URBFEP Model for Basin Scale Simulation of Urban Floods Constrained by Sewerage's Size Limitations

Abstract

Rain drainage in urban catchments is highly complex and depends on numerous and widespread restrictions to water flows caused by the layout of urban areas and building morphology, as well as by the size of sewers which are usually designed for low return period values (2÷10 years). The higher the rainfall return period, the higher the influence of such limitations and the correspondent hydrographs show reductions in peak values due to the reservoir effect generated by flood waters. The modelling of such processes is based on mathematical algorithms of transients associated with rainfall-runoff phenomena and with 1D/2D flow routing processes that, during more intense rainfall, occur simultaneously in the sewer and on the surface (dual drainage systems). However, when flood risk planning relates to the catchment scale for a vast territory with many urban areas, the model no longer focuses on a detailed simulation of what happens inside each urban area, but rather on an estimate of the main characteristics of the urban floods and of the hydrographs discharged into the receivers. In this case, it is necessary to use simpler models, but which are still able to provide a reliable representation of such phenomena. For such purpose, the conceptual model URBFEP (URBan Flood Equivalent Pipe) has been developed in order to obtain a reliable representation of these restricted urban flood processes. This model is presented here, demonstrating its ability to represent the real behaviour of urban sub-catchments in comparison to the results obtained in physically based simulations in a set of real urban areas selected as pilot cases.