Grey Solutions versus Nature-based Solutions : Which infrastructures to prevent pollution in urban water bathing sites?

Résumé 0

City development along rivers in Europe has gone hand in hand with structural works to reduce water-related risks, such as levees (dikes) or dams for floods, and the burial of polluted rivers and sewerage networks, which have become invisible. Today this legacy is being challenged by the environmental turn of water-related risk policies towards more nature-based solutions and the aspirations of city dwellers for greener landscapes and a greater access to blue spaces. This environmental turn affects the framing of water-related risk prevention policies. Grey infrastructures, costly in investment and operation, whose design has been thought out on a sectoral basis to combat a single risk (flooding, pollution or drought) are no longer given priority. Environmentalists recast them as danger in the fate of climate change and biodiversity loss. Instead, nature-based solutions (NbS) would meet several objectives, would be cheaper and more robust in the face of global change. We call this debate the dualism of grey infrastructures versus NbS, which tends to disqualify the former for the benefit of the latter.The development of bathing sites projects in urban rivers is becoming very popular in several major European cities. The promoters of this outdoor activity argue that city dwellers practicing river bathing would be more likely to reconnect with the natural environment, to get to know it better and take better care of it. Such projects would also fulfil the claims for the right to the city and to nature in cities. Yet European regulation mainly addresses river bathing through the faecal contamination risk. In order to comply with the 2006 EU bathing directive, municipalities must enhance sewage treatment performances to avoid contaminated discharge upstream of bathing sites. We study the policy choices made in two cities, Paris in Berlin, regarding the prevention of pollution for bathing sites in urban water. We observe that Berlin public authorities consider NbS to reach the bathing directive objectives. In Paris, along with the political commitment of organizing the fluvial and nautical events of the 2024 Olympic Games on the Seine River, water managers took decisions in favour of more grey infrastructures. Based on press coverage, in situ observations and semi-structured interviews in both capitals, we explain what the drivers for such choices were. We account for material differences in structural legacies as well as the strategic use of the rhetoric of urgency and the reference to the Olympic commitments in order to impose grey investments instead of NbS.