11/30/2010 

COLLECTION AND
DISTRIBUTION OF WATER
By Zerihun Alemayehu

Addis Ababa University

AAiT Addis Ababa Institute of Technology

Department of Civil Engineering

Collection and Distribution of Water

• Deals with the transport of water from the source
through the treatment plant to the consumers.
• It requires
▫ intake structures,
▫ transmission lines,
▫ distribution pipe networks and
▫ other essential accessories.

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

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Surface water Intakes

• Floating intakes
• Submerged intakes
• Tower intakes
• Shore intakes
• Pier intakes

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

Reservoir Intake

AAiT Water Supply & Urban Drainage

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Tower Intake

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

Submerged Lake Intake

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

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River Intake

 Major components
 Screen inlet
 Intake pipe
 Intake sump
 Suction pipe
 Pumps
 Gate and foot valves
 access
AAiT Water Supply & Urban Drainage
By Zerihun Alemayehu

Intake Structures

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

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locating the positions of intakes

• Avoid wastewater discharge points and pollution hazard
• enable withdrawal of water from a range of levels
• Magnitude and direction of stream or current velocities
should not affect the function and stability of the intake
structure.
• Reliable access roads and power sources should be available
• should be near to treatment plant
• Should not interfere with navigation requirements,
• major environmental impacts should be avoided

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

Design Criteria for intake structures

• Design capacity = Q max-day
• Intake velocity should be  8 cm/s
• vertical positions intake ports should be such
that good quality water is withdrawn.
• Locate the top intake port at a distance not less
than 2 m from the normal water level and the
bottom port at least 1 m above the bottom.

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

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Intake design
• Volume of sump detention time. A detention
time of at least 20min is recommended.
• At least two sumps - to avoid interruption of
service.
• Height (with a freeboard about 0.5m)
• Location of the bottom of the sump should be >
1.5m below the lowest stream level or > 1m
below stream bed.

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

Example 1: River Intake design

River bank
• Given the following
information proportion a HWL 1209.1 m
suitable river intake.
▫ Daily demand 5000 m3
▫ Pump capacity: 50 l/s LWL 1202.5 m
(working 8 hr/day)
 1200.1 m

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

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Example 1 Solution

• Capacity of each pump daily = 8x3600x50/1000=1440 m3

• Number of pumps = 5000/1440 = 3.47  4
• Hourly flow of each pump = 5000/(4x8)=156.24 m3/h
• Take detention time, Td = 20 min
•  capacity = Td x Q = (20/60)x 156.24 = 52.08 m3

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

Example 1 Solution

1209.1-1202.5=6.6 m

1.5 m

• Effective height of sump = 6.6 + 1.5 = 8.1

• Free board = 0.5
• Total sump height = 8.6 m
• If we use circular sump diameter = 2.86 m
AAiT Water Supply & Urban Drainage
By Zerihun Alemayehu

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Pipelines and appurtenances

The selection of pipe materials is based on
▫ carrying capacity
▫ strength
▫ ease of transportation and handling
▫ availability
▫ quality of water
▫ cost (initial and maintenance)

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

Pipelines and appurtenances

• Cast iron pipes:
▫ highly resistant to corrosion, strong but brittle,
▫ easy jointing, withstanding high internal pressure, long life
▫ very heavy and difficult to transport

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

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Pipelines and appurtenances

• Steel pipe:
▫ strong, very light weight and
can withstand higher
pressure than cast iron pipes.
▫ cheap, easy to construct and
can be easily transported
▫ cannot withstand external
loads, affected by corrosion
and are costly to maintain.

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

Pipelines and appurtenances

• Cement-lined cast iron pipes:
▫ cement protect against corrosion.
▫ very small coefficient of friction than unlined cast
iron pipes.

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

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Pipelines and appurtenances

• Plastic pipes:
▫ corrosion resistant , light weight and economical.
▫ Rigid (unplasticized) uPVC is stronger and can
withstand much higher pressure for a given wall
thickness.

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

Pipelines and Appurtenances

• Valves:
▫ to isolate segments of a pipeline, to regulate rate
of flow, to control pressure, and to allow release
or entry of air from pipe system.
• Factors considered in the selection of valves:
▫ include purpose and operation,
▫ capacity required,
▫ head loss and rate of flow,
▫ cost,
▫ availability, etc.
AAiT Water Supply & Urban Drainage
By Zerihun Alemayehu

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Pipelines and Appurtenances

• Shutoff valves:
▫ to stop the flow of water through a
pipeline
▫ spacing from 150 to 370m
▫ a minimum of three of the four
pipes connected at a junction are
valved.
▫ fire hydrant, in inlet, outlet, and by-
pass lines
▫ Gate valves and butterfly valves

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

Pipelines and appurtenances

• Check valves:
▫ semiautomatic device and
permits water flow only in one
direction.
▫ in the discharge pipes of
centrifugal pumps prevent
backflow
▫ in conjunction with altitude
valves

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

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Pipelines and appurtenances

• Altitude valves :
▫ to automatically control the
flow into and out of an
elevated storage tank or
standpipe to maintain
desired water level
elevations.
▫ include double-acting
sequence valve, single-acting
type, or differential altitude
valve

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

Pipelines and appurtenances

• Air-release and vacuum valves :
▫ Air-release valves installed at high
points of distribution piping, in
valve domes, and fittings, and in
discharge lines from pump to
discharge the trapped air.
▫ Vacuum valves are used to protect
pipelines from collapse as they are
emptied, by allowing air to enter
the pipes.
AAiT Water Supply & Urban Drainage
By Zerihun Alemayehu

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Pipelines and appurtenances

• Pressure reducing valves (PRV). :

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Pipelines and appurtenances

• Pressure sustaining valves (PSV) :

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Distribution systems
• Depending upon the level of the source of water
and the city, topography of the area, and other
local considerations,

▫ Gravitational system,
▫ Pumping without storage, and
▫ Pumping with storage.

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

Distribution systems
• Gravitational system:
▫ action of gravity without any pumping
▫ most economical and reliable
▫ for cities situated at foothills

min. 
demand
max. 
Reservoir demand

City

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

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Distribution systems
• Pumping without storage:
▫ treated water is directly pumped into the
distribution mains without storing
▫ High lift pumps operate at variable speeds  to
match variable water demand
▫ Disadvantageous (power failure)  no reserve
flow

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

Distribution systems
• Pumping without storage:
HGL
min. 
Pump head

HGL demand
max. 
demand

City

Pump

Reservoir

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

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 11/30/2010 

Distribution systems
• Pumping with storage:
▫ treated water is pumped at a constant rate 
stored in elevated distribution reservoir
distributed to the consumers by the action of
gravity
▫ excess water during low demand period gets
stored in the reservoir  supplied during high
demand periods.
▫ pumps work at uniform rate high efficiency
▫ quite reliable (even during power failure)

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

Distribution systems
• Pumping with storage:
Low demand
Peak  
demand

 
Pump    
City Elevated Tank
 

 
Reservoir
AAiT Water Supply & Urban Drainage
By Zerihun Alemayehu

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 11/30/2010 

Layout of distribution systems

• Pipe networks :
▫ Primary or arterial mains
 from the pumping stations and from storage facilities
to the various districts of the city.
 valved at intervals of not ≤ 1.5 km
▫ Secondary lines or Sub-mains
 run from one primary main to another
 located at spacings of 2-4 blocks
▫ Small distribution mains or branches
 Supply water to every consumer and to the fire
hydrants

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

Layout of distribution systems

• layout of distribution pipes generally follows the
road pattern
• four types of pipe network layouts –
▫ dead end system or branch system,
▫ gridiron system,
▫ ring system, and
▫ radial system.

AAiT Water Supply & Urban Drainage

By Zerihun Alemayehu

17 
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Layout of distribution systems

• Dead end system
BRANCHE
▫ solved easily MAIN PIPE (M) S B SUB-MAIN (S)

▫ Lesser number of shut-off valves

B
▫ Shorter pipe lengths and the easy B
S
BRANCH (B)
to lay pipes B
S
▫ cheap and simple and expanded B
B B
easily
▫ dead ends prevent circulation B
B
B S
of water B S

▫ Problematic if a pipe is damaged B

Fig. 3.7
M

AAiT

Layout of distribution systems

• Gridiron systems
▫ Discharge, friction loss and pipe
size is less
▫ Not problematic if a pipe is
damaged
▫ No dead ends allows
circulation of water
▫ Good for fire fighting
▫ more pipelines and shut-off
valves
▫ high cost of construction
▫ design is difficult and expensive
AAiT Water Supply & Urban Drainage
By Zerihun Alemayehu

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Layout of distribution systems

• Ring systems: Main Pipe
▫ closed ring, circular or rectangular
▫ suitable for well-planned towns
and cities
▫ Generally at high demand areas
▫ Not problematic if a pipe is Sub mains
damaged
▫ No dead ends allows circulation
of water
▫ Good for fire fighting
▫ more pipelines and shut-off valves
▫ high cost of construction
▫ design is difficult and expensive Fig. : Ring System

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Layout of distribution systems

• Radial systems
▫ For city or a town having a
system of radial roads MAIN PIPE

emerging from different centers

BRANCHES
▫ distribution reservoirs at these
centers
DISTRIBUTION
▫ From mains  pumped into RESERVOIRS
the DRs placed at different SUB-MAIN

centers and then to the service

areas.
▫ ensures high pressure and
efficient water distribution
Fig. : Radial System

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