A large number of formulae have been developed to assist in hydraulic calculations to determine the flow rate that a pipeline can carry. The two most common formulae are Mannings and Colebrook-White:

Mannings
Mannings is the most popular equation for stormwater design because it is simple to apply and it generally provides an acceptable level of accuracy. In calculations involving FRC™ pipes the use of the Mannings equation may give reasonable flow estimates if an allowance is made for the variation of the roughness coefficient with pipe size and flow velocity.

Colebrook-White
A more accurate method for calculations involving FRC™ pipes is to utilize the Colebrook-White formula. The following Colebrook-White design chart for FRC™ should allow quick and easy estimates without involved calculations.

Where
n = Manning roughness coefficient
S = Hydraulic gradient (m/m)
k = Hydraulic roughness (m)
V = Velocity (m/s)
R = Hydraulic radius = D/4 (m)
D = Pipe internal diameter (m)
g = Gravitational acceleration (m/s2)
v = Kinemtic viscosity of water (m2/s)

Note: This flow chart has been prepared using the Colebrook-White equation where the friction coefficient (f) is determined from the formulae:

Where
Re: Reynolds number

The Institution of Engineers’ publication, ‘Australian Rainfall and Runoff’ recommends that the roughness factor (k) for FRC™ pipes has the same characteristics as AC and therefore, in line with AS2200, lies in the range 0.015 to 0.060mm. The chart has been prepared using a (k) value of 0.060mm.

Please note:  
The internal FRC™ pipes diameters have been used.
This chart has been calculated for water viscosity at 20C

Please refer to chart in the Product and Design Data manual for further details.