Conference Agenda

Combined sewer overflows (CSO) strongly impact water quality of receiving water bodies. The spilled volumes increase due to climate change. It becomes more and more urgent to find solutions in order to mitigate these CSO. Nature based solutions (NBS) are effective infrastructures which help to better control runoff and hence contribute to decrease the spilled water quantity. However, the efficiency of their implementation is impacted by the location selected for their installation. In order to find the relevant location where NBS have to be implemented, an original hydrological and hydraulic disconnection model (HHDM) was developed. The use of this HHDM enabled to reveal the characteristics of the disconnected regions that allow to mitigate CSO. Different levels of deployment of the disconnection strategy were simulated for each sub-catchment of the city of Figeac-France. Initially, the results showed that peripheral catchments with large impervious areas contribute little to the outflow. Additionally, the implementation of NBS on a small, urbanized sub-catchment has a greater capacity to reduce overflows than that of a peripheral sub-catchment with a large impermeable area but low runoff capacity. Subsequently, territorial characteristics and proximity to the targeted combined sewer overflow structures play a key role in contributing to overflows.