Experimental Modeling of Submerged Pivot Weir

An inclined rectangular overflow structure, also called a pivot weir, consists of a rectangular plate, angled downstream from the vertical, that can be used as an upstream water level control device. A pivot weir is submerged when the upstream water level is influenced by the downstream flow depth. In this paper, to investigate factors influencing submerged flow conditions, an extensive experimental program including 251 experimental trials was carried out using weir inclination angles of 39.6°, 53°, 85°, and 90° and weir heights ranging from 0.263 to 0.312 m. A formula to distinguish between free and submerged flow conditions was developed using the Π theorem of dimensional analysis and the incomplete self-similarity (ISS) theory, and the submergence threshold curve was calibrated by the measurements carried out in this study. Employing a similar theoretical procedure (dimensional analysis and ISS theory), the tailwater depth for which a downstream standing wave starts and a stage-discharge relationship for submerged conditions also were developed. A comparison with the submerged stage-discharge formula proposed by the United States Bureau of Reclamation revealed that the proposed method could be more accurate for the entire operating range and conditions evaluated.