Formation of wood obstructions at bridges: processes, related problems, and prediction tools

Although wood in rivers provides environmental benefits, its transport and accumulation at bridges, especially during high-flow events, can cause significant issues regarding bridge stability and increased backwater effects. Indeed, the dynamics of wood in rivers have been investigated by the scientific community in terms of wood transport, recruitment mechanism, probability of wood accumulation at bridge piers, and its potential impacts. Nonetheless, the implementation of such scientific findings in bridge engineering practices is still poor, and only a few national legislations propose guidance for the evaluation of wood-related impacts on bridges. In this paper, the “Hydraulic Compatibility of Bridges” committee working within the Italian Group of Hydraulics is presenting a methodology for assessing the impacts of wood accumulation on bridges. This contribution aims at expanding a preliminary procedure that analyzed the effects of wood obstruction at bridges by (i) including an estimate of the potentially recruited Large Wood (LW) volume and (ii) proposing a geometrical approach for the evaluation of the accumulation dimensions. The procedure is then applied to a case study to demonstrate its implementation.