NC State researchers find increased fecal contamination in coastal waters due to sunny day flooding

High tide on your next beach trip might wash up fecal bacteria.

A new NC State study examined how “sunny day flooding” is impacting water quality at the coast.

Sunny day flooding, also called high tide flooding or nuisance flooding, happens on clear days with no rain when high tides overflow inland.

Researchers say the frequency and severity of tidal flooding is increasing on North Carolina’s coast due to land sinking, groundwater drilling, changes in Gulf Stream currents, and sea level rise.

“North Carolina is seeing one of the highest rates of sea level rise,” said Megan Carr, lead author of the study and PhD student at NC State.

“What we know from our study is the floodwaters are fecally contaminated,” Carr said. “During high tides, we have floods which move through underground infrastructure, such as stormwater networks.”

Janet Reagan, a retired grandmother who recently visited Atlantic Beach for a vacation, says she’s concerned by the findings.

“Absolutely gross!,” she said. “You want to know about the quality of the water you swim in and I’d definitely be interested in knowing more about that.”

Carr took daily samples over a two-month period, including over a period of the highest tides, called king tides.

She found some areas, including shallow roadway floods, were off-the-charts contaminated.

“On a couple of occasions the samples maxed out our bacteria detection limits in the laboratory,” Carr said.

Contamination levels are highly variable for different locations, but Carr said the high levels were usually temporary.

“I don’t look at puddles the same way anymore,” Carr said.

The sunny day flooding problem is expected to get more severe with climate change and aging infrastructure.

In 2050, Oregon Inlet is projected to have 110–166 high-tide days, up from five in 2021, and Duck is projected to have up to 120 high-tide days, up from 11 in 2021.

“It’s something that we must keep looking into so we don’t put public health at risk,” Carr said.

The next king tide event in North Carolina is expected to be August 17-21, 2024.

SAFETY TIPS AND RESOURCES FOR SUNNY DAY FLOODING

Waterfront properties and low-lying roadways are most likely to experience tidal or “sunny day” floods. If you encounter tidal floodwater, minimize or avoid contact with it.

Because floodwaters from tidal or storm flooding may contain biological and chemical contaminants, the CDC suggests the following:

• If you have an open wound, avoid exposure to floodwater.
• If you have an open wound and have already been exposed to floodwater, wash the wound well with soap and clean water, and cover it to reduce the chance of infection. If the open wound develops redness, is painful, or appears to be swelling or oozing, seek immediate medical attention.
• If you have been in contact with floodwater, wash your hands with soap and water as soon as possible. Also, be sure to wash children’s hands, particularly before consuming food.
• Do not allow children to play in floodwater. Similarly, do not allow children to play with toys that have been exposed to contaminated floodwaters and not then disinfected.
• Consider replacing soil, mulch, sand in sandboxes, and wood chips around outdoor playground equipment if they have been flooded.