Zürich's Bachkonzept — Four Decades of Urban Stream Daylighting & Sewer Separation

Around 1850, approximately 160 km of streams flowed openly through Zürich's neighbourhoods. Rapid urbanisation and sewer culverting reduced this to about 60 km by 1980, mostly confined to forested areas outside the settled city.

Launched in 1988, the City of Zürich's Bachkonzept ("stream concept") set out to separate clean rainwater from wastewater at source and, wherever feasible, uncover ("daylight") culverted streams rather than simply expand sewer capacity. The approach was tied directly to sewer renewal, infrastructure upgrades and neighbourhood planning, so daylighting happened opportunistically as streets and pipes were rebuilt over the following decades.

The City of Zürich's environmental protection office reports that roughly 40 km of streams now flow openly through the settled city, of which about 20 km have been daylighted or revitalised since the Bachkonzept began. A 2025 peer-reviewed study in the Journal of Environmental Planning and Management examined the Bachkonzept alongside Seoul's Cheonggyecheon mega-project, describing Zürich's cumulative, small-scale approach — over 25 km of daylighted segments accumulated across decades — as a genuinely transformative long-term model, in contrast to single flagship interventions.

Neither source publishes quantified biodiversity, water-quality or carbon figures, and roughly 10 km of the city's stream network remains culverted; the programme is therefore best evidenced on stormwater and flood-risk outcomes rather than ecological metrics.