Miami-Dade County

Climate fix for rising seas could foul Miami’s Biscayne Bay

Marine biologists Jeff Absten, right, and Jim Duquesnel gather water samples during the King Tide in Biscayne Bay with a Data Sonde in October. Water samples showed elevated levels of pollution in the bay linked to stormwater pumped from Miami Beach during the high tide.
Marine biologists Jeff Absten, right, and Jim Duquesnel gather water samples during the King Tide in Biscayne Bay with a Data Sonde in October. Water samples showed elevated levels of pollution in the bay linked to stormwater pumped from Miami Beach during the high tide. Miami Herald Staff

Last fall as Miami Beach triumphantly drained its streets, beating back seasonal King Tide flooding that has come to symbolize the perils of climate change, scientists got a different view of what the future may hold: one of the world’s most celebrated beaches surrounded by water too foul for swimming.

New pumps installed to keep the city dry flooded Biscayne Bay with a soup of phosphorus, nitrogen and other pollutants that can feed toxic algae blooms, according to a study overseen by Florida International University geologist Henry O. Briceno. In parts of the bay, the mass flushing caused nutrients to increase six-fold. If pumping were to become a regular practice, nutrients that are “like caviar for algae” could fuel nasty-smelling blooms that kill marine life and turn water a bright pea green, he said.

“You have a dry city. A very safe city,” with increased pumping, Briceno said. “But you won’t have any beaches to bring tourists.”

Over the next three to five years, the city plans to install 20 times as many pumps — between 60 and 70 altogether — capable of pumping up to 20,000 gallons a minute as part of a $300 million-plus fix to keep the island high and drive.

Briceno, who used the annual flooding event to conduct a rare island-wide experiment in real time, relayed his findings to Miami Beach officials. Officials said the work indicates more monitoring is needed, but is not conclusive.

“It gives you a good idea of the potential, but it doesn’t really prove anything other than this is something we need to look at,” said Miami Beach City Engineer Bruce Mowry.

Spikes in pollutants could have been caused by the city’s new, more powerful pumps flushing a century-old system, Mowry said. The city is also equipping pumps with devices meant to filter out pollution and plans to increase street sweeping and gutter cleaning to keep contaminants from reaching the bay. Mowry also pointed out that the new pumps passed muster with environmental regulators.

“I guess the question to be asked is: Is this enough?” he said.

Miami Beach, a natural mangrove barrier island sliced and diced by Miami’s early real estate moguls, sits on porous limestone rock, like a calcified sponge. When seas rise during annual fall and spring high tides, water washing over seawalls poses less of a threat than fresh groundwater, which floats on seawater, pushing up through holes in the ground. Mowry calls it vertical flooding. In the past, as seas crept higher, vertical flooding caused the city’s old gravity stormwater system to act like artesian wells, with water bubbling up through pipes, he said.

Last fall, the city focused its efforts on its most flood-prone — and most trafficked — locations near West Avenue and Sunset Harbor, installing three new pumps and rehabbing three old ones to keep water from washing back into streets as the tide drove water levels higher.

But Briceno worried the city was “only looking at one face of the coin,” and not at how water, pushed through ground polluted with old septic tanks, animal feces and other contaminants, affected the bay. So a month before the tides, he created a grid for sampling. Researchers collected water near sewer outfall pipes in the bay, midway into the bay and on the eastern edges of Star, Flagler Memorial and Rivo Alto islands. At the height of the tide in October, they returned for a second round of sampling.

Briceno said his experiment was really meant to provide a snapshot of what to expect.

“The city is being kept dry, which is excellent. That’s a success, protecting people’s health and property and tourism,” he said.

But what about the health of the bay?

“I imagine to live in Miami Beach in the future is going to cost you a lot of taxes,” he said.

Briceno predicts Miami Beach and other communities that want to drain increasing amounts of water will need to treat it to eliminate hazardous elements, or use deep injection wells where they can store it until limestone filters out pollutants. Mowry believes the solution could be a combination of keeping streets and pipes clean and more efficient pumping.

“This is not one thing,” he said. “It’s a big thing and the world is going to have to address it.”

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