The North Carolina Department of Transportation has an award-winning flood warning system that gathers data from various state and federal agencies. Already able to access this data and include it in computer forecasts, now NCDOT is adding stream gauges to monitor rainfall and water levels as new highways are constructed in order to increase the data available.

The system is nationally recognized by the American Association of State Highway Transportation Officials and was a Top 12 finalist in the 2023 America’s Transportation Awards competition. In 2021, NCDOT won the grand prize in the same category for its Salem Parkway project involving the reconstruction of Interstate 40 in downtown Winston-Salem.

According to Andrew Barksdale, NCDOT public relations officer, “The flood warning system is not unique in the country, but it is probably the largest or one of the largest because we have the largest amount of road coverage. Many cities have stream gauges in flood-prone or low-lying areas: We have stream gauges that alert 911 to send police and check the area. It gives us a lot more information for a lot more of the state whenever there is a major storm.”

The system is partially modeled after North Carolina Emergency Management’s flood inundation mapping system. It’s operated by the NCDOT Hydraulics Unit.

In 2018, Hurricane Florence caused massive flooding and devastation throughout the state of North Carolina, leading to deaths and to millions of dollars in damage to the road network. At the height of the storm, travelers were encouraged to avoid North Carolina since moving throughout the state was unpredictable. In such an instance, when Department of Transportation leaders needed to know which roads and major highways were going to flood, NCDOT could not tell them. It was more of a “wait and see” method, with NCDOT waiting to receive reports and calls after the storm to determine where to deploy resources.

After that, a $2 million grant was given to NCDOT by the North Carolina General Assembly to update the flood warning system. That system became fully operational in 2022.

Once it was phased in, people had to be trained on the program. Now the department is slowly expanding the data network and adding more stream gauges.

The system is made up of a network of over 500 river or stream gauges that monitor over 15,000 bridges and culverts and more than 2,000 miles of state-maintained roads. Critical information comes from the North Carolina Emergency Management network of stream gauges and elevation data, covering over 2,000 miles of roadway.

The stream gauges consist of a cabinet, which houses the modem; a battery; and a data logger. A cellular antenna connects the gauge to the cellular network. A solar panel charges the battery, running the modem and data collector. A sensor on the gauge fires an ultrasonic beam into the water, which bounces up, and the system times the amount of time it takes to fire the signal, create bounce back and be received. This determines the elevation of the water, and the data is sent to the data logger.

The system is comprised of three main programs. Flood Inundation Mapping and Alert Network for Transportation covers more than 2,000 square miles of state-maintained roads primarily in eastern and southeastern North Carolina; BridgeWatch monitors over 15,000 bridges and culverts throughout the state; and the Transportation Surge Analysis Predictive Program monitors 11,000 miles of roads near the coast vulnerable to storm surge. Information regarding predictive modeling and rainfall forecasts is received from other agencies.

NCDOT interprets the data to determine if there is going to be a problem. Additionally, the National Weather Service provides information regarding the timing and impact of storms and hurricanes.

Since the beginning of 2023, NCDOT now also receives data from the Coastal Resilience Center of Excellence, which helps predict when roads will flood due to tidal surges before a hurricane nears the coast.

The department continues to expand the information system to provide better information not only for its programs but also for its partners.

Once information about dangerous water levels is received from the flood warning system, NCDOT will go out and confirm. The public website DriveNC.gov has a map that is then updated with relevant information such as road closings. “It helps us warn the public in real-time during a serious storm,” Barksdale said. “We get better, more timely information to the public. It has the potential to save lives, especially next time we have a major hurricane.”

Once a storm has passed, employees on call go out with equipment such as signs, barricades and chainsaws.

“All the systems work in concert to provide critical information in real-time,” he emphasized. “They’re always on.” This gives officials a better idea of how to better respond, how to deploy resources most efficiently and the best way to warn the public. “Because of Florence, resiliency is one of our policies,” said Barksdale.

When Hurricane Idalia came through the state in August 2023, the new flood warning system was up and running. “Some areas of the state received no rain, while other areas received nine inches of rain in 24 hours,” he described. “There were over 100 alerts sent out to staff about potential problems.

“Columbus County was one of the hardest hit areas for bridges and major culverts. There we were able to prioritize and tell staff where to monitor flooding the closest. We inspected every alert.” There were probably 30 to 40 roads temporarily closed for flash flooding.

“It really allows us to figure out which areas are going to be impacted, prepare better when there is a bigger storm coming and respond faster to close roads. It helps us operate the transportation network more efficiently and respond more quickly.”

Aside from the flood warning system, NCDOT is also focusing on building up previously flooded bridges and roadways with more dirt and gravel. In one instance, a culvert is being replaced with a bridge in order to better protect a roadway on which one side had washed away during a storm. Overall, Barksdale stated, “The flood warning system is a powerful tool to give us critical information ahead of a storm, respond more quickly and warn the public better. We get more information sooner, and it helps us deploy resources better for our road network.”

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