Hurricane Helene Ruined Highways. Here’s How to Restore—and Make Them Flood-Resistant for the Future
With the realization that climate change can cause destruction everywhere, engineers are evaluating the most effective ways to safeguard essential routes from severe storms.
A WEEK AFTER Hurricane Helene swept through the southeastern United States, areas of western North Carolina hit by the storm are still dealing with over 400 road closures. “A government official informed a local newspaper, ‘There are locations we cannot access.’” Images that have emerged from the area depict local roads completely submerged, while others remain under water.
That such severe flooding could occur in this region of the country—well inland and long praised by real estate professionals as a “climate refuge”—shows that the destructive impacts of climate change can be experienced everywhere and at any time. Last week, certain areas in North Carolina experienced over 2.5 feet of rainfall within three days. The storm and its resulting floodwaters have claimed the lives of at least 200 individuals across the country, with more than 100 still unaccounted for in the mountains of North Carolina.
A crucial aspect of the recovery in North Carolina and beyond will involve reconstructing the roads, both to ensure supplies reach their destinations and to restore a sense of normality. Typically, states are accountable for constructing and upkeeping their own roadways, and recent years have witnessed an increasing number of them confronting the challenges posed by climate change. “Every transportation department is focusing on enhancing infrastructure resilience due to the rise in severe weather occurrences,” states Kevin Marshia, a former official from Vermont’s transportation sector, currently serving as the engineering director at the American Association of State Highway and Transportation Officials, a nationwide group.
At the outset of the disaster response in North Carolina, federal agencies transported essential food and supplies to residents using “air bridges”—airlifts—and also mules. The Army Corps of Engineers has sent specialists to the area to assist with debris cleanup, water management, and inspections of roads and bridges. Florida—considered a national frontrunner in safeguarding assets from flooding—claims to have provided teams for assessing infrastructure damage and temporary bridge supplies, likely consisting of lightweight steel components that can be assembled with minimal tools.
Typically, authorities aim to restore transportation on impaired roads with temporary solutions, such as limiting traffic to lanes capable of safely accommodating vehicles. In the immediate future, engineers may, for instance, substitute a washed-out 4-foot culvert (a drainage pipe beneath a roadway) with any available pre-fabricated size nearby, aware that they will need to later return to install a deeper, 20-foot model, explains Marshia.
The Updated 50-Year Flood
To prepare infrastructure for climate change in the long run, the foundation begins with data. Historically, engineers rely on a particular past flood as a design benchmark, states Steve Muench, a civil and environmental engineering professor at the University of Washington who researches transportation infrastructure. A 50-year storm is one that can occur roughly every 50 years; a 100-year storm is significantly more severe and can be anticipated every century.
Engineers now understand that increasingly severe weather patterns indicate they cannot design solely based on past data. According to Muench, for each project, transportation engineers must determine “how to transition their design processes from relying on historical data to utilizing improved climate forecasting.”
These enhanced “armored” road projects generally have higher costs. However, a greater number of public officials—though not every public official—have come to understand that strengthening their roads to withstand worsening weather will be cost-effective over time. Usually, Muench explains, the answer isn’t overly complex: Simply construct the infrastructure at a greater elevation. However, engineers cannot create roads and bridges to withstand every catastrophe, as this would result in costly, overly constructed projects that would “take generations to complete,” according to Muench.
‘Rice Krispie’ Pathways
When engineers are constructing roads anew, they have begun to incorporate various materials to prepare for the likelihood of rapid water influx. Over the last ten years, road construction teams have progressively implemented a greater number of permeable, “spongy” road surfaces.
Permeable concrete, in contrast to standard concrete, typically omits sand from the usual “gravel, sand, cement, water” mix. It also features a reduced water-to-cement ratio, resulting in a dense paste prior to drying. “It resembles caramel popcorn or a Rice Krispie treat,” remarks Nara Almeida, who examines the substance as an assistant teaching professor in the civil engineering program at the University of Washington Tacoma.
On standard concrete roads, water gathers and accumulates, with the standing water ultimately harming its different layers, especially the crucial underlying ones that support heavy vehicle loads. However, the greater porosity of pervious concrete enables water to pass through the material more effectively, allowing it to reach and be absorbed by the ground—a beneficial trait for roads that experience significant moisture.
Porous concrete does come with its disadvantages. It’s not as strong as typical concrete, indicating it’s more suitable for sidewalks, parking areas, and low-traffic roads than highways that anticipate many heavy vehicles. (Studies on enhancing the material with steel, natural fibers, glass, and synthetic fibers are continuing.) Its porosity indicates it’s not well-suited for cold environments, where water can infiltrate, freeze, and damage the material within. The concrete requires frequent pressure washing or vacuuming to “clear” it of the type of debris commonly found on the road—dust, leaves. Due to the necessity for states to change vendors and processes to implement the newer material, projects may become more expensive for them. However, Almeida notes that certain locations have placed the material alongside interstates, which are considerably less prone to frequent tire impacts.
In the end, however, when a large amount of water rapidly flows over a road or the foundation of a bridge, which engineers refer to as “scour,” there isn’t much that can be done. “We’ve all splashed around in the backyard with water and hoses—it’s quite harmful,” states Muench, the engineering professor. A component of climate resilience involves preparing in advance and having the immediate repair materials close at hand, enabling communities to recover swiftly.
