Planned diversion projects designed to take sediment from the Mississippi River to build marsh near the Breton and Barataria sounds won approval from a state coastal board Wednesday — a vote that means this long-desired work will finally move beyond planning.
The Coastal Protection and Restoration Authority recommended advancing the Mid-Barataria sediment diversion near Myrtle Grove and the Mid-Breton sediment diversion at Wills Point. The approval means these two diversions will move forward toward engineering and design.
“Finally, taking some of these diversions out of the planning stage,” said Kyle Graham, CPRA’s executive director. Two other planned diversions farther down the Mississippi River will be studied more, but they won’t be moving forward at this time, he said.
Much of coastal Louisiana was built when the meandering Mississippi River deposited sediment carried through floodwaters, but then levees were built, halting the flow of the replenishing waters into the marshes.
For decades, the idea of putting the river back to work, even on a limited basis, was studied as a way to distribute sediment to marsh areas. As the state moved to create the Coastal Protection and Restoration Authority after hurricanes Katrina and Rita, the sediment diversions became a part of each master plan for restoration and protection the state has produced.
In 2013, CPRA approved using $13 million from Deepwater Horizon criminal fines on a number of studies of lower Mississippi River sediment diversions.
“We’ve all waited for these results for some time,” said King Milling, a CPRA board member.
Studies have been undertaken to determine where the sediment is located, its flow pattern through the river, and how the diversions might impact navigation channels. Some of that work continues, but enough has been done to learn about the diversions’ potential impact on land building and fisheries. In addition, planners sought to determine whether the work would cause any flooding for coastal communities.
The Mid-Barataria sediment diversion near Myrtle Grove was approved to allow a maximum of 75,000 cubic feet per second of Mississippi River water to move through, while the Mid-Breton diversion at Wills Point will be 35,000 cubic feet per second.
In testing other concerns, like impacts on fisheries, CPRA staff used computer models that assumed all four diversions would operate for about four months every spring when the river experiences high water levels. Graham said that’s the most fresh water that could be put into the system and doesn’t reflect what would normally occur — but they wanted to test the worst-case scenario.
Concerns about the widespread destruction of fisheries or the shoaling of navigation channels don’t appear to be justified, the staff found, although Graham said more project-specific work will be done as the work progresses.
For example, the state ran two separate models to study what all four diversions could do to fish and found that while different species would move around, the overall number of fish available wouldn’t dramatically change.
“One of the fears is that we would make these basins fresh and they would remain fresh, and that’s not what we see,” Graham said. “The takeaway is we don’t see significant damage to any given fish species.”
Those in the oyster fisheries also have been concerned because these bivalves depend on salinity in the water to survive. Computer models show that while some of the more productive areas of oysters may move around a bit in southeast Louisiana, the diversions don’t drastically change total production.
CPRA also will start running computer models with just the two approved diversions to get a better idea of impacts and benefits, Graham said.
In addition, staff will meet with government officials, fishermen and other groups along the coast to present the diversion information and recommendation. Proposed funding amounts to start work on the engineering and design will be included in the fiscal year starting in 2016 and need approval by the CPRA board and the legislature.
A request for design money will be included in the CPRA’s annual plan set to be put before the state legislature during the 2016 session. It’s likely to be funded through $1.27 billion set aside for Louisiana barrier island and diversion work through the National Fish and Wildlife Foundation as a result of Deepwater Horizon criminal settlements.
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