Results of Parshall Flume Tests

Abstract

Presented are: (1) A reanalysis of Parshall's original experimental data obtained for the improved Venturi (Parshall) flume; and (2) a reanalysis of data obtained by the writer during model tests of the Parshall flumes at the rate measuring stations installed by the U.S. Department of Agriculture's Soil Conservation Service (SCS) on the Waco, Tex., Blacklands experimental watershed. Parshall's and the Waco data were originally analyzed graphically to develop rating equations. The reanalysis used the least‐squares method. The reanalysis shows that in the head‐discharge equation the Waco coefficient and exponent do not vary with flume size, whereas Parshall's exponent varies with flume size for the 0.30 m (1 ft) to 2.44 m (8 ft) flumes and the coefficient varies with flume size for the 3.05 m (10 ft) and larger flumes. The quality of both sets of data is excellent: no explanation has been found for the albeit small differences. The reanalysis lends confidence that the equations presented by Parshall predict the discharge to within the 5% accuracy claimed by Parshall. Similar accuracy is obtained using the writer's equations. The Waco data show that the entrance wingwalls should be curved and that the head‐discharge relationship is valid for heads as low as 18 mm (0.06 ft).