Sills and macro-roughness elements as countermeasures for bridge scour

Bridge are key infrastructures deserving attention because of their strategic role. In particular, bridges whose piers and foundations are located in water bodies are subjected to complex, localized erosion processes which may lead to undesired consequences, such as the failure of the structure. Therefore, in the last decades many researchers have analyzed the phenomenon, developing and implementing countermeasures that can mitigate the risk of a collapse. Among others, structural countermeasures like riprap, collars, and sacrificial piles have shown to be effective in reducing the maximum scour depth, under certain hydraulic conditions and geometric configurations. However, there are still some countermeasures that require further investigations. Namely, only recently, the effectiveness of transversal structures like sills and gabions have been tested. However, there are still many aspects that remain unclear, like the kinetics of the scour evolution depending on locations of the sills. In addition, macro-roughness elements may be also adopted downstream of bridge piers to protect the channel bed. This paper aims at comparing the effectiveness in controlling scour process of the last two countermeasures and provides interesting insights on the physics of the phenomenon that may be useful for practitioners. Future lines of research are also discussed.