1. A certain community at the middle income level generates wastewater, a daily
ID: 1885667 • Letter: 1
Question
1. A certain community at the middle income level generates wastewater, a daily flow rate of 2.80 x 101 uday into a pipe A. Pipe B, contributes flow from another high income community of 85 000 people to pipe C. Assume the peak flows of pipes A and B to reach pipe C at the same time and determine: i. The total PWF in pipe C ii. The diameter of pipe C ii. Write down the acceptable minimum and maximum velocities acceptable in sewer flows, and use them to check whether the flow velocity in Pipe C is acceptable. The pipe C has a slope of 1:140 and a Manning's n of 0.013, assuming the pipe flows up to its full capacity at PWFExplanation / Answer
According to IS 1172 code, the water demand for HEG is 200 lpcd.
Cosidering 80% water goed to drainage.
Flow to pipe B = 80% ×200×85000=13.6×106 litres/day
Since, peak of A and B is at same time
Peak flow through C=flow through A + flow through B
=2.8 × 10^4 + 13.6 × 10^6 =13.628×10^4 litres/day=0.1577 m3/s Answer i
We know, Q=AV
Q=0.25××d2 × (1/n)× R2÷3 × S1÷2 where R is hydraulic radis R=d÷4
0.1577=0.25××d2 × (1÷0.013) × (d÷4)2÷3 ×(1÷140)0.5
0.07782=d8÷3
d = 0.3838 m
d= 383 mm answer ii
Since 383 mm isn't available provide 400 mm dismetrd pipe.
V= Q÷A
=(0.1577)÷(0.25*×.383^2)
=1.368 m/s
Hence this velocity is acceptable as general range is 0.6 m/s to 3.5 m/s.
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