Session A9 - Lessons learned: Stakeholder mobilisation in urban renewal projects

This paper presents the project aiming at opening the Pont-Yblon rainwater retention basin, located in the municipality of Le Blanc-Mesnil, north of Seine-Saint-Denis, to the public. The aim of the project is to transform the status of this water management site from a single-purpose facility dedicated to flood control into a multi-purpose site that can be visited by the public while preserving the flora and fauna specific to the surrounding wetlands. The paper presents the steps undertaken to define the project, which led to the gradual broadening of its objectives through the integration of ecological and social considerations that emerged during the study phase. Reconciling these objectives requires establishing a dialogue with stakeholders at different territorial levels.

Nearly 80% of impervious surfaces fall within the private domain, which highlights - within a context of regulatory compliance for sanitation systems and adaptation to climate change - the need to involve private stakeholders (developers, social housing providers, industries, and individuals) in stormwater disconnection and in sustainable, integrated stormwater management. The Montmuzard district, in the heart of Dijon, illustrates this approach through an urban renewal project carried out in the 2010s by a social housing provider, incorporating on-site stormwater infiltration with no discharge into the public sanitation network. With more than ten years of hindsight, this project demonstrates the technical and operational feasibility of stormwater disconnection on private property and in a context of urban densification. It confirms that sustainable, integrated stormwater management can be a lever for environmental performance, climate resilience, and quality of life—provided it is designed in synergy with the landscape and urban uses.

Villa El Libertador (south of Córdoba) experiences recurrent flooding that causes significant damage to the population. This is due to the densely populated and highly impervious neighborhood, which lacks a hierarchical stormwater drainage network, and additionally receives significant upstream agricultural runoff. Flows spread mainly over the surface of the low-slope topography, generating sheets of water in the streets. The Maestro Sur canal, the main collector derived from a former irrigation canal, has a, almost flat slope: it stores water, fills rapidly, and frequently overflows, making it the system’s bottleneck. The proposed program aims to improve runoff management while improving urban planning by developing public spaces into resilient green corridors. The iterative approach incorporated hydraulic design of mitigation measures, such as retention basins to protect against upstream runoff and re-profiling of the canal to facilitate flow, as well as landscape integration with visuals illustrating the green belt and the restoration of the canal's ecological and recreational functions. Considering existing urban planning documents and involving stakeholders in the design work was also a key element in the success of the development program.

The urbanistic project of Quartier de Seine Ouest (Parc d’Affaires) takes place in the economic and urbanistic transformation of the Parisian metropolitan area. This former industrial space is completely rethink in order to consider the global landscape and the hydrological and urbanistic context. This project has been intrinsically built with the evolution of the local regulation, which allowed a deep work about resilience and adaptation in a global warming context. The aim was to prevent the area against natural disaster to consider water as a resource rather than a constraint. The urban project of Quartier de Seine Ouest was an opportunity to think of solutions to design a sponge-neighbourhood where the green spaces are maximized, as well as permeable or semi-permeable surfaces take part to the regular water management. Heavy rainfalls are infiltrated in open rain garden. Water run-offs are designed to be open and based on a gravity-fed network. The whole neighbourhood is hence designed to consider the flood risk by the River Seine by a detailed study of water-flows and flood spaces in the neighbourhood. The city and regulation evolution continues in the SMA-BTP lot, a southern-west borrow of Quartier de Seine, where grey waters of one of the buildings is treated and reused to hydrate green spaces. This allows the vegetation growth and evapotranspiration and so refresh of the place. The project of Quartier de Seine Ouest represents a model of coordinated evolution of an urban project and the local regulation towards global change.