Float speed

[crusher39]

What kind of speed can I expect floating a river. Discharge is at 158 cfs with a gage height of 4.25 ft. Can I do the math? 158 cfs/4.25 ft*avg width of 30ft and get 1.24 ft/s=.85 mph? Doesn't seem like it should work. Gage height doesn't work that way does it? Is there a way to get velocities of local rivers? Trying to plan out a float and need an ETA for pickup.

Thanks in advance for the help.