Well, after taking the summer off (and oh there will be posts about what happened in some other places), I’m finally back. Charlotte gave me a big welcome return, too. Hot, steamy temperatures and some big old thunderstorms, too. After having lived in Los Angeles, where actual thunderstorms are rare, I have to admit that I really enjoy the big storms. Well, I enjoy them most when they occur at a time when I can sit on my deck and watch them happen. The sheer power of some of these storms is impressive- just feeling the thunder vibrate through the air is phenomenal.
Sometimes, these storms have other side effects. In the first week of August, we had a huge storm. I tried to go sit out on the deck for it, but the rain was coming down so hard and fast and the winds were blowing so much that I couldn’t sit there without getting soaked. Instead, I watched it from the window and enjoyed the rattling of the building. By early afternoon, though, the storm had moved on, so I took myself for a run. Here’s where we move onto a larger, ecological scale. As I went running around Freedom Park, I found that Little Sugar Creek had flooded the parking lots of Freedom Park and was pushing up to the bridges at Princeton. The volume of water flowing through the creek was amazing. The creek at that location had to be at least 12 feet higher than normal levels. I don’t have an actual value- that’s my estimate based on having stood in the creek before. Now think about that observation for a second, especially keeping the creek’s shape in mind. As the level increases in height, the creek also widens, so the actual volume of water required to fill up that space is immense. And since the water was still that high an hour after the storm ended, that’s a LOT of water running into the creek.
A quick look through the literature brings up all sorts of articles about estimating flood frequency in the rivers and streams of North and South Carolina. A line in one short article from a conference really caught my eye, though. Actually, it’s two separate lines.
1. “Urban development can reduce the average basin lag time to as little as one-fourteenth of its value for natural conditions.”
What does that line mean? Well, in talking about basin lag times, the author is talking about how quickly water from a storm enters the stream systems. Under natural conditions, rain water takes longer to reach a stream system and so the rate at which the streams fill decreases (by 1/14). Since water is always moving down the stream, that makes flooding less likely.
2. “A 5-year flood discharge for a watershed with development…is approximately equal to a 40-year flood discharge for the same watershed with natural drainage conditions.”
What? Natural systems reduce the likelihood of flooding? Yep! In the world of conservation biology, that’s called an ‘ecosystem service’. Natural areas slow down the rate at which water moves into a stream system and therefore reduce the likelihood of flooding. That’s big stuff!
What does all this mean for Charlotte? Well, first of all, it means we should really be thankful for Little Sugar Creek and the associated greenway. Below is a picture from Westfield Drive, along the lower end of the greenway trail (taken by another gawker, since I didn’t think to bring my camera on the run). The amount of overflow from that storm was still immense, but it would have been much worse if there weren’t natural areas to slow it down and to absorb so much of that storm run-off.