Hydrodynamics and turbulence in a positive surge. A comparative study

A positive surge results from a sudden change in flow that increases the depth. It is the unsteady flow analogy of the stationary hydraulic jump and a geophysical application is the tidal bore. Positive surges are commonly studied using the method of characteristics and the Saint-Venant equations. The paper presents the results from new experimental investigations conducted in a large rectangular channel. Detailed unsteady velocity measurements were performed with a high temporal resolution using acoustic Doppler velocimetry and non-intrusive free-surface measurement devices. Two series of data were collected with a horizontal bed slope, a constant flow rate (Q=0.060 m³/s) and two different downstream gate openings after closure, which resulted in undular (non-breaking) and in breaking bores, respectively. The analysis of undular free-surface profiles revealed a good agreement with previous both theoretical and experimental studies. Unsteady flow turbulence analysis revealed some significant patterns in streamwise and transverse velocities.