By Kathy Fitzpatrick, Martin County Coastal Engineer
Small coastal communities are particularly vulnerable to powerful storms. They often have a small tax base that doesn’t generate enough revenue to repair significant storm damage.
As the atmosphere grows hotter, storms are becoming more frequent and destructive. Martin County learned that expensive lesson in 2017 when Hurricane Irma sideswiped the county. The damage to county infrastructure was an estimated $13 million and included damage to sensitive ecosystems and vulnerable coastlines.
Located on the state’s east coast, Martin County is home to many aquatic ecosystems, including sensitive estuarine tidal systems. One way to minimize the damage from storms is to create more resilient natural systems that can store excess water, dissipate storm energy and provide invaluable habitat.
The Jensen Beach Impoundment (JBI) is one such area. It is located on the barrier island (Hutchinson Island) along the Indian River Lagoon.
Nearly lost to the 2017 hurricane, this 150-acre mangrove wetland is an Estuary of National Significance that is home to nearly 2,500 plant and animal species. The JBI mangrove habitat, with its complex root structure, provides essential storm protection and shoreline stabilization for the barrier island.
A study by The Nature Conservancy in Collier County found that a healthy mangrove community reduced both flooding and storm damage by about 24%.
The JBI comprises one of the largest contiguous area of mangroves on Hutchinson Island. These mangroves are essential to the health of the lagoon’s estuarine system because they provide water storage, allow for nutrient cycling, foster productivity at the base of the food chain, and function as breeding grounds. JBI provides safe habitat for juvenile birds and fish, critical habitat for protected species, and substrate for oyster growth.
Decades ago, officials encircled the area with a berm to control Black Saltmarsh mosquito breeding. The berm also blocked the fish from moving between the estuarine and the shallow mangrove habitats. The need to balance human comfort with ecosystem health was recognized. Interior channels and culverts were added later to better facilitate water circulation and fish movement through the impoundment and into the estuary.
Hurricane Irma severely damaged that plumbing. Strong onshore winds and associated storm surge pushed water through the St. Lucie Inlet and into the lagoon. That water flooded over the impoundment berm for days on end.
The true impact on the impoundment was not realized for several months, until drone footage revealed acres of dead and dying mangroves. Investigations revealed several factors that contributed to this die-off: a long period of extreme high water; storm surge and winds toppled trees that blocked water flow; and sediment clogged the channels.
Without adequate circulation, oxygen levels became depleted and created an anoxic environment that killed the remaining mangroves.
The project to restore the mangrove habitat in the impoundment was developed in partnership with state agencies and an environmental non-profit organization.
The hydrological restoration is removing blockages and returning the channels to their intended depth. To reduce the potential for these events to recur and enhance the flow channels, redundant circulation paths were created by installing three new interior culverts and one additional culvert connection to the lagoon.
Environmental education centers will connect students to the environment as they monitor water quality and the growth and distribution of new mangroves within the impoundment.
Kathy Fitzpatrick is the Coastal engineer for Martin County and serves as the resilience coordinator working with the amazing team of Martin County’s engineers and scientists that were responsible for the JBI project and so much more.
“The Invading Sea” is the opinion arm of the Florida Climate Reporting Network, a collaborative of news organizations across the state focusing on the threats posed by the warming climate.