Courtesy of De Dakdokters
Below stretches a filter layer, which prevents the soil from seeping into the next layer, a lightweight tank system to contain water. And finally, underneath you have additional layers to keep water and tree roots from penetrating the actual roof. “In effect, you have a flat rain barrel on your roof,” says Kasper Spaan, climate adaptation policy developer at Waternet, Amsterdam's public water management organization, which is participating in RESILIO. ”.
The water level on the green roof is managed by smart valves. If the weather forecast indicates a storm is coming, the system will release water stored on the roof ahead of time. That way, when a downpour occurs, the roof will be filled, meaning less rainwater will flow into gutters and drains in the surrounding area. In other words, the roof becomes a sponge that the operator can wring out as needed. “In a ‘squeezable’ sponge city, you make the entire city malleable,” Spaan said.
This makes traditional stormwater management systems more flexible but also more complex. So the RESILIO project used Autodesk software to model the impact of blue roofs and flood risk in Amsterdam, while adjusting for climate change.
“You can look at historical flood models and then you can do simulations to help you understand: If I can take that much capacity out of the sewer network, when a storm comes , I would reduce flooding by 10, 15, 20 percent,” said Amy Bunszel, executive vice president of architectural design, engineering and construction solutions at Autodesk. “So our software allows them to do simulations and experiments with many different trade-offs.”
In addition to its sponge city benefits, blue roofs can cool the top floor of a building, essentially “sweating” stored water. With the right native plants, they can also enhance biodiversity by serving native pollinators. Going one step further, scientists are also experimenting Planting plants on the roof under solar panels, called rooftop agriculture. Theoretically, combining it with blue systems could actually improve the performance of solar panels by cooling them with evaporated water.
