Rapid operation of a Tainter gate: generation process and initial upstream surge motion

In water supply channels, the brusque operation of control gates may induce large unsteady flow motion called surges. Such a rapid operation of gates must often be restricted, although it may be conducted to scour silted channels and sewers. Herein a physical study was conducted under controlled flow conditions to study the turbulent mixing in the very-close vicinity of a rapidly opening/closing Tainter gate, with a focus on the unsteady transient mixing induced by the gate operation. The data suggested that the negative/positive surge generation was associated with large instantaneous free-surface fluctuations. The velocity measurements indicated significant variations in longitudinal velocity during the surge generation, as well as large fluctuations of all velocity components. The processes were associated with large Reynolds stress levels. A succession of rapid closure and opening of undershoot gates provided optimum conditions to scour silted canals, and the present results gave some detailed insights into the physical processes.