Investigation of stage-discharge relationship in broad-crested weirs with elliptical curve shape

Weirs are of critical importance in many fields of hydraulic engineering such as water resources management, irrigation systems and flood control. These structures, which are widely preferred due to their simple design and operation, work on the principle of determining the flow rate of water by measuring the depth of flow in water conveyance structures. In this study, the relationship between the measured levels and the corresponding flow rates in a weir structure with a half elliptical geometry placed in an open channel is investigated. In order to observe how the elliptical geometry affects the flow through the weirs, 9 different weirs were fabricated with 3 different weir heights (P= 8,10,12.5 cm) and 3 different weir lengths (L= 32,42,53 cm). For the purpose of this study, the parameters affecting the flow coefficient were determined and analyzed using dimensional analysis. As a result of 150 experiment al runs, it was observed that the weir geometry did not affect the water surface in the upstream and downstream regions of the weir, but the water surface on the weir curves similarly to the curvature of the weir crest. Increasing the weir height causes an increase in the flow height and a decrease in the discharge coefficient. At a given weir height, increasing the weir length decreased the curvature of the flow and thus the value of the discharge coefficient decreased. Empirical equations were derived to determine the flow coefficient and results were quite consistent with the weir equation in the literature.