Determination of the discharge through the spillways with radial gates is essential, depending on the application of these spillways in check dams and flood discharge systems in larger dams. On the other hand, physical modeling is often required due to the complexity and impact of various factors. This study investigated the efficiency of various methods in estimating the discharge through the spillways with radial gates using 958 experimental datasets from physical models of flood discharge systems in 17 large reservoir dams in Iran. In addition to dimensional analysis of the parameters, affecting the discharge of spillways with radial gates, new equations were proposed to determine the gate opening and the deviation angle of the gate. The mean absolute relative error in estimating the discharge at every flow condition showed a decreasing trend from about 9.1 % (for the previous methods) to about 3.9 % (the proposed equation in the present study). Later, the effects of different factors on the discharge through the spillways with the radial gate in large dams were evaluated. The results showed the errors of the previous methods in estimating the discharge for transient flow conditions, nonstandard spillways, increase in the number of gates, and operation of only one gate with up to 22.2 %, 11.8 %, 21.5 %, and 10.5 %, respectively. However, under the abovementioned conditions, the mean absolute relative error of the proposed method error of discharge estimation, in the present study, decreased to about 4 %, 4.3 %, 3.3 %, and 3.5 %, respectively. Accordingly, using the new proposed equation involving the different factors to determine the discharge through the spillways with the radial gates in larger dams is recommended.
