Supporting flooding risk assessment in ephemeral streams in Southern Italy

The delimitation of flood-prone areas is of crucial importance for assessing the risk associated with extreme natural events and for planning/regulating the development of a given territory. This work undertakes the floodplain delineation problem for some ephemeral streams known as “lame” located in Apulia region (Southern Italy). This territory is characterized by a rather flat morphology and absence of base flow along the main waterways, except for rare and exceptionally severe rainfall events. In such particular context, traditional synthetic hydrologic models can be hardly used due to the lack of monitored rainfall-runoff data and the unpredictable runoff propagation over the peculiar catchment morphology. This paper presents the results of a “full-2D” model which simulates the runoff generation and propagation over the entire catchment (both inside and outside the ephemeral streams), once infiltration, surface roughness and rainfall event conditions are defined into every cells of the bi-dimensional domain. A sensitivity analysis of the model considering different values of ground infiltration and surface roughness parameters is presented. The results show that different prior assumptions lead to quite different peak discharge values predicted in few control sections even when such complex “full-2D” rainfall-runoff model is used.