Design of surface drainage systems according to hazard criteria related to flooding of urban areas

Resumen

This Doctoral Thesis treated the general problem of urban flooding caused by medium and heavy storm events. One of the aims of this work was to propose some procedures to analyze correctly the flood considering, at the same time, the flow propagation and the presence of the surface drainage system in the urban catchments. Other important aim was to establish several design procedures of surface drainage systems according to hazard criteria related to flooding in urban area. Particularly this work concerned urban flooding generated by the excess of surface runoff directly produced by the rainfall-runoff transformation and that could not be introduced into the sewer system due to a poor capacity of the surface drainage system. In order to analyze this problem exhaustively, it was necessary to study in detail several aspects as the hydraulic performance of the surface drainage structures, the hydraulic behavior of the catchments during storm events (through 1D and 2D approaches and accurate topographic information), the hazard characterization related to human subjects in case of urban flooding. An efficient surface drainage is an essential condition to prevent the risks and damages due to the floods produced during storm events in urban areas and to keep a good street service level for a safe vehicular and pedestrian circulation. Moreover modeling of the sewer systems, and mainly modeling of urban dual drainage, cannot be adequately represented without a big regard for the hydraulic efficiency of the surface drainage structures (inlets, transversal grates, etc.). In fact this type of structures governs, at the same time, the rate of water removal from the gutter and the amount of water that can enter into the storm drainage system. Through some experimental campaigns it was possible to study the hydraulic efficiency of several surface drainage structures and to carry out rigorous methodologies to estimate the hydraulic performance of this type of structures on the base of their geometry and the flow parameters upstream them without the need of previous experimental tests. Other experimental campaign allowed to achieve some hazard criteria related to the pedestrian circulation in urban areas in case of heavy storm events. Particularly a physical model reproducing a flooded street in real scale was built and a specific testing protocol was defined (specifically human subjects were tested crossing the platform with a large range of circulating flows and several geometric configurations). In this way human stability in a flooded urban street was studied for a large spectrum of flow conditions and considering a wide range of people characteristics (weight, height, etc.) too. Finally 834 tests regarding 23 human subjects were carried out considering different light conditions. The results of the experimental campaign demonstrated that the actual hazard criteria elaborated for the characterization of the hazard in the floodplains are not adequate for urban flooded areas characterized by low flow depths and high flow velocities. Finally a linear relationship was achieved in order to predict, on the base of the human subject's weight and the height, the specific product number between flow depth and velocity at which hazard episodes can occur. The hydraulic characterization of surface drainage structures and the definition of the hazard levels in urban areas in case of flooding were two important milestones to study the hydraulic behavior of some catchments of Barcelona during storm events through simplified methodology (like rational method) and detailed approach (1D and 2D simulations). In this case the hydraulic performance of the existing surface drainage systems was analyzed, and in case of poor efficiency of them, new solutions were proposed on the base of specific the hazard criteria adopted.