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August 4, 2020

To learn more about USGS’s role in providing science to decision makers before, during, and after Hurricane Isaias, visit the USGS Hurricane Isaias page at 

As Tropical Storm Isaias raced north up the Atlantic Seaboard Tuesday at speeds of as much as 30 miles per hour, U.S. Geological Survey crews from South Carolina to New York fanned out across rain-swollen waterways to measure the effects of the storm. At least 87 USGS hydrologists and hydrologic technicians were in the field across the region.

Their work includes measuring water flows on some rivers and streams where water levels are high; documenting signs of flooding in places where waters have already peaked; and collecting water samples for testing to determine whether the storm’s runoff has affected water quality.

Right after the storm, the USGS’s early information can help emergency managers decide where to locate relief centers, so that aid can reach the most severely affected communities quickly, and can help the U.S. Army Corps of Engineers manage flood control at dams and reservoirs across the region.

In the coming weeks, USGS flood information can help the Federal Emergency Management Agency tell the difference between wind and water damage – important information for property owners and insurers. Over the long term, it can help emergency managers plan for future floods; improve computer models used by the National Weather Service to forecast flooding; and provide information used by FEMA to update the nationwide flood zone maps that underpin the federal flood insurance program.

This rapid deployment gauge that was installed August 1 in Swansboro, NC to monitor potential flooding caused by Isaias.
This rapid deployment gauge was installed August 1 in Swansboro, North Carolina on the White Oak River to monitor water levels in order track potential flooding caused by Tropical Storm Isaias. Photo by Bryce McClenney, USGS. (Public domain.)

Work Begins in the Carolinas Within Hours of Landfall

Isaias made landfall as a Category 1 hurricane around midnight Tuesday, its eye crossing the coast just north of the South Carolina-North Carolina border, bringing wind-driven water onto beaches and into bays and tidal rivers and producing close to five inches of rain in some areas. Nine USGS scientists from field offices in Charleston and Raleigh were quickly in the field measuring high water flows and recording peak water levels.

Using hand-held instruments, the crews are taking water flow measurements on flood-swollen rivers and streams. They are also looking for high water marks—telltale lines of seeds, leaves, grass blades and other debris left behind on buildings, bridges, other structures and even tree trunks as floodwaters recede. When they find high water marks, they label them, photograph them, survey them, and record crucial details about them. The field work is highly skilled and time-sensitive, because peak water flows can quickly pass, and high water marks can be obliterated by weather and by property owners’ cleanup efforts.

Image shows USGS field crew conducting measurements on flooding streams
USGS hydrologic technician Logan Jeffries uses a hand-held instrument called an Acoustic Doppler Velocimeter to measure streamflow August 4 on Tenmile Creek near Clarksburg, Maryland. Photo: Matt Baker, USGS. (Public domain.)

Measuring Storm Effects in Chesapeake Bay Region

As Isais pushed north Tuesday, it dumped more rain on the Mid-Atlantic states. In Virginia, USGS hydrologist Russell Lotspeich said the storm moved so quickly that it dropped less rainfall than expected. Four Virginia crews were collecting water quality samples in the upper reaches of three rivers that flow into the Chesapeake: the Potomac, Shenandoah and James. Two other crews were working closer to the coast in Central and Northern Virginia, measuring stream flows and looking for high water marks.

In neighboring Maryland, Delaware and the District of Columbia, with up to six inches of rain forecast for the area, 29 USGS staffers were in the field. In Maryland’s Baltimore, Frederick, Harford, Howard and Montgomery counties, seven crews were measuring stream flows. Two more crews were measuring flows closer to the coast, in New Castle County, Delaware.

Four crews were collecting water quality samples in suburban areas near Baltimore and Washington, DC, as well as in two counties on Maryland’s Eastern Shore. The samples will be tested for flood-borne sediment, a potential contributor to Chesapeake Bay pollution. Sediment can carry chemicals and fertilizer, bury shellfish beds and block light from reaching underwater grasses. The USGS monitors sediment flows into the Chesapeake Bay watershed as part of a joint federal-state-and District of Columbia initiative to improve the Bay’s water quality.

Image shows a USGS streamgage partially submerged in floodwaters
This USGS streamgage on Schantz Spring near Wescosville, Pennsylvania was partially submerged after floodwaters from Tropical Storm Isaias quickly rose and flooded the area. USGS crews arrived on scene August 4 to measure water levels and flows in the area. Photo by Thomas Hunt, USGS. (Public domain.)

Field work makes it possible to reconstruct flooding

In Pennsylvania, 17 people were in the field Tuesday. Seven crews were measuring high water levels and five crews were collecting sediment samples, with the work concentrated in Chester, Montgomery and Lancaster counties. In New York, 21 more water science experts began work late Tuesday.

The physical signs of flooding provide information that can confirm or correct other lines of evidence. Among these are measurements from a network of permanent and temporary river and streamgages; satellite photos; and computer modelled flood projections. Taken together, this evidence will allow USGS experts to reconstruct where, when, at what depth, and in what volume the storm’s floodwaters gathered.

The USGS continues to take all appropriate preparedness and response actions as Isaias approaches the Atlantic coast. People potentially affected by the storm can visit or for tips on creating emergency plans and putting together an emergency supply kit. 

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