…In the sewer, where it is supposed to go, crazy. Right, I know, but then what? Well, it flows into a stream which flows downhill because water is subject to the force of gravity and then into a river which is also a slave to the laws of physics and ends up in the ocean…duh. Why are we talking about this? Because it is something that most people don’t give a second thought to…it rains, water goes in sewer end, of story…but with the previous drought, recent rainfalls and water quality concerns, it is something that people should be thinking about.
Let’s begin by thinking about what the Omaha metro area, or any city, was like before intensive human settlement. Most likely you have a bucolic picture in your mind of rolling prairie, lush forests with bunnies and deer frolicking happily until they are savagely attacked and eaten by a mountain lion which, before it can savor its delectable meal, is savagely attacked and eaten by a pack of velociraptors which is savagely…wait… sorry, my imagination got away from me there. Let’s go back to those rolling prairies and lush forests. With the area covered in vegetation, much of the rain that fell infiltrated into the ground. The soil helped to filter the rain water which was either taken up by plants or seeped slowly through the ground. The vegetation also served as an impediment to rain that flowed over the ground, delaying its arrival at the stream like a pesky security guard at the airport that makes you almost miss your plane.
Now, let’s compare it to the system we have now. We have paved over much of that vegetation which allows for zero infiltration. In addition, the speed at which the run off reaches the stream is much faster than before. Water flows quickly over pavement into storm sewers that deliver the water as fast as possible into streams. But wait, you say, I have large areas of lawn, surely that is much better. Sorry to say, but not really. Much of the ground is compacted due to construction and run off from turf, while slightly better than concrete, it is still insignificant. What this has done is thrown our hydrologic system out of whack. Anyone who has seen the streams in Omaha after a significant rain storm will know what I mean. They turn from relatively placid streams of 1-2’ deep and 6-8’ wide into raging torrents 30-50’ wide and 10-20’ deep.
The technical term for this is hydrologic bounce, which, while sounding like loads of fun, isn’t. As opposed to the case mentioned above, in areas where there is lots of vegetation, the streams do not rise nearly as much during rain storms because the runoff is infiltrated or slowed down. The infiltration also serves another purpose. The groundwater slowly feeds streams when it isn’t raining so they’re base levels are much higher between rain events.
OK, you say, let’s do it. Let’s get rid of streets and freeways and parking lots and go back to a time where everyone drove horse and buggies, churned their own butter and had to fend off attacks from vicious packs of velociraptors. I bet the new 1 horsepower 2014 Ford Wonder Wagon (literally a wagon) with Bluetooth could outrun those velociraptors, yeah right. The good news is we don’t have to go back to the old days, we can have our cake and eat it too. We can still drive cars that outrun dinosaurs and help restore some of the balance we had before. This is where storm water best management practices (BMP’s) come into play. In the next post, we’ll discuss various types of these and what they do.
