Staying ahead of Hurricane Dorian with geo-information

September 6th, 2019, Published in Articles: EE Publishers, Articles: PositionIT, Featured: PositionIT

As Hurricane Dorian moves north in the Atlantic Ocean, brushing the United States’ Southeast coast with strong waves, winds, and rain, the United States Geological Survey (USGS) is providing comprehensive scientific capabilities and information that decision makers, emergency responders and communities can use to help them prepare, cope and recover from the storm.

The USGS’s ability to forecast coastal change; track storm tides, river and stream levels and flow; measure coastal and inland flooding across entire regions; capture high-resolution ground elevation and topographic data; and create detailed maps used by disaster teams responding in the aftermath of storms have helped it stay ahead of the storm.

Planning and preparation

Hydrographer Keith Lambert installing a rapid deployment gage at New Mill Creek at Chesapeake, VA Sept. 5, in advance of Hurricane Dorian. Photo: Blake Dudding, USGS

Before a coastal storm is predicted to make landfall, the organistion begins collecting data that can improve forecasting, guide relief work, and speed up recovery from the powerful storms’ effects.

The Coastal Storm Response Team, a multidisciplinary group of specialists from throughout the USGS, works closely with the National Hurricane Center and other federal agencies and confers daily when forecasters indicate a hurricane or tropical storm is likely to make landfall in the US. The Storm Team closely follows the storm’s forecast intensity and track. Once a hurricane or tropical storm is considered likely to strike somewhere in the US, the team leaders decide whether it is necessary and safe to deploy field crews to the storm’s projected path along the coast.

Since Dorian, as a tropical storm, was expected to hit Puerto Rico on 28 August 2019, the team began meeting on 26 August 2019. But the storm gave Puerto Rico a near miss, stalled over the Bahamas and then slowly moved up the Florida coast. So preparations for the hurricane have adapted and expanded in response to changing forecasts from the National Hurricane Center.

Sensing the storm

Teams of USGS hydrologists and hydrologic technicians have deployed more than 350 storm-tide sensors, beginning 29 and 30 August in Florida, then rolling along the coasts of Georgia, South Carolina and North Carolina over the long Labor Day holiday weekend. By 5 September, technicians were deploying about a half-dozen sensors in coastal Virginia as the storm was forecast to affect that state’s Tidewater region.

The sensors are gathering information used by the National Oceanic and Atmospheric Administration (NOAA) and by emergency managers to monitor the timing, extent and magnitude of storm tides. The data they provide will improve storm-tide and coastal change forecasts for future events.

Storm-tide sensors record water-level and wave data. The sensors, housed in vented steel pipes a few centimetres wide and about 30 cm long, are designed to be rapidly installed on bridges, piers, and other structures that have a good chance of surviving a hurricane, and are part of the USGS Storm Tide Monitoring Network. They remain in place throughout the storm, until it is safe for USGS crews to collect them.

The sensors collect water pressure readings that help define the depth, duration and timing of a storm tide. Some of them are arranged in long transects perpendicular to the coast, to help measure how local topography, natural features and land use can reduce or increase wave heights and the resulting flood damage.

That information helps public officials assess storm damage, tell the difference between wind and flood damage, and improve computer forecast models.

Crews also installed rapid deployment gauges (RDGs) at locations that are not monitored year-round, but are at risk of flooding due to an approaching storm. These RDGs provide real-time information to emergency managers tracking floodwaters, such as water level, precipitation, wind speed, humidity and barometric pressure.

Both sets of instruments help augment the USGS’ nationwide real-time network of about 8500 stream gauges that transmit both streamflow and water levels, and another 1700 stream gauges that transmit only water levels. The National Weather Service uses data from stream gauges that provide both water level and streamflow to develop flood forecasts, and the US Army Corps of Engineers uses the data to make flood-control decisions. The stream gauges and RDGs that provide only water levels are used by local agencies to track flood locations and plan emergency response and allow the public to monitor local rivers and stream levels in real time.

Forecasting coastal change

Hurricanes generate dangerous waves and high water levels that can move large amounts of sand, destroy buildings and infrastructure, and take lives. Through processes like dune erosion, overwash and inundation, storms reshape the country’s coastline. USGS coastal change experts have forecast how Dorian may affect the coastline using a sophisticated system they developed called the Coastal Change Hazard Forecast model.

This model provides detailed, frequently updated forecasts of Dorian’s likely effects on sandy shorelines along the Atlantic coast. It predicts where protective sand dunes are likely to erode at their bases or be overtopped by storm waves, and where seawater could inundate coastal areas behind the dunes. These forecasts can help emergency managers decide which areas to evacuate, which roads to use, and where to position heavy equipment for post-storm clean-up.

On 5 September, USGS coastal change experts updated the forecast and found that 53% of the sandy beaches from Georgia to Delaware were very likely to undergo beach and dune erosion from Dorian’s strong waves and surge. The Carolinas’ beaches are projected to face the highest rates of dune erosion, with 75% of South Carolina and 61% of North Carolina beaches likely to suffer some level of erosion. About 41% of Georgia’s beaches and 34% of Virginia’s dunes were also forecast to suffer some erosion, with only 1% of Maryland’s coastal beaches and none of Delaware’s beaches forecast to erode.

The same forecast set the chance that dunes would be overwashed by waves as 7% for Georgia, 40% for South Carolina, and 12% for North Carolina dunes. Overall, overwash was very likely for 16% of the dunes from Georgia to Delaware.

Fig. 1: The comprehensive Event Support Map by the USGS Coastal Storm Response Team for Hurricane Dorian, which includes various maps and various datasets in one website with an easy-to-use and easy-to-navigate user interface.

Inundation, the most severe coastal impact, occurs when beaches and dunes are completely and continuously submerged by water. Inundation was forecast as very likely for 7% of dunes in South Carolina and 1% in North Carolina. Other states’ beaches were not projected to be inundated.

The model works by combining NOAA-modelled waves and surge with the USGS’ detailed coastal elevation data to estimate total water levels at the shoreline and the probability of coastal erosion. Forecasts in the portal are updated as NOAA projections of storm path and strength change.

Informing first responders and the public

During Hurricane Dorian and all other major hurricanes, the USGS strives to ensure that the disaster response community has quick access to timely, accurate, and relevant geospatial imagery, products, and services.

First responders often rely on the USGS National Geospatial Program, which collects, archives and shares digital records on the nation’s topography, natural landscape and human-made environment. The program’s Geospatial Information Response Team, also known as the GIRT, works within the USGS and with partner agencies to provide key information to federal, state and local agencies, emergency managers and first responders. Information such as the storm’s track, the USGS facilities that lie in its path, lidar elevation data, and the locations of hospitals, airports, government buildings and other important sites, is shown on multi-layered websites or on custom-printed maps.

Fig. 2: A custom-made composite Storm Event Map brings together a variety of information, including the storm track, hurricane watches and warnings, landscape features, major roads, streamgages, rapid deployment gauges and more.

As Florida was preparing for Hurricane Dorian’s arrival, USGS worked with the Defense Logistics Agency to prepare more than 2600 detailed topographic maps of ten Florida counties likely to be affected by the storm, so that first responders could have detailed information at hand.

To make a broad range of information easily accessible to the public, first responders, emergency managers and government decision makers, the GIRT also quickly collects and posts information for each major hurricane in an event support map. On the publicly accessible Event Support Map website for Dorian, anyone interested in detailed information can find many sources on a single web page.

A custom-made composite Storm Event Map brings together a variety of information, including the storm track, hurricane watches and warnings, landscape features, major roads, stream gauges, rapid deployment gauges and more. (Click anywhere on the map to view details.) Also on the website are the most recent Coastal Change Hazard Forecast for erosion on sandy beaches; a Flood Event Viewer where readings from individual stream gauges and rapid deployment gauges are available in near-real time; satellite imagery and photos; and elevation information.

In partnership with the Heritage Emergency National Task Force, which includes Federal Emergency Management Agency (FEMA) and the Smithsonian Institution, the GIRT has also included arts, historical and cultural institutions in the storm’s path on the Hurricane Dorian event support map. The goal is to help emergency responders get information or help to these sites as quickly as possible.

Also included on the USGS’ public event support map is information from other government agencies, such as forecasts from the National Hurricane Center, NOAA imagery, and crowdsourced hurricane photos collected by FEMA.

Collecting and assessing signs of flooding

Once the storm danger has passed, USGS field crews travel to flooded areas to make real-time streamflow measurements, verify the accuracy of stream gauge readings, and quickly repair or replace damaged or lost gauges. Crews will also search areas affected by flooding for high-water marks, which are used by scientists to determine how high the flood waters reached.

Fig. 3: The most recent Coastal Change Hazard Forecast for erosion on sandy beaches are also included on the site. (This screenshot was taken on 6 September 2019 at 15.40 GMT+2.)

This data helps insurers and property owners document damage, help affected areas rebuild, and inform the forecasting, response, and recovery efforts of agencies like the National Weather Service, the Federal Emergency Management Agency, and the US Army Corps of Engineers.

Field crews will also collect the storm-tide sensors and other instruments that were deployed in advance of the storm. That process has already begun in South Florida, and crews plan to start collecting sensors in Georgia and the Carolinas over the weekend (7 – 8 September 2019). The wave-height and barometric pressure information recorded on the devices is downloaded and analysed to help improve future flood and coastal change forecasts.

Rebuilding after a big storm, getting ready for the future

Hurricanes reshape the landscape, sometimes subtly, sometimes dramatically. Hurricane Maria in 2017 damaged or destroyed 83 stream gauges in Puerto Rico. Hydrologic technicians from the Caribbean-Florida Water Science Center, working under difficult conditions, repaired or replaced all 83, and deployed 33 new rain gauges that were paid for with special disaster recovery funds. The stream gauges transmitted information throughout then-Tropical Storm Dorian’s close brush with Puerto Rico, and the island’s emergency managers used the new rain gauges to track the storm’s rainfall.  In Florida, 99 stream gauges that were damaged during 2017’s Hurricane Irma are back online and ready to monitor any flooding.

Fig. 4: The Flood Event Viewer map shows readings from individual streamgages and rapid deployment gauges in near-real time.

The supplemental storm funding the USGS received also allowed the acquisition of high-resolution lidar data for large areas of Florida. Lidar uses pulses of light beamed from an airplane to develop very detailed elevation information, which can be used to create precise maps of the land’s surface. USGS now has lidar data for Florida’s east coast watersheds from the Florida/Georgia line to the southern boundary of Broward County. That lidar data will give researchers an important baseline for measuring coastal change and assessing potential damages caused by Hurricane Dorian.

To learn more about USGS’ role providing science to decision makers before, during and after Hurricane Dorian, visit the USGS Hurricane Dorian page at www.usgs.gov/dorian. For more information please visit these websites:

Ready.gov or listo.gov for advice on the steps they can take to help protect lives and property.
Ready.gov for children— What to do before, during and after a hurricane
USGS Coastal Change Hazards: Hurricanes and Extreme Storms – Information on coastal change
USGS Flood Information—Information about current and past flooding
USGS WaterAlert – Sends email or text messages from the USGS streamgage of your choice
USGS WaterWatch— Provides current USGS water data for the nation
NOAA’s National Hurricane Center

Acknowledgement

This article was originally published by USGS on 5 September 2019 and is available online here.

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