Hydraulic Structures in Irrigation Distribution Systems

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Hydraulic Structures in Irrigation Distribution
Systems 

• Chapter 5

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Valves in pipe networks

• On-Off valves
• Throttling valves
• Pressure Regulating Valves
• Check Valves
• Surge Control Valves
• Pressure Relief Valves
• Vacuum relief valves (Air release valves

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Pressure regulating valve
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Flow measurements in pipelines

• differential pressure flow meters
• Venturi meters
• Orifice meters
• Elbow meters
• Rotating mechanical flow meters
• Bypass flow meters
• Ultrasonic flow meters
• Magnetic Flow meters

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Magnetic flow meters
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Ultrasonic flow meters
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Control structures in open channels

• Intake structures
• Check structures
• Check-drops
• Drop and chute structures

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Flow measurements in open channels

• Volumetric method
• Velocity area method
• Using float method
• Current meters
• Control sections
• Thin plate weirs
• Broad Crested weirs
• Flumes

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Thin plate weirs
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Assumptions

• no head losses (E1 E2) (the means no
  significant turbulence)
• water surface elevation remains constant, note
  this is physically impossible, but actual errors
  are small
• pressure at crest (station 2) Patmo throughout
  depth.

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Thin weirs- full width
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• For Cd0.611, weir equation becomes
• For SI units, g 9.81 m/s2, or
• For foot units, g32.2 ft/s2, or
• In general, discharge could be given by
• Where, C is a weir coefficient.
•  

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Contracted rectangular weir
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Triangular weir
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Broad crested weir
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Weirs

• Advantages
• Accurate measurement.
• Simple and easy to construct with non-obstruction
  by moss (type of algae) or floating materials.
• Durable
• Disadvantages
• Require considerable fall of water surface.
• Deposition of sand, gravel and silt upstream of
  weirs

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Example

• An end-contracted weir of total length 286 ft and
  crest height 5 ft is used to discharge water
  without exceeding a head of 2.5 ft from a tank
  300 ft wide. The weir carries piers that are 10
  ft clear distance apart and 2 ft wide, to support
  the footway. Determine the discharge. Cd 0.6