Substratos para uso em telhados verdes: Avaliação da retenção hídrica e qualidade da água de escoamento.

Abstract

Green roofs are an interesting alternative to mitigate the risk of flooding given the huge area of unused roofs of impermeable surfaces in urban areas. Thanks to its ability to store water, green roofs can significantly reduce the peak flow events with higher rainfall. Investigations on the composition of substrates based on local materials and designs suitable for tropical climatic regions are less frequent. Vegetation and substrate are elements of a green roof that need to be adapted to each microclimate and not universalized. The objective of this study was to evaluate the performance of different substrate compositions based on local soil, coconut biomass, soil conditioner and commercial components in order to maximize retention capacity of rainwater and lower maintenance needs. A pre-test columns evaluated the water retention capacity and relative wet weight dry weight x 15 substrate compositions. The compositions were the best performing substrates S1 (15% soil + 55% + 30% coconut commercial components), S2 (30% soil + 40% + 30% coconut commercial components) and S3 (60% + 10% soil + coco 30% commercial components). The physicochemical characterization of substrates, soil and coconut fiber was performed. Then a test column evaluated the water retention capacity of the two substrates under precipitation conditions: a gentle (8.77 mm / h), and another strong (42.0 mm / h). The results showed that the substrates S2 and S3 showed better retention results for both intensities of rainfall. It was observed that S1, which showed better retention capacity in the pre-test, performance was inferior to the others which can be attributed to the higher concentration of coconut fiber composition and the consequent emergence of preferential paths along the profile of the column, through which water drained more quickly. In lighter precipitation events, the substrates while retaining 60-100% of the total applied. When applied a stronger intensity of precipitation, the band retention was between 40% and 59%. However, the variables analyzed to evaluate the quality of the water drainage of the substrates (pH, CE, P, NO3, NH4, Ca, Mg, Cu, Fe, Mn, Zn, Cr, Co, Ni) were higher than the values generally found in the literature, indicating that the compositions here adopted for the substrates can bring in a source of water pollution. The substrates for use in green roofs presented in this study met its goal for retaining water, but the quality of percolated water makes its use impractical until now. There was the need to study further the quality of water leached for each component of the substrates individually in order to identify sources of the elements present in high concentrations become pollutants. It can be considered the removal of some (s) of the components present in the composition to achieve a satisfactory level of quality of the water flow.