2011 Mississippi River Spring Floods

[biged05]

Yep, just as I figured. Helmut took the lead on all the technical stuff and did such a better job than me lol . But that's ok I'm absorbing it all in too!

igeaux.mobi

[Bandwagon King]

_ The paper does indeed give a brief synopsis of how they came upon the different flow rates to determine what a project design flood is at various stations of the River. However, they still define a Project Design Flood in CFS and not stage.

What one needs to remember is that any given stage at a SINGLE point along a river DOES NOT define what the flow rate is. What defines the flow rate is the DIFFERENCE in stage between two or more stations of a river AND the distance between those stations. It has everything to do with the slope of the hydraulic grade line and the cross sectional area of the channel (that is the cross sectional area of the channel until it gets to areas affected by tides).

It is entirely possible to have a stage of lets say 50.0 at a given point in a river and have, lets say 150,000 cfs flow rate during one event and then have a stage of say 50.5 at the same point and still have the same flow rate of 150,000 cfs. The flow rate at any given point is ENTIRELY dependent on the relative stage of the points upstream AND downstream.

The TOP of the water is literally falling down the river and how fast it falls depends on the relative difference in the top of the water from one point to another. (it's hard to explain the concept because common sense asks how can something fall when it's on the ground).

It took me a long time to fully comprehend this concept, but once I did, it made perfect sense. To this day, I will stand on a drainage structure (especially one that I designed) and just watch the water (even in the rain). Really satisfying to watch it work as designed. It also helps me to understand the nature of the beast. _

Once again, thanks for this reference, & I really do appreciate the engineering involved in the study & the design of this massive project as well as the hard work that was done to make our flood control system what it is today. I do see that flow rate estimates are absolutely important to the design of these structures as well as the projected river crests & flood stage warning systems.

However, flow rate estimates are just that, estimates. While I find it pretty wild to know that there are people that can figure these rates out & computer models that can warn people weeks ahead of time of possible danger & give them time to make proper preparations, I also understand it is impossible to take every variable into account that causes the river to flood at one stage in the river & not another. I know that by reading the information on the link you just sent me, the NWS & the Corps are bound by moral authroity to give highest probable & worst case scenarios. In this particular instance we are having an anomally of river flooding through country that is in a drought situation. this is making a huge difference in the amount of water being discharged into the GOM & I would assume making it very difficult to calculate rover flow rate accurately. That is why sooner or later someone is going to have to say hey guess what, the water on the Mississippi is going down up & down the river. I don't think it's going to flood after all.

Call me crazy, but this is one of those times the government has actually done something right & the results are better than expected.

[biged05]

Man, I wouldn't say it's not going to flood. It may not go outside the levees into protected areas down here, but this is definitely a flood. LOL

igeaux.mobi

[Bandwagon King]

_ Man, I wouldn't say it's not going to flood. It may not go outside the levees into protected areas down here, but this is definitely a flood. LOL

igeaux.mobi _

I didn't mean to make it sound trivial, but I am talking about the local area of the lower Mississippi/ Atchafalaya. The river cresting at Vicksburg & Natchez several days early & 1-2' lower is huge for us.

[HelmutVII]

Only Hydrologic models take into consideration antecedent precipitation indexes. Hydraulic models do not and if they do, they probably don't handle it very well.

In any case, the Morganza water has not yet reached Morgan City, we will see what happens. In the mean time the basin is indeed acting as a basin (a hydraulic capacitance) and is doing a very good job.

You are correct in saying that the ethical thing to do is to predict the worst and hope it does not happen. Hurricane forecasters are in the same pickle. To do contrary would be a disservice to the public and border on negligence.

[HelmutVII]

_ I'll have my life vest on in the Mississippi this weekend patrolling around Angola, but I sure as hell ain't jumping in the water. I'll make sure to take pictures to post on here.


igeaux.mobi _

Please do post pics. I am planning on going to Morganza this weekend and will do the same.

I spoke to my brother this evening and he has not gone to Bonnet Carre yet but he told me they structure is working at 105% capacity WITHOUT all the gates open. He said it's really humming and is thinking of going to the structure this weekend. He also said the water is cascading out of the spillway just south of the interstate at the tree line.

He also said that none of the fresh water diversion structures are in operation. Their capacity is so small that it would make little difference. Also, the delta H on the structure would be so big that it would probably damage the structure if it was opened. It would also kill the oyster beds that were just reseeded after the BP mess last year. To open them up now would just about put an end to all oyster fishing in the area.

[jumboragncajun]

I do know that levels in a pipe of known or uniform cross sectional area and length and known fluid properties can tell you everything you need to know. That is NOT open-channel flow. Many many other variables that had been repeatedly mentioned by myself, big ed, and others that are obviously experienced and informed , contribute to create the levels......at a single particular location... why is that so effin hard to comprehend. It's just like you to turn the convo into something to a subj you might know about. ie oilfield.

When I say I don't need to study charts because I understand the science that makes the effin charts.

Can I tell you what the water level in Butte LaRose will be? No. I never said I could. There are too many unknown variables for ME to determine that. If you give me all the unknowns, it can easily be determined. All I was saying is that your approach is flat out wrong. And normally, I listen or read your spewed conjured ideas that you claim to be hard facts, and don't think a thing about it. But you get on a keyboard and start telling people with 30+ yrs exp in this field that they are wrong because you read a chart, I'm just politely telling you that your reasoning/basis is wrong. That's it. Your too dense to have a conversation with. Frankly, you lost all credibility with me in an earlier post that clearly showed your lack understanding of how this basin system works. Not worth the time arguing after that. If you asked questions, that'd be one thing, plenty here have....but you adamantly proclaim....and then condemn..... On this topic and any other.



igeaux.mobi

[phideaux]

When I say I don't need to study charts because I understand the science that makes the effin charts.
igeaux.mobi _

Rack him!

[Bandwagon King]

_ Ok this is going to be a ling one and I'm typing on my phone also hopefully I don't Repeat anything b/c I know other posts are coming in.

King,

The determination of how many gates to open is based on flow. Is flow and stage related? Yes but it's all about flow. Let's see if I can show you why in my opinion. A river is dynamic we all know that it changes in width and depth therefore the height needed to pass the water (flowline) changes. We are actually looking at some sections of river now where it appears the river bottom may actually be rising and it's not the usual shoaling in. We use flow as indicated by the project flood diagram. Here is one example of why flow is used. When we opened morganza the head on the gates were very high...let's say 20' just for discussion. Now when they opened the first gate there was about 10,000 cfs flowing thru it. Then a second was open and it was about the same thru that one. Now we've opened more gates the head has been reduced with water levels on the opposite side getting higher, therefore the flow thru each gate has been reduced. So what they do is take a measurement upstream and one downstream of the structure to make sure the flow does not exceed 1.5 mil cfs. If they did not open any more gates as the water levels on each side equalized then we would force more than 1.5 mil cfs thru the system below morganza and yes in turn make the water levels rise. But it is based on a total cfs. I hope that part is a little more clear now. Can we adjust downstream levels with the gates or in the case of bonne carre bays? Yes they are doing that now. They are trying to keep the river at the carrolton gate around 17'. So they have opened more bays there to allow less flow past new Orleans so the coast guard can keep the channel open. Can it handle the 1.25 mil south of bonne carre? Yes but to keep everything open and to try and affect industry the least we are passing more thru bonnet carre.

Now as far as Morgan city and calumet are concerned, they are not keeping up. How do I know the? 1) I've been watching water levels in the basin for a while now and today watched the water along the west basin levee again. 2) it can't handle water that is coming in but has not reached there yet. The water from morganza as of this morning had not made it to I-10 yet. So the river has yet to be affected by the water from morganza, much less the river being affected in Morgan city and calumet. Jumbo's thinking does not sound off. I don't really have the time to look over all the charts and information we have out there and make better points, just too damn busy with the water itself. I'll be honest and say from the new predictions and other things I'm seeing the crest predictions may be a little high, but I'm not going on just the charts your looking at. Let's hope that's true but I wouldn't count on it. The next few days will start to tell the story.

I know I've forgot some of the things that I wanted to say, but my mind is running in too many directions right now.

igeaux.mobi _

Once again I've misspoken. When I say the river at Morgan City & Calumet are handling it just fine, from the numbers I am seeing that between the shear volume the basin can handle plus the amount of water passing through Morgan City & Calumet, plus the fact that there is a lot of water being absorbed by the vegetation & the groundnd it looks very good for Butte Larose, Amelia, & Stephensville right now. I am also very encouraged that the Corps is working this thing in such a coordinated way, looking at all the data to make its decisions. You can see the tools such as satellite imagery, computer modelling, electronic readings up to the minute, & a host of other tools helping you guys in your information gathering & decision making.

[Bandwagon King]

_ Mathematically Q (quantity) = V (velocity) x A (area). The problem in large rivers (like the Mississippi) is how do you measure velocity? It can vary substantially from one point to another at any given section. So what you have to do is take velocity measurements at many points to get a velocity profile at a give section. The next thing to do is to determine the area. The problem is scour, how much and how is it affecting the cross section of the river. So what they are doing is making and ESTIMATE of flow rate given an ESTIMATE of the cross sectional area of the channel and using the velocity profile. This is not an exact science and it borders on an art.

If the slope of the hydraulic grade line is high then the velocity is high and will produce a higher flow rate for a given area. If the cross section is scoured then the area is greater and can also produce a higher flow rate (again in those areas not affected by tide ---generally those areas were the bottom of the channel is greater than 0.00 msl) _

This is exactly what I have been saying. The flow rate estimates are very important & are the basis for projecting flood stages as far as I would know. The river levels themselves are either the confirmation or contradiction to those flow rate estimates. The math is theory the water level is fact.