Ten years that have transformed the Limmat Valley

The streets are flooded, the tarmac is sizzling, and the sewerage system is at breaking point. What sounds like a state of emergency is becoming the norm if nothing is done. The water research institute Eawag and the Limeco wastewater association are jointly setting up a real-world laboratory designed to demonstrate how an entire region can become more resilient to extreme weather events. The Limmat Valley is set to become both a test bed and a model.

Real-world laboratories do not provide theory. They test solutions in the very places where they are later intended to be implemented. The Blue Nexus Lab, or BlueX for short, is a ten-year project and operates directly within local communities. Eawag brings experience from Fehraltorf to the project, where a similar laboratory has been operating since 2016. There, a dense monitoring network has demonstrated that reliable data prevents costly misguided investments.

The ‘sponge city’ as the answer
The core principle is as simple as it is effective. Rather than immediately channelling rainwater into the sewerage system, it is stored on site, allowed to infiltrate the ground or released at a later time. Limeco has already calculated the potential. Full implementation of ‘sponge city’ measures could reduce combined sewer overflows into watercourses by up to 90 per cent. Even by conservative estimates, halving this figure would be a breakthrough.

Less water, less energy
What is good for the environment also takes the strain off the infrastructure. Less rainwater in the sewer network means less pumping and lower energy consumption at the wastewater treatment plant. Currently, around a third of the extraneous water consists of rainwater. ‘Sponge city’ measures tackle this issue head-on, making the new wastewater treatment plant – due to be built by 2050 – smaller and more cost-effective.

Coordination is key
Nine towns and local authorities in the Limeco catchment area are on board. Limeco is taking on the groundwork that would take each local authority years to complete on its own. All stakeholders meet twice a year to exchange ideas. BlueX provides the organisational framework to link research and practice directly.

A flagship project with far-reaching impact
What is being developed in the Limmat Valley will not remain confined to the Limmat Valley. The findings from BlueX are intended to be applicable throughout Switzerland, for local authorities, planners and decision-makers facing the same challenges. Cooler public spaces, less flooding, more green space. The research has a concrete aim. The Limmat Valley demonstrates that climate adaptation is not wishful thinking, but planning.

Text: Christoph Grüninger • Image: Limeco