عنوان مقاله [English]
Side weirs are hydraulic structures used for flow diversion in irrigation and drainage systems. Piano-key side weirs (PKSW) were investigated since 2017. For the specific width of a diversion channel, the discharge coefficient of PKSWs is far greater than that of classic rectangular side-weirs (CRSWs). In this study, the discharge coefficient of various types (A, B, C, and D) of Trapezoidal Piano Key Side-Weirs (TPKSWs) have been measured and compared with the discharge coefficient of CRSWs under the free-flow condition. The results showed that the performance of TPKSWs can be classified: Type A> Type B>Type C>Type D. But, these results were different for normal TPKWs. Discharge efficiency (e) of TPKSWs relative to CRSWs decreases with increasing the upstream head. At (ratio of the upstream flow depth to the weir height)>1.45, the discharge efficiency of types-A, -B, -C, and -D TPKSW approached 1.91, 1.81, 1.75, and 1.67, respectively. Moreover, this study presented a three-degree polynomial function to estimate the discharge coefficient of TPKSW.