Michele Zone said:
This is really interesting and I have done a little surfing to try to understand it better, in context. But, alas, I don't have the time to do a thorough job at the moment.
A couple of points:
JordanB's comments that a "5 year event" means that the system will only be overrun twice a decade is something I am really skeptical of. I would want to see the actual wording and definition of the source. If the expression "5 year event" is used in the same way that the phrase "100 year flood" is used, then its actual definition would be "an event with a one in 5 chance of happening in any given year" rather than "an event which happens once every 5 years". .
Of course that's what it means. Rainstorms don't tend to be regular. Notice I said "on average" and "about." I was putting the idea of a five year event in context. Granted, it's possible could be ten five year events in one decade, and none the next. On average though, they will occur every five years.
Additionally, when data on river flood levels et al are gathered over a longer period of time, estimations of the size of a so-called "100 year flood" typically go up substantially.
This is measuring rainstorms, not floods. Not sure what kind of difference that makes.
I actually did "back of the napkin" calculations to come up with a five year event. The current Chicago sewer system (which is needed to deliver the water to TARP) is designed to handle that, but having TARP might increase the capacity of the sewers by moving water through them faster. Plus, it has capacity for 3.6 inches of rain runoff. Not knowing how quickly the treatment plants process the water or how much rain can be stored in the sewers, I'm guessing that comes out to about a 4.5 inch+ rain (more if it falls more slowly). That sounds like about a five year event.
On top of that, urbanization dramatically increases flooding, in terms of frequency and severity, by every measure: flash floods increase, volume of the flood increases, and so on. I realize that Chicago is already highly urbanized but that doesn't mean there isn't room for yet more surface to be paved over.
Well, the region we're talking about is nearly totally built-out, except for infill, which is more likely than not to be replacing a paved or gravel lot and actually might decrease the runoff. There might be some increses, but it likely won't be more than a few percentage points difference ether way.
Also, the focus nowdays isn't on paving over as much as possible. Now, the emphesis is on combining nature with the city, opening up greenspace, etc.
Plus, the possibility of more reservoirs will exist.
I am generally skeptical of any claims that a very large scale engineering project has achieved its ends without causing a whole new set of problems.
Any?! How about the Panama Canal? Closer to home, how about the Sanitary and Shipping Canal in Chicago? Before it was built, Chicago was known as "typhoid city," with some of the worst drinking water in the world. Horrible epidemics were part of the routine. Afterwards, Chicago had one of the safest and cleanest water supplies in the world. Granted, the river was still an open sewer, and that wasn't addressed until the 1930s when the first treatment plants were built, and serious progress wasn't made on cleaning it up until TARP, but the S&SC fulfilled its objectives with even fewer side effects than were suggested before it was built (like, for instance, the fact that it did not seriously pollute the Mississippi river system).
The Aswan Dam is sort of the "poster child" for large scale engineering projects that beautifully achieved all of its objectives but with disasterous and unexpected "side" issues.
I'd be very suprised if the side effects of the damn weren't well understood before it was built. More likely, they just weren't acknoledged by the authorities at the time. A similar thing is happening now with the Three Gorges Dam, which will be an ecological disaster on a similar scale when completed.
Fact is, there are many large projects from throughout history that were very sucessful by any measure, as well as ones that were miserable failures. It's becoming increasingly obvious that the single largest project, the Interstate System in the United States, was a failure, for instance, but assuming that just because a project has a large scope, it will be a failure, is overly simplistic.
The TARP is already a sucess. If they quit building it right now, it has already cleaned up the river and lake so much that it would be an unparalleled success.
Look at this:
The building on the right is just a few years old. These are new
residential developments along the river. Now, being along the river is such a huge draw, since it dosen't reek, that it's spurring millions of dollars of development in the city. Not to mention the increased livability of the city that comes from having a clean river and a lake that's safe to swim in, and to mention the already incredible flood control the TARP has provided for the city.
