2011 Mississippi River Spring Floods

[HelmutVII]

_ Tell me that it wasn't too many Pat O'Brien Hurricanes----- but when you look at the river from Jackson Square the river looks higher than where you stand ---TRUE?????? _

The elevations shown in the attached link show the current stage at about 15.8 with an estimated 17.0 from 5/12 to 5/25 and then still at 16.2 on 6/1. Given that New Orleans elevations run in the single digits, the river is indeed higher than where you stand.

http://www.srh.noaa.gov/lmrfc/?n=ms_extended_forecast

Lets hope the levees hold, because if they break in New Orleans sometimes in the next month, Katrina would look like a cake walk.

[Bandwagon King]

_ The elevations shown in the attached link show the current stage at about 15.8 with an estimated 17.0 from 5/12 to 5/25 and then still at 16.2 on 6/1. Given that New Orleans elevations run in the single digits, the river is indeed higher than where you stand.

http://www.srh.noaa.gov/lmrfc/?n=ms_extended_forecast

Lets hope the levees hold, because if they break in New Orleans sometimes in the next month, Katrina would look like a cake walk. _

I have a question for all you guys. I have been travelling the Atchafalaya all this week going back & forth to a well I've been working on 15 miles South of Morgan City. The sea wall in Morgan City attaches to the river locks in Bayou Bouef & then the sea wall was extended down where the river runs along Avoca Island South of Morgan city where it just stops. The problem as I see it is the river gets really shallow just south of that point with massive sand bars, where Bayou Shane joins the Atchafalaya. This causes the water to go around that sea wall & then back up into Amelia then up to Lake Palour & on into Stephensville. This could even cause Houma, Gibson, Vacherie, Thibodeaux & any low lying areas all the way to the west bank of the Mississippi to concievably flood.

Why not dredge the Atchafalaya out where this point is, to allow for freer flow to the gulf? I mean it's not but 10 miles to the gulf from there. It is easy to see where all the back up is occuring because there are some huge logs getting caught in the eddys at that point right now. I would really appreciate some of your thoughts on this.

[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.