Effect of un-steady flow conditions on scour features at stepped gabion weirs

The study of scour mechanism downstream of low-head control structure is a fundamental topic for hydraulic engineers. Generally, the analysis of scour process is conducted under steady flow conditions, assuming that the maximum discharge is occurring for a time sufficient to guarantee that the equilibrium scour configuration is reached. Nevertheless, generally, the scour process occurs in corre-spondence with a flood event, which is characterized by discharge varying with time. This last condition is still less studied and analyzed in terms of effects on scour process. In other words, researches were mainly focused on the maximum scour depth occurring in correspondence with peak discharge, but they rarely take into account the evolution of the scour process under un-steady flow conditions. The aim of the present paper is to analyze the variation of the scour morphology, in particular scour depth, assuming unsteady conditions. In particular, one structure typology was tested: stepped gabion weir with upstream impermeable filtering layer. The results shows that the scour phenomenon deeply depends on the inflow conditions.