Rock grade control structures and stepped gabion weirs: Scour analysis and flow features

Rock and stepped gabion weirs are peculiar hydraulic structures that received relatively little attenti on in technical literature. Neverthe- less, they can be successfully used for river restoration instead of tradi- tional hydraulic structures. They have the advantage of being elastic structures and to preserve the natura l environment. They can easily adapt to the in situ conditions and can be effortle ssly modified according to the different hydraulic or geometric cond itions which can occur in a natural river. The present study aims to anal yze the effects of their presence on flow pattern and on the scour hole occurring downstream. The analysis involved scour processes, hydraulic jump types, stilling basin morphol- ogy and flow patterns. Two different hydraulic jump types were distin- guished and classified. It was show n that the flow regime deeply influences the scour process, which evolves much more rapidly when a Skimming Flow regime takes place. Empirical relationships are pro- posed to evaluate maximum scour depth, maximum axial length, and non dimensional axial profiles.