Turbulent mixing induced by rapid gate opening in a canal

Abstract

In an open channel, the operation of a gate is associated with a lowering of the water level on one side and the generation of a negative surge. Herein some physical modelling of rapid gate opening was studied under controlled flow conditions in a relatively large size facility. The gate opening induced a negative surge travelling upstream into the canal. Detailed free-surface and velocity measurements were performed with three types of roughness. The experiments were repeated 25 times and the results were ensemble-averaged. The propagation of negative surges was gentle and barely perceptible, but very close to the gate. Large free-surface fluctuations and turbulent velocity fluctuations were recorded beneath the negative surge, as well as turbulent Reynolds stresses. For all bed configurations, the data of surge leading edge celerity showed a characteristic trend with an asymptotical value: (U+Vo)/(g do)1/2 = 1 independently of the bed roughness. The results implied that the bed roughness had little effect within the experimental flow conditions.