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Current groundwater levels in South Florida are a major contributor to inland flooding.

December 13, 2017

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As South Florida raises groundwater levels to fight saltwater intrusion, the threat of inland flooding will only increase, according to newly published research results.

Although high groundwater levels in South Florida are a major contributor to inland floods, especially during the wet season or extreme rain events, traditional flood models don't account for the groundwater beneath our feet, scientists have found.

Now, hydrologist Michael Sukop of Florida International University and colleagues have released a model that points to South Florida's groundwater policies as a cause of the region's flooding.

The results are published this month in the journal Science of the Total Environment. The study was funded by a grant from the National Science Foundation (NSF).

South Florida protects its drinking water sources from saltwater intrusion by keeping groundwater levels high. As sea level rises, groundwater levels may need to be raised even higher, which could cause yet more flooding, Sukop said.

It's a trade-off, he said, that water resource managers need to deal with as they try to control floods, while ensuring water supplies for human consumption and maintaining the integrity of the environment.

"This research shows that sea-level rise, rainfall and groundwater can interact to create significant 'nuisance' flooding -- flooding that leads to public impacts such as road closures," said Tom Torgersen, program director for NSF's Water, Sustainability and Climate Program, which supported the research.

Added Sukop, "Many current flood models treat the land as an impermeable surface when, in fact, South Florida's land surface is highly permeable and the water table is very close to the surface.

"Our model offers a different way of understanding and addressing the flooding problem. When it rains hard enough, or when tides are high, the water table can come all the way to the surface and cause flooding."

Sukop collaborated with Jeffrey Czajkowski, managing director of the Wharton Risk Management and Decision Processes Center at the University of Pennsylvania, and researchers from nine other universities and government agencies to assess flooding risks posed by groundwater, including the economic costs.

"Our analysis reveals the historical relationships between flood insurance claims and groundwater levels in Miami-Dade County," said Czajkowski.

"We're able to quantify the economic trade-offs of simultaneously meeting both the flood control and freshwater demands of the urban sector, information we expect to be useful in South Florida where new strategies for managing the region's water resources are being sought."

Sukop examined groundwater levels in parts of northeast Miami-Dade County. Looking at data from the past 40 years, he found that groundwater levels are rising at the rate of local sea level. As a result, parts of Miami could see a doubling in the number of damaging floods and a tripling in the number of severe floods by 2060, Sukop said.

The researchers hope the information will help water resource managers and urban planners better understand flooding and the economic impacts of keeping water tables high to control saltwater intrusion.