2011 Mississippi River Spring Floods

[CajunRed]

_ Scenerio 1: Morganza Spillway Opened at 50%; Bonnet Carre Opened at 100%

http://www.mvn.usace.army.mil/bcarre...1Scenario1.pdf

Scenerio 2: Morganza Spillway Not Opened; Bonnet Carre Opened at 100%

http://www.mvn.usace.army.mil/bcarre...1Scenario2.pdf

Scenerio 3: Morganza Spillway Not Opened; Excess water moved through Old River; Bonnet Carre' Spillway operating at 100% capacity.

http://www.mvn.usace.army.mil/bcarre...1Scenario3.pdf _

It appears to me as a lay person that short of seeing Morganza opened, water levels in the Butte la Rose/Henderson areas and then below to Morgan City would be manageable. Opening Morganza means an extra 5 or so feet of water...on top of the rise that they would have gotten anyway. That's big. That means that homes in those areas that might have been just short of getting water in their homes in 1973 will now have 5 feet or so of stagnant water staying in there were many days.

[Bandwagon King]

_ To start answering one of your questions this morning about the river coming up at Berwick and Morgan City already. The Old river Control structure is operated in such a way to divert 30% of the flow of the Mississippi water into the Atchafalaya river until the flow in the Mississippi River at the Red river landing reaches 1.5 million cfs. (After that the flow is split 50/50). Normally lets say the flow at that point is say 800,000 cfs (just to pick a number) 30% of that is 240,000 to the basin and then to Morgan City. 30% of 1.5 million is 450,000 cfs in the basin almost double 240,000. So right now there is about 450,000 cfs of water to Morgan City without Morganza opening. So the Morganza spillway does not need to be open for the water level to rise at Morgan City.

Secondly, When you get into river delta regions (like below Morgan City) the depth of the channel makes very little difference in the conveyance of water at higher levels. For example, if there would be no flood now, and they decided to go out and dredge the existing channel to a depth of one mile deep, how would that affect the water level of the channel. The answer is no affect at all, why, because every scoop of soil taken out of the bottom of the channel would be replaced by water coming in from the Gulf of Mexico. The only thing you would have been successful in doing is facilitating salt water intrusion. In flow conditions where there is a constant supply of water and the land slope is not great (rivers in Louisiana), the only way to significantly increase conveyance is to make the river wider at the water surface. (sounds like a flood to me).

I have to generate some maps and take some photos to TRY to more fully explain physically what is going on south of Morgan City but I have to go to work. If you have time today get on Bing or Google earth, travel up the west levee from Morgan City and try to find the Wax Lake outlet and the Charenton flood gates on the levee. Follow the Wax Lake outlet to the Gulf and you will see an almost perfect river delta. (About the same thing is happening at the Charenton outlet). Think about what is happening at that delta and try to relate that to what is happening at the confluence of the Atchafalaya and Bayou Shane. _

Thanks for your answers. It is pretty mind boggling for me to think that the water amounts being pushed down stream by this whole thing could make that big of a difference in the swelling of the Atchafalaya as it is occuring now through the locks. I guess being an oilfield guy it would be like explaining that if you have a well flowing on a 10/64th choke with an upstream pressure of 2000 PSI it may allow 1MMCFD through that choke, but if you increase the pressure & volume on the upstream side of that choke it could potentially increase the flow rate by 60 times that amount.

I have also not understood in the past seeing the levee system in Krots Springs & Morgan City how the river would back up into the spillway between Henderson & Butte Larose. the water would also rise between the West Atchafalaya between the west levee & the Rhama levee. This always puzzled me & I thought there were some kind of locks that the core operated to hold the water back or allow it to flow out. Correct me if Iam wrong, but the river, not having any levees between Butte Larose & Cherington allows the river to back up naturally into the tributaries below I-10. Would lthis be correct?

My biggest concern for bridges is the one at Calumet Cut. If the water rises to the side of that bridge, I don't see it maintaining structural integrity.

[biged05]

Bandwagon king,

You are correct about the water backing up to I 10. Once the water in the atch. Gets past the river levees it spreads over the whole basin and when it's too much to drain past morgan city in an efficient manner it starts backing up towards I-10.

Krotz springs, mellville, and simmsport are all in the basin, but they have ring levees that protect the towns, the only problem is they have grown over time and people have settled outside te levees.

igeaux.mobi

[HelmutVII]

_ Thanks for your answers. It is pretty mind boggling for me to think that the water amounts being pushed down stream by this whole thing could make that big of a difference in the swelling of the Atchafalaya as it is occuring now through the locks. I guess being an oilfield guy it would be like explaining that if you have a well flowing on a 10/64th choke with an upstream pressure of 2000 PSI it may allow 1MMCFD through that choke, but if you increase the pressure & volume on the upstream side of that choke it could potentially increase the flow rate by 60 times that amount.

I have also not understood in the past seeing the levee system in Krots Springs & Morgan City how the river would back up into the spillway between Henderson & Butte Larose. the water would also rise between the West Atchafalaya between the west levee & the Rhama levee. This always puzzled me & I thought there were some kind of locks that the core operated to hold the water back or allow it to flow out. Correct me if Iam wrong, but the river, not having any levees between Butte Larose & Cherington allows the river to back up naturally into the tributaries below I-10. Would lthis be correct?

My biggest concern for bridges is the one at Calumet Cut. If the water rises to the side of that bridge, I don't see it maintaining structural integrity. _

Everything in nature is driven by some sort of differential, whether that be a differential in pressure, voltage, temperature magnetic force etc. Water flow is measured in feet of head. This can be easily calculated as energy either kinetic or potential. The calculation of energy is necessary to determine the Energy Grade line which in turn determines direction and type of flow. You can regulate gas flow by regulating differential pressures. The corps of engineers regulates river flow by adjusting water surface elevations. In both cases Bernoulli's Energy equation, mass balances and continuity are used just in different ways.

Rob Perillo on the KATC web site has a good animation that explains "backwater flooding" in the areas you are talking about. It's fairly informative and gives a broad overview of how it works.

Also from that website is this

http://www.katc.com/news/morganza-sp...-corps-option/

It discusses the three alternatives and it comes to the conclusion that Morganza will be opened with the decision coming in the next 24 to 48 hours. The 1.5 cfs threshold at the Red river landing should be reached sometime late Friday or early Saturday.

I am planning to go with a friend of mine to witness history. At the same time we will make a detour to the new Audubon bridge and cross the Mississippi River there.

While the folks in the basin will be harmed, the thing to remember is the basin is indeed that "a basin" and a designated floodway. Should one have an interest in the floodway they should be prepared to accept the fact that, on occasion, they will get flooded. What is about to happen, has been, is and will continue to be the plan of operation of the Atchafalaya FLOODWAY. It is the logical thing to do (almost Vulcan in character, Spock would approve).

[Rebel02]

Question:

It's been pretty obvious that the Morganza would be opened (either partially or completely) for at least a week now. Why not open it up before it is necessary to? Wouldn't this allow for the water to begin flowing south? Wouldn't this potentially eliminate the coming large surge of water through the Atchafalaya?

[biged05]

There won't be a surge of water like people think. They will open it slowly. Also, it is not a sure thing they will open it. As obvious as it may be to some, there is always more to the decision, and the structures are operated on actual data not projections no matter how accurate projections are becoming. I do wish they would make a decision though so everyone can prepare accordingly one way or another.

igeaux.mobi

[NewsCopy]

In the latest agonizing decision along the swollen Mississippi River, federal engineers are close to opening a massive spillway that would protect Baton Rouge and New Orleans but flood hundreds of thousands of acres in Louisiana Cajun country. With that ...

The rest of the story

[Bandwagon King]

_ There won't be a surge of water like people think. They will open it slowly. Also, it is not a sure thing they will open it. As obvious as it may be to some, there is always more to the decision, and the structures are operated on actual data not projections no matter how accurate projections are becoming. I do wish they would make a decision though so everyone can prepare accordingly one way or another.

igeaux.mobi _

With the putting off of opening the gates, is it ok to infer that the worst case scenarios are not going to happen? Also, just because they may have a partial opening of the gates is it possible that their may not be any or very little flooding in some of the lower lying towns that people are concerned about?

I heard good news this evening that the lower river levels are actually going down a little with the opening of the Bonnie Carrie. Does that have a big effect on whether or not the Morganza will be opened & how much?

[HelmutVII]

Well Saturday May 14 is the day

http://www.2theadvocate.com/news/Mor...Saturday-.html

This is now, and will be, history as we watch.

[CajunRed]

If you are talking about THIS area...the worse case scenario is about to happen.

With the putting off of opening the gates, is it ok to infer that the worst case scenarios are not going to happen? Also, just because they may have a partial opening of the gates is it possible that their may not be any or very little flooding in some of the lower lying towns that people are concerned about?

I heard good news this evening that the lower river levels are actually going down a little with the opening of the Bonnie Carrie. Does that have a big effect on whether or not the Morganza will be opened & how much?

igeaux.mobi