Before Condo Collapse, Rising Seas Have Long Pressured Miami Coastal Properties

The 12-story condominium tower that crashed down early Thursday near Miami Beach was built on reclaimed wetlands and is perched on a barrier island facing an ocean that has risen about a foot in the past century because of climate change.

Source: Washington Post | Published on June 28, 2021

Miami Skyline with palm trees

Underneath its foundation, as with Miami Beach, is sand and organic fill -over a plateau of porous limestone – brought in from the bay after the mangroves were deforested. The fill sinks naturally and the subsidence worsens as the water table rises.

Investigators are just beginning to try to unravel what caused the Champlain Towers South to collapse into a heap of rubble, leaving at least 159 people missing as of Friday. Experts on sea level rise and climate change caution that it is too soon to speculate if rising seas helped destabilize the oceanfront structure. The 40-year-old building was relatively new compared with others on its stretch of beach in the town of Surfside.

But it’s already clear that South Florida has been on the front lines of sea level rise and that the effects of climate change on the infrastructure of the region – from septic systems to aquifers to shoreline erosion – will be a management problem for years to come.

The Champlain Towers South building was recently found to have been sinking in the 1990s and may have continued to sink since then, according to Shimon Wdowinski, a professor at Florida International University’s department of earth and environment, who has studied the area.

Wdowinski co-wrote a paper published in April 2020 that said satellite imagery showed a 12-story condominium building in the eastern part of the Miami Beach area had sunk by about two millimeters per year between 1993 and 1999. Wdowinski said in an interview on Thursday that this was the Champlain Towers South building.

“I was shocked to see it collapsed,” Wdowinski said.

Land subsidence is a gradual settling or sudden sinking of the surface when material that supports it is displaced or removed, according to the U.S. Geological Survey. Erosion and the disappearance of groundwater are two of several factors that cause it.

Wdowinski, whose findings were first reported by USA Today, cautioned that it was not clear whether the subsidence he found was connected to the building’s collapse.

“It appears to be something very localized to one building, so I would think the problem was more likely to be related to the building itself,” he said.

The roof of the building was recently being replaced and other repairs were planned, according to an attorney for the building’s condominium association.

Kenneth Direktor said it was “thoroughly inspected” recently as part of a process in which buildings in Surfside must be recertified every 40 years. The 136-unit condo had recently turned 40 years old and the report on the inspection has been completed and submitted to town authorities.

“There was nothing in the report that would have indicated a life-safety concern,” he said.

Surfside Vice Mayor Tina Paul told The Washington Post that the building had passed its inspection this week.

Miami and nearby beach communities have experienced substantial sea level rise, up to 12 inches over the past century, according to some estimates.

That includes nearly six inches since the mid-1990s, according to a Capital Weather Gang analysis of federal data. That has led to a 320% jump in nuisance flooding in the area over the last 23 years.

According to a new storm water master plan released by the city of Miami in April, it would have to spend nearly $4 billion over the next 40 years to protect the city from floods that result from sea level rise.

The money would be spent on six-foot-high sea walls, massive underground pipes and wells to control a rapid influx of water. Regardless of how much the city spends, some residents would have to retreat from areas that can’t be protected from flooding.

The porous limestone underneath Miami allows the rising seas to filter up through the ground, causing flooding during high tides even on sunny days. The groundwater surge threatens freshwater supplies and septic systems, which are already failing in Miami-Dade County.

The mix of swelling groundwater and tidal cycles juiced by climate change mean coastal buildings and their concrete foundations spend more time in water than they did in the past, said Albert Slap, the chief executive of RiskFootprint, a Boca Raton, Fla.-based company that assesses buildings’ vulnerability to hazards such as storm surge and flooding.

“This is a tragic, devastating event, and it could be a canary-in-the-coal-mine type event,” he said. “It’s not just one building. This could be something that could affect other buildings.”

Slap noted that many coastal structures built on sand that have underground parking lots already rely on around-the-clock sump pumps to keep out groundwater.

“The groundwater enters the pores of the concrete and ultimately weakens it and erodes it,” he said. “So the foundations are subject to a lot of geological forces that could compact the soil underneath; it could cause voids. We just don’t know.”

Video from the scene of the collapse showed rescue workers in the basement parking garage working in knee-deep water, although the source of that water was unclear.

Harold R. Wanless, a professor at the University of Miami and an expert on sea level rise, cautioned that there are too many other possible explanations for the condo collapse to speculate if sea level rise played a role in the tragedy. But investigators needed to get to the bottom of that, he said.

“We’ve got to find out what it is,” he said. “Because it makes living or working in high rises very unattractive right now. Why did this happen?”

Wanless said this area of Surfside was still a few feet above normal sea level. One of the possibilities that must be taken into consideration is whether a sinkhole or some type of collapse happened under the building, he said, but added that this area hasn’t been known for sinkholes.

“About 20 feet down is limestone but that’s not an area that has had any sinkholes that I’m aware of,” he said.

A search of the Florida Geologic Survey’s site for sinkhole reports in the area of the condo’s address on Collins Avenue yields no results. Unlike Miami, which is more prone to sinkholes, Miami Beach is an area where the FGS says “sinkholes are few, shallow, of small diameter and develop gradually.”

“There’s no reason for this building to go down like that, unless someone literally pulls out the supports from underneath, or they get washed out, or there’s a sinkhole or something like that, because it just went down,” Surfside Mayor Charles Burkett said at a Thursday morning news conference.

Another Surfside official, Commissioner Eliana R. Salzhauer, also questioned whether the land underneath the building had been compromised.

“I think this is all tied to sea level rise and our overdevelopment,” she said. “And Mother Earth comes back, and the ocean comes back, and takes it.”

Miami has also long suffered from “king tides,” which are higher-than-normal tides caused by alignments of the sun and moon that have been exacerbated by rising sea levels from melting glaciers and polar ice. These tides, which tend to be strongest in the fall, have routinely caused flooding in the city.

The Army Corps of Engineers recently proposed a $6 billion sea wall up to 20 feet high running six miles along the coast to protect against storm surge. It would not cover Surfside, nor would it protect from tidal flooding elsewhere in the city.