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UNIT -1
INTRODUCTION
Importance of Irrigation
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
Estimates of magnitude world-wide: 544 million acres
(17% of land 1/3 of food production)Purpose
Raise a crop where nothing would grow otherwise (e.g., desert areas) Grow a more profitable crop (e.g., alfalfa vs. wheat) Increase the yield and/or quality of a given crop (e.g., fruit) Increase the aesthetic value of a landscape (e.g., turf, ornamentals) 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
Reasons for yield/quality increase
Reduced water stress Better germination and stands Higher plant populations More efficient use of fertilizer Improved varieties
Other Benefits of Irrigation
Increase in Crop Yield Protection from femine
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Cultivation of superior crops Elimination of mixed cropping: Economic development Hydro power generation Domestic and industrial water supply
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 rescannable 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 canales 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 furrowsdepends 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.
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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
errodiability and the velocity of flow.
slope may be related to discharge as follows.
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.
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Soil type, stream size and irrigation depth are the important factors
indeterming 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. Sprinkler2. Drip irrigation
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 dustyarea.
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
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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 isone 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 lobour.
CONSUMPTIVE USE OF WATER
The amount of irrigation water that is needed depends not only on the
amount of water already available from rain fail, but also on the total
amount of water needed by the various crops.
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 amountof 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
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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 plantedand while they are establishing
themselves. After that, they can be left to the natural cycle of the elements.
Popular 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. Populardrought-olerant 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 floweringperennial 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
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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 bereplanted 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.
Water Requirement of Different Crops
Amount of water required by a crop in its whole production period is called
water requiremrnt. The amont 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
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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 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. Thetotal 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 evapotranspiration of the crop (ETm)
In this exercise, the irrigation water requirement is calculated for a 10-day
period during the harvest stage.
Evaluation of Percolation loss (I)
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The command area is divided in irrigation blocks. First, these irrigation
blocks are crossedwith 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:
TexturePercolation loss
(mm/day)
Clay 4
Loam 12
Sandy clay 14
Clay loam 7
The percolation table isjoinedwith the cross table to get the percolation foreach 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 m per day for clay channels and 0.01 m per day for
concrete channels. A new table indicating water loss per channel type is
created andjoinedto 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 aggregatedto evaluate the total conveyance loss per irrigation
block.
Evaluation of maximum evapotranspiration (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
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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
Maximum evapotranspiration 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 atabcalc 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
reclassifiedin 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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Factors Influencing Crop Water Requirements for Irrigation
i. Influence of climate
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 - AVERAGE DAILY WATER NEED OF STANDARD GRASS
DURING IRRIGATION SEASON (mm)
Climatic zone Mean daily temperature
low (< 15C) medium (15-25C) high (> 25C)
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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 waterthan 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 (see Chapter 6, Crop Husbandry).
Table - 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
Melons
Onions
Peppers
Grass
Clean cultivated nuts & fruit
trees
Barley
Beans
Maize
Cotton
Lentils
Millet
Safflower
Sorghum
Soybeans
Sunflower
Wheat
Nuts & fruit trees with
cover crop
ii. Influence of crop type on crop water needs
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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, ofcourse, 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, forexample, 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.
There are three broad classes of irrigation systems:
Pressurized distribution
Gravity flow distribution
Drainage flow distribution.
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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.
3. Control of drainage flow irrigation System
Irrigation by control of the drainage system, subirrigation, 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 individualirrigation systems have a variety of advantages and particular applications.
Irrigation systems are often designedto 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,
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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.
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
power and water lines and other obstructions,
the shape and slope of the field
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UNIT-2&4
IRRIGATION METHOD
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.
TANK IRRIGATIONIndia, an irrigation tank or tank is an artificialreservoirof any size. (The word sagar
refers to a large lake, usually man-made).[1]
It can also have a natural or man-madespring included as part of a structure. Tanks are part of an ancient tradition of harvesting
and preserving the local rainfall and water from streams and rivers for later use,primarily for agriculture and drinking water, but also for sacred bathing and ritual. Often
a tank was constructed across a slope so to collect and store water by taking advantageof local mounds and depressions.
[2]Tank use is especially critical in parts ofSouth India
withoutperennialrainfall where water supply replenishment is dependent on a cycle ofdry seasons alternating with monsoon seasons.
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. 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.
http://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Reservoirhttp://en.wikipedia.org/wiki/Reservoirhttp://en.wikipedia.org/wiki/Reservoirhttp://en.wikipedia.org/wiki/Irrigation_tank#cite_note-glossary-0#cite_note-glossary-0http://en.wikipedia.org/wiki/Irrigation_tank#cite_note-glossary-0#cite_note-glossary-0http://en.wikipedia.org/wiki/Irrigation_tank#cite_note-glossary-0#cite_note-glossary-0http://en.wikipedia.org/wiki/Irrigation_tank#cite_note-Tank_management-1#cite_note-Tank_management-1http://en.wikipedia.org/wiki/Irrigation_tank#cite_note-Tank_management-1#cite_note-Tank_management-1http://en.wikipedia.org/wiki/Irrigation_tank#cite_note-Tank_management-1#cite_note-Tank_management-1http://en.wikipedia.org/wiki/South_Indiahttp://en.wikipedia.org/wiki/South_Indiahttp://en.wikipedia.org/wiki/South_Indiahttp://en.wikipedia.org/wiki/Perennial_planthttp://en.wikipedia.org/wiki/Perennial_planthttp://en.wikipedia.org/wiki/Perennial_planthttp://en.wikipedia.org/wiki/Perennial_planthttp://en.wikipedia.org/wiki/South_Indiahttp://en.wikipedia.org/wiki/Irrigation_tank#cite_note-Tank_management-1#cite_note-Tank_management-1http://en.wikipedia.org/wiki/Irrigation_tank#cite_note-glossary-0#cite_note-glossary-0http://en.wikipedia.org/wiki/Reservoirhttp://en.wikipedia.org/wiki/India -
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Flow of floodwater is hampered which may cause heavy damage tothe 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 CANAL Irrigation:
1. Soft soil and level land of the Indus Plain makes digging of canalseasier than in the rugged lands of Balochistan.
2. By canal irrigation millions of gallons of water are utilized that wouldflow into the Arabian Sea.
3. Cheap labour and availability of cement reduces the cost of canalconstruction
4. Canal system irrigates a vast area. Even the deserts have been madeproductive.
5. Irregular supply of water in the rivers is then regulated byconstruction of dams & barrages.
6. Huge quantities of water from Monsoon rainfall & melting of snowcan be stored in reservoirs during summer season.
7. Southward slope of the rivers makes construction of canals easier,because water flows southwards naturally.
Lining of Irrigation CanalsMost of the irrigation channels in Iraq are earthen channels. The
major advantage of an earth channel is its low initial cost, these suffer
from certain disadvantages, like the following:-
1- Maximum velocity limited to prevent erosion.
2- Seepage of water into the ground.
3- Possibility of vegetation growth in banks, leading to increased friction.4-Possibility of bank failure, due to erosion.
5-More maintenance requirement.Types of Canal LiningTypes of lining are generally classified according to the materials
used for their construction. Concrete, rock masonry, brick masonry,
bentonite-earth mixtures, natural clays of low permeability, and different
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mixtures of rubble, plastic, and asphaltic materials are the commonly
used materials for canal lining. The suitability of the lining material is
decided by:
A- Economy.
B- Structural stability.
C- Resistance to erosion.
E- Durability.
F- Hydraulic efficiency.
[A] Concrete Lining[B] Precast concrete lining[C] Shotcrete Lining[D] Bricks, Tiles and Stone lining[E] Asphaltic Lining[F] Earth Linings1- Stabilized Earth LiningsSub-grade is stabilized using either clay for granular subgrade or by
adding chemicals that compact the soil.
2- Loose Earth Blankets
Fine grained soil is laid on the sub grade and evenly spread. However,
this type of lining is subject to erosion, and requires a flatter side slopes
of canal.
3- Compacted Earth Linings
The graded soil containing about 15 percent clay is spread over thesubgrade and compacted.
4- Buried Bentonite Membranes
Bentonite is a special type of clay soil, found naturally, which swell
considerably when wetted.
5- Soil-cement Linings:These linings are constructed using cement (15 to 20 per cent by
volume) and sandy soil (not containing more than about 35 per cent of silt
and clay particles). Cement and sandy soil can be mixed in place and
compacted at the optimum moisture content. This method of construction
is termed the dry-mixed soil-cement method.
3- Failure of Canal LiningThe main causes of failure of lining are the water pressure that
developed behind the lining material due to high water table, saturation
of the embankment by canal water, sudden lowering of water levels in the
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channel, and saturation of the embankment sustained by continuous
rainfall. When the water level in canal was raised and lowered the banks
suffering from instability due to erosion and seepage through the banks
may be occurs. In order to minimize the seepage, a secondary berms were
constructed along the length of bank at various locations.Diversion head works: Weirs and Barrages, Layout of diversion head works andcomponents, failure of hydraulic structures on previous foundations, Blighs Creep
theory, Lanes weighted theory and Khoslas theory, concept of low net, u/s and d/scutoffs and protection measures, design of vertical drop weir.
Canal Structures: Types of falls and their location, design principles and Trapezoidalnotch fall, siphon well drop, straight glacis fall. Canal regulation works, alignment of off
taking canal. Distributary head regulators and cross regulation and their design. Canalescapes, types of metering flumes, types of canal modules and proportionality,
sensitivity, flexibility.
Cross Drainage Works: Definition, classification, design principles of aqueducts,siphon aqueducts, canal siphons, super passages and inlet and outlets, selection of crossdrainage works.
Bridges and Culverts: Discharge, Waterway and sour depth computations, Depth of
Bridge foundation, spans and vertical clearance, efflux computations, pipe culverts andbox culverts.
Water Power: Classification of Hydropower plants, definitions pf terms, load, head,power, efficiency, load factor, installed capacity, utilization factor, capacity factor, use of
mass curve and flow duration curve. Components of power plant-intakes, fore/bay,
penstocks, functions and types of sewage tanks, General arrangement of power house,sub-structure and super-structure.
.
Design of HydraulicStructures
Design of HydraulicStructuresCOURSE Contents
1. Introduction
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2. Gravity Dams Site selection,
Forces,
Stability analysis.3. Diversion Works Weirs and
Barrages
4. Canals Design and Canal Falls.
5. Cross Drainage Works
6. Head Regulators and Crossregulators
IS CodesIS Code 6512: Criteria for Design of Solid Gravity
Dams
IS Code 1893: Criteria for Earthquake ResistantDesign of Structures
IS Code 7784-Cross-Drainage Works: Part 1 -
General
IS Code 7784- Cross-Drainage Works: Part 2 -
Aqueduct
IS Code 7784- Cross-Drainage Works: Part 2
Syphon AqueductIS Code 7784- Cross-Drainage Works: Part 2
Canal Syphon
IS Code 7784- Cross-Drainage Works: Part 2
Superpassage
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IS Code 7784- Cross-Drainage Works: Part 2
Level Crossing
UNIT-3 DIVERSION AND IMPOUNDING STRUCTURES
Why study Hydraulic Structures?
INTRODUCTIONDevelopment of water resources of
a region
Requires
Conception
Planning
Design
Construction
Operation
of various facilities to utilise andcontrol water, and
to maintain water quality.
Utilize/Need water
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Domestic & Industrial uses
Irrigation
Power generationNavigation
Other purposes
Water Resources Engineering
Utilisation of water
Control of waterWater quality management
Water is controlled and regulated
Flood control
Land drainage
Sewerage
Bridges
Not cause damage to property,
inconvenience to the
public, or loss of lifeWater-quality management
Required quality of water for
different uses
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Preserve Ecological balance
Contamination of
Groundwater/Surface waterWater Resources development
projects are planned
to serve various purposes
Main Purposes
Domestic & Industrial uses,Irrigation
Power generation, Navigation,
Flood control
Secondary Purposes
Recreational, Fish and wild life,
Drainage control,
Watershed management, Sediment
control,
Salinity control, Pollutionabatement
Miscellaneous Purposes
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Employment, Accelerate
development etc
Single-purpose andMulti-purposeWater Resources projects Two
Main Steps
First step How much water is
available?
Knowledge of HydrologyPrecipitation average
Abstraction Losses
Runoff, Yield of basin
Flood Peak runoff
Reservoir sizing Mass curve
Second step How to utilise and
control water?
Require various structure
Hydraulic StructuresTypes of Hydraulic Structures
Storage
Diversion
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Transportation
Regulation
ControlMain source of water is
Precipitation
Precipitation is not uniform over
space and time
Monsoon, North East, Himalaya,W. Ghat
Store water at surplus location
during surplus
period Storage structures
Reservoirs
Dam and Reservoir coexist
Dam solid barrier across river
Reservoir artificial lake u/s of
damReservoirDam
Reservoir
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Dam Spillway
RESERVOIRS RESERVOIRSTypes of Reservoirs Single-purposeand Multi-purpose
Storage (or conservation) reservoirs
Flood control reservoirs
Multipurpose reservoirDistribution reservoirs
Balancing reservoirs
Flood Control runoff exceeding
safe capacity of
river is stored in the reservoir.
Stored water is
released in controlled manner
Detention Reservoirs regulated byGATES
Adv: More flexibility of operation andbetter control of
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outflow; Discharge from various
reservoirs can be adjusted
Disadv: More expensive; Possibility ofhuman error
Retarding Reservoirs UNGATES
Adv: Less expensive; Outflow is
automatic so possibility ofhuman error
Disadv: No flexibility of operation;Discharge from various
reservoirs may coincide heavy flood
Multipurpose ReservoirsServe two or more purposes. In India,
most of the reservoirs
are designed as multipurpose reservoirs
to store water for
irrigation and hydropower, and also toeffect flood control
Distribution Reservoirs
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Serve two or more purposes. In India,
most of the reservoirs
are designed as multipurpose reservoirsto store water for
irrigation and hydropower, and also to
effect flood control
Distribution ReservoirsSmall storage reservoirs to tide over the
peak demand ofwater. The distribution reservoir is
helpful in permitting
the pumps to work at a uniform rate. It
stores water
during the period of lean demand andsupplies the same
during the period of high demand. As the
storage is
limited, it merely helps in distribution of
water as per
demand for a day or so and not forstoring it for a long
period. Distribution reservoirs are mainly
used for
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municipal water supply but rarely used
for the supply of
water for irrigation.RESERVOIRS RESERVOIRSBalancing ReservoirsA balancing reservoir is a small reservoir
constructed d/s of
the main reservoir for holding waterreleased from the
main reservoir.
RESERVOIRS RESERVOIRSStorage Capacity of ReservoirsStorage capacity of a reservoir depends
upon the topography of
the site and the height of dam.
Engineering surveys
The storage capacity and the water
spread area at different
elevations can be determined from thecontour map.
In addition to finding out the capacity of
a reservoir, the
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contour map of the reservoir can also be
used to determine
the land and property which would besubmerged when the
reservoir is filled upto various elevations.
To estimate the compensation to be paid
to the owners of the
submerged property and land. The time
schedule,according to which the areas should be
evacuated, as the
reservoir is gradually filled, can also be
drawn..
UNIT-5
IRRIGATION WATER MANAGEMENT
Both the elevation-area curve and the
elevation- storage curve on
the same paper. Abscissa - areas and
volumes - opposite
di ti
Area-Elevation Curve
from contour map An
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elevation-area curve is
then drawn between
the surface area asabscissa and the
elevation as ordinate.
Elevation-Capacity
Curve: is determined
from elevation-area
curve using diffformulae.
Storage Capacity calculation
formulae
1. Trapezoidal formula2. Cone formula
3. Prismoidal formula
4. Storage Volume from cross-sectional
areas
Basic Terms and Definitions1. Full reservoir level (FRL): is the
highest water level to which
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the water surface will rise during normal
operating
conditions. Also called the full tank level(FTL) or the
normal pool level (NPL).
2. Maximum water level (MWL): is the
maximum level to which
the water surface will rise when the
design flood passes overthe spillway. Also called the maximum
pool level (MPL) or
maximum flood level (MFL).
3. Minimum pool level: is the lowest level
up to which the water
is withdrawn from the reservoir under
ordinary conditions.
It corresponds to the elevation of the
lowest outlet (or
sluiceway) of the dam. However, in the
case of a reservoir forhydroelectric power; the minimum pool
level is fixed after
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considering the minimum working head
required for the
efficient working of turbines.
Basic Terms and Definitions4. Useful storage: volume of water stored
between the full
reservoir level and the minimum pool
level. Also known as
the live storage.
5. Surcharge storage: is the volume of
water stored above the
full reservoir level upto the maximum
water level. Thesurcharge storage is an uncontrolled
storage which exists
only when the river is in flood and the
flood water is passing
over the spillway. This storage is available
only for the
absorption of flood and it cannot be used
for other purposes.
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6. Dead storage: volume of water held
below the minimum pool
level. The dead storage is not useful, as itcannot be used for
any purpose under ordinary operating
conditions.
7. Bank storage: If the banks of the
reservoir are porous, some
water is temporarily stored by them whenthe reservoir is
full.
8. Valley storage: The volume of water
held by the natural river
channel in its valley upto the top of its
banks before the
construction of a reservoir is called the
valley storage. May
be important in flood control reservoirs.
9. Yield from a reservoir: Yield is the
volume of water whichcan be withdrawn from a reservoir in a
specified period of
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time. The yield is determined from the
storage capacity of
the reservoir and the mass inflow curve.10 Safe yield (Firm yield): is the
maximum quantity of water
which can be supplied from a reservoir in
a specified period
of time during a critical dry year. Lowest
recorded naturalflow of the river for a number of years is
taken as the
critical dry period for determining the
safe yield
11. Secondary yield: is the quantity of
water which is available
during the period of high flow in the
rivers when the yield is
more than the safe yield. It is supplied on
as and when basisat the lower rates. The hydropower
developed from
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secondary yield is sold to industries at
cheaper rates.
12. Average yield: is the arithmeticaverage of the firm yield
and the secondary yield over a long
period of time.
13. Design yield: is the yield adopted in
the design of a reservoir.
Fixed after considering the urgency of thewater needs and
the amount of risk involved. The design
yield should be such
that the demands of the consumers are
reasonably met with,
and at the same time, the storage required
is not unduly
large.