Design procedure for sanitary sewers
How to Design Sanitary Sewer
Design flow:
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Calculate the average wastewater flow, Qavg = (70-80) % of average water consumption.
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Select a peak factor, PF = [(18+√P)/(4+√P)], where P = population in thousands.
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Calculate the peak wastewater flow, Qpeak = (PF * Qavg)
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Calculate the allowance for industrial and commercial sewage at the rate of 3734 m3/km2/d (Qind)
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Calculate the infiltration allowance, Qinf = (5-10) % of Qavg
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Find the design discharge by adding peak flow, industrial and commercial allowance and infiltration allowance, i.e., Qdesign = Qpeak + Qind + Qinf
Diameter of the sewer:
Assume a suitable value for cleaning velocity, determine the area (diameter) of the sewer by using the relation, Area, A = (Qdesign/V)
Slope using Manning’s equation determine the slope of sewer, V = [(1/n) *(R2/3)*(√S)]
