Question

A combined sewer of circular section is to be laid to serve a particular area. Design the sewer from the following: Area to be served = 100 hectares Population 90000 Impermeability factor = 0.50 Time of entry = 3 min. Time of flow = 17 min. Rate of water supply = 135 Iped. Assume any other data if necessary

Answer 1

[AI-generated answer — Bot GPT 3.5]

To design the combined sewer, we need to calculate the following:

1. Peak flow rate:
Peak flow rate = (Population * Water supply rate) / (Impermeability factor)
Peak flow rate = (90000 * 135) / 0.50 = 24,300 l/s

2. Peak flow in the sewer:

Peak flow in the sewer = Peak flow rate * Time of entry
Peak flow in the sewer = 24,300 * 3 / 60 = 1215 l

3. Minimum flow in the sewer:

Minimum flow in the sewer = Peak flow rate * Time of flow
Minimum flow in the sewer = 24,300 * 17 / 60 = 6891 l

4. For circular sewer, the formula for flow in a circular sewer is:

Q = 1.49 * D^2 * S^0.5

Where:
Q = Flow rate in m^3/s
D = Diameter of the sewer in meters
S = Slope of the sewer

Given that the area to be served is 100 hectares, we can calculate the diameter of the sewer:

Area = π * D^2 / 4
100 hectares = π * D^2 / 4
D = √(100 * 40000 / π) = 2√100000 / π = 200 / π = 63.7 m

5. Slope of the sewer:
Assuming a slope of 0.001, we can calculate the flow rate in the sewer:

Q = 1.49 * (63.7)^2 * (0.001)^0.5 = 7.60 m^3/s

Therefore, a combined sewer of circular section with a diameter of 63.7 m and a slope of 0.001 can serve the particular area.