Temporal Evolution of Clear-Water Scour Depth at Submerged Weirs

Equilibrium clear-water scour depths predicted by existing equations based on the peak flow rate of a flood hydrograph can be overly conservative for submerged weirs in mild-slope sandy rivers, because the equilibrium timescale normally is much larger than the timescale of a flood event. Therefore it is important to understand the clear-water scour development at submerged weirs in order to improve the accuracy of scour estimation. This paper presents new data on the temporal evolution of the downstream clear-water scour depth at a submerged weir under steady flow conditions and analyzed the impacts of flow intensity, weir height, sand coarseness parameter, and weir slope on the development of the downstream clear-water scour depth. This study defined a dimensionless equilibrium time scale te* and evaluated its dependencies on the aforementioned parameters. Predictors for te* and the temporal downstream clear-water scour depth at submerged weirs are proposed.