A COMPARISON OF VELOCITY EQUATIONS IN NATURAL STREAM CHANNELS IN NORTHWEST OHIO

The Manning equation is the most widely used and accepted empirical resistance equation for measuring flow velocity. However, it contains the variable, n, the use of which requires skill and experience of the user, which both introduce uncertainty into flow velocity results. This research project compared the Manning equation (1981), with four other less commonly used equations: Chezy, Darcy, Riggs, and Dingman. Because these last four equations contain only measurable quantities, these should provide more consistent flow results than the Manning equation. I measured slope, wetted perimeter, hydraulic radius, and flow velocity in three second order streams in Northwest Ohio for use in these equations. Results show that data calculated using the Chezy, Darcy, and Riggs equations provide good agreement with each other and the actual measured velocity. Conversely, neither the Dingman nor Manning calculations agree with the meausured velocity, although the results from the Manning equation are consistent underestimates.