Sinking land to blame for floods?
Oliva points to development as reason for flooding. Is this true?
The statement
In a recent interview, Florida House Speaker Jose Oliva was asked about preparations for sea-level rise and whether that’s on his legislative agenda. The question prompted Oliva to suggest the flooding in South Florida “has a lot to do with the infrastructure on Miami Beach, what was built there...” Which made us ponder the question: Is Miami Beach sinking because of the way it was developed, and does that account for flooding from sea-level rise?
The facts
Here is Oliva’s full quote: “Miami Beach is suffering more from it [flooding] than Key Biscayne is, and that has a lot to do with the infrastructure on Miami Beach, what was built there and the fact that Fisher put a lot of sand on Miami Beach and they had a lot of fill and they built there. And maybe it’s also settling throughout time as things tend to do.”
First off, the Fisher in Oliva’s statement is Carl Fisher, who was behind much of the development in Miami Beach in the early 20th century.
We asked Oliva’s office for evidence supporting his statement, and an aide forwarded a summary of a joint study by the University of Miami and the University of Padua in Italy about subsidence — another word for sinking — on Miami Beach.
Sure enough, the study concluded that parts of Miami Beach are sinking on the island’s west side at a rate of 2-3 millimeters per year, about the width of a nickel. Over the past 80 years, the study estimated, some houses might have sunk 6-9 inches.
We reached out to one of the study’s authors, Shimon Wdowinski, to find out more.
Wdowinski, now an associate professor at Florida International University, said the parts of Miami Beach susceptible to sinking are largely confined to areas facing Biscayne Bay, where mangroves were torn out and replaced with fill material. Over time the fill and the mud and peat below it dry out and change in composition, which can cause sinking.
Harold Wanless, a geologist at UM, said sinking is a non-issue on much of Miami Beach, where pilings for large buildings are driven deep into the limestone formations. Those don’t sink.
Even if some isolated areas are prone to sinking, experts say that process halts after a period of decades.
In contrast, that real threat from rising seas lies in the future. NASA’s Jet Propulsion Laboratory estimates a global sea level increase of 3 inches since 1992. The sea level by 2030 is projected to be 6-10 inches above the 1992 level, accelerating to 14-26 inches by 2060.
Oliva appears to be highlighting an issue that has significantly less to do with the long-term future of coastal areas like Miami Beach and Key Biscayne than the impacts of rising sea levels due to melting Antarctica and Greenland ice sheets and other environmental changes, such as warming ocean temperatures.
We shared Oliva’s statement with John Englander, an oceanographer who studies rising sea levels.
In an email, he responded, “...in the coming decades, as Greenland and Antarctica melt at a faster pace, the rate of global SLR (sea level rise) will overwhelm most of the localized nuance. Instead of focusing on those slight variations, all low-lying coastal areas need to recognize increased flooding from the short term flood events and the quasi-permanent higher sea level.”
Oliva isn’t the first politician to offer alternative theories about the effects of, and reasons for, rising sea levels. Rep. Mo Brooks of Alabama suggested it might have something to do with silt deposits in the ocean from the world’s major rivers. That claim as been debunked.
The bottom line
Asked about sea-level rise, Oliva said flooding on Miami Beach is attributable to portions of the barrier island sinking because of development practices. He is correct that portions of Miami Beach have been sinking over the years, but his answer overstates the localized nature of that phenomenon. His answer also offers a narrow view of the problem and misses the big picture of sea-level rise and what it’s going to mean to Florida’s coast. We rate his statement Mostly Fake.