2011 Mississippi River Spring Floods

[Bandwagon King]

_ The conditions that are expected are an "upstream control" not a "downstream control" event. The level of the water in these areas is mostly controlled tide. Since there is water in the channels already, the excess capacity is that area of conveyance ABOVE the current water levels. (If a glass is half full then the excess capacity of the glass is the top half of the glass). Since the water level upstream is higher already, the increased conveyance would happen at a higher level. So anything that is at or below the current channel bottom levels would have little affect on the conveyance. (making the channel deeper is not the answer making the channel wider is, make a half full glass wider at the top).

Also since the water surface, is higher the slope of the water surface is higher causing an increase in velocity. If there is any debris in the river I would suspect that it would soon be flushed out. Not to say that it would not be replaced by more debris from upstream.

The thing that controls water flow in an open channel is not necessarily the slope of the bottom of the channel but the slope of the top of the water. (more specifically the slope of the Hydraulic Grade Line HGL. don't ask me to explain that in a message board as it is a 400 level course in Civil Engineering schools).

Bottom line, once the water gets that close to the Gulf (water surface elevation of zero) the water will seek that level through the line of least resistance (water is lazy) which is tide dependent not channel bottom dependent at this location.

That's the best I can do maybe somebody else can make a stab at a better explaination. _

If the volume of water flowing down from a higher elevation to a lower elevation was allowed to be relieved earlier by allowing the hydraulic force of the lower elevation to become 0 in counterforce, wouldn't that go a long way in allowing the upper level hydraulic force to relieve it's stress sooner & thereby allow for an earlier lower crest in river levels? All I know is south of any levees & within 5 miles of the mouth of the Atchafalaya river at the GOM the river has risen some 4' above normal levels. This is not simply due to above normal tides. If you drain 6" of water down a 3" pipe & you continue to do this more than the 3" pipe can handle the 6" pipe will become backed up even if your draining it straight down. I know that the Atchafalaya is no more than 1-2' deep for almost the whole width of the river & has a very shallow narrow ship channel, although it is twice as wide below Bayou Shane, as it is above Bayou Shane. This is helping cause the Atchafalaya to rise in Berwick & Morgan City right now, even though the Atchafalaya is really meant to handle the watershed from the Red & Ouachita rivers.

If the river rises in Berwick until the hydraulic force up river causes it to flow hard enough to push that water out, it causes Bayou Shane to back flow into Amelia & even up to Stephensville, thereby exasterbating an already dangerous situation.

Please correct me if I am wrong. But if not so, why are they going to sink a giant barge across Bayou Shane to try to keep lower Terrebonne parish from flooding? I am just saying that if you add up all the little things that could be done together, they add up to possible avoidance of a huge freaking mess.

I really believe that someone has done cost analysis of letting this type of occurance happen avery 40 years & finds it to be more cost effective to allow several thousand people to be totally wiped out, than to take a completely comprehensive view of flood control & hurricane protection.

No offense to the parties opining here. I have great respect for the corps of engineers.

[CajunRed]

When I first saw the Corps' Inundation Map, I thought I was misinterpreting what it was saying.as it was showing up to 15 feet in Henderson Lake ABOVE current levels.

Unfortunately, my interpretation was correct. The Corps' latest prediction for Butte la Rose is 29 feet.which will top the small interior levees that follow along the river. That means water levels in Henderson Lake will be only 4 or 5 feet below I-10. And many homes and camps along eithe road to Butte la Rose will be well under water. Even the rest stop facilities at I-10 will be flooded.

Guys.that is downright scary.

Thanks for the map. If I am reading correctly, it is showing Henderson Lake in "green".which is 10 to 15 feet above current levels. Ouch! That would be very scary.

igeaux.mobi

igeaux.mobi

[HelmutVII]

_
I really believe that someone has done cost analysis of letting this type of occurance happen avery 40 years & finds it to be more cost effective to allow several thousand people to be totally wiped out, than to take a completely comprehensive view of flood control & hurricane protection.

No offense to the parties opining here. I have great respect for the corps of engineers.

Since a picture is worth 1000 words I will need to shoot some photographs to show you how it works. I will try to do that by tomorrow. Once you see the photos I think you will understand. Once I post the photos, I will then be able to explain a "thought experiment" to you.

[Boomer]

_ Since a picture is worth 1000 words I will need to shoot some photographs to show you how it works. I will try to do that by tomorrow. Once you see the photos I think you will understand. Once I post the photos, I will then be able to explain a "thought experiment" to you. _

How is the book coming along---I am serious!!!!!!! Make sure that T-Bine keeps all these forcasts --etc!!!!

[HelmutVII]

_ How is the book coming along---I am serious!!!!!!! Make sure that T-Bine keeps all these forcasts --etc!!!! _

I don't know about a book, but I'm thinking Randy Newman might be writing another song.

[cjr3888]

These are pictures I took at the Bayou Benoit Landing from the top of the levee. First picture is Sunday (low tide) and the next two are Wednesday (high tide). If we get the amount of water projected, it might reach the top but probably won't. I saw government trucks (USGS) parked out there today, which is never a good sign. At least they parks on the other side of the levee so the fisherman could park at the landing.

[Cajunbander]

So, where would be a good place to take pictures of the high water in the Atchafalaya (I'm amazed I spelled that right) Basin? I'm not familiar with that side of Lafayette, I'm more familiar with Lafayette going west.

[CajunRed]

They are talking about levels that are FIFTEEN feet above what you are seeing here, so this is not even close to representing what we will see about two weeks from now.

These are pictures I took at the Bayou Benoit Landing from the top of the levee. First picture is Sunday (low tide) and the next two are Wednesday (high tide). If we get the amount of water projected, it might reach the top but probably won't. I saw government trucks (USGS) parked out there today, which is never a good sign. At least they parks on the other side of the levee so the fisherman could park at the landing.

igeaux.mobi

[HelmutVII]

_ If the river rises in Berwick until the hydraulic force up river causes it to flow hard enough to push that water out, it causes Bayou Shane to back flow into Amelia & even up to Stephensville, thereby exasterbating an already dangerous situation.

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.

[Big Buds]

Is there any possibility of the flood waters cresting I-10?

[awadelewis]

_ Is there any possibility of the flood waters cresting I-10? _

Current worst-case projections say it won't with the crest being about 4 to 6 feet below the level of the Basin Bridge.

[Big Buds]

_ Current worst-case projections say it won't with the crest being about 4 to 6 feet below the level of the Basin Bridge. _

Does that change the structural integrity of the bridge? Having that much water flowing beneath it.

[Chop]

What would happen in a worst case if they opened the Morganza and had mechanical problems and could not close it?

[MetryCajun]

_ What would happen in a worst case if they opened the Morganza and had mechanical problems and could not close it? _

I do not think that would be a problem. These are not automated gates. They are manually pulled up by a crane. Also, the river will receed at some point this summer where water would not flow through the gates even if they were left opened.

[MetryCajun]

Here is a good reference story on the Mississippi River and the River Control Structure.

http://americaswetlandresources.com/.erControl.html