irrigation(GTU)

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Water Managements

• Zarna Chovatiya

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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

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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

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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

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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

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• 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.
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• 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.

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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

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• 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.

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• Relation between duty, delta and base period

In birdie text book pg no 47
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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

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• 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

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• 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

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• 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
•  

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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.

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• 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

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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

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• 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

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In birdie text book pg no 47
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• 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.

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• 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

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• 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
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• 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
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• 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
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• 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

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• 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

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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.

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• 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.

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• 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.

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• 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.

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• 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

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• 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
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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
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• 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

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• 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
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• 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

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• 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.

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• 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

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• 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

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• 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

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• 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

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• 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

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

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• 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

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• 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

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• 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

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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
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• 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

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• 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.

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• 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.

57

• 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.