The Froude number (Fr = v / sqrt(g x d), where v is flow velocity, g is gravitational acceleration, and d is flow/channel depth) determines whether open-channel flow is subcritical (Fr < 1, tranquil/streaming flow, where surface disturbances can propagate upstream), critical (Fr = 1), or supercritical (Fr > 1, rapid/turbulent flow, where surface disturbances cannot propagate upstream); the flood plain width given in this problem is extraneous information not required for this calculation, since the Froude number depends only on flow velocity and channel depth.