Know Your Stormwater

“If we were tenants, the earth our home, and Mother Nature the landlord, we’d have been evicted long ago”. Variously Attributed

Last Saturday I had an opportunity to talk with a good friend who is a biologist, forester, and water quality expert with the North Carolina Department of Natural Resources. In other words, this guy know some things about water.

We talked about a unique form of water in the so called Quality/Use Cascade referred to as Stormwater.

Stormwater is, of course, the water that falls from the sky as rain or other precipitation. Studies indicate that while the total sum of stormwater is more or less geographically constant it’s interval intensity is increasing. In other words, we have the same amount of stormwater but it’s coming in much more intense bursts that our stormwater systems (when they exists at all) are ill equipped to deal with.

Here’s the deal with stormwater. If it falls on undeveloped, more or less level land it can usually get back into the groundwater, it’s ultimate destination. If it does run into a creek or stream it usually does not include large amounts of sediment or cause bad erosion.

If this same water falls on a roof or driveway or other impervious surface the results are much different. Such stormwater is:

1. Concentrated (think gutter downspouts)

2. Moving fast (speed and concentration cause erosion)

3. Warmer than it would have been otherwise (it’s exposed to warm surfaces and to the sun for longer than it would be naturally).

So my friend at NCDENR challenged me and all you other green building folks to do a few things to correct our poor stormwater practices.

1. Keep stormwater on site in a rain garden or settlement basin. This has the effect of slowing the water down, dispersing it, and allowing it to cool, and helping it get back into the aquifer. This sounds simple enough but is actually kinda hard to do.

As if we needed another reason to keep our buildings as small as possible here’s another one. Smaller roofs or catchment areas mean less stormwater to deal with. Same with driveways and other impervious surfaces. The less we collect the less we have to “uncollect”, such as it were.

This line of thinking also suggest another reason (besides saving expensive potable water) for harvesting rainwater for irrigation, sanitation, etc; its that much less to attempt to reintroduce back into the ground. Of course even the largest stormwater harvesting storage system (cistern) is eventually going to fill up and overflow and then you’re right back at the problem of getting it back into the ground.

This reasoning also points to the merits of green roofs. A green roof is going to absorb more of this stormwater, slow the runoff down, and generally keep it cooler. Green roofs act like sponges that hold onto water and let it go slowly; they are effectively stormwater “shock absorbers”.

So the days of just dumping your stormwater onto the street or directly into a creek are rapidly coming to an end. When you’re planning a new building try to leave space for a rain garden. Try to keep your downspouts separate and dispersing to different areas. Plan you contours to slow surface water down and spread it out. Harden swales with erosion resistant materials and vegetation. Where possible, create green roofs.

Doing these things should hold the door for native flora which of course benefit native fauna. It’s easy to see how all these things (stormwater, habitat, wildlife) tie back into one another and are inseparable pieces of the whole.

One last thing my friend shared with me that really got me pondering. If you think of stormwater as a burden, it is a burden. If you think of it as an asset, it is an asset.

I would love to hear stormwater stories and how to deal with it from anyone who’s been working on this issue.

Thanks for reading.

Steve Farrell