When Hurricane Florence struck North Carolina in 2018, 11 people there died from freshwater flooding—all of them in cars.
The storm also caused 2,500 road closures in the state, including parts of Interstates 95 and 40, which were shut down for more than a week because of flooding. The state estimated bridge, culvert and road washouts as well as other transportation infrastructure damage at more than $227 million.
This year, with hurricane season underway, a new advanced warning system will alert North Carolina officials in real time which specific roads and bridges are likely to flood soon, so the state can prepare and warn the public.
The network of river and stream gauges will, ideally, allow the Department of Transportation to prevent people from driving on flooded roads and help officials to respond more quickly and get roads reopened.
“The primary reason is to save lives. A lot of deaths occur because of drowning and flooding, rather than wind,” said Matt Lauffer, the transportation agency’s hydraulics design engineer. “The other part is to help the department prepare for, respond to and recover more rapidly from extreme events. We can get resources to places where roads are flooded.”
Nearly a dozen states are using such real-time monitoring to assess potential flooding at specific bridges or roads, according to David Claman, a hydraulic engineer for the Federal Highway Administration.
Although states and cities have used real-time flood gauge monitoring for years, the need for hyperlocal warnings only will grow because of climate change.
Two states—Colorado and Maryland—are doing advance flood monitoring for roads because of environmental changes, Claman said in an email. In Colorado, wildfires have significantly increased the runoff and debris for streams, and in Maryland, coastal roads are at risk because of the rise in tides.
Some cities also have early flood warning programs.
In Fort Worth, Texas, for example, residents can see real-time flood warning risk level information at monitored low-water road crossings so they can protect themselves from hazardous flood conditions.
And Raleigh, North Carolina, city officials have launched a pilot program to help forecast flooding conditions before a storm, notify the public and close roads sooner.
Floods can be deadly. Other than heat-related fatalities, more deaths occur from flooding than any other weather hazard, according to the National Weather Service. The national 30-year average for flood deaths is 88 a year—higher than tornadoes or hurricanes.
Drivers and passengers account for nearly half of all flash flood fatalities—last year, 76 of 145 deaths.
In Iowa, a year after historic river flooding struck much of the eastern part of the state in 2008, the legislature established the Iowa Flood Center at the University of Iowa. It not only does academic research, but also develops tools and data that predict and monitor floods.
The center helps communities prepare for floods so their damage can be minimized, according to Director Witold Krajewski. It deploys about 300 sensors on bridges across the state that monitor real-time stream levels.
The system, which also uses data from federal sensors on bridges, is available online and can send mobile alerts to people’s phones if sensors show potential flooding.
“We’ve had horrible and widespread floods over the years,” Krajewski said. “Having access to that system allows people to make local decisions, such as moving their tractor away from the stream to higher ground.”
Krajewski said the center worked with the Nebraska Department of Transportation and the University of Nebraska-Lincoln to deploy eight sensors in that state earlier this year as part of a research project.
Iowa also is one of nine states that use BridgeWatch, among the early flood warning software systems designed by private companies.
The system alerts state transportation officials so they can work to avert a dangerous event, said Joseph Scannell, CEO of USEngineering Solutions Corp., a Hartford, Connecticut-based company that makes BridgeWatch software.
BridgeWatch can cost states from $70,000 to $80,000 for a small system to up to $500,000 for a large one, Scannell said.
North Carolina’s system, also supported by BridgeWatch, receives data from gauges at more than 400 sites that measure the water surface using radar or sonar every 15 minutes, according to the transportation agency’s Lauffer. If water near or under a bridge is flooding, the system notifies officials.
The agency, using a $2 million grant from state lawmakers in 2019, also worked with the state Department of Public Safety to create software that delivers data from existing gauges into models that predict flooding on streets and highways.
Parts of the I-40 corridor, for example, which spans the entire state from west to east, are monitored with both stream and river gauges and rainfall monitoring to alert agency staff of potential road flooding conditions, Lauffer said.
So far, about 50 gauges, most east of I-95, are mapping about 2,700 miles of roadway, but those numbers are growing, Lauffer said. In a state with more than 80,000 miles of road and 40,000 miles of river, the potential for flooding is vast.
“Those gauges have been in a long time. But they didn’t tell us anything about the roadway network,” Lauffer said. “What’s new this year is that we can analyze flooding on the roadways.”
Lauffer said the system will be able to monitor not just rainfall from a coastal storm or a hurricane but also flash flooding that can quickly make roads dangerous for drivers.
The plan is to incorporate all the flood warning data onto the department’s DriveNC.gov app, which will alert the public about the status of state roads and detours, Lauffer noted.
“Ultimately, the idea is to operate the transportation network more efficiently,” he said.