Desempenho de técnicas compensatórias na mitigação do perigo de inundações em uma bacia urbanizada fechada

Abstract

The impermeabilization of surfaces due to urbanization changes the hydrological regime and the natural flows of water in cities, bringing an increase in the urban flooding risk with the potential to cause damage to the human life and property. For this reason, an urban flood risk assessment has been applied in the sustainable urban stormwater management. The risk of flooding is commonly evaluated by hydrological models, while the mitigation is mainly given by the implementation of urban drainage systems. Compensatory techniques (CT) are identified as effective solutions to reduce urban flooding and have been widely used because they restore the hydrological conditions of the watershed and are also a more sustainable alternative to conventional systems based on canalization. These techniques can be particularly useful in closed (or endorheic) basins, where the flow is routed to lower inland regions producing large floods. Therefore, the present work aims to evaluate the performance of compensatory techniques associated with the existing conventional drainage system in a closed urbanized tropical basin to mitigate the urban flood hazard. The study was developed in a sub-basin of Natal/RN using 1D/2D modeling with the Personal Computer Storm Water Management Model (PCSWMM), considering scenarios of bioretention cells (BC) and microreservoirs (MR) in extreme rainfall events. From the results of the flooded areas in the basin, it was observed that the 2D modeling proved to be very useful in predicting the hydrological behavior of closed basins, where the most critical areas occur in the central depressions. The CT simulation showed a very limited performance in the mitigation of flood prone areas, a fact that can be explained by the low availability of areas due to the intense urban occupation of the basin, in addition to the magnitude of the events evaluated, which reduces the efficiency of the CT. The results also showed a better efficiency of BC due to the larger occupation in the basin and the infiltration, which increases the volume captured by the cells.