by Mike Fritz
November 19, 2008
Here at the American Society of Civil Engineers International Low-Impact Development (LID) Conference in Seattle, I’m swept up body and spirit by the growing throng of several hundred enthusiastic devotees to the cause of polluted runoff (a.k.a. “stormwater”) reduction. As a non-engineer EPA bureaucrat, I’m a first-time participant in this biennial LID pilgrimage. But after three days of PowerPoint presentations and an all-day field trip to Portland, Oregon, which is the other “LID Mecca,” I’m just about ready to compose my own rap tune out of cool LID lingo and design “treatment trains” (combinations of multiple LID techniques) in my sleep. When I get home I’ll definitely take a new look at my own roof downspouts and concrete driveway, and think about how much reinforcement my carport will need before I can put a vegetable garden on the roof!
I used to be an engineer when I was a kid growing up in the suburbs of hilly central Connecticut. One of my favorite activities was building snow dams in the street gutter when the rain finally came and melted the snow on our particularly steep hill. It was great fun to pack the snow into a big ice dam and then, when the call came to go inside for dinner – invariably at 5:00 sharp – kick the dam open and send a big slushy gusher down the street. Down at the bottom of the hill it always flooded out of the street and into the Perraults’ front yard. (Maybe that’s why I felt guilty when I saw them at Sunday Mass.)
Of course at that time, I didn’t see any connection between that phenomenon – the runoff gusher – and the fact that we could always catch trout in the Quinnipiac River upstream of the city but never caught any downstream. Or why we never found any oysters when we went way downstream to tromp through the mud in Long Island Sound, even though my grandfather and uncles told great stories of burlap sacks full.
From what I’ve learned thus far, the “treatment train” at a house like mine would go something like this:
- First, don’t cut down any trees and plant as many additional trees and shrubs as possible.
- Basically get rid of the lawn.
- Catch all the rain you can on a green roof, where it either evaporates or gets used up by the plants. That’s evapotranspiration.
- For the remainder of the water that comes down your downspouts, run it directly into a rain garden, where a lot of mulch, trees, shrubs and native plants soak it up (more evapotranspiration), and lots of it goes through the soil into the groundwater. That’s infiltration.
- If you have a driveway, garden path or sidewalk, replace the non-porous (impervious) concrete and asphalt with porous (pervious) stuff. More infiltration.
- If there’s still a surplus of water, run it through a vegetated swale (more evapotranspiration) and into another basin with more trees, shrubs and mulch. The surface of the swale should be a little lower than the surrounding land so that it may form a pond for a little while when there’s a really heavy rain. That’s biorentention.
By that point, you should have pretty well mimicked what the Chesapeake Bay watershed used to be: a beautiful hardwood forest with clean waters in healthy streams. With this LID “treatment train,” now we can all be engineers! Choo Choo!