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Opening Morganza: What could the impact be?

Posted at 5:05 PM, May 28, 2019
and last updated 2019-05-28 18:48:00-04

The U.S. Army Corps of Engineers has announced officially that the Morganza Spillway will open this weekend.

The Morganza Spillway is a safety valve for the Old River Control Structure, which keeps the Mississippi River in place. In short, the Mississippi is so high that to guarantee the integrity of the control structure the water has be diverted into the Atchafalaya Basin, the natural Mississippi spillway.

But what could this mean for the Basin?

The spillway has been opened only twice before: most recently in 2011, and for the first time in 1973.

Here’s some of the data collected following the 2011 opening, to give an idea of what could happen now. If you’d like to read the report for yourself, scroll down.

For the 2011 opening, we found a report compiled by LSU, the Louisiana Geological Survey and the state Department of Natural Resources that attempted to estimate the impact. The report was not able to tally a full economic impact, though.

“Although many aspects of the economic impact of the flood on the Basin cannot be readily estimated due to the lack of available information, using the data collected from various agencies, parishes and individuals, the known impact can be estimated at over $56,000,000,” the report states.

Adjusting for inflation, that would be more than $64 million in 2019 dollars. But that does not include the losses to private individuals who lost homes, camps and businesses.

The report looked at direct losses, and estimated that crop and livestock losses were more than $45 million in 2011, or about $50 million in 2019 dollars.  The report wasn’t able to estimate fisheries losses.

Also included in the losses were repairs to public infrastructure that was damaged, including boat launches and roads, estimated at $7 million in 2011, or $8 million in 2019 dollars.


The report estimates that more than 95,000 acres of crops were flooded, most of it soybeans and forage. Most of those crops were lost for the full season, the report estimates.

Another 370 acres of land, dedicated to aquaculture at that time, also was flooded. And, 31,000 acres of pasture were flooded, which impacted cattle ranchers, the report states. Almost 5,000 cattle were evacuated, with only a dozen or so lost to drowning, the report estimated.

Wildlife and Fish

After the floodway was opened, Louisiana black bears were displaced. They were spotted on levees, and swimming out of the floodway, and back into the floodway, on a regular basis. It was assumed that some cubs were lost during the flood.

Wildlife agents also estimated losses in the state’s whitetail deer herd. Some estimates set the death rates at around 30 percent for the herd in that area, which impacted deer hunting in the basin for the following season. Before the flood, wildlife officials set the herd’s numbers at about 5,400, meaning the flood probably killed up to 1,600 of them.

And, wildlife agents estimated that smaller mammals and ground nesting birds were significantly impacted by the flood. They saw impacts to wild turkeys, and also to nesting alligators, whose eggs were lost.

The report recorded feedback from sport fishermen and wildlife agents that indicated the flood impacted sport fishing. Fish kills happened in the Henderson Lake area and Cow Island Lake were reported, both attributed to low oxygen levels. The Henderson Lake fish kill left hundreds of thousands of fish dead, including threadfin shad, freshwater drum, large mouth bass and lesser numbers of crappie and bluegill. The low oxygen level was related to rotting vegetation that was flooded.

Basin crawfishermen reported low oxygen water and a lack of flow, which forced them to move traps more frequently to avoid bad water, the report states. Some said higher prices helped offset the low harvest. But LSU officials said the season turned out average, or just slightly below average.

Human Impact 

The report found damage to homes and other human-related structures and infrastructure in six parishes: Iberia, Iberville, Point Coupee, St. Landry, St. Martin and St. Mary.

In Iberia Parish, there was almost no damage, and no damage to homes or camps.

In Iberville Parish, nearly 200 camps and two homes flooded in the Basin, with 250 structures, public and private, flooded in total.

In Pointe Coupee Parish, about 30 camps flooded, and some people did evacuate.

In St. Landry Parish, about 30 camps and homes were damaged, and an Atchafalaya campground was underwater for about 20 days near Krotz Springs. An emergency levee was built in Krotz Springs, and it remained up until October that year.

The Bayou Darbonne boat launches closed, including the Levee Landing boat launch and the Public boat launch under U.S. Hwy 190 near Port Barre. The boat launch at the Grimmett Canal, located south of U.S. Hwy 190 off of Spillway Road near Port Barre, was closed. The boat launches on the Atchafalaya River were closed to the public as well. All of these launches were closed from mid-May, when the spillway was opened, until mid-June.

In St. Martin Parish, about 40 structures were damaged by flood water, primarily in the Butte La Rose, Sherburne and Happy Town areas.

In St. Mary Parish, nearly 200 camps were flooded, and 45 businesses and homes flooded. Six boat launches were closed for most of May in Centerville, Berwick, Bayou Pigeon and Bayou Chene. The Avoca Island Ferry was closed as well. St. Mary reported the use of 80,000 50-lb sand bags, and 5,000 1.5-ton sand bags. More than 12 miles of earthen levees and 10,000 feet of basket levees were constructed. In 2011, the barge was sunk in Bayou Chene to prevent backwater flooding, just as is planned this year.


Recreational navigation was impeded by rafts of water hyacinth during and following the 2011 flood, the report states; this problem was worst in the upper Henderson Lake area of the Basin. Four miles of waterway between Henderson Lake and Butte La Rose were closed for three weeks as well.

Commercial navigation was impacted because of the closures of the Old River locks; the Atchafalaya River; the Bayou Sorrell lock and the Berwick lock. That, in turn, affected business and industry that relies on deliveries via the water, the report states.


Within a couple days of the opening of the spillway, about 165 oil or gas wells were shut-in, with an estimated loss of 3,318 barrels/day of oil production, and 23.3 thousand cubic feet/day of natural gas production. The report estimates that oil production in the basin was reduced by about 30 percent during the flood, with a recovery by August. Natural gas production was reduced by half, but hadn’t recovered by the time the report data was collected. The economic losses were estimated at $2.4 million for oil and $612,000 for gas.

There also were two oil leaks during the flooding; one when a storage tank collapsed near Catahoula and again when a small release happened near Bayou Postillion.

Here’s the full report if you’d like to read it: