ATM Explores Dredging Alternative for Fernandina Harbor Marina – Fernandina Beach News-Leader

Called water injection dredging, the method has been used in Europe for over 20 years, but in the United States has so far been implemented only in New Orleans according to Semmes.

“Some Europeans call it natural dredging,” Semmes told commissioners Nov. 1. “It returns sediment back to the estuary with a minimum of energy costs.” Semmes also noted WID had been used continuously since 1988 in the Netherlands, Germany and the United Kingdom.

The dredging method would mobilize sediments near the bottom of the river using low pressure, then move them out of the marina basin using high volumes of water. Fernandina harbor’s conditions, he said, are ideal for the WID technology.

“In the case of Fernandina Harbor Marina, the edge of the naturally deep river channel … is fairly precipitous,” an ATM report stated. “The material moved to the channel will quickly disperse throughout the system to areas where it naturally would settle if the marina had not been excavated.”

Semmes told commissioners that the Fernandina Harbor Marina where it is sited now has never been a good location for docks and boat slips. Because it is located on natural mud flats, rather than having piers built over the flats, the marina will always need regular maintenance dredging to keep boat slips deep enough, he said.

In the late 1990s, ATM recommended realigning and adding slips parallel to the current on the north side of the marina. The city complied with those suggestions, but at the time could not afford to take additional measures to deal with siltation, such as creating a low elevation wall to train the current, and restoring the marsh to its natural state.

Semmes said that, although the technology is relatively low-cost, there are no WID dredges as yet in Florida and equipment and operators would have to be brought in.

The biggest obstacle to the alternative method is government regulations and permitting, Semmes said, although so far the Florida Department of Environmental Protection has been “very receptive.”

Semmes also said it would be best to start using WID in a small experimental project with the least possible environmental impact. While costs are still being determined, Semmes said the new technology was estimated at about $ 3 a cubic yard – considerably cheaper than current methods. The WID method also has the least environmental impact, he said.

Other methods of dealing with siltation could include a rapid dewatering of sediments and possibly developing a disposal facility at New Island, located southwest of the marina, Semmes said.

However, the New Island site would have to be developed and the cost to dredge and move the spoils was estimated to be between $ 30 and $ 76 a cubic yard, depending on different factors. But the ATM report did note that if WID does not work out, those options could be pursued.

Permitting costs for WID, however, are estimated to be higher than other methods because it is a new technology for Florida.

Vice Mayor Tim Poynter, after hearing the presentation, said it was “worth the risk” to look at the new dredging method.

“The state may help if we do the pilot program,” Poynter said. “It certainly would save the taxpayers a lot of money. … There really isn’t much of a decision here.”

Commissioner Eric Childers said he also recommended moving forward with pursuing the WID technology. “I hate to see a dredge site (at New Island) across from the downtown,” he added.

Commissioner Jeffrey Bunch said he was also in favor of exploring the new technology.

Joe Springer, manager of Westrec, the city’s marine management company, urged commissioners to go forward with water injection dredging. “There will be natural attention brought to it,” he said. “There will be a lot more interest in this project than cranking up and dredging, and moving it to another location.”

Semmes also recommended that the city consider structural changes to the marina such as expanding side-tie docks to the north and expanding the marina westward into the deep channel.

“It seems to me we can’t afford to keep spending money on the same thing over and over again,” Poynter said. “There’s got to be a better way of doing this. Every two to three years we’re spending $ 400,000 to get the mud out. … You saw the pictures. (The marina) is built on a mud flat.”

By Angela Daughtry
adaughtry@fbnewsleader.com
November 28, 2011
fbnewsleader.com