I did want to say a few things about the recent Mississippi River flooding that's been in the news - especially since there's been some bad reporting (Really? Who would have thought?) in the media - including the New York Times.
Today, the Army Corp of Engineers blasted a levee along the Mississippi at a location called Bird's Point near Sikeston, MO to divert floodwaters and reduce water levels at Cairo (pronounced Kay-row), Illinois on the Ohio River near its confluence with the Mississippi.
The Ohio River at Cairo was at 61.25 feet yesterday afternoon which was higher than the 1937 record of 59.5 feet. Weather patterns in the Ohio Valley have resulted in 1-2 feet of rain in the area over the past couple of weeks. The top image below shows the Mississippi and Ohio rivers on April 29, 2011 while the bottom image shows the same area last spring (no flooding).
The real problem for Cairo, of course, is that it's built in a horrible place - smack dab on a piece of floodplain between the Mississippi River to the west and the Ohio River to the east.
Here's a great blog post at Clastic Detritus by Brian Romans on Flooding Creates Floodplains. I love this quote from his post - "Floodplains are not regions that just happen to be adjacent to rivers — they exist because of river processes. Floodplains don’t simply experience periodic flooding, they are the result of periodic flooding." Cairo's on a floodplain, it will flood. We try to prevent this by building levees along the river but levees can fail when the water level gets high enough as it's doing now.
So what is the Army Corp of Engineers doing? Many reports in the media are portraying this as a last-ditch desperate attempt to save Cairo from flooding by blowing the levee and flooding innocent farmer's land. The real story is that the Corp of Engineers is carrying out a plan in place since 1927 to utilize a floodway designed and built for this very purpose. Farmers who have land in the floodway were fully aware of the risks and built there anyway (hint - you shouldn't build a home in something called a FLOODWAY). Read Rising Floodwaters Compel Hard Decisions for more information about this.
Allowing the water into the floodway will reduce the level in the river and help the levees hold back floodwaters everywhere else. It's a tradeoff but one we have to do since we drained much of the marshland along the Mississippi and developed on the floodplains. Rivers will periodically flood. Levees won't always hold the waters back. If insurance companies refuse to sell you flood insurance, there's a damn good reason!
This is why everyone should take a basic geology class. We discuss things like this (and earthquakes, volcano hazards, tsunamis, mudslides, and other geologic hazards that people blithely ignore).