WATER SUPPLY DISTRIBUTION On completion of this module you should be able to

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WATER SUPPLY DISTRIBUTIONOn completion of this
module you should be able to

• Describe a water supply distribution system
• describe the components of pipe distribution
  systems
• appreciate the Queensland Planning Guidelines for
  Water Supply and Sewerage
• design simple gravity and rising mains
• determine the required storage capacities and
  location in a water supply distribution

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WATER DISTRIBUTION SYSTEMS

• A network of pipes storage tanks to meet
  demand at satisfactory pressure
• Grid or branching layout
• Supply zones and storage tanks
• Design flow rates

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Reticulation pipe networks
Branching system
Grid system
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PIPE APPURTENANCES

• Stop, butterfly valves
• reflux or non-returning valves
• pressure reducing, pressure sustaining valves
• pressure relief valves (surge)
• air valves
• hydrants

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PIPE APPURTENANCES
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Design of Urban Water Supply Schemes

• Trunk main from headworks to distribution
  reservoirs must cater for MDMM capacity
• Supply mains from service reservoirs and
  reticulation network must achieve MH demand
• Maximum pressure 80 m head in pipelines
• Minimum pressure 22 m (12 m under firefighting)

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Some design parameters

• Annual demand is the total demand for a
  community, ML/year
• Average daily demand (ADD) Annual demand/365,
  ML/d
• Mean day maximum month (MDMM) 1.5 x ADD
• Maximum day (MD) 1.5 x MDMM
• Maximum hour (MH) MD/12 or 2.25 x ADD/12

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Design of Gravity Main

• Determine the maximum capacity
• Select pressure at load centre, check for
  pressure at high and low points
• Ascertain TWL of service reservoir and total
  losses
• Static head must not be excessive. Consider
  adjusting elevations or introduce break-pressure
  tank
• Design for appropriate pipe diameter through a
  process of iteration

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Design of Gravity Main
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Maximum capacity
This depends on the location of the delivery
system

• For trunk main from the headworks to the
  distribution storage tank, the design capacity is
  MDMM
• For other mains and within the reticulation
  system, the pipe must be designed to carry the
  maximum instantaneous flow i.e. MH demand.

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Hydraulic equations

• Use Darcy-Weisbach and Moody equations
• Determine the head losses (friction and minor)
• Friction loss f L v2 /(2gD)

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Design of Rising Main

• Operating hours must be less than 24 hours
• Operating cost and not construction cost may be a
  significant factor
• Pump power is directly related to head losses
  which increases with the square of flow velocity
• Use economic analysis

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Service Reservoir

• Provides adequate pressure and acts as a buffer
  between supply and demand
• Operating storage
• Breakdown storage
• Firefighting

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Types of Service Reservoirs

• Surface tank
• Standpipe
• Elevated tank

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Location of Storage ReservoirStorage reservoir
is an essential component of a distribution
system. A strategic location is important in
terms of cost and service

• Locate centrally and as close as possible to the
  area it serves to minimise head losses and
  capital construction costs
• Locate at an elevation (natural or constructed)
  high enough to provide adequate pressures
• To accommodate fluctuation in demand, high and
  low supply operations regimes are to be provided

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Reservoir location influences pressure
distribution
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Use of rise and fall main
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End of Module 19 - Water distribution systems