Politicians and business boosters turned out last week — among them Jacksonville Mayor Alvin Brown, U.S. Rep. Corrine Brown, Chamber of Commerce president Daniel Davis — to celebrate their joint clout in muscling the U.S. Army Corps of Engineers to approve deepening 13 miles of the St. Johns River, from 40 to 47 feet. Money for the dredging project was also inserted into a waterways bill that will soon go to the U.S. House of Representatives and Senate.

Those leaders say dredging the river will mean a boon for jobs and businesses in Northeast Florida, as giant container ships (called Panamax ships) that will begin crossing the widened Panama Canal in 2015 and stopping at ports along the East Coast discover Jacksonville as a place to load and unload.

U.S. Rep. Ander Crenshaw, R-Jacksonville, called the developments “a giant step forward for Northeast Florida’s economy.”

But outside that circle of cheerleaders, skeptics abound. St. Johns Riverkeeper Lisa Rinaman argues that the proponents downplay the environmental damage that so drastic an alteration of the river will cause, and greatly exaggerate the potential economic benefit. And if the river is dredged to a depth of 47 feet while Central Florida begins to suck water out of the river for its drinking supply — as the state’s water planners have proposed — the effects could be devastating: Salinity levels could rise, triggering a change in the river’s ecology that threatens the vegetation, trees and marine life that depend on the fresh water.

The U.S. Army Corps of Engineers’ modeling of the potential impacts of dredging didn’t adequately explore those possibilities, Rinaman says. “They say, ‘We will be monitoring the river after the fact, and if there is more harm, we can fix it.’ Once harm is done, you can’t reverse history.”

University of North Florida sociology and economics professor David Jaffee questions the way the federal government is preparing for the Panama traffic. Instead of consulting with shippers and determining which ports would be logical first and second stops for heavily loaded ships and targeting funding there, the federal government seems to be handing out money to every port along the coast to do improvements and leaving them to duke it out for the business.

“It seems to be an irrational competition, and it should be a national plan,” Jaffee says.

Jaffee says that a fully loaded Panamax vessel needs 50 feet of water depth. Jacksonville won’t have that even when the dredging is completed in 2019. And one of those vessels sitting high in the water won’t fit under the Dames Point Bridge. Plus, Jacksonville is competing against Savannah, Charleston, Norfolk, and New York and New Jersey for those big ships. There’s no guarantee they’ll end up here.

JaxPort has been behind those other cities in winning approval for dredging or terminal improvements, and shippers are already plotting their routes for the Panamax traffic, Jaffee adds. “If it was the only port on the East Coast or it was the largest on the East Coast, it might make sense to deepen the channel to 50 feet to sustain its position. To think if the St. Johns River is deepened to 47 feet, we would suddenly see this surge of cargo is absurd. Why would these shippers leave these other ports? They are not sitting idly by waiting.”

JaxPort spokesperson Nancy Rubin says the Corps’ approval and Jacksonville’s inclusion in the waterway bill catches JaxPort up to its competitors. “Our timeline is exactly the same now,” she says. “[Those other cities] are also waiting for their piece of waterways legislation.”

She points out that Jacksonville is already a stop for Asian shippers through Mitsui O.S.K. Lines. “Until the port is deepened, the ships can’t carry as many containers onboard as they would like to. Every foot of depth we go in the river means more opportunity and benefits, more jobs,” she says. “Can we compete? Yes. We have these ships now and we will have more of them.”

Jaffee, however, argues that it’s more logical for JaxPort to play a secondary role in moving cargo after the Panamax ships are unloaded onto smaller vessels, and in continuing to expand its business with the Caribbean island nations and Latin America. Going after the big ships carries big financial risks: Jacksonville is committing to paying as much as 40 percent of the cost of the project. Jaffee predicts that the dredging will cost upwards of $1 billion; if he’s right, the already-cash-strapped city will be on the hook for as much as $400 million.

“Business is generally behind anything that promises growth and jobs. You have to play the game,” Jaffee says. “But I think it’s possible Jacksonville might dredge to 47 feet and see larger ships coming in with no increase at all in cargo. Rather than three ships carrying containers, one ship will come in carrying them all. That wouldn’t translate to all this economic growth and jobs expansion and revenue.” o