Mapping the mountains

Published 10:35 pm Tuesday, September 17, 2019

Polk gets U.S. Geological Survey to map landslides

COLUMBUS—The May 2018 landslides caused from a sudden heavy rainstorm that caused three fatalities and three homes destroyed included 65 landslides and counting. 

The Polk County Board of Commissioners met last week and heard from Rick Wooten with the North Carolina Geological Survey. 

Sign up for our daily email newsletter

Get the latest news sent to your inbox

Wooten said the May 2018 landslides included 12 major debris flows and 50+ other debris slides and debris flows. 

The county has asked the NC Geological Survey to create maps for the county. Wooten said his office is reviewing landslides in Polk County and is finding where landslides have happened in the past as it is possible they will happen again. 

Wooten explained what causes landslides, saying there is enough water where the material liquefies and moves down the mountain very rapidly, which is what happened in the U.S. 176 case last May. Wooten said the debris was likely moving at a speed of 20-30 mph. 

“That’s the reason they are very destructive and without warning,” Wooten said. 

Wooten said Howard Gap Road, which has been closed since January of this year with the road crumbling, is called a debris slide. He said only about 5 percent of the slide is on the North Carolina Department of Transportation right of way, with 95 percent being on private property. 

“We anticipate that being a long-term effort,” Wooten said. 

He said another section of Howard Gap has dropped down 30 feet and that the Howard Gap slide is roughly 800 feet long by 750 feet wide and covers 10.5 acres. 

The last major landslides in Polk County occurred during Hurricanes Frances and Ivan in 2004. 

The July 15-16, 1916 Hurricane, that caused major flooding in Polk County, included 50 documented fatalities throughout western North Carolina, 18 landslide fatalities and record rainfall of 22 inches in 24 hours. 

Wooten said the last time the state was an aware of a major event in western North Carolina was the 1916 floods. 

“We have not seen anything like that since,” he said. “Let’s hope we don’t.” 

Since 1876 there have been 7 events that have triggered hundreds of landslides, with that number including 2018 and 1916 in the state. 

“The average frequency is once every 170 years,” Wooten said. “The average frequency in North Carolina is about every 16 years. So it’s reasonable to assume they are going to continue in some fashion. Looking down the road it may be a long, long time before this happens again, or it could be this hurricane season.” 

Wooten said it typically happens when there are two hurricanes back to back. And it more depends on how hard it rains for how long than the total rainfall. 

Wooten said field work is underway in Polk County and the geological survey has identified close to 100 landslides in Polk County. The maps are scheduled to be complete sometime in 2020. The maps will show where landslides have happened in the past and where landslides are likely to happen. 

Wooten said the geological survey is working with the University of North Carolina-Asheville and plans to make the maps easy for the public to understand. 

“Our intent is to make that information available so people can make smart decisions about where they build and how they build,” Wooten told commissioners. 

Once complete, the maps will be available to the public, as well as county departments, such as the planning department. 

Wooten agreed to come back quarterly to update commissioners on the process.