Home > Chrome, World Background > THE GREAT SALTMARSH OF LOUISIANA


or, “why the Kentucky Free State does NOT have access to the sea”



The Mississippi River has changed course many times and – for several decades – has been likely to swing to the west (following the course of the Atchafalaya River which is a stteper and shorter distance to the Gulf of Mexico). If it did so, the river would no longer flow past Baton Rouge and New Orleans .  Instead of discharging through the Bird’s Foot Delta into deep Gulf of Mexico water (a distance of 315 miles) the longest river in North America would flow into the shallows of Atchafalaya Bay (only 142 miles away).

The US Army Corps of Engineers (USACE) has been given the task of preventing this economic disaster.  The Corps built the Old River Control Structure, a billion-dollar marvel of engineering.  It is a  series of dams built on a quiet, unpopulated stretch of the Mississippi River in Louisiana, a few miles east of the tiny town of Simmesport.


The Old River Control Structure suffered catastrophic failure in the first Spring after Death Day.  This was the final blow to all attempts to rebuild.

Colossal amounts of water  moved down the Atchafalaya River system , creating ten-storey-deep scour holes that migrated along the riverbed, undermining bridge pilings. The Interstate 10 and the U.S. Highway 190 bridges collapsed.

The  gas and oil pipelines built beneath the bed of the River  ruptured  and spilled what remained of their contents . Floodwaters  isolated and then destroyed Houma, Raceland, and Thibodaux. Morgan City was drowned and then buried  by silt as floodwaters receded. Rotting bodies were trapped in buildings,  snagged in tree branches and beached on high ground when water levels dropped.

At the Old River Control Structure, the Mississippi River’s bed is below sea level.  The reduced flow in the Mississippi River downstream from the structure was overcome by the pressure of saltwater from the Gulf of Mexico. Seawater rapidly extended upstream from the Gulf,  contaminating water supplies needed for drinking and industry, first in Port Sulphur and then in New Orleans itself.

The Mississippi River channel just south of the Old River Control Structure silted in, cutting off barge traffic and isolating what remained of  New Orleans and Baton Rouge.

The outlet of the Atchafalaya River (which allows ship traffic to move in and out of Morgan City) silted in.


Next entry will describe some of the group’s who live in the Marsh



Categories: Chrome, World Background
  1. Mark Martin
    August 8, 2014 at 3:11 pm

    I guess I need a little clarification. Are you indicating that the new delta that forms at the outlet of the Atchafalaya River would not allow for ships to navigate? That seems a little unlikely since the flow through the Atchafalaya River would be roughly equivalent to what was going through the Mississippi before the failure. Also since river travel would be important to many economies in the area and dredging is Tech Level C-D activity, some group would dredge a channel for navigation.

    • August 24, 2014 at 10:11 pm

      Well, the US Army Corps of Engineers currently spends tens of millions to dredge the lower Missippi and there are several businesses that operate dredgers. After Death Day, silt and rubble would accumulate. After a few decades, the task would be ridiculously expensive

  2. Mark Martin
    August 11, 2014 at 1:00 pm

    Nice use of some 80’s research studies. I do have a question, just for clarity. When you say the outlet of the Atchafalaya River at Morgan City is silted in, are you just saying the old channel to the city is silted in and the new Atchafalaya outlet and growing delta are a little farther west?

  3. Doyle Hunt
    February 14, 2016 at 1:58 pm

    Having worked for the Corps of Engineers in New Orleans, I’m very familiar with Old River Control Structure. There is only one flaw in the premise as written. The Atchafalaya River wouldn’t capture the entire flow of the Mississippi River. With the demise of the Old River Low Sill Structure and/or the Old River Auxiliary Structure and/or the Old River Navigation Lock and/or the non-Corps of Engineers Sidney A, Murray Hydroelectric Plant directly adjacent (a likely nuke target, in my opinion), the distribution of flow would flip-flop, with about 70% of the flow going down the Atchafalaya and 30% of the flow remaining in the Mississippi. Nuking the hydroeletric plant might alter the topography and bathymetry enough to shift the entire flow, however, depending on the exact placement of the crater.

    An interesting side effect is that when there is a lot of rainfall and/or snowmelt in the Midwest (Upper Mississippi and Ohio River basins) and little rainfall in the Red River basin, you would see back-water flooding as water flows upstream into the Red River from its point of confluence with the Atchafalaya. This is because Old River (the short waterway connecting the Mississippi to the Atchafalaya, once mostly blocked by a permanent logjam called the “Great Raft” until the logjam was cleared by Capt. Henry Miller Shreve in 1838) and the Red River meet to form the Atchafalaya River. Contrary to what we learned in school, the Red River is not a tributary of the Mississippi River; the Red has flowed into the Atchafalaya for centuries. So if the flow from the Mississippi into the Atchafalaya exceeds the flow from the Red, you’ll see back-water flooding in the Red as far upstream as it takes for water elevations to equalize.

    A team that awakens near the Red River anywhere downstream of Alexandria, LA in the late spring might be very surprised to find the Red River flowing in the wrong direction for a while before the floodwaters recede and the Red River resumes its normal direction.

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