Qg   : Desired Flow Rate
Qd   : Full Flow Rate
J     : Inclination of Pipe (m/m)
Vg   : Desired FlowVelocity (m/s)
Vd   : Full Flow Velocity (m/s)
h/Di : Rate of Fullness (%)

First the chosen pipe’s flow rate (Qd) is checked from table 1. Then the (Qg/Qd) rate is calculated from table 2, according to the given value the (h/Di) rate of fullness and (vg/vd) flow and full flow velocity recorded.

If the (h/Di) rate of fullness is not at the required value then the diameter of the pipe will be increased, and then the same procedure will be repeated.

For Example: :

If the required flow rate of the pipe is (Q) 100 lt/s and the inclination is1/100. In this case, we use the Manning formula to choose the pipe diameter;

From the Table 1 if we choose the inclination 1/100 but instead we use the flow rate that is bigger than 100 lt/s. The chosen pipe’s proportions would be; the diameter is Ø 350 mm, the full flow rate is (Qd) 236,6 lt/s, the velocity (vd) is 2,46 m/s. From the given values the calculations of Qg/Qd rate=100/236,6=0,423.

In table 2 the Qg/Qd rate is presented as the rate of fullness which is 45.5 % and the velocity as v/vd=0,962.

ROUGHNESS COEFFICIENTS USED IN PE PIPE SEWER SYSTEMS :

CALCULATION USING MANNING FORMULA:

V = Velolcity (m/s)

n = Coefficient of Manning

R = Hydraulic semi-diameter (m)

J = Hydarulic inclination (m/m)

CALCULATED BY KUTTER FORMULA:

V = Velolcity (m/s)

n = Coefficient of Manning

R = Hydraulic semi-diameter (m)

J = Hydarulic inclination (m/m)