2019 Mississippi River

[Duckster]

If the Corps and the State will get going on adding more Mississippi River diversions flowing at will during high water south of NOLA into the marshes and let at least a small amount flow down Bayou Lafouche maybe the sediment will get put to good use. Try to mimic pre 1927 without putting human lives at risk. And if Morganza is not opening why not divert more flow into the Atchfalaya R. then kicking more into the Teche-Vermilion diversion during high waters?

[HelmutVII]

If the Corps and the State will get going on adding more Mississippi River diversions flowing at will during high water south of NOLA into the marshes and let at least a small amount flow down Bayou Lafouche maybe the sediment will get put to good use. Try to mimic pre 1927 without putting human lives at risk. And if Morganza is not opening why not divert more flow into the Atchfalaya R. then kicking more into the Teche-Vermilion diversion during high waters?

There is the Caernarvon diversion just downstream of New Orleans

https://waterdata.usgs.gov/usa/nwis/...95124089542100

But they pass only about 400 to 600 cfs. Not much but there has been some delta formation at the outffall. They could pass more but you would have to ask the oyster fishermen why. Just sayin.

Subsidence in that area is in the order of about 1.5 cm per year. (1 foot in twenty years) So they need to make up that amount just to stay even. Kind of hard to do that with 400 to 600 cfs. of decant water from the Mississippi.

The Wax Lake outlet and the Atachafalaya have really nice delta formations. The source is decant water from the Mississippi at Morganza. the one to the west is Wax Lake outlet and the one to the right is the Atchafalaya.

[Cajunfanatico]

There is the Caernarvon diversion just downstream of New Orleans

https://waterdata.usgs.gov/usa/nwis/...95124089542100

But they pass only about 400 to 600 cfs. Not much but there has been some delta formation at the outffall. They could pass more but you would have to ask the oyster fishermen why. Just sayin.

Subsidence in that area is in the order of about 1.5 cm per year. (1 foot in twenty years) So they need to make up that amount just to stay even. Kind of hard to do that with 400 to 600 cfs. Of decant water from the Mississippi.

One of my favorite classes a hundred years ago, taught by a guy named Reese, was Louisiana Geography. One of the many interesting subjects I enjoyed in his class was the discussion of the Army Corp of Engineers levee system and its effects, pro and con (mostly con), on S. Louisiana's coastal marshes.

The Mississippi River, before it was "tamed", swung back and forth across S. Lousiana over the eons building marshlands in its path. When the mouth of the river swung to the west, former beachheads in SW Louisiana soon became cheniers as hundreds of yards of new marsh formed in front of them from the sediment being dumped into the relatively shallow Gulf. When the river swung back to the east, a new beachhead in the form of a chenier appeared and hundreds of years later with another major flood, the river changed its course once again and the process repeated itself.

Just look at any Louisiana map and you can see the old deltas.

Today, with the river's course harnessed, most of that sediment is no longer making its way westward and is instead being dumped off the contintental shelf into deep water. I think Wax Lake Outlet is about as far west as Miss River sediment now makes it via the Morganza Spillway.

Loved that class. One of only two I didn't have to take the final.

[HelmutVII]

One of my favorite classes a hundred years ago, taught by a guy named Reese, was Louisiana Geography. One of the many interesting subjects I enjoyed in his class was the discussion of the Army Corp of Engineers levee system and its effects, pro and con (mostly con), on S. Louisiana's coastal marshes.

The Mississippi River, before it was "tamed", swung back and forth across S. Lousiana over the eons building marshlands in its path. When the mouth of the river swung to the west, former beachheads in SW Louisiana soon became cheniers as hundreds of yards of new marsh formed in front of them from the sediment being dumped into the relatively shallow Gulf. When the river swung back to the east, a new beachhead in the form of a chenier appeared and hundreds of years later with another major flood, the river changed its course once again and the process repeated itself.

Just look at any Louisiana map and you can see the old deltas.

Today, with the river's course harnessed, most of that sediment is no longer making its way westward and is instead being dumped off the contintental shelf into deep water. I think Wax Lake Outlet is about as far west as Miss River sediment now makes it via the Morganza Spillway.

Loved that class. One of only two I didn't have to take the final.

Go to my post 35 in this thread where I try to the best of my ability to describe land formation in Lafayette parish. the link to the NRCS soil survey has tons of very interesting information. Go to post 106 where I try to describe the location of the Coteau Ridge.

The maps in the NRCS soil survey will show ancient Ox Bows and river scars if you know what to look for.

You posted while I was editing.

[Cajunfanatico]

If the Corps and the State will get going on adding more Mississippi River diversions flowing at will during high water south of NOLA into the marshes and let at least a small amount flow down Bayou Lafouche maybe the sediment will get put to good use. Try to mimic pre 1927 without putting human lives at risk. And if Morganza is not opening why not divert more flow into the Atchfalaya R. then kicking more into the Teche-Vermilion diversion during high waters?

Every time the Morganza spillway is opened above current flow rates, the useful life of the Atchafalaya Basin as a flood control option for the Mississippi River is shortened. Why you might ask? It's because the Mississippi River flows at a velocity that allows it to carry sediment a rate far higher than that same water can carry as it flows through the basin. Once in the basin, the flow rate slows, and the sediment drops out, literally filling up the basin. Dredging is an option, but a pretty poor one in the long term.

One day, probably not in our lifetimes, an historic Mississippi River flood will result in the Atchafalaya capturing the flow waters of the Mississippi River. It will be a disaster of biblical proportions as the state of Louisiana will efectively be cut in half.........the Morganza Control Structure will be destroyed as will Hwy 190 and I-10 bridges over the Atchafalaya. Morgan City will be washed out into the Gulf of Mexico, and New Orleans and Baton Rouge may end up with a trickle passing by their cities.

[Cajunfanatico]

Go to my post 35 in this thread where I try to the best of my ability to describe land formation in Lafayette parish. the link to the NRCS soil survey has tons of very interesting information. Go to post 106 where I try to describe the location of the Coteau Ridge.

The maps in the NRCS soil survey will show ancient Ox Bows and river scars if you know what to look for.

You posted while I was editing.

I admit that I haven't read the entire thread. The Coteau Ridge, is the ridge visible as one nears Opelousas, is that correct? If memory serves, that's the ancient western edge of the Miss River's meanderings over recent geologic time......last 10,000 years or so, again, if memory serves.

Another interesting note too about that sediment being dumped off the contintental shelf at the river's current location. It results in huge underwater mudslides from time and those oil and gas platforms in that immediate area typically "cluster" their wellheads as opposed to the more spreadout layout on other platforms. This was explained to me by a Penzoil engineer, Brian Stewart to be exact, who said it was a way of protecting the tubing from being bent or even ruptured in mudslides.

[HelmutVII]

Land building in south Louisiana has gone on for eons. Regularly during the course of drilling water wells we produce wood chips from over one hundred feet deep. I recently was involved in a water well near Ville Platte. We hit wood chips from 135 ft to about 150 feet with very little if any sand. We came to the conclusion that we drilled straight down through a tree. I have the e-log and chip samples on my desk at the office to prove it. (strangest e-log you will ever see.) It must have been some significant event that caused that tree to be buried. Probably a flood of cataclysimic proportions at the end of the last Ice Age because the elevation of the bottom of that tree was at minus 100 by present day datum (give or take). It was about two miles from the crest of the Coteau Ridge so it was probably a Red River flood.

[HelmutVII]

Every time the Morganza spillway is opened above current flow rates, the useful life of the Atchafalaya Basin as a flood control option for the Mississippi River is shortened. Why you might ask? It's because the Mississippi River flows at a velocity that allows it to carry sediment a rate far higher than that same water can carry as it flows through the basin. Once in the basin, the flow rate slows, and the sediment drops out, literally filling up the basin. Dredging is an option, but a pretty poor one in the long term.

One day, probably not in our lifetimes, an historic Mississippi River flood will result in the Atchafalaya capturing the flow waters of the Mississippi River. It will be a disaster of biblical proportions as the state of Louisiana will efectively be cut in half.........the Morganza Floodway will be destroyed as will Hwy 190 and I-10 bridges over the Atchafalaya. Morgan City will be washed out into the Gulf of Mexico, and New Orleans and Baton Rouge may end up with a trickle passing by their cities.

My post 106 of this thread discussed the Coteau ridge south of Opelousas.

[Cajunfanatico]

My post 106 of this thread discussed the Coteau ridge south of Opelousas.

Okay, but amirite, does it not represent the old western edge of the Mississippi River floodplain?

[HelmutVII]

Okay, but amirite, does it not represent the old western edge of the Mississippi River floodplain?

Yes, the coteau ridge is what is considered the edge of the Pleistocene era banks and Flood plains of the Mississippi river.