Reducing Stormwater Runoff with Rain Gardens, Green Roofs, and Living Walls

About a week ago, Pittsburgh experienced a flash flood that took four lives in a matter of minutes. This came after a quick, hard downpour days before Irene was even making her way up the coast. While Pittsburgh is surrounded by rivers, our floods are rarely caused by breaches of those banks.  Rather, they are the result of a sewer system that’s unable to accomodate a large deluge of water in the combination of heavy rainfall, weak pipes, and runoff from pavement and yards.  As one eyewitness put it, the manholes seemed to explode out of the ground that day.

There are two kinds of sewer systems. Separate systems have, as you’ve probably guessed, two different sets of pipes for waste water and stormwater (systems built after 1940). However, in Pittsburgh and many other communities, we have a combined system – one network transporting both waste and stormwater (systems built before 1940). You can probably imagine that’s it’s not very difficult for this system to be overworked. In fact, just 1/10 of an inch of rain is enough to push them into overload! When an influx of stormwater hits the pipes, two major issues can occur: the overflowing pipes will leak sewage straight past the treatment plants and into the rivers where we kayak, boat, and fish, and/or we find our streets, driveways, and basements buried in water.

Fixing systems like this is costly and cumbersome. According to 3 Rivers Wet Weather, it could cost up to $3 billion! Fortunately, there are some solutions that don’t necessitate a costly overhaul of entire sewer systems, and in combination can significantly reduce the amount of water flowing through those pipes.

Rain Gardens

It sounds almost majestic, doesn’t it? Rain gardens…. And they can be!  But anyway, what on earth is a rain garden, you ask. It’s simply a garden (generally with native plants) that is designed to absorb lots of water, filtering it into the ground instead of our pipes!  So what makes it different than any other garden?  In many parts of the US, we have dense clay soil that can only accept so a little bit of water before refusing the rest and sending it back out into the streets to end up in the you-know-what. So if you dug your garden just to fit the roots of your plants in, or even just buried some seeds in the ground, chances are you’re still battling that solid clay in your yard. For rain gardens, the goal is to make the soil as amenable as possible to large quantities of water. In many cases, this means removing the entire layer of topsoil (clay!), and replacing it with a mixture of loamy-sandy-composty soil. During heavy rains, when water is pouring through your downspouts, overrunning your gutters, and seeping into your walls (or is that last one just my house?), it ends up watering the beautiful native plants in your rain garden instead of pushing our sewer pipes to the point of exploding manholes.

Green Roofs

Green roofs have been in the news for awhile now, and probably aren’t new to anyone reading this. Not only do they capture, filter, and drain water, reducing the amount of swift stormwater runoff, they also help control the climate of their buildings.  Chicago currently has the most green roofs of any U.S. city, and this is a pretty strong selling point for other metro areas to follow suit:

“In August of [2001], researchers recorded a rooftop temperature of 119 degrees in the planted area, compared with a blistering 169 degrees on an adjoining black tar roof. Since then, the green roof has saved the city an estimated $3,600 in annual cooling and heating costs. If all Chicago roofs were similarly clad, city officials believe peak energy demand could be cut by 720 megawatts, or enough electricity for 750,000 consumers. Similarly, the load on the city’s storm sewer system could be slashed by roughly 70 percent.” – From this article 

Living Walls

Living walls like this one on PNC Bank building in downtown Pittsburgh are similar to their rooftop counterparts. They collect and absorb rainwater, help regulate temperatures, and may also break up heavy winds.  Artsy, practical, and can even be enjoyed from the sidewalk!

Personally, one of my life goals is to someday have a green roof AND a rain garden!  I would love to hear your thoughts in the comments.  And for a few moments of awe, do a quick google image search on green roofs… you won’t regret it.

Leave a comment


  1. Dave Porigow

     /  September 1, 2011

    I have been wanting to put in a green roof at school just outside my classroom. Need to convince the powers that be. Nice blogs. Entertaining and informative

  1. Friday Faves – Sept 2 | The Back Patio

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