Session A8 - Urban development: adaptation and resource conservation

Urban vegetation increasingly suffers from negative climate change-associated effects, e.g. drought stress, significantly diminishing ecosystem services. To sustain these functions, artificial irrigation is often unavoidable but relying on potable water is not sustainable. This case study in Frankfurt am Main presents a Blue-Green Infrastructure implementation where the estimated annual irrigation demand is secured through alternative resources. The concept yields 4,800 m³/year of harvested stormwater runoff from roofs and building facades and utilizes 10,000–35,000 m³/year of drainage water discharged from a sustained groundwater drawdown. As the pumped water from the groundwater drawdown exhibits elevated salinity (conductivity >1000 µS/cm), a blending strategy with rainwater is applied to ensure adequate irrigation water quality. Integrating a 60 m³ storage tank alongside the building's 480 m³ retention volume allows for a drinking water substitution of up to 70%. This approach not only enhances resilience but also reduces operational costs by minimizing wastewater discharge fees. As for now, the project has received its grant approval from the City of Frankfurt, transitioning this circular water management approach from concept to implementation.

Winner of the innovative project call 'Le Grand Pari(s) de l'Environnement', this experimental project aims to reuse water collected at the bottom of underground structures for watering a public garden, thereby creating an urban cool island fed by a local and sustainable resource. Led by Société des Grands Projets and designed by fbcc and Urbanwater, it is deployed on the surface of an auxilliary undergournd structure of the Grand Paris Express in Aulnay-sous-Bois. The system incorporates phytoremediation systems for treating the pumped water, intended for irrigating vegetated areas, with overflow into an infiltration swale when capacity is exceeded. In a context of climate change and summer water stress, this project explores the potential of underground  water that seeps into underground structures – available year-round – as a resource for urban cooling. Its quality, superior to that of wastewater, nonetheless requires additional natural treatment through phytoremediation. The ongoing experimentation (2025-2026) tests several filter configurations and plant palettes to meet sanitary requirements for public irrigation. The results will guide the design of the permanent garden, planned for 2027, subject to approval by the relevant authorities. The overall objective is to demonstrate the feasibility of short-loop reuse systems for water collected in underground structures and their beneficial integration into Grand Paris Express infrastructure.

In July 2020, Stade Rennais Football Club (SRFC) decided to keep its training centre at the Piverdière site in Rennes, abandoning plans to relocate to the outskirts of the city. At the same time, a major project to expand and modernise the centre was launched. As soon as it was announced, the project met with opposition from some members of the public and environmental associations. Preliminary studies identified two priority environmental issues : land consumption and water management. In response, an ambitious water management project was initiated and implemented. This document provides feedback on the process and presents the actions and works carried out.

The gradual replacement of natural grass football pitches with synthetic turf over the past few years has led the Geneva State Water Authority (OCEau) to ask the following questions:

• What are the differences in terms of water discharge to the receiving body during rainfall?
• What is the annual hydrological balance of a sports pitch with synthetic turf compared to one with natural grass?