Shanghai Sponge City Project

I am alerted to a new concept for urban greenery; sponge city planning. As someone who lives in a city that sits on a spongy mass of gravel and clay, that oozes water in season (we're on a relatively gentle flood alert today) I am naturally fascinated.

Lingang/Nanhui in Shanghai is the green infrastructure experiment generating the headlines. The principles?

• Permeable pavements - cutting rainwater runoff and reducing pollution of surface water. This can be retrofitted through replacement of existing concrete impermeable paving.
• Wetland areas - crossed by raised walkways, these are also public parks and nature reserves.
• Rooftop plants - absorbing water but also enabling temperature control through slow evaporation
• Rain gardens - in traditionally wasted space such as central reservations. 
• Rain recovery tanks - to take rooftop run-off.
• Restoration of natural waterways - a lot of small rivers get filled in during construction; identifying and re-establishing these supports traditional flow and soil stability.
• Man made storage lakes - variable depths and expanse depending on water needs of the time.

The percentages are exciting and the goals are high (a sponge city should absorb 70% of rainwater!) Like lots of infrastructure experimentation in China, progress is bewitchingly fast; I have little doubt that new principles and cheaper materials will emerge. Hard-wearing and fully permeable surfaces are particularly needed, as our effective and low-maintenance green roofing solutions. Many of the rest are familiar already; the estate I live in is carved across by gullies which twitch away our floods into the Thames, doubtless cut through the same spaces as earlier ditches.

Of course, the challenges of the Chinese cities are on a whole nother scale, and the imagination of the solutions are stunning. Look at these beautiful images of a rain park before and after monsoon rains, more seductive than any mighty bridge, maybe. There are hints of more to come; permeable, water storing roads?

From this damp city that is (right now) building seasonal lakes and installing drainage-first roads, I feel theere is too much focus on getting the water away and not enough on keeping it in the cities to grow our trees and cool our walls. I'd like us to become more of a sponge city.