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High Water Marks

“It is reasonable to expect that greater floods than those of the known past will occur…” from Floods on French Broad River & Spring Creek: Vicinity of Hot Springs, NC, a 1960 TVA publication.


I’ve always loved dramatic weather. George Stewart’s classic novel Storm was a favorite book from my childhood. It depicts an event – what we might now call an atmospheric river – that overwhelmed California. There was a brief period when I was around 8 or 9 that I aspired to be a meteorologist, and I tracked the temperature and barometric pressure on a graph on my wall. I’ve come full circle, serving since 2019 as a volunteer NWS COOP Observer, recording rainfall and temperature data for Celo 2 S, a station with a nearly continuous dataset for the past 75 years. For its first 50 years, Celo’s records were kept by Elpenor Ohle, the founding physician of the Celo Health Center. This station happens to pair with Celo’s USGS river gauge on the South Toe River (in operation since 1957). 


River flood signs
Digging deeper into local records turns up past events that measure up to these high water marks. There was once a gauge on the South Toe in Newdale, a few miles downstream from the current one. It was around to record the notable floods of August 13, 1940, and June 16, 1949. At some point in the future we’ll add new events (perhaps replacing the lowest marks on the rung). When we make those changes and additions to our high water marks, the 1940 flood would likely rank just below 1977, and 1949 would fall between the back-to-back storms (Frances and Ivan) in September, 2004. I can only guess at where the famous flood of 1916 would fall. My estimate is that it would be right up there with 1977 and 1940. That flood was worse a bit further downstream – it was a widespread, slower moving event that had a more powerful effect on larger watersheds.

Last week Drew Perrin and I installed these beautiful signs, hand-painted by Drew’s wife Carly Todd, to indicate historic high water marks of the South Toe River. From hunger stones in Central Europe to tsunami stones in Japan, there is a long history of human communities tracking high - and low - water marks. I proposed these signs at our land trust's community meeting so that people would have a visual reminder of how high the waters have risen in the past, and how high we can expect them to rise again in the future. Drew and Carly are the directors of Camp Celo; in the off-season Carly is a scenic charge artist for Sesame Street, and her craftwork is evident in the river signs. While we were discussing the design of the signs, Carly recollected the scramble to evacuate hiking trips that were camping on top of the Blacks during the arrival of Tropical Storm Fred, the cause of the most recent high water mark (8/18/2021). 


Fred filled our rain gauge with 6” of rain over the course of 3 days, but over 3” of that total fell in just a 3 hour period. We are relatively close to the river’s headwaters – the watershed above our river gauge is only 43 square miles. So water that falls in the valley and the surrounding mountains fills the river quickly, and runs out of the valley just as fast. These high water events are typically just moments in duration – the river rises above flood stage for an hour or two, peaks, then rapidly drops when the rain subsides. A historic flood in our valley is more likely to be caused by high rainfall rate than high rainfall total. Six inches spread over the course of two days is no big deal. Six inches in six hours causes headaches and anxiety – the river flirting with flood level. Six inches in three hours could be a record flood. A truly devastating event, one that will likely occur at some point in the future, would be akin to a theoretical storm laid out in the 1960 TVA document quoted above: 12.9 inches in 6 hours. A storm of this magnitude may seem unimaginable to us, but we should start imagining. Fred was a little rough on our valley, but highly destructive a few watersheds to the southwest. The headwaters of the Pigeon River received 14 inches in 12 hours, with 8 of those inches in under 3 hours. 


One of the few certainties that comes with our current climate crisis is that a warmer atmosphere holds more moisture. Storms from the Gulf or Atlantic have always been powerful, but now they can carry even more water inland. If one of those storms should stall or slow as it moves over the mountains, we will see rainfall and flooding like we’ve never seen before.


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This flood caused the highest water on this creek since 2004. It was from a less widespread, shorter rainfall event that flooded the 100 acre watershed of the creek far more than the 43 sq mile watershed of the river.


This video shows the river flowing at 6500 cubic feet per second, which happens to be 6.5' in height. The record flood of 1977 was 11 feet higher, and ~5x the volume of water.


A revised list of high water marks that include data from the Newdale gage would look like this:

Date

River height, in feet

11/6/1977

17.41

8/13/1940

~17

9/8/2004

15.5

6/16/1949

12.1

9/17/2004

11.62

5/30/2018

10.85

8/18/2021

10.55

8/17/1994

10.49


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