Clear Water Local Scour by Submerged Three-Dimensional Wall Jets: Effect of Tailwater Depth

The present study deals with scour caused by three-dimensional jets issuing from a square cross-section nozzle onto a noncohesive sand bed. Experiments were conducted using two different nozzles and three tailwater depths. The densimetric Froude number was maintained below ten, while the jet expansion ratio was held greater than ten. The results indicate that the densimetric Froude number, tailwater depth, and grain size-to-nozzle width ratio, all have an influence on the extent of scour. However, each parameter has a dominant influence at different flow conditions. For example, at values of densimetric Froude numbers less than five, nondimensional tailwater depth and grain size-to-nozzle width ratio have no effect on the maximum depth of scour. At higher densimetric Froude numbers, the effect of tailwater depth appears to be important at larger values of grain size-to-nozzle width ratio. A set of scaling parameters based on nozzle hydraulic radius, grain size, and densimetric Froude number provides for a better scaling of the time variation of the scour parameters.