Development of rectangular broad-crested weirs for flow characteristics and discharge measurement

Abstract

One of the important problems which designers and engineers are faced with is proper measurement of water flow rates in open channels and rivers. To solve this problem, the water discharge to be precisely measured in water conveyance systems such as off takes and distribution ditches. The common procedure to meet this requirement is achieved by using water-measuring structures such as flumes, orifices, weirs and current meters. Among the mentioned structure, engineers prefers the weirs because of their simple structure and economical features. The broad-crested rectangular weirs are very common which are widely used in water ways and canals. In this study, the effect of steeping in the upstream side of rectangular broad-crested weirs over discharge coefficient and flow characteristics is investigated. Five weirs with 15, 30, 45, 60 and 90 weir angles were developed and flow discharge coefficient, negative velocity over the weir crest edge and water surface profiles along the weir crest evaluated in laboratory hydraulic flume. The obtained results showed by decreasing the slope of the upstream side, discharge efficiency and the discharge capacity of the weir are increased subsequently. Consideration of experimental data it is obvious that by using the proposed weir with slope of 15 degree in comparison with standard weir, the efficiency is increased up to 19.17%. It is noteworthy that by reducing the slope, return current on the crest is not observed.