HAZARD ‐ HYDROLOGY

Hydraulic forcings on bridges are of different nature and generated by different water‐driven processes; these can be both fast‐evolving events (high water levels, debris flows, trees accumulations) generated by flood events, or slow processes (e.g., morphological changes in the river). Such processes depend on the hydrological behaviour of the river basin at different time (and space) scales and requires the evaluation of different hydrological variables to be properly estimated in the site of interest, to support the design or the bridge analysis. The Italian Group of Hydraulics is developing an initiative to define comprehensive and up‐todate guidelines to quantify the hydraulic‐related forcings on bridges; this is particularly relevant as most of the bridge collapses in Italy can be related to hydraulic effects while the regulations provide little or no guidance about practical design and verification methods. This manuscript will focus on methods for the estimation of hydrological variables that are used to quantify the forcing actions on bridges.