Time-dependent local scour downstream of positive-step stilling basins

Abstract

Local scour downstream of spillways is an important problem in hydraulic engineering. The objective of this experimental study was to investigate the temporal evolution of local scour downstream of a spillway followed by a positive-step stilling basin. Experiments were conducted in a rectangular channel using four different sediments for the mobile bed. Additional tests concerned the incipient motion of sediment particles. The main parameters governing the scour process were found to be the tailwater densimetric Froude number and the relative tailwater depth. No experimental evidence was found on similar scour profiles. Scour starts at a much reduced tailwater densimetric Froude number when compared with Shields. The temporal variation of the scour hole geometry was estimated using simple power-law equations relating the scour geometry to the controlling scour parameters.

Keywords:

• Densimetric Froude number
• hydraulic jet
• scour
• stilling basins
• time dependence