USGS deploying more gauges for Florence, preparing to measure flooding

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To learn more about USGS’ role providing science to decision makers before, during and after #Florence, visit the #USGS Hurricane Florence page at https://www.usgs.gov/florence.

A USGS hydrologic technician installs a Rapid-Deployment Gauge in Georgia.

Photo: Jym Chapman, USGS hydrologic technician, installs a rapid deployment gauge at Soil Erosion Lake near Fort Gordan in Augusta, Georgia, Sept. 15. Photo by Chris Smith, USGS. (Public domain.)

In the Carolinas and Georgia today, where a weakening Tropical Storm Florence continues to batter residents with rain, ocean waves and strong winds, U.S. Geological Survey scientists are still performing field work to monitor the storm while also preparing to deploy when floodwaters recede.

Ongoing USGS efforts include crews preparing equipment for deployment in the affected areas. One crew near Fayetteville, North Carolina, is performing streamgage maintenance, installing a rapid-deployment gauge, and elevating a streamgage on the Little River in an effort to raise it above projected flood forecast levels.

“The stage sensor for this streamgage flooded in 2016 during Hurricane Matthew. At that time the streamgage was raised by about 2 feet to prevent the future threat of flooding. The current flood forecasts for Florence are indicating even higher flood waters than we’ve seen before at this location, again threatening this gauge” said Doug Walters, USGS Supervisory Hydrologist. “We are hoping by raising the streamgage an additional 1.5 feet, it won’t be flooded and will continue to transmit critical water-level data throughout the duration of this storm event.”

In Georgia, two crews installed three rapid-deployment gauges around Augusta, at the request of the U.S. Army Corps of Engineers to monitor the real-time water levels of three reservoirs. These specialized gauges measures water-surface elevation and various meteorological parameters and transmit the data in real-time via satellite. RDGs are indispensable tools used for flood forecasting and augment existing streamgage networks to increase situational awareness and support emergency managers.

USGS crews are preparing equipment and getting ready to respond to Florence

USGS crews are preparing equipment and getting ready to measure the heavy flooding forecasters have said Tropical Storm Florence will likely cause. Photo by Brian McCallum, USGS. (Public domain.)

In addition to the small number of USGS staff already in the field, dozens more are ready to deploy as soon as flooded roads are passable to begin assessing the scope and intensity of flooding. To do this they will begin making streamflow measurements, repairing or replacing damaged or lost scientific instruments that were set out to track dangerous coastal and inland flooding, and collecting high-water marks to determine how high the water reached in flooded areas.

The USGS studies the effects of hurricanes and tropical storms to better understand potential impacts on coastal and inland areas. USGS’s network of sensors in rivers, streams, tidal and coastal waters provide critical information for more accurately predicting and modeling storm effects like flooding. The knowledge gained by studying real-world storms can also contribute to safer, more cost-effective designs for buildings, bridges, roads and other structures, and inform public safety measures.

Before Florence made landfall as a large, slow-moving category one hurricane Thursday, September 14, USGS scientists in the Carolinas, Virginia, Maryland and West Virginia placed at least 205 storm-tide sensors and rapid deployment gauges in places that may be impacted by storm surge or floodwaters, but where the USGS does not have permanent streamgages. On Friday, USGS scientists installed eight storm sensors in Pennsylvania, anticipating that the storm may move in that direction, bringing heavy rainfall.

These emergency devices augment a network of thousands of existing streamgages in the region. The network provides information to the National Weather Service, the Federal Emergency Management Agency and other agencies involved in issuing flood and evacuation warnings and coordinating emergency responses. River and streamgages and rapid deployment gauges generally show water levels and water flows, and in some cases they also show rainfall and wind data collected for the National Weather Service.

Storm surge is 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 coastal landscapes.

Florence’s storm-surge reached the coast at about high tide Friday morning, amplifying its effects on beaches and its potential to damage protective sand dunes, said Kara Doran, team leader of the USGS Coastal Change Hazards storm team based in St. Petersburg, Florida. The team’s coastal erosion experts use a computer model that analyzes beach impacts to predict the probabilities of dune erosion, overwash and inundation for a wide area. The predictions are based on results of the USGS Coastal Change Forecast model, which has been in use since 2011, and is continually being improved.

Chart shows high water at Duck, NC through Sept. 17

The Coastal Change Hazards Storm Team has forecast changing water levels at specific locations over time.(Credit: Kara Doran, USGS. Public domain.)

Once a storm has crossed the coast, however, fresh information about water levels along North Carolina ocean beaches comes from an experimental new tool, the Total Water Level and Coastal Change Forecast Viewer. This computer model can track changing water levels at specific places along the North Carolina coast over a period of days, projecting where, when and for how long the dunes will be affected by storm-surge.

“Because Florence is slow-moving, our forecast is for the storm to cause a long-lasting coastal erosion process with more than one set of impacts,” Doran said. You can use the Total Water Level and Coastal Change Forecast Viewer to see how water levels are expected to keep changing at multiple sites along the North Carolina coast over the next several days. You can also track the recorded extent of floodwaters, both along the coast and inland, by visiting the USGS’ Flood Event Viewer.

One major hurricane hazard is inland flooding caused by heavy rainfall. Florence is likely to cause potentially life-threatening flash flooding as it continues to move inland the National Hurricane Center has forecast.

To track inland flooding, the USGS gathers data from its network of long-term, real-time streamgages, and from rapid deployment gauges. When flooding is occurring, USGS field crews make real-time streamflow measurements to verify the streamgages’ readings. After the storm passes, the crews quickly replace storm-damaged or lost gauges. During and right after hurricane flooding, these records help the Federal Emergency Management Agency target emergency relief to the hardest-hit areas.

For more than 125 years, the USGS has monitored flow in selected streams and rivers across the U.S. The information is routinely used for water supply and management, monitoring floods and droughts, bridge and road design, determination of flood risk and for many recreational activities.

Access current flood and high flow conditions across the country by visiting the USGS WaterWatch website. Receive instant, customized updates about water conditions in your area via text message or email by signing up for USGS WaterAlert.