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Sunny day flooding can temporarily increase fecal bacteria in coastal waters, study finds

Sunny day flooding in downtown Beaufort, NC.
Courtesy of the Sunny Day Flooding Project
Sunny day flooding in downtown Beaufort, NC.

Sunny day flooding in coastal communities can temporarily increase the levels of fecal bacteria in coastal waters, according to a study from researchers at N.C. State University.

Sunny day flooding, also known as high tide flooding, is the temporary flooding of low-lying areas near the coast during high tides. It can inundate roads and overwhelm storm water drainage systems.

Natalie Nelson, study co-author and professor of biological and agricultural engineering at N.C. State, explained the frequency of sunny day flooding is expected to increase because of sea level rise. This could pose potential public health hazards.

"What we've documented through our study is that when these tidal floods occur, there's increased opportunity to have contaminated floodwaters that pedestrians make contact with," Nelson said. "(For example) we've seen children playing in these sort of sunny day floodwaters, and the levels of fecal bacteria we detected were above the levels deemed safe for recreational waters."

There are also potential repercussions for the coastal waterways that the floodwaters drain into, said Megan Carr, lead author of the study and a Ph.D. student at N.C. State.

"On one hand, we did see higher concentrations of fecal bacteria in coastal waters as floodwaters ... receded," Carr said. "On the other hand, we did not see this in every instance and in every location — and we also found that the higher concentrations of fecal bacteria usually only lasted for a few hours."

For the study, researchers collected water samples at three sites along Taylor's Creek in downtown Beaufort. Samples were collected every day during the months of June and July in 2022.

Finally, Nelson pointed out a broader implication of this study: Outdated infrastructure that wasn't built with sea level rise in mind.

"Stormwater drainage systems were never designed to have water come back up through them in this way," Nelson said. "It creates new challenges ... in terms of how we need to adapt to rising seas, because we know that seas will continue to rise moving forward and at accelerating rates."

The paper was published in April in the open-access journal GeoHealth.

Celeste Gracia covers the environment for WUNC. She has been at the station since September 2019 and started off as morning producer.