As forecasts show that Hurricane Dorian has the potential to cause extensive flooding and erosion along the famous Low Country coasts of the Carolinas and Georgia, U.S. Geological Survey scientists are quickly installing at least 150 storm-tide sensors [video] and at least 22 other instruments that will track the hurricane’s effects along the North and South Carolina coasts. 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.

On Monday and Tuesday, Sept. 2 and 3, field crews from the USGS’ South Atlantic Water Science Center plan to install 70 storm-tide sensors in South Carolina and 90 in North Carolina. A total of 28 hydrologists and hydrologic technicians, 14 from each state, were in the field on the Labor Day holiday. In South Carolina, many of the crews are working in the eight counties under mandatory evacuation orders, with special permission from state authorities.

 “Hurricane Dorian has slowed down so much that it is building up a significant storm surge,” USGS Supervisory Hydrologist John Shelton said, “and if Dorian sticks around long enough we could see some significant coastal flooding in the Low Country.” 

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.

Most of the instruments deployed for Dorian are designed to measure the height and duration of the storm-tide as the storm approaches shore, makes landfall, and departs. Others will monitor water levels on inland water bodies, with some reporting water level data in near real-time; the field crews will gather data from them immediately after the storm has passed. The USGS’ Flood Event Viewer for Hurricane Dorian shows the location of the instruments that will record the storm’s effects on water levels as it moves onshore.

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. The USGS has storm surge experts, as well as sophisticated equipment for predicting and monitoring flood and tide conditions, and has been consulting with the National Hurricane Center and other agencies to prepare for Hurricane Dorian.

Prepared to Capture Coastal Storm Surges

Storm surges are increases in ocean water levels caused by extreme storms. 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 ten miles of every storm tide sensor; the two devices work together to correlate the storm’s intensity with wave heights.

Adding Temporary Streamgages to Track Dorian

The USGS Streamgaging Network operates scientific instruments that record water levels and other key pieces of information on rivers and streams throughout the nation, with the support of local, state, and federal agencies. During storms and floods the USGS uses this nationwide network to provide near-real-time data about water levels to the National Weather Service, Federal Emergency Management Agency, the U.S. Army Corps of Engineers, and others. 

When a major hurricane is expected to make a U.S. landfall, the USGS augments the network by installing special streamgages called rapid deployment gauges, or RDGs, in areas where flooding is likely, but no permanent streamgage exists. RDGs measure water levels and local weather data in areas susceptible to storm-tide flooding and transmit that information by satellite in near-real time for flood forecasting and emergency response. The public can see the information in near-real time by clicking on the RDG symbol in the Flood Event Viewer.

Field crews plan to install 12 RDGs in South Carolina and 10 on the North Carolina mainland.

If flooding does occur, USGS field crews will make real-time streamflow measurements to verify the streamgages’ readings. After the storm passes, the crews will quickly replace any storm-damaged or lost gauges. During and right after hurricane flooding, these records help FEMA target emergency relief to the hardest-hit areas.

Resources to Help Everyone Prepare

As USGS takes action to prepare for Hurricane Dorian, people in the path of the storm can get tips on creating emergency plans and putting together an emergency supply kit at www.ready.gov or www.listo.gov.