Avaliação de metodologias de cálculo de taxa de drenagem em cenários com a utilização de telhados convencionais e telhados verdes

Abstract

The objective of this project was analyzing effluent flow scenarios, as a tax incentives criterion in the maintenance and operation of the urban drainage network in a subdivision located in Jacarepaguá neighborhood, in Rio de Janeiro. The methodology used geoprocessing tools to produce data on land use and occupation in the current scenario, and for prospective definition, green roof areas were considered as compensatory measures for urbanization in the region. Data from the Municipal Department of Urbanism and the register of the rainwater network of Fundação Rio-Águas, in the city of Rio de Janeiro, were used, which overlays generated, in the current scenario, average flows of 6.74 liters per second in the plots of land and a flow at the end of the network of 605 liters per second. After the implementation of the green roof compensatory measure in the watershed buildings, average flows of 4.08 liters per second (39% of the current flow) were obtained, and a flow at the network’s outlet of 448.56 liters per second (26 % of flow), on the “dry” period, and average flows of 6.08 liters per second (10%), with a flow at the end of the network of 573.57 liters per second (5%) on the “wet” period. In order to obtain the tax incentive, referring to the amounts collected from maintenance and network operation, drainage rates were calculated using specific methodologies, and the values obtained by the "Equivalent Residential Unit" method were considered, as they demonstrate an efficient collection and equal to the maintenance system budget. For the current scenario, the maximum values of R$676.14 (141.88 USD) and minimum values of R$42.82 (8.99 USD) were found, with a standard deviation of R$128.28 (26.92 USD), varying according to the waterproofing and plots size. After the green roof implementation, the rates were calculated, and the average values found of R$158.52 for the “dry” period and average values of R$248.75 for the “wet” period. It can be concluded that the average reduction in the collection of the drainage fee with the green roof application was 16% compared to the current scenario. The aforementioned reduction favors assessments of charging the population with a tax incentive by the city of Rio de Janeiro’s city hall, with a view to defining public policy strategies.