Hydrologic attenuation and the hydrologic benefits of implementing eco-productive green roofs in marginal urban areas

In the present study, the hydrologic attenuation of an ecoproductive green roof is assessed using three indicators: lag-time, runoff coefficient and water volume retention. Two types of plants-an herbaceous (Lactuca sativa) and a Cruciferae (Raphanus sativus)-were utilized in this analysis of eight rain events monitored on four houses in the La Isla neighborhood of Soacha, Colombia (4° 34’ 22.3”, 74° 10’ 53.5”; 2,701 meters above sea level). Maximum lag-times, volumetric retention percentage and minimum equivalent runoff coefficients of 32 minutes, 80% and 0.1, respectively, were obtained. The hydrologic benefits of implementing such green roofs is determined by comparing the drainage infrastructure required with and without green roofs and by assessing the probability of flooding at the study site with or without green roofs. In order to analyze these benefits, the Monte Carlo simulation method allows observation of the hydraulic behavior of sewers in drainage areas where green roofs are implemented. When the green roofs are installed, a maximum savings (in economic terms) of approximately 22% and a reduction in flooding probability of approximately 35% are observed.