Relative influence of urban-development strategies and water management on mixed (separated and combined) sewer overflows in the context of climate change and population growth: A case study in Nantes

This paper explores the link between urban planning and hydrological mechanisms. Using a hydrological model, it assesses the relative influence of different urban-development and water-management modes on sewer-system overflows. It combines and compares the impacts of three climate change scenarios going up to 2100, which take into account the implementation of various urban-development strategies, as well as two demographic scenarios. Using this method, the study weighs the importance of the different hydrological mechanisms at play and proposes land-development strategies to implement with regards to climate change and population. The city of Nantes, the hydraulic network of which is well documented, serves as a case study. The results show that, in Nantes, climate change might have a smaller impact on overflows than population growth and urban development in certain scenarios. To limit overflows, insofar as there is no change in water use, this study suggests densifying existing urban areas served by a separative sewer system. It also provides a comparative appraisal of common and alternative water-management practices to reduce overflow. Simulations of different scenarios can help to foster a better understanding of the relationship between urban management and hydrological mechanisms.