The increased occurrence and intensity of flooding events have represented a real threat to bridge reliability and end-user safety. As flood vulnerability assessment is a valuable tool for enhancing the resilience of bridges to climate change, it is of interest to push the development of such methods. To this end, a computationally efficient methodology to assess the flood vulnerability of a bridge was developed and implemented in a case study. A particular focus was devoted to modelling wood debris loads on the bridge pier, for which two different approaches were implemented. The first is a standards-based approach, whereas the second is based on up-to-date research data. The results indicate that the second approach is less conservative as it leads up to a 40% higher exceedance probability for the considered limit states. The interaction between wood debris loads and local scour was also examined and proved to have a relevant impact on the vulnerability of the bridge. These results highlight the shortcomings of the existing standards in providing accurate results. It is perceived that not only will the new quantitative tool be valuable in ensuring optimal bridge design, but it will also be beneficial for assessing bridge risk mitigation measures.

The growth and establishment of riparian vegetation on river bedforms is of hydrological as well as ecological importance as it helps in enhancing spatial heterogeneity and thus the biodiversity of river corridors. Yet, during floods, flow drag and scouring may reduce the rooting length of plants determining plant mortality via uprooting. In order for uprooting to occur, bed scouring must proceed until the rooting length reaches a critical value and drag forces exceed root residual anchorage. Therefore, the critical rooting length of a plant represents a crucial parameter to estimate the probability of plant removal due to flow erosion. However, difficulties in quantifying such length at the field scale have limited so far the performances of biomorphodynamic models for river bed evolution. In this work, we propose to assess the critical rooting length from controlled plant pullout experiments. To this aim, a free‐body model of the forces acting on a flexible plant in a stream at different erosion stages is developed. At incipient uprooting, we conjecture that the root resistance at the critical rooting length equals that of a plant with equal rooting length when pulled out in static conditions. To illustrate our approach, we validate our model on three different data sets obtained from small‐ and real‐scale plant uprooting experiments. A comparison between modeling and experimental observations reveals that the model provides valid results, despite its deterministic approach. The critical rooting lengths are finally used to assess the probability density function of the time to uprooting via a physically based stochastic model.

Freshwater ecosystems along river floodplains host among the greatest biodiversity on Earth and are known to respond to anthropic pressure. For water impounded systems, resilience to changes in the natural flow regime is believed to be bidirectional. Whether such resilience prevents the system from returning to pristine conditions after the flow regime changes reverse is as yet unclear, though widely documented. In this work, we show that temporal irreversibility of river floodplains to recover their status may be explained by the dynamics of riparian water‐tolerant plant roots. Our model is a quantitative tool that will benefit scientists and practitioners in predicting the impact of changing flow regimes on long‐term river floodplain dynamics.

Wood dynamics affects riparian ecosystem functioning and river morphology. The spatial and temporal dynamics of wood pieces in river corridors, in particular of deposited rejuvenated wood logs, depend on their biomechanical properties and resistance to uprooting. The ability of stranded wood logs to withstand drag forces depends on how efficiently their roots have sprouted and on the interarrival time, magnitude, and duration of the moderate floods to which they are subjected. We performed static pullout tests on small‐scale wood logs (Salix species) of four different sizes, growth stages, and sediment moisture content. Statistics of root biomass growth rate and related spatial distribution along the trunk reveal important insights for upscaling dynamics. Similarly, force‐displacement curves indicate the maximum resistance and related energy for uprooting. Autocorrelation analysis of the sequence of force drops in the force‐displacement signal reveals the statistical nature of the mechanism of load redistribution among roots. These results are then used to advance a physically based mathematical model of the resistance of wood log roots to flow‐induced drag forces. Given that the magnitude, duration, and return period of hydrologic events are typically correlated, our model implies the existence of windows of opportunity for wood logs to either survive or remobilize.