Nov 13, 2022
If you don't already live in a sponge city, you soon will. Less pavement and more green spaces help absorb water instead of funnelling it all away - a win-win for people and urban ecosystems.
Like many things, water is great in moderation - urbanites need it to survive, but downpours can flood streets and homes. And as you might have noticed, climate change isn’t good at moderation.
In response, urban planners are increasingly thinking of cities less as rain jackets - designed to whisk water away as fast as possible before it has a chance to accumulate - and more as sponges. By deploying thirsty green spaces and digging huge dirt bowls where water can gather and percolate into underlying aquifers, “sponge cities” are making rain an asset to be exploited instead of expelled.
“Where once there were forests and fields and wetlands that would soak up the rain, these have been paved over and replaced with surfaces that do not absorb rain,” says Michael Kiparsky, director of the Wheeler Water Institute at the University of California, Berkeley.
Any good city planner knows the value of green spaces, but traditionally these have been used mainly for public enjoyment. Sponge city designers also use them as a tool for managing increasingly furious rainstorms.
Pittsburgh is an example of a city that's sponge-ifying. Amongst its solutions are the humble rain garden, a simple plot of vegetation on a property or roadside that captures water washed off the street. Yet another option is building what’s called “vegetated swales”: essentially ditches filled with grass and other plants that gather stormwater and help it seep into the ground.
Other cities, like Los Angeles, have the opposite problem - but the same requirements. There's not enough rainfall in Los Angeles, so rather than sponge-ifying to gently disperse water to avoid flooding, they need to capture water.
Climate change means that, like the East Coast, Southern California will see more intense storms, except they’ll come less frequently. That means big dumps of water will become more valuable - and if the city can find a way to capture them, they can alleviate its dependence on water imported from Northern California and the Colorado River.
So, whether a city is too dry or too wet - or anything in between - authorities everywhere are waking up to the notion that sponge-ifying metropolitan spaces is a very good idea.
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