2019 Mississippi River

[mahtoo]

1973 was a significant event. They almost lost a wing wall for the low sill structure. Follow the link for a brief discussion of the ORCS Morganza complex.

http://www.americaswetlandresources....erControl.html

I drove through the Morganza complex in 2011. It was scary, the Mississippi river was wide, very very very wide. I would suspect that one day the Atchafalaya will eventually capture the Mississippi river one day as it is the shortest route to the Gulf of Mexico. (The energy grade line is steeper down the Atchafalaya than the Mississippi and the only thing in it's way is the ORCS)

this is a US Corps of Engineers link

https://www.mvn.usace.army.mil/Porta...olBrochure.pdf

The south east (south end of the structure on the river side) wing wall was lost.

[mahtoo]

While that is currently the plan, Tennessee and Arkansas are continuing to get hammered with rain and have severe flooding now. Also the Miss River has silted in an incredible 30' between ORCS and BR since 2011.

I'd be shocked if they don't open all flood control structures in some fashion.

I am curious as to where the 30' siltation figure comes from.

[cajun4life]

While the silt is there, the general rule of thumb is that for every foot the water level rises a foot of the river bed is scoured and transported downstream. The Ohio river basin has had extreme rainfall this entire winter. This could be a repeat of 2011 or 1973. 1973 is when they almost lost the ORCS. They were throwing cars, railroad cars and BFR in the hole on the side of the structure to keep from losing it.

From what I have read, the rate of flow is not swift enough above BR to scour the river. The Atchafalaya doesn’t have this problem as it has a relatively straight path to the GOM.

Just from the looks of what’s happening upriver (Midwest) I think we are in trouble if we continue to have high precipitation throughout the middle and lower miss river basin.

[cajun4life]

I am curious as to where the 30' siltation figure comes from.

https://www.workboat.com/news/coasta...course-change/

[cajun4life]

https://www.workboat.com/news/coasta...course-change/

I am curious as to where the 30' siltation figure comes from.

[mahtoo]

https://www.workboat.com/news/coasta...course-change/

Thanks. I'll read up on that.

[cajun4life]

Thanks. I'll read up on that.

Some is far fetched, but possible, I guess.

[mahtoo]

Some is far fetched, but possible, I guess.

Agree. I'm going to try to get some verification on what is stated in the article.

[angeleast]

From what I have read, the rate of flow is not swift enough above BR to scour the river. The Atchafalaya doesn’t have this problem as it has a relatively straight path to the GOM.

Just from the looks of what’s happening upriver (Midwest) I think we are in trouble if we continue to have high precipitation throughout the middle and lower miss river basin.

what is worst case scenario for course change .. which cities would be in danger

[HelmutVII]

From what I have read, the rate of flow is not swift enough above BR to scour the river. The Atchafalaya doesn't have this problem as it has a relatively straight path to the GOM.

Just from the looks of what's happening upriver (Midwest) I think we are in trouble if we continue to have high precipitation throughout the middle and lower miss river basin.

Correct, BUT once the lower reaches of the Mississippi river scour, the scour will work its way up stream. There could be a significant delta building event at the Mississippi river this year. Given the extreme wet weather that the upper Mississippi and Ohio river basins have had this winter any additional rainfall will just make the situation worse as the antecedent precipitation index is quite high righ now.

The Atchafalaya does not have the silt problems because the water supply is from the ORCS. The ORCS takes water from the upper levels of the Mississippi river. Most of the silt load is at the bottom of the river. (The Atchafalaya water is decant water from the Mississippi).

Going back in time we discover that the Atchafalaya was, at one time, the Mississippi river. The old Mississippi river deposited silt as it reached the Gulf of Mexico and built land until it made that course longer than its current course. That portion of Louisiana below Baton Rouge had not been formed yet because the river had not changed its course. In engineering terms the Atchafalaya is the "OLD RIVER" and that is why they call it the Old River Control Structure. From a hydraulic standpoint the Atchafalaya is a DISTRIBUTARY of the Mississippi river.

Going Further back in time the Bayou Teche was the course of the Mississippi River and the Vermilion River was a distributary of the then Mississippi river when it occupied the route of the Bayou Teche.

Go here https://www.nrcs.usda.gov/Internet/F.../lafayette.pdf

and advance to page 13 of the PDF document and it will provide a very thorough discussion of the land forms of Lafayette Parish. Basically from the Coteau Ridge east are alluvial deposits of the Mississippi River and from the Coteau Ridge west are alluvial deposits of the Red River (believe it or not). Both depositions are from Pleistocene era which were later covered with loesse (wind borne) deposits. Examination of old quad maps of eastern Lafayette parish shows evidence of ancient Ox Bows and river scars The soil maps in the link above also indicate ancient OX Bows and river scars. These scars and ox bows are remnants of the ancient (Pleistocene era) locations of the Mississippi River.

One of the triggers for opening the Morganza spil way is the velocity of the water in the river. As the water gets higher and the velocity gets above 2 feet per second the scour gets to be aggressive. When the water gets up to the river side of the levees the levees start to scour (the grass rolls up into balls). In order to prevent that from happening they open the Morganza spill way.

[RaginCajun77]

From what I gather Morgan City and surrounding cities would be lost. It is highly likely that bridges that cross the Atchafalaya would be lost as well based on my reading. It would be a catastrophic event, pipelines lost, economy would suffer.

[angeleast]

From what I gather Morgan City and surrounding cities would be lost. It is highly likely that bridges that cross the Atchafalaya would be lost as well based on my reading. It would be a catastrophic event, pipelines lost, economy would suffer.

Freaking nightmare ... the displaced people would be unimaginable