More good news/bad news from New York.

In an editorial two weeks ago, the New York Times endorsed green infrastructure solutions for managing stormwater runoff. We’re pleased as punch to see this issue getting deserved attention. But there was one part of the editorial that had us scratching our heads.

The last paragraph concludes, “Green infrastructure can reduce runoff by only 5 percent or so, and some old-fashioned “gray infrastructure,” like new storage tanks, will be necessary to achieve City Hall’s long-term goal of a 40 percent reduction. But this is definitely a creative step forward.”

Their cited figure of five percent seems low to me, and I have not heard or read it elsewhere. Unless we are talking about skyscrapers – i.e., a tall building with a very small footprint/roof, on a site that is almost all impervious — you should be able to treat a lot more than 5 percent of the runoff with green infrastructure. In fact, even with a skyscraper you could theoretically utilize green or living walls and treat quite a bit of stormwater. Cost would likely be an issue, but the solution itself is feasible.

Furthermore, the editorial fails to specify what 5 percent refers to. Is it 5 percent of total annual runoff produced from the site? Or 5 percent of the amount that currently runs off the site?

As far as I know, there is no universal maximum percent of runoff that you can treat with green infrastructure. Cost would be a limiting factor on some challenging sites far before it becomes technically impossible to use green infrastructure solutions.

Green infrastructure’s primary goal is to treat small storms, so remember that it’s possible that only a small percentage of the total annual rainfall is treated. Still, treating the water quality storm — which is typically 90% of all storm events — will provide significant water quality and quantity benefits, even if it treats a lot less than 90% of total annual rainfall volume.

Image: FreeVerse Photography