Any of the other parameters in the Manning Equation could be calculated if it is the only unknown. Q Flow Rate ft 3 s v Velocity fts A Flow Area ft 2 n Mannings Roughness Coefficient R Hydraulic Radius ft S Channel Slope ftft. Step 2 Draw a line between the S and Sxscales and note where it intersects the turning line.
Rh 113894 121 ft.
Q VA 271 ftsec 8 ft2 217 ft 3sec. V kn n Rh23 S12 1 where. P 2 p 2 - 2159 94 f5. The Mannings n is a coefficient which represents the roughness or friction applied to the flow by the channel.