In this study, the hydraulic performance of a semi-circular rotary gate, along with a gradual transition with three different lengths in a rectangular canal, was investigated. Experiments were conducted using various flow rates, upstream water depths, and gate opening angles. The interaction of the flow with the edge of the rotary gate causes flow division and lateral variations in the water surface. Results showed that these variations decrease as the gate opening angle increases, with the highest instability occurring at an angle of 35 degrees and the lowest at 85 degrees. The velocity and discharge on the right side of the gate were higher, but both decreased with an increase in the gate angle. The velocity on the left side was almost constant, but the discharge increased due to a larger flow cross-section. More flow was diverted to the left side with an increase in the gate opening angle. The discharge on the right side was increased while the discharge on the left was decreased by increasing the length of the gradual transition. Increasing the gate angle or reducing the transition length resulted in a greater share of flow passing through the left side overall. Energy loss increases directly with flow rate and has an inverse relationship with the gate opening angle. The highest energy loss occurred at a 35-degree opening and the lowest at 85 degrees. Finally, relationships are presented that determine the discharge through both sides of the rotary gate and the energy loss in this structure.