Resposta hidrológica de uma bacia hidrográfica urbana à implantação de técnicas compensatórias de drenagem urbana - Bacia do Córrego do Leitão, Belo Horizonte, Minas Gerais

Abstract

Intense urbanization results in greater soil sealing and the consequent increase in surface runoff. When high soil sealing rates and high slopes are observed in small watersheds, the occurrence of precipitations of great volumes and short duration increases the great probability for flash floods. These factors eventually combine in the Leitão stream catchment, causing floods since the beginning of its occupation, which motivated the construction of a detention basin. This study evaluates the hydrological response of the watershed to rainfall-runoff events in the following situations: current scenario; without the detention basin; watershed with maximum soil sealing allowed by legislation; and with green infrastructure implantation in 100%, 50% and 10% of the suitable area. Hydrological modelling was performed using the Storm Water Management Model (SWMM) and the hydraulic using Hec-RAS. Accurate cartographic and topographic bases were obtained, geoprocessing tools were applied and hydrologic characteristics were calculated to construct the scenarios. The rainfall was represented through the data of three raingages located on the watershed. Six level gages installed along the stream provided the data used in the model calibration and validation. Seven events were selected for the calibration and 13 for the validation. The fitness function reached good results: the average Nash-Sutcliffe coefficient was of 0.72, the mean error of peak flow of 11%, and the mean error of runoff volume was 12%. Project rainfalls of 2, 10, 50 and 100 years of return period, with 60 minutes duration were simulated for each scenario, as well as two events selected among the observed ones. In the scenario without the detention basin, an average elevation of 70% in the peak flow along the stretch under the Prudente de Morais Avenue was observed, while an elevation of 10% was observed in the outfall. In the scenario with maximum soil sealing, the outfall peak flow increased 30 %, on average . On the other hand, in the scenario with green infrastructure implementation in 100%, 50% e 10% of available areas, the outfall peak flow was reduced in 60%, 30% and 5%, respectively. Results evidenced the detention basin efficiency in flood reducing, the importance of green area preservation to reduce the peak flow, as well as the watershed potential to green infrastructures implementation and the hydrological benefits that these can promote, increasing infiltration and reducing runoff.