Flooding events in urban areas occur quite frequently as a consequence of rain events of lower intensity thanudthe design one, even in case of correct network dimensioning. Inlets are in those cases the critical nodes, andudefficient drainage is only ensured when care is taken on their appropriate design and positioning within the pluvialudflood-prone areas. Classical approach for design and position of these hydraulic structures can result in high leveludof uncertainty in defining properly risk levels in urban areas. Further, evaluation of flood hazard in urban areasudis made even more difficult if one considers that pluvial flooding can be caused by storm events characterisedudby a low return times and they may involve even small portions of the urban areas. This contribution is focusedudon the derivation of flood hazard maps in a probabilistic framework to overcome the classical problem of singleuddeterministic prediction of flood extent for the design event and to introduce the concept of the likelihood ofudflooding at a given point as the sum of input data and parameterization uncertainty.udIn particular, a stochastic generation of inlet efficiency scenarios with varying their position in pluvial flood-proneudareas has been performed and rainfall forcing modelled using a bivariate approach based on copulas.udThis methodological approach has been implemented in a selected study area in the town of Genoa. At this aim,udin October-December 2009, a survey was carried out in order to investigate the operational conditions of the inletsudthroughout the study area. Based on the observed conditions the frequency distribution functions of inlet efficiencyudare determined according to the different sub-areas with specific anthropogenic characteristics.
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