Monday, May 9, 2011

Record Flooding Threatens to Change Course of Mississippi River

The Mississippi River is experiencing a record flood.  I was tempted to call it a raging flood, but in the flat Mississippi flood plain, there is no raging water to be had, unless a levee ruptures... otherwise just a slow, unstoppable advancing mass of water.  In many places this flood is proving to be the 'worst' on record (although it is important to keep in mind that before people built levees there, vast areas were naturally flooded on a regular basis).  The flood is bringing up squabbles over whether to open floodways, and whether areas should have been developed in the first place.  There is even concern that the Mississippi will shift - that its lower stretches will divert into the Atchafalaya River and leave New Orleans and much of the lower Mississippi's previous course as a backwater.

The flood crest seems to have spared Cairo, Ill... but a designated floodway had to be flooded via dynamiting a levee.  Because this area so rarely had to be flooded in the past, people were farming and living on this land which is now under water.  Dynamiting the levee created quite an uproar.  The uproar was countered by accusations of classism/racism because Cairo is mainly a poor, African-American town and the people living in the floodway are relatively affluent and predominantly white.  I've never been to the area and am not advocating nor denying this view... but the bottom line is that letting a city be destroyed because people living in a floodway didn't want to be flooded isn't very reasonable.

Further downstream, where the flood crest has not yet arrived, there is a lot of concern regarding the Old River Control Structure, a diversion built in the 1960s to keep the lower Mississippi River in its current channel.  Deltas like the huge Mississippi River delta form when naturally shifting channels deposit sediment in different places as they meander.  Before levees were built, the Mississippi frequently shifted course, building the delta as it wandered.  In the 1960s it began shifting its flow into the Atchafalaya River, which would bypass Baton Rouge and New Orleans completely.  People decided it would be best to keep the river where it currently is, so a diversion structure was built to fulfill this goal.

On May 22, the river at this structureis forecast to rise to over 3 feet higher than ever recorded before  Some are concerned that this could destroy the structure completely, diverting the vast majority of the river down this new course.  The results of this would be economically disastrous (for an in-depth description, see here ; for an excellent summary, see this post by Randall Munroe of )  Needless to say, the city of New Orleans, already crippled by lingering effects from Hurricane Katrina and the Deepwater Horizon oil spill, would take a terrible economic hit if this came to pass.

Hopefully it doesn't... for now.  Geologically, it is inevitable.  Rivers flood and shift course.  Eventually the Mississippi will shift again, and in fact over time every part of its flood plain and delta will be inundated by the river in turn.  This is a river that is millions of years old and has carried much of the (many iterations of the) eastern half of the Rocky Mountains, piece by piece, to the ocean.... a river that has carried glacial meltwater from the melting of miles-thick ice sheets, through overflow of what is now the great lakes...  A levee that lasts 100 years seems permanent to us, but to a river like the Mississippi it is meaningless.

Peoples lives are held in the floodplains.  I don't want to minimize this.  it is a horrible thing that their homes are flooded and their lives are at risk.  Often times, their loss comes due to abuse of watersheds upstream.  It certainly is not 'fair'.

But it it is what it is.  We continue to live in flood plains.  Rivers continue to flood.  If watershed degradation continues, and if climate change intensifies storms the way many believe it will, these events will continue.  Levees are impermanent, expensive, and shift the problem downstream.  The only long-term way to 'manage' a huge river is to preserve or restore the wetlands that naturally exist on flood plains, to hold back the water.  We may be able to use the land for other purposes too, but we need functioning wetlands if we want to be able to use the rivers too.  We just don't have the money and resources to maintain these levees.

The flooding isn't confined to the Mississippi River basin either.  Lake Champlain has passed its record high point and is dropping slowly.  Unfortunately a raging north wind is pushing waves south, and even as the lake slowly drains, it sloshes south like a bathtub full of water.  For those in the southern end of the lake, especially north-facing areas, the worst is coming now.

Our planet is a temperamental place, and it offers few promises for the future.  Make sure to enjoy the present, if you are lucky enough to not be fleeing a flood right now.