Scour and hydraulic jump downstream of block ramps in expanding stilling basins

The scour process downstream of block ramps is strongly affected by both the stilling basin geometry and the hydraulic conditions. Particular effects include the ramp slope and the geometry of the stilling basin. The aim of this experimental study is to analyze these effects on both the scour mechanism and the hydraulic jump of symmetrically expanding stilling basins, for different hydraulic and geometric conditions. The analysis of the scour phenomenon is fundamental for a correct stilling basin design. The scour hole downstream of a block ramp can have a prominent ecological function as it forms a natural pool for fish. Experiments were conducted for various tailwater levels, ramp slopes and granulometries of the bed material. A qualitative description of the scour hole process is given and simple relationships were derived to predict its main hydraulic and geometrical parameters.