Opting for Softer Infrastructure to Reduce Miami’s Coastal Flood Risk

As the reality of rising sea levels settles in, America’s coastal communities are grappling with how to brace themselves for the coming onslaught without sacrificing character and livability.

As one of the U.S. cities most vulnerable to climate change, Miami would be on the cutting edge of this conundrum. Over the past year, a clash over how best to protect the city from future storm surges showed both the perils and possibilities of these debates.

In 2020, the Army Corps of Engineers rolled out a plan to build a sea wall to protect parts of the Back Bay area, but residents, policymakers, and developers pushed back. They argued that the unsightly structure would mar downtown Miami and exclude many residents from protection. The federal agency, for its part, retorted that local actors were being unrealistic about the dangers facing the city. The Miami-Dade County council formally rejected the plan at the end of August.

But Miami officials insist that they are not just reflexively objecting to the Army Corps’ proposal, and that they know that hard barriers will have to be part of the solution. There are alternatives on hand, like the one paid for and promoted by local development group Swire Properties, which incorporates more natural barriers and a reduced flood wall.

“I think this is really important nationally, because if you look at the [proposed federal] infrastructure bill, you will see ‘coastal storm risk management’ and ‘coastal resilience,’” says Jim Murley, chief resilience officer for Miami-Dade County. “What we’ve seen in practice today, those terms mean what the Corps is doing with us. . . .People think we totally abandoned the idea of structures. We didn’t! But how do you develop them in a highly dense urban area?”

From Swire and Miami’s perspective, the Army Corps proposal was too detached from community input or feedback, despite the outreach and meetings the agency held, many of which had to be held online due to the COVID-19 pandemic.

The Army Corps’ rejected plan would cost as much as $6 billion and extend six miles (9.6 km), running between the coast and vulnerable neighborhoods. One-sixth of it would line part of scenic Biscayne Bay, where deep piles would have to be driven into the water to support a structure soaring up to 20 feet (32 km) in height above sea level.

The sea wall was not the only part of the Army Corps’s plan, but it was by far the most unpopular. The public and local politicians embraced many of the agency’s other proposals, including the flood proofing of thousands of local businesses, building flood gates at the mouths of rivers, and paying to elevate homes out of harm’s way. Many of these latter ideas had the benefit of protecting against both storm surge and flooding from more everyday sources of danger like water rising through the porous limestone Miami is built upon.

The Army Corps’ plan is a reaction to Hurricane Irma, in 2017, which did not directly hit Miami but caused extensive flooding nonetheless. Since then, the agency had been working on a plan to try to head off the next such crisis.

But from the perspective of Swire, the plan was set up to fail even if the Corps’ heart was in the right place.

“They had done some community outreach groups, but then went back to their barracks and conjured up a solution without stress testing it against public opinion,” says Kieran Bowers, president of Swire Properties. “When they presented it to the public, it was pretty clear that this was going to be a concrete edifice carving its way through the bay and parts of the city. That woke people up pretty quickly to this being not a best practice or a particularly good idea.”

Bowers says part of the issue was that their approach was made in isolation from its surrounding built and natural environment. Although initial public reaction was muted, once Swire and other development interests in Miami began pushing back, they brought a lot of other opponents to their side quickly.

“It was obviously a very unflattering image and I think it’s very hard to recover from that,” says Bowers. “We believe that the private sector has some degree of obligation to help contribute to public sector debate on matters of such fundamental importance, like storm surge or sea level rise.”

Swire hired the engineering and infrastructure company Moffatt & Nichol to craft an option they thought would be both more visually palatable and better at preserving property values. The concept is a layered defense of the city, which begins with submerged oyster reefs. Those are followed by an earthen wall called a berm, with a boardwalk built atop it. This second layer will be further strengthened with mangrove trees, which have proven especially effective at slowing waves, and it could easily be built up higher in future with additional sediment and rock. A third and final barrier would be a smaller seawall than the federal proposal at the shoreline.

The idea is to dissipate the energy of the waves as they approach the city, thus lessening the need for a soaring sea wall of the kind originally proposed by the Army Corps. That way there is no single point of failure, and both the oyster reefs and the berm (with boardwalk) will introduce further amenities to the city–not just protection.

“You have these levees that can still function to be public access and bring social benefits,” says Lynette Cardoch, director of resilience and adaptation at Moffatt & Nichol. “You’re not disconnecting people from the ocean and the things that make Miami unique.”

Cardoch says the intent of the Swire proposal, and the general pushback against the Corps plan, was not intended to end the conversation or be disrespectful to the federal engineers. Instead, the city, and private interests like Swire, want to continue the conversation with the Corps and push plans in a new direction.

“It shouldn’t be a binary conversation of either concrete wall or nature,” says Bowers. “And we’re not pushing this as a silver bullet solution. Maybe there’s an even better one out there. We’re just saying this is an alternative, but I’m sure there are some very smart people out there that can come up with something even better and more cost effective.”

Bowers says he was surprised by how muted early reaction to the proposed Army Corps sea wall was, and that, along with other business and development interests Swire organized to try and present an alternative. After all, with Miami attracting more and more population in the COVID-era, it is incumbent upon private actors like him to contribute to the conversation and preserve what is unique about the region.

“We decided to put forward an alternative vision that is not reliant on a city process or various types of [public] funding,” said Bowers. “We know who we should be contacting, we know that we can fund it very, very quickly, and come up with something that is at least going to be an asset to the city and not a blight.”

These issues are not exclusive to coastal environments. Cities like Chicago are also being looked at by the U.S. Army Corps of Engineers as heavier rainfalls and droughts are causing increased flooding.

More from Urban Land:

• Four Approaches to Reducing the Urban Heat Island Effect

• ULI Coastal Forum Looks at How Toronto Is Floodproofing for the Future