The Manning Formula is used for Velocity calculations within the software.
n = Manning's roughness coefficient (see Pipe Roughness)
R = Hydraulic Radius
S = Hydraulic gradient
The equation is in metre-per-second units but the n values are the same as those specified in the foot-per-second format of the equation (e.g. smooth concrete pipe n = 0.012 approximately). The formula is sometimes known as Strickler's formula and 1/n as the Strickler's coefficient.
A concrete pipe with a smooth interior would have a Manning's n of approximately 0.012.
Manning's n may be derived from 1/Strickler coefficient.