'Sponge' infrastructure in Los Angeles captures 8.6B of water from atmospheric rivers

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Earlier this month, the future fell on Los Angeles. A long band of moisture in the sky, known as an atmospheric river, dumped 9 inches of rain on the city over three days—over half of what the city typically gets in a year. It’s the kind of extreme rainfall that’ll get ever more extreme as the planet warms.

The city’s water managers, though, were ready and waiting. Like other urban areas around the world, in recent years LA has been transforming into a “sponge city,” replacing impermeable surfaces, like concrete, with permeable ones, like dirt and plants. It has also built out “spreading grounds,” where water accumulates and soaks into the earth.

With traditional dams and all that newfangled spongy infrastructure, between February 4 and 7 the metropolis captured 8.6 billion gallons of stormwater, enough to provide water to 106,000 households for a year. For the rainy season in total, LA has accumulated 14.7 billion gallons.

To exploit all that free water falling from the sky, the LADWP has carved out big patches of brown in the concrete jungle. Stormwater is piped into these spreading grounds and accumulates in dirt basins. That allows it to slowly soak into the underlying aquifer, which acts as a sort of natural underground tank that can hold 28 billion gallons of water.

During a storm, the city is also gathering water in dams, some of which it diverts into the spreading grounds. “After the storm comes by, and it's a bright sunny day, you’ll still see water being released into a channel and diverted into the spreading grounds,” says Castro. That way, water moves from a reservoir where it’s exposed to sunlight and evaporation, into an aquifer where it’s banked safely underground.

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