Lt. Gov. Nungesser Questions Louisiana CPRA Marsh-Building Strategy
The state of Louisiana has lost in excess of 2,000 square miles of land to the Gulf of Mexico since the 1930s. In an effort to restore some of the land loss, the state created the Coastal Protection and Restoration Authority (CPRA) to develop plans to not only prevent land loss but to rebuild the land.
One significant proposal is to divert Mississippi River water, with its sediment, into the surrounding marshes with the intent of that sediment building land, much as the natural process did before flood-control levees restricted the annual flooding river by limiting the overflow within its banks and adjacent batture.
The Mid-Breton Sediment Diversion on the east bank near Wills Point about Mile 70 AHP (Above Head of Passes) and a similar Mid-Barataria Sediment Diversion on the west bank of the Mississippi River further south near Myrtle Grove (approximately Mile 55) are designed in hopes of building new land along Louisiana’s fragile coast.
Since the inception of the Mid-Breton Sediment Diversion, its capacity has grown from 5,000 cubic feet per second (cfs.) in the 2012 Coastal Master Plan to 35,000 cfs. in the 2017 Coastal Master Plan. Then in 2020, in the proposal submitted for the federal permitting process, the CPRA again increased the flow to 75,000 cfs.
The size of the proposed Mid-Breton Sediment Diversion (MBSD) project was reduced by the CPRA at its meeting in November 2021. The request was reduced to 50,000 cfs. in November 2021, to stay within the $800 million project budget, the Times-Picayune reported.
The project design was said to be about 30 percent completed in November 2021, and Chip Kline, CPRA chairman, said by looking at cost-benefits “we are right-sizing the program.”
When a river gauge upstream in nearby Belle Chasse records the Mississippi River flow exceeding 450,000 cfs., the Mid-Breton Sediment Diversion gates will be opened. Maximum flow in the MBSD will occur when the Belle Chasse gauge reaches 1 million cfs.
“Overall, a potential 50,000 cfs. sediment diversion planned for Mid-Breton will significantly benefit the estuary and support the goals of CPRA and the Coastal Master Plan,” Brad Barth told the CPRA at its November 21, 2021, meeting. Barth is project manager.
By comparison, the Times-Picayune reported the two 2019 openings of the upriver Bonnet Carré Spillway dumped as much as 300,000 cfs. of water into Lake Pontchartrain. The spillway is a flood-control project and was designed not to build land, but to divert Mississippi River water to prevent overtopping of the downstream levees in New Orleans.
Excess water that flows into Lake Pontchartrain travels through the Rigolets and Chef Menteur Passes and eventually through the Mississippi Sound and into the Gulf of Mexico.
CPRA computer modeling projected at 50,000 cfs. the Mid-Breton Sediment Diversion will create as much as 20,000 acres, or 31 square miles of land over a 50-year period. At 35,000 cfs., models showed 15,000 acres or 23 square miles built, while at 75,000 cfs. diversions create 30,000 acres or about 47 square miles.
Pushback
Local residents, parish governments and fishermen associations have lined up in opposition to the proposed diversion channels. Spearheading the opposition is Lt. Gov. Billy Nungesser.
“The state CPRA has been promoting diversions as the cornerstone of coastal restoration for the state and has become a ‘too big to fail scenario,’” Nungesser said in an email to The Waterways Journal. “It has become a marker for the administration to be able to say that this is the largest coastal restoration project the world has ever seen.”
Nungesser was Plaquemines Parish president during the BP oil spill and was a successful businessman in the oil field service business before entering politics. Passionate in his desire to protect the marshes where he grew up, Nungesser was frequently interviewed by news crews covering the BP oil spill.
Plaquemines Parish includes both banks of the Mississippi River for the final 60-plus miles before it empties into the Gulf of Mexico.
During response to the BP well blowout, Nungesser was a huge proponent of creating coastal sand berms in shallow water, using backhoes mounted on marsh buggies, to block oil from reaching marshes, a critical habitat for the seafood industry.
The berms, when finally approved, were constructed in 19 days and successful in blocking oil from reaching the fragile salt water estuaries.
In speaking engagements opposing the diversion channels, Nungesser shows a slide presentation in which he quotes a study showing the inability of the three existing diversion canals in creating land.
Nungesser quotes Dr. Eugene Turner, LSU Boyd professor, Department of Oceanography and Coastal Sciences:
“There is no evidence of a net gain or conservation within the sites after the diversions began (Davis Pond, Fort St. Philip, Caernarvon). The three diversions did not create/restore land but did result in land loss. At Fort St. Philip, it was described as a loss accelerant in a USACE (Corps of Engineers) study because it has not regained the 52 percent land lost when it opened in 1973.”
Nungesser said one of the critical issues in coastal restoration is reducing land-robbing storm surge. The Plaquemines Parish master plan, separate from the state’s, proposes developing forested ridges to reduce storm surge, instead of marshes that a diversion would create. A map of the parish plan shows the location of numerous suitable ridges.
Forest ridges use the location of natural land elevations in marshes. Construction methods can vary, but essentially small levees are built with suitable equipment. Dredged material consisting mostly of sand and muck is pumped into the leveed area.
The levees are pierced, allowing the excess water to run off. After repeating several series of levees and pumping lifts, the sand is graded with an elevation of as much as 8 feet. Plans call for rock armoring to help prevent storm surge erosion during weather events.
Vegetation, up to small scrub oak trees, is planted based on proper elevation of the ridges. The vegetation not only retains the sand, it tends to collect more, growing the ridge over time.
“With over 86 percent of hurricanes that hit Louisiana passing through Plaquemines Parish, the critical priority for the parish was to lower storm surge,” Nungesser explained.
“Forested ridges lower storm surge 8:1 over areas of marsh grass, knocking down a 5-foot wave to less than a foot. This is simply the most cost-effective measure with the least amount of environmental impact that will reduce storm-surge damage within our lifetime,” he said.
Diverting fresh, but polluted, Mississippi River water into the brackish coastal waters lowers the salinity, adversely affecting wildlife, he said.
While necessary to prevent overtopping the levees during the extended high river of 2019, Nungesser claimed opening the Bonnet Carré Spillway caused “almost $250 million in environmental/economic damages to both Louisiana and Mississippi, ultimately killing 337 shallow water bottlenose dolphins.”
By comparison, the BP well blowout and spill, which was the largest oil spill in United States history, killed 91 dolphins, he said.
“The dolphins are the canary in the coal mine and show the devastation to the ecosystem at the very end of the damage cycle,” Nungesser said.
In the federal permit application, Nungesser said CPRA requested a waiver from the Marine Mammal Protection Act. CPRA requested a waiver that only “requires the monitoring and rehabilitation of shallow water dolphins after the MBSD is in operation.”
“How do you monitor or rehabilitate a deceased dolphin, or a dolphin that has been severely impacted by river water intrusion?” he asks.
Louisiana fishermen land more than 1 million pounds of seafood each year, Nungesser’s presentation explains. Louisiana tourism is “directly tied to our fisheries, and our world-famous restaurants and cuisine.”
The Marine Mammal Commission commissioned a study by the University of St. Andrews of the impact of the Mid Breton Sediment Diversion on shallow-water bottlenose dolphins.
Louisiana and Mississippi are home to the world’s largest population of bottlenose dolphins, the presentation said. The St. Andrews study estimates a 70 percent morbidity rate for the dolphins and concludes that within 50 years of the Mid Breton Sediment Diversion operating, bottlenose dolphins will be extinct.
