Large wood in rivers and accumulation at bridge piers

Abstract:

Large Wood (LW) is recognized to have positive effects on the fluvial ecosystems, but during floods and in urbanized areas the transport of LW may increase hazards for humans and infrastructures. This is particularly important at critical cross-sections such as bridges, where wood accumulation may produce relevant damages. Indeed, LW accumulation at bridge piers has been identified as one of the most frequent causes of bridge failures and damages in the Unites States and in Europe (De Cicco et al., 2020).

In this work, we propose a new methodology to evaluate the hazard due to accumulation of LW at bridge piers during a flood of a given return period. The methodology involves various aspects that include: identification of potential LW sources along the river catchment, characterization of LW transport (distribution of log length), probability of accumulation at a given bridge pier and evaluation of the geometry of the LW accumulation.

Regarding the recruitment process, Francalanci et al. (2020), while modelling the LW uprooted during the 2015 flood (return period of 50 years) in the Ombrone Grossetano river, found the uprooted trees were mostly those laying within 5 m from the main channel, with diameters smaller than 40 cm. The probability of LW accumulation is mainly a function of approaching river flow velocity and transported key log length (i.e. long logs that rest at the pier thus triggering the formation of LW accumulation); Schalko et al. (2019). Importantly, the length of key log represents the geometrical scale for the dimensions of the accumulation (Panici et al. 2020).

The new methodology will be applied to various test cases including bridges on the Arno and Po rivers in Italy.

De Cicco, PN, Paris, E, Solari, L, Ruiz‐Villanueva, V. 2020. Bridge pier shape influence on wood accumulation: Outcomes from flume experiments and numerical modelling. J Flood Risk Management.
Francalanci, S., Paris, E., Solari, L. 2020. On the vulnerability of woody riparian vegetation during flood events. Environ- Fluid Mech.
Panici D., De Almeida G. A. M.. 2020. Influence of Pier Geometry and Debris Characteristics on Wood Debris Accumulations at Bridge Piers. J. Hydr. Eng.
Schalko I, Schmocker L, Weitbrecht V, Boes RM. 2019. Laboratory study on wood accumulation probability at bridge piers. J. of Hydr. Res.