design of sewerage system
DESCRIPTION
Design of Sewerage systemTRANSCRIPT
BYBY
G. KRISHNANG. KRISHNAN
DESIGN OF DESIGN OF SEWERAGE SYSTEMSEWERAGE SYSTEM
Sewage – Mixture of water and waste productsSewage – Mixture of water and waste products
Types of Sewage:Types of Sewage:Domestic sewage - consists of liquid wastes originating Domestic sewage - consists of liquid wastes originating from urinals, latrines, bath-rooms, kitchen sinks, wash from urinals, latrines, bath-rooms, kitchen sinks, wash basins etc. of the residential, commercial or institutional basins etc. of the residential, commercial or institutional buildings.buildings.Industrial Sewage - consists of liquid wastes originating Industrial Sewage - consists of liquid wastes originating from the industrial processes of various industries, such as from the industrial processes of various industries, such as dyeing, paper making, brewing etc.dyeing, paper making, brewing etc.
The sum of domestic and industrial sewage, may be The sum of domestic and industrial sewage, may be termed as sanitary sewage or simply sewagetermed as sanitary sewage or simply sewage
Design of Sewerage SystemDesign of Sewerage System
SEWAGE COMPOSITIONSEWAGE COMPOSITION
L iq u id9 9 .7 to 9 9 .9 %
C arb oh yd ra te2 5 %
P ro te in s6 5 %
F ats1 0 %
O rg an ic 7 0 %(d erived from livin g th in g s)
G rit S a lts M eta ls
In org an ic - 3 0 %
S olid s0 .1 to 0 .3 %
M ic ro -o rg an ism sin m illion s
S E W A G E
TYPICAL WASTE WATER SYSTEMTYPICAL WASTE WATER SYSTEM
Sewage Treatment Plant
Disposal to water bodies
Raw Sewage pumping main
Raw Sewage Collection System
Pumping station
Reuse for industrial
application
Difference in the Design of water supply pipes and sewer pipes:Difference in the Design of water supply pipes and sewer pipes:
1.1.The water supply pipes carry pure water without containing any The water supply pipes carry pure water without containing any kind of solid particles, either organic or inorganic in nature. The kind of solid particles, either organic or inorganic in nature. The sewage, on the other hand, does contain such particles in sewage, on the other hand, does contain such particles in suspension and the heavier of these particles may settle down at suspension and the heavier of these particles may settle down at the bottom of the sewers, as and when the flow velocity reduces, the bottom of the sewers, as and when the flow velocity reduces, thus ultimately resulting in the clogging of the sewers.thus ultimately resulting in the clogging of the sewers.
2.2.The water supply pipes carry water under pressure, and hence The water supply pipes carry water under pressure, and hence within certain limits, they may be carried up and down the hills within certain limits, they may be carried up and down the hills and the valleys, whereas the sewer pipes carry sewage as and the valleys, whereas the sewer pipes carry sewage as gravity conduits and they must therefore be laid at continuous gravity conduits and they must therefore be laid at continuous gradient in the downward direction up to the outfall point, from gradient in the downward direction up to the outfall point, from where it will be lifted up, treated and disposed of. where it will be lifted up, treated and disposed of.
Design of Sewerage SystemDesign of Sewerage System
Hydraulics of SewersHydraulics of Sewers
MANNINGS FORMULA
V = [ (1/n) (R2/3 S1/2)]
Where S = Bed slope of the sewer (1 in 100)
D = internal diameter of sewer in mm
R = Hydraulic mean depth in m
= Area / wetted Perimeter
V = velocity in mps
n = Manning’s coefficient of roughness
Mannings Coefficients (n)Mannings Coefficients (n)
Fair interior surface condition *
Salt glazed stoneware pipes 0.014
Cement concrete pipes 0.015
Cast iron pipes 0.013
Brick, unglazed sewers/drains 0.015
Asbestos cement 0.012
Plastic (smooth) pipes 0.011
Values of an full depth forPipe MaterialS.No.
1
Good interior surface condition
2
3
4
5
6 0.011
0.011
0.013
0.012
0.013
0.012
Partially filled Circular Sewer SectionPartially filled Circular Sewer Section
d/D v/V q/Q
1.0 1.000 1.000
0.9 1.124 1.066
0.8 1.140 0.968
0.7 1.120 0.838
0.6 1.072 0.671
0.5 1.000 0.500
0.4 0.902 0.337
0.3 0.776 0.196
0.2 0.615 0.088
0.1 0.401 0.021
Hydraulic Elements of Partial flow Sewers
Design CriteriaDesign Criteria Diameter of the sewers and the slope should be decided Diameter of the sewers and the slope should be decided
to meet the following conditionsto meet the following conditions Minimum size of the sewer should be not less than 150mm. Minimum size of the sewer should be not less than 150mm. If any future development is anticipated beyond the head reach, If any future development is anticipated beyond the head reach,
the starting sewer can be of 200mm diameter.the starting sewer can be of 200mm diameter. The velocity of flow and slopes (grade) of sewers are The velocity of flow and slopes (grade) of sewers are
very important criteria in the sewer design. very important criteria in the sewer design. A self-cleansing velocity of 60cm/s and 80cm/s should A self-cleansing velocity of 60cm/s and 80cm/s should
be maintained at the present peak flow, and at the be maintained at the present peak flow, and at the ultimate peak flow respectively.ultimate peak flow respectively.
Sewer section should be designed to run at partial full Sewer section should be designed to run at partial full condition always not exceeding 0.80 full depth at the condition always not exceeding 0.80 full depth at the ultimate peak flow.ultimate peak flow.
Velocity of flow in the SewersVelocity of flow in the Sewers Should neither be less than 0.3mps nor greater than 3mps. Should neither be less than 0.3mps nor greater than 3mps. Optimum velocity of flow for self-cleansing, is 0.6mps for Optimum velocity of flow for self-cleansing, is 0.6mps for
the present flow. the present flow. Larger velocity will involve steeper slope and extra Larger velocity will involve steeper slope and extra
excavation.excavation. Some important facts about velocity of flow are as follow:Some important facts about velocity of flow are as follow:
Velocity of flow is equal to full flow velocity when the flow is half full,Velocity of flow is equal to full flow velocity when the flow is half full, Velocity of flow is more than full flow velocity when the flow is more Velocity of flow is more than full flow velocity when the flow is more
than half full,than half full, Velocity of flow is rapidly decreasing when the flow is less than half Velocity of flow is rapidly decreasing when the flow is less than half
full,full, Velocity of flow is maximum when the depth of flow is 0.82 D,Velocity of flow is maximum when the depth of flow is 0.82 D, The carrying capacity of the sewer is the maximum when the depth The carrying capacity of the sewer is the maximum when the depth
of flow is approximately 0.9D.of flow is approximately 0.9D. Velocity of flow has to be checked for minimum self Velocity of flow has to be checked for minimum self
cleansing velocity whenever the sewer is flowing less than cleansing velocity whenever the sewer is flowing less than half full,half full,
SHAPES OF SEWER PIPESSHAPES OF SEWER PIPES
The sewer pipes are normally circular in section, although The sewer pipes are normally circular in section, although some other sections such as basket handle shape, egg some other sections such as basket handle shape, egg shape, horse shoe shape, parabolic shape, semicircular shape, horse shoe shape, parabolic shape, semicircular shape, semi elliptical shape, rectangular shape etc.shape, semi elliptical shape, rectangular shape etc.
SHAPES OF SEWER PIPESSHAPES OF SEWER PIPES
SHAPES OF SEWER PIPESSHAPES OF SEWER PIPES
FORCES ACTING ON SEWER PIPESFORCES ACTING ON SEWER PIPES
The structural design of the sewer pipes should be such The structural design of the sewer pipes should be such as to enable them to withstand the various forces likely to as to enable them to withstand the various forces likely to come on them. The following forces generally come into come on them. The following forces generally come into play in the sewer pipes:play in the sewer pipes:
1.1.Internal pressure of sewageInternal pressure of sewage
2.2.Pressure due to external loadsPressure due to external loads
3.3.Temperature stressesTemperature stresses
4.4.Flexural stresses.Flexural stresses.
SEWER MATERIALSSEWER MATERIALS
Vitrified clay (or stone ware), cement concrete, asbestos Vitrified clay (or stone ware), cement concrete, asbestos cement and cast iron are the most common materials cement and cast iron are the most common materials used for constructing sewer pipes. While selecting a used for constructing sewer pipes. While selecting a particular material for constructing sewer pipes, the particular material for constructing sewer pipes, the important factors which must be considered are:important factors which must be considered are:
i.i.Resistance to corrosionResistance to corrosion
ii.ii.Resistance to abrasionResistance to abrasion
iii.iii.Strength and durabilityStrength and durability
iv.iv.Light weightLight weight
v.v.ImperviousnessImperviousness
vi.vi.The economy and costThe economy and cost
vii.vii.Hydraulically efficientHydraulically efficient
MANHOLESMANHOLES
Manholes are masonry or R.C.C. chambers, constructed at Manholes are masonry or R.C.C. chambers, constructed at suitable intervals along the sewer lines, for providing access suitable intervals along the sewer lines, for providing access into them.into them.
The manholes, thus help in joining sewer lengths, and also help The manholes, thus help in joining sewer lengths, and also help in their inspection, cleaning and maintenance.in their inspection, cleaning and maintenance.
Location and spacing of Manholes:Location and spacing of Manholes:
The manholes are generally provided at every bend, junction, The manholes are generally provided at every bend, junction, change of gradient, or change of sewer diameter. Unless there change of gradient, or change of sewer diameter. Unless there are practical difficulties, the sewer line between two manholes are practical difficulties, the sewer line between two manholes is laid straight with even gradient.is laid straight with even gradient.
Even when the sewer line runs straight, the manholes are Even when the sewer line runs straight, the manholes are provided at regular intervals.provided at regular intervals.
The spacing between the manholes, in such a case, however, The spacing between the manholes, in such a case, however, depends mainly upon the size of the sewer line.depends mainly upon the size of the sewer line.
The manhole spacing's, generally adopted, on straight The manhole spacing's, generally adopted, on straight sewer reaches, are given below:sewer reaches, are given below:
Dia up to 0.3 m 45 m
Dia up to 0.6 m 75 m
Dia up to 0.9 m 90 m
120 m
250 m
300 m
Recommended Spacing's of Manholes on straight reaches of sewer lines as per IS 1742-1960
Size of the SewerS.No.
1
2
3
4
5
6
Dia up to 1.2 m
Dia up to 1.5 m
Dia greater than 1.5 m
CLASSIFICATION OF MANHOLESCLASSIFICATION OF MANHOLES
Depending of their depth, the manholes may be classified as:Depending of their depth, the manholes may be classified as:
i.i.Shallow manholes – is about 0.7 to 0.9 m in depth, and is Shallow manholes – is about 0.7 to 0.9 m in depth, and is constructed at the start of a branch sewer or at places, which constructed at the start of a branch sewer or at places, which are not subjected to heavy traffic. Such a manhole is provided are not subjected to heavy traffic. Such a manhole is provided with a light cover at its top, and is called an inspection chamber.with a light cover at its top, and is called an inspection chamber.
ii.ii.Normal manholes – is about 1.5 m in depth and is constructed Normal manholes – is about 1.5 m in depth and is constructed either square (1m x 1m) or rectangular (1.2m x 1m) in cross either square (1m x 1m) or rectangular (1.2m x 1m) in cross section. Its section is not changed with depth, as its done in a section. Its section is not changed with depth, as its done in a deep manhole.deep manhole.
iii.iii.Deep manholes – is having depth more than 1.5m. The Deep manholes – is having depth more than 1.5m. The section of such a manhole is generally not kept the same. The section of such a manhole is generally not kept the same. The size in the upper portion is reduced by providing an offset as size in the upper portion is reduced by providing an offset as shown in the figure below.shown in the figure below.
ORDINARY MANHOLEORDINARY MANHOLE
DEEP MANHOLEDEEP MANHOLE
CIRCULAR DROP MANHOLECIRCULAR DROP MANHOLE
DESIGN OF SEWERAGE SYSTEMDESIGN OF SEWERAGE SYSTEM
Select sewage treatment and disposal location Select sewage treatment and disposal location depending up on the availability of land or water depending up on the availability of land or water courses,courses,
Divide the town into number of zonesDivide the town into number of zones,, Factors to be considered in zoning:Factors to be considered in zoning:
Special features such as railway line, NH, river etc., Special features such as railway line, NH, river etc., can be treated as zone boundaries since gravity sewer can be treated as zone boundaries since gravity sewer crossing of these features is expensive.crossing of these features is expensive.
An area of the town having a descending slope can An area of the town having a descending slope can form a zoneform a zone
To restrict the depth of cutting to the pre-determined To restrict the depth of cutting to the pre-determined level (5 to 6m) since excavation under ground water level (5 to 6m) since excavation under ground water table condition and / or in hard rock is difficult and table condition and / or in hard rock is difficult and expensive.expensive.
The site is available for the pumping station.The site is available for the pumping station. Exceeding the maximum depth of cutting for short Exceeding the maximum depth of cutting for short
lengths to avoid introduction of lift station is lengths to avoid introduction of lift station is permitted.permitted.
DESIGN OF SEWERAGE SYSTEMDESIGN OF SEWERAGE SYSTEM
Decide the location of the sewage pumping station Decide the location of the sewage pumping station (SPS) for each of the zones at the lowest elevation (SPS) for each of the zones at the lowest elevation and also considering the site available.and also considering the site available.
SPS shall have facility for pretreatment to remove SPS shall have facility for pretreatment to remove floating large particles and grit; about 30m x 30m land floating large particles and grit; about 30m x 30m land may be required.may be required.
When adequate extent of land is not available lift When adequate extent of land is not available lift station can be provided instead of SPS.station can be provided instead of SPS.
Lift station is a small pumping station without facility Lift station is a small pumping station without facility for pretreatment for pretreatment
DESIGN OF SEWERAGE SYSTEMDESIGN OF SEWERAGE SYSTEM
Main pumping station (MPS) is located nearer to the STP Main pumping station (MPS) is located nearer to the STP site. MPS will collect sewage from all zones and pump to site. MPS will collect sewage from all zones and pump to STPSTP
SPS of one of the zones nearer to STP may be converted SPS of one of the zones nearer to STP may be converted as MPS as MPS
Prepare a map of sewer network by aligning the sewer Prepare a map of sewer network by aligning the sewer lines in roads along the natural slope of the terrain to lines in roads along the natural slope of the terrain to drain into the collection well,drain into the collection well,
Don’t align sewers against the slope and across the Don’t align sewers against the slope and across the ridges ridges
In exceptional case, aligning across a small ridge is In exceptional case, aligning across a small ridge is permitted permitted
DESIGN OF SEWERAGE SYSTEMDESIGN OF SEWERAGE SYSTEM - - contdcontd
Adequate number of Manholes are necessary to facilitate Adequate number of Manholes are necessary to facilitate cleaning cleaning Maximum spacing for small diameter sewers:Maximum spacing for small diameter sewers: 30m30m Maximum spacing for larger diameter sewers:Maximum spacing for larger diameter sewers: 60m to 100m60m to 100m
Mark the positions of the manholes in the sewer layout Mark the positions of the manholes in the sewer layout map.map.
Assess the Assess the number of anticipated HSCsnumber of anticipated HSCs; Ensure at least ; Ensure at least 50% of the properties will have connections50% of the properties will have connections
Assume correct Assume correct Peak FactorPeak Factor (based on the contributing (based on the contributing population to the section under consideration) to assess population to the section under consideration) to assess Peak FlowPeak Flow. . Peak factor of 3 is preferable for all sections.Peak factor of 3 is preferable for all sections.
Sewers are designed as a gravity system for Sewers are designed as a gravity system for partial flow partial flow conditioncondition only only
DESIGN OF SEWERAGE SYSTEMDESIGN OF SEWERAGE SYSTEM -Contd.-Contd.
Consider subsoil condition and level of ground water Consider subsoil condition and level of ground water table and fix the maximum depth of cutting, which may table and fix the maximum depth of cutting, which may be 5 to 6m,be 5 to 6m,
For the assumed zoning, by rough calculation For the assumed zoning, by rough calculation considering the maximum length of the zone and considering the maximum length of the zone and assuming a grade of 1 in 200 calculate the depth of assuming a grade of 1 in 200 calculate the depth of excavation and check with the maximum depth of excavation and check with the maximum depth of cutting cutting
If the calculated depth is within the permissible depth of If the calculated depth is within the permissible depth of excavation proceed further for the detailed designing of excavation proceed further for the detailed designing of sewers adopting the zoning. sewers adopting the zoning.
If the calculated depth of cutting exceeds the If the calculated depth of cutting exceeds the permissible cutting, revise the zoning of the town, by permissible cutting, revise the zoning of the town, by shifting the location of pumping station or introducing shifting the location of pumping station or introducing additional pumping station/lift stations.additional pumping station/lift stations.
Lift stationsLift stations Lift stations are required to elevate and transport sewage in Lift stations are required to elevate and transport sewage in
sewerage systems when continuation of gravity flow is no longer sewerage systems when continuation of gravity flow is no longer feasible. feasible.
In flat terrain, area close to seashore, sewers enroute to a In flat terrain, area close to seashore, sewers enroute to a pumping/treatment plant may increase in depth to the point where pumping/treatment plant may increase in depth to the point where it is impractical to continue gravity flow economically because of it is impractical to continue gravity flow economically because of the high cost of excavation. the high cost of excavation.
Here, a lift station can be installed to lift the sewage to the Bell-Here, a lift station can be installed to lift the sewage to the Bell-mouth chamber in a sewer at a higher level mouth chamber in a sewer at a higher level
Lift station is an enlarged size MH fitted with submersible pump Lift station is an enlarged size MH fitted with submersible pump with float control operationwith float control operation
Provide Submersible non-clogging pump of 2 – 2.5 DWF (2Nos., 1 Provide Submersible non-clogging pump of 2 – 2.5 DWF (2Nos., 1 No. stand by)No. stand by)
Lift station may be adopted when the design peak flow is less than Lift station may be adopted when the design peak flow is less than 1000 lpm1000 lpm
Overflow arrangement from the lift station to the nearby drain is Overflow arrangement from the lift station to the nearby drain is necessary to avoid surcharging of sewersnecessary to avoid surcharging of sewers
LIFT STATIONS
DESIGN OF SEWERAGE SYSTEMDESIGN OF SEWERAGE SYSTEM -Contd.-Contd.
Sufficient Sufficient gradesgrades should be adopted to maintain a should be adopted to maintain a minimum self-cleansing velocityminimum self-cleansing velocity
0.6mps for the present peak flow0.6mps for the present peak flow 0.8mps for the ultimate peak flow0.8mps for the ultimate peak flow
Minimum depth of cuttingMinimum depth of cutting 800mm to 1000mm800mm to 1000mm; Minimum ; Minimum depth is fixed in such a way to have the house sewer is safely depth is fixed in such a way to have the house sewer is safely connected to the street sewer. Minimum depth should also provide connected to the street sewer. Minimum depth should also provide necessary cover to the sewer to protect it from load from the trafficnecessary cover to the sewer to protect it from load from the traffic
Maximum depth of cuttingMaximum depth of cutting 5.0 to 6.0m5.0 to 6.0m depending up on depending up on water table condition and type of substratawater table condition and type of substrata
Use Manning’s formula for computing velocity and flow Use Manning’s formula for computing velocity and flow in the sectionin the section
Steps in the design of Sewerage systemSteps in the design of Sewerage system Review the performance of the existing sewerage systems in Review the performance of the existing sewerage systems in
operationoperation Insufficient flow due to lack of connections leading to silting Insufficient flow due to lack of connections leading to silting
and clogging in sewersand clogging in sewers Flow of sewage in the open drains even after installation of Flow of sewage in the open drains even after installation of
sewerage system and fail to protect the environment (land sewerage system and fail to protect the environment (land and water) from pollution and make them for beneficial usesand water) from pollution and make them for beneficial uses
Inadequate O&M of STP (Even simple maintenance of WSP is Inadequate O&M of STP (Even simple maintenance of WSP is not carried out properly)not carried out properly)
Study the various options available with reference to capital and Study the various options available with reference to capital and O&M cost O&M cost Collection systemsCollection systems:: 1.Conventional sewerage system 1.Conventional sewerage system
2.Small bore sewerage system 2.Small bore sewerage system Sewage treatmentSewage treatment:: 1.Conventional methods 1.Conventional methods
2. Low-cost methods 2. Low-cost methods Select Appropriate collection system and Sewage treatment Select Appropriate collection system and Sewage treatment
methodmethod
Steps in the design of Sewerage networkSteps in the design of Sewerage network
The sewage generated from an area is collected through The sewage generated from an area is collected through a sewer network consists of sewers and conveyed to the a sewer network consists of sewers and conveyed to the sewage pumping station for onward conveyance to the sewage pumping station for onward conveyance to the sewage treatment plant for further treatment and sewage treatment plant for further treatment and disposal. disposal.
The sewer network is formulated with the help of The sewer network is formulated with the help of contours. Generally, the sewage pumping station (SPS) contours. Generally, the sewage pumping station (SPS) is located at low-lying area of the catchments. is located at low-lying area of the catchments.
In addition to the contour levels, the distance of the In addition to the contour levels, the distance of the farthest point of the network from the SPS is also taken farthest point of the network from the SPS is also taken into consideration while deciding the number of sub-into consideration while deciding the number of sub-catchment areas or zones of the sewage collection catchment areas or zones of the sewage collection system. system.
Steps in the design of Sewerage networkSteps in the design of Sewerage network
After formulation of the zones with networks, After formulation of the zones with networks, manholes are marked at every 30 metres apart manholes are marked at every 30 metres apart from junctions and change in directions. from junctions and change in directions.
The network consists of trunk sewer, main sewer, The network consists of trunk sewer, main sewer, submain, branch, sub-branch and laterals etc. submain, branch, sub-branch and laterals etc. and the line numbers were given accordingly. and the line numbers were given accordingly.
Manhole numbers are assigned based on the line Manhole numbers are assigned based on the line number. number.
The nomenclatures of manhole numbers are The nomenclatures of manhole numbers are generally as per the guidelines specified by generally as per the guidelines specified by Central Public Health & Environmental Central Public Health & Environmental Engineering Organisation (CPHEEO) Manual. Engineering Organisation (CPHEEO) Manual.
Steps in the design of Sewerage networkSteps in the design of Sewerage network
The Sewer system has been designed by forming The Sewer system has been designed by forming segments comprising of 3-4 manholes. segments comprising of 3-4 manholes.
A contributory area is assigned to each segment A contributory area is assigned to each segment depending on various types of land use in the depending on various types of land use in the segment. segment.
The contributing area for the segment is then The contributing area for the segment is then converted to an Equivalent Residential Area converted to an Equivalent Residential Area (ERA). (ERA).
The ward density is applied while calculating The ward density is applied while calculating segment-wise population based on contributing segment-wise population based on contributing ERA. ERA.
This exercise is repeated for whole network to This exercise is repeated for whole network to arrive segment - wise population. arrive segment - wise population.
Steps in the design of Sewerage networkSteps in the design of Sewerage network Contributory area of a segment of a stretch of 100 m Contributory area of a segment of a stretch of 100 m
length of sewer is calculated. This area is then converted length of sewer is calculated. This area is then converted into Equivalent Residential Area (ERA) by applying into Equivalent Residential Area (ERA) by applying suitable factors to various land uses as indicated below:suitable factors to various land uses as indicated below: Residential Area (RA)Residential Area (RA) == 1.01.0 InstitutionalInstitutional == 0.250.25 Commercial AreaCommercial Area == 0.250.25 IndustrialIndustrial == 0.10.1
The total ERA therefore is calculated as:The total ERA therefore is calculated as: ERA =ERA = 1.0 x Residential area + 0.25 x Institutional area + 0.25 x 1.0 x Residential area + 0.25 x Institutional area + 0.25 x
Commercial area + 0.1 x Industrial areaCommercial area + 0.1 x Industrial area Multiplying ERA by population density of the Multiplying ERA by population density of the
corresponding ward gives the number of persons in that corresponding ward gives the number of persons in that contributing area. contributing area.
A return of 80% of the rate of water supply is treated as A return of 80% of the rate of water supply is treated as waste water generation from each individual. waste water generation from each individual.
Further, infiltration of ground water into the system is also Further, infiltration of ground water into the system is also considered. considered.
Design ApproachDesign Approach -Contd.-Contd.
Consider subsoil condition and level of ground water table Consider subsoil condition and level of ground water table and fix the maximum depth of cutting, which may be 5 to and fix the maximum depth of cutting, which may be 5 to 6m,6m,
For the assumed zoning, mark the trunk sewer alignmentFor the assumed zoning, mark the trunk sewer alignment By rough calculation assuming an average grade of 1 in By rough calculation assuming an average grade of 1 in
200 calculate the depth of excavation and check with the 200 calculate the depth of excavation and check with the maximum depth of cutting maximum depth of cutting
If the calculated depth is within the permissible depth of If the calculated depth is within the permissible depth of excavation proceed further for the detailed designing of the excavation proceed further for the detailed designing of the collection system adopting the zoning. collection system adopting the zoning.
If the calculated depth of cutting exceeds the permissible If the calculated depth of cutting exceeds the permissible cutting, revise the zoning of the town, by shifting the cutting, revise the zoning of the town, by shifting the location of pumping station or introducing additional location of pumping station or introducing additional pumping station/lift stations.pumping station/lift stations.
Mark the positions of the manholes in the sewer network Mark the positions of the manholes in the sewer network map.map.
Numbering of Manholes and SewersNumbering of Manholes and Sewers
Manholes are generally Manholes are generally numbered from the pumping numbered from the pumping station end backwards along the station end backwards along the Main sewer. Main sewer.
Numbering of manholes and Numbering of manholes and sewers can be done in many sewers can be done in many ways. ways.
The sewer shall be designated by The sewer shall be designated by the manhole to which it joins. the manhole to which it joins.
Numbering manholes is furnished Numbering manholes is furnished in Fig. in Fig.
In case of design of sewer In case of design of sewer network using computer network using computer programme, manholes are programme, manholes are considered as nodes. considered as nodes.
Node numbers are assigned in Node numbers are assigned in any sequence and the sewer is any sequence and the sewer is designated as a link with designated as a link with connecting node numbers.connecting node numbers.
G.L. @ Man Holes
1 – 92.15m
2 – 92.35m
3 – 92.50m
4 – 92.80m
5 – 92.90m
6 – 93.10m
7 – 93.20m
8 – 93.20m
9 – 93.65m
3A – 92.60m
3B – 92.65m
4A – 92.90m
4B – 93.05m
4C – 93.10m
7A – 93.60m
7B – 93. 65m
SEWER NETWORK AND DATA
HYDRAULIC CALCULATION TABLE OF SEWER NETWORK
SectionLINE NO
Cumulative Population
Sewerage Generation(ltr/
sec)
Full Bore discharge 2040
Dia (mm)Slope 1 in (Mtr)
Slope Lengt
hVf from mannings formula
QF (lps)
Q/Qf d/Df v/Vf v (m/s) Q/Qf d/Df v/Vf v (m/s)GROUND
LEVEL (m)
INVERT LEVEL (m) EDRC
Start End 2010 2040 2010 2040 2010 2040 Start End Start End
0.6 0.8 0.8
A467 A638A1-001
9149015043
5328.79
2540.626 675.782 1000 1.00 2030 0.00049
26240 0.801
628.5728
0.53 0.58 0.8740.6998
40.87 0.7889
0.9973
0.79857
78.729 78.529 72.381 72.499
A638 A637A1-002
8514013221
5305.97
2475.148 593.935 1000 1.00 1850 0.00054
0586 0.839
658.4424
0.47 0.54 0.8420.7062
50.69 0.6867
0.9437
0.79156
78.529 78.596 72.499 72.546
A637 A573A1-003
17730 50990 84.956 183.245 229.057 600 0.60 10000.001
293 0.812229.354
30.38
0.4786
0.7892
0.6405 0.8 0.750.977
50.7933
378.596 78.612 72.946 73.239
A573 A575A1-004
15770 45360 75.565 181.125 226.406 600 0.60 10000.001
60 0.812229.354
30.33
0.4429
0.7546
0.61242
0.79 0.74440.974
70.7910
578.612 78.793 73.239 73.299
A575 A576A1-005
15250 43850 73.073 175.095 218.869 600 0.60 980 0.0010204
18 0.820231.682
90.32
0.4357
0.7476
0.6129 0.76 0.72780.966
20.7921
278.793 78.876 73.299 73.317
A576 A578A1-006
14790 42530 70.869 169.825 212.281 600 0.60 960 0.0010417
146 0.828234.083
80.31
0.4286
0.7407
0.61354
0.73 0.71110.957
70.7932
878.876 79.304 73.317 73.469
A578 A579A1-007
13270 38120 63.585 152.215 190.269 600 0.60 850 0.0011765
73 0.880248.769
70.26
0.3917
0.7040.6197
20.62 0.64
0.9148
0.80529
79.304 79.613 73.469 73.555
A579 A581A1-008
11210 32220 53.715 128.656 160.820 500 0.50 8000.00125
93 0.804157.692
80.35
0.4571
0.7684
0.61743
0.82 0.76110.983
20.7900
379.613 80.268 73.655 73.772
A581 A582A1-009
10470 30100 50.169 120.191 150.239 500 0.50 760 0.0013158
132 0.824161.789
40.32
0.4357
0.7476
0.61633
0.75 0.72220.963
30.7941
580.268 80.298 73.772 73.945
A582 A583A1-010
9460 27170 45.329 108.491 135.614 450 0.45 710 0.0014085
7 0.795126.388
60.36
0.4643
0.7754
0.61651
0.86 0.78330.994
50.7907
180.298 80.298 73.995 74.005
A583 A584A1-011
9430 27100 45.185 108.212 135.265 450 0.45 710 0.0014085
138 0.795126.388
60.36
0.4643
0.7754
0.61651
0.86 0.78330.994
50.7907
180.298 79.766 74.005 74.199
A584 A585A1-012
7400 21270 35.458 84.932 106.165 450 0.45 580 0.0017241
209 0.880139.837
30.26
0.3917
0.704 0.6193 0.61 0.63330.910
70.8011
379.766 79.617 74.199 74.560
A585 A586A1-013
6240 17940 29.900 85.963 107.453 450 0.45 560 0.0017857
46 0.895142.312
50.22
0.3583
0.6680.5980
30.61 0.6333
0.9107
0.81531
79.617 79.933 74.560 74.642
A586 A587A1-014
5120 14740 24.533 70.629 88.286 400 0.40 490 0.0020408
53 0.885111.130
20.23
0.3667
0.6770.5990
10.64 0.6533
0.9231
0.81675
79.933 79.786 74.692 74.800
A587 A588A1-015
4010 17550 19.215 84.094 105.117 400 0.40 390 0.0025641
76 0.992124.565
60.16
0.3083
0.6140.6089
40.68 0.68
0.9396
0.93186
79.786 79.896 74.800 74.995
PROBLEMS IN THE SEWERSPROBLEMS IN THE SEWERS
The settleble solids are likely to settle in the sewer when The settleble solids are likely to settle in the sewer when the flow is very less and the velocity is less than self the flow is very less and the velocity is less than self cleaning velocity.cleaning velocity.
Settled solids should be flushed at least once in a day by Settled solids should be flushed at least once in a day by maintaining self cleansing velocitymaintaining self cleansing velocity
Self cleansing velocity could be achieved only during the Self cleansing velocity could be achieved only during the peak flow.peak flow.
If self cleansing velocity is not achieved in any section of If self cleansing velocity is not achieved in any section of the sewers even with peak flow, artificially self cleansing the sewers even with peak flow, artificially self cleansing velocity should be achieved by flushingvelocity should be achieved by flushing
TYPICAL SEWAGE PUMPING STATIONTYPICAL SEWAGE PUMPING STATION
TYPICAL SEWAGE PUMPING STATIONTYPICAL SEWAGE PUMPING STATION
Survey and InvestigationSurvey and Investigation
Survey and investigation are pre-requisites both for Survey and investigation are pre-requisites both for framing the feasibility report and the preparation of framing the feasibility report and the preparation of sewerage projectsewerage project
The engineering designs are dependent on the The engineering designs are dependent on the correctness of the data collected and its proper correctness of the data collected and its proper evaluationevaluation
The survey for data collection includes the following two The survey for data collection includes the following two stepssteps Collection of basic informationCollection of basic information Project surveysProject surveys
Basic information should be collected on the following aspects Physical AspectsPhysical Aspects Development AspectsDevelopment Aspects Other AspectsOther Aspects
Physical AspectsPhysical Aspects
Topography or elevation difference of the town and the Topography or elevation difference of the town and the adjoining area for deciding location of disposal worksadjoining area for deciding location of disposal works
Subsoil conditions, depth of groundwater table and its Subsoil conditions, depth of groundwater table and its fluctuations. fluctuations.
In the absence of any records, preliminary data should be In the absence of any records, preliminary data should be collected by putting at least 3 trial bores or trial pits per collected by putting at least 3 trial bores or trial pits per hectarehectare
Underground facilities like storm water drains, house Underground facilities like storm water drains, house service connections of water supply/drainage, electrical service connections of water supply/drainage, electrical and telephone cables, andand telephone cables, and
Location of streets and adjoining areas likely to be mergedLocation of streets and adjoining areas likely to be merged Possible sources of information are:Possible sources of information are:
Existing maps and plans from revenue or town surveys or Survey Existing maps and plans from revenue or town surveys or Survey of Indiaof India
Topographical map of survey of IndiaTopographical map of survey of India Aerial photographsAerial photographs Existing instrumental surveys by MunicipalitiesExisting instrumental surveys by Municipalities
Development AspectsDevelopment Aspects Type of land use such as commercial, industrial, Type of land use such as commercial, industrial,
residential and recreationalresidential and recreational Census population, density of population, trends of Census population, density of population, trends of
population growthpopulation growth Types and number of industries and location of their Types and number of industries and location of their
wastewater discharge pointswastewater discharge points Rainfall detailsRainfall details Details of existing drainage and sewerage facilitiesDetails of existing drainage and sewerage facilities Basis of design and information on the maintenance of Basis of design and information on the maintenance of
the existing sewerage system if available; effluent the existing sewerage system if available; effluent disposal sites and their conditionsdisposal sites and their conditions
Possible sources of informationPossible sources of information Census recordsCensus records Town and metropolitan Master plans and Land use plansTown and metropolitan Master plans and Land use plans Meteorological dataMeteorological data Pollution Control BoardPollution Control Board
Other AspectsOther Aspects Changes in political boundaries by merger of adjacent Changes in political boundaries by merger of adjacent
communitiescommunities Feasibility of multi-municipal systemsFeasibility of multi-municipal systems Prevailing water pollution prevention regulations, and Prevailing water pollution prevention regulations, and
other rules relating to discharge of industrial and domestic other rules relating to discharge of industrial and domestic wasteswastes
Present status of the government or municipal authority Present status of the government or municipal authority sponsoring the project, its capacity, and adequacy to sponsoring the project, its capacity, and adequacy to satisfactorily implement and maintain the projectsatisfactorily implement and maintain the project
The impacts likely to be caused to the community during The impacts likely to be caused to the community during execution and feasibility of minimizing themexecution and feasibility of minimizing them
Possible sources of informationPossible sources of information National ActsNational Acts State and Municipal Laws and ByelawsState and Municipal Laws and Byelaws
Project SurveysProject Surveys Preliminary Project SurveysPreliminary Project Surveys
Collect data on capacity required, basic arrangement and size, Collect data on capacity required, basic arrangement and size, physical features affecting general layout physical features affecting general layout
Data on cost and the escalation of prices of basic materials and Data on cost and the escalation of prices of basic materials and methods of financing; methods of financing;
All the basic data obtained must be reliable but need not be in All the basic data obtained must be reliable but need not be in precise and detail precise and detail
Detailed Project SurveysDetailed Project Surveys These surveys form the basis for the engineering design as well as These surveys form the basis for the engineering design as well as
for the preparation of plans and specificationsfor the preparation of plans and specifications Must be precise and contains contours of all areas to be served Must be precise and contains contours of all areas to be served
with all details that will facilitate the designerwith all details that will facilitate the designer Include network of bench marks and traverse surveys to identify Include network of bench marks and traverse surveys to identify
the nature and extent of the existing underground structuresthe nature and extent of the existing underground structures Construction SurveysConstruction Surveys
Establish all control points such as base lines and bench marks for Establish all control points such as base lines and bench marks for sewer alignment and grade with reference to permanent objectssewer alignment and grade with reference to permanent objects
Data to be collected in a detailed surveyData to be collected in a detailed survey
The layout plan of the town with contours showing the The layout plan of the town with contours showing the roads and drainage courses,roads and drainage courses,
The municipal map showing ward boundariesThe municipal map showing ward boundaries Levels along the road at interval of 10m. Levels along the road at interval of 10m. The levels at street junctions, lowest plinth level of the The levels at street junctions, lowest plinth level of the
building and the sullage outletbuilding and the sullage outlet The width of the street and the road formedThe width of the street and the road formed The location and extent of vacant municipal sites The location and extent of vacant municipal sites
available within the town as well as on the periphery of available within the town as well as on the periphery of the town for locating pumping station and STP.the town for locating pumping station and STP.
The availability of Revenue poramboke land on the The availability of Revenue poramboke land on the outskirt of the town and/or dry lands at reasonable cost outskirt of the town and/or dry lands at reasonable cost for locating the treatment plant and disposal works,for locating the treatment plant and disposal works,
Data to be collected in a detailed surveyData to be collected in a detailed survey -Contd-Contd
The hydrology of water courses if any, with details of The hydrology of water courses if any, with details of minimum flow and maximum water levelminimum flow and maximum water level
The level of groundwater table in summer and winter The level of groundwater table in summer and winter and subsoil conditions, collected from the existing open and subsoil conditions, collected from the existing open wells,wells,
The subsoil particulars along the alignment of the The subsoil particulars along the alignment of the sewers by putting trial pits and trial boressewers by putting trial pits and trial bores,,
Population of the town as per the latest census and Population of the town as per the latest census and present population,present population,
Future population estimated based on other projects Future population estimated based on other projects such as water supply project or by forecast method,such as water supply project or by forecast method,
Data to be collected in a detailed surveyData to be collected in a detailed survey -Contd-Contd
The details of existing water supply and proposed The details of existing water supply and proposed water supply improvements projects if any.water supply improvements projects if any.
Elevations of the sills of building and the depth at Elevations of the sills of building and the depth at which the house drainage is existingwhich the house drainage is existing
Character, age and condition of the pavement of Character, age and condition of the pavement of street/roadstreet/road
The details of underground facilities like cables of The details of underground facilities like cables of telephone and electricity; telephone and electricity;
When good information is lacking, it may be advisable When good information is lacking, it may be advisable to have pits excavated in streets to obtain the require to have pits excavated in streets to obtain the require data.data.