DESIGN LAYOUT OF DISTRIBUTION SYSTEMS

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DESIGN LAYOUT OF DISTRIBUTION SYSTEMS

• CE 370

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Distribution System Layout

• Layout of water distribution system is a function
  of
• source of water supply
• topography of distribution area
• variation in water consumption

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Source of Water Supply

• water is supplied at one point (i.e. treatment
  plant)
• distribution storage (elevated tank or
  ground-level tank plus booster pump) is required
  in remote areas to maintain water pressure
• water is supplied at several points (wells)
• storage capacity is reduced and pipe sizes
  required are smaller.

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Topography

• water is supplied at high elevation
• it flows by gravity through the water network.
• water is supplied at low elevation
• must be pumped up into the water network (pipes
  and storage).

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Water Consumption

• is a function of residential, commercial and
  industrial demands.
• planning and zoning is applied to control
  variations in water consumption.
• Climate and economical aspects could also
  influence the layout of a water distribution
  system.

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• The objective of an engineer designing a water
  distribution system is to provide a stable
  hydraulic gradient to maintain adequate pressure
  throughout the service area and enough pumping
  and storage capacities to meet emergency demands.
• The following figure shows simplified water
  distribution systems which illustrate the basic
  principles of design.

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EVALUATION OF DISTRIBUTION SYSTEMS
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Quantity

• the water source plus the storage facilities must
  be able to provide enough water to meet both
  current and future demands (ten years ahead).
• records of average daily, peak daily, peak hourly
  rates of consumption of the past ten years are
  needed, beside other factors related to community
  growth, to project the future needs.

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Intake Capacity

• surface water intakes must be large enough to
  deliver enough water to meet municipal use and
  treatment plant needs during any day of peak
  demand.
• if storage is not available, water intake
  capacity must be large enough to meet fire
  demand, maximum hourly flow, and inplant process
  needs at the same time.

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Pumping Capacity

• Low-lift pumps transport water from the source to
  the treatment plant.
• High-lift pumps transport water from the
  treatment plant to the distribution system.
• Well pumps deliver water to the treatment
  facilities or directly to the distribution
  system.
• Booster pumps are needed to increase pressure in
  the distribution system of large communities or
  in areas with widely varying elevations.
• Pumping stations must have enough capacity to
  provide the amount of water at flow and pressure
  rates needed to meet both daily and hourly peak
  demand plus fire flow.
• Pumping stations must be reliable through
  duplication of units, standby equipment, and
  alternate sources of power

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Piping Network

• Arterial and secondary feeder mains must be
  designed to supply water service for 40 or more
  years after installation.
• Actual lifetime of pipes of mains under normal
  conditions is 50 to 100 years.
• Sub-mains must be at least 6 inches in diameter
  in residential districts and 8 inches in
  important districts.
• Distribution lines are laid out in gridiron
  pattern
• Avoid dead-ends
• Adequate number of valves must be installed to
  allow shutoff in case of emergency
• Valves should be located in a way so that no more
  than one block will be out of service in case of
  emergency.