Experimental and field verifications of radial gates as flow measurement structures

Radial gates are common structures in irrigation projects. This paper presents some theory-based equations for explicit estimation of the discharge from a radial gate under free and submerged flow conditions using energy and momentum (E-M) principles. The proposed equations were calibrated using extensive experimental data collected from the literature and this study for three types of radial gate under free and submerged flow conditions. The submergence threshold of radial gates is concluded, based on the concepts of hydraulic jump and the intersection of free and submerged head-discharge curves. The results indicated that the error in estimating the discharge increases under transition ( - 2.5 <= Sr% <= + 2.5), gate lip (1 < y(0)/w <= 2), and high submerged (y(t)/y(0) >= 0.95) flow conditions. However, in these flow limit conditions, the discharge error can be considerably decreased by adjusting the tailwater depth to flow depth just after the gate and using the energy equation for the sections before and after the gate. The efficiency of the proposed methods was evaluated based on the data series from field measurements of radial gates in 29 check structures at irrigation canals in the United States and Iran. The results showed that the discharge could be estimated using the proposed equations in field conditions with acceptable accuracy.