RUNNING OUT OF ROOM?
Dredged Material Poses Challenges

by Victoria Parsons

Stretching 40 miles from the sea buoy near Egmont Key to the cruise ship docks at Channelside, the Tampa Bay shipping channel is the lifeblood of the region's ports. Without the channel, modern ships - with drafts of up to 40 feet - could never traverse a bay that averages only 12 feet deep.

Maintaining the channel, however, is a constant challenge. Sand and silt, carried up the channel in tidal flows or down the channel from streams and rivers, settles at the bottom. All together, debris collects at a rate of more than a million cubic yards per year - enough sand and silt to fill Raymond James Stadium to the top 10 times. To keep underwater highways clear, the material must removed be dredging, either scooped in clamshell cranes or vacuumed out with giant pipes.

Finding cost-effective, environmentally safe ways to store that dredged material is a key challenge facing bay managers. Existing storage sites - many built 25 years ago - are nearing capacity and Tampa Bay may run out of space in the next five years unless existing sites are expanded and alternative sites found.

Typically, dredged material from federal channels in lower Tampa Bay is barged to an offshore site where capacity is virtually unlimited.

However, most of the silt and sand collects in upper Tampa Bay near the Port of Tampa, and it's generally not economically feasible to barge materials long distances. Until recently, material dredged from the upper part of the bay was placed on spoil islands where 20-foot dikes keep sand and silt from seeping back into the bay. Those islands - 2D to the north and 3D to the south - are running out of room.

Plans are being finalized now to double the height of the dikes to about 40 feet, using dredged material already stored inside the dikes. That will increase total capacity to about 30 million cubic yards each, which should extend their lives until at least 2030. Another option to expand the islands calls for raising the dikes again, this time to 50 feet, when the additional capacity is needed.

The U.S. Army Corps of Engineers is charged with ensuring that "federal channels" - the major channels and shared berths in the three ports - remain navigable. Working with the Tampa Bay Estuary Program, the Corps published a report in July 2000 that details plans for dredged material disposal through 2025. Finding beneficial uses for dredged materials and raising the dikes on spoil islands is expected to provide necessary space through 2025, but the Corps, working with Tampa Bay environmental community, hopes to find beneficial uses (see related story) for much of that material.

"That's a ballpark number," said Tracy Leeser, a planning technical leader for the Corps' Tampa Bay initiative. "It's the estimated capacity of known possible sites, but it's still a very iffy thing."

Coping with congestion

At the same time bay managers are grappling with material from maintenance dredging, ports and the businesses they serve continue to grow.

An estimated 5,000 ships travel the nautical highway every year, carrying food, fuel, fertilizer, cruise ship passengers and myriad cargo from ports around the world. That cargo is critical to the region, contributing an estimated $15 million annually to the local economy.

But like much of the region's transportation infrastructure, it's an ongoing challenge to expand capacity without breaking the bank or damaging the environment.

The congestion is "a nice problem to have," because it means ports are growing, says John Thorington, director of government operations for the Tampa Port Authority, "but it's also a problem we need to address."

The port - and several key people within the Army Corps of Engineers - are pushing to improve the channel and possibly create a passing zone at Cut B, just west of the turnoff to Port Manatee. "Within the shipping community, I would say it's urgent," notes Leeser.

The congestion has been building for years, but the addition of Fantasy class cruise ship - 855 feet long and 125 feet wide with a draft of 27 feet - requires wide safety zones and basically shuts down the channel for several hours six times a week. Other ships, including those carrying liquid propane gas and anhydrous ammonia, also require wide safety zones. "A passing zone would greatly alleviate the congestion," Thorington said.

Still, anything that the Corps recommends could be up to 10 years away, assuming that Congress funds the work after the Corps determines that it should be constructed.

There are some precedents for expediting the passing zone, and Thorington is working with the Corps at the district level to speed authorization and construction. "We're trying to make the case that there are significant safety, environmental, commercial and security values attached to the widening," he said. "There is universal appeal within the port community and we're committed to doing everything we can to make it happen as quickly as possible."

Expansion has economic, environmental costs

Along with the costs - estimated at about $20 million - scientists must consider the environmental impact of further widening the channel. "There's a tremendous history of opposition to channel widening," says Robin Lewis, an environmental consultant and longtime bay advocate. "There are a lot of serious questions dating back to the early 1970s that still have not been addressed, and any dredging that increases the depth of the channel has potential negative impacts."

First is the question of breaching the aquifer while digging the channel and allowing fresh water to leak out. "We raised that question 30 years ago, and it has not been addressed to this date," Lewis said.

Additionally, dredging clearly destroys natural habitat and may impact other habitats by increasing saltwater inflow and wave action.

"Wider channels increase the tidal prism and allow more salt water into the bay. Increasing the depth of the channel also allows larger ships, which means larger wakes," he said.

Large wakes and increased wave action may be one reason why seagrasses are not recovering as quickly as scientists had hoped when water quality improved in Tampa Bay. "Wakes increase wave action, and may play a role in the decline of longshore bars that help protect seagrasses," Lewis said. "We don't know for sure, but we need to know what's happening today before we start expanding the channel."

Work still years away

Unless Thorington and the Tampa Port Authority are successful at expediting construction of the Cut B widening, it will be considered as part of a "general re-evaluation" of the ports of Tampa, Manatee and St. Petersburg. Congress directed the Corps to begin the re-evaluation in 2001, but construction is not scheduled to begin until 2008, Leeser said.

"We're still in a very preliminary stage of the Tampa Harbor study," she said. "All we have so far is a list of the things that could be done - 'wish lists' from the ports, the pilots, other channel users and the environmental community that define problems and ideas for solutions."

Over the next 18 months, Leeser and the Corps will sift through those ideas to define feasible alternatives and narrow options down to those that address the most important problems.

"I like to have at least four plans, including one that doesn't call for any structural changes at all," she said. "From there, we'll begin a formal analysis of the plans, including costs and environmental impacts."

From a historical perspective, the Cut B widening is likely to make the final list, Leeser said. The original plans drawn in the late 1960s called for a 600-foot-wide shipping channel but piers on the old Sunshine Skyway Bridge may not have been able to accommodate a channel that wide.

"The conclusion I'm drawing is that the 500-foot channel was limited by a bridge that is no longer there."

A dozen projects - ranging from the Cut B passing zone to widening and deepening other channels in both Hillsborough and Pinellas counties - are being reviewed, but not all will make the final list. "To be recommended, the benefits to taxpayers have to be greater than the costs," she said. "It's pretty unlikely that more than three or four of the measures on that list will actually be implemented."

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