A 160-year-old idea on how best to use the Mississippi River to build land in and around New Orleans is making the rounds again as fishermen look for a way to minimize the impact of planned river diversions on their industry.

The diversions would shift fresh water and the sediment it carries from the Mississippi River into coastal marshes.

Al Sunseri, co-owner of P&J Oyster Co., spent part of January with other oystermen in Washington, D.C., talking to congressmen about that old-is-new-again idea: building levees around sections of the coastline that would receive the diversions.

These leveed-off sections, or “colmates,” would allow the sediment to settle in a specific area and result in a slower release of fresh water into fishing grounds.

Under the state’s plans, the sediment diversions would operate more like natural crevasses — with lots of water and sediment flowing into the marshes when the river is high and with less flowing when the river is low.

State coastal planners say they’re already working on ways to maximize land building while minimizing hardships on fishermen. Although many ideas are being considered — from building terraces to slowing the river water down and helping the sediment drop out faster — actually building containment levees for the diversions would represent significant engineering challenges while curtailing the hoped-for benefits, the planners say.

“Part of the benefits of diversions is re-establishing natural processes, and some of those have far-flung effects,” said Bren Haase, chief of planning and research for the state Coastal Protection and Restoration Authority. The benefits can include the transport of fine-grained sediment that can travel a couple of miles away from the river. That process would be curtailed if the outflow area was sealed off.

In addition, planners say, the sediment diversions could be controlled so that they would take advantage of periods of high sediment levels in the river but wouldn’t need to operate often or for long periods.

Previous tests with diversions such as West Bay in Plaquemines Parish have demonstrated that building “speed bumps,” or small islands, in the path of a diversion helps to slow down the water so that more of the sediment falls out quickly.

Sunseri said he’s been talking with the state and other coastal groups about the idea of building containment areas for the diversions, but “they were really nonresponsive.”

Some fishermen and oystermen are concerned that large pulses of freshwater and sediment into areas they now use would destroy their industry — which in recent years already has had to deal with multiple hurricanes and the largest oil spill in U.S. history.

Other fishermen disagree and say some of the best fishing comes in areas where the river escapes its bonds and flows into marsh areas of the coast.

The Coastal Protection and Restoration Authority voted in October to move forward with planning the Mid-Barataria diversion near Myrtle Grove at 75,000 cubic feet per second of flow and Mid-Breton at Wills Point at 35,000 cubic feet per second.

“Everyone seems to think we’re totally opposed to diversions,” Sunseri said. “We support diversions. We just support controlled diversions.”

The uncertainties that come along with the diversions are numerous. Sunseri said there are no answers as to how successful they’ll be or how long they might need to operate to build land.

“With these colmates, you know you’re going to build land,” he said. “And it won’t hurt fisheries.”

Sunseri said he sees the idea as a middle ground where diversion advocates and the fishing industry can meet to get coastal land built through diverting a portion of the river.

It’s not a new idea, explained Dennis Lambert, an engineer who wrote an article about the subject for this month’s Louisiana Civil Engineer magazine.

It recounts how French-born Marie Joseph Raymond Thomassy arrived in the state to form the Louisiana Salt Manufacturer Co. in 1855. Eventually, he saw that the way salt was produced — building drying ponds, pumping in water and letting the water leave slowly — could also be the answer to New Orleans’ desire at the time to fill in swamps.

At the time, Lambert said, there were two schools of thought on how to do that: dredge canals and forcibly drain the swamps, or let the river flow sediment into areas to more naturally raise the land.

The canals idea won out, but Lambert said the other idea could help bridge the gap between commercial fishermen and the state as the latter moves forward with sediment diversion plans along the Mississippi.

“I think it’s so important with all the controversy. … Common sense tells you you need to use the river. Common sense tells you you need to contain it,” Lambert said. “It’s all about slowing the water down.”

“I believe in the diversions,” he said, but the issue will come down to the details of how the diversions are done and how that water gets slowed down.

That’s what the state and other stakeholders are working out now as the state coastal authority’s new leadership takes the helm over the next few months.

Follow Amy Wold on Twitter, @awold10.