This equation is modified by Manning by incorporating dependence of hydraulic radius on the bottom slope and is given by
                                                (5)
In this equation, the parameter is the Manning resistance coefficient. Its value depends on the surface material of the channel's wetted perimeter and is obtained from experiment. It is also not dimensionless and has the unit of . The typical values of are given in Table 1.

Table 1: Values for Manning coefficient (Ref. 1; Table 10.1)