Situated at the mouth of the Matanzas River and in the crosshairs of countless hurricanes over the centuries, St. Augustine's primary threat has always been water, in the form of river flooding, extreme tides, and storm surge.
The Spanish colonial government first addressed these dangers in 1696, building a coquina and limestone seawall to protect its settlers and soldiers. From 1837-1846 (Florida was granted statehood in 1845) the U.S. Army rebuilt the deteriorating seawall with an improved mix of coquina and cement which, with frequent maintenance and repairs, held up reasonably well for over 160 years, the release states.
From 2012-2014, with the help of a $4.7 million FEMA Flood Mitigation Assistance grant, a new 1,200-foot reinforced concrete seawall was constructed, enhancing the city's flood defenses while preserving the historic value of the old seawall and the tourist-friendly atmosphere of the neighborhood. The new wall not only provides improved protection from flooding, but also supplements the city's tourism industry; built 13 feet farther into the bay, the project includes a pedestrian walkway along the waterfront that also provides a close-up view of the historic, coquina seawall, according to the release.
On Oct. 7, the new seawall received its first major test as Hurricane Matthew swept up the Florida coast, unleashing a seven-foot storm surge on St. Augustine bay. Water crested over the top of the seawall, causing moderate flooding throughout the area, which was exactly what the engineers had planned for; they'd designed it to provide full protection for a Category 1 storm. Matthew hit as a Category 3.
"Even though we knew it could only perform to a certain level, it exceeded that to some degree in this storm. It performed at or above the original design," Miles Anderson, Florida Department of Emergency Management bureau chief of mitigation, said in the release. "It didn't give us 100 percent protection, but it did what it was designed to do."
The key was finding the right balance between flood protection, historic preservation, and economic vitality, while also performing the work under strict environmental and archaeological guidelines.
"St. Augustine is an historic city," said Gabriela Vigo, Region IV hazard mitigation assistance specialist. "So, we have to be sure when implementing mitigation measures not to disturb or destroy that history. This includes the St. Augustine river view.
"To comply with Section 106 of the National Historic Preservation Act we had to do an environmental assessment that resulted in a FONSI, a Finding of No Significant Impact," Vigo adds. "We had to have an archeologist on site during construction. We had vibration monitors set up during the whole process because we had all those historical homes that needed to be protected. And when you're using a cofferdam to build the walkway and the new seawall, you don't know what you're going to find there - all of that is historical property."
Vigo says that the majority of damage over the years resulted from nuisance flooding, frequent but not high-intensity events such as full-moon tides or severe swelling from rain upriver. "This seawall will protect the historical buildings and the quality of the city against those kind of nuisance events," she said, "but it was never meant to protect against a Category 3 or 4 hurricane."
The scope of the project addressed issues beyond minimizing potential floods. A new stormwater management system, in compliance with federal, state, and local regulations, consists of an exfiltration trench and three Vortechnics storm-water treatment vaults to improve the water quality at the discharge from the city's existing hydrologic basins. Each vault is installed beneath the new promenade, extending through the seawall into the Matanzas River.
The project cost a total of $6.3 million, with FEMA contributing 75 percent, or $4.7 million.
Perhaps the most important factor in the success of the seawall was the cooperation and collaboration of its stakeholders, the release states. Looking back on the many stages of the project, Miles Anderson said, "The whole community was engaged - residents, city administration, business community ...; everybody was really engaged. And when they're engaged, it happens."
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