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500 Year Floodplain

The great bubble of water that mushroomed out of the banks of the Iowa River has moved on into the Mississippi, causing even more devastation as it moves south. Farms and towns have been flooded, roads have been closed, and barge traffic has ceased. Can’t something be done to prevent this, if not stop it?

In a word, “No”.

The levees that were built to contain these rivers were built to a 100 year standard. That means that they are designed to contain the kind of flood that happens once every 100 years. The next highest line is that of a 500 year flood, one that we should see only every five centuries. Nothing is built to contain that much water, but it seems like a reasonable risk.

The problem is that this stretch of the Mississippi has seen a 500 year flood twice in 15 years now. As far north as Saint Paul we’ve seen nearly a dozen 100 year floods in the last fifty years. Somehow, the rivers are beating the odds that we set up for them, and beating them easily.

This comes from many different factors. One is that more urbanization produces more “impermeable” surface, meaning asphalt and concrete. Water rolls off of these surfaces and into the storm sewers rather than slowly seep into the ground. The storm sewers all dump into the rivers water that otherwise keep the land healthy and moist.

Another problem is increase “tiling”, or installation of drainage systems that allow farmland to be carved out of swamps. This land has been made fertile by centuries of the Mississippi meandering back and forth. There’s a lot to be gained by putting it into production, but the swamps that held back water and provided a refuge for frogs and waterfowl now only produce corn and soybeans. The water courses gently into the river.

More importantly, the levees themselves are often a problem. Every time the river is constrained into a narrow channel, the water it carries has no place to go but downstream. Water flows as it wants to, unstoppable in its quiet might. A levee that controls the Mississippi here in Minnesota is a potential threat to the people of Iowa and Illinois.

The problem comes down to the simple fact that the rivers of the upper Midwest give us life, and we have many reasons to stand far too close to them.

Our insistence on control over these rivers has created the problem we have. We thought we could chart and channel them and make accurate predictions as to how they would behave, but our own actions have made that impossible. Our neglect of the Mississippi has been stunning, even going as far as to dump a bridge into it once in a while. We think we can do nearly anything with a force that is far mightier than we apparently can even imagine.

The place to start when thinking about rivers like the Mississippi and all her tributaries is that all of this happens for a very good reason. Events that are supposed to take place every 100 or 500 years or so happen far more frequently when we refuse to recognize that these rivers are alive and strong. They made the land that we live in and love. They are, after all, the reason we are here in the first place.

We forget that at our own peril.

One thought on “500 Year Floodplain

  1. Pingback: Rising Water « Barataria – the work of Erik Hare

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