Monday, July 28, 2008

Here's mud in your eye

A recent headline on Yahoo! News decried the loss of soils in the recently flooded states to the north of us. This is particularly significant to us on the southern end of the Mississippi River.

A lot of people have said that we could solve Louisiana's coastal erosion problem by just letting nature do the work for us. We need "The river wild" they say.

But here's a part of the story nobody likes to talk about: sediment load.

That is, how much mud does the muddy Mississippi River contain?

The answer: Not nearly as much as she used to.

Going back as far as 1935 and the birth of the Soil Conservation Service, government at all levels has teamed with private citizens to halt the flow of topsoil washing into the nations' rivers. In recent years EPA has been tightening what is called Total Maximum Daily Load (TMDL) regulations--standards that seek to keep turbidity down.

These and a hundred other well-meaning and beneficial initiatives mean that water flowing past New Orleans today contains just a fraction of mud one would have found in that same water even just a few decades ago.

And what that means is if historically the river was able to build a few hundred square miles of marsh per century, it would take centuries longer to do the same job today.

Would it help to let the river run wild? Yes, but don't count on any help from our neighbors north of the 30th parallel. They need that mud just as much as we do.


Schroeder said...

I think I've heard Rich Campanella comment on the much-diminished sediment load, but I've never drawn the logical conclusion as you have that soil conservation is a big part of the equation. I still wonder why it is, however, that cultivation encroachment up to the edge of waterways is a factor in chemical runoff from farms which produces the Gulf dead zone.

Don said...

There may be less sediment than during the years when we weren't worried about soil conservation, but I'll bet there's more than there was before the plains were covered by farms.

Anonymous said...

Why not site USGS data. They actually perform the sediment flow measurements.

You also fail to site the Corps engineered widening of the flood plain beginning at Cape Girardeau. This has done more that anything you have sited to diminish the amount of soil sediment reaching the lower delta plain.

Tim said...

I agree--USGS is a leader in this research. That's why the link included in my post was to, a site maintained by the USGS National Wetlands Research Center.

I don't understand the second comment, that "widening of the flood plain beginning at Cape Girardeau" has reduced soil loads. I think you might be confused about how rivers work. The lower Mississippi River has been thoroughly channelized to limit and control the river's access to flood plains. A good example is here in New Orleans where the river has been prevented from flooding the city since the 1920's.

Next time you visit New Orleans, make sure to visit the Moonwalk and the Washington Battery between Jackson Square and the river. From there you'll get a sense for the disaster that would occur on a regular basis if not for the levees and floodwalls.



mominem said...

My initial reaction was to wonder what the sediment load was in the early 19th century before the plains went put under the plow.

I wonder if we aren't closer to those levels now.