Modelo conceitual para gestão de águas de drenagem urbana em regiões semiáridas

Abstract

Rapid urbanization poses a threat to urban drainage systems worldwide. Diffuse pollution in urban catchments carried by stormwater in surface runoff and the indiscriminate discharge of sewage into macro drainage systems are responsible for the deterioration of drainage water quality and altered flow rates, affecting the environment and public health. For urban drainage systems to move towards sustainable development, sustainable drainage alternatives and practices with systemic approaches and stormwater management strategies in different dimensions (environmental, social and economic) are needed. This study aims to produce a conceptual model for urban watershed drainage water management that can be used as a planning tool for existing urban spaces, and that is able to induce watershed sustainability. This research was carried out in the Piabas Creek watershed, more specifically, in the urban area of Campina Grande, in the state of Paraíba. To achieve the objective, it was essential to use three mathematical models. Hydrological modeling, in the Storm Water Management Model (SWMM) program, was necessary to understand the functioning of the macro drainage system regarding water quality and quantity, considering different scenarios (sewage disposal interception, detention reservoirs and low impact development structures - LID). The Life Cycle Assessment (LCA) methodology was also employed to determine the potential environmental impacts, health risks to the population, and damage to ecosystem quality associated with urban stormwater pollution and the environmental costs of emissions. A budget of the proposed intervention measures to improve the quality of these waters was carried out. Multi-criteria analysis was performed to integrate the experts' preferences regarding the degree of importance of the LCA indicators, ranking the intervention scenarios that contribute most to urban stormwater sustainability. Finally, the conceptual model was produced to assist decision-makers in managing these waters. The hydrological modeling was efficient in understanding the functioning of the macro drainage system, with minimal continuity errors. After the simulation, the results of water quality and flow of the input flows (sewage and leachate) in the system subsidized the life cycle inventory, indispensable to start the LCA modeling in the OpenLCA program. The LCA results expressed in impact categories (indicators) demonstrated the environmental, social and economic impacts of urban stormwater from Piabas Creek. It was observed that the most impactful input stream for the eight environmental impact categories and the two social indicators is sewage, accounting for 70% (on average) of the potential impacts to the environment. The leachate from the scenario with the highest LID structure implementation area coverage (medium LID) showed a reduction in environmental impacts of around 90%. Interception of sewage discharge managed to reduce environmental impacts by around 60% and the implementation of medium LID in the sub-basins reduced between 29.5% and 25.4%. These were the scenarios that most reduced the environmental, social and economic impacts (regarding environmental externalities). The most impacting environmental indicators were global warming, particulate matter formation, and freshwater ecotoxicity, also highlighting freshwater eutrophication. It was found in the social LCA, in all scenarios, that urban stormwater pollution poses risks to human health and damage to ecosystem quality. Sewage interception was the intervention that presented the lowest implementation costs, followed by detention reservoirs. The multi-criteria analysis ordered the intervention scenarios that best contribute to the management of urban drainage water. According to the results obtained, the integration of intervention scenarios is suggested in order to establish the sustainability of the study area. The proposed conceptual model is presented as an urban planning tool that contributes to the organizational advancement of urban stormwater management. It is feasible and easy to implement, as long as they obtain information about the study area, requiring multidisciplinarity among decision-makers to solve a decision problem. The sequence of actions presented in the conceptual model provides managers and policy makers with facilitating decision-making towards the sustainability of these waters.