Design Water Supply Handout

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DesignofWaterSupplyNetworks

CIVL5995ProjectI

AhmadSana

DepartmentofCivilandArchitecturalEngineering

SultanQaboosUniversity,Oman

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Designof

water

distribution

system

Amunicipalwaterdistributionsystemisusedtodeliverwatertothe

consumer.

Wateriswithdrawnfromalongthepipesinapipenetworksystem,for

computationalpurposesalldemandsonthesystemareassumedtooccur

atthejunctionnodes.

Pressureisthemainconcerninawaterdistributionsystem.Atnotime

shouldthewaterpressureinthesystembesolowthatcontaminated

groundwatercouldenterthesystematpointsofleakage.

Thetotalwaterdemandateachnodeisestimatedfromresidential,

industrialand

commercial

water

demands

at

that

node.

The

fire

flow

is

addedtoaccountforemergencywaterdemand.

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Componentsofawaterdistribution

system

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FunctionalComponentsofaWaterUtility

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Largediameterwatermains

5

PressureReducingandCheckValve

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ATypicalPumpingStationSchematic

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Pumphouse

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Centrifugalpumps

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Typicalelevatedwater

tanks

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Reservoirpumptanksystem

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Pumpcurves

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Typesofvalves

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Typicallayoutofwatersupplysystem

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Usingboosterpumps

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Operationofawatersupplysystem

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Systemheadcurve

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Pumpoperatingpoint

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Operatingpoints(Max.and Min.)

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Operatingpointsforvariouspumps

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Operationpointsforvariouspipes

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Typicalpipenetwork

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WaterDemandTotalwaterdemandatanodeisequaltotheaveragewaterdemandper

capitamultipliedbythepopulationservedbythatnode.

Thepopulationmaybeestimatedbyanyoftheavailablemodelsof

populationgrowth.Thesemodelsusethepreviouslyavailablepopulation

data

for

future

projections.Forexample,accordingtoArithmeticmodel:

P(t)isthepopulationattimetandP0isthereferencepopulation.

ktPtP 0)(

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Public Authority for Electricity and Water, Sultanate of Oman

DesignGuidelinesandStandardsforWater

SupplySystems


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Demandpattern

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FiredemandInsurance Services Office, Inc. (ISO, 1980) formula: iiii PXOCNFF )( where, NFFi is needed fire flow at location i, Ci is the construction factor based on

size and type of construction of the building, Oi is the occupancy factor reflecting

the kinds of material stored in the building (value range from 0.75 to 1.25), and

(X+P)i is the sum of the exposure factor and communication factor that reflects the

proximity and exposure of other buildings (value range from 1.0 to 1.75).

ii AFC 220min)/L(

Ai is the effective floor area in square meters, typically equal to the area of the

largest floor in the building plus 50% of the area of all other floors, F is a

coefficient based on the class of construction. The maximum value of Ci and

typical F values are given below:

Classof

Construction

Description F Max.Ci(L/min)

1 Frame 1.5 30,000

2 Joisted masonry 1.0 30,000

3 Noncombustible 0.8 23,000

4 Masonry, noncombustible 0.8 23,000

5 Modified fire resistive 0.6 23,000

6 Fire resistive 0.6 23,000 34


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FiredemandCombustibilityclass Examples Oi

C1 Noncombustible Steel or concrete products storage 0.75

C2 Limited combustible Apartments, mosques, offices 0.85

C3 Combustible Department stores, supermarkets 1.0

C4 Freeburning Auditoriums, warehouses 1.15

C5 Rapid burning Paint shops, upholstering shops 1.25

Average value of (X+P)i is 1.4. The NFF should be rounded to the nearest

1000L/min if less than 9000 L/min and to the nearest 2000L/min if greater than

9000L/min.Requiredfireflow(L/min) RequiredfireflowDuration(h)

140 kPa

Maximum pressure (not strict) : 650kPa.

Storage facilities1. 20% to 25% of the maximum daily demand volume

2. Fire demand3. Emergency storage (minimum storage equal to average daily system demand)

4. Minimum height of water in the elevated storage tank based on minimum

piezometric head in the service area

5. Normal operating range 4.5 to 6.0 m.

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Design Water Supply Handout