. Under surface
irrigation systems this may be unfeasible or impractical as either the supply to the field is not
readily available or the minimum depths applied would be too great.
Construction of Water Wells
How to construct water wells?
A water well is a lot more than a drilled hole, but for many people, the above ground part
of the drilling process is the only part they see. A water well is a specially engineered hole
in the ground; For ground water monitoring, or for scientific research purposes, wells may
be drilled in a way that allows the specialists to closely examine the rock formations and
take frequent water samples. Augured wells and diamond core drilling are drilling
techniques often used for scientific purposes. Most home wells are drilled to 8 or 6 inches
in diameter. Municipal or irrigation wells are likely to be drilled at larger diameters,
sometimes as much as 24 inches or more.
Types of well drilling methods
Three methods typically used for drilling water wells are rotary, air hammer and cable
tool:
1. Rotary Method of drilling wells
2. Air Hammer Method
3. Cable tool Method

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1. Rotary:
In rotary drilling, a drill bit is attached to a length of connected drill pipe. The drill bit will
be made of tough metals such as tungsten, and as the drill is rotated, the bit acts to grind
up the rock. The broken pieces (cuttings) are flushed upward and out of the hole by
circulating a drilling fluid (sometime called drilling mud) down through the drill pipe and
back to the surface. This drilling fluid also serves to cool and lubricate the drill bit, and by
stabilizing the wall of the hole, it can prevent possible cavein of unstable sands or crumbly
rock before the well casing or well screen is installed.
As the drill intersects water bearing rock formations water will flow into the hole. Most
drillers carefully monitor the depth of water "strikes" and keep a note of the formations in
which they occur.
2. Air Hammer:
In areas of hard rocks many drillers prefer to use a well drilling technique that uses
compressed air to operate a down-hole air hammer on the end of the drill string that helps
to break up the hard rocks. The compressed air also blows the crushed rock fragments
out of the hole to the surface along with any water that flows in the well during drilling.
3. Cable Tool Method:
Another drilling technique uses a "pounder" machine, usually referred to as cable tool
drilling. With this method, a heavy bit is attached to the end of a wire cable and is raised
and dropped repeatedly, pounding its way downward. Periodically, cuttings are bailed out
of the hole. The method is slow and in most places has been replaced by rotary drilling.
However the cable tool method is responsible for millions of successful wells around the
world.
Type 1
Well with impervious lining Resting on impervious layer
1. Pit is excavated
2. Masonry lining is built up on a kerb upto few meters above ground level
3. Kerb - ring (R.C.C) having cutting edge at bottom
4. Kerb is descended by loading sand bags
1. Masonry sinks down, it is further built at top
2. Vertical alignment is done through plumbob
3. When w.t is reached, further sinking is done by pumping water
4. A JHAM self closing bucket which is operated by pulley and rope
5. The soil is retained and water oozes out
6. The sinking continues till impervious layer is reached.
7. Then bore hole (small dia) is made through impervious layer which is protected
by timber lining

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Type 2
Wells with pervious lining such as brick stone and fed through pores Sides are lined with
bricks or stones without mortar
 Water enters through sides
 Ffor stability concrete plug (1m depth) is installed
 Pervious lining is surrounded by gravel filter
Type 3
No lining at all in kacha wells or unlined wells
 Temporary wells in hard soils
 When water table is high (4m high)
 Cheap and useful but collapse
Cross section of centrifugal pump for tube well
Discharge of open wells 3-6 l/sec
Discharge of tube well 40-45 l/sec
 Tube well is an assembly of pipes and strainers
 It is bored deep into ground intercepting one or more bearing strata (aquifers)
 A centrifugal pump is connected to main pipe of tube well
Considerations / Precautions in drilling wells
1. Great skill is needed to guide and control a water well drill as it penetrates sand,
gravel, clay and solid rock formations deep underground.
2. The drill rods can weigh several tons; if the drill pushes too hard or turns too fast,
the drill bit will wear out; if it does not push hard enough, it won't penetrate the
rocks.
3. There are often several rock layers in a single well; each may need different drilling
pressures. Once water is encountered, the driller will need to keep a close watch
on the drilling process.
4. No matter which method of drilling is used, the top part of the well is usually lined
with steel or plastic well casing.
5. The diameter of the drilled hole is usually an inch or two wider than the diameter
of the casing.
6. The space between the drilled hole and the casing (the annulus) has to be filled to
prevent the chance of polluted surface water from migrating downward along the
outside of the casing where it might contaminate the aquifer. This filling is called
"grout"

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Types of Strainers in Wells
Following are the types of strainers used in water wells:
1. Cook strainer
2. Browlie
3. Ashford
4. Leggett
5. Phoenix
6. Layne and brownlie
1. Cook strainer
 American patent and costly strainer
 It is made up of brass tube on which slots are made with cutting machine
 Slots 0.15 to 0.4 mm
2. Brownlie strainer
 Made of a polygonal convoluted steel plate having holes
 Surrounded by wire mesh consisting of copper wires
3. Ashford strainers
 Delicate strainer
 Consists of perforated tube with a wire around it
 A wire mesh is soldered over it
 It is protected by a wire net
4. Leggett strainer
 Expensive
 Provided with cleaning device
 Shape of a cutter which can be turned into slits and controlled from ground source
5. Phoenix strainer
Mild steel tube consists of openings coated with cadmium to keep away from choking caused by
corrosion.

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Design Of Non Erodible Channels
The Initial dimensions of a channel are determined by uniform flow or manning formula. But
final dimensions are determined on the basis of
1. Hydraulic efficiency
2. Empirical rule of the best section.
3. Practicability And Economy
Factors Considered In The Design:
1. Kind of material to find.
2. Minimum Velocity (2-3ft/s)
3. Maximum velocity.
4. Bed slopes.
5. Side slopes
6. Free board.
7. Kind of material is important to find the roughness coefficient of channel.
8. Minimum Velocity is 2-3 ft/sec -> non silting velocity to prevent aquatic growth.
9. Maximum velocity is upto 8 ft/sec more than the above value, the lining blocks, are
pulled away by moving water.
10. Bed slope is dependent upon topography and energy required for flow of water.
11. Side Slope: It Depends upon the material forming the chemical section e.g earth with
lime stone h1 : 1v
earth with concrete h1/2 : 1v
12. Free Board: Distance between top of channel to max water surface it should prevent
waves it should be 5-13 % of depth.
U.s B.r ---> F = underroot cy
F = Free Board In ft C=1.5 --->20ctt
Y = Depth in ft 2.5--->3000cft
Best section ---> Max Q for min p( wetted perimeter)
Best Section Of Half Hydrogens, Trapezoid (formula) Underroot 3y power 2, 2underroot 3y , y/2
4/3 2y 3/2y 3/5
Rectangular 2y power 2 4y y/2 2y 2y 2.5
Designing Steps For Non Erodible Channel:
1. Collect All information And estimate n and s.

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2. Computer section factory AR2/3 = nq/1.486 s 1/2.
3. Substitute The values of a and r from
A = (b+zy) y
p = b+2y underroot 1+z power 2
R = (b+zy)y/b+2y underroot1+z power 2
Causes, Importance And Prediction of Flood
Flood is a natural even which has always been an integral part of geological history of
earth. It occurs along rivers, streams and lacks.
Importance of flood:
1. Most of the hydraulic are designed on flood record.
2. Small hydraulic structures are based on a minimum of 25 years flood records e.g
all structure constructed in the canal, soil conservation practices etc.
3. Medium type structures are mainly based on 50 years flood records e.g culverts,
drainage structures and waterway structures.
4. Large irrigation projects are based on 100 years of flood record e.g Dams,
reservoirs, headwork’s, barrages.
Causes of floods:

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Intensive rainfall and high melting of snow are two main causes of flood.
Factors affecting flood
Meteorological factors
Physiological factors
 These factors are given as fallows
o Main made activity:
o Aforestation and deforestation
 Intensive rainfall:
o High flood occurs due to intensive rainfall.
 Slop of Catchment.
 Magnitude of Catchment
 Soil type.
 Catchment shape.
 Improve drainage system/poor drainage system.
 Climatic changes.
 Form of precipitation.
 Water logging
Control of flood:
 Check on deforestation and well planed watershed management project
 Check dams and reservoirs
 Distribution of water at various streams
 Empowering drainage system
 Decrease water logging
 Construction of levees and improvement of steams
Prediction and flood estimation:
 No method is available for knowing the exact amount and intensity of rainfall by
which flood can be determined
 Similarly rainfall and flood prediction cannot be performed but with certain
precision
 The expected flood and its consequent damage can only be judged and appointed
and hence while designing flood protection and judgment of design engineer is of
utmost importance
 Various methods have been used for flood estimation
 Some methods are based on basic characteristics and others are based on the
theory of probability by using previous flood data and some others are based on
the study of rainfall and runoff data

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 From marks of height flood on rivers bank, the area of flow the Wetted parameter
and slope can be found
Peak discharge can be calculated from Mannig eq. Q = 1/n R2/3 S ½ A .
Uses & Effects of Canal Irrigation
 Cheap labour and availability of cement reduces the cost of canal construction
 Huge quantities of water from Monsoon rainfall & melting of snow can be stored in
reservoirs during summer season.
 Irregular supply of water in the rivers is then regulated by construction of dams & barrages.
Canal system irrigates a vast area. Even the deserts have been made productive.
Causes:
 Abundance of silt eroded from the Karakoram, Hindu Kush and Himalayan mountains.
 Deforestation - ruthless cutting of trees for fuel and timber. Rivers form narrow and deep
valleys in the mountainous areas. Most of the eroded material is washed down into the
plains and piles up in reservoirs of the dams.
Effects:
 Blockage of canals because silt accumulates.
 Weakens the foundation of dams.

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 Reduced capacity of reservoir and less flow of water affects the generation of hydro-
electric power. It also results in availability of less water for irrigation purposes.
 Flow of floodwater is hampered which may cause heavy damage to the dam because of
mounds of silt which block the flow of water.
 Large-scale afforestation especially on the foothills of Himalayas.
 Cemented embankment of canals. .
 Installation of silt trap before the water flows to the dams.
 Structural measures such as operating the reservoir at lower level during flood and
allowing free flow during low flow season for sluicing sediments from the reservoir.
Uses of Irrigation:
1. Soft soil and level land of the Indus Plain makes digging of canals easier than in the
rugged lands of Balochistan.
2. By canal irrigation millions of gallons of water are utilized that would flow into the
Arabian Sea.
3. Cheap labor and availability of cement reduces the cost of canal construction
4. Canal system irrigates a vast area. Even the deserts have been made productive.
5. Irregular supply of water in the rivers is then regulated by construction of dams &
barrages.
6. Huge quantities of water from Monsoon rainfall & melting of snow can be stored in
reservoirs during summer season.
7. Southward slope of the rivers makes construction of canals easier, because water flows
southwards naturally.

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Factors Affecting Crop Water Requirements
The following are the factors which affect on the water requirements of the crops,
1. Climate
2. Type of Crop
3. Water table
4. Ground Slope
5. Intensity of Irrigation
6. Conveyance Losses
a. Type of soil
b. Subsoil water
c. Age of canal
d. Position of FSL w.r.t to NSL
e. Amount of Silt carried by canal
f. Wetted perimeter
7. Method of Application of water
8. Method of Ploughing
9. Crop Period
10. Base Period
11. Delta of a Crop
i. Influence of Climate

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In hot climate the evaporation loss is more and hence the water requirement will be more and
vice versa.
A certain crop grown in a sunny and hot climate needs more water per day than the same crop
grown in a cloudy and cooler climate. There are, however, apart from sunshine and temperature,
other climatic factors which influence the crop water need. These factors are humidity and wind
speed. When it is dry, the crop water needs are higher than when it is humid. In windy climates,
the crops will use more water than in calm climates.
The highest crop water needs are thus found in areas which are hot, dry, windy and sunny. The
lowest values are found when it is cool, humid and cloudy with little or no wind. From the
above, it is clear that the crop grown in different climatic zones will have different water needs.
For example, a certain maize variety grown in a cool climate will need less water per day than
the same maize variety grown in a hotter climate.
Effect of major Climatic Factors on Crop Water Needs
Climatic factor Crop water need
High Low
Sunshine Sunny (no clouds) Cloudy (no sun)
Temperature Hot Cool
Humidity Low (dry) High (humid)
Wind speed Windy Little wind
Table 4 - AVERAGE DAILY WATER NEED OF STANDARD GRASS DURING
IRRIGATION SEASON (mm)
Climatic zone Mean daily temperature
low (< 15°C) medium (15-25°C) high (> 25°C)
Desert/arid 4-6 7-8 9-10
Semi-arid 4-5 6-7 8-9
For the various field crops it is possible to determine how much water they need compared to the
standard grass. A number of crops need less water than grass, a number of crops need more
water than grass and other crops need more or less the same amount of water as grass.
Understanding of this relationship is extremely important for the selection of crops to be grown
in a water harvesting scheme.
Table 5 - CROP WATER NEEDS IN PEAK PERIOD OF VARIOUS CROPS
COMPARED TO THE STANDARD GRASS CROP
-30% -10% Same as Standard Grass +10% +20%
Citrus
Olives
Squash Crucifers
Groundnuts
Barley
Beans
Lentils
Nuts & fruit trees with cover
crop

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Melons
Onions
Peppers
Grass
Clean cultivated nuts & fruit
trees
Maize
Cotton
Millet
Safflower
Sorghum
Soybeans
Sunflower
Wheat
ii. Influence of crop type on crop water needs
As different crops require different amount of water for maturity, duties are also required. The
duty would vary inversely as the water requirement of crop. The influence of the crop type on the
crop water need is important in two ways.
a. The crop type has an influence on the daily water needs of a fully grown crop; i.e. the peak
daily water needs of a fully developed maize crop will need more water per day than a fully
developed crop of onions.
b. The crop type has an influence on the duration of the total growing season of the crop. There
are short duration crops, e.g. peas, with a duration of the total growing season of 90-100 days
and longer duration crops, e.g. melons, with a duration of the total growing season of 120-160
days. There are, of course, also perennial crops that are in the field for many years, such as fruit
trees.
While, for example, the daily water need of melons may be less than the daily water need of
beans, the seasonal water need of melons will be higher than that of beans because the duration
of the total growing season of melons is much longer. Data on the duration of the total growing
season of the various crops grown in an area can best be obtained locally. These data may be
obtained from, for example, the seed supplier, the Extension Service, the Irrigation Department
or Ministry of Agriculture.
Table gives some indicative values or approximate values for the duration of the total growing
season for the various field crops. It should, however, be noted that the values are only rough
approximations and it is much better to obtain the values locally.
iii. Water Table
If the water table is nearer to the ground surface, the water requirement will be less & vice versa.

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iv. Ground Slope:
If the slope of the ground is steep the water requirement will be more due to less absorption time
for the soil.
v. Intensity of Irrigation:
It is directly related to water requirement, the more the intensity greater will be the water
required for a particular crop.
vi. Conveyance Losses:
Take place from barrage to the field (outlet). So design should be according to requirement of
water plus losses. Major loss of water in an irrigation channel is due to absorption, seepage or
percolation and evaporation. In earthen channels losses due to seepage are much more than the
losses due to evaporation. The absorption losses depend upon following:
1. Type of soil
In sandy soil water percolates easily so water required is more. While in clayey soils water
requirement is less.
2. Subsoil water
3. Age of canal
4. Position of FSL with respect to NSL
5. Amount of Silt carried by canal
6. Wetted perimeter
vii. Method of Application of water:
In sprinkler method less water is required as it just moist the soil like rainwater whereas in flood
more water is required.
viii. Method of Ploughing:
In deep ploughing less water is required and vice versa.
ix. Crop Period:
It is the time normally in days that a crop takes from the instance of its sowing to harvesting.
x. Base Period:

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Is the time in days between the first watering and last watering to the crops before harvesting.
Note: Base Period is normally less than the crop period depending upon the type of crop.
xi. Delta of a crop:
Total depth of water required by the crop in unit area during base period. In other words it is the
total depth of water required for maturing the crop.
Volume = Depth x Area.
Now to get the total amount of water for crops (i.e water for Kharif and Rabi crops) add water
for each crop individually as
Q = Volume / Time
Classification of Irrigation Schemes
Classification of Irrigation Schemes
Irrigation Projects are divided into the following three categories viz., Major, Medium and Minor
Projects. The criteria of classification is as under:

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 Projects having CCA more than 10,000 ha. are classified as Major Projects
 Projects having CCA more than 2,000 ha. to 10000 ha. are classified as Medium Projects
 Projects having CCA less than 2,000 ha. are classified as Minor Projects
Irrigation Projects include storage dams, diversion works, barrages, lift irrigation schemes and tube
wells.
Classification of Irrigation Water Quality
All irrigation waters contain some dissolved salts. Dissolved salts are present because some
chemical elements have a strong attraction for water and a relatively weak attraction for other
elements. Two such chemical elements, for example, are sodium and chloride. The amounts of
these elements contained in water must be very high before sodium will combine with chloride to
form the solid material sodium chloride, common table salt.
The total amount and kinds of salts determine the suitability of the water for irrigation use. Water
from some sources may contain so much salt that it is unsuitable for irrigation because of potential
danger to the soil or crops.
Irrigation water quality can best be determined by chemical laboratory analysis.
1. Storage governed
2. Hydraulically-governed
3. Inertia-governed
4. Controlled/regulated
5. Pressurised command

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Mathematical Relation Between Duty, Delta and
Base Period
Definitions
Base Period:
It is the period from the first to the last watering of the crop just before its maturity. It is denoted
by “B” and expressed in number of days.
Delta:
It is the total depth of water required by a crop during entire base period. It is also
called consumptive use. It lies in base period. It is expressed in terms of depth and denoted by
“Δ’.
Duty:
The duty of water is defined as number of hectares that can be irrigated by constant supply of water
at the rate of one cumec throughout the base period. It is expressed in hectares/cumec and is
denoted by “D”. For example if 3 cumecs of water is required for the crop sown in, an area 5100
hectares, the duty of the irrigation will be 51003 = 1700 hectares/cumecs and the discharge of 3
cumecs is required throughout the base period.
The Mathematical Relation Between Duty, Delta and Base Period in both systems is explained as
follows:

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Mathematical Relation Between Duty, Delta and Base
Period In M.K.S System
Let,
Duty = D (hectares/cumecs)
Delta = A meters Base period = B days By definition,
One cumec of water flowing continuously for “B” days gives a depth of water “A” over an area
of “D” hectares.
Volume of water @ 1m3
sec in one day = 1x24*60*60 = 86400 m3
Volume of water @ 1m3
sec in "B" days = 1x24*60*60 = 86400B m3
= 86400 m2
m — (i)
As, 1 Hectare = 10000 m2
1 m2
= 1104 H
Then, equation (i) becomes,
Volume of water @ 1 m3
sec in "B" days = 86400B m3
= 86400B*1104 H-m Volume of water @
1 m3
sec in "B" days = 8.64 x B H-m — (ii)
Depth of water required by crop, A = Volume Area A = 8.64xB H-mD H A = 8.64*B D m
In F.P.S System:
Let,
Duty = D (Acres/cusecs)
Delta = A feet Base period = B days By definition,
One cusec of water flowing continuously for “B” days gives a depth of water “A” over an area of
“D” acres.
Volume of water @ 1 ft3
sec in one day = 1x24*60*60 = 86400 3
Volume of water @ 1 ft3
sec in "B" days = 1x24*60*60 = 86400B ft 3
= 86400 ft2
ft —(i)
As, 1 Acre = 43560 ft2
1 ft2
= 143560 Acre Then, equation i becomes,

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Volume of water @ 1 ft3
sec in "B" days = 86400B ft3
= 86400B*143560 Acre-ft Volume of
water @ 1 ft3
sec in "B" days = 1.983*B Acre-ft —(ii)
Depth of water required by crop,A = Volume Area A = 1.983 B Acre-ftD Acre A = 1.983xB D ft
Types And Location of Canal Headworks
Definition:
Any hydraulic structure which supplies water to the off taking canal. Diversion head-work
provides an obstruction across a river, so that the water level is raised and water is diverted to the
channel at required level. The increase water level helps the flow of water by gravity and results
in increasing the commanded area and reducing the water fluctuations in the river.
Diversion head-work may serve as silt regulator into the channel. Due to the obstruction, the
velocity of the river decreases and silt settles at the bed. Clear water with permissible percentage
of silt is allowed to flow through the regulator into the channel.
To prevent the direct transfer of flood water into the channel.

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Functions of a Headwork
A headwork serves the following purposes
 A headwork raises the water level in the river
 It regulates the intake of water into the canal
 It also controls the entry of silt into the canal
 A head work can also store water for small periods of time.
 Reduces fluctuations in the level of supply in river
Types of Canal Headworks
1. Storage headwork
2. Diversion headwork
Storage Headworks
When dam is constructed across a river to form a storage reservoir, it is known as storage head
work. It stores water during the period of excess supplies in the river and releases it when demand
overtakes the available supplies.
Diversion Headworks
When a weir or barrage is constructed across a river to raise the water level and to divert the water
to the canal, then it is known as diversion head work. The flow in the canal is controlled by canal
head regulator.
Functions of Diversion Headworks
 It raises the water level in the river so that the command area can be increased.
 It regulates the intake of water into the canal.
 It controls the silt entry into the canal.
 It reduces fluctuations in the level of supply in the river.
 It stores water for tiding over small periods of short supplies.
A diversion headwork can further be sub-divided into two principal classes:
1. Temporary spurs or bunds
2. Permanent weirs and barrages
Temporary spurs or bunds
Temporary spurs or bunds are those which are temporary and are constructed every year after
floods, however, for important works, weirs or barrages are constructed since they are of
permanent nature if properly designed.
Weirs: