After the Storm – Hurricane Matthew and the Floods

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In the aftermath of Hurricane Matthew, USGS crews have been collecting the record number of storm-tide sensors deployed prior to the storm and are now determining high water marks, collecting water quality samples, and assessing the impacts of storm surge on south eastern beaches caused by erosion, overwash and inundation.  

Visit the USGS Hurricane Matthew webpage to learn more. 

 

Although the is storm over, the flooding continues, as does the  flood work of the USGS. In North Carolina, at least 24 peaks of record were set on local rivers, as heavy rain during Hurricane Matthew fell on ground already saturated just weeks ago by Tropical Storm Julia. As of today (October 14), some rivers were still rising and expected to crest this weekend.

Gathering the Data

USGS crews from Florida north into Virginia have recovered almost all of  the hundreds of storm-tide sensors at almost 300 locations that were deployed to measure and record storm surge impacts. Waves drive most of the physical destruction accompanying storm-surge. Data from the sensors will be used to by USGS to quantify storm-tide dynamics (wave heights, frequencies, speeds, and extent) for various storm conditions, topographies, ecologies, built environments, and land uses. This information will be used by the USGS and other federal, state and local agencies to develop or design better storm-tide models, more accurate flood forecasts. The data can also be used to design more effective flood-protection infrastructure, stronger buildings, and wiser land use policies. Crews are also repairing USGS gauges damaged by the storm.

Measuring the Height of the Water

Hydrologic technician Samantha Kephart.points out a high water mark
Hydrologic technician Samantha Kephart points out a high water mark.

The Flood Event Viewer for Hurricane Matthew provides key water-level information at different sites along the coast.  Emergency managers, disaster responders, state and local floodplain management officials and the public can select a data point on the map and learn how high the flood level got during Matthew, and whether a gauge recorded a record-high peak, when, and at what stage. Some rapid deployment gauges (green triangles on the viewer) also provide graphs of the water levels from the time of deployment of the RDG to its recovery.

If there were no sensors to record the flood-level, USGS crews will visit the site afterwards and look for visual clues of peak flood height. They will mark, survey and document those high water marks. These data will also be available via the flood viewer. USGS crews have to date flagged almost 600 coastal locations.

Many streams also experienced record flood and flows and flood heights. For example, in addition to the North Carolina records already mentioned, five peaks of records were recorded in Florida, and three in South Carolina. USGS crews measure flood flows at USGS streamgages to determine the flow rates.  The measurements are generally made using sophisticated acoustic Doppler equipment.  The measured flow rates are used to calibrate the USGS streamgages and ensure that the flood data the gauges collect is accurate and reliable.  Once that is assured, the USGS can estimate the rarity of the flood flows for that location.  Scientists often measure the rarity of a flood flow based on its recurrence interval, which is essentially the probability a flood of this level might happen in a given year.  These data will be the basis for the design of future dams, other water-related infrastructure such as water or waste-water treatment plants and highway bridges, and for delineating the Federal Emergency Management Agency floodplain maps.

When a field crew is unable to reach a streamgage during the flood, they will use surveying equipment to calculate the height of the high water and the geometry of the channel and determine an estimate of the flood flow.

 

What’s the Water’s Quality

Graph of Neuse River at Kinston, North Caroina, from ~1987 - 2016
Graph of streamfow and water-quality sample collection at the Neuse River at Kinston, North Caroina, from ~1987 through 2016

Water-quality samples were collected at long-term sampling sites in the USGS National Water Quality Network in North Carolina and South Carolina and are scheduled to be collected at a long-term network site in Georgia. High-water events on the scale of Hurricane Matthew can cause changes in water quality that affect human health and the environment and result in high constituent water-quality loads by flushing large quantities of nutrients, sediment, pesticides, and bacteria into downstream waters and estuaries. Excessive nutrients in rivers, streams, and coastal areas can cause algal blooms that result in hypoxic conditions and threaten valuable commercial and recreational fisheries.

Sustained monitoring at long-term sites over a wide range of flow conditions, as illustrated in the graph below for the Neuse River at Kingston, North Carolina, can help answer important water-quality questions such as: is water-quality getting better or worse; what natural or human factors are driving observed changes in water quality; and how do extreme hydrologic events, such as a hurricane, affect water quality? Initial results from water-quality sampling after Hurricane Matthew should become available in approximately 2 to 3 weeks from the date of sample collection.

USGS collection and analysis of data during and after hydrologic events, such as floods and major storms, helps science, relief, and health agencies better understand the effects of such events on water quality in the short (days to months) and long term (years to decades), providing important information to emergency responders and long-range planners responsible for managing the resource.

 

Coastal Change Portal Hurricane Matthew 2016
Coastal Change Portal Hurricane Matthew 2016 showing probabiliteis of caosal erosion along the Florida coast to North Carolina

Assessing Coastal Change

Hurricane Matthew hugged the southeast coastline from October 6-9 impacting beaches stretching from Florida to North Carolina. Storm surge and run-up caused by large waves elevated water levels at the shoreline and caused beach erosion, overwash of coastal sand dunes, and breaching of a barrier island in Matanzas, Florida.The USGS National Assessment of Coastal Change Hazards storm team has started to compare post-storm imagery collected by NOAA to predictions of coastal change made in advance of the storm, and can be seen on the USGS Coastal Change Hazards Portal.

As predicted, overwash occurred in locations with low dune elevations including multiple areas within Canaveral National Seashore, Florida. This week the St. Petersburg Coastal and Marine Science Center will be collecting low-altitude aerial photos to document dune erosion that occurred during Hurricane Matthew and field crews will begin surveying some overwash areas on the Florida east coast.  In addition, over the next few weeks airborne-based elevation surveys will be coordinated to eventually quantify the amount of sand eroded from this large stretch of coast.

Check the Maps

The USGS National Geospatial Program has established a Disaster Coordination Preparedness & Response Map for Hurricane Matthew which incorporates both Civil Air Patrol and National Oceanic and Atmospheric Administration imagery.  Users can see aerial photos for locations affected by the storm, by clicking on the purple and green dots on the map and selecting “image URL.”  The International Charter for Space and Major Disasters has been activated for the United States, Haiti, Cuba, and the Dominican Republic. Satellite imagery and aerial photography from national and international partners will be compiled and distributed on the USGS Hazards Data Distribution System.  USGS also has a Hurricane Matthew’s Water Footprint page, where users can see an animation of the hurricane’s impact on precipitation and streamflow.

To learn more about USGS research and monitoring efforts associated with Hurricane Matthew, visit the USGS Hurricane Matthew webpage.