Discharge Coefficient of a Circular-Crested Side Weir in Rectangular Channels

Side weirs are frequently used for water-level control in irrigation systems, sewer networks, and flood protection. Researches on side weirs have generally focused on determining the hydraulic characteristics of sharp-crested side weirs. A common type of this weir, which has larger capacity to pass the flow, is the circular-crested weir. To the authors' knowledge, investigation of hydraulic features of this weir as side weir has been ignored in literature. Based on an experimental model for subcritical flow conditions and under the hypothesis of constant specific energy, the hydraulic characteristics of the circular-crested side weir with various weir heights, widths, and downstream slopes are taken into account to formulate an expression for the discharge coefficient. The results indicate that the upstream Froude number, the weir height to weir length, specific energy to the weir radius, and downstream slope of the weir are the important variables that affect the discharge coefficient of circular-crested side weirs. A comparison between circular-crested and sharp-crested side weirs confirms that circular-crested side weirs are more economical and efficient than sharp-crested side weirs, due to the greater discharge coefficient. (C) 2016 American Society of Civil Engineers.