Diferentes tipos de telhados verdes no controle quantitativo da água pluvial

Abstract

Because of the rapid process of population increase in urban centers and the consequent soil waterproofing, the draining systems of rain water are insufficient because of the increasing superficial outflow, output peaks and flood spots. In order to attenuate these problems, the use of techniques related to the reduction of the superficial outflow is being encouraged in different scales, being the green roofs indicated as alternatives. In broad terms, the green roofs are structures which have different layers: plants, substrates and draining, which perform different tasks in accordance with their characteristics. Although the usage of green roofs is already encouraged, their real contributions on the rain water output are not well-known. In this paper, it is shown the result of a research carried out with four different systems of commercial green roofs and a system developed from recyclable materials, that aimed to evaluate the retention capability of each system and how the substrate and the draining system may interfere in the values. In order to achieve this goal, it was built an experimental stand system where five types of green roofs were set up with two compositions of substrate: without clay and with expanded clay. The commercial systems known as simple alveolar, grilled alveolar, hexagon module with gaiter were used as well as the system produced with recycled elements developed throughout this study. It was taken the hydrologic assessment for five months, with 35 events where it was assessed the precipitation and the superficial outflow coming from the draining of green roofs. The monitoring allowed to determine, for each kind of system, parameters that reflect the retention capacity of the rain water outflow, as a coefficient of outflow, the value of curvenumber (CN), and associate the retention capacity of the outflow to the previous soil humidity conditions (AMC). The results showed a significant difference in the rain water outflow retention among the modules and the substrates, being the most efficient system the module with gaiter, which presented retention value capacity of 13.3 mm/m² without expanded clay, and 14.2 l/m² with expanded clay. The coefficient of average outflow for this kind of green roof varied from 0.13 and 0.17, and, under these conditions CN assumed the values of 80.3 and 82.5 for the clay and non-clay substrates, respectively. The second most efficient system was the hexagonal one, followed by the alveolar one and the least efficient was the one built with recycled material, which had the outflow coefficient near 0.8. The results showed how the typology of the green roof as well as the substrate composition affects the capacity of storing water.