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Associate Professor in the Biological and Agricultural Engineering Department, NC State University

Characterizing Water Quality Impacts of Tidal Floods on NC Communities

Tidal floods, also commonly referred to as sunny-day floods, describe when marine water ends up in an area that is usually dry land, often by flowing back up a stormwater system. During high tides or other high-water events, such floods occur due to both sea-level rise and because of the way in which infrastructure has been designed and implemented in coastal communities.


Natalie Nelson, Associate Professor of the Biological and Agricultural Engineering Department at NC State University, leads a research team that primarily focuses on predictive modeling of environmental systems, with an emphasis on water quality in both coastal and inland systems.

According to Professor Nelson, there is a concern that when tidal floods occur, flood water is potentially picking up what could be poor water quality waters within the underground storm water system, and then pushing that poor quality water into overground areas that people could encounter.

Natalie Nelson

How could sunny-day flooding impact water quality and public health?

wo students sampling flood waters.

For the Collaboratory-supported project, we’ve started to sample the flood waters, and what we’ve initially seen is that these tidal floods can have elevated fecal contamination.

The main concern when you have fecal contamination, depending on the source of the feces, is if you were to ingest the water. You may think – “well people aren’t going and drinking flood waters” – but you can see kids playing in them, and all it takes is splashing water into your mouth, depending on the level of contamination, to make a person, and especially a child, sick.

Additionally, if you have an open wound, like a cut or rash, you have a way for that contaminated water to break through your skin and are then also at risk of potentially contracting the pathogens that are in that water.

How does your research benefit the citizens of North Carolina?

The citizens of North Carolina are increasingly experiencing tidal floods, and we don’t fully understand what the potential impacts are of coming in contact with these floods. So, by understanding more about what the potential water quality hazards are, we can also better understand how to protect citizens who are facing these floods. The floods are becoming more frequent, so it’s a problem that will increase in severity.

After this research study has concluded in June 2024, what are the next steps?

We don’t know the source of the contamination, so for right now, we are still just trying to characterize the extent to which we see potentially concerning levels of fecal indicator bacteria in the water. Then, I think the natural next step will be to look for sources as well, and also try to understand the role of failing infrastructure under sea-level rise.

It’s the infrastructure piece that I think is important because the more we understand about how the fecal contamination could potentially be related to infrastructure, the more we’ll understand to what extent is fecal contamination in floodwaters pervasive and what types of solutions could potentially be designed for addressing this type of problem.