In fact, a new study by University of South Florida researchers Mark Luther and Steve Meyers shows that storm surges in downtown Tampa could increase significantly if Egmont Key disappears.
The USF team simulated water levels using data collected from 1948 to 2010, then ran the same simulation without Egmont Key in place. While much of the lower bay would not be impacted, storm surges at northernmost spots of Hillsborough Bay could increase by up to five inches. Higher waves and stronger currents that are now broken by the island would slow the return of water to the Gulf after it had been pushed into the bay. The models also predicted a 4-inch increase in Old Tampa Bay during 100-year storms.
“It’s always hard to predict what could happen in any storm and we need to be clear that this is the worst-case scenario,” Meyers said. “We totally removed Egmont Key from the model and that’s not likely to happen in the near future.”
However, because the areas that would be impacted are highly developed, the economic impact of even a small increase in water levels could be significant, he adds. The study, published recently in the journal Frontiers in Marine Science, also notes that similar effects could be seen with even 25-year storms.
Historically significant, politically challenged
Egmont Key, which blocks about one-third of the bay’s mouth, has eroded significantly over the past 70 years, with much of the erosion attributable to the ships’ wakes coming from the nearby channel which connects Port Tampa Bay and Port Manatee to the Gulf of Mexico. Slightly over half of the island has disappeared, with parts of a historic fort built during the Spanish-American War now underwater on the western shore that borders the shipping channel.
The eastern shore has fared better, with a lighthouse built in 1858 still standing on dry land. A critically important shorebird nesting beach is located at its southern tip. Egmont also provides important habitat for both gopher tortoises and sea turtles.
Part of the problem stems from multiple layers of ownership. It was designated a National Wildlife Refuge in 1974 with part of the island managed by the U.S. Fish and Wildlife Service. It also is managed as part of the Florida Park Service and is on the National Register of Historic Places.
The key player in protecting the island from additional erosion, however, is the U.S. Army Corps of Engineers (USACE), which is required by Congress to demonstrate that funds they use for beach renourishment have a positive economic impact. And since Egmont’s “value” is far less tangible than an expensive condominium, it’s more difficult to justify federal funds for renourishment.
“Egmont is definitely a concern for the Jacksonville District (of the USACE) but the feeling is that if Congress thought it was important enough to protect, they should allocate funds directly to the FWS,” notes Aubree Hershorin, USACE biologist.
The Corps, however, did fund a project to track the impact of dredged materials that had accumulated in the shipping channel, collecting at a rate of 600,000 to one million cubic yards per year. Typically, these materials are not considered appropriate for beach renourishment because the Florida Department of Environmental Protection has very high standards for sand deposited on state beaches. Material used in renourishment projects cannot cause surrounding waters to become murky or impede the ability of sea turtles to lay eggs on them, either of which could be an issue with materials from maintenance dredging.
“The biggest concern was that the siltiest materials would move right back into the shipping channel where they had been dredged,” notes Zachary Tyler, then a USF graduate student who is now working for the USACE’s Vicksburg office. “We didn’t see that happening.”
With a special permit from the FDEP, a total of 62,000 cubic feet of sand from maintenance dredging in the lower section of the shipping channel was placed in the swash zone – the turbulent layer of water that washes up on the beach after an incoming wave has broken – at the middle of the island where the erosion is most severe. The silty material moved offshore in a matter of days – or hours in some cases – but not far enough to re-enter the shipping channel. The sandier material moved inland, although it didn’t stay in place as long as experts had hoped. Geotubes, which should have slowed erosion when they were installed in 2014, already are visible.
Even though the renourishment didn’t last as long as experts had hoped, beach erosion has been temporarily halted – compared to a loss of nearly 200 feet of beach from August 2012 to February 2014 when the island’s limestone base was exposed in sections, Tyler’s report notes.
There were no impacts to sea turtle nesting or any days in which cloudiness of nearby waters exceeded state limits, he adds.
The Corps will finalize a report on beneficial uses for dredged material in Tampa Bay later this year. It expects to continue using materials from maintenance dredging of the shipping channel at Egmont Key, but that only occurs every seven years and the island is eroding faster than that.
A potential new partner may be the Seminole Tribe of Florida. Egmont was used as a staging site where Seminole Indians were held before they were sent north to the Panhandle in the late 1880s and then to reservations in the western U.S. Many Seminoles who were held in pens on the island died and were buried in unmarked graves. “We’re hoping that the Seminoles can effectively lobby Congress to save an important burial ground for their ancestors,” said Richard Sanchez, president of the Egmont Key Alliance, which is working to save the island.