Brooklyn Botanic Garden’s Guide to Rainwater Harvest
New York’s water system, like those of many old American cities, is a low-tech network of cisterns and pipes that hasn't changed much in the 150 years since it was built. In that time, the population has grown from less than half a million to 8.5 million people. Furthermore, most green space has been replaced with buildings, asphalt, and concrete, leaving very little permeable surface to soak up excess water during a storm.
Rain can overwhelm the antiquated storm drains so that they overflow into the general sewage system and force polluted water into local waterways. Some days, you can actually see raw sewage flooding into the Gowanus Canal. Other overflows aren’t as obvious at first but lead to water pollution and consequent beach closings when bacteria levels become too high.
How can you help ease this burden? As a city dweller, your options depend on the type of building you live in and the kind of garden you maintain but everyone can do something, and every drop counts.
Rain Harvesting Methods to Use in the City
Row House or Other Small Building
Plant a small rain garden, hook up a rain barrel, or start a container garden.
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If your building has an external downspout, consider installing a rain barrel to collect runoff from the roof. The Department of Environmental Protection provides free 60-gallon rain barrels for New York City residents.
If your home includes a garden or yard, you can also create a rain garden to soak up some excess storm water. These can be small, simple depressions filled with a few well-chosen plants or a more complex design that incorporates gravel and drains beneath the soil surface to funnel away water.
There are also a few simple accommodations you can make to reduce runoff.
Large Apartment Building
Consider an intensive green roof system or a modest rooftop container garden. Take care of the city's curbside rain gardens on your block.
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The most comprehensive approach would be to install a green roof. Granted, retrofitting a building with a green roof will require a committed co-op board or building owner and a significant investment. But besides mitigating storm-water runoff, there are other benefits: increased energy efficiency and usable outdoor space. BBG's handbook Green Roofs and Rooftop Gardens provides an overview of extensive and intensive green roof systems.
School or Community Garden
Connect a set of rain barrels or other harvesting system to an adjacent building or shed. Plant a rain garden, and use more compost!
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Soil absorbs water like a sponge, and plants take it up in their roots, so any garden will contribute to storm-water management. If you belong to a community garden or help maintain a school garden, you can maximize that space’s ability to hold excess water during the crucial early moments of a storm, when most overflows occur.