Appalachian Debris Flows: The Need to Increase Awareness and Preparedness - Stephen Keighton, WFO Blacksburg, NWS

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Appalachian Debris Flows:

The Need to Increase

Awareness and Preparedness

Steve Keighton

Science and Operations Officer

NOAA/NWS Blacksburg, VA

Presented at the 2010 ER Flash Flood Workshop

June 2-4, 2010

Acknowledgements

• Larry Lee and WFO GSP (sharing presentations and local policy)

• Rick Wooten, NCGS (slides from several presentations)

• Barbara Watson (Camille anniversary slides)

• Peter Corrigan, WFO RNK (for review of this presentation)

Background/Motivation

• Recent events in wrn NC, and 40 th anniversary of

Camille in wrn VA serve as reminders to the threat

• Rapid increase in population/construction in prone areas

– next major disaster just a matter of time

• Recent USGS (Wieczorek) and NCGS (Wooten) research, including digitized mapping

• WFO GSP collaboration with NCGS, event reviews, and specific policy (Lee and others)

• Can we do more to be prepared?

Terminology

Landslide: general term encompassing many varieties of earth/slope movements: “the movement of a mass of rock, debris, or earth down a slope”

Debris flow: (also known as mudslides) relatively fastmoving landslide, usually comprised of mix of water and fine sediments as well as larger rocks and other debris

(typically the most damaging kind of landslide)

Rock slide: several to numerous rocks or boulders breaking loose from steep banks, often at cuts in natural slopes, typically caused more by freezing-thawing then heavy rainfall

Others terms include: debris slides, earth slides, rock falls, debris fans, slope movements, and others.

Source: http://landslides.usgs.gov

Susceptibility

Source: USGS

Historical debris flows in Appalachians

Source: USGS Fact Sheet 2008-3070 (Wieczorek and Morgan)

Recurrence Intervals

Historical Landslide Events in Western NC

Rick Wooten, NCGS

• ~ 3 years, a storm of high-intensity rainfall occurs over the mountains of the eastern US, posing a high debris flow hazard (Wieczorek et al

. 2004)

• ~ 9 years, a landslide event occurs in western NC (Gillion et al

. 2007)

• Major debris flow events happen in western NC every 20 – 30 years (Clark 1987)

• ~ 15 years for Virginia (Wieczorek et al. 2009)

• For local areas the interval is much longer (ex: Madison Co VA ~3,000 yrs)

Camille

August 19-20, 1969

Camille

August 19-20, 1969

Up to 27” of rain, most fell in 8-hrs (overnight)

Thousands of debris flows

Severe flash flooding and river flooding

153 dead or missing

(>100 injured)

313 homes destroyed

133 bridges wiped out

25 mi primary roads,

175 mi secondary roads washed away

Macon Co NC

(Peeks Creek)

Sept 17-18, 2004

Remnants of Frances and Ivan

X

Macon Co NC

(Peeks Creek)

Sept 17-18, 2004

Photo: Brian Campbell, NWS

Significant debris flow during

Ivan rainfall raced down Peeks

Creek

4 deaths, several injuries

15-20 homes destroyed or damaged

Photo courtesy of David Phillips

Macon Co NC

(Peeks Creek)

Sept 17-18, 2004

Photo: Jonathan Lamb, NWS

Landslides from Frances and Ivan

A Debris Flow Problem…

• Debris flows and flash floods are

NOT the same thing (although NWS uses debris flows to verify flash flood warnings)

• We have no way of knowing what slopes are in immediate danger of failing, or if one has failed

• A specific debris flow warning would be nearly impossible to issue

• The best we can do right now is to mention the threat in a statement or warning

• However, this could change

Top photo Brian Campbell (NWS), bottom photo Jonathan Lamb (NWS)

Landslide Threat

Increased Public Awareness

• NCGS Asheville Regional

Office mapping locations of known landslides and potential threat areas

– Slope movements/deposits

– Stability Index Map

– Downslope hazards

• All 19 Mountain and Foothill counties will be mapped

– Macon, Watauga, Buncombe complete

– Henderson (2010?)

Both images NCGS

Landslide Threat

Increased Public Awareness

GIS mapping by NCGS (Gillon et al 2007)

Slope Movements / Deposits

–where landslides occurred

Slow Moving Landslides

–where landslides are occurring

Stability INdex Map (SINMAP) Results -where debris flows-slides might start

Downslope Hazards

–where debris flows/slides might go

Bedrock Geology

–mapped problematic rock units

Landslide Threat

Increased Public Awareness

• Maps and data intended as planning tools

– Public education

– Local government land use planning and permitting

– Emergency management

Maggie Valley, NC. Photo by Rick Wooten, NCGS

Landslide Threat

Increased Public Awareness

• Understanding high threat locations

Slope properties Slope modification

Development of rainfall intensity

–duration curves

(USGS)

Source: Wieczorek et al, 2009

General rules of thumb

(NCGS and USGS)

• High antecedent moisture conditions followed by high rainfall rates

• 5” of rain in <24 hours: reasonable threshold for localized slope movement events

• 10” of rain in <24 hours: widespread slope movements

• 3.5 - 4” per hour rainfall rates dramatically increase threat

Still could use more rain gages in prone areas

WFO GSP local policy

• Specific section of SDM on landslides

• Background info including threshold guidelines

• Includes some example Call-to-Actions to be included in flash flood warnings:

THIS FLASH FLOOD WILL INCREASE THE RISK OF LANDSLIDES AND ROCKSLIDES… ESPECIALLY

IN AREAS WHERE SLIDES HAVE OCCURRED IN THE PAST. BE ESPECIALLY ALERT IF YOU ARE

NEAR A MOUNTAINSIDE STREAM… A STREAM AT THE BASE OF A MOUNTAIN… OR A STREAM IN

A MOUNTAIN COVE. WATCH FOR LOOSE OR MOVING SOIL AND ROCKS OR AN ABRUPT

INCREASE IN STREAMFLOW… AND LEAVE THE AREA QUICKLY IF OBSERVED. IF YOU ARE

DRIVING ON MOUNTAIN ROADS… WATCH AND LISTEN CAREFULLY FOR THE DANGERS OF

FALLING ROCKS… MUD… TREES… AND DEBRIS.

RESIDENTS AND MOTORISTS IN AND BELOW RECENTLY BURNED OR CUT OVER AREAS SHOULD

BE ALERT TO HEAVY MUD AND DEBRIS FLOWS WHICH MAY BLOCK ROADS AND CULVERTS.

DANGEROUS FLOODING AND PROPERTY LOSS COULD RESULT IN AREAS WHERE RUNOFF IS

RESTRICTED OR BLOCKED.

WFO GSP local policy cont…

• …and example Call-to-Actions for flood watches (this one for more than 10” rainfall):

RAINFALL OF MORE THAN 10 INCHES FREQUENTLY TRIGGERS WIDESPREAD AND DAMAGING

LANDSLIDES AND ROCKSLIDES. IF YOU LIVE ON A MOUNTAINSIDE OR IN A COVE AT THE BASE

OF A MOUNTAIN… ESPECIALLY NEAR A STREAM… CONSIDER MOVING TO ANOTHER LOCATION

FOR THE DURATION OF THIS WATCH. AVOID TRAVEL ALONG MOUNTAIN ROADS DURING THE

BRUNT OF THE STORM.

Landslide Advisory Process

Example of increased coordination

1. NCGS evaluates antecedent moisture and NWS QPF

2. Coordination among agencies through NCEM conference call

3. NCGS issues Landslide

Advisory through DENR and

NC EOC

4. NWS include calls-to-action in Flash Flood

Watch/Warning products

T.S. Ivan 1620 UTC 16 September 2004

Terra MODIS image from SSEC, Univ. of Wisconsin

Summary

Can we better protect lives/property from

Appalachian debris flows?

• Increase our own awareness

• Increase public awareness (educational and safety campaigns

– USGS “fact sheets”)

• Increase coordination with

USGS and state geological agencies (additional GIS mapping)

• WFO GSP policy great starting point to consider

References

• landslides.usgs.gov

www.geology.enr.state.nc.us/Landslide_Info/Landslides_main.htm

Clark, G.M., 1987: Debris slide and debris flow historical events in the Appalachians south of the glacial border.

Reviews in Engineering Geology, Volume VII, Debris Flows/Avalanches: Processes, Recognition, and Mitigation. J.

E. Costa and G. F. Wieczorek, Eds., The Geological Society of America, Boulder, CO, 125-138.

Gillon, K., R. Wooten, R. Latham, A. Witt, T. Douglas, S. Fuemmeler, J. Bauer, J. Nickerson, 2007: Current results of landslide hazard mapping in western North Carolina.

Presentation at Geohazards Technical Forum, Marshall Univ.

Wieczorek, G.F., Eaton, L.S., Morgan, B.A., Wooten, R.M., and Morrissey, M., 2009: An examination of selected historical rainfall-induced debris-flow events within the central and southern Appalachian Mountains of the Eastern

United States: U.S. Geological Survey Open-File Report 2009

–1155, 25 p.

Wieczorek, G.F., Mossa, G.S., and Morgan, B.A., 2004: Regional debris-flow distribution and preliminary risk assessment from severe storm events in the Appalachian Blue Ridge province, USA: Landslides, v. 1, p. 53-59, available at: www.springerlink.com/content/atmj2qx90yh24q0q/fulltext.html

.

Wieczoreck, G.F., Morgan, B.A., and Campbell, R.H., 2000: Debris-flow hazards in the Blue Ridge of central Virginia:

Environmental & Engineering Geoscience, v. 6, no. 1, p. 3-23.

Wooten, R.M., Gillon, K.A., Witt, A.C., Latham, R.S., Douglas, T.J., Bauer, J.B., Fuemmeler, S.J., and Lee, L.G.,

2008, Geologic, geomorphic, and meteorological aspects of debris flows triggered by Hurricanes Frances and Ivan during September 2004 in the Southern Appalachians of Macon County, North Carolina: Landslides, v. 5, no. 1, p.

31

–44. Also available online at www.springerlink.com/ index/2705hw84480m5420.pdf.

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