Micro reservoirs and runoff in the Itaim basin in Taubaté, SP, Brazil

Abstract

 

Urbanization of the watersheds in developing countries is generally accelerated and disorderly. The urbanization process generates soil impermeability, which impedes the infiltration of rainwater, accelerating surface runoff to favor accumulation of water at the lowest points, causing flooding. The construction of micro reservoirs for rainwater storage and infiltration within residential areas can minimize flood problems. In the present study, the effective precipitation and its reduction in the Itaim stream basin in the city of Taubaté, SP, were estimated by usage of 3400 and 6800 liters micro reservoirs to capture water on 125 m² roofs in different soil occupations, according to the Law 412/2017 of the Master Plan of Municipal Physics of Taubate (PDFMT). Effective precipitation was estimated using the curve number (CN) method, while variation in land use and occupation considered the land area in accordance with current legislation, with urban expansion at 50 and 100% over the macrozone rural, as well as 100% urban consolidation. The results showed that surface runoff (Pe) in the Itaim basin increases with the expansion of the urban area, as well as urban consolidation. The use of micro reservoirs considerably reduces runoff volumes. The micro reservoir, with a storage volume of 3400 liters, made it possible to restrict the flow promoted by rain of up to 25 years of return period, simulating the urban expansion of 50% over the rural area, while the reservoir with 6800 liters in capacity contains rain of up to 200 years return period for the same simulation condition. Although this type of structure was not considered in the municipal land use and occupation law, this study demonstrates that the use of hydraulic systems or elements with potential to reduce runoff can be an important means to ensure the sustainability of urbanization. of watersheds with planned stormwater disposal.