Monday, May 9, 2011

Will the Mississippi River Change Course?

Port Townsend, today. Record flooding continues along the murky Mississippi. There is a lack of intelligent reporting. Did you catch the reporter from NBC standing chest deep in floodwater? If he understood that floodwater is a hazardous material, he might not act so stupid. A pointless escapade, potentially dangerous to the individual.

Gages found on indicate this may be the record flood of all time.

Flooding began way up stream, closer to the headwaters of the dozens of tributaries to the Mississippi. Every time a parking lot is built, or a shopping center, or an industrial park, or a new house with a driveway, or new streets, open land, that once absorbed rain and snow melt, is deleted.

So, runoff water has nowhere to go except into creeks, streams, and rivers. That's why, in every successive flood, people say, "I've never seen her this high!"

Besides paving the land, man has been tinkering with the river, the Mississippi River in particular. When rich farmland is flooded, we build levees and dikes to keep water out. Ironically, that mechanism created the rich farmland in the first place!

As the Mississippi flows south out of farm country, paramount in the Corps of Engineers plan is the protection of major cities including Baton Rouge and New Orleans. The entire area is heavily industrialized and a major hub of commerce.

A series of control structures will be coming into play over the next few days. We have already witnessed the opening of the Bird's Point - New Madrid Floodway last week. That was required to protect Cairo, Illinois and New Madrid, Missouri, as well as dozens of smaller communities. The bottom end of that Floodway was "unplugged," when two fuse plugs were blasted, allowing water to flow freely through the floodway, and back into the Mississippi below New Madrid.

As you watch your evening news, listen for the following names of Flood Control Structures, soon to be activated to ameliorate flooding:

  • The Old River Control Structure (ORCS)
  • The Morganza Spillway
  • The Bonnet Carré Spillway
Click on this interactive map to zoom in and located the Flood Control Structures.


The ORCS is at River Mile 303.7. This aging structure, 70 miles north of Baton Rouge, has been heavily assaulted during several Mississippi floods. In 1973, it was damn near undercut and swept away! The Corps opened the Morganza Floodway down stream to save the ORCS.

The ORCS is the only structure keeping the Mississippi from flowing into the Atchafalaya River, bypassing Baton Rouge, and New Orleans! The Atchafalaya has already absorbed the Red River. By carefully controlling a certain amount of water to flow from the Mississippi into the Atchafalaya, flooding can be ameliorated down stream.

Further downstream below the ORCS is the Morganza Floodway. Again, this structure keeps the Mississippi River from returning to a historic riverbed. This structure is 4,000 feet long, with 125 gate bays. It was completed in 1954.

It was partially opened once, in 1973, to relieve pressure on the ORCS.This structure will be opened this week. The map below shows the dramatic impact that will have, in order to save Baton Rouge and New Orleans.

Click on the map. When the map opens, there will be a magnifying glass with a "+" mark. Click on that symbol to maximize the map.

The final Flood Control Structure, the Bonnet Carré Spillway ("bonnie care-ray"- "square bonnet"), is just 26 miles north of New Orleans. This structure keeps the Mississippi from following another old path into what is now Lake Pontchartrain.

The Bonnet Carré Floodway, completed in 1931, consists of an 8,000-acre floodway and a concrete, leaky weir control structure that parallels the Mississippi River for a mile and a half.

The structure consists of 350 gated bays, alternating high and low to regulate flow. Each bay holds 20 timber "needles," for a total of 7,000 needles.

To open the bays, needles are lifted by two cranes moving on tracks atop the structure. Water spills into the floodway, traveling six miles between guide levees into Lake Pontchartrain.

The timber needles measuring 8” x 11.5” x 10' (or 12') depending on location. The loose fit of the needles also allows seepage of river water into the floodway during high Mississippi River stages.

Opening a Spillway is referred to as "pulling needles." This short video clip shows Corps Engineers "pulling needles" on the Bonnet Carré Spillway. The number of bays actually opened, is determined by how much diversion is sought. Looks like this could take a while!

Something that does not seem to occur to many folk is to watch TV stations on line, in the areas affected by flooding. You do not need to know the call letters of the stations. In the Google search engine, type something like this - Memphis TV stations - and voila! Find a legitimate network affiliate such as NBC, CBS, or ABC.

The Mississippi River is big and strong. She has changed courses many times. Oxbow lakes along her length are mute evidence as to where she once flowed.

I highly recommend you read this document, which explains the reason for the Old River Control Structure. It will help you understand the complex relationship of the various control structures.

So when you hear the structures named on TV, you will have an informed understanding of what is happening and why.

Flood control is a delicate balancing act, to keep the Mighty Mississippi River from changing course!

See Also:
Critters 'n Crap
Tick. Tick. Tick.
"Balance of Harms" The Blast at Bird's Point
"Balance of Harms" Morganza Opened

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