Research update: How does chronic shallow flooding affect coastal communities?

The frequency of flooding in coastal communities is increasing, even when there is not a storm. These floods go by many names — sunny day floods, high tide floods, nuisance floods — and they can be caused by sea level rise, tides, wind, groundwater, rainfall runoff and river flows. In projects supported by North Carolina Sea Grant and the National Science Foundation, Dr. Katherine Anarde and Ph.D. student Thomas Thelen are trying to measure, model and understand the impacts of chronic shallow flooding in coastal North Carolina.

Tides now rise and fall on higher average sea levels, resulting in a higher frequency of “sunny day” flooding of roadways during high tides. Sea water can also infiltrate drainage networks at low tide levels such that ordinary rain storms now cause flash floods. The travel disruptions from flood-induced street closures, as well as damage to vehicles and infrastructure from salt water, can impose chronic stress on communities. At a local level, the causes and frequency of these floods are often not well understood, nor are the impacts to people and communities — partly because flooding by large storm events like hurricanes receives more attention, and partly because these hyper-local, multidriver floods are difficult to monitor and predict.

As part of a two-year North Carolina Sea Grant project that began in February 2022, Anarde and Thelen, alongside other researchers from the University of North Carolina at Chapel Hill, are working with the Town of Carolina Beach to deploy a real-time water level sensor network to continuously measure the stormwater network capacity. This data will validate a coupled hydrodynamic and hydrologic model of flooding in the town, which will then be used to simulate future flood risk and potential adaptation strategies.

“I am passionate about this project because it is science for action, shaped by community needs,” Thelen said. “The findings from this research will directly inform coastal resilience solutions and policies that will help our waterfront communities adapt to the rising seas of the coming decades.”