Experimental Study on Hydraulic Characteristics of Trapezoidal Control Gate with Upstream Water Diversion Outlets in Irrigation Area

To support precise measurement and control of water volume in irrigation area, this study investigated the influence of diversion outlet on the flow pattern in front of control gate, as well as the variation laws of flow coefficient and head loss of trapezoidal control gate under different slopes and water diversion angles. We observed the flow pattern at diversion outlet and analyzed the causes, and further established the flow formula for trapezoidal control gate by using dimensional analysis method and calculated the head-losses based on 495 groups of discharge tests under different water diversion conditions. The discharge tests involved different gate openings and water heads with three slopes (m=1.5, 1.75, and 2) and five water diversion angles (θ=30°, 45°, 60°, 75°, and 90°). Results revealed that a backwater area was formed in front of the control gate. The coefficient of determination of the flow formula was R2=0.934, and the average relative error of the flow was 2.83%. Relative head loss decreased as the relative opening of the control gate increased. The results demonstrated high accuracy of the proposed flow formula for trapezoidal control gate, which offers a basis for flow measurement in trapezoidal channels in irrigation areas.