Semi-Natural drainage systems for storm water management and flood risk reduction for a watershed in Lombardy region, Italy.

In recent years, the relationship between cities and water has been affected by climate change and the explosion of urban areas (Font, 2007). In Europe, the attention toward green infrastructures (Maes, Barbosa, Baranzelli et Alii, 2015). has become a relevant topic within the debates and an important goal within urban ecological agendas, while floods happen more and more often, with heavier impacts on the urban realm.
Technicians of many disciplines (engineering, urban designers, geographers, and ecologists) support public actors in designing policies and strategies to control the phenomenon, however those solutions are often problem solving oriented, barely integrated within the urban form, with little sensitivity to urban liveability. Consequently, the urban combination of water management features needs to be overhauled, paying special attention to critical situations related to impermeable soils in growing urban environments.
The aim of this contribution is to present an approach to storm water management to cope with flooding issues in a sector of the postmetropolis (Soja, 2011). Showing the case of Seveso river watershed in Lombardy region, Italy, the researchers demonstrate that the integration between green infrastructures and existing urban ecosystems could: (i) increase the pervious surface (ii)generate an urban interface and (iii)produce a liveable urban space.
After an accurate analysis of the Seveso watershed, the research focuses on a critical sub-basin that presents a high rate of impervious landcover, placed within the regional park Parco Nord Milano (Paoletti, 2011). Supported by qualitative calculations, the change of soil pattern into an absorbing landscape helped to measure the positive impact of vegetation in the urban environment for the flood risk mitigation.
The introduction of a semi-natural drainage systems based on a network of site specific interventions in the urban realm produces a significant improvement of storm water caption and retention. Detention basins and water channelization networks gave the chance to improve the land mosaics (Forman, 1995; Waltner-Toews et al, 2008) pattern. Indeed, the planning of the blue green infrastructures helped to connect the ecosystems of the regional park that surrounds the project area increasing liveability and ecological performance.
In conclusion, the research reflects on the multi scale approach to landscape design as a tool to integrate storm water management green blue infrastructures within the urban form.