PSI - Issue 84

Francesco Ballio et al. / Procedia Structural Integrity 84 (2026) 151–158

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Fig. 7. Increase of (a) backwater rise; (b) hydrodynamic load as a function of on the accumulation volume.

The different trend of backwater rise between the prior and present experiments (Fig. 6a) may be explained by the different position of the piezometric probes compared to the bridge. In the present experimental campaign, due to constraints in the placement of the frame on which the bridge was hanging, the latter was located further downstream compared to the prior runs (around 0.4 m). Since it was impossible to move the piezometric probes, the relative position between the bridge and the piezometric probes returning the backwater rise was different in the prior and present runs. In particular, closest piezometric probe upstream was at around 0.3 m from the bridge in the prior experiments and around 0.6 m from the bridge in the present ones; in addition, the closest piezometric probe downstream was different in the two couples of experiments. However, the observed deviation in Fig. 6(a) corresponded to a difference in backwater rise of less than 2% of the water depth of the incoming flow. The plots of Figs. 6 and 7 overall demonstrate that the backwater rise and the hydrodynamic force could reach, in the presented experiments, values of more than twice the initial ones. The relationship between the increase of backwater rise and the accumulation volume, depicted in Fig. 7(a), is in qualitative agreement with the results and the interpolation function reported by De Becker et al. (2025), who mentioned a steeper rise for lower volumes and a milder rise after the volume has become larger. Instead, the behavior of the hydrodynamic force appeared different, without an evident decrease of the slope of the scatter in Fig. 7(b) for the largest values of W cont . Conclusions The experimental facility used in the present research, suitably equipped with water level and force measuring devices, allowed to quantify a trivial expectation that the progressive accumulation of wood at a bridge deck increase the backwater rise and the hydrodynamic load exerted by the flow onto the structure. The experimental approach of determining an accumulation volume based on the wood mass conservation principle successfully furnished volume values whose estimation by combining projected areas would have been cumbersome. However, the experimental trends were qualitatively similar when the backwater rise and the hydrodynamic load were plot as functions of projected area or volume of the accumulation. It was demonstrated that, for a Froude number of 0.27–0.29, length of driftwood logs of around 0.4 times the flume width and 1.3 times the bridge vertical opening, wood supply rates in the range of 1.5–4.3 ×10 -4 times the water flow rate, both the backwater rise and the hydrodynamic load could reach values larger than twice the initial ones. Further research will involve performing multiple runs in order to obtain more general experimental trends. Acknowledgements This study was carried out within the RETURN Extended Partnership and received funding from the European Union Next- GenerationEU (National Recovery and Resilience Plan-NRPP, Mission 4, Component 2, Investment 1.3