Q = V. A =
k
/
n
A R
⅔ S
½
Q: flow rate (ft
3/s, in
3/s, m
3/s, cm
3/s)
V: velocity (ft/s, in/s, m/s, cm/s)
A: cross-sectional area of flow (ft
2, in
2, m
2, cm
2)
k: for US Customary units: k=1.4859 ft
⅓/s; for SI units: k=1 m
⅓/s
n: Manning Coefficient (unitless)
R: hydraulic radius (ft, in, m, cm), R = A/P, where P is wetted perimeter
S: longitudinal slope of channel (ft/ft, in/in, m/m, cm/cm)