Source: US Geological Survey
RESTON, Va. – As U.S. Geological Survey staff prepare for Hurricane Milton to hit Florida’s west coast as soon as Wednesday, agency experts are still dealing with the after-effects of Hurricane Helene that made landfall in Florida late last month and continued a path of destruction north through Georgia, North Carolina, South Carolina and Tennessee.
While USGS experts are deploying wave sensors and forecasting coastal change in anticipation of Milton’s arrival, many of their agency colleagues have been hard at work mapping landslides, repairing and replacing damaged streamgages, and analyzing sensor data to provide the science information needed to help emergency responders and local officials with ongoing Helene recovery efforts.
“Thank you to all our USGS employees and our partners for their dedication and commitment in supporting hurricane response efforts throughout the region,” said Holly Weyers, USGS Southeast Regional Director. “I’ve seen remarkable resiliency exhibited by our entire team in the face of incredible challenges. I’m proud of all our USGS employees and our partners and their ability to work together to find effective solutions, even in the most demanding situations, as we continue to support the needs of the communities in the affected areas. You have all made a remarkable difference.”
To meet requests for local technical assistance, USGS activated its landslide event team last week to collect remotely sensed imagery and map landslides to gain a better picture of the extent and severity of landslide impacts. USGS continues to support requests from the North Carolina and Tennessee geological survey offices to identify landslide locations and landslide impacts to state transportation networks and the infrastructure environments. Hurricanes are known to lead to landslide and debris flow hazards in the southern Appalachian Mountains so experts at the USGS Geologic Hazards Science Center helped create a multi-agency Landslides Observations Dashboard to map landslides associated with Helene and aid state officials in determining the extent and severity of landslide occurrence and impacts. At time of publication, the dashboard shows more than 450 landslides across North Carolina, South Carolina, Tennessee and Virginia, with nearly 320 of these having impacted rivers, roads or structures.
Two USGS landslide experts conducted aerial reconnaissance flights between October 3 and October 5 in partnership with U.S. Fish & Wildlife Services to obtain a better understanding of the extent and severity of landslide impacts in the southern Appalachian region. USGS experts continue to review the data and imagery from these flights to confirm locations of some landslides and assist local authorities as they work to protect lives and vital infrastructure.
Locations of landslides identified by the team can be viewed on the USGS Landslide Observations Dashboard.
Well before deadly Hurricane Helene made landfall September 26 on the Florida Big Bend region, USGS water monitoring, coastal storm hazards, and modeling experts were preparing for its arrival and gathering data needed to help emergency managers and communities prepare for and respond to the onset of the large and powerful storm.
Days prior to the storm striking, hydrographers from the USGS Caribbean Florida Water Science Center in Davie, Florida, deployed wave sensors and barometric pressure sensors to monitor large waves and surge along the coasts. USGS also activated seasonal hurricane real-time gauges in Florida and USGS crews in several other states in Helene’s projected track maintained streamgages critical to helping with flood forecasting.
After making landfall as a Category 4 storm with 140 mph winds, Hurricane Helene caused coastal flooding along the entire west coast of Florida and damaged multiple gauging stations that are operated out of the Caribbean Florida Water Science Center. Due to the speed of the storm, the state did not receive a high amount of rainfall, so there was minimal inland flooding and USGS teams were not deployed for high water measurements.
Helene quickly moved north and further inland, bringing heavy rain and destructive winds across Georgia and the southern Appalachian region, resulting in widespread power outages. Areas such as Atlanta, eastern Tennessee, and western North Carolina experienced extreme or record high river levels, flash floods, landslides, and extensive river flooding. The mountainous terrain around Asheville, North Carolina, and upstate South Carolina worsened the flooding, creating dangerous conditions for local communities.
The storm saturated the region and many USGS streamgages recorded extreme and historic water levels. Several gauges exceeded the peak of record in north Georgia and western parts of the Carolinas. According to the USGS Asheville field office, dozens of sites serviced by the office observed peak gauge heights that exceeded the current ratings following the storm runoff. Major basins affected included the French Broad and Catawba Basins in western North Carolina, urban tributaries of the Chattahoochee Basin in low-lying parts of Atlanta, and the Ogeechee and Savannah River Basin in Georgia and South Carolina. USGS officials estimated 10 to 20 gauges in Asheville and the upstate South Carolina area were damaged or inundated because of the storm.
USGS experts from the South Atlantic Water Science Center and the Lower Mississippi-Gulf Water Science Center conducted post-storm field operations at safely accessible sites, obtaining high-flow measurements, completing repairs and needed equipment checks, and conducting verifications for streamgages that were inundated but not destroyed during the catastrophic flooding. USGS crews from the Virginia-West Virginia Water Science Center field offices in Marion and Leetown conducted discharge measurements and water-quality sampling in the New River, Shenandoah, and Potomac basins. The most significant flooding was found in the New River basin, with the peak at New River at Galax reaching the second highest peak of record ever documented. New River at Glen Lynn, at the West Virginia border, reached the fourth highest peak on record, which dates back over 100 years.
With federal and state emergency response agencies conducting extensive rescue and recovery operations, and numerous washed out and blocked roads in the region causing unsafe conditions, it’s no surprise that USGS teams were limited in their immediate ability to assess damage to streamgage networks and replace equipment in several states. Response team members estimate that some locations where streamgages are located still won’t be accessible for at least several weeks.
Despite some limitations, dozens of USGS experts were able to safely deploy to other areas to collect sensors, repair gauges and gather scientific data about the storm surge and flooding Helene caused. A USGS team retrofitted a radar gauge at the Nolichucky River below the Nolichucky Dam in Tennessee to bring data back online, while a second team conducted survey work to verify peaks of record at several locations in Tennessee where crest stage gauges were either overtopped or destroyed. In North Carolina, crews from the USGS Asheville and Raleigh field offices continue to repair damaged gauges, flag and survey high water marks, and conduct post-storm field operations for completion of indirect discharge measurements needed for more than 40 streamgages.
USGS scientists and field crews in Florida continue to access the damage to the streamgage network and replace equipment across three of the hardest hit counties in the state. Crews also retrieved the 13 wave sensors that were deployed between Venice and Panama City days before the hurricane hit the Florida coast. The sensors measure water levels and provide insight on wave height and frequency, storm tide and storm surge. USGS scientists are analyzing the collected data to help identify areas hit the hardest by storm surge and guide emergency responders and local officials with recovery efforts. The resulting information can be used to fine-tune future storm surge and coastal change forecasts during what is proving to be a busy hurricane season.
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