2011 Mississippi River Spring Floods

[HelmutVII]

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.

[CajunRed]

Thanks for the info.

(...and thanks for not explaining HGL. I was having an anxiety attack.) :-)

igeaux.mobi

[HelmutVII]

_ Thanks for the info.

(...and thanks for not explaining HGL. I was having an anxiety attack.) :-)

igeaux.mobi _

No problem I was not looking to do it either on a Monday morning.

If anybody wants to study this further I would suggest reading the Bible of this topic "Open-Channel Hydraulics" by Dr. Ven Te Chow (sometimes called the Chow book). It is sometimes described as the best text book every written. (Probably by those that did not take a college level course with it.)

The answer to most of the questions posed by many people is "It depends". Because there are so many variables involved in situations like this it is very difficult to make any prediction as to what is going to happen where and when. Many are asking what the affect on the Bayou Teche or Vermilion Rivers. Since the watersheds for the Teche and Vermilion to not communicate with the Mississippi or the Achafalaya because of the levies, the answer is - it will have no affect UNLESS the levies break. Then the affect that would happen would depend on where the break is and what the difference in the levels of the water between the watersheds (amongst others).

To my knowledge, the only time there was any communication between the watersheds was in the 1927 flood. One of the worst floods in the Lafayette area (Vermilion watershed) was in August 1940 which was a rain event when 27.33 inches was recorded from August 6 to 9 1940. This was a localized rainfall event and not an upstream flooding event.

[RaginCajun77]

Live Streaming from the Bonnet Carre spillway:

http://www.ustream.tv/channel/bonnet-carre

[Boomer]

_ Live Streaming from the Bonnet Carre spillway:

http://www.ustream.tv/channel/bonnet-carre _

Late Monday night---What is the latest????? I feel like i have a direct contact with the Weather Channel!! Will they open the Morganza Deal??? Are things better---I know that no rain sure helps!!!!

[Boomer]

How do levees finally give in---there was talk of the ones around LSUBR being vulnerable from the stress or dampness/wetness???? Who makes the final decision as to whether to blow a portion of a levee and where----This is so interesting and your knowledge so great of the situation!!! Thanks for your time and effort---Had I not changed my major muchos tiempos and after spending 13 straight years in college ---NO MAS!!!! Nice way to make a living!!!

[CajunRed]

The request to allow Morganza to be opened has been made. Officials anticipate that the answer will be YES...with the actual opening to occur on Thursday.


igeaux.mobi

[HelmutVII]

From "the Advocate" on Tuesday May 10

http://www.2theadvocate.com/news/121535339.html

Kind of like waiting for a Hurricane except you know exactly where it's going to land. you know it's going to bad but not how bad.

[HelmutVII]

_ How do levees finally give in---there was talk of the ones around LSUBR being vulnerable from the stress or dampness/wetness????

Amongst other ways they are over topped or a sand boil develops on the land side. The sand boil, is formed by the water finding a path in the ground under the levee to the land side. This creates flowing water that washes out a larger path. They usually ring the sand boil with sand bags up to a level where the water stops flowing which can be as high as the level of the water in the river.

The bank can be eroded away on the outside of a curve in the river too.

[CajunRed]

Scary stuff, Helmut. Thanks again for your comments and updates. That degree you worked so hard for many years ago was indeed worth it.

From "the Advocate" on Tuesday May 10

http://www.2theadvocate.com/news/121535339.html

Kind of like waiting for a Hurricane except you know exactly where it's going to land. you know it's going to bad but not how bad.

igeaux.mobi

[Zeebart21]

_ The request to allow Morganza to be opened has been made. Officials anticipate that the answer will be YES...with the actual opening to occur on Thursday.


igeaux.mobi _

WOW! I will have to cross the basin when I head home Friday...that will be something I have never seen before...

I would imagine we will be seeing deer, bear, and other critters in some awfully odd places.

Beware.

Z

[VObserver]

Z,

I crossed the basin the first week it opened, which happened to coincide with the 1973 opening of Morganza. If this one is like that, you will not believe the water level..