Supercritical Flow Measurement Using a Large Parshall Flume

A full-prototype physical model was laboratory tested to determine a rating equation applicable to large Parshall flumes with supercritical flow. The experimental program was composed of a 1.5-m (5-ft.) Parshall flume configuration and included 11 tests with discharges up to (30.15 cfs) and Froude numbers varying from 0.67-1.31. The resulting 1.5-m (5-ft) Parshall flume data were compared to existing rating equations for predicting discharge in a Parshall flume with subcritical and supercritical flow. A new rating equation specific to supercritical flow in large Parshall flumes was developed. Further, an analysis was conducted, which determined that varying regression coefficients on an existing supercritical flow-rating equation also produced an accurate rating equation for large Parshall flumes. A convergence ratio was defined and used to determine the flow regime within the flume where the 1.5-m (5-ft) Parshall flume data, combined with previously-published small Parshall flume data, indicated three convergence ratio zones: (1)subcritical, (2)transition, and (3)supercritical. Guidance was provided for rating equation selection based on the convergence ratio zone and flume size. (C) 2013 American Society of Civil Engineers.