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SEWER DESIGN CALCULATION

Waste Water Flow Rate

1.

Average Flow = 225 liters per person

= 225 x 1 x 10-3

m3/s

2. Peak Flow Factor = 4.7 / P 0.11 (P is estimated population equivalent

in thousand)

Hydraulic Design

1. Minimum Velocity = 0.8 m/s

2. Maximum Velocity = 4.0 m/s

3. Minimum Depth of Invert = 1.5 m

4. Minimum Size of Sewer = 225mm VCP5. Minimum Size of Laterals = 150mm VCP

Manholes

1. Distance between Manholes

Maximum 100m for sewer up to 225 mm diameter

2. Location of Manholes

Upstream end of all sewer

Every change in direction

Every change in gradient Every change in size of sewer

All intersection and junction

Materials

Vitrified Clay Pipe (VCP)Sewers up to 225 mm diameter

METHOD OF CALCULATION

1. Design for Sewerage Flow Rate

Peak Flow, Q peak = Average flow, Q averagex Peak Flow Factor

= Q averagex 4.7 / P0.11

(NOTE: P is population Equivalent in Thousand)

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2. Flow Data in Verified Clay Pipe

From Mannings Formula,

V = 1/n R 2/3S 1/2 ------------------------ (1)

From Continuity Equation.

Q = V A ------------------------ (2)

Applying (1) into (2)

Q = (1/n R2/3

S) A

Where

V = velocity (m/s)

R = hydraulic radius (m)

S = gradient

Q = capacity (m3/s)

A = cross-sectional area of pipe (m2)

n = Mannings coefficient (0.013 for VCP)