Friday, December 8, 2017

How to Build a City That Doesn’t Flood? Turn it Into a Sponge

The number of ​cities around ​the world is ​growing quickly.​ In her book,​ ​ Replenish: ​The Virtuous ​Cycle of Water ​and Prosperity ​ , Sandra ​Postel, the ​director of the ​Global Water ​Policy Project, ​reports that ​over the past ​35 years, the ​number of ​cities in China ​alone has ​climbed from ​193 to 653.​ ​As urban and ​suburban areas ​expand , the ​stormwater ​runoff problems ​will grow as ​well. ​

But now ​there’s a ​movement around ​the world to ​build smarter ​and “​spongier” ​cities that can ​absorb ​rainwater ​instead of ​letting it flow ​through miles ​of pavement and ​cause damaging ​floods. ​From Iowa to ​Vermont and ​from San ​Francisco to ​Chicago , urban ​infrastructure ​is getting a ​reboot. ​

Creating ​better ​stormwater ​management ​systems ​requires using ​green ​infrastructure ​elements in ​urban planning ​and restoring ​some of the ​rain-retention ​capacity that ​cities have ​lost to ​urbanization. ​These elements ​can be roughly ​broken into two ​categories: the ​man-made ​engineered ​replacements of ​the natural ​water pathways ​and the ​restorations of ​the original ​water routes ​that existed ​before a city ​was developed. ​

Man-Made ​Solutions: Rain ​Gardens, ​Bioswales, and ​Porous ​Pavements ​

Traditional ​road construction,​ made with ​asphalt, gravel ​and sand, is a ​very compacted ​structure that ​leaves little ​space between ​the particulates,​ and thus no ​room for the ​rainwater to ​seep through. ​In the ​construction ​industry that ​gap measure is ​described by ​the term “​air void,”​ which is ​typically set ​at four percent ​for the ​traditional ​pavement mix, ​says Richard ​Willis, ​Director of ​Pavement ​Engineering and ​Innovation at ​National ​Asphalt ​Pavement ​Association. ​More