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5th December, 2009
HYDRAULIC DESIGN OF SEWERS
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DESIGN PERIODS
Sewers: 30 years
Sewage Pumping Stations
Civil Structures: 30 years
Equipment:phases of 15 years
Sewage Treatment Plants:phases of 10 to 15 years
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POPULATION FORCASTS AND WATER
DEMAND FORCASTS
City/ Town Level
Wards Level
Sewerage Zone Level
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In well developed Urban areas, sewage flows may
be as high as 90% of water supply due to industrial wastes
contribution.
Generally average sewage flow may be taken as 80% of
water supply. However sewers should be designed for at
least 100 lpcd.
(CPHEEO manual on Sewerage)
PER CAPITA SEWAGE FLOW
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PEAK FACTORS
(Ratio of Maximum to Average Flow)
Contributing
Population
Peak Factor
Up to 20,000 3.0
20,000 to 50,000 2.5
50,000 to 7,50,000 2.25
Above 7,50,000 2.0
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INFILTRATION OF GROUND WATER
Units Minimum Maximum
l/Ha.d 5,000 50,000
l/km.d 500 5,000
Lpd/manhole 250 500
Approximately Infiltration can be assumed to be about 10 to
15% of average sewage flow.
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MANNINGS FORMULA
General form,V = (1/N) x ( R S)
For Circular Conduits,
V = (1/N) x (3.968 x 10-3
)D
S
And Q = (1/N) x (3.118 x 10-6)D8/3 S
Where, Q = Discharge in lps;
S = Slope;
D = Internal Dia of pipe in mm;
R= Hydraulic radius (A/P) in mm;
V= Velocity, in m/sec;
N= Mannings coefficient of roughness
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COEFFICIENT OF ROUGHNESS N
Material Condition N
Stoneware Pipe a) Good 0.012
b) Fair 0.015
Reinforced
Cement Concrete
a) Good 0.011 to 0.013
b) Fair 0.015
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Minimum size of public sewer - 150mm
Minimum velocity for present peak flow - 0.6m/sec
Maximum velocity to avoid erosion - 3.0m/secTrial full flow velocity - 0.75 to 1.0 m/sec
Minimum depth of cover over crown - 1.0 m
Depth of flow - 0.8D at ultimate peak flow
(CPHEEO Manual on Sewerage)
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DESIGN PARAMETERS
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Manholes to be provided at;Every change in alignment, gradient, diameter
Head of all sewers
Junction of sewers
Intermediate locations with spacing not greater that 30m
on manually cleaned manholes.
90 to 150m spacing for900 to 1500mm dia mechanicallycleaned sewers
150 to 200m spacing for 1.5 to 2.0m dia mechanically
cleaned sewers.
MANHOLE SPACING
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DEPTH OF FLOW WITH SIZE OF SEWER
Size (mm) d/D
Upto 400
> 400 upto 900
> 900mm
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SEWER 3 software of the World Bank
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HYDRAULIC ELEMENTS OF CIRCULAR
SEWERS RUNNING PARTIALLY FULL
d/D a/A p/P r/R For N/n=1.0 N/n For variable N/n
v/V q/Q v/V q/Q
(1) (2) (3) (4) (5) (6) (7) (8) (9)
1.00 1.000 1.000 1.000 1.000 1.000 1.00 1.000 1.000
0.90 9.949 0.795 1.192 1.124 1.066 0.94 1.057 1.002
0.80 0.858 0.705 1.217 1.140 0.988 0.88 1.003 0.869
0.70 0.748 0.631 1.185 1.120 0.838 0.85 0.952 0.712
0.60 0.626 0.564 1.110 1.072 0.671 0.83 0.890 0.557
0.50 0.500 0.500 1.000 1.000 0.500 0.81 0.810 0.405
0.40 0.373 0.436 0.857 0.902 0.337 0.79 0.713 0.266
0.30 0.252 0.369 0.684 0.776 0.196 0.78 0.605 0.153
0.20 0.143 0.295 0.482 0.615 0.088 0.79 0.486 0.070
0.10 0.052 0.205 0.254 0.401 0.021 0.82 0.329 0.017
0.00 0.000 --- --- --- 0.000 --- --- ---20
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Qaverage= 0.0094 cumec,
Peak factor = 2.5
Actual Qpeak= 0.0094 x 2.5 = 0.0235 cumec
Try 150mm size;
From Table, forvfull= 0.908m/sec, Grade 1 in 90
Qfull= 0.0161cumec
< Actual Qpeak0.0235 cumec
150mm size not adequate
ADEQUACY OF PIPE SIZE AND VELOCITY
AT PEAK FLOW..(1)
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ADEQUACY OF PIPE SIZE AND VELOCITY
AT PEAK FLOW..(2)
Try 200mm size
From Table, ForVfull= 0.898 m/sec; Grade 1 in 135
Qfull= 0.0282 cumecFord/D = 0.5, q/Qfull= 0.4050 for N/n variable;
q = 0.4050 x 0.0282 = 0.0114 cumec
< 0.0235
200mm size is inadequate
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A Q AC O S A OC
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ADEQUACY OF PIPE SIZE AND VELOCITY
AT PEAK FLOW..(3)Try 300mm size
From Table, ForVfull= 0.902 m/sec; Grade 1 in 230
Qfull= 0.0638 cumec
Ford/D = 0.5, q/Qfull= 0.4050 for N/n variable;
q = 0.4050 x 0.0638 = 0.0259 cumec
> 0.0235
300mm size is adequate.
Actually q/Qfull= 0.0235/0.0638 = 0.368From diagram, forq/Qfull= 0.368, d/D = 0.48
From diagram, v/Vfull= 0.78
vactual
= 0.902 x 0.78 = 0.703 m/sec
> 0.6m/sec OK 25
DESIGN OF SEWER SYSTEM
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DESIGN OF SEWER SYSTEMLine Location Manholes Ground
level at
starting
manhole
Length Area Served (ha) Population Sewage
flow
mld
Ground
water
infiltration
mld
From To Increment Total
1 2 3 4 5 6 7 8 9 10 11
1. Street R.8.5 R.8.4 38.275 120 0.80 0.80 240 0.054 0.016
2. Street R.8.4 R.8.3 37.960 116 1.2 2.0 600 0.135 0.040
3. Street R.8.3 R.8.2 36.873 114 1.40 3.40 1020 0.230 0.068
4. Street R.8.2 R.8.1 36.895 116 0.90 4.30 1290 0.290 0.066
5. Street R.8.2 R.8.1 36.420 75 0.70 5.0 1500 0.34 0.10
Peak flow Diameter
mm
Slope Discharge lps Velocity mps Total
fall m
Invert Elevation m
mld lps Q Full Q Actual V Full V Actual Upper end Lower end
12 13 14 15 16 17 18 19 20 21 220.205 2.37 150 0.008 14 2.37 0.75 0.57 0.96 37.125 36.165
0.5112 5.92 150 0.008 14 5.92 0.75 0.72 0.93 36.135 35.205
0.873 10.10 150 0.008 14 10.10 0.75 0.82 0.91 35.175 34.265
1.10 12.73 150 0.008 14 12.73 0.75 0.86 0.93 34.235 33.305
1.29 14.92 200 0.005 24 14.92 0.70 0.74 0.38 34.275 33.89526
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SEWER 3
WORLD BANK
SOFTWARE
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ECHOING INPUT VARIABLE
Title of the Project: WRR75n
Name of the User: CHAWATHENumber of Pipes: 20
Number of Nodes: 21
Minimum Velocity, m/sec: 6
Maximum Velocity, m/sec: 3
Minimum Allowable Cover, m: 2.44
Maximum Allowable Cover, m: 7
Number of Existing Pipes:Number of Commercial Diameters: 10
Number of Excavation Layers: 5
InFiltration Rate in percentage: 1
Maximum Allowable Slope as X (1:X): 30
Minimum Allowable Slope as X (1:X): 1000
Diameter Progression Considered? (Y/N): Y
Manning 'n' to be kept constant? (Y/N): N
Lay Pipe Parallel to Ground? (Y/N): Y
Provide Drop if Min Cov Violates? (Y/N): N
Lowest/Mean/Highest/Auto Dia? (L/M/H/A): L
Type of Backfill: Saturated TopsoilUnit Weight of BackFill Soil kg/sq m: 1840
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PIPE DATA
Pipe No. From Node To Node Length m Manning n Diameter mm Min. Vel. m/sec Max. Vel. m/sec
1 1 2 106.00 0.0130 0.6 3.00
2 2 3 121.00 0.0130 0.6 3.00
3 3 4 106.00 0.0130 0.6 3.00
4 6 5 121.00 0.0130 0.6 3.00
5 5 4 131.00 0.0130 0.6 3.00
6 4 7 167.00 0.0130 0.6 3.00
7 8 7 106.00 0.0130 0.6 3.00
8 9 8 137.00 0.0130 0.6 3.00
9 10 9 152.00 0.0130 0.6 3.00
10 7 11 152.00 0.0130 0.6 3.00
11 12 11 106.00 0.0130 0.6 3.00
12 13 12 106.00 0.0130 0.6 3.00
13 14 13 152.00 0.0130 0.6 3.00
14 11 15 182.00 0.0130 0.6 3.00
15 18 17 121.00 0.0130 0.6 3.00
16 17 16 191.00 0.0130 0.6 3.00
17 16 15 106.00 0.0130 0.6 3.00
18 15 19 121.00 0.0130 0.6 3.00
19 19 20 152.00 0.0130 0.6 3.00
20 20 21 182.00 0.0130 0.6 3.00
O A A
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NODE DATANode No. Flow lps Elevation m Peak Factor Pumping (Y/N/F) Minimum Cover (m)
1 113.300 152.40 1.00 2.44
2 84.960 150.88 1.00 2.44
3 56.640 148.44 1.00 2.44
4 141.600 146.30 1.00 2.44
5 113.280 149.83 1.00 2.44
6 113.280 149.35 1.00 2.44
7 169.920 143.26 1.00 2.44
8 113.280 144.78 1.00 2.44
9 133.280 147.83 1.00 2.44
10 226.560 149.35 1.00 2.44
11 198.240 141.73 1.00 2.44
12 113.280 143.26 1.00 2.44
13 198.240 144.78 1.00 2.44
14 254.880 147.83 1.00 2.44
15 198.240 138.68 1.00 2.44
16 85.960 140.21 1.00 2.44
17 56.640 141.43 1.00 2.44
18 113.280 142.65 1.00 2.44
19 56.640 137.46 1.00 2.44
20 141.600 136.55 1.00 2.44
21 0.000 135.64 1.00 2.44
COMMERCIAL DIAMETER DATA
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COMMERCIAL DIAMETER DATA
Pipe Diameter Maximum
d/D
Trench
Width m
Unit Cost Rs. /m
length
Strength (km/m)
Internal External
500.0 550.0 0.5 0.85 550.0 2300.00
600.0 650.0 0.5 0.95 650.0 2400.00
800.0 850.0 0.5 1.15 850.0 2500.00
1000.0 1050.0 0.67 1.35 1050.0 2600.00
1200.0 1250.0 0.67 1.55 1250.0 2700.00
300.0 350.0 0.67 0.65 350.0 2200.00
150.0 200.0 0.75 0.5 200.0 2000.00
200.0 250.0 0.75 0.55 250.0 2100.001300.0 1350.0 0.75 1.65 1350.0 2800.00
1500.0 1550.0 0.75 1.85 1550.0 2900.00
EXCAVATION COST DATA
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EXCAVATION COST DATA
Depth of Excavation in m Unit Rate Rs/cub m Vol
From To
0.00 3.00 1.00
3.00 6.00 2.00
6.00 9.00 3.00
9.00 12.00 4.00
12.00 50.00 6.00
PIPE DETAILS
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PIPE DETAILSPipe No. From Node To Node Peak Flow (lps) Length (m) Diameter mm Pipe Slope Ground Slope Existing
Pipe
1 1 2 113.413 106.00 500.0 67 69.6
2 2 3 198.458 121.00 500.0 47 49.73 3 4 255.155 106.00 500.0 47 49.6
4 6 5 133.393 121.00 500.0 73 79.6
5 5 4 266.787 131.00 500.0 86 85.8
6 4 7 623.683 167.00 800.0 190 54.8
7 8 7 473.593 106.00 600.0 68 69.6
8 9 8 360.200 137.00 500.0 44 44.9
9 10 9 226.787 152.00 500.0 96 99.7
10 7 11 1267.366 152.00 1000.0 98 99.6
11 12 11 566.966 106.00 600.0 50 69.5
12 13 12 453.573 106.00 600.0 67 69.6
13 14 13 255.135 152.00 500.0 47 49.8
14 11 15 2032.771 182.00 1200.0 222 59.8
15 18 17 113.393 121.00 500.0 97 99.2
16 17 16 170.090 191.00 500.0 152 156.6
17 16 15 256.136 106.00 500.0 67 69.5
18 15 19 2487.345 121.00 1200.0 148 99.3
19 19 20 2544.042 152.00 1200.0 142 166.1
20 20 21 2685.783 182.00 1200.0 127 200.0
PIPE LEVEL DETAILS
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PIPE LEVEL DETAILSPipe No. Ground Elevation Crown Level Invert Level Execution Depth
U/S (m) D/S (m) U/S (m) D/S (m) U/S (m) D/S (m) U/S (m) D/S (m)
1 152.4 150.9 150.0 148.4 149.4 147.8 3.1 3.1
2 150.9 148.4 148.4 145.8 147.8 145.3 3.2 3.2
3 148.4 146.3 145.8 143.6 145.3 143.0 3.0 3.3
4 149.4 147.8 146.9 145.3 146.4 144.7 3.1 3.1
5 147.8 146.3 145.3 143.7 144.7 143.2 5.5 3.1
6 146.3 143.3 141.7 140.8 140.8 140.0 3.1 3.3
7 144.8 143.3 142.3 140.8 141.7 140.1 3.1 3.1
8 147.8 144.8 145.3 142.2 144.8 141.7 3.0 3.1
9 149.4 147.8 146.9 145.3 146.4 144.8 3.5 3.1
10 143.3 141.7 140.8 139.3 139.8 138.2 3.2 3.5
11 143.3 141.7 140.7 138.5 140.0 137.9 3.2 3.8
12 144.8 143.3 142.3 140.7 141.6 140.0 3.0 3.2
13 147.8 144.8 145.4 142.2 144.8 141.6 5.9 3.2
14 141.7 138.7 137.1 136.2 135.8 135.0 3.0 3.7
15 142.6 141.4 140.2 139.0 139.7 138.4 3.0 3.0
16 141.4 140.2 139.0 137.7 138.4 137.2 3.1 3.1
17 140.2 138.7 137.7 136.1 137.2 135.6 4.1 3.1
18 138.7 137.5 135.8 135.0 134.6 133.8 3.7 3.7
19 137.5 136.6 135.0 134.0 133.8 132.7 3.8 3.8
20 136.6 135.6 134.0 132.5 132.7 131.3 4.4 4.4
PIPE MISC DETAILS
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PIPE MISC DETAILS
Pipe No. Dia. Mm d/D Partial Velocity (m/sec) Pipe Slope Remarks
1 500.0 0.39 1.60 67
2 500.0 0.48 2.13 47
3 500.0 0.55 2.31 47
4 500.0 0.40 1.55 73
5 500.0 0.61 1.81 86
6 800.0 0.67 1.74 190
7 600.0 0.66 2.39 68
8 500.0 0.66 2.62 44
9 500.0 0.63 1.74 96
10 1000.0 0.59 2.63 98
11 600.0 0.67 2.82 50
12 600.0 0.64 2.37 67
13 500.0 0.55 2.31 47
14 1200.0 0.75 2.23 22215 500.0 0.43 1.40 97
16 500.0 0.61 1.36 152
17 500.0 0.61 2.04 67
18 1200.0 0.75 2.73 148
19 1200.0 0.75 2.80 142
20 1200.0 0.75 2.95 127
NODE DETAILS
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NODE DETAILSNode No. Node Type Peak Factor Peak Flow (lps) Ground Elevation (m) Excavation Depth (m) Pumping Provided (Y/N)
1 REF 1.00 113.300 152.40 3.0
2 1.00 84.960 150.88 3.1
3 1.00 56.640 148.44 3.2
4 CONF 1.00 141.600 146.30 3.0
5 1.00 113.280 149.83 3.1
6 REF 1.00 113.280 149.35 5.5
7 CONF 1.00 169.920 143.26 3.1
8 1.00 113.280 144.78 3.1
9 1.00 133.280 147.83 3.0
10 REF 1.00 226.560 149.35 3.5
11 CONF 1.00 198.240 141.73 3.2
12 1.00 113.280 143.26 3.2
13 1.00 198.240 144.78 3.0
14 REF 1.00 254.880 147.83 5.9
15 CONF 1.00 198.240 138.68 3.0
16 1.00 85.960 140.21 3.0
17 1.00 56.640 141.43 3.1
18 REF 1.00 113.280 142.65 4.1
19 1.00 56.640 137.46 3.7
20 1.00 141.600 136.55 3.8
21 TAIL 1.00 0.000 135.64 4.4
RELATIVE SIZES AND LEVELS OF
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Outgoing sewer size to be at least equal
to the size of the largest of incoming sewers.
Sewers to be continuous.The crown of the outgoing sewer not to be higher
than that of incoming sewers.
Hydraulic flow line in the outgoing seer not to behigher than that in the incoming sewers.
RELATIVE SIZES AND LEVELS OF
INCOMING AND OUTGOING SEWERS AT
MANHOLE
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