Three freshwater diversion projects discussed at Tuesday’s Coastal Wetland Planning, Protection and Restoration Act Technical Committee meeting had one thing in common: They are all being discontinued due to the large cost of dredging.
The concern is the shoaling — the accumulation of sediment that can get in the way of navigation — that diversions sometimes cause.
The added shoaling would need to be dredged out, which greatly increases the cost of the project above what the program can handle.
Diversions from the river take water and sediment into surrounding shallow water or wetlands.
They are a major component of the state’s plan to stabilize Louisiana’s disappearing coastal wetlands.
Diversions mimic how the river once built coastal Louisiana before the construction of levees no longer allowed floodwater to spread outside the river banks.
Two of the proposed diversions on the Mississippi River in Plaquemines Parish — Benneys Bay Diversion and Fort Jackson Sediment Diversion — have been recommended for removal from the project list.
The main reason is the price range for dredging the induced shoaling associated with the project over time ranges from $100 million to $300 million, said Darryl Clark, technical committee board member.
“It has the potential to be more successful than West Bay because there is marsh that could trap the sediment,” Clark said in support of the Benneys Bay Diversion, but he said the wetland program doesn’t have the money to keep up with dredging.
However, the inability to move forward with the project is a symptom of a larger issue that will need to be addressed, said James Harris, of the U.S. Fish and Wildlife Service.
If there are caveats to building these diversions that include dredging 100 percent of the shoaling, even if not 100 percent of it is caused by the diversion, it’s going to put diversion projects out of reach financially, he said.
If that’s the case, “then we can, in my opinion, we can forget about large-scale restoration in the lower river,” he said.
Plans to close an operating diversion on the lower Mississippi River are under way and for the same reason — it’s too expensive to keep dredging a nearby anchorage area.
The West Bay Diversion, built in 2003 through the federal-state Coastal Wetland Planning, Protection and Restoration Act, is slated for closure.
This diversion is south of Venice in Plaquemines Parish, and it has built land this year thanks to the Mississippi River flooding in the spring.
However, the task force is moving forward with plans to close the project because an agreement stated the program had to pay for any shoaling in a nearby anchorage area.
The cost of that dredging was going to be more than the CWPPRA program could afford to pay.
In the meantime, Mississippi River flooding brought in a lot of sediment, and an emergent delta is forming — just as planners said they had hoped it would.
“It’s really sad to hear this consideration of closure at the moment,” said Maura Wood, senior program manager for coastal Louisiana restoration with the National Wildlife Federation.
Although the agreement to build the diversion included a provision that the task force would pay for dredging of the nearby anchorage, “to me, that’s not a diversion problem,” Wood said.
She urged the technical committee to come up with some creative way to address the issue that would allow the diversion to continue to work.
Kirk Rhinehart, representing the state as a member of the technical committee, said the anchorage was shoaling before the diversion was open and will continue after it’s closed.
In that case, maybe it’s possible to work with navigation and the U.S. Coast Guard to find an alternative solution.
“We want to keep this open. We want to build land,” Rhinehart said.