The Repository Hook Echo

Hurricane Helene: The River Gauge That Beat 1916

October 30, 2026 · Runtime 15:26 · Watch on YouTube

Hurricane Helene came ashore near Perry, Florida, on the night of 26 September 2024, a Category 4. Its worst flooding came almost 400 miles away, in the mountains of western North Carolina. On the French Broad River at Asheville, the USGS gauge, with continuous records since 1895, peaked at 24.82 feet, 1.72 feet above the Great Flood of 1916. But the flow was 113,000 cubic feet per second against 110,000 in 1916: by water, the same flood. Upstream, on the Swannanoa, the gauge record holds a single value between 1:15 and 5:30 in the afternoon: the peak, with its flow flagged as an estimate.

Chapters

  1. 0:00 Asheville, after the flood
  2. 0:56 Landfall at Perry, Florida
  3. 1:47 Rain before the hurricane
  4. 2:48 1916: two storms, nine days apart
  5. 3:31 The second blow
  6. 4:44 What a stream gauge measures
  7. 5:23 The French Broad, reading by reading
  8. 6:07 A correction: 24.67 or 24.82
  9. 6:27 Higher than 1916, not more water
  10. 7:30 The Swannanoa
  11. 8:09 Four hours without readings
  12. 9:25 Our count: 24 gauges
  13. 10:52 Above the rating curve
  14. 11:53 Marshall, Hot Springs, Lake Lure
  15. 12:51 Landslides and the toll
  16. 14:16 What the record supports
  17. 15:05 Next: Mayflower and Vilonia, 2014

Transcript

Asheville, after the flood 0:00

During Hurricane Helene, a river gauge in Asheville beat a record from 1916. The storm came ashore in Florida, almost four hundred miles to the south. Its worst flooding came here, in the mountains of North Carolina, on rivers that had been rising for two days before it arrived.

We downloaded every fifteen-minute reading from the stream gauges in these mountains, to see what the instruments recorded while the water rose, and where the record goes quiet. This is how the radar at Tallahassee saw Helene come ashore, at ten past eleven at night.

At Asheville, the gauge kept reading through the peak, and the number it left has already been corrected once. A few miles upstream, on the Swannanoa River, the record has a hole in the worst hours. This episode reads the flood the way the instruments did, from the coast to the mountains.

Landfall at Perry, Florida 0:56

The National Hurricane Center puts the landfall about ten nautical miles southwest of Perry, Florida, on the night of September twenty-sixth. Helene was a Category Four, with sustained winds of one hundred and twenty knots, about one hundred and forty miles an hour, and a central pressure of nine hundred and thirty-nine millibars.

The report calls it the strongest hurricane to come ashore in the Florida Big Bend since reliable records began, around 1900. And it did not slow down. It was moving north-northeast at twenty-seven knots, about thirty miles an hour.

From Perry to the river gauge at Asheville is about three hundred and eighty-five miles in a straight line. At that speed, roughly half a day. By the early morning of the twenty-seventh, the rain bands around the center were over the mountains.

Rain before the hurricane 1:47

But the mountains had already been under heavy rain for two days. Moisture streaming north from the storm met a slow-moving cold front over the southern Appalachians on the twenty-fifth and twenty-sixth. Forecasters call it a predecessor rain event: heavy rain that arrives ahead of the hurricane itself.

The Weather Service office in Greenville-Spartanburg wrote that the predecessor rain alone produced up to ten inches in parts of the mountains. The hurricane center wrote what that did: the soil was saturated, and the rivers were rising before the core of Helene arrived.

The gauge shows it. In our download of the French Broad at Asheville, at midnight on September twenty-fourth the river stood at one point three three feet, carrying about seven hundred and forty cubic feet of water per second. By the afternoon of the twenty-sixth, before the hurricane had even reached land, it stood at ten feet, with thirty times the flow.

1916: two storms, nine days apart 2:48

This had happened before. In July 1916, two tropical cyclones hit the region nine days apart. The first, a major hurricane, came ashore on the Alabama coast on July fifth. It produced no flooding, but it left the ground saturated and the streams running high.

The second, a Category Two, came ashore in South Carolina on July fourteenth. An observer at Altapass, North Carolina, recorded twenty-two point two two inches of rain in twenty-four hours. At least eighty people were killed. At Asheville, the French Broad rose to twenty-three point one feet, a record that stood for one hundred and eight years.

The second blow 3:31

In 2024, the second blow came on the morning of September twenty-seventh. The rain bands of Helene swept over soil that was already saturated, with rainfall rates as high as two to three inches an hour, the hurricane center wrote.

The heaviest totals fell along the Blue Ridge escarpment, where the mountains rise abruptly above the foothills and the rivers have their headwaters. Totals of fourteen to twenty inches were widespread there, the Weather Service wrote, with locally two feet or more.

The highest total in the hurricane center's report is at Busick, North Carolina: thirty point seven eight inches in three days. Across a large area, from northwestern South Carolina into southwestern Virginia, the three-day totals had less than a one in a thousand chance of happening in any given year.

The wind was there too. At Mount Mitchell State Park, an ECONet weather station recorded sustained winds of seventy knots and a gust of ninety-two, about one hundred and six miles an hour. On some east and southeast-facing slopes above three thousand feet, the forest lost eighty percent or more of its canopy.

What a stream gauge measures 4:44

Here is what a stream gauge actually measures. A sensor in a small station on the bank records the height of the water surface, every fifteen minutes. The flow is not measured there. It is computed from the height, through a curve the USGS builds by measuring the river by hand, again and again, at different levels.

That curve is called a rating. And a rating only reaches as high as the river has been measured. Remember that, because in this flood the water went above the top of the curve at most of the gauges in these mountains.

The French Broad, reading by reading 5:23

This is the French Broad at Asheville, reading by reading. Ten feet on the evening of the twenty-sixth. Thirteen feet by six in the morning. Then the climb steepens. The fastest rise in our download is almost half a foot, in the fifteen minutes after two thirty in the afternoon.

Around noon, the river crossed eighteen feet, the level the Weather Service calls major flooding. In the next five and a half hours it rose another seven feet.

The highest number in the record is twenty-four point eight two feet, at five thirty-eight in the afternoon. The flow was one hundred and thirteen thousand cubic feet per second, about one hundred and fifty times what the river carried three days earlier.

A correction: 24.67 or 24.82 6:07

In our last episode, we said twenty-four point six seven. That was the provisional peak the USGS reported three days after the flood: the reading at five thirty. The approved record is a single value eight minutes later, between two fifteen-minute readings. The documents we found do not explain that extra reading.

Higher than 1916, not more water 6:27

Against 1916, the gauge is higher by one point seven two feet. That is the number the reports repeat: the Great Flood of 1916, beaten. But the gauge also records the flow, and the flow tells a smaller story.

In 1916, the peak flow at Asheville was one hundred and ten thousand cubic feet per second. In 2024, it was one hundred and thirteen thousand. Three percent more water, through the same place, a century apart.

The height of a river depends on its channel. Bridges, fill and the riverbed itself all change over a hundred years, and the same flow can stand higher. The 1916 line in the USGS record even carries a note of its own: the gauge datum changed during that year.

So at Asheville, the record supports this: by height, Helene beat 1916. By the amount of water, it matched it. The largest flood in this river's record has now happened twice, one hundred and eight years apart.

The Swannanoa 7:30

The other half of the story is a tributary. The Swannanoa River comes down from Black Mountain and joins the French Broad in Asheville, upstream of the gauge. Along it, the Weather Service wrote, dozens of people were killed and hundreds of structures destroyed.

The Swannanoa has its own gauge, at Biltmore, with peaks back to 1916. In our download, it reads every fifteen minutes through the morning of the twenty-seventh. At one fifteen in the afternoon it reads twenty-five point five six feet, and it is climbing almost half a foot every fifteen minutes.

Four hours without readings 8:09

Then the readings stop. Between one fifteen and five thirty, the record holds a single value: twenty-seven point three three feet, at three o'clock. When the fifteen-minute readings come back, the water is already falling.

That single value is the peak, and it is marked differently from the rest. The flow attached to it, sixty thousand eight hundred cubic feet per second, is flagged as an estimate. In 1916 the Swannanoa peaked at twenty point seven feet. Helene was six point six feet higher, with more than two and a half times the estimated flow.

The USGS file holds one more line for this river, from long before any gauge: a flood in April 1791, its day unknown, estimated at twenty-six feet. Helene was higher than that too.

How do you measure a peak your gauge did not read? In the days after, the USGS sent crews across western North Carolina to flag and survey high-water marks, the lines the water left behind, including in the Swannanoa basin. The documents we found do not say which method set the Swannanoa's peak.

Our count: 24 gauges 9:25

We ran the same comparison across the region: every USGS gauge in the six mountain basins of western North Carolina with at least thirty years of peaks before 2024. That is twenty-four gauges. Fifteen of them set a new record for flow.

The largest margin was on the Ivy River near Marshall: thirty-eight thousand four hundred cubic feet per second, two point six seven times its record from 1965. On the South Toe River near Celo, below Mount Mitchell, the flow was more than double its record from 1977.

Several of those old records were only twenty years old. In September 2004, two hurricanes, Frances and Ivan, flooded these same mountains ten days apart. On the Pigeon River near Canton, Ivan's peak was forty-eight thousand cubic feet per second. Helene's was sixty-seven thousand three hundred.

And seven of the twenty-four have a gap of more than an hour in their readings, all of them on the twenty-seventh, during the flood. The Ivy River gauge went silent for almost a day.

The hurricane center's final count is larger than ours, because it covers four states and shorter records: at least sixty-three stream and river gauges exceeded their record flood levels. At least fourteen of them had a hundred years of records.

Above the rating curve 10:52

And here is where the rating curve matters. Of the eighty-one sites serviced by the USGS field office in Asheville, about sixty had peak heights above their current ratings. At those gauges the height was recorded, but the curve did not reach high enough to turn it into a flow.

For about thirty gauges, the USGS wrote, the peak flows would need indirect measurements, because direct measurements could not safely be made during the flood. Two days later, the list of candidates had passed forty.

On September thirtieth, the USGS dispatched seventeen field crews. By the next day, its crews had made one hundred and sixty-five discharge measurements at eighty-five gauges across three states, measuring rivers that were still running high.

Some gauges did not survive at all. Across the state line in Tennessee, a USGS team confirmed that the streamgage on the Nolichucky River at Embreeville was completely destroyed.

Marshall, Hot Springs, Lake Lure 11:53

Below Asheville, the French Broad runs through the town of Marshall. The Weather Service wrote that the flood destroyed part of Asheville's River Arts District and much of downtown Marshall. The gauge at Marshall recorded one hundred and nineteen thousand cubic feet per second, flagged as an estimate, against one hundred and fifteen thousand in 1916.

Farther downstream, at Hot Springs, near the Tennessee line, the gauge recorded one hundred and thirty-four thousand cubic feet per second, against one hundred and ten thousand in 1916. The farther down the French Broad, the more of the tributaries' water it carried.

East of the divide, on the Rocky Broad River, the flood ran through Chimney Rock and into Lake Lure. Cove Creek, a small stream near the lake, set a record almost twice its old one, from 1957. Months later, the Army Corps of Engineers was still pulling the debris out of the lake.

Landslides and the toll 12:51

Water was not the only thing that moved. The USGS documented more than two thousand landslides. In the Fairview area, southeast of Asheville, landslides killed fifteen people, according to the hurricane center.

Helene is responsible for at least two hundred and fifty deaths in the United States, at least one hundred and seventy-five of them direct: the deadliest hurricane in the contiguous U.S. since Katrina in 2005. One hundred and seven of the deaths were in North Carolina.

Freshwater flooding, including landslides, caused at least ninety-four of the direct deaths, seventy-seven of them in North Carolina. The storm that came ashore with one hundred and forty mile an hour winds killed most of its victims with water, in the mountains.

The damage estimate is seventy-eight point seven billion dollars, the seventh costliest hurricane in the United States. In Asheville, clean water was not restored until November eighteenth, fifty-three days after the storm.

The hurricane center's report counts the rescues as well. In western North Carolina, the Coast Guard rescued at least eight hundred and sixty-five people, mostly from floodwaters. In Buncombe County alone, there were more than four hundred and ninety water rescues.

What the record supports 14:16

Here is what the instruments support. At Asheville, Helene set a new height record and matched 1916 in water. On the streams that feed the French Broad, the floods went far beyond anything their gauges had recorded: two and a half times the flow of 1916 on the Swannanoa, and of 1965 on the Ivy.

Here is what they cannot say. How the Swannanoa's peak was set: the record flags the flow as an estimate and says no more. And how high the water went at the gauges that stopped, or were destroyed.

One question we could not close. At Asheville, the provisional peak was the reading at five thirty, and the approved one is a single value eight minutes later. If you know how that reading was taken, tell us in the comments.

Next: Mayflower and Vilonia, 2014 15:05

Next, a tornado that tracked forty-one miles across central Arkansas in April 2014, the deadliest single tornado in the state since 1968. The radar at Little Rock was close enough to watch it, scan by scan. That is the next episode. Mayflower and Vilonia, 2014.

Description and sources

Helene made landfall about 10 n mi southwest of Perry, Florida, at 0310 UTC on 27 September 2024 (11:10 PM EDT on the 26th), with 120 kt winds and 939 mb (NHC Tropical Cyclone Report). A predecessor rain event had already soaked the southern Appalachians on the 25th and 26th. Our download of the USGS records: the French Broad at Asheville rose from 1.33 ft (738 cfs) on 24 September to 10 ft before landfall, crossed 18 ft (major flood) around noon on the 27th, and peaked at 24.82 ft and 113,000 cfs at 5:38 PM EDT. The provisional peak first reported, 24.67 ft, was the 5:30 PM reading. In 1916 the same gauge recorded 23.10 ft and 110,000 cfs. On the Swannanoa at Biltmore, readings stop after 1:15 PM (25.56 ft); the record holds 27.33 ft at 3:00 PM, flow estimated at 60,800 cfs, and readings resume at 5:30 PM with the water falling. Across 24 USGS gauges in western North Carolina with at least 30 years of peaks, 15 set a flow record and 7 have gaps of more than an hour on the 27th.

PRIMARY SOURCES

ARCHIVE PLATES — with author, date, archive and licence (CC BY photos credited by name).

  • NCDOTcommunications — 2024-09-27 08:46:01 | Wikimedia Commons | CC BY 2.0
  • NCDOTcommunications — 2024-10-15 11:00:47 | Wikimedia Commons | CC BY 2.0
  • NCDOTcommunications — 2024-10-07 13:46:21 | Wikimedia Commons | CC BY 2.0
  • NCDOTcommunications — 2024-10-15 11:01:06 | Wikimedia Commons | CC BY 2.0
  • NCDOTcommunications — 2024-10-07 11:50:54 | Wikimedia Commons | CC BY 2.0
  • NCDOTcommunications — 2024-10-08 13:13:49 | Wikimedia Commons | CC BY 2.0
  • NCDOTcommunications — 2024-10-07 10:26:37 | Wikimedia Commons | CC BY 2.0

... and 2 more plates, each credited on screen in the video and listed in this project's manifest.

Hook Echo reads a disaster through the instruments that recorded it: radar, sensor, survey and report, with the primary sources above.

About the material. Video: U.S. Army Corps of Engineers and FEMA footage from western North Carolina, published on DVIDS. Photos: N.C. Department of Transportation (NCDOTcommunications), CC BY 2.0, via Wikimedia Commons. Radar: NOAA NEXRAD Level II (KTLH, KGSP), rendered by us with the National Weather Service colour scales; on the Greer radar the mountains block the lowest beam toward Asheville. Our measurement uses the USGS instantaneous and annual peak records (NWIS). Every diagram is drawn in code. Nothing in this video is AI-generated imagery. The narration is synthetic (Google Gemini text-to-speech), checked word by word against the script.

#HurricaneHelene #Asheville #Flood