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Title: irrigation(GTU)


1
Water Managements
  • Zarna Chovatiya

2
1. INTRODUCTION
  • Necessity of irrigation
  • Inadequate rainfall
  • Uneven distribution of rainfall
  • Increasing the yield of crops
  • Growing a number of crops
  • Growing perennial crops(crops such as sugarcane)
  • Growing superior crops (crops such as oil seeds,
    cotton, fruits, vegetables etc.)
  • Insurance against drought

3
Merits of irrigationIt is broadly classified
as direct and allied benefits
  • Direct benefits
  • Allied benefits
  • Increase in crop yield
  • Cultivation of superior crops
  • Protection from famine
  • Elimination of mixed cropping
  • Increase in revenue
  • Saving foreign exchange
  • Canal plantation
  • Communication facilities
  • Aid in civilization
  • Overall development
  • Hydroelectric power
  • Flood control
  • Domestic and industrial water supply
  • Inland navigation
  • Increase in ground water storage

4
Demerits of irrigation
1) Water logging2) Damp climate3)
Mosquitoes nuisance
  • Major projects
  • Minor projects
  • The irrigation projects having a culturable
    commanded area of more than 10,000ha are
    classified as major projects
  • Examples Bhakra nangal, Beas Indira Gandhi
    canal, Damodar valley, Hirakund, Nagarjun sagar
    etc.
  • The irrigation projects having a culturable
    commanded area of less than 2000ha are classified
    as minor projects
  • Examples construction of open wells, tube wells,
    small canals and tanks

5
Classification of irrigation methods
  • A. Natural irrigation
  • 1. Rainfall
  • 2. Inundation canal system
  • B. Artificial irrigation
  • 1. Flow irrigation
  •  
  • Perennial canal
  • non-perennial
  • canal system
  • 2. Lift irrigation
  •  
  • Open well

  • tube well
  • 3. Sprinkler irrigation
  • 4. Drip irrigation

6
  • 2. WATER REQUIREMENT OF CROP
  • Suitability of soil for crops
  • Nitrogen, phosphorus and potassium are
    extensively used by the
  • plants and therefore called primary
    nutrients.
  • Calcium, magnesium and sulphur are called
    secondary nutrients.
  • Iron, zinc, boron, copper, chlorine is called
    micro-nutrients.

Soil type occurrence Suitable crops
Black soil Maharashtra, parts of Gujarat and Tamil nadu, valleys of Tapti, Narmada Krishna and Godavari rivers. Sugar cane, cotton, ground nut, wheat, maize, tobacco, fruits etc.
Red soils Tamil nadu, Orissa, A.P., Maharashtra, M.P., west Bengal Rice, maize, pulses, oat, millets etc.
Forest soil Himalayan ranges, vindhya and satpura ranges, eastern and western Ghats. Tea, rice, potato, fruits, coffee etc.
Desert soils Rajasthan, sea coasts, part of punjab Barley, millets, oil seeds, coconut
Indo- gangetic alluvium Bihar, Assam, Haryana, Punjab, west Bengal, U.P. Jute, rice, wheat, maize, tobacco etc.
7
  • Methods of improving soil fertility
  • The deficient soil can be improved or cured by
    any of the following four methods
  • By giving sufficient rest to the land
  • By adding different manures or fertilizer to
    the land
  • By adopting suitable farming methods
  • By crop rotation
  • Water holding capacity of soil
  • Water holding capacity mainly depends upon the
    porosity of the soil.
  • The porosity is defined as the ratio of the
    volume of pores to the total volume of a soil
    mass. Usually expressed in percentage.
  • Porosity (n) Vv/V
    100
  • Where Vv is the volume of voids and V is the
    total volume.
  • Porosity is related to the void ratio (e) by the
    relation
  • n e/1e
  • The void ratio is defined as the ratio of the
    volume of voids to the volume of solids.
  • e Vv/Vs
  • Thus the greater the porosity of a soil the
    greater is the water holding capacity.

8
Duty of water
  • Duty
  • Duty is usually defined as the area of land which
    can be irrigated if one cumec of water was
    applied to the land continuously for the entire
    base period of the crop. It is expressed in
    hectares/cumecs
  • The base period is the period between the first
    watering and last watering. It is slightly
    different than crop period which is the period
    between the time of sowing and the time of
    harvesting the crop. Both expressed in days.
  • It is defined as the total depth of water
    required by a crop during the entire base period.
  • It is the limited period for which for its growth
    any crop requires more quantity of water. It is
    known as kor period. It varies between 2-4 weeks
  • It is the extra water to be supplied for watering
    a particular crop, which extends from one season
    to another
  • Base period
  • Delta
  • Kor
  • period
  • Over-lap allowance

9
  • Duty of water
  • Time factor
  • The ratio of the number of days the canal has
    actually run to
  • the number of days of irrigation period.
  • Gross command area
  • The total area including roads, villages etc.
    which can be economically irrigated from the
    project is called GCA
  • Culturable commanded area
  • That area over which cultivation is possible
    within project G.C.A. is known as culturable
    commanded area. It is obtained by deducting
    uncultured area like ponds, forest, village etc.
    from the G.C.A.
  • Crop
  • period
  • The base period differs from crop to crop. When
    base period is more, more water will be required,
    which will result in reduction of duty of water.
    For small base period crops, the duty of water
    shall be more.

10
  • Relation between duty, delta and base period

In birdie text book pg no 47
11
Factors affecting duty
  • Type of soil
  • Type of crop
  • Structure of soil
  • Slope of ground
  • Climatic conditions
  • Method of cultivation
  • System of irrigation
  • Method of application of water
  • Age and frequency of cultivation
  • Condition, type and location of the canal
  • Method of assessment of water
  • Skill of cultivators
  • Base period
  • Salt content of soil

12
  • Consumptive use of water
  • The consumptive use of water for a crop is the
    quantity of water consumed by it for evaporation,
    transpiration and metabolism.
  • This also includes the water consumed by
    accompanying weed growth, if any
  • Water supplied by rainfall to the crops and
    subsequently evaporated without having entered
    the plant system is also a part of the
    consumptive use.
  • The value of the consumptive use is different for
    different crops, even for the same crop, its
    value is different stages and places. It varies
    throughout the day, the week, the month

13
  • Consumptive use of water
  • The values of the monthly consumptive use are
    generally
  • determined for a given crop at a given place
    to estimate the
  • total water requirements.
  • The consumptive use depends on a number of
    factors,
  • enumerated below
  •  
  • Evaporation wind velocity
    nature of leaves of plants
  • Humidity water table
    length of growing season
  • Temperature soil and topography
    day-time hours
  • Growing season intensity of sunlight
  • Cropping pattern amount foliage
  • Precipitation stage of growth
  •  
  • Direct measurement and empirical methods can be
    use for
  • determination of the consumptive use

14
  • Methods of reckoning duty
  • Consumptive use of water basis
  • Inductive method
  • Critical growth period basis
  • Major crop grown in each season
  • Refer pg no 63 book birdie das
  •  

15
3. HYDROLOGY
  • Precipitation
  • It is the falls of water in various forms on
    the earth form the clouds. The usual forms of the
    precipitation are rain and snow, although it may
    also occur in the form of sleet, glaze, hail, dew
    and frost
  • Mean annual rainfall
  • The daily rainfall collected from a rain gauge
    stations is totaled to obtain the yearly rainfall
    of that year. The mean annual rainfall is also
    known as the average annual rainfall. In India
    the precipitation cycle repeats roughly after 35
    years.
  • Infiltration
  • It is the process by which water enters the
    soil from the ground surface. Infiltration first
    replenishes the soil moisture deficiency. The
    excess water then moves downwards by the force of
    gravity. This downward movement under gravity is
    called percolation.
  • Infiltration responsible for subsurface and
    ground water flow.

16
  • Infiltration
  • The supply to ground water reservoir also
    depends upon infiltration. The water that enters
    the ground also provides moisture for the plant.
    The infiltration rate is used for the computation
    of the water loss due to infiltration for the
    determination of the surface runoff.
  • Runoff
  • A part of the precipitation flowing of a
    catchment area through a surface channel is
    called runoff.
  • It is defined as the portion of the rainfall
    that makes its way towards river or ocean as
    surface or subsurface flow
  • Estimation of runoff
  • English desouza formula
  • For ghat region of west India R
    0.85P-30.5
  • For Deccan(plain)region RP
    /254(P-17.8)
  • 2) Khoslas formula RP-0.48Tm(annual runoff)
  • RmPm-Lm
  • Lm0.98Tm for Tmgt4.5oC

17
Factors affecting runoff
  • a) Climatic factors
  • b) Physiographic factors
  • Form of precipitation
  • Intensity of precipitation
  • Duration of precipitation
  • Rainfall distribution over the catchment
  • Direction of storm movement
  • Antecedent precipitation index
  • Meteorological factors
  • Type of soil
  • Land use
  • Area of basin
  • Shape of the catchment
  • Slope of the catchment
  • Orientation of the catchment
  • Natural drainage
  • Artificial drainage works
  • Storage characteristics of the basin

18
  • Flood frequency studies
  • Recurrence interval denotes the number of years
    in which a flood can be expected at least once.
    It is usually denoted by Tr and is given by
  • Tr 100/B
  • Where B is the frequency which denotes the
    likelihood of flood being equaled or exceeded.
  • A 5 frequency (B) means that the flood has 5
    out of 100 chances of being equaled or exceeded.
  • Hydrograph
  • It is a graphical plot of discharge of a
    natural stream or river Versus time.
  • Unit hydrograph
  • It present 1 cm of runoff from a rainfall of
    some unit Duration and specific areal
    distribution.
  • Advantages of unit hydrograph
  • Calculation of ordinates of hydrographs
  • Expected volume of runoff from a basin can be
    computed
  • Flood hydrograph can be prepare

19
In birdie text book pg no 47
20
  • Estimation of peak flow by empirical formulae
  • In this method area of a bsin or a catchment is
    considered mainly. All other factors which
    influence peak flow area merged in a constant.
    A general equation may be wtitten in the form
  • Q C.An
  • Where Q is peak flow or rate of maximum
    discharge
  • C is a
    constant for the cachment
  • A is area of
    the catchment and n is an index.

21
  • The constant for a catchment is arrived at,
    after taking following factors into account
  • Basin characteristics. (B) storm
    characteristics
  • Area v intensity
  • Shape v duration
  • slope v distribution
  • Limitations
  • This method does not take frequency of flood
    into consideration
  • This method can not be applied universally
  • Fixing of constant is very difficult and exact
    theory can not be put forth for its selection.
  • Some important empirical formulae are mentioned
    below
  • Dickens formula
  • Ryves formula
  • The inglis formula
  • Nawab Ali nawazs formula
  • Khoslas formula
  • Bessons formula

22
  • GROUND WATER

(A) Sources of water
Sea water Streams
and rivers Ponds and lakes impounding reservoirs
  • (B) Subsurface water sources(ground water)
  • Open and tube wells,
  • springs, infiltration galleries
  • karez
  • These are permeable formations having structure
    which permits appreciable quantity of water to
    move through them under ordinary field
    conditions.
  • Examples coarse materials sands and gravels
  • There are two types of two acquifer
  • Unconfined acquifer
  • Confined acquifer

Aquifer
  • These are impermeable formations which contain
    water but are not capable of transmitting or
    supplying a significant quantity. E.g. clay

Aquiclude
23
  • Aquifuge
  • These are impermeable formation which neither
    contains water nor transmits any water.e.g. Rocks
    like basalt, granite etc.
  • It is a partly permeable geological formation. It
    transmits water at such a slow rate that the
    yield is insignificant. Pumping by well is not
    possible.
  • Examples sand lenses in a clay formation will
    form an aquitard.
  • It is the ratio of the volume of voids in a soil
    mass to its total volume. Expressed as a
    percentage
  • n Vv/V100
  • It is the ratio of the volume of water in an
    aquifer which can be extracted by the force of
    gravity to the total volume of the saturated
    aquifer
  • SyVw/V100

Aquitard
Porosity
Specific yield
24
  • Specific
  • retention
  • It is the ratio of the volume of water that can
    not be drained out to the total of the saturated
    aquifer.
  • SrVr/V100
  • It is the ease with which water can flow in a
    soil mass. The coefficient of permeability is
    equal to the discharge per unit area of soil mass
    under unit hydraulic gradient. It has dimension
    of velocity.
  • It is equal to the discharge rate at which water
    is transmitted through a unit width of an aquifer
    under a unit hydraulic gradient Tkb , it is
    usually expressed as m2/s
  • It is the volume of water released from a prism
    of unit cross sectional area as the water table
    drops by a unit depth. It is dimensionless as it
    is the ratio of the volume of water released to
    the original unit volume
  • It is the storage coefficient per unit saturated
    thickness of the aquifer

Co-efficient of permeability (hydraulic
conductivity)
Transmissibility (transmissivity)
Storage coefficient (storativity)
Specific storage
25
  • Types of wells
  • Water well is a hole, usually vertical,
    excavated in the earth for bringing ground water
    to the surface.
  • 1) Open wells
  • open wells are the wells which have
    comparatively large diameters but low yields
    and are not very deep. The diameters of the open
    wells usually vary from 1-10m and yield is about
    20m3/hour or less.
  • 1) shallow and deep well
  • 2) kachha well and well with
    pervious/impervious lining
  • 2) Tube well
  • it is a long pipe sunk into the ground
    intercepting one or more water bearing strata.
    Its diameter ranges from 80-600m.
  • 1) strainer well
  • 2) cavity well
  • 3) slotted well

26
  • Yield of open well
  • Constant level pumping test
  • Recuperation test
  • Recharging of under ground water sources
  • Recharging of open wells
  • Infiltration bore well
  • Hidden dam
  • Infiltration tank
  • Infiltration tank in river bed
  • Infiltration bore or tube well in river bed
  • Recharging of lost rivers
  • Check dam

27
5. RESERVOIR PLANNING
  • Investigations for reservoir planning
  • Engineering survey
  • Geological survey
  • Hydrological survey
  • Selection of site for a reservoir
  • The height of dam should be as high as possible
    with minimum possible length.
  • The geological conditions at the site should
    permit minimum percolation losses, with minimum
    runoff.
  • The basin should have cup shaped bottom.
  • The depth of water in the basin should be more.
  • Site should be free from such minerals and salts
  • Site should be such that the run-off water has
    the minimum percentage of silt.
  • The reservoir bottom should be of maximum
    possible imperviousness.
  • The reservoir basin should have deep narrow
    opening at the site, so that length of the dam
    should be minimum.

28
  • Zones of storage
  • Dead storage
  • The volume of water held below the minimum pool
    level is called the dead storage. It is not
    useful, as it cannot be used for any purpose
    under ordinary operating conditions.
  • Live storage
  • The volume of water stored between the full
    reservoir level and the minimum pool level is
    called the live storage. It is also available
    for various purposes of the reservoir. In most of
    the cases it is the conservation storage of the
    reservoir.
  • Flood storage
  • It is the volume of water stored above the full
    reservoir level up to the maximum water level.
    It is an uncontrolled storage which exits only
    When the for the absorption of flood and it can
    not be used for the other purposes.

29
  • Reservoir losses
  • Evaporation losses
  • it is generally estimated by following formula
  • Volume of water lost mean surface area x pan
    evaporation x pan coefficient
  • Absorption losses
  • it depends mainly on the type of soil. These
    losses are comparatively large in the beginning
    when the soil is dry. These losses are quite
    small and neglected.
  • Seepage losses
  • it occurs due to continuous flow of water under
    pressure from the reservoir to the adjoining
    strata. To prevent it the proposed reservoir
    basin should be thoroughly investigated by a
    geologist and checked for water tightness. If
    necessary suitable measures, such as grouting of
    the basin, should be adopted to reduce seepage.

30
  • Reservoir sedimentation
  • The sediments are produced in the catchment of
    the river by erosion.
  • Rivers carry a large amount of sediment load
    along with water. These sediments are deposited
    in the reservoir on the upstream of the dam
    because of reduction of velocity.
  • Sediments reduce the available capacity of the
    reservoir.with continuous sedimentation the
    useful life of the reservoir goes on decreasing.

31
  • Measures to control reservoir sedimentation
  • Selection of suitable site
  • Proper design
  • Provision of sluices
  • Creating large reservoir
  • Control of sediment inflow
  • Check dams
  • Vegetation screens
  • Control of sediment deposition
  • Physical removal of sediments
  • Soil conservation

32
  • 6. Dams
  • Classification of dams

Dams can be classified according to different
criteria, as given below
Storage dams Detention dams Diversion dams Debris
dams Coffer dams
Classification based on function served
Classification based On hydraulic design
Over flow dams Non-over flow dams
33
Masonry dam Concrete dam Earth dam Rock fill
dam Timber dam Steel dam Combined concrete cum
earth dam Composite dam
Classification based on material used
Over flow dams Non-over flow dams
Classification based on rigidity
Gravity dams Earth dams Rock fill dams Arch
dams Buttress dams Steel dams Timber dams
Classification based on structural behavior
34
  • Selection of type of dam
  • Topography and valley shape
  • Geology and foundation condition
  • Availibity of construction materials
  • Overall cost
  • Spillway size and location
  • Earthquake hazard
  • Climatic condition
  • Diversion problem
  • Environmental consideration
  • Road ways
  • Length and height of dam
  • Life of dam
  • Miscellaneous consideration

35
  • Gravity dam
  • Basic definitions (components)
  • Axis of the dam
  • Length of dam
  • Structural height of the dam
  • Maximum base width of the dam
  • Hydraulic height of the dam

Forces acting on a gravity dam A gravity dam is
subjected to the following main forces
  • Weight of dam
  • Water pressure
  • Uplift pressure
  • Wave pressure

silt pressure ice pressure wind
pressure earthquake forces
36
  • Joints in gravity dams
  • As a gravity dam is a huge concrete structure,
    it is essential to provide suitable joints
    appropriate places. Depending upon the location
    and the purpose served, the joints are classified
    as follows
  • 1) Construction joints
  • 2) Contraction joints
  • Transverse joints

  • Longitudinal joints

37
  • Keys in gravity dams
  • Keys are provided at the joints in gravity dams.
  • Keys are interlocking projections of concrete
    provided at the surfaces of the joints to
    transfer the load from one part to the other.
  • a) Vertical keys
  • it is provided in transverse joints to transfer
    horizontal shear. These keys also assist in
    reducing the leakage of water from the upstream
    of the dam to the downstream through the
    transverse joints
  • B) Horizontal keys
  • it is provided in longitudinal joints to
    transfer vertical shear. The faces of the
    horizontal keys should be aligned, as far as
    possible, approximately parallel with the
    principal planes for the reservoir full condition
    so that there are no shear stresses on the faces
    of the keys.
  • The modern practice is to provide keys only in
    the longitudinal contraction joints and not in
    the transverse contraction joints.

38
  • Water tightness of the joint
  • Various types of rubber, metal, asphalt and
    PVC stops are used in preventing leakage through
    the vertical contraction joints.
  • These water stops are also used in horizontal
    joints.
  • The rubber or metal water stops are used
    across the joints near the upstream face of the
    dam.
  • Rubber water stops should be used only in wet
    and dark locations
  •  
  • Constructing gravity dam
  • By constructing diversion tunnel
  • By constructing the dam in two stages.
  • Or
  • Diversion of the river
  • Foundation excavation and treatment
  • Installation of construction plants
  • Erection of form work
  • Concreting operation
  • Installation of gates and other mechanical
    items

39
  • Equipment used in gravity dam
  • There are basically two types of instruments used
    in gravity dams.
  • 1) Imbedded and internal
  • Strain meters
  • Stress meters
  • Pressure meters
  • Resistance thermometer
  • Displacement meters
  • Deformation meters
  • Load transducers
  • Water level meters
  •  
  • 2) Surveying
  • Electronic theodolites
  • Leveling instruments

40
  • Earthen dam
  • Classification of earthen dam
  • a) Based upon the method of construction
  • Rolled fill earth dam
  • Hydraulic fill earth dam
  • b) Based upon the section of the dam
  • Homogeneous earth dams
  • Zoned earth dams
  • Diaphragm type earth dams
  • Components of earth dam
  • Height of dam and free-board
  • Top width of the dam
  • Upstream, downstream slopes
  • Slope protection measures
  • Impervious cores
  • Casing and cutoff
  • Seepage control measure
  • Drainage system

41
  • Phreatic line
  • In earthen dam the seepage or phreatic line is
    the line within dam which separates the saturated
    or unsaturated zones.
  • Below this line there are positive hydrostatic
    pressures in the dam. At the phreatic the
    hydrostatic pressure is equal to zero or
    atmospheric pressure.
  • Above this line, there is negative hydrostatic
    pressure and such zone is known as capillary
    saturation.
  • Construction of earthen dam
  • Preparation of the site
  • Embankment construction
  • Puddle wall construction
  • Junction of the earthwork
  • Closure of dam

42
  • Measures of reduction of seepage
  • Prevention of seepage through foundation
  • By providing drainage trenches
  • By providing downstream seepage berms
  • By providing impervious blanket layer on upstream
    slope
  • By providing impervious cutoff.
  • Prevention of seepage through dam
  • By providing horizontal drainage filter
  • By providing toe filter provision of rock-toe in
    the dam keeps phreatic line within the dam
    section. It also provides good facility for the
    drainage. Its height is usually kept 0.3 to 0.4H,
    where H is the head of water. The design of the
    toe-filter should be done properly, satisfying
    the filter requirements.
  • By providing filter downstream of the toe this
    filter also intercepts the seepage of water
    through the embankment, and makes the D/S slope
    safe against piping. This measure also protects
    it against earthquake.
  • By providing downstream coarse section
  • By providing chimney drains extending upward into
    the embankment

43
  • Criteria for safe design
  • No overtopping
  • No seepage failure
  • No structural failure
  • Proper slope protection
  • Proper drainage
  • Economic section

44
  • Spillways
  • Types of spillways
  • Side channel spillway
  • Straight drop spillway
  • Ogee spillway or overflow spillway
  • Trough spillway or chute spillway
  • Shaft spillway
  • Siphon spillway
  • Types of gates
  • Following types of spillway gates are commonly
    used
  • Flash board gates
  • Stop logs or needle gates
  • Radial gates
  • Drum gates
  • Bear top gates
  • Vertical lift gates
  • Rolling gates

45
  • 7. DIVERSION HEAD WORKS
  • Components of diversion head works
  • A weir or a barrage
  • A divide wall
  • Approach channel
  • Scouring sluices
  • Fish ladder
  • Silt controlling devices
  • Canal head regulator
  • Marginal bunds
  • Guide banks

46
  • Purpose
  • It raises the water level on its upstream side
  • It regulates the supply of water into canal
  • It controls the entry of silt into canals
  • It creates a small pond on its upstream and
    provides some pondage
  • To prevent the direct transfer of flood water
    into the canal.
  • It helps in controlling the vagaries of the
    river.
  • Barrage and weir situation with sketches

47
Comparison of weir and barrage
A barrage is generally better than a weir. Most
of the diversion head works these days
usually consist of barrages.
WEIR
BARRAGE
Initial cost is low
Initial cost is quite high
Because the crest is at high level, there is great silting problem
There is a good control over silt entry into the canal
There is a large afflux during floods which causes large submergence
The afflux during flood is small, so submerged area is less.
It lacks an effective control on the river during flood
It has a good control on the river during flood and the outflow can be easily regulated by gates
48
  • Control of silt entry
  • By providing scouring sluices in the body wall of
    the weir at the entrance to the off-take channel
  • By creating a still pond in front of the head
    regulator. This is effected by constructing a
    divide wall
  • By providing a permanent pavement on the bottom
    of the approach channel.
  • By providing a silt excluder
  • By allowing clear water from higher level to the
    canal. This is effected by
  • Providing raised silt to the canal
  • Reducing the silt levels of the scouring sluices
  • Providing sluices gates in tiers

49
  • Scour sluices/under sluices
  • These are openings provided in the body wall of
    the weir.
  • Their main function is to prevent the
    obstructions to the flow of water through the
    main sluice. These are provided near the wing
    walls of the weir.
  • Functions of scour sluices
  • Transportation of the deposited silt in front of
    the head regulator at the u/s to the d/s side,
    thus preventing the entry of bed silt in the
    canal.
  • Reducing the maximum flood level.
  • Creating a clear, unobstructed river channel at
    the approach portion of the head regulator.
  • Location and operation
  • They are constructed at one side or smaller
    compartment in front of the still pond created by
    the divide wall.
  • These are operated by means of gates provided
    for this purpose. They are operated by levers
    provided at the top of the weirs.

50
  • Silt excluder
  • It is a structure which excludes the silt from
    irrigation water as the name implies.
  • It separates the lower silt laden portion of the
    water from the upper silt free portion. It
    consists of a series of parallel tunnels of low
    high.
  • The tunnels are constructed in the pocket
    parallel to the flow of water in the river. The
    height of tunnels depends upon the silt
    distribution in the flow of water.
  • The lower portion of the flow which contains
    heavy silt load enters the tunnels. The coarse
    silt load is then drive towards the scouring
    sluices.
  • This water passes to the d/s side of the weir
    through the sluices. Thus only clear water is
    allowed to enter the canal.

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  • Head regulator
  • It is a structure constructed at the entrance of
    the canal where it takes off from the river. The
    regulator serves the following purposes
  • It regulates the flow of irrigation water
    entering into the canal.
  • It can be used as a meter for measuring the
    discharge.
  • It regulates and prevents excessive silt entry
    into the canal.

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SILT EXCLUDER
SILT EJECTOR
It is located in the under sluices section of the river
It is located on the canal at some distance away from the head regulator
It is heavy as it is subjected to large forces
It is relatively light
It can be done only once before the water enters the canal
It can be done a number of times by installing various extractors on the canal
Overall cost is high
Low cost if the ejector is not very far off from the head regulator
The tunnels are quite large and are not liable to be clogged
The tunnels are small and many be choked by debris
Working head is always available
Working head is reduced when the canal supply is low
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8. Canals Classification of canal

Based on nature of source of supply
Permanent
inundation
Based upon the purpose of the canal
Irrigation
Water supply
Navigation
Carrier
Power generating
Feeder
Based on financial output
Protective
Productive
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Classification of canal

Based upon the relative position in the network
Main canal
Branch canal
Distributor
Minor
Water course
Based on the alignment
Contour
Ridge or watershed
Side slope canal
Based upon the materials of construction
Side slope canal
Side slope canal
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  • Contour canal
  • These canals are constructed nearly parallel to
    the contour lines of the area. Usually main
    canals are constructed along the contour lines
    for some length near the diversion head work.
  • Branch canals and distributaries are also
    constructed as far as possible on the contour
    lines.
  • The contours chosen for the alignment should
    include all the contours of the area to be
    irrigated.
  • The contour canal irrigates the areas whose
    elevation is lower than the elevation of the
    canal, because water flows under gravity from it
    to the fields.
  • Contour canals usually have one bank, because as
    the other side is higher, it does not require
    second bank. Sometimes these canals are also
    known as single bank canals.
  • They may also have both the banks depending upon
    the situations. For proper flow longitudinal
    slope is provided to the bed of the canal.

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  • Ridge canal
  • The canals constructed on the ridge or watershed
    line are known as ridge canals.
  • These canals are usually taken off from the
    contour canal.
  • As this canal can irrigate fields on its both the
    sides, its command area is more.
  • These canals also do not meet with any cross
    drainage works, therefore their construction cost
    is also low.
  • While doing the construction of these canals if
    the ridge takes sharp turn, the alignment of the
    canal should be made straight as far as possible,
    because it reduces the length of the canal and
    thereby construction cost.
  • Most of the irrigation canals are ridge canals.

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  • Ridge canal
  • The canals constructed on the ridge or watershed
    line are known as ridge canals.
  • These canals are usually taken off from the
    contour canal.
  • As this canal can irrigate fields on its both the
    sides, its command area is more.
  • These canals also do not meet with any cross
    drainage works, therefore their construction cost
    is also low.
  • While doing the construction of these canals if
    the ridge takes sharp turn, the alignment of the
    canal should be made straight as far as possible,
    because it reduces the length of the canal and
    thereby construction cost.
  • Most of the irrigation canals are ridge canals.
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