in this presentation the design method and criteria for sewerage system is explained.

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Final Year Project
Design of Sewerage System For Bannu Campus

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Group Members
Irfanullah 0770
Shoukat Ullah 0763
M.Fawad Khan 0732
Supervised By:
Dr. Afed Ullah Khan
Department of Civil Engineering UET Peshawar BANNU Campus

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Contents
• Introduction
• Design requirement
• Calculation of sanitary sewage
• Calculation of storm runoff
• Design of combined sewer
• Calculation of dia of sewer

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Introduction

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Sanitary Sewage
The sewage which originates of dwellings, industrial facilities, commercials
and institutions.
source-shutterstock.com

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Storm Runoff
Storm sewage or storm water is the flow derived from rainfall events and introduced into
sewers intended for its conveyance.
Source -researchgate.net

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Partial Combined Sewer
The sewer are designed as sanitary sewer but sufficient excess capacity
are provided to carry a part of storm discharge also. In this type
domestic sewage and storm water of buildings are carried out in one
set.
Source- WASA Lahore

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Design Requirements

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Papulation forecast
Description Population
Present 700
Future 800
Total 1500

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Peak Factor
Ratio of the maximum flow to the average flow, denoted as PF, is
observed to be dependent on contributory population.

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Average Sewage Flow(m3 /day) Peak Factor
≤ 2500 4.0
2500 – 5000 3.4
5000 – 10000 3.1
10000 – 25000 2.7
25000 – 50000 2.5
50000 – 100000 2.3
100000 – 250000 2.15
250000 – 500000 2.08
> 500000 2.0
Peak Factor
Source-WASA Lahore

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Minimum Sewer Size
225 mm is taken as the minimum sewer size. The reason being that, the
choking does not take place even with the bigger size particles, which
are usually thrown into the sewers through manholes.
Source-WASA Lahore

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Minimum Cover Of Sewer
1 m is taken as the minimum cover over the sewers to avoid damage
from live loads coming on the sewer.
Minimum cover
Source- WASA Lahore

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Direction of Sewer Line
In choosing the alignment of a sewerage system, the following factors
shall also be considered,
•Sewer should flow, as for as possible the Natural Slope.
•The objectives to serve all existing and future land development.
•Site constraints.
•Proximity of trees and other vegetation.
•The hydraulic performance.
•Social and economic impact.

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Slope Of Sewer Line
Sewer dia (mm) Minimum
slope(percent)
Maximum
slope(percent)
150 1.0 33.0
200 0.40 22.0
250 0.28 15.0
300 0.22 11.0
375 0.15 8.3
400 0.14 7.8
450 0.12 6.5
525 0.10 5.1
600 0.08 4.2
Source-Sewerage manual with Eurocodes

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Trenching
• The width of the trench shall be ample to allow the pipe to be laid
and jointed properly and to allow the backfill to be placed and
compacted as needed. The trench sides shall be kept as nearly
vertical as possible. When wider trenches are dug, appropriate
bedding class and pipe strength shall be used.
• Ledge rock, boulders, and large stones shall be removed to provide a
minimum clearance of 100 mm below and on each side of all pipe
and joints.

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Invert Level
The lowest inside level at any cross-section of a sewer pipe is known as
Invert Level at that Cross-section.
Invert Level = NGSL/Road Level – Depth of Sewer – Thickness of
Sewer – Dia. of Sewer.
Source-WASA Lahore

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The proper maintenance and operation of the sewerage system is
essential if the systems are to achieve their designed objectives.
Maintenance Objectives
•To monitor the capacity of the system and to restore the flow capacity.
•To monitor and maintain the structural integrity of the system.
•To prevent excessive infiltration and inflow.
Maintenance Of Sewerage Systems

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Manhole
Source- WASA Lahore
Manhole is made or precast manhole is installed for
• Cleaning and
• inspection
At place where change occur
• In sewer direction
• Diameter and
• Slope.

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Manhole
Manhole inside Dia
(mm)
45° Deflection
Max size of pipe (mm)
90° Deflection
Max size of pipe (mm)
1220 610 460
1525 915 690
1830 1070 760

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Spacing Of Manhole
Sewer size Spacing not more than
225mm to 380mm 100 m
460mm to 760mm 120 m
Greater than 760mm 150 m
Spacing
Source- WASA Lahore

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Calculations

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Calculation Of Sanitary Sewage

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Calculation Of Storm Runoff

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Total Sewage Flow
Total sewage = storm runoff + sanitary sewage
Total sewage = 1824 + 1824 = 3648 m3/day

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Calculation of Dia Of Sewer

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Slope Of Sewer Line

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References
• Sewerage manual with Eurocodes “Drainage Service Department” Govt
of Hong Kong Special Administrative Region
• “Water Supply and Sewerage” by E.W Steel and Terenge J. Mcghee
• WASA Lahore

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