June 6, 2011
The High Costs of Straight-jacketing a River
The Mississippi floodplain after the floods, May 4, 2011. While the Mississippi River was flooding this spring and as the news coverage heated up, I tried to match the satellite before-and-after images to all the hyperbole I saw on TV. It quickly became clear to me that there is a mismatch in what people are […]
The Mississippi floodplain after the floods, May 4, 2011.
While the Mississippi River was flooding this spring and as the news coverage heated up, I tried to match the satellite before-and-after images to all the hyperbole I saw on TV. It quickly became clear to me that there is a mismatch in what people are experiencing as individuals and what the river is experiencing.
The floodplain on April 29, 2011.
Take a look at the satellite images. Observe the channels the river has carved back and forth on its natural floodplain. And remember that the flooding today is well within the limits of the river’s historical bounds. To the river, this spring’s flood was not a remarkable event; it is simply part of the river’s natural lifecycle. Yes, this season’s high levels of runoff have been impacted by all our tinkering with the river’s basin through the years, but it has become clear, to everyone who cares to look, that in our diligence to change the contours of the river, we have cut it off from the floodplain that it needs to spread its copious waters.
Our historic approach for developing the river’s floodplain has been defined by short term goals. We’ve built levees so we can farm its rich fertile soils; but these levees now prevent the river from replenishing that very fertility. We moan about the farmers’ losses without considering the decades of gain the farmers have received from the fertile soil. We’ve built small communities and large cities in this same floodplain because the river provided an important transportation corridor, yet we aren’t willing to spend the money to relocate or harden critical infrastructure.
Even those unaware of the science of fluvial geomorphology know, intuitively, that rivers flood over their banks on a regular basis. So why does this well-documented, regularly-experienced event catch us by surprise every time? Each spring the river will rise and wants to claim the floodplain that has been its own for millennia. This floodplain was, in fact, created and shaped by the river itself.
The floodplain last year, on April 29, 2010.
This spring, once again, we witnessed a failure of public policy which has lead to crowding and constraining the river at enormous cost and through great effort. With memories of the recent floods, and for public policy to be effective, it’s time to look beyond the short-term needs of a community and to evaluate options that are going to be sustainable over the long haul.
Generally, our land-use policies do not acknowledge the room the river needs to store its water in its floodplain. We seem blind to the vast sums that will be needed to keep the river from claiming what –over the long run–it will take back. Rather than recognizing the extreme costs that straight-jacketing the river imposes on our environment as well as on our economy, our public policy demands the ongoing expenditure of billions of dollars to maintain the status quo of farms, communities and cities deep in the river’s floodplain, behind walls that are clearly inadequate to protect us against rising waters.
The economic value of large cities in low lying floodplains may justify the large costs of floodwalls and pump systems. Certainly the dynamiting of a levee to save Cairo, Illinois, and the opening of the Morganza Spillway to save Baton Rouge and New Orleans should be seen as just the beginning of what needs to be a regular system that allows the river to reconnect with its floodplains.
Every agricultural levee should have gates to allow regular flows out onto the floodplains. Why, we must ask ourselves, do we maintain a policy of sluicing all that valuable silt and topsoil out to the Gulf of Mexico and over the edge of the continental shelf? Why are we not permanently removing a substantial percentage of the river levees and finding ways to creatively work with the river’s hydrologic cycles instead of fighting them?
Yes, there will be years when there is high water and crops will be impacted by it. But let’s also understand that these periodic floods are the river’s way of replenishing the floodplains – and the fertility of the farmland. When working with our rivers, let’s remember that what is a long haul for us is just a blink of the eye for the river.
Kevin Shanley, FASLA, advocates for giving rivers the room they need. He is actively involved in restoring and protecting the bayous of Houston, TX where he lives and works as CEO of international landscape architecture and urban design firm SWA Group and the Chairman of the Bayou Preservation Association.
NASA images courtesy MODIS Rapid Response Team, Goddard Space Flight Center.