Session A4 I Awards - Regional strategies

The Zhenjiang Sponge City pilot (2015–2025) demonstrates a fully integrated green-blue-grey system for climate-resilient urban water management in a dense, 29 km² urban watershed. The project’s systemic approach successfully manages 30-year return period storms (e.g., 256 mm/24 h), has effectively eliminated chronic waterlogging at all 48 historical hotspots, and enhances water quality to China's Class III standard. The core strategy combines Low Impact Development (LID) principles (restoring the developed sites’ hydrology to pre-development conditions as close as possible) with end-of-pipe blue treatment facilities that are integral to Sponge City construction. These facilities, including the innovative high-performance wetlands and dual-use community parks, provide significant temporary storage for runoff exceeding the 30-year design. The critical "grey" backbone is a 6.2 km, 4-meter diameter deep tunnel, which is buried up to 34 meters and uniquely crosses the Yangtze River to convey upstream and heritage areas’ runoff and Combined Sewer Overflows (CSOs) to terminal ecological oxidation ponds in an island in the Yangtze River. Ten years of monitoring and observations confirm exceptional real-world performance: retrofitted districts experienced no waterlogging incidents at any of the 48 former chronic hotspots across hundreds of storms with >99% onsite rainfall retention recorded. The system captures ≥76% of annual runoff and has proven to be a scalable, effective model for hybrid infrastructure in high-density cities worldwide.

The shift from 'all-pipe' grey infrastructure urban planning practices to integrated and sustainable stormwater management involves an evolution of professions and the organization of local authorities. To address the many challenges related to this shift, Grenoble-Alpes Métropole has been experimenting since September 2023 with the Interdepartmental Circle “Water in the City”. The structure of the Circle was first defined through the elaboration of a framework document. Representatives of approximately twenty different departments concerned with integrated stormwater management then participated in various workshops, in order to develop a detailed action plan with follow-up. This prioritized action plan is implemented by the different departments of Grenoble-Alpes Métropole, and has allowed for the development of several solutions facilitating and accelerating the fabrication of a sponge city at the territorial scale (formation of a decision-making body, establishment of training sessions, creation of tools, communications strategy, etc.). Facilitation of and participation in the Interdepartmental Circle are time-consuming and require strong commitment from all stakeholders, and the integration of municipal representatives remains a challenge. However, an increase has been observed in the taking into account of integrated stormwater management in projects.

Faced with growing climate challenges that heighten flooding, coastal erosion, and water quality risks—crucial to Thau’s shellfish-farming economy—the territory has developed a new stormwater management strategy. It builds on two key studies: the Soil Quality Index (SQI), which assesses vulnerability to soil sealing, and the Master Plan for Integrated Stormwater Management (SDGEPI), which maps watersheds, identifies issues, and defines a coherent technical and regulatory framework. The approach rests on three pillars: promoting infiltration at the source through alternative designs, protecting aquatic environments and tackling diffuse pollution, and clarifying the organizational roles linked to Aquatic Environment and Flood Prevention and Urban Stormwater Management. Operational priorities include dynamic modeling of water flows to anticipate risks, awareness and training initiatives for local officials and technicians, and stronger coordination among municipalities, basin syndicates, and the Water Agency to pool solutions and sustain investments. This strategy supports national goals for sustainable water management - combining resilience, environmental protection, and balanced urban growth.

The “Eau en ville initiative”, led by the Cantonal Water Office of the Canton of Geneva since 2019, aims to sustainably transform urban water management based on the Sponge City concept. For the past six years, it has driven a genuine shift in practices, with nearly 150 projects supported at various scales. Awareness-raising plays a central role in the initiative, through conferences, publications, and a large media outreach (several thousands of people). Project support is strengthened by collaboration between the water, environment, agriculture and nature offices within the Water-Soil-Tree triptych, as well as by the activation of a multidisciplinary professional community. The initiative also relies on experimentation (virtual reality, pilot projects, soil regeneration) and on training actions, including the first French-speaking Swiss certification for Sponge City coordinators. Finally, legal and financial adaptations are underway to generalize these practices, while the coming years will focus on continuing experience-sharing, developing regulations, documenting exemplary projects, and strengthening internal skills.