Performance Comparison of Semicircular Weirs with Varying Crest Roughness

Abstract

Broad crested semicircular weirs are usually used for flow measurement in open channel hydraulics. Since the corresponding theoretical equations of broad crested weirs are not adequate for practical purposes, empirical models are employed as alternative. In this work, the flow parameters of broad crested semicircular weir models were investigated experimentally using a laboratory flume. The crests of these weir models were ‘inverted’ with semicircle geometry. Discharge and water heads over the weir models were determined for various crest radii of 5 cm, 7 cm and 10 cm with the corresponding weir heights of 20 cm, 18 cm and 15 cm respectively. These models were coated with surface roughness using soil particles of diameters 1.18 mm, 2.36 mm, 4.75 mm and a normal weir model as control. It was discovered that, increase in the particle size results in an increase in discharge coefficient of the weir models given an overall increment of 45% as hydraulic performance of the weirs. The model with radius 5 cm, coated with an aggregate of diameter 2.36 mm was found to be the most effective model with the highest discharge coefficient of 1.453.