Bridges in small basins with intense sediment transport

Abstract

Majority of the bridge collapses are due to hydraulic reasons. The Italian technical standards of constructions (NTC 2018) provide few indications about the design and verification criteria of bridges with respect to river processes. In the last year, a working group on the ʺHydraulic Compatibility of Bridgesʺ (sites.google.com/view/giiponti) was set up, with the aim of formulating proposals for good practices and guidelines for assessing the bridge hydraulic compatibility, as a basis for both bridge safety and flood risk analysis. The working subgroup on ʺSmall basinsʺ aims to provide analysis tools for small river basins: they have peculiar features, requiring the adoption of appropriate criteria for the analysis of forcing scenarios and safety measures to be implemented for the hydraulic compatibility of river‐crossing bridges. Particular attention should be addressed to climatic variations that, although gradual, can induce strongly non‐linear responses: when certain rainfall thresholds, which were possibly never or rarely reached in the past, are exceeded, extreme events can be triggered (e.g. debris flow, mudflow), exposing the population and the territory to unexpected disasters and calamities. The present manuscript reviews the current best practice for analyzing the hydrologic response, the sediment balance, the flow propagation and the dynamic impact force against bridges in the case of mountain basins, pointing out limitations and possible future developments required in order to develop guidelines for bridge safety assessments and flood risk analysis of the surrounding area.