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Rock Street, San Francisco






















¡  For it to be
efficient, must have the ability to transport the sewage effectively.

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¡  It’s classified
based on the type of the wastewater flowing in the pipe:


§ sanitary sewer                           – carry only the
water from residential, commercial and industrial with the stormwater excluded.


§    stormwater sewer –
carries the water coming from roofs, paved areas, pavements and roads.


§ combined sewer  – sanitary sewer + stormwater sewer.






¡  Design must be in accordance with


§    MS 1228:1991: Code
of Practice for Design and Installation of Sewerage system



¡  It’s designed to
discharge the wastewater flows as required.



¡  Sewage treatment plant (STP)


§   converts the sewage
into a form which can be safely discharges to the environment, or reused for
various compatible purposes.


§    Effluent discharge
must meet the standard A & B





¡  The diameter of the pipe is

§   chosen based on the
availability of the size provided


§    Consideration of
the economy


§   sufficient size to
handle the total discharge, Q. (Q > Peak flow total )


¡  Lateral sewer

§   minimum of 150mm


§   receives the
channel sewage from individual buildings to another branch sewer, or directly
to an on-site treatment plant





¡   Reticulation sewer

§    225mm to 300mm.


§    receives the
channel sewage collected from groups of individual properties to branch sewers


¡   Main sewers/ trunk/ outfall sewer

§    450mm to above
900mm diameter.


§    receives sewers
from branch sewers and transfer flows to large sewage treatment plant.


¡   Branch sewers

§    300mm to 450mm


the sewage from reticulation sewers and thereafter transfers the flow to small
sewage treatment plants, or to main sewers





¡   The depth of sewers is

§    1.2m below the
ground surface.


§    invert depth –
minimum of 1.2m


¡   Velocities

§    minimum of 0.8 m/s


?     self-cleansing

?     prevents the sludge
to settle in the pipelines


§    maximum is at 4.0


?     prevent scouring of
sewer by erosive action of suspended matter.


¡   The slope

§     1:200 to 1:25 in
order to maintain the velocity.





¡  Design should be:

§    Allow easy access
for inspection and cleaning for the pipe


§    Made from durable


§    cause minimum interference
to the sewage flow.


§    minimum of 1.2 m in
depth from the ground level


§    at least at 100m
apart of each other for eases of maintenance


§    Gradients from 1:
40 to 1: 110 will should be use to give normally give adequate flow velocities.



¡  Locations are situated

§    end of line


§    intersection of


§    changes in grade
and alignment except in curved sewers.






The minimum diameter of manholes constructed from precast concrete


Sewer dia. (mm)

Chamber dia. (mm)
















¡   Drop manhole


§    installed to reduce
the turbulence in the manholes cause by the elevation differences.


§    if the difference
between the incoming sewer and manhole invert is more than 500mm


§    If the difference
between the incoming sewers is less than 600mm,


§    invert shall be
filleted at the corners to prevent solids deposition





¡  6 procedure




Network sewer

Sewerage layout plan


Determination of population equivalent


Determination of peak flow, discharge, type and size of pipe


Determination of velocities


Determination of
invert level and outlet level






¡  Based onMS 1228 :
1991 : section 4.3.2 several factors must be condiser in the planning:




sewerage pipe must be located in the surrounding area of the road.


§    The pipe to be
located in private property due to certain topographies must apply for
permission to certain individual before the construction can begin.


any construction work can begin, the layout and overall existing building, pipe
and electrical must first to be determine.


§   During the
construction work, the separation of sewer and main water should be requires of
minimum horizontal separation of 3 m and a minimum vertical separation of 46 cm
from water mains.






The system must be drawn to show the location of the pipe and so on.The
process involved of:


§    Preparing the
sewerage layout plan to show the flow of sewerage, position of the network,
size of pipe and position of manholes



Sewer follow natural drainage ways to minimize excavation and pumping
requirements. Large trunk sewers are usually constructed in low-lying areas
closely paralleling streams or channels. In general, pipes should cross
contours at right angles.


¡     Located pipe

place for easy connection for future user


provide access for maintenance.


accomplished by placing them in streets or other rights-of-way.






¡  number expressing
the ratio of the sum of the pollution load produced during 24 hours by
industrial facilities and services to the individual pollution load in
household sewage produced by one person in the same time.




¡  parameter use to
convert the number of person contributing to volumetric flow rate of wastes



¡  flow rates are measured in cubic meters per




¡  calculated for both
existing land use and for expected future development.

Type of establishment

Population equivalent



5 per house



3 per 100m² area


Educational Institutions



– Day Schools

0.2 per student


– Residential Schools

1 per student



4 per bed Hotels 4 per



0.3 per employee


Market (Wet Type)

3 per stall


Market (Dry Type)

1 per stall


Petrol Stations

18 per service bay


Bus Terminal

4 per bus bay


Taxi Terminal

4 per taxi bay



0.5 per person


Church or

0.2 per person



0.2 per person


Swimming Pool or
Sports Complex

0.5 per person


Public Toilet

16 per WC (water



0.2 per passenger/day



0.3 per employee



10 per machine











¡  PE = population equivalent x per capita


¡ PE =
population equivalent x 225 L/c.d                                                                                                                                                                                               (1)




¡ Cumulative
PE = PE 1 + PE2








¡   Peak flow

§    the combination of
infiltration and inflow, and wastewater flow.


§    in unit of flow
rate per contribution area or unit of flowrate per pipe length.





















flow discharge, Qd depends on the pipe gradient and diameter of the



Pipe area, Apipe = ? r2


Perimeter, P = 2
? r


Hydraulic radius = A/P





¡ Design must be Qd >
Peak Flow


?           (6)







¡  Manning
coefficient, n


§  Depend on the
selected pipe material














Manning coefficient, n




0.013 ? n ? 0.015

Vitrified clay

0.013 ? n ? 0.015

Cast iron

0.013 ? n ? 0.015


0.015 ? n ? 0.017

Corrugated metal pipe

0.022 ? n ? 0.025

Asbestos cement

0.013 ? n ? 0.015

Earthern channel

0.025 ? n ? 0.030










§    Full flow velocity
Vfull can be calculated
from the pipe discharge

§  4m/s > V (full
flow) > 0.8 m/s












¡  Manhole level

§    find by ground
surface elevation



Fall in sewer = Upper end elevation – Lower end elevation                                                                                                                                                                                            (8)


Sewer invert lower end = Gound surface elevation – fall in sewer (9)


¡  However, if ground surface gradient is not

§    new pipe gradient
can be proposed


Fall in sewer =
slope x Lower end elevation



Sewer invert upper end = Gound surface
elevation – cover of

pipe – diameter
of pipe










Criteria                                                                                                  Remarks


gradient, s                                                                     0.5 % ? s ?
4 %


Full flow
velocity, Vfull                                       0.8 m/s ? Vfull ? 4 m/s


Discharge, Qd                                                                         PF < Qd

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