CONTENTS

1. DESIGN CRITERIA

3. CALCULATION OF OILY STORM SEWER SYSTEM

3. HYDRAULIC RADIUS

4. STORM SEWER SYSTEM

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1. DESIGN CRITERIA

1.1 Design flow rates (GP 03-02-01, 4.2.5) b )

The drainage system shall be designed in conformance with the criteria outline below
Flow rate due to rain water shall be calculated using the "Rational Formula" :

Q = ( 1 / 3600000 ) × C × I × A

where, Q = Runoff rate in (m3/sec)

C = Weighted runoff coefficient, Dimensionless
A = Drainage area (m2)
I = Design rainfall intensity (mm/hr)

In areas with different values of the runoff coefficient are drained by the section being
consider, the sum of all areas multiplied by relevant runoff coefficients, shall be introduced
in the discharge formula above :

A × C = A1 × C1 + A2 × C2 + …. + AN × CN

1.2 Runoff Coefficient © (GP 03-02-01, 4.2.6) c)

The runoff coefficient for a given area is defined by the ratio between the volume of
water flowing through the system and the volume of rain water fallen in the given area.

The rain water sewer shall be sized adopting the runoff coefficient given for the various

types of surface in the following table :

SURFACE CONDITION RUNOFF COEFFICIENT (C)

Paved Area 1.00
Unpaved Area 0.75

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1. DESIGN CRITERIA

1.1 Design flow rates (GP 03-02-01, 4.2.5) b )

1.3 Rainfall Intensity

I = 71.12 mm/hr

1.4 Sewer line sizing

Design flow rate in sewer and ditches shall be calculated by Manning formula :

Q = Ao × V = Ao × R2/3 × S1/2 × ( 1 / n )

where, Q = Discharge (m3/sec)

Ao = Cross - sectional area (m2)
n = Coefficient of conduit roughness (m1/3s)
R = Mean hydraulic radius (m)
p = Wetted perimeter
S = Hydraulic slope of conduit (m/m)

The roughness coefficients for the most common materials are listed below :

MATERIALS ROUGHNESS COEFFICIENT (n)

Steel pipe 0.011
Concrete pipe 0.013
Concrete Ditch (troweled) pipe 0.013

1.5 Velocity of flow

MINIMUM DESIGN VELOCITY ≥ 0.75 m/sec

MAXIMUM DESIGN VELOCITY ≤ 3.00 m/sec

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2. CALCULATION OF STORM SEWER SYSTEM

2.1 STORM WATER SEWER PIPE (RAIN-WATER FLOW)

RAIN-WATER FLOW ♦ C.S PIPE ( n = 0.011 )

CB & MH NO.
Run-off Rainwater DIA. Wet Hydraulic Discharge
Length Area Slope Invert EL. Velocity Remarks
Coefficient A×C Σ(A × C) Rainfall Flow area radius Capacity of Drain

3 2 Check for
START END (m) (A:ha) (C) Q0(m /sec) D(m) (‰) OUTLET (m) INLET (m) (m ) R(m) (m/sec) Q(m3/sec) Q0<Q Velocity

FGRU AREA
CB-01 REDUCER 6.90 0.0202 1.00 0.0202 0.0202 71.12 0.0040 0.20 11.00 7.950 7.875 0.023 0.0592 1.44904 0.0340 O.K!! OK

CB-02 REDUCER 4.70 0.0212 1.00 0.0212 0.0212 71.12 0.0042 0.20 9.00 7.950 7.910 0.023 0.0592 1.31071 0.0308 O.K!! OK

REDUCER MH-O-001 4.20 1.00 0.0414 71.12 0.0082 0.30 11.00 7.875 7.830 0.053 0.0889 1.89878 0.1004 O.K!! OK

MH-O-001 MH-O-002 11.20 1.00 0.0414 71.12 0.0082 0.30 4.50 7.830 7.780 0.053 0.0889 1.21446 0.0642 O.K!! OK

MH-O-002 MH-O-005 3.45 1.00 0.0414 71.12 0.0082 0.30 3.00 7.580 7.570 0.053 0.0889 0.99161 0.0524 O.K!! OK

MH-O-005 PIT 39.00 1.00 0.0000 0.0414 71.12 0.0082 0.30 3.00 7.570 7.455 0.053 0.0889 0.99161 0.0524 O.K!! OK

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2.2 STORM WATER SEWER PIPE (FIRE-WATER FLOW)

RAIN-WATER FLOW ♦ C.S PIPE ( n = 0.011 )

CB & MH NO.
Run-off Rainwater ♦ Firewater DIA. Wet Hydraulic Discharge
Length Area Slope Invert EL. Velocity Remarks
Coefficient A×C Σ(A × C) Rainfall Flow Design Firewater area radius Capacity of Drain

Check for
START END (m) (A:ha) (C) Q0(m3/sec) Qf(m3/sec) D(m) (‰) OUTLET (m) INLET (m) 2
(m ) R(m) (m/sec) Q(m3/sec) Qf<Q Velocity

(CB-01/02)

CB-01 REDUCER 6.90 0.0306 0.20 11.00 7.950 7.875 0.023 0.0592 1.44904 0.0340 O.K!! OK

CB-02 REDUCER 4.70 0.0306 0.20 9.00 7.950 7.910 0.023 0.0592 1.31071 0.0308 O.K!! OK

REDUCER MH-O-001 4.20 0.0306 0.30 11.00 7.875 7.830 0.053 0.0889 1.89878 0.1004 O.K!! OK

MH-O-001 MH-O-002 11.20 0.0306 0.30 4.50 7.830 7.780 0.053 0.0889 1.21446 0.0642 O.K!! OK

MH-O-002 MH-O-005 3.45 0.0306 0.30 3.00 7.580 7.570 0.053 0.0889 0.99161 0.0524 O.K!! OK
EXISTING
MH-O-005 39.00 0.0306 0.30 3.00 7.570 7.455 0.053 0.0889 0.99161 0.0524 O.K!! OK
(SUMP)

(CB-03)

CB-03 MH-O-003 6.10 0.0306 0.20 9.00 7.950 7.900 0.023 0.0592 1.31071 0.0308 O.K!! OK
OMH17-2
MH-O-003 8.20 0.0306 0.30 5.00 7.670 7.630 0.053 0.0889 1.28016 0.0677 O.K!! OK
(EXISTING)
EXISTING OMH17-2
4.00 0.15 5.00 7.950 7.930 0.013 0.0444 0.80645 0.0107 O.K!! OK
(SUMP) (EXISTING)
OMH17-1 OMH17-2
34.00 0.15 5.00 7.830 7.660 0.013 0.0444 0.80645 0.0107 O.K!! OK
(EXISTING) (EXISTING)
OMH17-2
PIT 72.80 0.0230 0.20 5.04 7.610 7.243 0.023 0.0592 0.98084 0.0230 O.K!! OK
(EXISTING)
MH-O-003 MH-O-002 32.20 0.0076 0.30 3.50 7.670 7.780 0.053 0.0889 1.07106 0.0566 O.K!! OK

MH-O-002 MH-O-005 3.45 0.0076 0.30 3.00 7.580 7.570 0.053 0.0889 0.99161 0.0524 O.K!! OK

MH-O-005 PIT 39.00 0.0076 0.30 3.00 7.570 7.455 0.053 0.0889 0.99161 0.0524 O.K!! OK

※ During firewater case, C/B-003 shall intake 0.0306m3/s of fire water which will be directed to OMH17-2.
The pipe line connecting OMH17-2 and Pit can only handle 0.0230m3/s of firewater so, overflow of 0.0076 m3/s shall be re-directed through MH-003, MH-002, MH-005 and then Pit.

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3. HYDRAULIC RADIUS

3.1 Hydraulic radius of pipe

0.458258 D

l A2
0.5D 0.2D 0.5D
A1 Θ' A1
θ
0.7 D

A3

1) Area
0.2
Θ= 90。 - COS-1 = 90。 - COS-1 0.40
0.5

πrΘ 0.5πΘD πθD

l= = =
180 180 360

A1 =
rl Dl D πθD πθD2
= = × =
2 4 4 360 1440

A2 = 0.5 × 0.458258 D × 0.2 D × 2 = 0.09165 D2

2 2
A3 = πD πD
0.5 × =
4 8

2
πθD πD2
A = 2A1 + A2 + A3 = 2 × + 0.09165 D2 +
1440 8

πθ π 2
= 2 × + 0.091652 + × D
1440 8

π π
= 2 × × ( 90。 - COS-1 0.4 ) + 0.09165 +
1440 8
= 0.5872 D2

2) Wetted perimeter
πD πθD πD
P= 2l + = 2x +
2 360 2
π π
= × ( 90。 - COS-1 0.4 ) + × D= 1.982 D
180 2

3) Hydraulic radius
A 0.5872 D2
R= = = 0.296 D
P 1.982 D

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4. STORM SEWER SYSTEM

4.1 STORM SEWER SYSTEM

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