Concepts: The flow in sewer pipe takes place under atmospheric conditions i.e. open channel flow and also its is assumed to be a uniform flow. Hence, Manning’s formula can be applied for the calculation of discharge, which is given as :
Q=A(R2∕3S1∕2) Where
N is roughness coefficient, depends on pipe material
R hydraulic radius depends on pipe geometry
S is bed slope at which pipe is laid
A is a cross-sectional area
Q is the rate of flow in sewer pipe
Calculation: Since, both sewer pipelines have same diameter and made of same material, they have same hydraulic radius and cross section area and roughness coefficient.
Therefore, it can be concluded that
QαS1∕2 Now ,
= = =1.67