THE OLD RIVER CONTROL STRUCTURE - SIMMESPORT, LOUISIANA

Click on the map for the larger view.

The map above shows the locations of the Old River Control Structure and the Morganza Floodway.



Above is an aerial view of the Old River Control Structure. Image from Wikipedia.



Shown above is the Morganza Floodway with one bay open. As of now, 11 bays are open. The US Corps of Engineers expects to open 31 of the 125 bays in the floodway.

In the comments to this post at Wounded Bird, Paul (A.) asks a question and references an article in the New Yorker by John McPhee, written in 1987:

Is the opening of the floodway to the Atchafalaya the beginning of the end for Baton Rouge and New Orleans?

In response, I wrote a long comment which I decided to edit and use in a post.

Paul (A.), I read the article by McPhee when it came out in 1987. He writes about the Old River Control Structure at Simmesport, north of the Morganza Floodway. The Mississippi River wants to take the most direct route to the Gulf of Mexico, which is through the Atchafalaya River basin. If that happened vast areas would be flooded, and the Baton Rouge and New Orleans ports would be finished as major ports. The passage of large ships between NO and north of BR would cease, because the Mississippi River would not have enough water to support major shipping.

The Old River Control Structure was built to direct the major flow to the Mississippi River rather than the Atchafalaya River at roughly 70%/30%. McPhee and others think that the structure could fail and the river eventually have its way, and they may be right. However, since the article was written, an additional structure was added to the ORCS complex, which serves as further reinforcement to prevent a failure. We shall see.

The purpose of the Morganza Floodway is entirely different. It's built to send water into the Atchafalaya River basin to protect Baton Rouge, New Orleans, and the refineries and chemical plants along the Mississippi between Baton Rouge and New Orleans in the event the Mississippi reaches flood stage, which it has now. The flooding of the Atchafalaya River basin is to lower the level of water in the Mississippi River to prevent overtopping of the levees and to reduce the intense pressure from the high waters in the river, to prevent breaches. Either event could have catastrophic consequences.

I hope this helps.

Posted with the caveat that I am neither a flood engineer nor an expert on flooding.

MORGANZA FLOODWAY WITH ONE GATE OPEN

From MSNBCNews.

MAP OF AREA THAT MAY BE FLOODED BY OPENING MORGANZA FLOODWAY

Click on the map for the enlarged view, and then click again for magnification. For those of you who may be concerned about us, you will see from the map that we are not in a zone which will be flooded when the Morganza Floodway is opened tomorrow. Thibodaux is just south of the center of the map.

The floodway will be opened to send more water down the Atchafalaya River basin in order to lower the volume of water in the Mississippi River from above Baton Rouge and New Orleans to prevent the river from overtopping the levees and to relieve pressure on the levees to prevent breaches which would flood a much larger number of people than those who will be flooded by opening the floodway. I feel sad for those who will be inundated, but even if the Morganza Spillway gates were not opened, certain areas near the Atchafalaya River would flood, because of water spilling over the top of the floodway gates. Water is lapping at the gates and leaking through them already.

I hope what I've written makes sense. Thank you for your concern.

THE THREAT OF THE RISING MISSISSIPPI RIVER

From NOLA.com:

Louisianians haven't lived though this dangerous a threat from the in more than a generation -- and that's an emergency that compels officials and residents alike to be prepared. It also warrants a full emergency declaration from the federal government.

Thousands of people across South Louisiana were evaluating their risk and making preparations Monday, as the Army Corps of Engineers continued taking measures to relieve pressure on river levees and minimize the expected flooding.

Crews began opening the Bonnet Carre Spillway in St. Charles Parish. Communities in the Atchafalaya Basin placed sand bags and alerted residents of possible evacuations if the Morganza Spillway is opened north of Baton Rouge. And Gov. Bobby Jindal directed hundreds of Louisiana National Guard troops to assist in those efforts and to be ready to help victims of flooding.

Corps of Engineers maps forecast flooding in large areas of St. Mary, Assumption, Terrebonne and other South Louisiana parishes if Morganza is opened for the first time since 1973. The corps still was estimating Monday how many homes and other structures may flood. But residents shouldn't have to wait for maps to make preparations. As Gov. Bobby Jindal warned: "If you got wet in 1973, you'll get wet this time. If you nearly got wet in 1973, you'll probably get wet this time."

As Gilda Radner said, "It's always something." Especially lately. One disaster follows another.



The Mississippi River at Rivertown in Kenner, Louisiana

If you turn around and face the other way toward the land, you are looking down, and you see very quickly that without the levee Rivertown and many other areas along the river would be flooded. We walked up a good many steps to get to the top of the levee.



The ship rides high, and the ships will ride higher as the river crests further south. Pray that the levees hold, and pray for the people who will be flooded by the opening of the Bonnet Carré Spillway and the Morganza Floodway.

UPDATE: The opening of the Bonnet Carré Spillway will not cause homes to flood, because the water will go into Lake Pontchartrain and the Rigolets, but it will, very likely, mess up certain of the oyster beds again. The poor oyster fishers have had a rough time of it what with the BP gusher and now the high river.