Evaluación del impacto de techos verdes en la mitigación de volúmenes de escorrentía en el drenaje urbano mediante modelos hidrológicos

Abstract

In the process of urbanization, natural surfaces are reduced while impervious surfaces are increased. Such conditions, prevent water infiltration and increase surface runoff. An alternative to solve this problem is to replace the common building roofs with green roofs. In this article, we propose to evaluate the impact of green roofs on the mitigation of the runoff volumes using pilot experiments of an extensive green roof type and a conventional roof with slopes of 2% and 5%. In order to recreate precipitation events, we built a rainwater simulator. With these simulations, we measured the roof runoff discharge to set up experimental hydrograms. These hydrograms were used to calibrate the SCS method parameters and to determine the Unit Hydrograph. As a result, we showed that the implementation of green roofs with 2%-slope reduces runoff volumes by 15.6% and the peak flow by 32.6%; whereas green roofs with 5%- slope the reduction in volume reaches 11.3% and the peak flow reduction reaches 27.2%. In the parameters calibration of the SCS method, the curve number (CN ranges from 88.9 to 96.5, the retention percentage (z) ranges from 1% to 10% and time of concentration (Tc) from 5.7 to 7.5 minutes. The most efficient method is the Unit Hydrograph, which presents NSE equal to 0.96 comparing to the SCS method that presents NSE values equal to 0.96. Nevertheless, the SCS method is easier to use and it does not need the use of experimental hydrograms. The results of this research, provide guidelines to the evaluation of green roofs impact in the urban drainage.