Thursday Poster Session - Governance & development

In 2023, the City of Montreal's Prieur Park was partially redesigned as a sponge park. Located in a natural depression, runoff naturally flowed into the park, offering an opportunity to transform it into a sponge park with minimal intervention. Following this project, the city wanted to evaluate the actual performance of the redesigned park, determine which interventions could be replicated for similar projects, and explore whether other configurations could be considered to optimize stormwater management. PCSWMM 2D models, calibrated using field observations, were developed to meet these objectives. The results show that the transformation effectively retains runoff volumes, relieving stress on the drainage network downstream. Furthermore, the addition of a bioretention cell at the park entrance would optimize the volume of water retained during heavy rainfall and improve observed erosion issues. 

The City of Paris has been implementing an ambitious rainwater management policy through the ParisPluie Plan, aiming to infiltrate rainfall as close as possible to its point of fall. This initiative is part of a broader strategy to enhance urban vegetation, mitigate heat islands, and adapt to climate change. This paper presents three Parisian projects that exemplify this integration: Rhin-et-Danube Square, Paris’ first floodable square; the greening of Croix-Nivert street; and the creation of an urban forest at place de la Catalogne. These projects deploy a range of source-control techniques, including vegetated swales, permeable surfaces, and sealed planters, to promote infiltration and reduce runoff. The article also examines technical challenges such as unstable subsoil and underground infrastructure, which influence design choices. Finally, it highlights the ongoing evolution of planning and maintenance practices within the City of Paris to embed rainwater management as a core environmental objective in public space development. 

The study presents a proposal for a fee to finance urban stormwater management in watershed areas, addressing the lack of adequate funding for urban drainage, which is often overlooked by municipal administrators. The method adapts the U.S. model of the Equivalent Residential Unit, replacing the traditional Total Impervious Area (TIA) with Directly Connected Impervious Area (DCIA).  DCIA provides a more accurate representation of the runoff volume that is actually conveyed to the public system. The estimation of DCIA, identified as a scientific gap, was obtained through geoprocessing techniques combined with field inspections. The results showed that DCIA decreases on larger parcels, while public roads account for the largest total contribution. The average DCIA/TIA ratio was close to 50%, with slight overestimation by the GIS-based method (4%). The analysis indicated that on-site inspection is indispensable for areas with few parcels, whereas for other strata, the combined approach demonstrated good accuracy. The Connected Residential Unit (CRU) corresponded to 172.46 m², equivalent to US$ 0.16 per m² per year, a value lower than those applied internationally based on TIA. The methodology demonstrated feasibility, with operational costs considered affordable and potential for replication in other catchments, offering a fairer and more efficient instrument for financing urban stormwater. 

The conversion of the former PSA industrial brownfield site in Moissy-Cramayel into the Moissy II Les Chevrons logistics business park is a successful example of redeveloping and adapting a private development to today’s challenges: zero net land take, climate change adaptation, and circular economy. The project is based on sustainable, integrated stormwater management, differentiated according to functional areas and pollution risks: shared access roads (streets and sidewalks), truck yards, roofs, and parking areas. It also incorporates extensive reuse of crushed concrete from the demolition of existing buildings, thereby limiting the need for new resources, as well as a test zone made of porous asphalt designed to observe how this pavement performs under heavy truck traffic. Delivered in 2022, the park shows no hydraulic issues and demonstrates the technical and operational feasibility of source infiltration in redevelopment projects that may present significant constraints, different from those of new urbanization.