Dredging to rejuvenate waters, wildlife

Publicized in: Fort Myers News Press
Publication Date: December 7, 2008
Related Website: http://www.news-press.com/article/20081207/GREEN/812080340/1002/NEWS01

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Over the next six months, Blind Pass will once again become a pass.

Energy Resources Inc. of Chesterfield, Mo., started a $3.2 million project last week to dredge 130,000 cubic feet of sand and reopen the pass that separates Sanibel and Captiva islands. The project is scheduled to be finished in May.

"This is a phenomenal idea," Sanibel resident John McCabe said. "There used to be phenomenal snook fishing in the pass. It's a dead-end place now. The change is going to be like night and day."

Passes between barrier islands are dynamic systems that can open and close naturally.

Blind Pass has closed and reopened many times. If it's closed for long, water on the bayside doesn't flush into the Gulf of Mexico, so it becomes stagnant, and water quality declines, as do fish and invertebrate populations.

It closed in 1999, was dredged open in March 2001 and closed again a month later - for that project, the state, the Captiva Erosion Prevention District, the city of Sanibel, Lee County and the West Coast Inland Navigational District spent $246,307 to remove 17,500 cubic yards of sand.

In 2001, a thin isthmus of sand seaward of the Blind Pass Bridge connected Sanibel and Captiva, and the dredging project only involved punching a hole in the isthmus because the bayside of the bridge is part of the state's Pine Island Sound Aquatic Preserve.

"Dredging in an aquatic preserve was strongly discouraged," county coastal engineer Robert Neal said. "The engineering tools we use show that the pass will not stay open unless we dredge in the preserve."

For this project, paid for by the state, Lee County and Captiva Erosion Prevention District, the state issued permits to dredge in the preserve.

So Energy Resources will dredge almost 4,000 feet on the inside of the bridge and 500 feet into Roosevelt Channel; they will also dredge 800 feet into the Gulf.

Depths of the dredging will range from 8 to 10 feet.

The depth and width of the dredged area will allow outgoing tides to flow at a maximum of 3.5 feet per second, or a little more than 2 knots.

In Southwest Florida, sand in Gulf water near the shore moves from north to south along the shorelines of barrier islands, across passes and onto the next island. Swift water flowing out of Blind Pass will not allow sand from Captiva to fall into the pass and close it, though maintenance dredging will be necessary from time to time.

"The issue is stagnation," said Vincent George, project manager of the state's Bureau of Beaches and Coastal Systems. "The flushing will reinvigorate the area."

With water flushing into and out of the pass, water quality inside the bridge improves, so seagrasses, fish and vertebrates will return.

Reopening the pass might also help bird populations, McCabe said.

Before the pass closed, birds nested in a series of small mangrove islands just south of the pass.

"That was just a tremendous bird rookery," McCabe said. "When the pass filled in, that whole area got filled in, and the raccoons were able to get in there, so the birds don't nest in there like they used to."

Digging is done with two cutter-head dredges, which are kind of like circular chainsaws. As the dredges dig, water jets turn the sand into a slurry, and the coarse beach-compatible sand is pumped onto Sanibel, while finer sand is pumped into the Gulf.

Nannette Lehr, who lives on a canal that empties into Dinkins Bayou near Blind Pass, had mixed feelings about the dredging project.

"I don't want to see Dinkins Bayou silted up - there's been talk about that," she said. "On the other hand, I understand that the flushing will help."

Neal was confident that Dinkins Bayou would not be harmed by the project.

"Obviously a lot of material is going to be moving around," he said. "But with the pass open, that material is going to be pushed out."

For his part, McCabe was thrilled about the project.

"I couldn't be happier," he said. "Unless they made it twice as wide and twice as deep."

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