Walking past one of the new state-of-art “bioswales” lining New York City streets, you might not notice it–at first glance, the green spaces don’t look that much different from the trees and curbside gardens that have been around for hundreds of years. Most of the action is happening underground: A layered system five feet deep can suck up as much as 2,000 gallons of water every time it rains, ultimately saving the city billions of dollars.
Why does absorbing rain matter? In a word, poop. New York, like many other cities, built infrastructure in the late 1800s that hooked up sewer pipes with drains on city streets. On a sunny day, that’s not a big deal; everything goes to a wastewater treatment plant. But when it rains too much, the pipes can’t handle the water, and raw sewage ends up overflowing into local waterways, like the ultra-polluted Gowanus Canal and Newtown Creek.
Many of these waterways have other problems–Newtown Creek, for example, used to be the site of dozens of oil refineries, and it’s now an official Superfund site. But as it begins a slow process of cleaning up decades of spilled oil and other industrial waste, tackling the issue of sewage will be a critical step in helping bring the stream back to life.
While the city could have tried to solve the problem through a new system of pipes and concrete, the green spaces will be cheaper. “The savings are in the billions because we’re deferring building massive treatment tunnels,” says Margot Walker, the director of green infrastructure partnerships at the city’s Department of Environmental Protection.
The bioswales also come with extra benefits. The mini-gardens will also help make the city cooler by reducing the urban heat island effect that comes from endless acres of pavement, ultimately making summer air-conditioning bills slightly lower. The trees and plants can also help clean the air. In some neighborhoods, they may also raise property values (whether that’s actually a good thing is another debate).
Over the next few years, the city plans to plant thousands of the bioswales along with other rain-guzzling projects like green roofs. “We’re really looking at every single opportunity to retrofit streets and sidewalks in priority areas,” says Walker. While New York isn’t the first city to use the technology, they’ll likely end up with most individual bioswales in the world, scattered at curbsides throughout the neighborhoods that drain to the most polluted water.
“We don’t have a lot of public or private area for lawns or rain gardens,” Walker says. “So we’re just trying to take advantage of the little places that we have.”