Modelagem hidrológica de técnicas compensatórias para manejo sustentável das águas pluviais urbanas na microbacia do Rio Arrombados , Cabo de Santo Agostinho/PE

Abstract

The rapid urbanization and associated actions have, in some cases, led to the improper occupation of riverbanks and stream margins. Thus, urban basins with extensive impervious surfaces exhibit higher runoff rates, resulting in more frequent flooding. In Brazil, conventional drainage systems were adopted to accelerate the transport of urban waters without considering downstream impacts. Given the difficulty of reversing or halting urban expansion, compensatory drainage techniques have been explored to reduce surface runoff generation. In this context, the objective of this study was to evaluate the effectiveness of compensatory techniques in mitigating flooding in the Rio Arrombados microbasin, located in the municipality of Cabo de Santo Agostinho/PE. Initially, the study basin was automatically delineated using a Digital Elevation Model (DEM) processed with QGIS 3.34. Subsequently, in situ surveys of the structures comprising the urban drainage system were conducted. Characteristics of the microdrainage network, such as the condition of stormwater inlets, and macrodrainage features, including factors degrading the watercourse — such as occupation and bank instability, sedimentation, channel constriction, the presence of waste, and the imperviousness of the natural riverbed — were identified. Priority areas for intervention to control urban stormwater were then proposed based on analyses of satellite imagery and geographic information systems, considering factors influencing runoff generation, transport, and accumulation: contributing area, concavity, land cover, slope, roads, and soil types. The compensatory techniques proposed included bioretention cells, rain gardens, permeable pavements, native vegetation planting, and green roofs. The Storm Water Management Model (SWMM) software was employed to model the current drainage scenario and an alternative scenario incorporating compensatory techniques, dividing the study area into sub-basins. The results indicate that the microdrainage system does not entirely cover the basin, with 50.0% of its structures requiring maintenance. Major macrodrainage issues involve river constriction and sedimentation. Surface runoff susceptibility was higher in areas with impervious land cover, soils with low infiltration capacity, and flat terrain. Within the basin, 18.1% of the territory was identified as viable for implementing the evaluated compensatory techniques, with rain gardens and bioretention cells showing the highest recommendation rates. The modeling of compensatory techniques resulted in a 9.2% reduction in runoff and a 13.6% increase in infiltration compared to the current drainage system. While flooding persists in nearly all sub-basins, both the volume and duration of flooding decreased, highlighting the positive impact of these practices on the basin's drainage system. Therefore, this study provides a diagnosis that can support the formulation of public policies aimed at improving drainage infrastructure in the basin. Additionally, the modeling offers a comprehensive perspective on sustainable alternatives that can be implemented to achieve efficient urban stormwater management.