alternatehistory.com

I found an interesting page on the control of the Mississippi

www.americaswetlandresources.com/background_facts/detailedstory/LouisianaRiverControl.html

which had me wondering: WI the formation of Turner's Bend in the 1500 was slightly different, resulting in more flow down the Atchafalaya, with the result that it never becomes logjammed?

Does this mean that Morgan City would become the main delta port, rather than New Orleans?
Does Shreve's Cut ever happen?

Alternatively, is there any outcome that might result in the river becoming unavigable from the sea except by major engineering works, and what would be the effect on development of the region?

Finally, the page discusses a hypothetical flooding event that could cause most of the outflow to be captured by the Atchafalaya. They discuss it happening in the 1970s, but what would be the most interesting time for it to take place, under this scenario, in the 19th century?

In the aftermath of the huge floods that would cause the main flow of the river to jump to the Atchafalaya River, aside from the cost, anxiety, tragedy, and aggravation of dealing with massive amounts of water being in the wrong place, there would be lingering issues that would change the way of life on the lower Mississippi. Instead of 70% flow down the lower Mississippi and 30% flow down the Atchafalaya, the percentages would probably reverse. The Atchafalaya would be a rushing, raging river, even during the fall for a period of time until it scoured the channel and filled in the lower reaches so that the flow would diminish. Morgan City would have to be relocated, as would other communities and many businesses, possibly including the massive infrastructure of the offshore oil and gas industry. Fisheries would be altered measurably all across the delta. Oyster reefs would be immediately destroyed, and would take several years to reestablish and become productive (no erysters!). It would probably take two decades to adapt to the new environment around present day Morgan City. Additionally, pipelines, bridges, and the like that cross the Atchafalaya would be destroyed or rendered unsafe. The ruptured natural gas pipelines would place stress on fuel supplies for energy companies, but they would quickly change to more costly fuel sources and have little or no interruption of service. Imagine the traffic jams when and if bridges on I-10, U.S. 90, and U.S. 190 collapse (what about the railroads)? All trans-state traffic would have to be rerouted to I-20 via I-55 through Jackson, Mississippi, adding up to 615 miles to the trip (not to mention time delays from the traffic jams). The protective levees of the Atchafalaya Basin would have to be upgraded to handle the new pressure from Spring flows. And, oh my gosh, think of the negative impact on the crawfish supply!

The lower Mississippi would still have a copious amount of water, but it would be slack compared to today. Shipping could continue to be an important industry, but it would be interrupted for a time. The slack water would allow (cause) the thalweg to fill in and stop deep-draft shipping. However, after intensive dredging efforts it may be found that a 50 ft channel can be easily maintained because of the tremendous decrease in sediment. New Orleans, possibly Baton Rouge, and all other cities and towns along the lower Mississippi would no longer be able to get their drinking water from the river. It would become too salty, since the lower fresh water flow would not offset the tidal movement of the Gulf. Can you imagine the cost of piping or trucking enough drinking (and flushing, etc.) water from north of Lake Pontchartrain to supply the needs of Greater New Orleans? Can you imagine Greater New Orleans without water for drinking and sanitation? Even when the water was just barely increasing in salinity, there would be severe damage to water heaters, fire sprinklers, fire truck pumping systems, and more. The quality of our coffee! As mentioned above, the fisheries (especially those associated with the fresh water river) would suddenly change. And what about the massive petrochemical industry corridor? Aside from the impact on shipping, which they could weather over time, industry could no longer use fresh river water for thermo-electric cooling. The saltier water would corrode all the pipes and related instrumentation. Of course, industry would change to salt-tolerant materials, but that would be costly and time consuming. Also, the sugarcane industry would have problems without sufficient fresh water.
All of this adjustment, and we have not delved into the intensity of impact on people=s lives during the crisis and the adjustment period. All normal routines would stop. Businesses would be closed, as would schools, normal government, etc., etc. Virtually the entire population would spend months and months just coping - just putting their and others= lives back together. Imagine the emotional strain to the population - people losing a lifetime of accomplishment. This would be a tragedy of monumental proportions. It would interrupt life much like World War II.
One can also imagine the impact on the nation. Massive use of Federal dollars to protect and restore Louisiana=s infrastructure. Loss of natural gas (there would be brown-outs throughout the eastern seaboard). Commerce would be interrupted by restriction of travel and Louisiana=s inability to focus on supplying items traditionally demanded from her natural resources by the nation. Prices of all Louisiana products (from the natural resources [fisheries, oil, gas] to industrial products [poly vinyl chloride, polyethelene, etc.]) would soar. The interruption of the pogie fisheries would be very negative for such food industries as chicken, catfish, and hogs (see the last section of the notes). New Orleans is one of the most important ports in the nation, and it would suddenly cease to function; all shipping and related industries on the Mississippi River would stop. International trade would be further imbalanced. The massive fertilizer business would shut down and the agriculture industry would falter.
And what about the economy of south Louisiana? For a period of time, all the revenue would dry up and tourism would collapse. Even Mardi Gras would possibly come to a halt!!! Only the mosquitoes would do well! And probably the cockroaches and Formosan termites.

Long term, we would adapt. Once the drinking and sanitation water issues were resolved, tourism would return. Coastal erosion could be reversed on the west side of the present-day Mississippi River. Shrimp, oysters, and other fisheries would probably flourish after a number of years due to new marshes being produced and nutrient rich sediments being redistributed.
This would obviously place a lot of stress on at least two generations of residents. We would survive, but it would be a new Louisiana and Mississippi River delta.​
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