Wednesday, January 23, 2008

Landslide Hazards in Watauga County

Last night the North Carolina Geological Survey presented its maps and data for landslide hazards in Watauga County to the county Planning Board. The collective intake of breath at the highly detailed information might constitute a pregnant pause.

Watauga County is the second North Carolina county to be surveyed and mapped for potential landslide hazards. The first was Macon County, where some five people were killed in September 2004 along Peeks Creek when a massive chunk of Fishhawk Mountain let go and slid over two miles down the valley. That slide (“debris flow,” is the language the NCGS prefers) was directly caused by the passage of Hurricane Ivan overhead.

It was that same Ivan that caused several slides in Watauga County on the same date, particularly the house-destroying movement in the White Laurel subdivision.

These fatalities and property destruction in Macon and Watauga counties prompted the state legislature to fund the mapping of landslide hazards, starting with the two counties where the greatest losses occurred in 2004. Macon County received its hazardous slopes map in 2007.

So far, what has Macon County government done with those maps? Word is that they’ve essentially hidden them from the public. The Macon County Commission has evidently expressed fear that if they release the information of potential landslide hazards to the public, they might be sued ... because, you know, information just gets people upset (the truth sets the fees, so to speak). Go to the official Macon County website and look for any evidence that its slopes have been mapped and evaluated according to the best scientific evidence for life- and home-destroying potential. Go on. I dare you. You won’t find a word.

Question is ... what will Watauga County do with its information, some of which was summarized by the NCGS representative last night:

● There have been at least 2,253 landslides in Watauga County from 1940 to the present, verifiable from aerial photography and/or on-site inspection

● There were 14 landslide fatalities in 1940, primarily in the Stony Fork section of the county

● At least 32 structures (homes, barns) were damaged or destroyed in 1940

● 136 new structures (principally new homes) have been built on the landslide tracks of the 1940 events

● 8% of the county is covered by slope movement deposits (“debris fans”)

● 20% of the county is “high hazard” based on a Stability Index Map, which can be specific down to individual parcels of land

● 41% of the county lies within “potential landslide pathways”

In just that bare summary, there’s much to raise the small hairs on your nape, particularly the 136 new homes built in or on the landslide tracks of 1940 debris flows ... when the science strongly suggests that a slope that failed once in the past will fail again. That and the 20% of the county that is “high hazard” for landslides.

The 1940 slides – thousands of them – happened because of a hurricane, just as the 2004 slides did. But those 64 years between 1940 and 2004 are deceptive. The NCGS charts the incidence of devastating slope failures as predictably happening somewhere in the NC mountains every 22-29 years ... in other words, about once a generation ... and catastrophic slope failures do not require a hurricane (although they do require, evidently, massive rainfall).

The NC legislature is still considering a bill to require disclosure of hazardous slope conditions to potential land buyers and some minimum development standards. Watauga County has now been given highly specific information about the potential catastrophes lurking in its uneven ground.

What will Watauga County government do with that information?

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