2011 Mississippi River Spring Floods

[CharlieK]

_ I have a question about the old river control structure. I have seen that the estimated flow through just that structure to be as high as 660,0000 CFS. which is like 110% of the capacity. How can something flow at 110% of its capacity. Isn't that like giving 110% on the field?

Is it not possible that they are talking about the OCS combined with the turbine plant? _

The way I understand it: It was designed to flow a certain amount. In other words it can handle a certain amount of water (volume and flow rate) forced through before they feel serious damage will occur. However, there is nothing stopping more water from being forced through it than the original designers thought might happen. This can occur because the head between the two rivers has increased over time. Just like there is nothing stopping the guy running the mud pumps from overpressuring the pipe. Just because it's rated for 10,000 psi or whatever doesn't mean I can't force more through it and break it. In this case God is running the pumps. Maybe a bad analogy but the best I could come up with quickly.

In our case though, the 620,000 cfs orignal design capacity has been increased by adding two more structures so the actual capacity is more like 1.14 million. It appears they have left the 620,000 cfs design limit on the structurs and use the new added capacity as safety factor.

[NewsCopy]

VICKSBURG, Miss. – Eddie Simmons was relieved to hear that the Mississippi River crested slightly lower than expected north of him in Vicksburg, confident his house would survive the flooding that is plaguing many states. Simmons, a retired logger, is ...

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[Bandwagon King]

_ The way I understand it: It was designed to flow a certain amount. In other words it can handle a certain amount of water (volume and flow rate) forced through before they feel serious damage will occur. However, there is nothing stopping more water from being forced through it than the original designers thought might happen. This can occur because the head between the two rivers has increased over time. Just like there is nothing stopping the guy running the mud pumps from overpressuring the pipe. Just because it's rated for 10,000 psi or whatever doesn't mean I can't force more through it and break it. In this case God is running the pumps. Maybe a bad analogy but the best I could come up with quickly.

In our case though, the 620,000 cfs orignal design capacity has been increased by adding two more structures so the actual capacity is more like 1.14 million. It appears they have left the 620,000 cfs design limit on the structurs and use the new added capacity as safety factor. _

I have another question. Is it not possible that by opening the Bonnie Carrie as early as they did thereby taking back pressure away from the river below the control structures that it has caused the Mississipi to flow quite a bit more water down its natural route than was being calculated? That this combined with opening the structure at Morganza is causing the Mississippi to relieve more water than has been calculated & therefore there is less passing through the ORCS than has been calculated? I am not hating on the math I am just saying that the river & the spillway ceratinly are not rising at the levels that they were projected to according to the dates & levels projected. I understand that we're not out of the woods yet, but its been almost 36 hours since the last argument started & Butte Larose is still at 21.00' & Morgan City is is still well below 9.00' as well as Calumet cut.

[sportsfanatic21]

I know zero about any of this (other than what I've read here), but does any of this discussion take into account the "back up" flooding that ive heard mentioned? And if so, how does that work? And what are the projections as to how much and where? Thanks for all the info guys.

igeaux.mobi

[Bandwagon King]

_ I know zero about any of this (other than what I've read ere), but does any of this discussion take into account the "back up" flooding that ive heard mentioned? And if so, how does that work? And what are the projections as to how much and where? Thanks for all the info guys.

igeaux.mobi _

This is my understanding. Back up flooding in Stephensville, Amelia, & Franklin would occur as a natrual result of the Atchafalaya rising in Morgan City to the point it would carry out so much volume that the rive below the levess would not be able to handle the drain off going into the marshes & bays. This would cause a natural bottle neck if you will & cause the water to back up into Bayou Shane, Bayou Beouf, & Lake Palour. This would in turn take the water out of its banks & into the roads & finnally, depending on the level of the river & the amount of flow out would cause water to get into people's houses. The same type of occurence would go on with the Franklin side of the river at Wax lake outlet. That is why paying close attention to the river levels at those outlets is important. I welcome any corrections.

[NewsCopy]

They deserve this for living in a floodplain. That's the easy response to the evacuations of thousands as Louisiana's Cajun country becomes an outlet for Mississippi River waters that would otherwise swamp New Orleans and Baton Rouge. But Karen O'Neill, a ...

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[NewsCopy]

so far,’’ said Joseph Mason, a Louisiana State University professor ... He cautioned that the flooding would slow transportation routes from the Lafayette region – where many oilfield service providers are located – to the Gulf of Mexico.

The rest of the story

[HelmutVII]

_ Ok sounds like the old river structures are flowing 661,000 cfs. Originally there were only two structures (low sill and overbank) which combined were designed for 620,000 cfs. Now there are two more structures (aux. and the hydro plant) that can flow an additonal 520,000 cfs. So we are at 661,000 out of a designed 1.14 million. Does that sound right Helmut et al?

http://www.mvn.usace.army.mil/bcarre...ht-19may11.pdf _

As of May 20, 2011 this is what is happening

ORCS the project design flood is 620,000 cfs flowing through the Power plant, the low sill structure, the over bank structure and the Auxiliary structure. It is Flowing 665,000 CFS or 107% of project flood.

Morganza 600,000 cfs is the project design flood, with 17 bays open it is flowing 114,000 cfs or 19% of project flood

Bonnet Carre 250,000 cfs is the Project Design Flood, with 330 of 350 bays open it is flowing 316,000 cfs or 126% of project design flood.

Operating over the project design flood is not a problem. If they came to me and asked me to design a spillway I would have many questions but two of them would be what is the MINIMUM (Project Design Flood) we need to pass and what is my design factor( I would expect that to be about 1.25 to 1.5). No way I'm going to design something like that with no head room. Because when you need something like this you really really really need it and it better work and not be undersized. Looking at the Bonnet Carre Numbers I suspect their design factor was about 1.35 to 1.4.

[Turbine]

Just a sidenote on the flood of 1927

Because of all the turmoil surrounding the flood of 27, UL was a safe haven and and UL's baseball season was cut short.

Baseball did not return till 11 years had passed.


igeaux.mobi

[HelmutVII]

_ I know zero about any of this (other than what I've read here), but does any of this discussion take into account the "back up" flooding that ive heard mentioned? And if so, how does that work? And what are the projections as to how much and where? Thanks for all the info guys.

igeaux.mobi _

Backwater flooding is flooding that approaches you from the downstream direction. This happens when the traditional downstream of the river you are on has a higher water level then the traditional upstream locations (traditional upstream and downstream are reversed). This can happen when two rivers are in confluence and one is is a flood state while the other is not. It can also happen with storm surge (the most common form of flooding on the coast). Both cases cause water to flow opposite to the traditional flow direction. Backwater flooding is common in this part of the country because the land is relatively flat.

Given the unpredictability of this flood it pretty hard to tell what the backwater flooding will be. I do suspect that there will be some.

they are now lowering the predicted flood at Butte La rose to 24.5 instead of 27.0. It's still a flood but not as bad. Probably all the new camps will be OK. I know none of the elevations we set in the area were less than 25.0 with most at 27.0. Looks like the older camps will have 3 to 4 feet of water. After this, there won't be any less than elevation 24.0 (depending on where you are) .

[HelmutVII]

_ I am not hating on the math I am just saying that the river & the spillway ceratinly are not rising at the levels that they were projected to according to the dates & levels projected. I understand that we're not out of the woods yet, but its been almost 36 hours since the last argument started & Butte Larose is still at 21.00' & Morgan City is is still well below 9.00' as well as Calumet cut. _

Once the Morganza spillway was opened it was predestined that any level seen downstream (on the Mississippi) of that was not going to get higher and all levels downstream were soon to be labeled as "Cresting" or "Crested". The intention was to operate Morganza so that downstream levels (on the Mississippi) did not rise. As it turns out they are able to do this (so far) with only 17 bays open.

If you go here

http://www.mvn.usace.army.mil/bcarre/morganza.asp

you will see that when they opened the 11 bays the flow rate actually went down because the downstream water elevation had risen reducing the delta H across the structure. As the water levels in the basin rise it will continue to reduce the delta H necessitating more bays to be opened.

Opening Bonnet Carre did the same thing for points downstream of it.

[Bandwagon King]

_ Once the Morganza spillway was opened it was predestined that any level seen downstream (on the Mississippi) of that was not going to get higher and all levels downstream were soon to be labeled as "Cresting" or "Crested". The intention was to operate Morganza so that downstream levels (on the Mississippi) did not rise. As it turns out they are able to do this (so far) with only 17 bays open.

If you go here

http://www.mvn.usace.army.mil/bcarre/morganza.asp

you will see that when they opened the 11 bays the flow rate actually went down because the downstream water elevation had risen reducing the delta H across the structure. As the water levels in the basin rise it will continue to reduce the delta H necessitating more bays to be opened.

Opening Bonnet Carre did the same thing for points downstream of it. _

Not as long as the river downstream on the Mississippi can handle the flow. As long as the Bonnie Carrie remains open, the river will continue to seek the point of least resistance which is straight down stream. The river doesn't know as it goes straight down stream whether it will be diverted to the spillway or down the river channel. The river down stream has begun to outrun the river upstream therefore opening any more bays should be unnecessary. That is what the charts were saying when the river crested @ Knox landing & St. francisville before it crested at Natchez.

The only thing I was worried about in making my call was how much water was strored between Greenville & Vicksburg. I saw the river crested in Vicksburg, but I knew until I saw it make a turn downward there was potential for exteneded enough high flow rate to cause the bays in the basin to have to be open for an extended period of like four weeks. This would cause some problems & could potentially hang us out to dry in a major weather event.

As I have seen the turn downward in Vicksburg I am most confident in saying the river will not see 25' in Butte Larose & won't see 10.5' in Morgan City. I am looking for a crest in the neighborhood of 23.5-24.25 feet in Larose, which is high & it will stay pretty high for about three weeks. I am also looking for the river in Morgan City to top out between 9.80' - 10.25'. This should not cause any flooding of a serious nature at all. I mean if you live in a house 3' from Bayou Boeuf or Bayou Shane on a 6" slab, you may get water in your house, but anyone who has sense enough to have their house at a reasonable base flood elevation should fair fine. MAJOR weather events not withstanding.