Design procedure for sanitary sewers
How to Design Sanitary Sewer
Calculate the average wastewater flow, Qavg = (70-80) % of average water consumption.
Select a peak factor, PF = [(18+√P)/(4+√P)], where P = population in thousands.
Calculate the peak wastewater flow, Qpeak = (PF * Qavg)
Calculate the allowance for industrial and commercial sewage at the rate of 3734 m3/km2/d (Qind)
Calculate the infiltration allowance, Qinf = (5-10) % of Qavg
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)]