What Happens When A Concrete Jungle Becomes A ‘Sponge City’
Via High Country News, a look at how engineering for flood resilience can address storms heightened by climate change.
The living roof of the H2 Hotel in Healdsburg, California, both cools the building and mitigates rainwater runoff.John D. Ivanko/Alamy Stock Photo
In early February,meteorologists warned Southern Californians that a supercharged storm was headed their way, potentially bringing catastrophic flash flooding. The predictions came true, and then some: Up to 10 inches of rain fell on parts of Los Angeles over a 24-hour period, shattering all-time precipitation records.
That meant as much as 21 million acre-feet of water — or one and a half times the entire annual volume of the Colorado River — fell on the 36,000-square-mile greater LA metro area.
When trillions of gallons drench a typical concrete-dominated cityscape, the water runs off rooftops and slides onto impermeable concrete driveways and into streets, turning them into virtual rivers. It cascades into stormwater drains and concrete-cased arroyos — picking up dirt, garbage, oil and other substances — before rushing into larger rivers and, ultimately, the sea. When it rains as much as it did in February, the chances of a system failure — drains clogging, gutters overflowing, flood-control structures collapsing — rise, setting the stage for an urban flooding catastrophe.
But this time, most of LA’s stormwater system held up. Not only that, but instead of sending all that water straight to the sea, the city managed to capture more than 8 billion gallons of it in reservoirs and groundwater aquifers for future use.
As much as 21 million acre-feet of water — or one and a half times the entire annual volume of the Colorado River — fell on the 36,000-square-mile greater LA metro area.
That’s partly due to stepped-up efforts to make the city a bit more spongelike, by retrofitting impermeable concrete that was designed to repel water and instead transforming it into a more absorbent landscape. That not only takes a load off drainage infrastructure, it also helps keep the water — and the pollutants in it — out of the Pacific Ocean.
These retrofits are neither cheap nor easy, but with human-caused climate change threatening to make both storms and droughts more severe, opportunities abound to make Western cities just a bit more spongelike.
