Integrated Blue and Green Corridor Restoration in Strasbourg: Green Toads, Citizens, and Long-Term Issues

Abstract

The Ostwaldergraben is an urban stream located in Strasbourg (northeast of France). Mostly fed by groundwater , it was enlarged some forty years ago, which led to a radical alteration of the flow dynamics and a strong siltation. According to the European Water Framework, the stream displayed a bad status with sediments polluted by discharges of former tanneries. Hence, a project of restoration —both of the stream and the adjacent wasteland—was launched by the City of Strasbourg in 2010 to solve these issues of environmental degradation in accordance with the European regulation. The stream bed was redesigned to energize the flows and to create meanders and vegetated benches. To improve the connectivity between two adjacent wetlands , new habitats and a network of ponds have been created. A hybrid type of stormwater treatment system—a pond followed by a constructed wetland —was implemented to complete the restoration project. In this chapter, we propose to study this project from its construction to its current development, through the lens of ecological engineering and a perspective on long-term issues. We aim at illustrating the facts that nature-based solution management can differ from technological management and that the ecosystem services provided by a nature-based solution result from trade-offs, which requires a global analysis of such restoration project. To reach this goal, the project will be studied from ecological, engineering, and sociological perspectives. Our study shows that the restored socio-ecosystem works on a rustic basis and provides several ecosystem services: supporting services (habitat for amphibians), regulating services (water quality enhancement), and cultural services (urban landscape greening).