Designing coastal waterfronts for South Florida’s wet future

At this past week’s ReeFlorida Symposium, a conference held at the Phillip and Patricia Frost Museum of Science, researchers from all over the U.S. gathered to share ideas on how to save Florida’s Coral Reef, the only barrier coral reef system in the continental U.S.

One presentation, by Florida International University’s Martina Potlach, looked at using nature as a role model to design coastal areas where humans can adapt to pending sea level rise.

She said that by the end of the century, large areas of South Florida are projected to be under some level of water.

The National Oceanic and Atmospheric Administration’s website says that “about 2 feet of sea level rise along the U.S. coastline is increasingly likely between 2020 and 2100 because of emissions to date. Failing to curb future emissions could cause an additional 1.5 – 5 feet of rise for a total of 3.5 – 7 feet by the end of this century.”

Assuming there is some reduction in emissions, a 4-foot rise in sea levels would inundate major parts of Fort Lauderdale and Wilton Manors.

Potlatch, with her background in landscape architecture and environmental sciences, argues we need to reconceptualize how shorelines work if humans are to live in coastal South Florida as storms intensify and the sea moves in — science-informed design is necessary going forward, because of climate change.

Seawalls are the go-to measure, she said, and referred to the Army Corps of Engineers’ proposal to build a 20-foot seawall through and in front of Miami in order to protect it from a future Category 5 hurricane. City planners rejected the idea and are formulating something that incorporates the green infrastructure Potlach favors.

She explained how a layered series of green infrastructure would help protect the human world along the coast. As waves or storm surge comes ashore, they would first hit coral reefs, then seagrass beds, then living oyster barrier islands and ridges, then a matrix of mangrove roots.

Each layer and complex surface dissipates wave energy. “Wave height and strength is attenuated before reaching the developed waterfront,” she said.

A fringe benefit is that each of these elements is fantastic habitat for a range of marine life including shrimp, lobsters, snook, manatees and dolphins.

There are challenges. In an effort to protect mangroves, the 1996 Mangrove Trimming and Preservation Act forbade the general public from trimming mangroves. A negative side-effect was that it caused developers to shy away from planting mangroves in waterfront landscaping, she said. It’s been frustrating, but now there are arborists licensed to trim the plants, which Potlach hopes will make landowners more willing to add the plants to their waterfront plans.

And the coral and seagrass buffers she envisions both require better water quality than what is currently flowing out of canals and rivers in Miami, Fort Lauderdale and Palm Beach County. High nutrients kill seagrass beds and sediment weakens coral.

That water quality is tied to the entirety of the Everglades, which starts flowing just south of Orlando, and is also linked to local lawn care, farms and golf course runoff.

Will seawalls be useless against a potential 6 feet of sea-level rise? To that she said, coastal resilience is “the ability of a community to bounce back after a hazard such as a hurricane, storm or flooding, rather than simply react to its impacts … it’s not to prevent an event altogether.”

“I think we need to selectively use seawalls, and to use them in moderation, and hybrid solutions are important.” Homeowners can use materials that encourage the growth of oysters, and there are seawall surfaces that mimic mangrove roots, both of which are better for biodiversity and for weakening wave energy than the current hard surface walls, which reflect waves as opposed to absorb their energy.

She thinks the biggest challenge is to shift our society’s perspective from managing, controlling and diverting water to working with water.