Hydrologists sometimes use Manning's equation to calculate the velocity v, in feet per second, of water flowing through a pipe. The velocity depends on the hydraulic radius R quarter of the diameter of the pipe when the pipe is flowing full; the slopes of the pipe, which gives the vertical drop in feet for each horizontal foot; and the roughness coeff
the material of which the pipe is made. The relationship is given by the following.
1.486 R2/351/2
n