Can mangroves save Miami’s coast from sea level rise? Experts say they could help

Members of an Urban Land Institute task force took a boat tour Monday to survey Miami’s waterfront, which is vulnerable to sea level rise. The city expects more than two feet of sea rise by 2060, which could swamp millions of dollars of real estate.
Members of an Urban Land Institute task force took a boat tour Monday to survey Miami’s waterfront, which is vulnerable to sea level rise. The city expects more than two feet of sea rise by 2060, which could swamp millions of dollars of real estate. aharris@miamiherald.com

‘Living shoreline’ might have been the most repeated phrase Friday morning in Miami’s city hall, where a panel of experts reviewed plans to protect the city’s coast from sea level rise.

They gave the city high marks for its efforts so far, including allowing extra tall first floors to allow for future elevation, but said Miami needs to focus more on the riverfront and come up with a master plan for all waterfront development. Not to mention figure out how to pay for potentially expensive projects. One politically touchy option the experts floated: A special tax on waterfront residents and businesses.

But panelists kept bringing up the need for more “living” shorelines — when a concrete sea wall is bolstered with plants like mangroves and native grasses, which break up thrashing waves, soak up floodwaters and even make the water cleaner.

Living shorelines are the big idea behind the upgrades proposed by the Downtown Development Authority to the city’s baywalk, the required public space between waterfront buildings and the coast.

The city has considered the idea in the past, including along a section of a church parking lot in Brickell it wants to convert, but said getting a permit from the county’s environmental department was such a challenge that staffers abandoned the effort, at least for now.

Downtown Development Agency

Miami and the Downtown Development Authority paid about $130,000 for the analysis by an expert team from the Urban Land Institute, which spent a week examining the city’s vulnerable spots and interviewing relevant people before presenting their findings Friday. They looked at parks, street ends and the baywalk and considered solutions for the looming threat of sea level rise.

And it’s coming soon. By 2045, surging seas could put more than 13,000 people — and $37 million in property taxes — at risk in the Magic City alone, according to calculations by the Union of Concerned Scientists.

Much of that risk is, naturally, clustered along the waterfront, which is home to skyscrapers full of people paying high rents to live near Biscayne Bay. The city’s original vision to have a continuous public space between the water and the condos is now seen as a new opportunity to protect Miami from the sea.

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“It’s not just a jogging path. It’s our front line defense for sea rise and storm surge,” said Miami Commissioner Ken Russell, whose narrow district covers the city’s bayfront. “It’s the divide between the water and the people and it’s the convergence point as well.”

The ULI experts gave a thumbs up to the draft ideas for the city’s baywalk, including living shorelines and porous pavement. Neal Schafers, from the DDA, said consultants plan to hand over their drafts to city staff “any day now,” where they’ll undergo final tweaks before heading to the city commission.

But it’s unclear just how feasible the new ideas are.

One of the ULI panelists, Susannah Ross, a landscape architect from Boston, said she heard in interviews that the main obstacle was permitting with the county because of environmental concerns like seagrass dieoff and loss of manatee habitat.

“They’re not being considered as regulations because there’s an understanding that the Department of Environmental Resources Management won’t approve anything that goes into the water,” she said. “It’s a shame to us that it’s environmental concerns coming up against other environmental concerns. We’re getting nowhere.”

DERM Director Lee Hefty clarified the department supports living shorelines, but said many of the suggested projects they’ve had issues with want to expand the shoreline into the bay rather than take up part of the existing real estate.

“The county — and DERM in particular — are very supportive of living shorelines projects. We’ve built a number of them ourselves,” he said. “The bay should be reserved for things that are part of the bay. We’re not promoting anymore dredging and filling into the bay.”

Concept sketches show possible visions of Brickell Bay Drive after a sea rise friendly revamp, which could include the installation of a living shoreline City of Miami

Living shorelines aren’t a new concept for Miami. The city was considering a demonstration project at the First Presbyterian Church at 690 Brickell Ave. last year. That plan to upgrade the church’s 250-foot patch of baywalk this year with a new seawall is still in motion — just without a living shoreline.

“It’s been in flux and part of that is the DERM conversation,” said Russell.

The city plans to pay for the upgrade itself, a loan that will be repaid whenever the property is redeveloped. Miami won a $150,000 grant from the Florida Inland Navigational District in 2017 to cover the design work, and FIND is currently considering whether to give the city half of the $1.5 million it needs to build the seawall.

“It was going to take too long to permit the living shoreline,” said Jane Gilbert, the city’s chief resilience officer. Delays may have impaired the city’s ability to get a FIND grant. She said they can potentially come back and add in grasses and mangroves later once the permitting comes through.

“It need not take too long to get a permit if the project is properly designed,” Hefty said.

The panel also suggested the use of living shorelines along the Miami River, which they noted as a much more vulnerable community of people that doesn’t have the same potential protection an upgraded baywalk offers.

“Generally the fancy people in high concrete buildings are going to be OK. What about the tens of thousands of people who live in homes at grade?” asked John Macomber, a finance professor at Harvard University.

Unlike the baywalk, where many of the buildings are already elevated and the only things that flood are parking garages, the floodplain along the river touches more homes that aren’t as prepared for rising seas.

“The river is a greater challenge for us,” said panelist Jay Valgora, head of Studio V Architecture in New York. “You may require greater investments here, where you can’t actually allow the water in.”

One solution the panel proposed: giant floodgates at the mouth of the river, like the London Thames Barrier. The hope is that it might be suggested (and partially funded) as the conclusion of the Army Corps of Engineer’s ongoing study of the area.

But what if Miami has to turn inward to find the money for any of these projects, much less a gigantic set of floodgates?

The panel suggested tax options, like a specific tax for the waterfront area or a vacancy fee, which they estimated could bring in $95 million a year. Or Miami could work with developers to encourage high density development on high ground, near mass transit and away from the vulnerable coast.

“We know these are ideas you’ve discussed before,” said panelist Matt Steenhoek, vice president of development at PN Hoffman in Washington, D.C. “What we’re suggesting is you look at them again, in a new light.”

The ULI team will return with a fleshed-out version of these recommendations in a few months.

Alex Harris covers climate change for the Miami Herald, including how South Florida communities are adapting to the warming world. She attended the University of Florida.