Race against time: Technicians rush to study Florence storm debris before it disappears

A horizontal line of seeds tells the story: The floodwaters brought by Hurricane Florence rose here to about chest height. Left behind on the door to a church outbuilding was the flotsam — including the seeds — that once floated on the floodwater’s surface.

The seed line is the kind of telltale sign Daniel McCay and Mary Winsor are looking for. As hydrologic technicians with the U.S. Geological Survey, it’s their job to collect information that helps emergency managers understand the true extent of a flood. Perhaps more importantly, the information helps improve emergency managers’ predictions.

On a fact-finding mission this week, McCay parks alongside Sycamore Hill Independent Holiness Church, and he and Winsor pull out their gear — measuring equipment, levels and an assortment of ways to leave a mark for crews that will come after them.

They cross the street to a church outbuilding that McCay had noticed days before. While measuring the level of the nearby Lumber River on Sept. 18, McCay had snapped a photo. It was before the river peaked, and water had crept more than halfway up the building’s front door.

USGS hydrographers Daniel McCay and Mary Winsor record information about a freshly-collected high water mark.

Anna Stull USGS

Now that the water has receded, McCay and Winsor return to flag the evidence. They memorialize the height of the seed line on the door frame with a marker and measure the distance to the threshold. It’s 4.4 feet.

McCay zooms into their location using Google maps on his phone and records their coordinates. They upload that data straight to the Internet, along with a photo and a description. Other technicians will come back with more sophisticated GPS and surveying equipment.

About three dozen USGS technicians have been collecting high-water marks across the Carolinas in the wake of Florence. State officials are also collecting this data, too. They’re all racing against the clock, trying to create the most complete record of the storm’s extent before it’s washed away.

“All it takes is a good rain, and all of that is gone,” said Chris Smith, a USGS supervisor who, like McCay and Winsor, is based in Georgia.

The stakes are high. Government decision-makers at all levels want to understand spatially how widespread the flooding was, and high-water marks are important for building those maps. Insurers use high-water marks when they make decisions on claims. The data is also essential “ground truth” for refining predictive models.

“The future is in predicting what’s going to happen,” Smith said.

Crews from Florida and Virginia are on their way to help.

Carli Brosseau: 919-829-4627; @carlibrosseau