Abstract
Abstract. In the last decades, new approaches were adopted to manage stormwater as close to its source as possible through technologies and devices that preserve and recreate natural landscape features. Green Roofs (GR) are examples of these devices that are also incentivized by city's stormwater management plans. Several studies show that GR decreases on-site runoff from impervious surfaces, however, the analysis of the effect of widespread implementation of GR in the flood characteristics at the urban basin scale in subtropical areas are little discussed, mainly because of the absence of data. Thereby, this paper shows results related to the monitoring of an extensive modular GR under subtropical weather conditions, the development of a rainfall–runoff model based on the modified Curve Number (CN) and SCS Triangular Unit Hydrograph (TUH) methods and the analysis of large-scale impact of GR by modelling different basins. The model was calibrated against observed data and showed that GR absorbed almost all the smaller storms and reduced runoff even during the most intense rainfall. The overall CN was estimated in 83 (consistent with available literature) with the shape of hydrographs well reproduced. Large-scale modelling (in basins ranging from 0.03 ha to several square kilometers) showed that the widespread use of GRs reduced peak flows (volumes) around 57% (48%) at source and 38% (32%) at the basin scale. Thus, this research validated a tool for the assessment of structural management measures (specifically GR) to address changes in flood characteristics in the city's water management planning. From the application of this model it was concluded that even if the efficiency of GR decreases as the basin scale increase they still provide a good option to cope with urbanization impact.
Highlights
The principles of the Low Impact Development (LID) indicate that the control of the added runoff by urbanization must be carried out as close as to its source as possible, in order to minimize or eliminate the effect of hydrological man-made changes to the environment
Carter and Rasmussen (2006) reported a CN value for the green roof (CNGR) of 86; a similar value of 84 was reported by Getter et al (2007); in turn, Miller et al (2010) reported values varying from 75 to 85 that is really close to our 78–87 confidence interval
This research validated a tool for the assessment of structural management measures ( Green roofs (GR)) to address changes in flood characteristics in the city’s water management planning
Summary
The principles of the Low Impact Development (LID) indicate that the control of the added runoff by urbanization must be carried out as close as to its source as possible, in order to minimize or eliminate the effect of hydrological man-made changes to the environment (i.e. achieve no impact due to urbanization in hydrological conditions). Green roofs (GR) are example of techniques applied to achieve this goal, as GR’s vegetation and its soil substrate controls the surface runoff, recovering the interception, water retention and evapotranspiration processes affected by land use changes (Yang et al, 2008). Using this technique in large scale helps maintaining the ecological and hydrological functions in the basin, being characterized by the Water Environment Research Foundation as a sustainable practice to rainfall drainage (Clark et al, 2006).
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