The state will need to be something of a helicopter parent, at least at first, to future sediment diversions along the Mississippi River, monitoring and adjusting how they are operated, according to a report released Thursday.
Operating diversions to maximize land building while minimizing negative impacts on the environment will involve monitoring how much water and sediment are coming down the river as well as studying how the wetlands are responding.
In addition, decisions about how diversions should operate to meet changing river conditions need to be made ahead of time to give people who live and work nearby advance notice, said Natalie Peyronnin, director of science policy with the Environmental Defense Fund.
“So no, you’re not making a decision on a daily basis,” she said.
The diversion expert group of 12 core members and 42 guest experts -- put together by the Environmental Defense Fund in cooperation with the Restore the Mississippi River Delta Coalition partners -- met over the past eight months to study how Louisiana coastal wetlands respond to diversions and to come up with recommendations on how a diversion should be run.
After the 2011 flood pushed record amounts of silt-laden water through the Mississippi River…
The report outlines the recommendations to build the most land possible with consideration to the fisheries and other environmental concerns
“In the last 50 years, Louisiana has lost 20 percent of its wetlands,” said LSU professor Andy Nyman, adding that if nothing is done, another 15 to 30 percent could be lost over the next 50 years.
Projects that divert sediment from the Mississippi River to surrounding wetlands in a controlled manner have been part of coastal restoration recommendations since at least the 1970s. The state Coastal Protection and Restoration Authority is currently engineering and designing two such diversions, the most advanced being the Mid-Barataria sediment diversion near Myrtle Grove.
Planned diversion projects designed to take sediment from the Mississippi River to build mar…
While touted as land builders, the diversions have some fishermen concerned the flow of water and sediment will destroy the estuary that provides their livelihood. The new report acknowledges there will be changes in fisheries, but adds the diversion can be operated to increase the overall productivity of wetlands.
“We decided operation should be focused on diversity rather than any one species,” Nyman said.
Without defining an exact plan, the expert group laid out how the Mid-Barataria diversion could operate during the winter-to-spring high-water season under a variety of scenarios. The idea is to mimic Mother Nature and get freshwater and sediment into the wetlands that normally would have flooded if the levees weren’t in place.
Winter operations have the least impact because plants are mostly dormant and there are not many species using the wetlands for nursery or breeding. In addition, cold fronts that push to the coast could help move sediment from bays and into the marsh.
Spring and early summer diversion operations would be more complicated because alligators, blue crab, juvenile brown shrimp and even bottlenose dolphins need to be considered.
In addition to seasonal considerations, diversions must be operated differently in the first five years until gradually opened at full flow. The gradual approach would allow plants, fish and other animals a chance to adapt and allow for channels to develop in the wetlands to disperse the flow, said University of New Orleans professor Alex McCorquodale.
People living and working along the coast also need to be considered, not only with environmental changes caused by diversions, but with how they can be part of operating the structures. While the operation of diversions need to be put together by studies, work must continue to determine how decisions impact people, said Shirley Laska, professor emeritus at the University of New Orleans. The most successful outcome of a sediment diversion will happen if the negative impacts are mitigated or compensated, she said.
Two fishermen with decades of experience between them expressed different expectations to a …
“We see there is a continual concern about what will happen when you have such a large diversion,” Laska said. “We have to be thinking more in advance than we have in the past.”