Calibration of submerged radial gates

Calibration equations for free-flowing radial gates typically provide sufficient accuracy for irrigation district operations. However, many water purveyors have difficulty in determining accurate discharges when the downstream water level begins to submerge the gate. Based on experimental laboratory studies, we have developed a new calibration method for free-flowing and submerged radial gates that allows for multiple gates and widely varying upstream and downstream channel conditions. The method uses the energy equation on the upstream side of the structure and the momentum equation on the downstream side, and thus is called the Energy-Momentum Method. An iterative solution is required to solve these two equations, but this allows calibration from free flow to submerged flow continuously through the transition. Adjustments to the energy equation for free flow are described, along with an additional energy adjustment for the transition to submerged flow. An application is used to describe the new procedure and how it overcomes the limitations of current energy-based methods.