Risk of Flood Stage Exceedance Upstream from a Bridge

Uncertainty in design discharge, known as a hydrologic uncertainty, is usually determined by hydrologic analysis by frequency analysis or by rainfall-runoff modelling. The problem of transforming the design discharge into a flood stage and evaluating its risk is a crucial one for flood risk mapping. It can be solved by applying the advanced first-order second moment (AFOSM) method [1,6]. This operation should also consider the hydraulic uncertainty, which is usually neglected. Hydraulic uncertainty results from different sources, according to its components and can be classified as: (1) the model formulation uncertainty, (2) the geometry of the structure uncertainty and (3) the model parameter uncertainty.