Design, fabrication and field test evaluation of a portable stainless parshall flume

Abstract

The study was conducted to design and evaluate the performance of a portable stainless Parshall flume for field use. It was fabricated at a machine shop in Molo, Iloilo City from October to November 2018 while field testing and evaluation were done on January 2019 in a lateral canal located in Brgy. Pagsanga-an, Pavia, Iloilo. The device consisted of: (a) converging section where the irrigated water enters and where the primary measurement is positioned, (b) throat section where the secondary measurement is positioned and (c) diverging section where the irrigated water exits from the flume. The flume also consisted of other parts like the spirit level, staff gauges and handle. The operation started when the Parshall flume was leveled and established in a non-lined open channel, then embankments or wingwall were constructed adjacent to the converging and diverging sections of the device. There were 10 tests performed which represented 10 different depths of water starting from 9 to 45 cm. The volumetric flow rate measured using the Parshall flume ranged from 5.879 x 10-3m3/s to 0.075 m3/s. Whereas, the computed volumetric flow rate using the float method ranged from 5.624 x 10-3 m3/s to 0.120 m3/s. The accuracy of the flume for the first 5 depths (9 cm to 18.5 cm) was computed to be within or close to the +/- 2 to 5% difference, which indicated a relatively accurate volumetric flow rate. The five remaining depths (22 cm to 45 cm), however, showed inaccuracies due to seepage. Adding the total material cost, labor cost and contingencies gave a total expense of PHP12,630.00 for the flume.