Why Flagler floods

This is the first in a series of articles that will explore the causes of flooding in New Smyrna Beach and surrounding areas. This story focuses on the Flagler Avenue area, one of the city’s two economic hubs.

The flooding of Flagler Avenue and the surrounding neighborhood two weeks ago resulted from a rare alignment of factors that will likely become more common in the years ahead.

The proximate cause of the flooding was two-pronged: “First, a seasonal high tide and second, an intense rainfall,” Jesse Meyers, the city’s senior civil engineer, said by email.

The job of draining Flagler Avenue falls largely to a single cement reinforced pipe under the street. Rainwater flows in through storm drains, and gravity carries this water westward to a sandy leaching field. The water slowly disperses into the Indian River which connects to the ocean at Ponce Inlet to the north of Flagler.

The drainage pipe under Flagler is not a large one, as these things go. Across the river, for example, the Canal Street business corridor is drained by an underground box culvert that measures five to six times larger than the Flagler pipe, Meyers said. This culvert runs the length of the canal that was built in the 18th Century by Andrew Turnbull’s indentured workers and is now under the sidewalk on the north side of the street.

The rain on Sunday, Sept. 7, came on the heels of other rains and it fell rapidly – at least 3.5 inches in a matter of hours, according to Fox 35. The rain was just too intense for Flagler’s pipe, Meyers said.

That was one factor.

Another factor was this: The rain coincided with the first of the seasonal king tides produced by the dynamic orbital geometry of the Earth, moon and sun. As the rain fell, the river surged toward a predicted high tide of 9:25 p.m. on the river at the tidal station at the North Causeway boat ramp. The high water in the river blocked the rainwater from draining into it.

This blocking phenomenon is not unique to Flagler. It’s happening elsewhere along the Florida coast. “Sea level rise is impacting gravity-flow drainage infrastructure, which is leading to more frequent and severe high tide (or “nuisance”) flooding,” according to the Florida Climate Center which is run by Florida State University for the Office of the State Climatologist.

The flooding on Flagler damaged at least a handful of businesses and properties, including Peanuts Sports Bar and Solea Bikinis, which was featured in a Fox 35 Orlando segment.

One flood might be a nuisance, but the severity of king tides is tied to sea levels, and sea levels are rising, according to data gathered by satellites since 1992 and before that by tidal gauges. “Sea levels across Florida are as much as 8 inches higher than they were in 1950, and the rate of sea level rise is accelerating,” according to the Florida Climate Center. “It is virtually certain that global mean sea levels will continue to rise throughout the 21st century and beyond.”

If this proves true, the king tides will only get worse.

It’s of course always rained hard in Florida in modern times, but scientists now understand the relationship between increasing temperatures, atmospheric moisture and precipitation. This has permitted them to define a trend and make a prediction.

“The broad consensus is that more rainfall is occurring in heavy rainfall events as the climate warms,” said David Zierden, Florida’s state climatologist, by email. He referenced a map in the 5th National Climate Assessment showing that the total precipitation on the wettest 1% of days in the Southeast grew by 37% from 1958 to 2021. “Modeling studies echo this result and show a continued increase in heavy rainfall events as the climate warms further,” he said.

The city government lists six current stormwater projects on its website, but none are meant to improve the drainage of the Flagler neighborhood.

The problem on Flagler is a complicated one, Meyers indicated. “We continuously review data, land changes and weather trends to maintain and improve out stormwater utility,” he said. “It is not as simple as adding or replacing with a larger pipe. Many of the systems in place have existed for many years and would not meet today’s requirements for water quality. A new or increased discharge to the river would need to be treated and permitted. This requires the creation of a retention/detention pond. In a built out area there is limited options to do this,” he said.

Vice Mayor Lisa Martin, who represents the Flagler neighborhood, is not satisfied with the stormwater status quo on Flagler or elsewhere in the city. “We’re being so self-destructive,” she said.

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