Stilt homes, raised roads, maybe a huge wall. Can Miami-Dade stay safe from storm surge

It’s been almost a century since a powerful hurricane drove storm surge up the Miami River, a worst-case scenario for what is now one of the most densely populated and at-risk coastal cities in the nation.

Ever since Hurricane Andrew set the bar in 1992 for how much damage a storm could do in South Florida, Miami-Dade has avoided the direct path of any of the powerful hurricanes that have crisscrossed the peninsula in recent decades.

But Hurricane Ian’s devastation on the Southwest Florida coast sent a chill up the spine of anyone in Miami worried about the next big one — and it sharpened the focus of federal planners working to design and build new barriers to avoid a similar outcome for Miami-Dade.

“That storm is a reminder of the vulnerability that exists in Miami-Dade County and other coastal communities,” Michelle Hamor, chief of the planning and policy branch of the Army Corps of Engineers, said in a recent kickoff meeting to design a multibillion-dollar federal project to address a devastating hurricane threat often downplayed in Florida.

“It was a clear demonstration of the power of a hurricane to move a wall of water ashore,” said Miami-Dade’s Chief Resilience Officer Jim Murley, in a Tuesday meeting about the project. “Storm surge is the reason the U.S. government has studies going on around the country to evaluate options we have for future protection of the people and the property in Miami-Dade County if we were to experience something as severe as a Hurricane Ian.”

The Back Bay Study, as it’s known, is the biggest potential project to confront the challenge of Miami-Dade’s huge storm surge risk, but it’s only one of several ways the county and state are tackling the looming problem.

A $5 billion solution

The Corps is revisiting a study of the best options to protect the county from its biggest risk in a hurricane — storm surge — after residents, politicians, environmentalists and the business community rejected massive storm surge walls that formed the cornerstone of the Corps’ original $5 billion 2021 plan.

The walls, up to 20-feet high in spots, would have stretched for miles along the coast. In one place it would have run along the bottom of Biscayne Bay, and tied into floodgates at the mouth of Miami’s big rivers and canals. The wall options were widely panned as ugly, environmentally destructive and socially divisive, with “winners” on the inside of the wall and “losers” on the outside. But by the Corps’ calculations, they would have saved hundreds of thousands of buildings in Miami-Dade from tens of billions of dollars in potential damage from a storm with surge rivaling Ian.

This time around, the Corps has given into community pressure for something a little greener, with a focus on natural-based solutions.

“We pushed really hard for that, with public input,” Miami-Dade Mayor Daniella Levine Cava said in an interview. “We’re very happy the Army Corps agreed with us to incorporate natural barriers in the plan to prevent the most disastrous parts of storm surge.”

That doesn’t mean there won’t be a wall at all. In a Tuesday presentation to Miami-Dade’s Biscayne Bay board, Hamor said the Corps was considering solutions that combined natural solutions like storm surge walls, as well as elevating and flood-proofing more homes and businesses to potentially shorten the length of wall needed.

“The question is, is there a scenario where a storm surge wall would make sense in our county?” Murley said.

It’s hard to understate how bad it would be if Miami-Dade got a direct hit from a hurricane with a massive surge. The Corps used computer models to estimate the loss from a worst-case scenario storm — think Hurricane Andrew, but probably a bit bigger. If that example storm hit today, the Miami River could see nearly nine feet of storm surge, and around seven feet in the Biscayne Canal.

Then, they added the projected impacts of ongoing sea rise. If that exact same storm were to hit in 2079, with the additional three feet of sea rise Miami could see by then, the numbers get much higher: twelve feet in the Miami River and eleven feet in the Biscayne Canal.

But with the delayed re-start of the Corps study, construction on any of the potential protections — like home elevations, flood-proofing important public buildings like hospitals and fire stations and mangrove replanting — could still be almost a decade away.

“It’s not if, it’s when the next storm hits Miami,” Col Patrick Kinsman, the Corps’ Norfolk district commander, told Miami commissioners last year. “Every year this 200-year storm could happen. We all hope it doesn’t, but eventually, it’s going to.”

In the meantime

But the federal project isn’t the only way South Florida is tackling its monumental storm surge risk. The two main solutions to the risk of the ocean coming ashore are to armor the shoreline and raise buildings — at least the important parts of them — up and out of the water’s way. And buildings in Florida have been moving up for more than a decade.

In 2012, the statewide building code, which sets a floor for local regulations and is revised every three years, was bolstered to expand the designated zones must vulnerable to surge, requiring the elevation of significantly more new construction above expected flood range. Coupled with updated FEMA flood maps across the state, new homes in flood-prone areas now have to be built as much as 10 feet off the ground in some spots.

In the Florida Keys, which had seen its islands swamped repeatedly by successive storms, that change has led to one of the most iconic (and common) types of home: the house on stilts.

Miami-Dade, though not quite so vulnerable as the Keys, has not gone that far yet. Nonetheless, the county has extensive stretches of coastline and beachfront where new build homes have to be elevated several feet.

Today, the habitable spaces in newer homes in neighborhoods along surge-prone areas of affluent Coconut Grove, Coral Gables and municipalities to the south are built atop massive mounds of fill, on columns, or above garages and flow-through open areas. In Miami Beach, gentrification and fear of surge have driven the demolition of dozens of historic houses that are replaced by mega-mansions sitting at a higher elevation, while new towers must have critical utility and mechanical services and connections well above ground level.

Last week, Miami-Dade County passed a new law mandating that property lots, roads and canal banks in unincorporated Dade (about a third of Miami’s municipalities that rely on this code) have to be built at least six feet up, specifically because of the risk of storm surge to much of the county.

While moving up doesn’t seem to pose political problems, moving away from water certainly does.

That same commission is still near deadlock on a related decision to redirect development from vulnerable areas. Four deferrals later, the Miami-Dade’s Commission is set to once again debate opening up the Urban Development Boundary to allow a massive industrial development in a high storm surge area in South Dade.

Developers have promised to elevate the property as much as seven feet to keep it above the risk of surge, which sparked concerns from next-door neighbors in one-story homes that already flood.

Meanwhile, intense development has no sign of slowing down in Brickell and Miami Beach, both of which face some of the most significant storm surge risk in the county.

Sea walls, ‘living shorelines’
Some coastal communities continue to rely on old approaches but are quickly exploring new ones.

Mostly residential, Key Biscayne’s and Miami Beach’s bayfronts are shored up by seawalls, many of which are crumbling or built too low for rising seas. Miami Beach has been gradually rebuilding or requiring developers to replace miles of old seawall, including along portions of Indian Creek, with higher and sturdier versions, but planners say that won’t be enough.

Instead, Miami-Dade County and municipal officials are pushing for nature-based solutions, such as artificial reefs on the ocean side and the creation of new mangrove islands and “living shorelines” within the bay to absorb and reduce the force and size of storm surge, among other ideas.

Along the Miami Beach and Key Biscayne oceanfronts, the Corps also has spent millions over decades replenishing beaches on the barrier islands, which naturally erode and change shape from tidal action and storms. Both municipalities have also re-created a first-line defense system of sand dunes and berms along their beaches to blunt or even block the expected surge. On South Beach, the dunes — which average nine feet in height along the city’s entire beachfront — are 18 feet tall in spots.

The Beach has also spent millions raising roadways and installing giant pumps to quickly get rid of stormwater. Its code now requires new buildings to be designed in such a way that the second story can be converted to a ground-level entry when streets in front are eventually raised, city planning director Tom Mooney said.

Still, planners concede, a big-enough surge would overwhelm those naturally-inspired defenses and invade streets and neighborhoods. And in spite of rules that improve water resistance for new construction, much of the Beach’s signature architecture, including its historic Art Deco and Miami Modern hotels and apartment buildings, sit at ground level, exposed to severe damage from surge.

“We do have a very mature dune system,” said Amy Knowles, the Beach’s chief resilience officer. “It’s very protective. That doesn’t reduce the hazards we face. We know we are very vulnerable. It’s not reasonable to think that what we’re doing would mean there would be no damage from a 15-foot storm surge. That is not something a coastal city can plan for.”

Key Biscayne is also starting on a surge protection plan its building director, Jeremy Calleros-Gauger, called “audacious.” It involved elevating miles of roads, under grounding utilities, hardening infrastructure and building well above the flood plain, all funded by a $100 million bond residents recently voted to approve.

These ideas, many of which are also in the county’s resiliency strategy, are meant to get buildings and infrastructure out of the way of rushing water to make recovery simpler and faster.

“We have to build higher, obviously. We have to first keep out of the water and when it comes, get rid of it quickly,” Levine Cava said. “Those are basically the approaches for a wetter future,”

This story was produced in partnership with the Florida Climate Reporting Network, a multi-newsroom initiative founded by the Miami Herald, the South Florida Sun Sentinel, The Palm Beach Post, the Orlando Sentinel, WLRN Public Media and the Tampa Bay Times.