One inch of rain falling on one acre of native, forested land produces zero runoff. That water is absorbed into the soil and vegetation where it is filtered and returned to groundwater and streams until it evaporated by a plant or sucked up by you to drink (after being treated with your stunning new UV filtration system, of course!).
One inch of rain falling on one acre of concrete produces a little over 27,000 gallons of runoff. Just stop for a second and think about how much water that is: 102,206 one liter water bottles all dumped out at the same time. 772 bathtubs full of water all getting the plug pulled at once. That's a crapload of water, folks!! In many cases, this is funneled into storm drains which then drain directly into streams (no, they do NOT, in most cases, connect to the sewer system). This water carries with it all the chemicals, sediments, and other pollutants it has picked up as it flows across the concrete, including copper from brake pad dust, polyaromatic hydrocarbons (PAH's, a carcinogen) from exhaust, oils and antifreeze from leaks, pesticides from yards, etc. All these goodies shoot straight into your water supply completely unfiltered along with a massive quantity of water that is guaranteed to erode the banks off of whatever unlucky stream is its recipient, unleashing a whole host of new problems that will need their own post!Moral of the story: concrete BAD, native vegetation GOOD (note, fescue grass is NOT native vegetation). Planted swales along street sides GOOD, curb and gutter BAD (we will explore that more in the future as well). Forests GOOD, shopping malls, big box stores, and ginormous parking lots with no opportunities for soil infiltration BAD.
Obviously, much as I desire it, we cannot get rid of all the parking lots and warehouse-sized buildings in the world. Sigh. But we can make them MUCH more functional and MUCH less damaging. It's all about good design. And you'll just have to stay tuned until the next post to find out!
Here's a hint until next time:
3 comments:
I love Monday fun facts. Question: what would cause more damage, paved parking lot or mud-holed and rutted out dirt parking lot?
Ooo, tricky! On a global scale, the parking lot hands down, since not only would you have the runoff, but all the crap to make the concrete itself, plus, since the dark surface makes a mini-urban-heat island effect, temperature regime modification.
On a local scale, not counting construction, I'm going to vote the concrete is worse, but only slightly. And it depends on the level use and compactness of the dirt one. The dirt may offer SOME slight level of infiltration and the ruts will hold water, allowing some sediment to settle out and water to be absorbed. You'll get more sediment runoff from the dirt one, BUT fewer pollutants. Assuming it is not constantly covered by cars, SOME vegetation will probably volunteer on it, giving it more absorption power. So I give a small increment of "Win via less damage" to the dirt lot.