Erosion at either dam or spillway foundations, destabilization in riverbanks, and damage in the natural environment located downstream of either dams or spillways represent crucial elements to be taken into account in the risk assessment of hydraulic structures. One of the main problems is related to the scouring that water flow may induce at the downstream boundary of spillways. This issue is exacerbated in the case of undersized stilling basins, i.e., when a significant level of energy migrates downstream by acting on unprotected natural riverbed. If the scour depths are large enough, the structural stability of the infrastructure will be threatened. This paper aims to illustrate an innovative technical solution suitable to protect the riverbed located just downstream of stilling basins by means of artificial Antifer blocks. These kinds of artificial blocks are widely used in the field of maritime construction, but in the literature, there are no theoretical formulations for their design within the frame of river engineering. In order to demonstrate the efficacy of the proposed technical solution, it is applied to a real case investigated by means of physical modeling. The riverbed located just downstream of the stilling basin of Liscione Dam (Campobasso, Italy) experienced scour due to high discharges during and after extreme rain events. Different protection strategies have been tested to assess the influence of different placement methods and packing densities on the stability of Antifer block armor layers. Experimental findings reveal that regular placements behave more stable than irregular placements with a similar packing density.

Issues such as the design or reauditing of dams due to the occurrence of extreme events caused by climatic change are mandatory to address to ensure the safety of territories. These topics may be tackled numerically with Computational Fluid Dynamics and experimentally with physical models. This paper describes the 1:60 Froude-scaled numerical model of the Liscione (Guardialfiera, Molise, Italy) dam spillway and the downstream stilling basin. The k-ω SST turbulence model was chosen to close the Reynolds-averaged Navier–Stokes equations (RANS) implemented in the commercial software Ansys Fluent ®. The computation domain was discretized using a grid with hexagonal meshes. Experimental data for model validation were gathered from the 1:60 scale physical model of the Liscione dam spillways and the downstream riverbed of the Biferno river built at the Laboratory of Hydraulic and Maritime Constructions of the Sapienza University of Rome. The model was scaled according to the Froude number and fully developed turbulent flow conditions were reproduced at the model scale (Re > 10,000). From the analysis of the results of both the physical and the numerical models, it is clear that the stilling basin is undersized and therefore insufficient to manage the energy content of the fluid output to the river, with a significant impact on the erodible downstream river bottom in terms of scour depths. Furthermore, the numerical model showed that a less vigorous jet-like flow is obtained by removing one of the sills the dam is supplied with.