Scientists Track Erosion Effects of Hurricane Dorian
As forecasts show that Hurricane Dorian has the potential to cause extensive flooding and erosion along the Low Country coasts of the Carolinas and Georgia, U.S. Geological Survey (USGS) scientists are racing to install at least 150 storm-tide sensors and other instruments that will track the hurricane’s effects.
The USGS has already installed 55 storm-tide sensors in Georgia and 158 in Florida, as well as other specialized devices to track the effects of hurricane-borne waves on those coasts.
A coastal erosion forecast for sandy beaches by the USGS’ Coastal Change Hazard Team on Monday predicted that dune erosion is likely on all of Georgia’s and South Carolina’s beaches, on about 60 percent of North Carolina’s beaches and on 85 percent of Florida’s beaches.
Storm surge, coastal erosion and inland flooding are among the most dangerous natural hazards unleashed by hurricanes, with the capacity to destroy homes and businesses, wipe out roads, bridges, water and sewer systems and profoundly alter landscapes. Scientists want to better understand storm surges so forecasters can more accurately model and predict surge-related flooding, engineers can design better storm-resistant structures and emergency responders can work more safely and effectively.
The USGS’ network of storm tide sensors along portions of the U.S. Atlantic and Gulf coasts can record water level and barometric pressure every 30 seconds to document storm surge crests, or waves of water, as they make landfall. Anticipating a storm’s path and intensity, USGS scientists often deploy storm tide sensors at other places along the coast just hours or days before a hurricane’s expected landfall.
The sensors are housed in steel pipes a few inches wide and about a foot long. Working quickly, and often in severe weather, field crews install them on bridges, piers and other structures that have a good chance of surviving a hurricane’s storm surge. The teams are also deploying barometric pressure sensors, one within 10 miles of every storm tide sensor. The two devices work together to correlate the storm’s intensity with wave heights.
Dune erosion is only the first level of damage a major storm like Dorian can cause. As waves and surge reach higher than the tops of dunes, overwash can occur, often transporting large amounts of sand across coastal environments – including roads, depositing sand inland and causing significant changes to the landscape. Overwash is currently predicted as very likely for 59 percent of Georgia dunes, 57 percent of South Carolina dunes, 22 percent of Florida dunes and 9 percent of North Carolina dunes. Overall, 28 percent of the dunes from Florida to North Carolina may experience some level of overwash.
Inundation, the most severe coastal impact, occurs when beaches and dunes are completely and continuously submerged by water. Inundation is forecast as very likely for nine percent of dunes in both Georgia and South Carolina. North Carolina and Florida are currently not projected to experience any inundation.
The prediction of Dorian’s effects is based on results of the USGS Coastal Change Forecast model, which has been in use since 2011, and is continually being improved. The Coastal Change Forecast model starts with the National Hurricane Center’s storm surge predictions and National Oceanic and Atmospheric Administration wave forecast models as input. The USGS model then adds detailed information about the forecasted region’s beach slope and dune height to predict how high waves and surge will move up the beach, and whether the protective dunes will be overtopped.
“Our coastal change forecast is for Dorian to cause long-lasting and widespread erosion of dunes from Florida through the Carolinas,” said research oceanographer Kara Doran, leader of the USGS Coastal Change Hazards Storm Team. “When hurricanes move slowly and remain at sea for long periods of time, they tend to build up large storm waves. These waves can travel hundreds of miles and begin causing dune erosion well before the storm arrives, on shorelines that are far from the center of the storm. And with Dorian now moving very slowly and forecast to stay offshore and move slowly up the coast, high surge, and strong waves are likely to persist over a period of days. So, the likelihood increases that the dunes could be overtopped and flooding could occur behind them as they are eroded by wave action.”