Temporal analysis of the scour process downstream of stepped gabion weirs

Stepped gabion weirs are hydraulic structures used for river restoration. They are extremely flexible, as they are able to adapt to the local conditions and can be easily built and modified according to the varied hydraulic and geometric conditions. Different flow features occurs in correspondence with the structure, according to the different hydraulic conditions. Downstream of the structure, generally a scour process takes place. It has to be carefully analysed in order to provide correct criteria which can assure structural stability. However, the scour hole geometry reaches its final equilibrium configuration only after a certain time from the scour process beginning. This paper aims to analyse the scour evolution phase, considering, in particular, the variation of the maximum scour depth occurring downstream of the structure at different instants before reaching the equilibrium configuration. The analysis was conducted for different upstream boundary configurations of the structure and varying the downstream hydraulic conditions. It was observed that the maximum scour depth increases very rapidly at the beginning of the scour process and then it reaches the equilibrium condition asymptotically.