As the flow is at uniform depth, so the hydrostatic pressure forces across either end of the control volume balance each other i.e. . Thus, Eq. (1) becomes,
                                                (2)
where is the specific weight of the fluid and . More often the open channel flows are turbulent rather that laminar. So, Reynolds number is quite large and for such flows, the wall shear stress is proportional to dynamic pressure and may be written as
                                                                        (3)
where is a constant that depends on the roughness of the pipe. Now, equating Eqs. (2) and (3), we get,
                                                                        (4)
This equation is known as "Chezy equation" in which is called Chezy coefficient. Its value is determined from experiment and also, it has the unit of .