Clear-Water Scouring Process in a Flow in Supercritical Regime

Abstract

The aim of this research is to measure the clear-water scouring produced by supercritical flow around a rectangular-shaped obstacle. The initial uniform flow condition without the obstacle is such that the Shields parameter remains slightly lower than critical so that the sediment constituting the mobile bed is not transported. The sediment begins to move after the obstacle is suddenly inserted; the two-dimensional (2D) water surface and the 2D bed topography fields around the obstacle are then measured at specific times after this. The initial flow pattern exhibits a typical bow-wave like hydraulic jump detached upstream from the obstacle that occurs over the rough plane bed. For the more widely studied subcritical regime configuration, the scour initiates on the sides of the obstacle and migrates towards its upstream face where the scour depth continues to increase over time. This causes the hydraulic jump to migrate downstream, approaching the obstacle with negligible effect on the bed topography. Downstream from the obstacle, the sediment deposits and forms a specific deposition zone whose maximum elevation also increases with time before reaching a plateau. The flow pattern downstream of the obstacle is strongly influenced by this deposition and exhibits two consecutive bow-waves aligned in the streamwise direction with the hydraulic jump located upstream. The experiment runs for two hours and even though all evolution rates decrease with time, this duration is not sufficient to obtain a stable situation of the flow pattern and bed topography. This paper ends with a similarity analysis of the typical field conditions for which this clear-water scouring process could occur.