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Assessing Landslide Risk with Lidar

photo Assessing Landslide Risk with Lidar
Assessing Landslide Risk with Lidar

In the mountains of North Carolina, assessing landslide risk is very important. Triggered by heavy rains, mountainside soils can become saturated and “unstuck.” As a result, what starts as a small landslide can quickly escalate into a huge debris flow that uproots trees and dislodges boulders, scouring everything in its path as it quickly flows downhill at speeds up to 30 mph. The cost – in both infrastructure and human lives – can be devastating.

From NC State by Tracey Peake.

A quick note on the terminology being used here. Landslides and debris flows are not the same. They are both considered “mass-wasting events” in that they move soil, debris, and rock downhill, but they differ in both water content and movement mechanism. Landslides move like a sled down a snowy slope, while debris flows, which contain more water, flow like a turbulent mountain stream – but with a lot more force.

Given the unpredictability of these mass-wasting events, figuring out where they may be more likely to occur seems a worthwhile project. Enter geologists Karl Wegmann, former NC State Ph.D. student Corey Scheip, and LiDAR.

LiDAR, which stands for light detection and ranging, is an instrument that allows geologists to make accurate 3D images of the earth’s surface through pulses of light.

Scheip and Wegmann were studying a landslide event south of Asheville in the Blue Ridge Mountains in 2018. A storm that dumped up to six inches of rain over three hours created 240 separate landslide-debris flows in the area.

“We were fortunate because North Carolina is a leader in having the entire state surveyed with very high-resolution LiDAR topography data,” Wegmann says. “And we had LiDAR data from both before and after the event, so we were able to calculate what got displaced and how.”

Traditionally, when geologists estimate whether an area is susceptible to landslides, they study the volume of debris flow after an event and try to figure out where it started.

But LiDAR data allowed Scheip and Wegmann to look at how water flows downward from the areas above the debris flow. They then calculated how much water a certain area might receive from a storm and how likely landslides might then be in that area.

For the complete article on assessing landslide risk CLICK HERE.

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