Cities Use Design to Tackle Stormwater Runoff

This is Womrath Park, one of a hand­ful of “green infra­struc­ture” projects Philadelphia has begun—with many more to come—aimed at tack­ling a wide­spread urban envi­ron­ment prob­lem. Ten tril­lion gal­lons of rain­wa­ter per year flow over rooftops and roads around the U.S., pick­ing up con­t­a­m­i­nants that include bac­te­ria, oil and grease, met­als, pes­ti­cides, and many oth­ers. When a rain­storm is big enough, the runoff causes over­flows from out­dated sewer sys­tems that com­bine both raw sewage and stormwa­ter in a sin­gle pipe. This tide of pol­lu­tants ends up in sur­round­ing water­ways that serve as drink­ing water sources and recre­ational areas.

“Stormwater runoff is one of the largest water pol­lu­tion issues fac­ing the U.S. today,” says Larry Levine, a senior attor­ney in the Natural Resource Defense Council’s water program.

Now, how­ever, numer­ous cities around the country—including Philadelphia, New York, Washington, Portland, and Seattle—have embarked on inno­v­a­tive stormwa­ter runoff fixes that rely not so much on the old “gray infra­struc­ture” of huge, piped sys­tems and sewage treat­ment plants, but rather on new green infra­struc­ture tech­niques to col­lect and treat stormwa­ter at the street level.

Green infra­struc­ture mim­ics how nature han­dles rain­wa­ter through the use of porous sur­faces, rather than imper­vi­ous sur­faces like road­ways. These tech­niques are decen­tral­ized. Instead of one facil­ity or large under­ground tank to store water when a big storm hits, the idea is to elim­i­nate the need for such stor­age through the use of green rooftops, road­side plant­i­ngs, care­fully land­scaped parks, rain gar­dens, rain bar­rels, and other swatches of nature dropped down inside the land­scape of mod­ern cities.

The plants and soils col­lect water dur­ing a storm, pre­vent­ing it from either run­ning into sewer sys­tems at all, or at least slow­ing it down to pre­vent over­flows. Green infra­struc­ture can also help clean some pol­lu­tion from the water and can even be used to gather water for re-use.

“The green infra­struc­ture approach says, ‘Let’s get the water out of those sewer sys­tems in the first place before it has a chance to con­vey all that pol­lu­tion into our water­ways,’” says Levine. “And the way to do that is to put back into our built envi­ron­ment fea­tures that mimic the way nature han­dles rain­wa­ter in the nat­ural water cycle. It doesn’t nec­es­sar­ily mean replac­ing a paved street with a park, but it means putting enough green space into the design of your road­way that you can cap­ture runoff from that paved space.”

These types of green projects carry numer­ous ancil­lary ben­e­fits, Levine notes, from improv­ing sur­round­ing prop­erty val­ues, to reduc­ing in the urban heat island effect, to low­er­ing asthma rates.

Green stormwa­ter infra­struc­ture means thou­sands of indi­vid­ual projects in big cities like New York or Philadelphia. The price tag—Philadelphia is spend­ing around $3 bil­lion, and the coun­try as a whole needs some­thing like $63 bil­lion just in fixes to stormwater-related sewage overflows—is high. But advo­cates say going green is even­tu­ally a far more cost-effective method than con­struct­ing large waste­water treat­ment plants. Philadelphia and other cities are using city and fed­eral fund­ing to finance these green infra­struc­ture projects.

Valessa Souter-Kline, a rep­re­sen­ta­tive of the Philadelphia Water Department, says the decen­tral­ized con­cept of green infra­struc­ture devel­op­ment rep­re­sents a major chal­lenge. “No one is say­ing ‘no’ to the idea,” says Souter-Kline, stand­ing at the bot­tom of the rain gar­den in Womrath Park. “The issue is the scale. You just need so much of this.” On any given project, she says, the Philadelphia Water Department will likely have to work with the streets depart­ment, parks and recre­ation, util­ity com­pa­nies, and other stakeholders.

Levine and oth­ers say the new meth­ods of stormwa­ter runoff con­trol deal with a key flaw in the land­mark 1972 Clean Water Act—“non­point source” pollution.

Click here to read the rest of this arti­cle at Yale Environment 360.