Integration of Nature-based Solutions for stormwater control and management

In the last decades, all over the world, cities have been characterized by the growth of urban population and urbanization. This involves some issues related to water resource management in terms of water supply during drought periods and stormwater control during rainfall events. In this context, Nature-based Solutions (NBSs) are increasingly encouraged and used as support for traditional urban drainage systems to make urban areas more sustainable and resilient to the effects of climate change. They contribute to runoff control and management and natural water balance restoration, providing several benefits to the environment and communities. Moreover, NBSs meet several Sustainable Development Goals (SDG) of United Nations Agenda 2030, such as Goal 6 (Clean Water and Sanitation), Goal 11 (Sustainable Cities and Communities), and Goal 13 (Climate Action). The study presents the integration of a rainwater tank with an infiltration system to limit both the water demand for drinking supplies and the overload of sewers. An analytical probabilistic approach is developed to balance the different purposes of the system and to overcome the limits of the traditional methods for performing multi-objective analysis. The proposed method enables the relationship between the main characteristics of the system and a return period and considers the possibility of storage capacity pre-filling from previous rainfall events. It can be applied under different climatic scenarios and management rules of the system. The goodness of the theoretical framework is verified by applying it to a real case study in Milano (Italy) and successfully tested by comparing the results of its application with those from the traditional methods proposed in the literature. The use of integrated NBSs can be useful for the optimization of both water supply and urban drainage systems in terms of limiting drinking water waste and flood risk and also acting on water resource protection in terms of high-quality source preservation and aquifer recharge.