Estudo do amortecimento de vazões de pico através de uma bacia de detenção e reservatórios de detenção in loco em uma sub-bacia hidrográfica no município de Pato Branco - PR

Abstract

Urban floods are one of the main source of government spending nowadays. This is due to the insistence on the use of conventional drainage to avoid outflows in urban environments, which leads to an increase of the downstream peak flow rate. Therefore, the non-conventional measures of urban drainage appear as a solution for such problems, since these seek to reserve the flows at the source, foreseeing a pre-urbanization of the drainage areas. The objective of this study was to evaluate the hydraulic behavior of a detention basin and on-site reservoirs, in relation to the reduction of peak flows. The Rational method and NRCS-CN method were used to determine the design flows in the cases, and the numerical method, Level Pool Routing, were used in the design of the reservoirs and of the basin. In the end, it was verified that the studied basin loses the efficiency when used to contain rains of a return period different than the one for which it was sized, which was 50 years. This is due to the outlet device of the basin has very large dimensions, which releases almost all the flow when less intense rains occurs. The on-site reservoirs presented excellent results regarding the reduction of outflow individually. However, when estimated the effect of these on the watershed as a whole, a very low efficiency has been verified. This is because the residential area in the watershed, that is the hypothetical location to implement the reservoirs, is not as significant as the remaining areas of the watershed, which, in general, also generate high surface runoff. In addition, an expenses budget of the on-site reservoirs was also made to be compared with to the budget of the construction of the detention basin, at where it was clear that the reservoirs were shown to have lower cost. It was concluded that the two methods of non-conventional urban drainage can reduce the peak flow of the watershed, but both with low efficiency in most cases. Thus, it is suggested that auxiliary drainage techniques, along with those presented in this study, can be used to contain the rainwater coming from the rest of the watershed to obtain better results in reducing the peak flow, and consequently avoid urban floods.