LAUSR

Abstract Side weirs are hydraulic structures usually used for flow diversion in irrigation, drainage and sewer networks. The piano key weir (PKW) is the newest form of labyrinth weir. It is more efficient and needs less reinforcing steel. PKW can be used as a side weir. The aim of this research is to study the geometric and hydraulic parameters of type-A trapezoidal piano key side weirs (TPKSWs) with two different total widths located on a curved channel. Dimensional analysis revealed that the discharge coefficient of TPKSW along the bend depends on the dimensionless parameters of the upstream Froude number ( F r 1 ), ratio of total weir width to main channel width (W/b), ratio of upstream-downstream length of the TPKSW to weir height (B/P), ratio of weir height to upstream flow depth ( P / y 1 ), sidewall angle of the TPKSW (δ) and angle of the bend curvature (β). The effect of each parameter on the discharge coefficient was estimated by calculating the statistical parameters. It was found that β had the greatest effect on the discharge coefficient. An empirical equation is presented for the discharge coefficient of the TPKSW in a curved channel using the nonlinear regression module in Statistica software based on the experimental data. Error indices were employed to determine the precision of the equation. The equation was satisfactory with a high coefficient of determination ( R 2 ≈ 0.978 ). The experimental results showed that the average discharge coefficient of the TPKSWs was about 2.68 times higher than that of the linear rectangular side weirs (LRSWs) in the curved channel. In the intake channel, the scour potential downstream of TPKSWs was lower than that of LRSWs. Because of the increased intensity of the secondary current, the discharge coefficient ( C d L ) of TPKSWs with W/b = 1.43 was 1.3–2.1 times higher than that of TPKSWs with W/b = 0.71.