ABSTRACT
Witt, Anne Carter. Using a GIS (Geographic Information System) to model slope instability and debris flow hazards in the French Broad River watershed, North Carolina. (Under the direction of Dr. Michael M. Kimberley.) Catastrophic, storm-generated mass wasting is a destructive erosional process in the portion of the southern Appalachians that extend s through western North Carolina. Steep slopes, a thin soil mantle, and extreme precipitation ev ents all increase the risk of slope instability, slope movement and failure. Since the late 1800’s, several intense storms and hurricanes have tracked through the French Broad watershed initiating thousands of debris flows and causing severe flooding. Studying the history of debris flows has identified triggering mechanisms that are particular to North Carolina and the recurrence interval of these events. This study was initiated to investigate and predict the spatial distribution of regional slope instability within the French Broad watershed by comparing the results of two GIS-based modeling applications: SINMAP (Stability Index Mapping) and ®
SHALSTAB (Shallow Landsliding Stability Model). As extensions to ArcView 3.x,
using the program’s default parameters were compared with those for four recharge events (50, 125, 250, and 375 mm/d). In the latter, parameters latter, parameters for soil density, cohesion, internal soil friction angle, and transmissivity were adjusted to better match existing watershed conditions. As with the SINMAP model, SHALSTAB was used to model instability using both a 10-meter and 30-meter DEM. Limitations in the SHALSTAB program only allow smaller (county-size) DEMs to be processed. Because of these limitations Haywood County was chosen for several model runs in SHALSTAB for comparison to the SINMAP results. Parameters for soil density, soil depth, cohesion, and soil friction angle were adjusted and results were compared to 23 mapped debris flow locations. The modeled results for the default SINMAP and SHALSTAB parameter values underestimate the extent of instability in the study area. By adjusting soil parameters, SINMAP calculated 88% -to- 94% of the inventoried landslides would fall into the “lower threshold”, “upper threshold”, and “defended” stability classes. Generally,
groundwater flow in the watershed and failure tends to occur along these planes of weakness. Neither model takes into account either antecedent moisture or the effect that geologic structure can have on concentrating groundwater flow.
USING A GIS (GEOGRAPHIC INFORMATION SYSTEM) TO MODEL SLOPE INSTABILITY AND DEBRIS FLOW HAZARDS IN THE FRENCH BROAD RIVER WATERSHED, NORTH CAROLINA
by ANNE CARTER WITT
A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Master of Science
MARINE, EARTH AND ATMOSPHERIC SCIENCES
Raleigh 2005
BIOGRAPHY
Anne Carter Witt was born in Lynchburg, VA on August 10, 1977. She grew up in Forest, VA and graduated from Brookville High School in 1995. In 1999, she graduated from Mary Washington College in Fredericksburg, VA with an undergraduate degree in Geology. Before being accepted into the Masters degree program at North Carolina State University, she worked for three years as a GIS analyst with Dewberry and Davis, LLC in Fairfax, VA.
ACKNOWLEDGEMENTS
I would like to express sincere thanks and appreciation to the following individuals: Rick Wooten with the North Carolina Geological Survey who provided me with landslide data and an open discussion discussion on the complexities of SINMAP. SINMAP. His guidance, patience and knowledge of slope movements and the geomorphology of western North Carolina are greatly appreciated. Thanks are also extended to Jody Kuhne from the North Carolina Department of Transportation whose tattered, long-forgotten landslide map was really the foundation for a digital landslide inventory in North Carolina. In addition, I would like to thank Drs. Helena Mitasova and Lonnie Liethold for their advice and counsel is serving as members on my committee. I would also like to thank Dr. Mary Schweitzer for being a last minute substitution during my thesis defense on one of the busiest days of her life. Many thanks are also extended to Dr. Jeff Reid for his time, guidance, critical comments, and dogg ed determination to see me finish. Thanks
best friend, Jamie Gibson. Finally, I would like to thank my parents and brother who provided the foundation for me to be the best that I could be and instilled a lifelong love of learning. Thank you for your love and support.
TABLE OF CONTENTS
Page LIST OF TABLES ........................................................ .......................................................................................................... .................................................. vii LIST OF FIGURES .................................................. ..................................................................................................... ..................................................... .. viii CHAPTER 1: INTRODUCTION..................................................... INTRODUCTION.................................................................................... ............................... 1 ESEARCH AIM AND OBJECTIVES .................................................. ...................... 3 1.1 R ESEARCH 1.2 SIGNIFICANCE AND SCIENTIFIC APPLICATIONS ................................................ .... 4 1.3 LANDSLIDE CLASSIFICATION ................................................ ............................... 6 1.3.1 Classification of Sharpe (1938) ................................................... ................... 7 1.3.2 Classification of Varnes (1978) and of Cruden and Varnes (1996) ............... 8 1.4 COMMON CAUSES OF SLOPE MOVEMENTS ...................................................... .......................................................... .... 9 1.4.1 Precipitation ................................................................................................. 10 1.4.2 Human Interference .................................................. .................................... 10 1.4.3 Tectonic Activity............................................................................................ 11 1.4.4 Geologic Material and Structures ................................................................ 11 1.5 DEBRIS FLOWS ................................................... ................................................ 12 IDGE AND WESTERN NORTH CAROLINA ..... 1.6 DEBRIS FLOWS WITHIN THE BLUE R IDGE ..... 14 1.7 SINMAP AND SHALSTAB ................................................. ............................. 16 ESEARCH .................................................. ............................. 18 1.8 LIMITATIONS OF R ESEARCH
CHAPTER 2: PROJECT SETTING ........................................................ ............................................................................ .................... 21
2.1 2.2 2.3
I NTRODUCTION .................................................. ................................................ 21 GEOLOGY.................................................. ....................................................... ......................................................... .. 21 SOILS 23
4.2.2 Debris Flow Flow Inventory ........................................................ .......................... 68 4.2.3 Soil Data ............................................. ................................................... ....... 68 4.2.4 Soil Density ................................................. .................................................. 69 4.3 SINMAP PARAMETERS ........................................................ ..................................................................................... ............................. 69 4.3.1 T/R (Ratio of Transmissivity to Effective Recharge)..................................... 71 4.3.2 Dimensionless Cohesion ..................................................... ............................................................................... .......................... 72 4.3.3 Internal Soil Friction Angle.......................................................................... 72 4.4 SHALSTAB PARAMETERS .................................................. ............................. 73 CHAPTER 5: RESULTS AND DISCUSSION ............................................................ 80
5.1 I NTRODUCTION .................................................. ................................................ 80 5.2 DEBRIS FLOW I NVENTORY .................................................... ................................................................................. ............................. 80 ESULTS ..................................................... 5.3 SINMAP R ESULTS ............................................................................................ ....................................... 81 5.3.1 Results – 30-meter DEM............................................................................... 83 5.3.2 Results – 10-meter DEM............................................................................... 84 5.3.3 SINMAP Interpretation................................................................................. 85 ESULTS................................................ ....................................... 87 5.4 SHALSTAB R ESULTS 5.4.1 Results – 30-meter DEM............................................................................... 89 5.4.2 Results – 10-meter DEM............................................................................... 90 5.4.3 SHALSTAB Interpretation ............................................................................ 92 5.5 SINMAP VS. SHALSTAB................................ ................................................ 93 5.6 GEOLOGY AND SOILS .................................................. ....................................... 94 5.7 JOINTING, FRACTURING AND FOLIATION ................................................ ........... 97 CHAPTER 6: CONCLUSIONS ....................................................... .................................................................................. ........................... 116 REFERENCES.......................................................................................... REFERENCES................................... ........................................................................... .................... 122 APPENDICES
133
LIST OF TABLES
Page Table 2.1: Table of the average, median, minimum, and maximum precipitation totals (mm/month) from 1895 to 2001 for the mountains of North Carolina (NCDC Climate Data Online, 2003)................................................................31 Table 3.1: Prehistoric debris flow studies in the southern Blue Ridge and the age-dating techniques utilized. ..................................................... ..........................................................................................53 .....................................53 Table 3.2: Major storms within the French Broad Watershed and their minimum, average, and maximum precipitation amounts. ...............................................6 3 Table 4.1: Table of the hydraulic conductivity (K, m/hr), transmissivity (T, m²/hr), and T/R (m) values used for each eac h precipitation threshold (50 mm/d, 125 mm/d, 250 mm/d, and 375 mm/d) in the SINMAP analysis. The numbers in blue are the lower bound values while the numbers in red are the upper bound values. .................................................. .................................................78 Table 5.1: The parameters used in all of the SINMAP model runs...................................99 Table 5.2: SINMAP stability stability index definitions (Pack et al., 1998b). ..............................100 Table 5.3: Mapped instability classes used in the SHALSTAB SHALSTAB model analysis. ............104 Table 5.4: Table comparing q/T and log (q/T) values and the precipitation rate required to initiate instability for soils with a transmissivity of 65 m²d and 17 m²/d (after (after Dietrich and Asua, 1998). ................................................... ....105 Table 5.5: Parameters used in the SHALSTAB model runs............................................105 Table 6.1: The advantages and disadvantages of SINMAP SINMAP and SHALSTAB. ...............121
LIST OF FIGURES
Page Figure 1.1: The morphology of a typical debris flow found in the Southern Appalachians (courtesy of the North North Carolina Geological Survey, 2003). ............................19 Figure 1.2: Threshold precipitation values necessary for producing debris flows in the southern Appalachian Mountains. Storms likely to start debris flows occur above the 125 mm/d threshold. Storms with precipitation values higher than 250 mm/d are deemed “rare” but do occur in North Carolina (after Eschner and Patric, 1982). ..................................................... .............................................................................................20 ........................................20 Figure 2.1: Location Map of the French Broad Watershed in western North Carolina. ...27 Figure 2.2: General geologic map for the French Broad Watershed. Individual geologic unit descriptions can be found in Appendix Ap pendix A (adapted from North Carolina Geological Survey, 1985). ................................................ ...............................28 Figure 2.3: General soil map for the French Broad Watershed. Individual soil descriptions can be found in Appendix B (adapted from U.S. Department of Agriculture, 1998). ...................................................... .............................................................................................................. .........................................................29 .29 Figure 2.4: The U.S. Department of Agriculture guide for the textural classification of soils. This guide is only for soils with a particle size of less than 2 mm in diameter. A rock fragment modifier (gravelly, cobbly, stony, bouldery) prefaces the textural name if particles larger than 2mm compose more than 15% of the soil (Buol et al., 2003)...................................................................30 Figure 2.5: Graph based on the data from Table 2.1 (NCDC Climate Data Online, 2003). ..............................................................................................................31 Figure 2.6: Average annual precipitation in inches within the French Broad Watershed. (Adapted from data provided by North Carolina Center for Geographic Information and Analysis m (http://204.211.135.111)). ...................32
moving northwestward over the watershed. This is the greatest recorded streamflow for the gauge at Asheville. ............................................ ................58 Figure 3.7: Total storm precipitation for August 14-15, 1940 adapted from U. S. Geological Survey, 1949). ................................................ ...............................59 Figure 3.8: Total storm precipitation for August 28-31, 1940 (adapted from U. S. Geological Survey, 1949). ................................................ ...............................59 Figure 3.9: Total storm precipitation for November 2-5, 1977 (adapted from Neary and Swift, 1987)......................................................................................................60 Figure 3.10: Total storm precipitation (inches) for the remnants of Hurricane Frances (National Weather Service, 2004b)..................................................................61 Figure 3.11: Total storm precipitation (inches) for the remnants of Hurricane Ivan (National Weather Service, 2004c)..................................................................61 Figure 3.12: A debris flow that blocked the westbound lanes of Interstate-40 near Old Fort Mountain in McDowell County (North Carolina Geological Survey, 2004a). ..................................................... ............................................................................................................. ........................................................62 62 Figure 3.13: The initiation zone of the debris flow that occurred on Fishhawk Mountain and devastated the Peeks Creek area of Macon County on September 17, 2004 (Wilett, 2004)...................................................................................................62 Figure 4.1: The infinite slope equation as defined by Hammond et al., (1992) and Pack et al., (1998b) where C r r is root cohesion, C s is soil cohesion, θ is θ is slope angle, ρ angle, ρ s is soil density, ρ density, ρ w is the density of water, g is acceleration due to gravity, D gravity, D is the vertical soil depth, D depth, Dw is the vertical height of the water table, and Φ is the internal soil friction angle. In the SINMAP model, the ratio of the v ertical soil depth to the vertical soil height is simplified so that depth is measured perpendicular to the slope (h (h). (Diagram after Hammond et al., 1992 and Otteman, 2001) ................................................. ...............................................76 Figure 4.2: Default parameters used in the SINMAP model model analysis. The values for the
In the legend, the first number is the degree if soil friction angle and the second number is the amount of cohesion (N/m³). ........................................107 Figure 5.9: Cumulative percent of debris flows for each log (q/T (q/T ) instability category for a variety of soil parameters for a 30-meter DEM (after Dietrich et al., 2001). ...................................................... .............................................................................................................1 .......................................................107 07 Figure 5.10: Cumulative percent of the area if Haywood County for each log (q/T (q/T ) instability category for a variety of soil parameters for the 10-meter DEM (after Dietrich et al., 2001).............................................................................108 Figure 5.11: Cumulative percent of debris flows for each log (q/T (q/T ) instability category for a variety of soil parameters for a 10-meter DEM (after Dietrich et al., 2001). ...................................................... .............................................................................................................1 .......................................................108 08 Figure 5.12: Mapped log (q/T (q/T ) results for a 10-meter DEM of Haywood County. The parameters used for this model run are essentially that same as those used in the SINMAP lower bounds: 26° soil friction friction angle, and zero cohesion. .......109 Figure 5.13: SHALSTAB results for a soil friction angle of 35° and cohesion of 2000 N/m³. .................................................... ........................................................................................................... ..........................................................110 ...110 Figure 5.14: Comparison of the output of SINMAP and SHALSTAB for 125 mm of recharge, 35° soil friction angle, 1922 kg/m³ soil density, and zero soil cohesion for a location in Haywood County. The red areas are calculated as unstable by both programs whereas the grey a reas are calculated to be stable. Visually the SHALSTAB results seem to cluster better while the SINMAP results are more scattered. Overall, the results are very similar. similar. ..................111 Figure 5.15: Results for SINMAP and SHALSTAB. Red areas are the areas calculated by both models as being unstable. The purple areas were only calculated by SHALSTAB and the green areas were only calculated by SINMAP............112 Figure 5.16: The mean stability index for each geologic unit in the French Broad Watershed. The most unstable unit, Zchs, is located in the northwestern portion of Haywood County. The most stable u nits, bz and Ctzp, are located in
CHAPTER 1: INTRODUCTION
Catastrophic, storm-generated mass wasting is a destructive erosional process in the portion of the Southern Appalachians that extends through western North Carolina. This study was initiated to investigate and predict the spatial d istribution of regional slope instability within the French Broad watershed by comparing the results of two GIS based modeling applications: SINMAP (Stability Index Mapping) (Pack et a l., 1998b) and SHALSTAB (Shallow Landsliding Stability Model); (Dietrich and Montgomery, 1998). Mass wasting is a general term used to describe the “dislodgement and downslope transport of soil and rock material under the direct application of gravitational body stresses” (Jackson, 1997). Mass wasting can range from very slow creep to a rock avalanche. The term is often synonymous with the term “mass movement” (Crozier, 1986). Both Crozier (1986) and Varnes (1978) advocate the use of the term “slope movements” for mass movement restricted to slopes, as “slope movement” a ppears to be
early 1900’s, several intense storms and hurricanes have tracked through western North Carolina, initiating hundreds of debris flows and causing severe flooding. In the Appalachian Mountain chain, it has been estimated that as many as 1,700 debris flows occurred in the 20th century, killing at least 200 people and destroying thousands of acres of farm and forested land (Scott, 1972). As extensions to ArcView® 3.x GIS software, both SINMAP and SHALSTAB compute and map areas of potential slope instability based upon digital-elevation data and observed landslide locations. These models combine steady-state hydrologic concepts and an infinite-slope-stability analysis with a digital elevation model (DEM) to calculate either a factor of safety (SINMAP) or the critical steady-state rainfall intensity necessary to trigger slope instability (SHALSTAB). As in any landslide investigation using modeling software, model results should be compared with mapped landslide locations whenever possible. In this study, preliminary field investigations were completed in three key locations in Haywood,
1.1
Research Aim and Objectives Few comprehensive research studies comparing slope-stability-modeling software
have been completed within a specific drainage basin in North Carolina. Most of the se studies have tended to focus on identifying landslide hazard areas on the U.S. West Coast or in other countries (Appt et al., 2002; 20 02; Dietrich et al., 2001; Montgomery et al., 2001; Zaitchick et al., 2003). Other studies have focused on identifying relict landforms and debris aprons in the Appalachians formed during periglacial conditions (Gryta and Bartholomew, 1987; Clark, 1987; Kochel, 1987; Jacobson et al., 1989; Liebens and Schaetzel, 1997). This study focuses on identifying debris-flow hazard areas and the factors that affect this instability. The objectives of this research are as follows: 1. To identify areas within the French Broad watershed prone to debris flows. 2. To identify triggering mechanisms particular to the watershed that promote instability and failure. 3. To determine which soil and geologic units are the most prone to instability and those that are the most stable, in general.
1.2
Significance and Scientific Applications The French Broad river basin is located in western North Carolina, in the central
portion of the Appalachian Mountain chain. The French Broad River itself flows through the City of Asheville, a major commercial and manufacturing center, and a popular mountain resort area. According to data collected by the U.S. Census Bureau (2000), approximately 426,000 people live within the French Broad watershed and this population is predicted to increase, particularly in and around the City of Asheville. Debris flows hazards are a major concern in mountainous areas as debris fans are favored areas of development due to their flat building surface and location above the floodplain (Ritter et al., 1995). With continued development deve lopment and tourism in the forested areas of the Blue Ridge, the risk to people and property will increase because of debris flows, especially during periods of high precipitation. The major hazard to human life and property from debris flows is from burial or impact by boulders and other debris. de bris. Usually starting on steep hillsides, debris flows can
mapping, and laboratory testing. After an initial analysis has been completed, policies for the establishment, management, and inspection of preventative measures should be completed (Crozier, 1986). This may also include the the restriction of development in areas considered landslide-prone or the removal or conversion of existing developments. Control measures in prone areas may also be designed and implemented including controlled drainage, planting, slope-geometry modification, and structures such as rock fences or other barriers (Schuster and Kockelman, 1996). 1 996). Continued poor land-management practices and deforestation add to the risk of soil mass movement by increasing runoff, erosion, and flooding. Human activity also disturbs large volumes of geologic materials with the construction of housing developments, commercial buildings, mines and quarries, dams and reservoirs, and particularly the emplacement of transportation systems along steep slopes (Schuster, 1996). Roadcuts and other altered or excavated areas along slopes are particularly susceptible to debris flows. Repeated landslides and rock falls have plagued the Interstate
download from the World Wide Web at a t no cost, making them economical econo mical for both government and businesses. Debris flows are not just an agent of destruction, d estruction, but also play a critical role in the processes of erosion and sediment transport in the Blue Ridge Mountains. They provide a major means of removing weathered material from steep a reas that normally experience little concentrated surface drainage (Scott, 1972). By studying the causes, characteristics, and effects of debris flows in the Southern Appalachians, we can better understand unde rstand their erosional importance, as well as their destructive influences. Improved knowledge of the Blue Ridge may also be extended to comparable sub-tropical mountainous areas in other parts of the world.
1.3
Landslide Classification There have been several attempts to create a suitable landslide classification
system that is useful for both scientific and engineering purposes. Early attempts occurred in Europe during the late 1800’s and early 1900’s (Sharpe, 1938). These
in Denver, CO. But this classification system, like many before it, was influenced by the classification system proposed by C.F.S. Sharpe (1938).
1.3.1
Classification of Sharpe (1938) In the late 1930’s, C. F. S. Sharpe became one of the first American scientists to
create a widely accepted landslide classification system. Sharpe created h is classification based primarily on the kind and rate of movement (making a distinction between slides and flows) and the forms forms of the resulting deposits. deposits. Other important factors included the moisture content in the moving mass and the type of material involved. Based on these factors, mass movement was separated into four groups, i.e. slow flowage, rapid flowage, sliding, and subsidence. Sharpe (1938) defined the mass-wasting process that typically occurs in the Southern Appalachians as debris-avalanche, a type of rapid flowage. A debris avalanche is a rapidly-moving, sliding flow with a long, narrow track that occurs on steep terrain in humid mountainous areas with significant vegetative cover. This type of slope movement
1.3.2
Classification of Varnes (1978) and of Cruden and Varnes (1996) The landslide classification system of D. J. Varnes (1978) was well-received and
has been repeatedly updated, the latest update having been published in Cruden and Varnes (1996). The goal of the current version of this classification was to provide definitions and vocabulary that allow an investigator inve stigator to observe and describe a landslide in the field succinctly and unambiguously. The Cruden and Varnes (1996) classification scheme emphasizes the type of material and the type of movement in a slide. Two terms are needed to describe any landslide, i.e. one that describes the material (rock, debris, earth) and one that describes the movement (fall, topple, slide, spread, flow). Other descriptors can then be added in front of the two-term classification as more information about the movement becomes available. These include the water content, c ontent, rate of movement, the current c urrent activity of the slide (reactivated, inactive, etc.), distribution, and overall style (complex, composite, etc.).
Driving forces cause material to move downslope and can increase depending on the mass of the material involved in the movement and the slope angle (Easterbrook, 1999). Frictional resistance opposes deformation or motion and is caused by the friction between grains within the material or by the material at the base of the slope. The resistance of a material to shear along a slip surface due to an applied external force can be referred to as the materials shear strength. Shear strength is determined by analyzing the amount of cohesion, effective normal stress, and internal friction between material particles (Ritter et al., 1995). When the gravitational driving force is greater than the frictional resistance the slope will fail (Easterbrook, 1999). While a single trigger may actually cause a slope to fail, a number of other destabilizing factors are often needed to contribute to a reduction in a material’s shear strength in order to ultimately initiate movement (Crozier, 1986). First, though, the topography must have a sufficient slope. Usually slopes of 35° or greater are prone to instability simply because of the effects of gravity (Sidle et al., 1985). But o ften other
material or along an existing plane of weakness. Thin, loose soils on hillslopes with sparse vegetation are particularly prone to failure during an inten se rainfall. Soils with a high rate of hydraulic h ydraulic conductivity (the amount of water that will move through a porous medium in unit time) have the ability to transmit water more quickly downslope. This decreases soil pore pressure and may help to increase shear strength. Typically, an unconsolidated, coarse grained, well- rounded, and well-sorted soil will have a higher value of hydraulic conductivity (Fetter, 1994). 1.4.2 Human Interference Road construction is a major contributor to slope failure and their mitigation can often incur enormous public cost. Excavation of the toe of a hillslope by emplacing a road, quarry, canal, or other type of cut, removes support and may induce anthropogenic slope moment (Cruden and Varnes, 1996). Road fill and traffic also increases weight on a hillslope, increasing shear stress on materials (Sidle et al., 1985). In developed areas, slope saturation may occur, even during moderate recharge events, because of
1.4.3
Tectonic Activity In tectonically-active areas, volcanic eruptions and earthquakes have often caused
slope instability and failure by causing uplift or tilting (Cruden and Varnes, 1996). Volcanic ash deposited on steep volcanic peaks, combined with the rapid melting of snow or heavy rainfall, can initiate deadly lahars, debris flows, and mudflows. Slope movements involving loose, saturated, low-cohesion soils commonly occur as a result of earthquake-induced liquefaction, a process in which shaking temporarily raises porewater pressure and reduces shear shear strength. Fault zones may also contain fractured, crushed, or low-metamorphic-grade rock that contain inherent wea kness and may be susceptible to failure (Sidle et al., 1985). 1.4.4
Geologic Material and Structures Some particular rock and soil types may be inherently weak and can influence
slope instability. Organic soils and clays naturally have low shear strength and are particularly prone to weathering processes (Cruden and Varnes, 1996). A predominantly
for groundwater during rain events and reducing cohesion between layers or bedding (Sidle et al., 1985). Structures parallel to the ground surface and downslope-dipping beds, particularly those that separate two distinct lithologic units, may also act as a viable failure plane.
1.5
Debris Flows Although several types of slope movements have been described in the high-relief
portions of the French Broad watershed, this study focuses on debris flows, i.e., rapid downslope movement of regolith. It was noted during field field work that a number of the regularly-occurring mass-wasting events were actually simple rock falls or slides along over-steepened roadcuts. Debris flows seem to be a less common mass-wasting event than those mentioned above, but may be devastating when they occur in populated areas. Unfortunately, there is a considerable amount of inconsistency incon sistency in terminology for modern rapid channelized downslope down slope movement of poorly sorted sediment. The terms, debris torrent, debris avalanche, debris flow, debris slide, mudflow, and mud flood are
The term “debris flow” is used herein to describe de scribe swift-moving mass-wasting events that occur predominantly in shallow, silty-to-gravelly soil on steep slopes during periods of exceptionally heavy precipitation (Cruden and Varnes, 1996) (Figure 1.1). “Debris” defines a material that contains 20-80 percent coarse-grained particles larger than 2mm. These materials may include boulders bou lders to clay with varying amounts of water (Ritter et al., 1995). The “flows” begin in depressions depressions or hollows on steep steep slopes and tend to move downslope following preexisting drainage channels. The most common movement interface is between the bedrock-soil contact, but slippage may also occur within deep soils (Clark, 1987). Debris flows from several different sources often converge into one main drainage channel, increasing the flow’s overall volume of water and material (Highland et al., 2004). 2004 ). Debris flows can travel for several kilometers before releasing their suspended load and coming to rest upon reaching an area of low gradient (Ritter et al., 1995). Debris flows may be triggered in a variety of ways. The most common trigger is
laden slurry that gains material as it travels downslope or as a shallow-slope movement that is mobilized into a flow (Ritter et al., 1995).
1.6
Debris Flows within the Blue Ridge and western North Carolina Debris flows have been reported to be the most common form of rapid slope
movement in the Blue Ridge (Mills et al., 1987). Debris flows have occurred throughout the Blue Ridge province and have been specifically documented in Virginia (Woodruff, 1971; Williams and Guy, 1973; Gryta and Bartholomew, 1987; 19 87; Gryta and Bartholomew, 1989; Mazza and Wieczorek, 1997), North Carolina (Holmes, 1917; Gryta and Bartholomew, 1983; Pomeroy, 1991; Wooten et al., 2001), West Virginia (Jacobson et al., 1989) and Tennessee (Clark et al., 1987). Mills et al. (1987) suggest that tha t the abundance of this type of slope movement may be due to the amount of thick, unconsolidated colluvium derived from crystalline rock. This colluvium is highly permeable and susceptible to weathering, both of which contribute to the generation of slope movements.
Precipitation rates that readily induce debris flows in western North Carolina range from 125 mm/day (Neary and Swift, 1987) to the upper end of observed precipitation (560 mm/day). These thresholds may vary due to lithology, vegetation, and topography but generally catastrophic rainfall is required to initiate debris flows in heavily vegetated areas (Kochel, 1990). Under these conditions, c onditions, rapid infiltration and a corresponding increase in soil saturation brings the soil mantle to field capacity. This tends to occur in shallow (< 1 m thick) mountain soils on slopes averaging 25-40 degrees, overlying an impermeable horizon of metamorphic rock or saprolite (Eschner and Patric, 1982). A temporary rise in piezometric pressure within slope sediment causes an increase in shear stress while decreasing shear strength. This, combined with a decrease in soil cohesion, reduces the shear resistance force enough to lessen the stability of the soil and eventually induce failure (Neary and Swift, 1987). Typically, debris flows have a characteristic long narrow shape. In the Southern Appalachians, the width of a debris flow, or the “chute,” may range from only a few
1.7
SINMAP and SHALSTAB There are many approaches to the problem of predicting shallow slope movements,
and almost as many predictive models. Simple models, b ased on identifying and classifying high-hazard areas on the basis of critical slope angle, do not take into account acco unt the effects of topographic form or position and lithology. More complex approaches to prediction should consider a wide range of variables such as drainage area, bedrock geology, soil thickness and cohesion, precipitation, vegetation and land use. Two such models, which take many of these variables into account, are SINMAP and SHALSTAB. SINMAP was designed as an extension to ArcView® GIS, a product of Environmental Systems Research Institute, Inc. SINMAP is applied to shallow transitional landsliding phenomena controlled by shallow groundwater convergence (Pack et al., 2001), as is generally gen erally found in western North Carolina. The SINMAP methodology is based on the infinite-slope equation, an equation that has been found to be adequately accurate in the analysis of debris flows for planning purposes in the U.S.
ranges are reached and yet stability is still retained, the stability index (defined as the factor of safety) is calculated as greater than one (Pack et al., 2001). The default output of a SINMAP session is a series of map grids that define areas of potential terrain instability; shaded green areas are considered stable whereas dark red areas have a high probability of failure, based on parameter inputs (Pack et al., 1998b). Like SINMAP, SHALSTAB is an extension of ArcView® and is theoretically similar to SINMAP. The SHALSTAB model is also based on the infinite-slope equation and uses a DEM for the input of topographic grid information. SHALSTAB assumes steady-state, saturated flow parallel to the slide surface and uses Darcy's law to estimate the spatial distribution of pore pressures (Dietrich and Montgomery, 1998). The authors of SHALSTAB intended the model to be as simple as possible and nearly “parameter free” (Dietrich et al., 2001). In other words, most of the input variables are derived directly from the slope and area grids created from the input DEM and do not require the user to calculate specific parameters based o n known soil properties which,
should be compared with mapped mappe d landslide features whenever possible (Dietrich and Montgomery, 1998).
1.8
Limitations of Research The prime limitation to both SINMAP and SHALSTAB is the availability of
high-quality digital-elevation data i.e. a 10-meter scale or smaller. Surface topography, determined from digital-elevation data, has great bearing on the location and frequency of shallow landsliding predicted by both models. Currently, only 30-meter and 1 0-meter DEMs are available for the western portion of North Carolina. Both SINMAP and SHALSTAB require the input of high-quality digital-elevation data to identify areas of steep slope. As more accurate DEMs and LIDAR data are released for this portion of the state, more accurate slope-instability and landslide-hazard maps can be developed. Limitations to SINMAP and SHALSTAB include the lack of high-quality soil data necessary to parameterize the models, the size of the study area, and the need to generalize soil and climate parameters over such a large area. Better quality results can be
Figure 1.2: Threshold precipitation values necessary for producing debris flows in the southern Appalachian Mountains. Storms likely to start debris flows occur above the 125 mm/d threshold. Storms with precipitation values higher than 250mm/d are deemed “rare” but do occur in North Carolina (after Eschner and Patric, 1982).
CHAPTER 2: PROJECT SETTING 2.1
Introduction The French Broad watershed is approximately 7330 km² and includes the counties
of Buncombe, Haywood, Henderson, Madison, and Transylvania, and portions of Avery, Mitchell, and Yancey counties (Figure 2.1). Major tributaries of the French Broad River include the Nolichucky, Toe, and Pigeon Rivers. The watershed includes large portions of Great Smoky Mountains and Pisgah National Na tional Parks. Two major interstates, Interstate40 and Interstate-26, cross the basin, as does the Blue Ridge Parkway. The French Broad River actually begins in Rosman, North Carolina (35 miles southwest of Asheville, NC) where four tributaries converge. Topography within the French Broad basin ranges greatly, from the relatively gently sloping floodplains along the banks of the French Broad River to steep slopes in the mountains and along roadcuts. The highest point in the watershed, and the entire Appalachian mountain chain, is Mount Mitchell at an elevation of 2073 m.
The Blue Ridge geologic province reaches its greatest east-west extent in the Carolinas, Tennessee and Georgia. The province is bounded on the northwest by the Blue Ridge fault systems (Holston-Iron Mountain, Great Smoky, and Cartersville Faults) and on the southeast by the Brevard fault zone, while the Hayesville and Greenbrier Greenb rier fault zones intersect in the middle of the French Broad basin (Hatcher and Goldberg, 1994). These faults transported a series of large crystalline thrust sheets over the Paleozoic rocks of the Valley and Ridge province, each with different tectonic histories and degrees of metamorphism (Hatcher, 1987). The western Blue Ridge is composed of a rift-facies sequence of clastic sedimentary rocks deposited on basement rock. The eastern Blue Ridge records a series of slope-and-rise sequences associated with rifting and continental collision (Hatcher and Goldberg, 1994). The Brevard Fault zone separates the Blue Ridge province from the Inner Piedmont block to the east. The block is a composite stack of thrust sheets containing a variety of metamorphic rocks, intrusive granitoids, and sparse ultramafic bodies (Horton and
particularly true when fracture surfaces are parallel to the dip surface. It was observed in the study area that even during a light precipitation event, groundwater flow through fracture zones was swift. This concentration of groundwater could quickly cause an increase in pore-water pressure in soils on a slope or create ephemeral channels for debris flows to follow. A similar correlation between joint orientation, direction of groundwater flow, and debris-flow initiation was noted in the Coweeta Basin, an experimental forest and research station just south of the watershed (Grant, 1987). In the SINMAP and SHALSTAB models, groundwater flow is incorporated by using a value for soil transmissivity (m²/s).
2.3
Soils The types of soil in the French Broad watershed reflect the regional geology
because variation in bedrock mineralogy partly controls soil mineralogy (Figure 2.3). Herein soil will be defined as “unconsolidated mineral or organic material on the immediate surface of the earth that has been be en subjected to and shows effect of o f genetic and
Mitchell and at very high elevations. Mesic soils have mean soil temperatures of 8° to 15° C (46° to 59° F) during June, July, and August, whereas frigid soils have mean temperatures less than 8° C (46° F) during the summer months (Buol et al., 2003). Generally, soils with a high susceptibility of failure tend to have a large mica content and develop over micaceous schist, slate, and phyllite (Scott, 1972). Soil cover varies in thickness and development depending upon slope and weathering and can range from less to one meter to several meters in depth (Clark, 1987). Steep slopes create a shallow soil veneer held together by plant roots that may overlie a rock or saprolite layer. More moderate slopes, i.e., those between 30 and 35 degrees, develop thicker soil profiles and are more prone than shallow soils to debris flows. This may seem contradictory, but steep slopes are not able to develop and retain soil cover and can easily be washed away, even during moderate rainfalls. Thus, an increase in soil depth and a decrease dec rease in slope increase the risk of slope instability (Scott, 1972). In the unglaciated portions of the Blue Ridge, chemical weathering plays an
colluvium and alluvium are deposited in valley bottoms and along rivers (Hatcher, 1987; Otteman, 2001).
2.4
Climate Due to the variation of altitude a ltitude (460-to-2073 m) within the French Broad
watershed, temperature and moisture regimes vary greatly from one place to another within this area. In fact, the mountains have ha ve some of the wettest and driest weather in North Carolina (Daniels et al., 1999). The greatest 24-hour rainfall total in the State (565 mm) was measured in the watershed at Altapass in Mitchell County on July 15-16, 1916 when a hurricane passed through the area. In contrast, the station with the driest weather on average is located in downtown Asheville in Buncombe County (State Climate Office of North Carolina, 2003). Mean annual rainfall in the southern Appalachians ranges from 1000 to 2700 mm (1-to-2.7 m) with snowfall only contributing 5 percent of the total precipitation (Neary and Swift, 1987). Rainfall occurs frequently as small, low-intensity rains in all seasons
Orographic influences generate extremely heavy rainfall in localized mountainous areas, even in storms with weak pressure gradients an d gentle air circulation (Scott, 1972). Generally, rainfall increases with elevation at a rate of 5 percent per 100 m (Swift et al., 1988), but altitude is not no t as important as orographic boundaries. The Blue Ridge produces an elongate area of high values of mean precipitation (Jacobson et. al., 1989). As can be seen in Fig. 2.6, there is a marked increase in the amount of annual precipitation in northern Transylvania County and southern Haywood County.
2.5
Vegetation Like rainfall, vegetation within the watershed varies with the the topography. Slope
aspect and shading by adjacent ad jacent higher mountains also influences the distribution of major tree species (Daniels et al., 1999). At lower elevations (below 1400 m) hardwoods, oak, hemlock and pine forests dominate. Hardwoods such as yellow poplar, ash, and black cherry are found in coves and along steep slopes whereas several varieties of pine and oak thrive in open areas (Scott, 1972). Except for the most rugged terrain, the region’s
Figure 2.1: Location Map of the French Broad Watershed in western North Carolina.
Figure 2.2: General geologic map for the French Broad Watershed. Individual geologic unit descriptions can be found in Appendix A (adapted from North Carolina Geological Survey, 1985).
28
Figure 2.3: General soil map for the French Broad Watershed. Individual soil descriptions can be found in Appendix B (adapted from U.S. Department of Agriculture, 1998).
29
Table 2.1: Table of the average, median, minimum, and maximum precipitation totals (mm/month) from 1895 to 2001 for the mountains of North Caroli na (NCDC Climate Data Online, Onl ine, 2003).
North Carolina Climate Division 01 - Southern Mountains Average Total Precipitation (mm/month) 1895-2001 JAN Average Median Minimum Maximum
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC DEC
TOTAL
117. 117.86 86 115. 115.82 82 142. 142.49 49 114.8 114.81 1 110. 110.74 74 121. 121.67 67 136. 136.14 14 133. 133.60 60 99.0 99.06 6 92.2 92.20 0 92.7 92.71 1 116. 116.08 08 1393 1393.1 .18 8 109. 109.98 98 112. 112.52 52 131. 131.83 83 111.7 111.76 6 100. 100.58 58 118. 118.36 36 131. 131.06 06 120. 120.65 65 91.9 91.95 5 82.5 82.55 5 90.9 90.93 3 110. 110.74 74 1312 1312.9 .93 3 8.38 8.38 13. 13.21 21 20.8 20.83 3 23.1 23.11 1 29.2 29.21 1 37.3 37.34 4 49.0 49.02 2 19.8 19.81 1 8.89 8.89 1.27 1.27 24. 24.13 13 9.14 9.14 244 244.3 .35 5 279.15 279.15 254.0 254.00 0 282.96 282.96 208.79 208.79 271.02 271.02 245.87 245.87 315.21 315.21 398.27 398.27 249.43 249.43 257.56 257.56 303.02 303.02 272.5 272.54 4 3337.8 3337.81 1
Monthly Mo nthly Precipitation Precipitation for the NC NC Southern M ountains 1895-2001 400 350 ) 300 m m250 ( s r e 200 t e m150 i l l i M100
50
Average Median Minimum Maximum
Figure 2.6: Average annual precipitation in i n inches within the French Broad Watershed. (Adapted from data provided by North Carolina Center for Geographic Information and Analysis map server (http://204.211.135.111 ( http://204.211.135.111)). )).
32
CHAPTER 3: PRE-HISTORIC AND HISTORIC DEBRIS FLOWS IN WESTERN NORTH CAROLINA
The Appalachian Mountains have a long history of producing destructive debris flows. Through the Pleistocene, temperature and moisture fluctuations associated with the transition from glacial to interglacial ages, destabilized exposed soil and rock. These pre-historic debris flows have formed prominent modern landforms and a rolling topography (Jacobson et. al., 1989). Records of flooding in western western North Carolina associated with with hurricanes and other strong storms exist back into the late 1700’s. Recorded instances of debris flows and other slope movements during major rain events began in the late 1800’s, but their generation and mechanics have been poorly understood until un til recently. This study is only a part of the ongoing n atural hazards research being conducted by the North Carolina Geological Survey (Wooten et al., 2004) and North Carolina Department of Transportation. Continued study of the history of debris flows can help identify triggering mechanisms that are particular to North Carolina an d the recurrence interval of these events.
poorly sorted, but may be either matrix-or-clast-supported (Figure 3.1). Typically, fans are composites of several mass-wasting events with a weathered surface on each colluvial unit in the sequence. This indicates that there may may be great differences in age between the units and upwards several thousand years have elapsed between debris-flow-forming events (Kochel, 1990). In the Great Smoky Mountains, characteristic recurrence intervals for major debris flows are on the order of 400 40 0 to 1600 years (Kochel, 1990) whereas catastrophic debris flows have been estimated to occur every 3000-6000 3000 -6000 years in Nelson County, Virginia (Kochel, 1984; Kochel and Johnson, 1984). Catastrophic geomorphic events, such as debris flows, have been the principal means of erosion of the central Appalachian mountain chain during the Quaternary. The long-term denudation rates in the Appalachians average 40mm/kyr (Hack, 1980). In the short term, a single debris flow can remove enough material to account for 1 kyr of erosion during a single storm (Mills, et. al., 1987). Numerous studies (Table 3.1) hypothesize that extreme precipitation even ts, associated
During glacial periods, North Carolina experienced a greater frequency of freeze-thaw cycles and physical weathering. Rock exposed at high elevations decomposed to a thin loose loose soil mantle (Mills, 2000). A dry polar climate dominated the region. In modern polar climates, monthly temperatures average below 10°C (50°F) year-round, resulting in little to no tree growth (Lydolph, 1985). Although a polar climate can create a ready supply of sediment through erosion and physical weathering, the lack of precipitation inhibits the formation of debris flows. In contrast, slow mass movements, such as solifluction and c reep, are common (Ritter et al., 1995). In Virginia, slope wash of material may have proliferated more than debris flows during the Pleistocene (Eaton et al., 1997; Eaton, 1999). In the Great Smoky Mountains National Park, block field and slope deposits depo sits produced by Pleistocene frost wedging have been identified Clark and Torbett (1987). After the late Wisconsin glacial maximum, near the end of the Pleistocene, the northward migration of the polar front would have allowed tropical moisture to reenter the area during the summer months (Kochel, 1990). Previously undisturbed soil and rock then became exposed to
high elevations (>1100 m), produced large volumes of colluvium (>106 m3) and may have transported material as far as 8 km in a single event (Hatcher et al., 1996). Giant Gian t Pleistocene rock and block slides also have been identified in both southwestern Virginia (Shultz, 1986) and the Great Smoky Mountains (Hadley and Goldsmith, 1963). These slides indicate that large sections (100-400 million m³) of sandstone detached along bedding planes and joints and slid downslope (Schultz, 1986). If so, these debris flows and slides were significantly larger than those produced during modern times. Studies of pre-historic debris flows and fans tend to use three major dating techniques, i.e., relative-age dating of soil-horizon development and clast weathering, carbon-14 dating of organic material, and thermoluminescence dating of colluvium and related sediments (Table 3.1). These studies quantitatively provide evidence of repeated debris-flow activity during the Quaternary (Clark, 1987). Relative dating, when used as the only means for quantifying the age of a colluvial or fan deposit, may be less reliable than the other two techniques. Nonetheless, relative-age
unless the weathering conditions in both areas are very similar. Nonetheless, relative dating is a useful descriptive tool and a good first approximation for modern debris flow hazard areas. These studies also provide evidence of periods of episodic mass-wasting that was more extensive than the processes occurring today. Few radiocarbon-dating studies have been completed in North Carolina due to a lack of datable organic material in the stratigraphic record and the presumption that some deposits are too old (Table 3.1; Jacobson et al., 1989; Mills and Allison, 1995b). Existing dates da tes in nearby Virginia range from as recent as 2,200 kyr to as old as 50,800 kyr (Eaton et al., 1997). Dates for North Carolina range from 16,000 – 25,000 kyr. Kochel (1990) believes that these older dates indicate that while debris-flow activity may have been impeded during glacial maxima, tropical moisture occasionally has invaded the area. Further radiocarbon dating, where possible, po ssible, would greatly improve our knowledge of the Pleistocene environment and pre-historic Holocene mass-wasting in western North Carolina a nd the Appalachians. Few historical accounts of o f debris flows have actually been recorded and a nd this is
3.2.1
June, 1876 The first recorded instance of debris flows affecting the N.C. Blue Ridge occurred on
June 15-17, 1876. The debris flows accompanied flooding that is often called the “June Freshet,” one of the greatest floods in the upper reaches of the French Broad watershed (Tennessee Valley Authority, 1960). At the time, a debris flow was generally attributed attributed to a “waterspout”, i.e., a sudden funnel-shaped cascade of water falling from the sky during a torrential rain event (Clingman, 1877). It was believed that the force of the falling water ripped away the soil from the side of the mountain, leaving only solid bedrock. The term “waterspout” was used not only to describe a meteorological event but also a geomorphic feature. The closest modern term to this "waterspout" is “microburst.” Clingman (1877) reports that at least 40-60 waterspouts were reported in portions of Macon and Jackson counties during the June, 1876 storm. Although Clingman (1877) did not provide a mechanism for the “waterspouts”, his detailed descriptions of the erosion and deposition are excellent, e.g., that of two debris flows that occurred in Macon County near the
noting as Fishhawk Mountain is the same area where four people where killed and 15 houses destroyed in a debris flow that occurred on Sept. 16, 2004 (see below). 3.2.2
May, 1901 From May 18-to-23, 1901 a series of low-pressure systems passed through western North
Carolina and brought heavy rain, with the heaviest precipitation occurring on May 21-22. The storm was centered near the Black Mountains Moun tains of North Carolina. Total precipitation amounts ranged from 8.99” (22.8 cm) in Marion, North Carolina to 5.04” (12.8 cm) in Asheville, North Carolina (Myers, 1902). Extreme flooding affected portions of the Nolichucky, Watauga, Little Tennessee, and Catawba Rivers systems systems (Myers, 1902; Scott, 1972). Later flooding in the spring spring and summer only added to the destruction. Total damage to farms, bridges, highways, and buildings in the French Broad watershed wa tershed was estimated to be four million dollars (U. S. Department of Agriculture, 1902). Most of the debris flows associated with the 1901 storm occurred in Buncombe, Henderson, Mitchell and McDowell Counties (Scott, 1972) (Figure 3.2). The Southern Railroad
end of the cavity a sharp and well-defined channel led down the hill to the stream at the base, this channel being from 5 to 6 ft. wide and from 4 to 5 ft. deep with side walls practically vertical cut down though a gravelly clay. …It is estimated that the excavation has a total content of about 2,500 cu. yds. of earth which seems to have disappeared utterly.”
The particular slide described by Myers (1902) destroyed a log house that was in the flow path. Other accounts by area residents describe cloudbursts of extreme intensity accompanying the “waterspouts” and that water bubbled and then burst from the ground at the head of many smaller slides (Myers, 1902). It can be assumed from these descriptions that the mass movements in Mitchell County were debris flows, given their high water-and-debris content, their characteristic flow path, and their rupture surface. 3.2.3
July, 1916 During July of 1916 two tropical cyclones moved through the French Broad watershed
causing extensive flooding and numerous debris flows. On July 5-6, 1916 a weak hurricane passed over the Mississippi and Alabama coast and moved northeast, eventually deteriorating into a tropical depression by the time that it reached western North Carolina (Southern Railway,
where 22.22 inches (56.4 cm) fell in a 24-hour period (Hudgins, 2000). This is also the greatest 24-hour rainfall total ever recorded in North Carolina. Generally, Ge nerally, the storms of 1916 produced two distinct regions of exceptionally heavy precipitation, i.e., one in Mitchell, Avery, and Caldwell counties, and the other in Transylvania and Henderson counties (Figure 3.5). Runoff from the second storm was estimated to be as a s high as 80-90 percent (Southern Railway, 1917). The first storm had already thoroughly soaked the soil, increasing antece dent moisture conditions, and filled most streams nearly to flood stage (Scott, 1972). Rainfall from the second storm exacerbated flood conditions (Figure 3.6). The July, 1916 storms killed about 80 people and caused $22M in damages (Southern Railway, 1917). In Asheville, several homes and buildings bu ildings were destroyed and four of the main river bridges were washed away (Tennessee Valley Authority, 1960). The Southern Railway Company suffered extreme financial losses and transportation within western North Carolina was disrupted for several days. Many railway lines were covered by debris flows, trapping freight and passenger trains between terminals. The Southern Railway (1917) reported that
0.6 to 6.1 m (2 to 20 ft) and averaged 1.5 to 1.8 m (5 to 6 ft). Bedrock was seldom exposed anywhere along any slide (Holmes, 1917). 3.2.4
August, 1940 In August of 1940, a pair of storms caused significant flooding and numerous d ebris
flows in the western mountains of North Carolina; the first occurred from Augu st 11-17 and the other from August 28-31. These storms also brought record flooding to portions of Virginia, Tennessee, and South Carolina. Approximately 30-40 lives were lost and there were at least $30M in damages (U.S. Geological Survey, 1949). The situation was similar to that of 1916, with two large storms occurring in the same month. The 1940 mid-August storm was strikingly similar to the to the second 1916 storm in terms of rainfall intensity and storm path (Figure 3.4). However, unlike the 1916 storm, the antecedent moisture conditions in 1940 were relatively dry, allowing for increased infiltration, hence lower overall flood discharge levels (U.S. Geological Survey, 1949). The first storm in 1940, an unnamed hurricane, made landfall between Beaufort, South
slow rate of movement allowed for heavy precipitation for several days over the North Carolina Blue Ridge, resulting in high rainfall totals. Maximum precipitation totals ranged from 13 to 16 inches (33 to 41 cm) at to as little as 5 inches (13 cm) in Asheville (Tennessee Valley Authority, 1960). A series of well-defined storms centers over the Appalachians Mountains extended toward the northeast from Blue Ridge, Georgia to Luray, Virginia (Figure 3.7), apparently due to an orographic influence on the storm precipitation (U.S. Geological Survey, 1949). The second storm in 1940 occurred during the period of August 28-31 but intense rainfall did not begin until the morning of o f August 29. Rainfall continued to fall until August 30 when it abruptly ended around noon. Only passing showers remained by August 31 (U.S. Geological Survey, 1949). This storm was a relatively local meteorological disturbance that only affected the French Broad and Little Tennessee watersheds watersheds (Figure 3.8). Precipitation was of both shorter shorter time duration and aerial extent than the mid-August storm, but of higher intensity. Rainfall amounts ranged from 8 to 13 inches (20 to 33 cm) on the western slopes of the Blue Ridge in 20 to 30 hours (U.S. Geological Survey, 1949). Given the antecedent moisture conditions due to the
During the mid-August storm of 1940, debris flows mainly occurred in the Blue Ridge Mountains, from the North Fork of the Catawba Ca tawba River northward into Watauga County near ne ar the North Carolina – Virginia border (Figure 3.2). During the late August storm, debris flows occurred mainly in the Upper Pigeon and Tuskasgee River basins (Figure 3.2). Because of the concentration of high-intensity rainfall within a small area, more than 200 debris flows occurred in an area of only 150 mi2 (388.5 km2) (U.S. Geological Survey, 1949). 3.2.5
November, 1977 In early November 1977, a storm system that had formed as a low-pressure system in the
Gulf of Mexico moved northwestward into the Appalachian Mountains (Neary and Swift, 1987). Rainfall began in western North Carolina in the early morning of November 2 and continued at a steady rate (20-50 mm/day) until November 5. This steady rain was followed by intense downpours (102 mm/hr) on the night of November 5-6 during which most of the debris flows were initiated (Nearly and Swift, 1987). This heavy precipitation, as in 1916 and 1940, was produced by convection associated with orographic lifting over the southern Appalachians. Four
ephemeral creekbeds or along hillslope depressions (Pomeroy, 1991). Scarps occurred in shallow residual soils less than 1 m deep over gneissic bedrock (Neary et al., 1986). All of the flows occurred in undisturbed, forested areas (Neary et al., 1986). Topography in the Bent Creek watershed is at least partially controlled by the underlying concentration of tension joints in the bedrock. Where there is a greater amount of jointing, topographic hollows tend to develop. These joints allow for the infiltration of groundwater, enhancing breakdown of the rock. This accelerates weathering, providing loose material for mass wasting (Pomeroy, 1991). Debris flows seem to originate on the bedrock-soil or bedrockcolluvium interface within these hollows. The November 1977 flood killed at least thirteen people; sixteen counties in western North Carolina were declared disaster areas. The most serious flooding oc curred along the French Broad River downstream from Asheville and in Yancey County where nearly every bridge was washed out (Eshner and Patric, 1982; Stewart et al., 1978). Flooding destroyed 384 homes, 389 miles (622 km) of highway, and 12 dams. In total there was over $50M in damages
towards the northeast, east, and southeast (Pomeroy, 1991 ). These slopes would only receive sunlight in the morning and thus would have higher soil moisture. 3.2.6
September, 2004 The 2004 Atlantic hurricane season was exceptionally brutal. Fifteen tropical or
subtropical storms formed in the North Atlantic. Nine of these storms became named hurricanes and six of these struck the United States (National Weather Service, 2004a). In North Carolina, Ca rolina, the remnants of three tropical systems, i.e., hurricanes Frances, Ivan and Jeanne, impacted the western part of the state in September. Frances France s and Ivan caused extreme ex treme flooding in Asheville and several debris flows and rockslides in the mountains, mo untains, affecting Interstate-40. Rainfall totals for the month over much of western North Carolina ranged from 10 to 25 inches (25 to 64 cm). This was 2-to-5 times greater than normal (Badgett et al., 2004). Hurricane Frances struck the east coast of Florida early on Sept. 5, 2004 and quickly weakened into a tropical storm (National Weather Service, 2004a). The storm then rapidly moved across the state, through the panhandle pa nhandle of Florida, and northeastward across the eastern
Sixty miles southwest of Asheville, Lake Toxaway received 14 inches (35.6 cm) of rain (Nowell, 2004). In total, 17 western counties were affected by flooding (Anonymous, 2004). Hundreds of people were evacuated from their homes and several had to be rescued from the rising water (Nowell, 2004). Areas of Asheville located near the Swannanoa River were flooded, particularly the shopping center near the entrance to the Biltmore Estate, were water stood as much as 5 feet (1.5 m) deep (Nowell, 2004). In Haywood County, flooding along the Pigeon River also inundated downtown Canton and Clyde. The remnants of hurricane Frances caused cau sed at least 21 reported incidents of mass wasting (Appendix C) along several major roadways in seven western North Carolina counties. However, only three counties within the boundaries of the French Broad Watershed experienced debris deb ris flows, i.e., Avery, Henderson, and Transylvania. The largest reported debris flow occurred east of Asheville on Interstate-40, near Old Fort Mountain in McDo well County (Figure 3.12). This slide crossed the westbound lane and the median to block four of the six lanes of a five-mile stretch of Interstate-40 (Nowell, 2004). In Watauga County, one h ouse was destroyed and eight
southwestward, crossed over Florida and then into the Gulf of Mexico. By September 23, the remnants of Ivan had strengthened into a tropical storm and the “re-born” storm made landfall land fall for the second time on September Sep tember 24 over southwestern Louisiana (National Weather Service, 2004a). The remnants of Ivan moved into western North Carolina early on September 16. Although Ivan had weakened weakene d to a tropical storm by the time it reached North Carolina, it still packed powerful winds and heavy he avy rain. Rainfall was not as heavy as that which fell during Frances, mainly because the storm moved rapidly northeastward, but the western portion of the state still received between 4 to 8 inches (10 to 20 cm) of rain. The heaviest precipitation fell in Transylvania, Jackson and McDowell Counties at high elevations. Black Mountain (near Asheville) received 11.5 inches (29.2 cm) of precipitation and Sapphire (in Transylvania County) reported 15 inches (38 cm) (Figure 3.11) (Badgett et al., 2004). Although Ivan produced less rain than Frances, high antecedent-moisture conditions and saturated soils allowed for more slope movements to be p roduced. A total of 53 slope
Further west, near the North Carolina-Tennessee border, a large portion of the eastbound lane of Interstate-40 collapsed due to undercutting by the swollen Pigeon River. A major debris flow also destroyed a home in Candler in Buncombe County (Cantley-Falk, 2004). The worst damage occurred in the community of Peeks Creek in Macon County. At around 10:10 p.m. on September 16, a debris flow originated near the peak of Fishhawk Mountain (Figure 3.13) destroying at least fifteen houses, injuring several people, and resulting in the deaths of four people peop le (and an unborn baby). The debris flow traveled approximately 2.25 miles (3.6 km), possibly in pulses, dropping nearly 2200 feet (670 m) in elevation as it progressed down a mountain cove and into the north fork of Peeks Creek (Cabe, 2004). The velocity of the flow was estimated to be 20.3 mi/hr (32.7 kph) near the scarp and 33.2 mi/hr (5305 kph) just upstream of the area of major damage (Cabe, 2004). The force of the flow scoured the streambed, ripped trees down and left other striped of bark; houses were removed from their foundations (North Carolina Geological Survey, 2004b; Ostendorff, 2004). Th e flow probably originated as a debris slide; a slab of cohesive rock, debris and earth the size of a
transformer, one resident described seeing debris spinning and flying around in the air in a circular motion above their house (Biesecker and Shaffer, 2004). In 1876, residents described seeing funnel-shaped spinning masses of water near the crest of the mountain (Clingman, 1877). Tornadoes are fairly rare in mountainous areas, but do d o occasionally develop. While there was wind damage throughout the Peeks Creek area after the passage of Ivan, this damage was more consistent with wind shear. So far, the National Weather Service has not been able to conclude if a tornado actually did touch down on Fishhawk Mountain, but they do not discount the eyewitness accounts of local residents (Cabe, 2004). The question remains, "Why did mass movements occur in these Macon County areas as opposed to elsewhere?" In the Peeks Creek flow, fracture planes in the rock, sloping 35-55 degrees, provided a smooth slip surface. Soil layers over this bedrock were thin, generally less than three feet (1 m) deep (Cabe, 2004). These physical properties of the terrain probably facilitated the debris flows on Fishhawk Mountain. Meteorologically, the rainfall rates from the remnants of hurricanes Frances and Ivan were not unusually intense for either event. However,
3.2.7
Precipitation Thresholds and Recurrence Intervals Generally, historical rainfall totals from 1901 to 2004 are well within the 125 mm/d to
250 mm/d precipitation thresholds suggested by Eschner and Pa tric (1982) as necessary for debris-flow generation (see Figure 1.2). Average rainfall amounts were greater than 125 mm/d in all cases, i.e., greater than the minimum amount of precipitation necessary to saturate soil and set the stage for debris flows (Table 3.2). While storms with rainfall totals of 250 mm/d are described as extremely rare, all but one storm produced maximum precipitation amounts that exceeded 250 mm/d (Eschner and Patric, 1982). Extreme precipitation does not necessarily guarantee that debris flows will occur, as during the July 5-6, 1916 storm, but extreme precipitation certainly increases the risk of o f slope instability. Escher and Patric (1982) suggested a return interval of 100 years or less for storms producing debris flows in western North Carolina. Nonetheless, historical rainfall data from 1901 to 2004 indicates that recurrent intervals may be smaller. According to Cabes (2004), there have been 14 storms or hurricanes that have triggered slope movements in western North Carolina
traveled over the area within 10 to 20 days of each other. o ther. Antecedent moisture seems to play a crucial role in predisposing slope to debris-flow d ebris-flow generation. Geoscientists, emergency management, and citizens living in these mountainous areas, must be vigilant in monitoring weather conditions, particularly with repeated sequences of heavy rain events.
Table 3.1: Prehistoric debris flow studies in the southern Blue Ridge and the age-dating techniques utilized.
Reference
Year Dating Technique
Locat ion Location
Age of Features > 11,000 BP 10,000 - 12,000 BP; 315 BP 17,000 - 22,000 BP
Kochel
1987 Radiocarbon
Davis Creek, VA
Jacobson et al.
1989 Radiocarbon
West Virginia
Behling et al.
1993 Radiocarbon
Kochel
1990 Radiocarbon
Eaton et al.
1997 Radiocarbon
Shafer
1984 Thermoluminescence
West Virginia Appalachian Mountains, 16,000 - 25,000 BP NC Upper Rapidan River Basin, 2,200-50,800 BP VA Flat Laurel Gap, NC Late Quaternary
Mills
1982 Relative-age Relative-age 1995a /paleomagnetism 1995b Relative-age
Mills and Allison Mills and Allison Liebens and Schaetzl Mills
North Carolina
?
Watauga County, NC
780 ka - 1Ma
Haywood County, NC
?
1997 Relative-age
Macon and Swain Co., NC ?
2000 Relative-age
Appalachians
?
Figure 3.2: Areas of major debris flows fl ows and landslides in western North Carolina (after Scott, 1972).
54
Figure 3.3: A sketch map of debris flows that occurred along Gouges Creek in Mitchell County, North Carolina in May, 1901 (Myers, 1902).
Figure 3.5: Total storm precipitation for July 14-16, 1916.
Figure 3.6: U. S. Geological Survey hydrograph from the river gauge located on the French Broad River in Asheville for the month of July, 1916. In early July, there is a large hydrographic spike generated by rainfall from the remnants of a hurricane that passed through the area. There is also a second large peak between July 16 and 17 generated by the flooding associated with a hurricane moving northwestward over the watershed. This is the greatest recorded streamflow for the gauge at Asheville.
Figure 3.7: Total storm precipitation for August 14-15, 1940 adapted from U. S. Geological Survey, 1949).
Figure 3.9: Total storm precipitation for November 2-5, 1977 (adapted from Neary and Swift, 1987).
Figure 3.10: Total storm precipitation (inches) for the remnants of Hurricane Frances (National Weather Service, 2004b).
Figure 3.12: A debris flow that blocked the westbound lanes of Interstate-40 near Old Fort Mountain in McDowell County (North Carolina Geological Survey, 2004a).
Table 3.2: Major storms within the French Broad Watershed and their minimum, average, and maximum precipitation amounts.
STORM STORM DATE DATE MIN (in) (in) AVG AVG (in) (in) MAX (in) (in) MIN (mm) (mm) AVG (mm) (mm) MAX MAX (mm) (mm) 1901 5 7 8.9 128 177.8 228.4 1916 (1)* 4 7 10 101.6 177.8 254 1916 (2) 1 10 22.2 25.4 254 564.4 1940 (1) 4 13 16 101.6 330.2 406.4 1940 (2) 3 8 13 76.2 203.2 330.2 1977 2 8 14 50.8 203.2 355.6 2004 - FRANCES 4 10.3 16.6 101.6 261.6 421.6 2004 – IVAN 4 9.5 15 101.6 241.3 381 *no debris flows produced
CHAPTER 4: METHODOLOGY
In order to quantify debris-flow potential in the French Broad Watershed, two deterministic process-based computer-modeling programs have been chosen, i.e., SINMAP (Stability INdex MAPping) (Pack et al., 1998) and SHALSTAB (Shallow Landsliding Stability Model) (Dietrich and Montgomery, 1998). Both use similar numerical models and steady-state hydrologic assumptions to quantify the influence of topography on pore pressure. These computer programs, instructions, and examples are freely available for download from their respective websites.
4.1
Infinite-slope Equation SINMAP and SHALSTAB are based on the infinite-slope form of the Mohr-
Coulomb failure law, an equation commonly applied as part of a slope-stability model within the GIS environment (Hammond et al., 1992; Montgomery and Dietrich, 1994; Wu and Sidle, 1995; Pack et al., 1998). The infinite slope equation is:
This assumption is reasonable because the drainage barrier, e.g., top of bedrock, and the ground surface are often parallel on colluvial slopes. The contrast in hydraulic conductivity between the overlying soil and the material forming the drainage barrier causes groundwater to flow nearly parallel to the ground surface, providing a surface for slope failure (Hammond et al., 1992). Another assumption is that the failure plane is assumed to be infinite in extent and the resistance to movement along the sides and ends of the slope movement are so insignificant that they may be ignored (Hammond et al., 1992). Finally, the soil is assumed to be of uniform thickness. Although SINMAP and SHALSTAB share similar physical assumptions and equations, they use different indices to quantify instability. SINMAP uses the infiniteslope equation to calculate a “factor of safety”, i.e., an estimated potential for instability whereas SHALSTAB quantifies terrain instability in terms of the effective recharge required to trigger instability. A comparison of the results and relative performance of these programs is difficult due to their dissimilar output. To simplify comparison, model
4.2.1
Digital Elevation Models Both SINMAP and SHALSTAB assume that the dominant control on debris-flow
occurrence is surface topography, specifically the interplay between slope and shallow subsurface flow convergence (Montgomery and Dietrich, 1994). To calculate topography, both computer programs require digital elevation data. In this study, DEMs at 10-meter and 30-meter scales were obtained from the United States Geologic Survey National Elevation Dataset (http://seamless.usgs.gov/ (http://seamless.usgs.gov/). ). Both SINMAP and SHALSTAB are highly sensitive to the accuracy of the DEM. Verification of da ta quality is advisable prior to running these models (Zhang et al., 1999; Dietrich et al., 2001; Guimaraes et al., a l., 2003). As explained by Michael Oimoen, a scientist from the USGS National Center for Earth and Resources Observations and Science (pers. comm., 2005), USGS DEMs used for this study were created from the digitized contours of scanned 1:24,000-scale topographic quadrangle sheets. The contours from these maps maps are digitized and either a 10 x 10 meter or 30 x 30 meter mesh grid is overlaid on top of the digitized contours. con tours. For
catchment or drainage area, and compute the slope for each grid cell (Dietrich and Montgomery, 1998; Pack et al., 2001). Both programs have procedures for increasing accuracy and eliminating potential errors inherent in the DEM grid. Pit-filling corrections are automatically executed within both programs to eliminate artificial sinks or depressions in the DEM. Given that such grid elements are rare in natural topography, they are a re assumed to be errors created during the initial preparation of the DEM (Pack et al., 2001). Both programs use a “flooding” approach where pits are filled, raising the elevation to that of the lowest neighboring grid cell. The processing time for DEMs with large spatial areas, such as a DEM for the entire watershed, can be extremely long, depending on the speed and memory availability of the user’s personal computer. Both SINMAP and SHALSTAB seem to have a DEM size limitation. Although SINMAP could process the entire watershed at the 30-meter scale, the 10-meter DEM had to be b e broken down into county-size co unty-size pieces. SHALSTAB
4.2.2
Debris Flow Inventory In order to complete the slope-stability model runs for SINMAP and
SHALSTAB, basic digital-line and polygon coverages were collected and formatted for use in ArcView 3.x and ArcGIS 8.3. 8 .3. Both programs require the input of landslide location data to verify the model results; SINMAP requires point data whereas SHALSTAB requires polygonal shapes of each landslide feature. Landslide location data for this study was obtained through a combination of aerial-photography interpretation, previous studies, field investigation, and data provided by both the North Carolina Geological Survey and the North Carolina Department of Transportation. Most of this data was not in a digital (e.g., GIS) format and was digitized into a single landslide-location database for the Frenc h Broad Watershed (Appendix D). Other GIS data, e.g., roads, hydrology, and geology, and digital orthophoto quadrangles (DOQs) were obtained through the North Carolina State University Geodigital Library website (http://www.lib.ncsu.edu/stacks/gis/ (http://www.lib.ncsu.edu/stacks/gis/)) and the North Carolina Center for
that give the proportional extent of the component soils and their properties. There are eighteen general soil types found within this watershed (see Figure 2.2). The STATSGO soils coverage for the State of North Carolina was downloaded as a polygon shapefile, imported into ArcGIS, and clipped to the extent of the French Broad Watershed. 4.2.4
Soil Density Both programs require the input of a value for soil density. This value is used to
represent the total bulk density of the soil over the entire study area. In SINMAP the default value for soil density is 2000 kg/m kg /m3 while in SHALSTAB the value is 1700 kg/m3. Otteman (2001) used a value of 1450 kg/m3 for her study area in the Bent Creek Experimental Forest in Buncombe County, North Carolina whereas in Madison County Virginia, a value of 1200 kg/m3 was used by Morrissey et al. (2001). A geologist with the North Carolina Department of Transportation estimates typical density values of 1441.6 kg/m3 to 2082 kg/m3 in soils of western North Carolina (Jody Kuhne, pers. comm., 2004). Although no independent soil-density analysis was completed, a value of
combined into one dimensionless cohesion factor. The SINMAP stability-index equation is given by:
where the variables a and θ are the specific catchment area and slope, respectively, and are derived from the topography determined using a DEM. The other parameters, C (cohesion), Φ (soil friction angle), R/T (recharge divided by transmissivity), and r (the ratio of water and soil density) are manually entered into the model. These parameters are considered more uncertain and are specified in terms of upper and lower boundary values (Pack et al., 1998b). The default values for the foregoing parameters are provided in Figure 4.2. Values may be adjusted to represent local conditions, cond itions, to identify landslide-prone areas more precisely, and to assure that a significant amount of the landslides are captured in areas
4.3.1
T/R (Ratio
of Transmissivity to Effective Recharge) The ratio of transmissivity of the soil (m2/hr) to the effective recharge (m/hr) has a
default range of 2000 to 3000 (m). When multiplied by the sine of the slope, the T/R value can be interpreted as the length of the hillslope (in meters) required to develop saturation (Pack et al., 1998b). The recharge rates used in this study have been derived from four precipitation thresholds, i.e., 50 mm/d, 125 mm/d, 250 mm/d, and 375 mm/d. Two of these precipitation thresholds, 125 mm/d and 250 mm/d, are described by Eschner and Patric (1982) as necessary for debris-flow initiation in the Appalachians (see Figure 1 .2). The 50 mm/d rate was chosen as a minimum rate, i.e., one where SINMAP should not indicate a large mapped area of instability. The last threshold amount, 375 mm/d, is used as a maximum, i.e., an extreme example of the precipitation that can ca n produce debris flows in the French Broad Watershed. Only a few times have recorded rainfall totals actually exceeded this rate (see Table 3.2).
the recharge rate to find the upper and lower T/R (m) values. The final T/R values used were an average of each of the eighteen soil units (Table 4.1).
4.3.2
Dimensionless Cohesion In SINMAP, root and soil cohesion is combined with soil density and thickness to
calculate a dimensionless cohesion factor, C (Pack et al., 1998b). Conceptually, this is the ratio of the cohesive strength of the soil and roots relative to the weight of a saturated thickness of soil, or the contribution of cohesion to the stability of a slope (Pack et al., 1998b). The equation used to determine dimensionless cohesion is: C = (Cr + Cs)/(hρsg)
(4)
where C r r is root cohesion (N/m2), C s is soil cohesion (N/m2), h is the soil thickness (m), 3
2
ρ s is the wet soil density (kg/m ), and g is the acceleration due to gravity (9.81 m/s ).
Various values for cohesion have been b een suggested in diverse SINMAP studies. The default values used for cohesion in SINMAP are 0 and 0.25 but b ut Morrissey et al. (2001) used values between 0 and 1.28. Wooten uses values of 0.6 to .96, suggesting that zero
shearing angle. The angle is constant for a specified material and depends on the size, shape, and surface roughness of the grains, the density of the soil, moisture content, and material saturation (Easterbrook, 1999). Values for the soil friction angle for certain soil types can be estimated from tables provided by Hammond et al., (1992). These tables require that the soil be classified according to the Unified Soil Classification (USC) system (ASTM D-2487-85 and D2488-84) which are part of the STATSGO attribute data. Although no independent soil analysis was completed, the 26° and 45° soil-friction angles used to calibrate the model were considered realistic for the study area (Hammond et al., 1992). Given that this study requires that parameters be generalized over large areas, a wide variation encompassing the properties of several different soil types, from clayey to sandy and gravelly soils, is more realistic than a small range of values.
4.4
SHALSTAB Parameters Like SINMAP, SHALSTAB is an extension of ArcView© and is theoretically
The two hydrologic-slope stability equations solved by SHALSTAB are shown above. Equation (5) solves for the the hydraulic ratio while equation (6) (6) solves for the the area per outflow boundary length. The equations have three topographic terms defined by the DEM: drainage area (a), outflow boundary length (b), and hillslope angle (θ ). ). Of the other four parameters, soil bulk density ( ρ s) and internal friction angle (Φ) can be assigned by the user. The ratio of transmissivity (T ) and effective precipitation (q) are solved by SHALSTAB and are given as the final output of the model (Dietrich et al., 2001). The authors of SHALSTAB made even more simplifications to the infinite-slope equation, and their slope-stability model, than did the authors of SINMAP. First, they
be “parameter free” when run with the default parameter values. In other words, they wanted a slope stability model where a user did not have to have any available soil data parameters to calibrate the model. When the default version of SHALSTAB is run, only the soil density and the internal soil friction angle can be adjusted. Later versions of SHALSTAB have included an option where the cohesion value and soil depth can be adjusted if necessary (Figure 4.3). The SHALSTAB model needed to be calibrated in a way in which it could be directly comparable with SINMAP. Some of the variables, such as soil density (1922 kg/m³) and soil thickness (2 m), could remain the same between the two models. But other soil property values, such as cohesion and soil friction angle, vary widely over the study area. This problem is overcome by SINMAP, which uses a range of values for cohesion, soil friction angle, and transmissivity over recharge. SHALSTAB only uses a single input value for cohesion and soil friction angle. As specific soil data is not available at the watershed-scale, a variety of parameters were tested during several
Figure 4.1: The infinite slope equation as defined by Hammond et al., (1992) and Pack et al., (1998b) where C r r is root cohesion, C s is soil cohesion, is slope angle, s is soil density, w is the density of water , g , g is is acceleration due to gravity, D gravity, D is the vertical soil depth, D depth, Dw is the vertical height of the water table, and Φ is the internal soil friction angle. In the SINMAP model, the ratio of the vertical soil depth to the vertical soil height is simplifed so that depth is measured perpendicular to the slope
Figure 4.2: Default parameters used in the SINMAP model analysis. The values for the gravitational gravitational constant and the density of water were not adjusted in this study.
Table 4.1: Table of the hydraulic conductivity ( K ( T , m²/hr), and T/R (m) values used for each precipitation threshold (50 mm/d, K , m/hr), transmissivity (T 125 mm/d, 250 mm/d, and 375 mm/d) in the SINMAP analysis. The numbers in blue are the lower bound values while the numbers in red are the upper bound values. SOIL HYDRAULIC HYDRAULIC 2 T (m /hr) MAPPING COND (m/hr) COND (m/hr) LOWER UNIT LOWER UPPER
NC005 NC006 NC088 NC089 NC090 NC091 NC092 NC093 NC094 NC095 NC096 NC097 NC098 NC099 NC100 NC102 NC103 NC104
0.024 0.014 0.005 0.003 0.005 0.009 0.009 0.009 0.01 0.005 0.005 0.003 0.008 0.025 0.004 0.01 0.01 0.007 0.005 0.012 0.012
0.331 0.152 0.038 0.027 0.115 0.053 0.091 0.032 0.075 0.021 0.027 0.156 0.015 0.081 0.099 0.035 0.025 0.046
0.048 0.048 0.028 0.010 0.006 0.010 0.018 0.018 0.020 0.010 0.006 0.016 0.050 0.050 0.008 0.020 0.020 0.014 0.010 0.024
2
T (m /hr) UPPER
0.662 0.304 0.076 0.054 0.230 0.106 0.182 0.064 0.150 0.042 0.054 0.312 0.030 0.162 0.198 0.070 0.050 0.092 AVERAGE
T/R T/R T/R T/R T/R T/R T/R T/R 50 (mm/d) 50 (mm/d) 125(mm/d) 125(mm/d) 250(mm/d) 250(mm/d) 375(mm/d) 375(mm/d) LOWER UPPER LOWER UPPER LOWER UPPER LOWER UPPER
24.0 14.0 5.0 3.0 5.0 9.0 9.0 10.0 5.0 3.0 8.0 25.0 4.0 10.0 10.0 7.0 5.0 12.0 3.0
331.0 152.0 38.0 27.0 115.0 53.0 91.0 32.0 75.0 21.0 27.0 156.0 15.0 81.0 99.0 35.0 25.0 46.0 331.0
78
9.6 5.6 2.0 1.2 2.0 3.6 3.6 4.0 2.0 1.2 3.2 10.0 1.6 4.0 4.0 2.8 2.0 4.8 1.2
132.4 60.8 15.2 10.8 46.0 21.2 36.4 12.8 30.0 8.4 10.8 62.4 6.0 32.4 39.6 14.0 10.0 18.4 132.4
4.6 2.7 1.0 0.6 1.0 1.7 1.7 1.9 1.0 0.6 1.5 4.8 0.8 1.9 1.9 1.3 1.0 2.3 0.6
63.7 29.2 7.3 5.2 22.1 10.2 17.5 6.2 14.4 4.0 5.2 30.0 2.9 15.6 19.0 6.7 4.8 8.8 63.7
3.1 1.8 0.6 0.4 0.6 1.2 1.2 1.3 0.6 0.4 1.0 3.2 0.5 1.3 1.3 0.9 0.6 1.5 0.4
42.4 19.5 4.9 3.5 14.7 6.8 11.6 4.1 9.6 2.7 3.5 20.0 1.9 10.4 12.7 4.5 3.2 5.9 42.4
Figure 4.3: Default values used for SHALSTAB.
CHAPTER 5: RESULTS AND DISCUSSION
5.1
Introduction The purpose of this chapter is to provide model results for SINMAP and
SHALSTAB for a variety of parameter ranges, to describe the effectiveness of each model, and to identify the most sensitive model parameters. SINMAP and SHALSTAB results are compared herein to identify weaknesses and strengths inherent to each model. Finally, results will be compared with respect to slope, aspect, geology, and soil type.
5.2
Debris Flow Inventory A total of 142 debris flows have been mapped in the 7330 km² study area (Figure
5.1 and Appendix D). All of these slope movements have been located using historical documents and maps, aerial photography, field identification, ide ntification, and data provided by both the North Carolina Geological Survey and the North Carolina Department of Transportation. Landslides were identified in all counties except for Avery County. Of the 42 geologic units that occur within the watershed, debris flows have developed on
coarse-grained soils may be attributed to rapid infiltration through these soils. In the thin soils of the Southern Appalachians, soil pore pressure can quickly increase as groundwater builds above the impermeable bedrock, increasing the risk of slope failure. The gradient and aspect of the debris-flow locations have been calculated using the 10-meter DEM (with ArcGIS Spatial Analyst extension), given that the 30-meter DEM seems to underestimate slope (Zhang et al, 1999). For the entire watershed, slope varies from 0 to 74 degrees. Debris flows have occurred on slopes ranging from 10 to 50 degrees, although 88% of the slopes are at least 20 degrees. The average slope on which debris flows have initiated is 28 degrees. The aspect slope angle, as calculated in ArcGIS, is the compass direction towards which a slope faces. The "aspects" of the debris-flow headscarps occur in diverse directions, but show an affinity toward the east (32), southeast (23), southwest (21), and south (21). East-facing slopes receive only morning sunlight during the winter and thus have higher soil moisture than south- and west-facing slopes. During high rainfall events,
summarized in Table 5.1. Although there is an option in SINMAP to create crea te multiple calibration regions, usually based on the properties of individual soil types, only one general calibration region has been used in this study. This was deemed appropriate due to the general nature of the soil data and the regional scale of the study. SINMAP defines six different stability-class definitions based upon the stability index (SI) (Table 5.2). The terms “stable”, “moderately stable”, and “quasi-stable”, are used to represent areas that should not fail under the most conservative input parameters. The areas modeled as having “lower threshold” and “upper threshold”, are those that respectively have a <50% or >50% probability p robability of instability. Areas defined as “defended slopes” are unstable throughout the range of the specified parameter. Where these slopes occur in the field, they are only stable due to factors not modeled by SINMAP. SINMAP. For example, they may be bedrock outcrop (Pack et al., 1998b). Parameters are adjusted so that the resulting map “captures” the maximum amount of observed landslides in regions with a low SI (stability index), while minimizing the spatial extent of low-stability
5.3.1
Results – 30-meter DEM The default SINMAP values seem to underestimate un derestimate instability in the watershed.
For the 30-meter DEM, the model predicts that 52% (73) of the observed debris deb ris flows would have occurred in the lower threshold for instability whereas none were found in the “upper” and “defended” stability classes (Figure 5.3). All of other 67 debris flows (48%) occurred in the more stable stability classes. In the next SINMAP calculation, a precipitation threshold of 50 mm/d was used with the 30-meter DEM. Soil friction angle, soil density, cohesion and T/R were adjusted (Table 5.1). Under these conditions, 93.6% (131) of the inventoried debris flows are predicted to occur in the unstable classes, but only one of these was predicted to fail unconditionally. In this model run, 62.7% (4431.8 km²) of the study area is predicted to be unstable. Thresholds of 125 mm/d, 250 mm/d, and a nd 375 mm/d were subsequently used with SINMAP. For all three simulated rain events, 131 observed debris flows occurred in
defended zone increases to 61.4 km² (0.9%) and includes eight (5.7%) of the debris flows. In the final calculation, the low value va lue for dimensionless cohesion was increased slightly from zero to 0.1 for a recharge event ev ent of 125 mm/d, with all other properties remaining the same. This should better model the effects of root cohesion in the watershed, a factor which often has a strong effect on slope stability, even during heavy precipitation. With cohesion increased, the area of predicted unstable land decreased to 3170.6 km² or 44.6% of the watershed, but still contained 124 (88.6%) of the inventoried debris flows. Increased cohesion also increased the stability zones so that 35.7% of the study area (2534.7 km²) became classified as unconditionally unc onditionally stable. 5.3.2
Results – 10-meter DEM When comparing the area of the 10-meter grid calculated by SINMAP to the 30-
meter grid, the total area of the 10-meter grid is less than the 30-meter grid (Appendix E). The 10-meter SINMAP model run seems to have assigned “NO DATA” values instead of
As with the 30-meter DEM model, the results for the four precipitation thresholds are very similar. The extent of the “stable”, “moderately stable”, and “quasi-stable” zones (2409 km²) and the number of debris flows (7) occurring within these classes are the same for all four recharge events (Figure 5.6). Only the “lower”, “upper”, and “defended” stability classes change slightly for each precipitation threshold, shifting to a more unstable class as the recharge increases. The number of debris flows that fall in the unstable classes (115) also remains the same for all four recha rge events. Compared to the 30-meter DEM, a larger portion of the watershed is predicted to be unconditionally unstable in the 10-meter DEM. For the 50 mm/d threshold, 24.8 km² of the area is predicted to be “defended” although no debris flows fall into this zone. For 125 mm/d of recharge, the “defended” zone increases to 70.8 km² (1.0%) and includes eight (6.6%) slides. In the calculation for 250 mm/d and 375 mm/d recharge, the unconditionally unstable area increases to 126.4 km² and 138.8 km², respectively, and contains 12 (9.8%) of the debris flows.
parameters used. The areas of greatest instability also match well with the steepest terrain and generally follow steep ridgelines. Overall, the model does well, accurately modeling approximately 94% of the inventoried debris flows in unstable zones with an SI less than 1.0 for both DEM scales and for all four precipitation precipitation thresholds. With a slightly increased cohesion value, accuracy decreases to about 88%, but landslide density increases as the model minimizes the extent of the areas mapped as unstable. The 10-meter DEM models a slightly greater percentage of instability in the watershed than the 30-meter DEM. Slopes that are derived from DEMs vary with the spatial resolution, becoming lower at larger pixel sizes (Zhang et al., 1999). Given the coarser resolution of the 30-meter DEM, the elevation d ata is more generalized and slopes are typically underestimated. Using the 30-meter DEM, SINMAP could not predict small areas of increased instability along narrow ridges and valleys. The greater resolution of the 10-meter DEM allows for better prediction of unstable areas (2.7% improvement) and a slightly greater percentage of inventoried debris flows within the
British Columbia so the default parameters reflect representative soil data for that coolclimate area (Pack et al., 1998b). Model calibration was based on the thick packages of coarse subangular till and colluvium found in British Columbia. Even with low values of hydraulic conductivity ( K ), a large value for soil thickness thickn ess (b) would result in a greater K ), transmissivity value. Deeper soils occur in the study areas of Pack et al. (1998b) than in the present study area, hence their use of T/R default values of 2000 m and 3000 m. Given these default values with a 2-meter soil thickness and a moderate (125 mm/d) recharge rate, the hydraulic conductivity lies between 5.21 5.2 1 m/hr and 7.81 m/hr. These rates are representative of well-sorted sand and gravel but are unrealistic for the French Broad Watershed (Fetter, 1994). Clearly, there are other factors at work in the Southern Appalachians that trigger debris flows, factors that are not yet taken into account by SINMAP.
5.4
SHALSTAB Results As with the SINMAP model, SHALSTAB was used to model instability using
condition. Consequently, if the tangent of the slope (θ ) is greater than or equal to the soil friction angle (Φ), the slope will be unstable, even under dry conditions (Dietrich and Real de Asua, 1998). High values of log (q/T ) are the SHALSTAB lower bounds, the unconditionally “stable” condition. Shallow slopes do not allow for high enough pore pressure in the soil, even during full saturation, and are rarely unstable (Table 5.3). For every grid cell, SHALSTAB calculates the amount of o f critical effective precipitation necessary to trigger pore-pressure-induced instability, at a constant rate of transmissivity. Areas with lower values are considered more unstable because they require less precipitation to cause them to fail than do areas with higher values (Table 5.4). SHALSTAB requires that landslide locations be supplied to verify the model results. Instead of simple point locations, polygonal shapes of each landslide scar are necessary for this model. In the case of Haywood County, 23 landslide polygons were interpreted and digitized from digital orthophotos and DEMs using ArcGIS 3-D Analyst. The landslide location has been placed within a stability class based upon the lowest q/T
upper and lower bounds. The parameters used in each SHALSTAB run are summarized in Table 5.5.
5.4.1
Results – 30-meter DEM The results for all parameters run in SHALSTAB with a 30-meter DEM are
summarized in Appendix F. Even though 23 landslide polygons were digitized for the county, only 22 of the landslides were actually calculated by SHALSTAB and used in the final results. As with SINMAP, the SHALSTAB default parameters seem to underestimate instability (Figure 5.7). Seven of the mapped debris flows occur in the unconditionally stable zone, with land characterized by gradients too low to fail even when saturated. Collectively, this comprises 974.9 km² (31.82% of the coun ty). All of the other debris flows occur in stability classes between –3.1 and –2.2, approximately 38% (421 km²) of the county. No landslides fall into the “chronic instability” zone, the category where areas are defined as potentially unstable even without the addition of significant rainfall
(20) assigned to the “chronic,” the “<–3.1,” and the “-3.1 - -2.8” categories. This is equivalent to 979.3 km² or 59.7% of the county. The next test involved increasing cohesion slightly to 2000 (N/m³); this value is equivalent to a dimensionless cohesion value of 0.1 as used in SINMAP. For soil friction angles of 26° and 35°, this increase in cohesion decreased the cumulative percentage of the area and number of landslides predicted to occur in unstable areas. For log (q/T ) values less than –2.8, the area decreased by 13% given a soil friction of 26° and 12% with a soil friction angle of 35°. Strangely, for a soil friction angle of 45°, there was no change in the calculated results for values of cohesion between zero and 2000 (N/m³). This seems to indicate that SHALSTAB is more sensitive to ch anges in soil-friction angle than soil cohesion. The most stable parameters were equivalent to the SINMAP upper bound, i.e., a soil friction angle of 45° and cohesion equal to 9427.41 N/m³. This high cohesion number is equal to a dimensionless cohesion value va lue of 0.25 when the soil depth is 2 m and soil
the clipping procedure in ArcInfo where some pixels were excluded from the final clipped DEM in the 30-meter scale due to the coarse nature of the data. Appendix F summarizes results for a 10-meter DEM and each of the tested parameters. The default parameters seem to underestimate instability in the county, even though more of the mapped landslides are captured in higher stability classes. Only two landslides (8.8%) fall into the “stable” class but the area is slightly smaller than in the 30meter model run, i.e., 870.1 km² or 53% of the county. The rest of the debris flows (21) are contained in the stability classes between –3.1 to –2.2 that encompass 37% (615.7 km²) of Haywood County. As with the 30-meter DEM, a variety of parameters were tested with the 10-meter DEM and both the cumulative percent of the county area and the area of landslides were calculated (Figure 5.10 and Figure 5.11). The smaller grid size of the 10-meter DEM increases the predicted extent of unstable ground in these latter calculations. The lower bound values (26, 0) were found to contain the most debris flows in the category of
`
The upper bound parameters, 45° and 9427.41 N/m³ calculate the most stable
land. A majority of the the debris flows (21) fell into the “stable” category that comprises 1633.7 km² of the county. But the areas of instability were also increased by 7.2% from those found by the 30-meter DEM. Two slides occurred in the “-3.1 – -2.8” and “-2.5 - 2.2”instability classes and unstable zones with a log (q/T ) of greater than –2.2 make up 5.4 km² of the county (8.5%). 5.4.3
SHALSTAB Interpretation Like SINMAP, SHALSTAB is more sensitive to changes chan ges to some parameters than
others. A significant increase in cohesion causes more of the study area to be designated as unconditionally stable, but overall the model is less sensitive to this parameter. SHALSTAB seems to be most sensitive to changes cha nges in soil-friction angle. With only a 9 degree increase in friction angle from 26º to 35º, the total extent of predicted instability, for a log (q/T ) less than –2.8, decreases by approximately 29%. Unconditionally stable areas increase by around 20%. SHALSTAB calculates the unstable terrain depending on
the interpretation of model effectiveness is based upon the potential for future masswasting in areas that have not yet failed (Guimaraes et al., 2003). This interpretation is necessary with the lowest tested values, a soil-friction angle of 26o and cohesion of zero. Using these parameters, SHALSTAB accurately models 90.9% to 100% of the mapped debris flows in the upper three instability categories (log (q/T ) less than –2.8). Despite the fact that these low values could be interpreted as a worst-case scenario for debris-flow initiation, they seem to overestimate the extent of instability in Haywood County (Figure 5.12). If one compares the debris-flow density for each instability category, mid-range parameters capture the most landslides in the smallest area. Using the 10-meter DEM with a 35° soil-friction angle and soil cohesion value of 2000 N/m³, six debris flows are captured in the “chronic instability” class within an area of 51.9 km² (3.2% of total area). This is a landslide density of 0.116 slides per square kilometer, but an accuracy of only 26% for the “chronic instability” region, and 60.9% for the three highest instability
comparison of the relative performance of the programs is difficult because they calculate completely different indices to quantify instability. In order to compare them, the SINMAP stability index and the SHALSTAB log (q/T ) must be transformed into an analogous format. This can be accomplished ac complished using the Spatial Analyst extension of ArcGIS. For direct comparison, the parameters used in SINMAP and SHALSTAB must be identical. A moderate soil-friction angle of 35°, a zero value for cohesion, and a soil density 1922 kg/m³ were chosen. Transmissivity and recharge were a lso kept at a constant rate of 1 m²/d and 125 mm/d, respectively, which set the SINMAP T/R value equal to 200 m. The SHALSTAB log (q/T ) value for these parameters is equal to –2.28. This procedure is similar to the one used by Dietrich et al. (2001). Figure 5.14 shows a comparison of the two programs for the same area a rea in Haywood County using identical parameters. Both programs calculated 705.4 km² (49%) of Haywood County to be unstable. SHALSTAB calculated slightly more of the coun ty as unstable (870.3 km² or
“Zchs”, i.e., slate of the Copperhill Formation (Figure 5.16). This unit is a graphitic to sulfidic slate-to-phyllite found in the Great Smoky Mountains National Park in Haywood County (North Carolina Geological Survey, 1985). Rock descriptions of the Copperhill Formation are scarce but in the geologic map of the Great Smoky Mountains of Hadley and Goldsmith (1963), "Zchs" corresponds to a map unit called “pЄa”, i.e., the Anakeesta Formation. According to Merschat (pers. comm., 2005), a geologist with the North Carolina Geologic Survey, the slate of the Copperhill and the Anakeesta are separate formations but are nearly identical. The Anakeesta is part of the Smoky Mountain Group and the Ocoee Supergroup. It is a pyritic “dark, fine-grained argillaceous rock” with interbedded metasiltstone and coarse sandstone (Hadley and Goldsmith, 1963). Both the Anakeesta and the Copperhill Copp erhill formations represent repetitive turbidite sequences at different stratigraphic levels (Merschat, pers. comm., 2005). Topography in this portion of the Great Smoky Mountains National Park is exceptionally ex ceptionally narrow and steep with “serrate crests and craggy pinnacles,” and thin residual soils (Hadley and Goldsmith,
chemical weathering and could account, in part, for the steep weathered topography and instability associated with this unit. Transverse and strike jointing also cause angular cliff exposures in the Anakeesta and Thunderhead sandstone in the Great Smoky Mountains National Park (Hadley and Goldsmith, 1963). The most stable geologic units in the French Broad Watershed were found to be that coded “bz ” on the Geologic Map of North Carolina (1985), i.e., the metamorphosed rocks of the Brevard Fault Zone, and that coded “CZtp”, i.e., porphyroblastic gneiss of the Sauratown Formation. Both of these units are located in the southeastern portion of the watershed and lie within the geomorphologic region known as the Western Piedmont. The Brevard Fault zone seems to form a dividing line between moderately unstable rock and stable rock (Figure 5.16). Both SINMAP and SHALSTAB predict the most unstable soil unit in the watershed to be that coded NC104, i.e., a general soil group that occurs in northern Haywood County, generally overlying the Copperhill Formation. This soil unit is
(U.S. Department of Agriculture, 2005). All of the stable soil units are located on the flat topography along the floodplain of the French Broad and Pigeon Rivers (Figure 5.17).
5.7
Jointing, Fracturing and Foliation One factor that neither SINMAP nor SHALSTAB takes into consideration is the
influence of geologic structure on groundwater flow. Groundwater flow through a fracture is notoriously difficult to model because the rate of transmissivity is strongly controlled by the size of the fracture aperture ape rture and the connectivity of the fracture network n etwork (Renshaw, 2000). Nonetheless, flow through joints and fractures, and over bedrock foliation planes parallel to the dip slope, may play a significant role in triggering debris flows in western North Carolina (Figure 5.18). In the Great Smoky Mountains National Park, it was noted that the heads of debris flows originate at the intersection of cleavage and joints or beds, or on the cleavage or bedding plane plan e (Southworth et al, 2003). Intersecting joints and fractures can cause groundwater flow to become concentrated in topographic hollows. During a heavy
Figure 5.2: A comparison of 30-meter and 10-meter DEMs in Haywood County, North Carolina. In the coarser 30-meter DEM, there is a great deal of pixelation. Lower resolution can lead to an underestimation of both the slope and instability in the study area.
Table 5.2: SINMAP stability index definitions (Pack et al., 1998b).
Condition
Cla Class
Predicted State
SI > 1.5
1
Stable Slope Zone
1.5 > SI > 1.25
2
Moderately stable slope zone
1.25 > SI > 1.0
3
Quasi-stable slope zone
1.0 > SI > 0.5
4
0.5 > SI > 0.0
5
0.0 > SI
6
Lower threshold slope zone Upper threshold slope zone Defended slope zone
Parameter Range
Possible Influence of Factor Not Modeled Range cannot Significant model instability destabilizing factors required for instability Range cannot Moderate model instability destabilizing factors required for instability Range cannot Minor destabilizing model instability factors could lead to instability Pessimistic half Destabilizing factors of range required are not required for for instability instability Optimistic half of Stabilizing factors range required for may be responsible stability for stability Range cannot Stabilizing factors model stability are required for stability
Map Color
green
blue
yellow
pink
red
tan
Table 5.4: Table comparing q/T and q/T and log (q/T (q/T ) values and the precipitation rate required to initiate instability for soils with a transmissivity of 65 m²d and 17 m²/d (after Dietrich and Asua, 1998).
q/T (1/m)
log (q/T ) (1/m)
.00079 .00158 .00316 .00833 .01266
-3.1 -2.8 -2.5 -2.2 -1.9
Precip for T = 65 m²/d (mm/d) 52 103 206 410 818
Precip for T = 17 m²/d (mm/d) 14 27 54 103 214
Table 5.5: Parameters used in the SHALSTAB model runs.
Soil Friction Angle *45 **45 45 45 35 35 26 ***26
Density (kg/m³) 1700 1922 1922 1922 1922 1922 1922 1922
Soil Depth (m)
1 2 2 2 2 2 2 2
Cohesion (N/m²) 0 9427.41 2000 0 2000 0 2000 0
Figure 5.8 Cumulative percent of Haywood County found in each log (q/T (q/T ) category for a variety of soil parameters for the 30-meter DEM (after Dietrich et al., 2001). In the legend, the first number is is the degree if soil friction angle and the second number is the amount of cohesion (N/m³).
Figure 5.10: Cumulative percent of the area i f Haywood County for each log (q/T ( q/T ) instability category for a variety of soil parameters for the 10-meter DEM (after Dietrich et al., 2001).
Figure 5.14: Comparison of the output of SINMAP and SHALSTAB for 125 mm of recharge, 35° soil friction angle, 1922 kg/m³ soil density, and zero soil cohesion for a location in Haywood County. The red areas are calculated as unstable by both programs whereas the gray areas are calculated to be
Figure 5.17: The mean stability index for each soil unit in the French French Broad Watershed. The most
Figure 5.18: Picture taken in October 2003 along the Blue Ridge Parkway, near Mt. Mitchell. Even during this light rain event, water is pouring out from fractures in the rock.
CHAPTER 6: CONCLUSIONS
Debris flows and other forms of mass-wasting in western North Carolina are a destructive force that deserves more attention from both local and federal-level planners and citizens living in these mountainous areas. Debris flows are difficult to predict and have such a low frequency that it is rare for them to recur in the same area within the average life span of area residents. Unlike a flood-hazard map, a landslide-hazard map is inherently imprecise with regard to the extent, location, and timing of future masswasting. After the tragic results of the September 2004 hurricane season, North Carolina Senate Bill 7, the Hurricane Recovery Recove ry Act of 2005 was written and passed p assed (available online at http://www.ncga.state.nc.us/ http://www.ncga.state.nc.us/). ). It recognizes the need for better understanding of debris flows and provides funds for disaster relief and to identify areas of potential slope instability. This study has incorporated historical rainfall data, geology, soil types, and geomorphology to help predict debris flows in the French Broad Watershed. A
pressure, decreases cohesion, and may induce slope failure. Steeply sloping areas may be of potential concern under these certain weather conditions and should be closely monitored. 3. Both SINMAP and SHALSTAB predict that certain geologic units are more prone to failure than others. Sulfidic shale beds of the Copperhill Formation in the Great Smoky Mountains National Park are particularly susceptible, largely due to their steep topography, thin soil cover, and vulnerability to chemical weathering. 4. Both SINMAP and SHALSTAB predict that certain soil units are more prone to failure than others. Particularly vulnerable to mass-wasting are those that form at high elevations on steep slopes, are well drained, have a moderate to rapid rate of permeability, and develop over less permeable bedrock. 5. The movement of groundwater may be concentrated through joints, fractures, fractures, and foliation, quickly increasing pore pressure and decreasing cohesion and
both slope and relief. A finer 10-meter grid maximizes the overall extent of predicted instability, but significantly increases computer-processing time. Extremely large 10-meter DEMs, covering more than one county, may cause either computer program to abort. 2. The modeled results for the default SINMAP and SHALSTAB parameter values underestimate the extent of instability in the study area. 3. A SINMAP stability index of less less than 1.0, designating instability, instability, has been calculated for 88% -to- 94% of the inventoried landslides whereas the corresponding stability threshold in SHALSTAB has designated 91% to 100% of the mapped debris flows. flows. The SHALSTAB threshold is a log (q/T ) value less than –2.8 for a soil-friction angle of 26° and cohesion of zero. Overall, these results seem to over-predict the areas of instability. 4. The results from both models are similar, calculating 81-95% of the same area of Haywood County as unstable. Visually, the SINMAP results seem
•
It can run large DEMs, e.g., watershed size, without aborting the program or causing errors.
•
Recharge values are used in the calculation of the T/R values so these precipitation thresholds can be tested.
2. Some of the disadvantages of the SINMAP model are as follows: •
During some model runs, some grid cells calculated as “NO DATA,” effectively changing the area calculated by the model.
•
The model was created for study areas that had thick soil packages and high transmissivity rates, neither of which characterize the French Broad Watershed.
3. Some of the advantages of the SHALSTAB model are as follows: •
When run with only the default values, the user needs little knowledge of the actual soil parameters, or even mapped landslides, to produce a map of relative instability.
5. Neither model takes into account either antecedent moisture or the effect that geologic structure can have on concentrating groundwater flow. Nonetheless, both of these factors probably have a significant effect on instability. Deterministic slope-stability analytical methods, e.g., SINMAP and SHALSTAB, are generally more useful in areas where ground conditions are fairly uniform throughout the study area (Dai et al., 2002). Due to the scale of this study, assumptions and generalizations about soil parameters had to be made, thus forcing these parameters to be uniform over a large area. From this broad reconnaissance study, the French Broad Watershed offers several avenues for further study: 1. Subsequent studies should use a smaller study area, so that a site-specific soil and geologic analysis may be completed. c ompleted. Precise measurements of hydraulic conductivity (permeability), soil density, soil-friction angle, and soil cohesion increase the accuracy of the predicted SINMAP and SHALSTAB results. 2. An accurate and detailed debris flow inventory should should be constructed when
topographic information. This kind of data would include 10-meter DEMs or smaller and LIDAR data.
Table 6.1: The advantages and disadvantages of SINMAP and SHALSTAB.
SINMAP
SHALSTAB
Advantages Disadvantages Advantages Allows for a range Requires knowledge Can be run without of input values/ of specific knowing soil recharge thresholds soil/recharge parameters can be tested parameters Factor of safety easy Must adjust Does not require to interpret parameters recharge values, can repeatedly to back-calculate capture landslides Can run large DEMs “NO DATA” grid Retains calculated cells/shifting grid cell area Does not take into account geologic --structure or antecedent moisture
Disadvantages Does not allow for a range of input values
Log (q/T ) value difficult to interpret
Aborts when using large DEMs Does not take into account geologic structure or antecedent moisture
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Appendices
Appendix A: Geologic Units Geologic Rock Type Unit CZab
Formation Name (if given)
Geologic Description
Composition
Interlayered; minor layers and lenses of Amphibolite and Biotite Gneiss hornblende gneiss, metagabbro, mica schist, and granitic rock
Metamorphic
CZbg
Metamorphic
Biotite Gneiss and Schist
CZgms CZtp
Metamorphic SAURATOWN MOUNTAIN Metamorphic SAURATOWN MOUNTAIN
Garnet-Mica Schist Porphyroblastic gneiss
Ccl
Sedimentary
LOWER CHILHOWEE
Arenite
Ccu
Sedimentary
UPPER CHILHOWEE
Arenite
Chg
Metamorphic HENDERSON GNEISS
Cr
Sedimentary
ROME FORMATION
DSc
Metamorphic
CAESARS HEAD GRANITE GNEISS
Dqd
Igneous
INTRUSIVE
Gneiss
Inequigranular, locally abundant potassic feldspar and garnet; interlayered and gradational with calc-silicate rock, sillimanite-mica sillimanite-mica schist, mica schist, and amphibolite. Contains small masses of granitic rock Interlayered with amphibole Feldspathic arenite, white to yellowish gray. Minor silty shale, feldspathic siltstone, and conglomerate in lower part Vitreous quartz arenite, white to light gray; interbedded sandy siltstone and shale Monzonitic to granodioritic, inequigranular
Shale and siltstone, variegated red to brown; interbedded fine-grained sandstone Equigranular to porphyritic, massive to well foliated; contains biotite and Granite Gneiss muscovite Contains biotite, muscovite, and Quartz Diorite and Granodiorite xenocrysts Shale and Siltstone
134
Dsc
?
?
?
PzZu
Metamorphic INTRUSIVE
Meta-Ultramafic Meta-Ultramafic Rock
SOgg
Metamorphic INTRUSIVE
Granite Gneiss
Ybam
Metamorphic UNCONFORMITY
Amphibolite
Ybgg
Metamorphic UNCONFORMITY
Biotite Granite Gneiss
Ygg
Metamorphic UNCONFORMITY
Granodioritic Gneiss
? Metamorphosed dunite and peridotite; serpentinite, soapstone, and other altered ultramafic rock Poorly foliated; interlayered with biotite augen gneiss Equigranular, massive to well foliated, interlayered, rarely discordant, metamorphosed intrusive and extrusive mafic rock; may include metasedimentary rock Pinkish gray to light gray, massive to well foliated, granitic to quartz monzonitic; includes variably mylonitized orthogneiss and para-gneiss, interlayered amphibolite, calc-silicate calc-silicate rock, and marble Greenish gray to pinkish gray, porphyroclastic to mylonitic; epidote, sericite, and chlorite common
Metamorphic UNCONFORMITY
Amphibolite
Equigranular, massive to well foliated, interlayered, rarely discordant, metamorphosed intrusive and extrusive mafic rock; may include metasedimentary rock
Ymg
Metamorphic UNCONFORMITY
Migmatitic Biotite-Hornblende Gneiss
Layered biotite-granite gneiss, biotitehornblende gneiss, amphibolite, calcsilicate rock; locally contains relict granulite facies rock
Ytg
Metamorphic TOXAWAY GNEISS
Gneiss
Poorly foliated to well foliated, equigranular to inequigranular, granitic
Ymam
135
Equigranular, massive to well foliated, interlayered, rarely discordant, metamorphosed intrusive and extrusive mafic rock; may include metasedimentary rock Finely laminated to thin layered; locally contains massive gneiss and micaceous granule conglomerate; includes schist, phyllite and amphibolite
Zaba
Metamorphic
ALLIGATOR BACK FORMATION
Amphibolite
Zabg
Metamorphic
ALLIGATOR BACK FORMATION
Gneiss
Zata
ASHE METAMORPHIC Metamorphic SUITE AND TALLULAH FALLS FORMATION
Amphibolite
Zatb
ASHE METAMORPHIC Metamorphic SUITE AND TALLULAH FALLS FORMATION
Biotite gneiss
Zatm
ASHE METAMORPHIC Metamorphic SUITE AND TALLULAH FALLS FORMATION
Muscovite-biotite Muscovite-biotite gneiss
Locally sulfidic, interlayered and gradational with mica schist, minor amphibolite, and hornblende gneiss
Zatw
ASHE METAMORPHIC Metamorphic SUITE AND TALLULAH FALLS FORMATION
Metagraywacke
Foliated to massive. Locally conglomeratic; interlayered and gradational with mica schist, muscovite biotite gneiss, and rare graphitic schist
Zch
Metamorphic COPPERHILL FORMATION
Metagraywacke
Zchs
Metamorphic
SLATE OF COPPERHILL FORMATION
Zgma
Metamorphic
GRANDFATHER MOUNTAIN Meta-Arkose FORMATION
Slate
136
Equigranular, massive to well foliated, interlayered, rarely discordant, metamorphosed intrusive and extrusive mafic rock; may include metasedimentary rock Interlayered with biotite-garnet gneiss, biotite-muscovite biotite-muscovite schist, garnet-mica schist, and amphibolite
Metagraywacke, massive, graded bedding common; includes dark-gray slate, mica schist, and nodular calcsilicate rock Slate to phyllite, dark gray, graphitic, sulfidic; includes metagraywacke with local graded bedding Sericitic, conglomeritic, locally cross bedded interlayered metasiltstone and slate
Zgmg
Metamorphic
GRANDFATHER MOUNTAIN Greenstone FORMATION
GREAT SMOKY GROUP, UNDIVIDED
Metagraywacke and metasiltstone
Schistose to massive, amygdaloidal; interlayered with metasedimentary rock Thick metasedimentary sequence of massive to graded beds of metagraywacke and metasiltstone with interbedded graphitic and sulfidic slate and schist
Zgs
Metamorphic
Zlm
Metamorphic Lincolnton Metadacite
Metadacite
Zm
Igneous
MAX PATCH GRANITE
Granite
Mottled pink and light green, coarse grained to porphyritic, massive; contains biotite
Zrb
Sedimentary
RICH BUTT SANDSTONE
Sandstone
Feldspathic; interbedded with dark argillaceous layers and laminae
Zs
SNOWBIRD GROUP, Metamorphic UNDIVIDED
Metasiltstone and sandstone
Zsl
Metamorphic LONGARM QUARTZITE
Quartzite
Zsp
Zsr
Zss
Sedimentary
PIGEON SILTSTONE
Sedimentary
ROARING FORK SANDSTONE
Metamorphic SANDSUCK FORMATION
Feldspathic metasiltstone, metasandstone, and phyllite. Basal schist contains lenses of quartz-pebble conglomerate Cross-bedded. feldspathic, locally conglomeratic; includes dark slate and metasiltstone
Siltstone
Thin bedded to laminated, commonly cross-bedded, metamorphosed; locally includes argillite and calcareous and ankeritic metasiltstone grading to silty metalimestone
Sandstone
Greenish gray, fine to medium grained, locally cross-bedded, metamorphosed; interbedded metasiltstone and phyllite
Slate
Slate and metasiltstone, dark green to black. Metaconglomerate lentils in upper part; calcareous metasandstone, sandy metalimestone, and quartzite in lower part
137
Zsw
WADING BRANCH Metamorphic FORMATION
Zwc
Metamorphic
ZYbn
bz
WALDEN CREEK GROUP, UNDIVIDED
Metamorphic
Metamorphic BREVARD FAULT ZONE
Slate
Slate
Biotite gneiss
Schist and phyllonite
138
Sandy slate to coarse-grained pebbly metagraywacke with local graded bedding. Basal quartz-sericite schist or phyllite Slate to metasiltstone, local limy beds and pods; interbedded with quartz-pebble metaconglomerate metaconglomerate and metasandstone Migmatitic; interlayered and gradational with biotite-garnet gneiss and amphibolite; locally abundant quartz and alumino-silicates. alumino-silicates. Stratigraphic position uncertain Fish scale schist and phyllonite, graphitic; interlayered with feldspathic metasandstone, marble lenses
Appendix B: General Soil Data MUSEQ
NC005 NC005 NC005 NC005 NC005 NC005 NC005
NAME
1 2 3 5 6 7 8
S5ID
TOXAWAY ROSMAN DELANCO COMUS HATBORO BRADSON SUNCOOK
% OF MAPUNIT
NC0021 NC0024 MD0155 MD MD0050 PA0016 NC0028 CT0001
NC006 1 CLIFTON NC0015 NC006 2 BRADDOCK VA0054 NC006 3 EVARD SC SC0083 NC006 4 BRADDOCK VA0231 NC006 5 TOXAWAY NC0021 NC006 6 URBAN DC0035 LAND NC006 7 CLIFTON NC0015
SURFACE TEXTURE
35 17 26 9 7 4 2
8
UNIF UNIFIE IED D AASH AASHTO TO
DEPTH LOW
DEPTH HIGH
PERM LOW
PERM HY COND HY COND HIGH LOW HIGH
SIL L SIL FSL L GR-L LS
CL ML ML ML ML SM SM
AA -4 A-4 A-4 A-2 A-4 A-2 A-2
0.0 2.5 1.0 6.0 0.0 6.0 3.0
1.0 5 .0 2 .5 6.0 0.5 6.0 6 .0
0.60 2.00 0.20 0.60 2.00 0.60 6.00
20.00 20.00 2.00 6.00 6.00 20.00 20.00
15 L 23 L 19 L 17 GR-L 9 L V AR
ML CL ML SM CL
A-4 AA -2 A-4 AA-2 A-4
6.0 6.0 6.0 6.0 0.0
6 .0 6.0 6 .0 6.0 1.0
0.60 0.60 0.60 0.60 0.60
6.00 6.00 2.00 6 .0 0 20.00
0.09 0.14 0.11 0.10 0.05
6 .0
0.60
6.00
0.05
9
L
2.0 ML
A-4
0.21 0.34 0.05 0.05 0.14 0.02 0.12 0.94 13.08 0.024 0.331
1 CHESTER 2 ASHE 3 CHESTER 4 CHESTER 5 C O D OR U S 6 ASHE 7 CH A N D L E R
MD0001 NC0186 MD0001 MD0001 PA0015 NC0019 NC0263
23 15 15 6 6 5 6
L ST-FSL L L L FSL ST-FSL
CL CL SM CL CL CL ML SM SM
A -4 A-2 A -4 A-4 A-4 A -4 AA-4
139
0.90 1 .3 8 0.38 1.02 1.80
2.0 6.0
0.55 0.014
NC088 NC088 NC088 NC088 NC088 NC088 NC088
7.00 3.40 0.52 0.54 0.42 0.80 0.40 (IN/HR) (M/HR)
6.0 6.0 6.0 6.0 1.0 6.0 6.0
6.0 6.0 6.0 6.0 2.0 6.0 6.0
0.60 2.00 0.60 0.60 0.60 2.00 2.00
2.00 6.00 2.00 2.00 20.00 6 .0 0 6.00
0.54 6.02 (IN/HR) 0.152 (M/HR)
0.14 0 .3 0 0.09 0.04 0.04 0.10 0.12
0.46 0.90 0.30 0.12 1.20 0.30 0.36
NC088 8 ASHE NC088 9 CHANDLER NC088 10 CHESTER NC088 11 SUNCOOK NC088 12 TATE NC088 13 WATAUGA NC088 14 WATAUGA NC088 15 FANNIN
NC0019 NC0263 MD0001 CT0001 NC0025 NC0091 NC0091 NC0020
3 3 4 3 3 3 3 2
FSL ST-FSL L LS L L L SIL
SM SM CL CL SM ML SM SM SM SM ML
A -4 AA-4 A-4 A-2 A-4 A-4 A-4 A-4
6.0 6.0 6.0 3.0 6.0 6.0 6.0 6.0
6.0 6.0 6.0 6 .0 6.0 6.0 6.0 6.0
2.00 2.00 0.60 0.60 2.00 0.60 0.60 0.60
6 .0 0 6.00 2.00 20.00 6.00 6 .0 0 6 .0 0 6 .0 0 0.21 0.005
NC089 1 CHESTER NC089 2 CLIFTON NC089 3 CHESTER NC089 4 CLIFTON NC089 5 CHESTER NC089 6 CODORUS NC089 7 WATAUGA NC089 8 WATAUGA NC089 9 CLIFTON NC089 10 FANNIN NC089 11 FANNIN NC089 12 PORTERS NC089 13 CLIFTON NC089 14 TATE
MD0001 NC0264 MD0001 NC0015 MD0001 PA0015 NC0091 NC0091 NC0015 NC0020 NC0020 NC0152 NC0015 NC0025
32 13 11 9 5 8 4 4 3 3 3 3 1 1
L ST-L L L L L L L L SIL SIL ST-L L L
CL CL SM CL CL ML CL ML SM SM ML ML ML ML ML ML
A -4 A-4 A -4 A-4 A -4 A-4 A-4 A-4 A-4 A-4 A-4 A-2 A-4 A-4
6.0 6.0 6.0 6.0 6.0 1.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0
6.0 6.0 6.0 6 .0 6.0 2.0 6.0 6.0 6 .0 6.0 6.0 6 .0 6.0 6.0
0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60
2.00 6.00 2.00 6.00 2.00 20.00 6.00 6.00 6.00 6 .0 0 6 .0 0 6.00 6.00 6.00 0.11 0.003
NC090 NC090 NC090 NC090 NC090 NC090
1 HAYESVILLE 2 HAYESVILLE 3 BRADSON 4 CO D O RU S 5 BRADSON 6 EVARD
NC0013 NC0013 NC0028 PA0015 NC0028 SC SC0083
25 15 13 11 9 7
L L GR - L L GR-L SL
SM SM SM ML ML SM SM
AA-4 AA-4 A-2 A -4 A-2 A-2
140
6.0 6.0 6.0 1.0 6.0 6.0
6.0 6.0 6 .0 2.0 6.0 6.0
0.60 0.60 0.60 0.60 0.60 0.60
6.00 6.00 20.00 20.00 20.00 6.00
0.06 0.06 0.02 0.02 0.06 0.02 0.02 0.01
0.18 0.18 0.08 0.60 0.18 0 .1 8 0 .1 8 0 .1 2 1.52 (IN/HR) 0.038 (M/HR)
0.19 0.08 0.07 0.05 0.03 0.05 0.02 0.02 0.02 0.02 0.02 0.02 0.01 0.01
0.64 0.78 0.22 0.54 0.10 1.60 0.24 0.24 0.18 0 .1 8 0 .1 8 0 .18 0.06 0.06 1.08 (IN/HR) 0.027 (M/HR)
0.15 0.09 0.08 0.07 0.05 0.04
1.50 0.90 2.60 2.20 1.80 0.42
NC090 NC090 NC090 NC090 NC090
7 ROSMAN 8 DELANCO 9 EDNEYVILLE 10 HATBORO 11 TOXAWAY
NC0024 MD0155 NC0023 PA0016 NC0021
6 4 4 4 2
L FSL FSL L SIL
ML ML SM ML ML CL
A-4 A -4 AA-2 A-4 AA -4
2.5 1.0 6.0 0.0 0.0
5.0 2.5 6.0 0.5 1.0
0.60 0.60 0.20 0.60 0.60
20.00 6 .0 0 6.00 6 .0 0 20.00
0.04 0.02 0.01 0.02 0.01
0.20 0.005
NC091 1 DITNEY TN TN0075 NC091 2 UNICOI TN0054 NC091 3 JUNALUSKA NC0181 NC091 4 BRASSTOWN NC0206 NC091 5 LONON NC0203 NC091 6 NORTHCOVE NC0204 NC091 7 SOCO NC0180 NC091 8 JUNALUSKA NC0181 NC091 9 BRASSTOWN NC0206 NC091 10 LONON NC0203 NC091 11 NORTHCOVE NC0204
27 CB-SL 18 ST V -L 12 CN-FSL 8 CN-FSL 10 CB-SL 7 STV-FSL 10 CN-FSL 4 CN-FSL 2 CN-FSL 1 CB-SL 1 STV-FSL
ML GM SM SM SM GM SM SM SM SM GM
A-4 A-2 A-4 AA -4 A-2-4 A-2-4 A-4 AA -4 AA -4 A-2-4 A-2-4
6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0
6 .0 6 .0 6. 6 .0 6. 6 .0 6.0 6.0 6 .0 6. 6.0 6. 6 .0 6 .0 6.0
0.60 2.00 0.60 0.60 0.60 0.60 2.00 0.60 0.60 0.60 0 .6 0
6.00 6.00 6.00 6 .0 0 6.00 6.00 6.00 6.00 6 .0 0 6.00 6.00
0.16 0.36 0.07 0.05 0.06 0.04 0.20 0.02 0.01 0.01 0.01
0.35 0.009
NC092 1 SYLCO NC092 2 DITNEY NC092 3 TUSQUITEE NC092 4 DITNEY NC092 5 DITNEY NC092 6 CATASKA NC092 7 SPIVEY NC092 8 HAYWOOD NC092 9 SYLCO NC092 10 UNICOI NC092 11 UNICOI
TN0014 TN0075 NC0158 TN0075 TN0075 TN0133 TN0109 NC0095 TN T N0014 TN0054 TN0054
32 41 3 1 2 14 2 2 1 1 1
SIL CB-L ST-L CB-L CB-L ST V - L ST V -L ST-L L ST V -L ST V -L
GC ML SM ML ML CL-ML GM SM GC GM GM
A-4 A-4 AA-2-4 A-4 A-4 A -4 A-2 AA-2-4 A-4 A-2 A-2
6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0
6.0 6.0 6. 6.0 6.0 6.0 6. 6 .0 6.0 6. 6.0 6.0 6.0 6.0
0.60 0.60 2.00 2.00 2.00 2.00 0.06 0.06 0.60 0.60 2.00
2.00 6.00 6.00 6.00 6.00 20.00 6.00 20.00 2.00 6.00 6.00
1.62 1.08 0.72 0.48 0.60 0.42 0.60 0.24 0.12 0.06 0 .0 6 2.10 (IN/HR) 0.053 (M/HR)
0.19 0.25 0.06 0.02 0.04 0.28 0.00 0.00 0.01 0.01 0.02 0.35
141
1.20 0.24 0.24 0 .24 0.40 4.54 (IN/HR) 0.115 (M/HR)
0.64 2.46 0.18 0.06 0.12 2.80 0.12 0.40 0.02 0 .0 6 0 .0 6 3.58 (IN/HR)
0.009
NC093 1 ASHE NC0186 NC093 2 CHESTER MD0001 NC093 3 CHESTER MD0001 NC093 4 ASHE NC0019 NC093 5 ROCK DC0015 OUTCROP NC093 6 ASHE NC0019 NC093 7 CLIFTON NC0264 NC093 8 TUSQUITEE NC0158
8
53 ST-FSL 15 L 12 L 9 FSL U WB 1 1 1
FSL ST-L ST-L
SM CL CL CL CL SM
A-2 A-4 A-4 A -4
6.0 6.0 6.0 6.0 6.0
SM SM SM
A -4 A-4 AA-2-4
6.0 6.0 6.0 6.0
6.0 6.0 6.0 6.0 2.00
2.00 0 .6 0 0 .6 0 0.60 0.00
6.00 2.00 2.00 6 .0 0
6.0 6 .0 6. 6.0
2.00 0.60 0.60
6 .0 0 6.00 6.00
1.06 0.09 0.07 0.05 0.16
0.41 0.010
NC094 1 CHANDLER NC094 2 WATAUGA NC094 3 CHANDLER NC094 4 CLIFTON NC094 5 WATAUGA NC094 6 ASHE NC094 7 FANNIN NC094 8 CLIFTON NC094 9 CLIFTON NC094 10 TATE NC094 11 CHANDLER NC094 12 CHESTER NC094 13 CLIFTON NC094 14 CODORUS
NC0263 NC0091 NC0263 NC0264 NC0091 NC0186 NC0020 NC0015 NC0015 NC0025 NC0017 MD0001 NC0015 PA0015
23 12 11 7 7 5 5 6 4 3 4 2 2 9
ST-FSL L ST-FSL ST-L L ST-FSL SIL L L L L L L SIL
SM SM SM SM SM SM SM ML ML ML ML ML CL CL ML ML
AA -4 A-4 AA -4 A-4 A-4 A -2 A-4 A-4 A-4 A-4 A-2 A-4 A-4 A-4
6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 1.0
6. 6.0 6.0 6. 6.0 6.0 6.0 6.0 6 .0 6 .0 6 .0 6.0 6 .0 6.0 6.0 2.0
2.00 2.00 0.60 0.60 0.60 0.60 2.00 0.60 0.60 0.60 0.60 0.60 0.60 0.60
6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.00 2.00 6.00 20.00 0.18 0.005
NC095 NC095 NC095 NC095
1 2 3 4
EVARD FANNIN PORTERS BREVARD
SC S C0083 NC0020 NC0152 NC0012
17 10 10 9
SL SIL ST -L L
SM ML ML ML
A-2 A-4 A -2 A-4
142
6.0 6.0 6.0 6.0
6.0 6.0 6.0 6.0
0.60 0.60 0.60 2.00
0.091 (M/HR)
6.00 6.00 6 .0 0 20.00
3.18 0.30 0.24 0.54 0.00
0.02 0.01 0.01
0.06 0.06 0.06 1.26 (IN/HR) 0.032 (M/HR)
0.46 0.24 0.07 0.04 0.04 0.03 0.10 0.04 0.02 0.02 0.02 0.01 0.01 0.05
1.38 0.72 0.66 0 .4 2 0.42 0.30 0.30 0.36 0.24 0.18 0.24 0.04 0.12 1.80 2.98 (IN/HR) 0.075 (M/HR)
0.10 0.06 0.06 0.18
1.02 0.60 0.60 1.80
NC095 5 FANNIN NC0020 NC095 6 TUSQUITEE NC0158 NC095 7 ASHE NC0186 NC095 8 PORTERS NC0152 NC095 9 ASHE NC0186 NC095 10 TUSQUITEE NC0026 NC095 11 EDNEYVILLE NC0023 NC095 12 ROCK DC0015 OUTCROP NC095 13 BREVARD NC0012 NC095 14 CHANDLER NC0263 NC095 15 TUSQUITEE NC0158 NC095 16 EVARD SC SC0083 NC095 17 EVARD SC SC0083 NC095 18 TUSQUITEE NC0026
1
8 SIL 8 ST-L 8 ST-SL 7 ST -L 5 ST-SL 5 L 3 FSL U WB
ML SM SM ML SM ML ML SM
2 2 2 1 1 1
ML ML SM SM SM SM ML ML
L ST -L ST -L SL SL L
A-4 AA-2-4 A -2 A -2 A -2 A-4 AA -2
6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0
A-4 AA-4 A-2-4 A-2 A-2 A-4
6.0 6.0 6.0 6.0 6.0 6.0
6 .0 6. 6.0 6.0 6.0 6.0 6.0 6. 6 .0 6.0 2.00 6 .0 6 .0 6. 6 .0 6.0 6.0 6.0
0.60 0.60 2.00 2.00 2.00 2.00 2.00 0.00
6.00 6.00 6 .0 0 6.00 6 .0 0 6.00 6.00
2.00 0.60 2.00 0.60 0.60 0.60
20.00 6.00 6 .0 0 6.00 6.00 6.00
0.05 0.05 0.16 0.14 0.10 0.10 0.06 0.02
0.13 0.003
NC096 NC096 NC096 NC096 NC096 NC096 NC096 NC096 NC096 NC096 NC096 NC096 NC096 NC096
1 PORTERS 2 PORTERS 3 CODORUS 4 CHESTER 5 TUSQUITEE 6 CHESTER 7 CH A N D L ER 8 PORTERS 9 PORTERS 10 TUSQUITEE 11 TUSQUITEE 12 FANNIN 13 FANNIN 14 WATAUGA
NC0152 NC0152 PA0015 MD0001 NC0158 MD0001 NC0263 NC0022 NC0022 NC0026 NC0026 NC0020 NC0020 NC0091
31 16 10 8 7 6 4 4 4 3 3 2 1 1
ST -L ST -L SIL L ST-L L ST-FSL L L L L SIL SIL L
ML ML ML CL SM CL SM ML ML ML ML ML ML ML ML SM SM
A -2 A -2 A-4 A -4 AA-2-4 A -4 AA-4 A-4 A-4 A-4 A-4 A-4 A-4 A-4
6.0 6.0 1.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0
6.0 6.0 2 .0 6.0 6. 6.0 6.0 6. 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0
2.00 2.00 0.60 0.60 0.60 0.60 0.60 2.00 2.00 2.00 2.00 2.00 0.60 0.60
6 .0 0 6 .0 0 20.00 2.00 6.00 2.00 6.00 6.00 6.00 6.00 6.00 6 .0 0 6 .0 0 6 .0 0 0.33 0.008
143
0.48 0.48 0.48 0.42 0.30 0.30 0.18 0.00
0.04 0.01 0.04 0.01 0.01 0.01
0.40 0.12 0.12 0.06 0.06 0.06 0.82 (IN/HR) 0.021 (M/HR)
0.62 0.32 0.06 0.05 0.04 0.04 0.02 0.08 0.08 0.06 0.06 0.04 0.01 0.01
1.86 0.96 2.00 0.16 0.42 0.12 0.24 0.24 0.24 0.18 0.18 0 .1 2 0 .0 6 0 .0 6 1.08 (IN/HR) 0.027 (M/HR)
NC097 NC097 NC097 NC097 NC097 NC097
1 EDNEYVILLE 2 EDNEYVILLE 3 TUSQUITEE 4 ASHE 5 TUSQUITEE 6 TOXAWAY
NC0023 NC0023 NC0026 NC0019 NC0026 NC0021
73 11 9 3 3 1
L L L GR-FSL L L
SM SM ML ML SM ML ML CL
AA-2 AA-2 A-4 A -2 A-4 A-4
6.0 6.0 6.0 6.0 6.0 0.0
6 .0 6 .0 6.0 6.0 6 .0 1.0
0.60 2.00 2.00 2.00 2.00 2.00
6.00 6.00 6.00 6 .0 0 6.00 20.00 0.99 0.025
NC098 1 WAYAH NC098 2 TANASEE NC098 3 PORTERS NC098 4 WAYAH NC098 5 WAYAH NC098 6 TANASEE NC098 7 PORTERS NC098 8 CULLASAJA NC098 9 EDNEYVILLE NC098 10 EDNEYVILLE NC098 11 CHESTNUT NC098 12 SPIVEY NC098 13 TUSQUITEE NC098 14 CHESTNUT NC098 15 TUCKASEGE E
NC NC0188 NC0197 NC0152 NC0188 NC0188 NC0197 NC0152 NC0237 NC0115 NC0115 NC0242 TN0109 NC0158 NC0242 NC0226
43 9 8 8 8 7 6 1 3 2 1 1 1 1
GR-L ST -L ST-FSL GR-L GR-L ST -L ST-FSL ST V - L ST-FSL ST-FSL ST-FSL STV-L ST-FSL ST-FSL 1 ST-L
SM SM ML SM SM SM ML SM SM SM SM GM SM SM ML
A-2-4 A-2-4 A-2 A-2-4 A-2-4 A-2-4 A-2 A-1-B A-4 A-4 A-2-4 A -2 A-2-4 A-2-4 A-2
6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0
6.0 6.0 6.0 6.0 6.0 6.0 6.0 6. 6 .0 6. 6 .0 6 .0 6.0 6.0 6. 6 .0 6.0 6 .0
0.60 6.00 2.00 6.00 2.00 6.00 2.00 6.00 2.00 6.00 2.00 6.00 2.00 6.00 2.00 6.00 2.00 6.00 2.00 6.00 2.00 6 .0 0 0.06 6.00 0.60 6 .0 0 2.00 6.00 2.00 6.00 0.17 0.004
NC099 1 FANNIN NC0020 NC099 2 FANNIN NC0020 NC099 3 TALLADEGA GA0037 NC099 4 IOTLA NC0140 NC099 5 EVARD SC SC0083 NC099 6 EVARD SC SC0083 NC099 7 TATE NC0025
36 20 17 9 6 6 3
SIL SIL SIL L SL SL FSL
ML ML SM SM SM SM ML
A-4 A-4 AA-4 A-2 A-2 A-2 A-4
144
6.0 6.0 6.0 1.5 6.0 6.0 6.0
6.0 6.0 6 .0 3 .5 6.0 6.0 6.0
2.00 0.60 0.60 2.00 0.60 0.60 0.60
6.00 6.00 2.00 20.00 6.00 6.00 6.00
0.44 0.22 0.18 0.06 0.06 0.02
4.38 0.66 0.54 0.18 0.18 0.20 6.17 (IN/HR) 0.156 (M/HR)
0.26 0.18 0.16 0.16 0.16 0.14 0.12 0.02 0.06 0.04 0.02 0.00 0.01 0.02 0.02
2.58 0.54 0.48 0.48 0.48 0.42 0.36 0.06 0.18 0.12 0.06 0.06 0 .0 6 0.06 0.06
0.60 (IN/HR) 0.015 (M/HR)
0.72 0.12 0.10 0.18 0.04 0.04 0.02
2.16 1.20 0.34 1.80 0.36 0.36 0.18
NC099 8 HATBORO NC099 9 TUSQUITEE
PA0016 NC0026
2 1
L L
ML ML ML
A-4 A-4
0.0 6.0
0.5 6 .0
0.60 0.60
6.00 6.00 0.39 0.010
NC100 1 EVARD NC100 2 OTEEN NC100 3 HAYESVILLE NC100 4 SALUDA NC100 5 TUSQUITEE NC100 6 TATE NC100 7 BREVARD NC100 8 HAYESVILLE
SC SC0083 NC0107 NC0013 SC0082 NC0158 NC0025 NC0012 NC0151
37 18 4 25 2 1 1 12
L L L L ST-L ST -L L S T-L
ML ML SM SM SM SM ML ML SM
A-4 A-4 A -4 A-2 AA-2-4 A -4 A-4 AA -4
6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0
6 .0 6.0 6.0 6.0 6. 6.0 6.0 6.0 6. 6 .0
0.60 0.60 0.60 0.60 0.60 2.00 0.60 0.60
2.00 6.00 6 .0 0 6.00 6.00 6.00 20.00 6.00 0.39 0.010
NC102 1 JUNALUSKA NC102 2 TSALI NC102 3 SPIVEY NC102 4 SANTEETLA H NC102 5 STECOAH NC102 6 SOCO NC102 7 JUNALUSKA NC102 8 TSALI NC102 9 CHEOAH NC102 10 SPIVEY NC102 11 SANTEETLA H NC102 12 JUNALUSKA NC102 13 TSALI NC102 14 BRASSTOWN
0.01 0.01
0.12 0.06 3.22 (IN/HR) 0.081 (M/HR)
0.22 0.11 0.02 0.15 0.01 0.02 0.01 0.07
0.74 1.08 0.24 1.50 0.12 0.06 0.20 0.72 3.92 (IN/HR) 0.099 (M/HR)
NC0181 NC0179 TN0109 NC0208
21 11 17 11
C N -L SM CN-L SM ST V -L GM CN-FSL SM
AA-4 A-4 A-2 A-4
6.0 6.0 6.0 6.0
6. 6.0 0.60 6.0 2.00 6 .0 0.60 6 .0 0.60
6.00 6.00 6.00 6.00
0.13 0.22 0.10 0.07
1.26 0.66 1.02 0.66
NC0184 NC0180 NC0181 NC0179 NC0190 TN0109 NC0208
6 5 6 4 8 5
C N -L SM C N -L SM C N -L SM C N -L SM C N -L SM STV-L GM CN-FSL SM
A-4 A-4 A-4 A -4 A-4 A -2 A-4
6.0 6.0 6.0 6.0 6.0 6.0 6.0
6.0 2.00 6.0 2.00 6.0 0.60 6.0 2.00 6 .0 0.60 6.0 2.00 6.0 0.60
6 .0 0 6.00 6.00 6.00 6.00 6.00 6.00
0.12 0.10 0.04 0.08 0.05 0.10 0.02
0.36 0.30 0.36 0.24 0.48 0.30 0.18
NC0181 NC0179 NC0206
1 1 1
C N -L C N -L C N -L
AA-4 A-4 AA -4
6.0 6.0 6.0
6. 6.0 6 .0 6. 6.0
6.00 6.00 6.00
0.01 0.02 0.01
3
SM SM SM
0.60 2.00 0.60
0.28 0.007
145
0.06 0.06 0.06 1.38 (IN/HR) 0.035 (M/HR)
NC103 1 EDNEYVILLE NC103 2 CHESTNUT NC103 3 STECOAH NC103 4 SOCO NC103 5 STECOAH NC103 6 SOCO NC103 7 SPIVEY NC103 8 TUSQUITEE NC103 9 PORTERS NC103 10 COWEE NC103 11 EVARD NC103 12 EDNEYVILLE NC103 13 CHESTNUT NC103 14 PORTERS NC103 15 SPIVEY NC103 16 TUSQUITEE NC103 17 SANTEETLA H NC103 18 SAUNOOK NC103 19 STECOAH NC103 20 DELLWOOD NC103 21 DILLARD
NC0115 NC0242 NC0184 NC0180 NC0184 NC0180 TN0109 NC0158 NC0152 NC0171 SC0135 NC0115 NC0242 NC0152 TN0109 NC0158 NC0208 NC0195 NC0184 NC0183 GA0061
13 9 8 5 6 4 5 3 6 6 8 4 2 6 6 1
ST-FSL ST-FSL C N -L C N -L C N -L C N -L ST V -L ST-L ST-FSL GR - L G R -L ST-FSL ST-FSL ST-FSL STV-L ST -L 2 C N -L
3 1 1 1
GR-L C N -L GR-FSL L
SM SM SM SM SM SM GM SM ML SM SM SM SM ML GM SM SM
A -4 AA -2-4 A-4 A-4 A-4 A-4 A-2 AA-2-4 A -2 A-2-4 A-2 A -4 A-2-4 A-2 A -2 A-2-4 A-4
6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0
6.0 6. 6 .0 6.0 6.0 6.0 6.0 6.0 6. 6.0 6.0 6.0 6 .0 6.0 6.0 6.0 6.0 6. 6 .0 6.0
0.60 6.00 2.00 6.00 2.00 6 .0 0 2.00 6.00 2.00 6 .0 0 2.00 6.00 2.00 6.00 0.60 6.00 2.00 6.00 2.00 6.00 0.60 6.00 0.60 6.00 2.00 6.00 2.00 6.00 2.00 6.00 0.60 6 .0 0 2.00 6.00
0.08 0.18 0.16 0.10 0.12 0.08 0.10 0.02 0.12 0.12 0.05 0.02 0.04 0.12 0.12 0.01 0.04
SM SM SM ML ML
A-2 A-4 A-2-4 A-4
6.0 6.0 2.0 2.0
6.0 6.0 4.0 3.0
0.60 0.60 2 .0 0 0.60
0.02 0.01 0 .0 2 0.01
6 .0 0 6 .0 0 20.00 2.00 0.22 0.005
NC104 1 TANASEE NC104 2 BURTON NC104 3 OCONALUFT EE NC104 4 PORTERS NC104 5 SPIVEY NC104 6 CHEOAH NC104 7 STECOAH NC104 8 TANASEE NC104 9 BURTON
NC0197 NC0114 NC0192
21 19 16
NC0152 TN TN0109 NC0190 NC0184 NC0197 NC0114
14 7 10 2 3 2
ST -L ST-L FL-L ST-FSL CB-L C N -L C N -L ST -L ST-L
0.78 0.54 0.48 0.30 0.36 0.24 0.30 0.18 0.36 0.36 0.48 0.24 0.12 0.36 0.36 0.06 0.12
0 .1 8 0.06 0.20 0.02 1.00 (IN/HR) 0.025 (M/HR)
SM SM SM
AA-2-4 A-2 A-4
6.0 6.0 6.0
6.0 0.20 6.0 2.00 6.0 2.00
6.00 6.00 6.00
0.04 0.38 0.32
1.26 1.14 0.96
ML GM SM SM SM SM
A -2 A-2 A-4 A-4 A-2-4 A-2
6.0 6.0 6.0 6.0 6.0 6.0
6.0 6.0 6 .0 6.0 6.0 6.0
6.00 6.00 6.00 6 .0 0 6.00 6.00
0.28 0.14 0.06 0.04 0.06 0.04
0.84 0.42 0.60 0.12 0.18 0.12
146
2.00 2.00 0.60 2.00 2.00 2.00
NC104 10 SANTEETLA H NC104 11 SOCO
NC0208 NC0180
5 1
L CN-L
SM SM
A-4 A-4
6.0 6.0
6.0 6.0
2.00 2.00
6.00 6 .0 0 0.46 0.012
147
0 .1 0 0.02
0.30
0.06 1.80 (IN/HR) 0.046 (M/HR)
Appendix C: Slope Movement Data for the 2004 Hurricanes Frances and Ivan HURRICANE FRANCES - SEPTEMBER 6-8, 2004 County Location Date Reported Source Description Avery County, Near Crossnore US-221 Both Directions NCDOT Road is one lane in certain locations Avery County, Near Crossnore Crossnore SR-1504 Both Directions, NCDOT HIGH WATER, MUDSLIDE Pineola Rd. Blue Ridge Parkway Mileposts: 322, 345, 348, 9/9/2004 Asheville Citizen- Most of those between mile 322 and 349 took out major 349, 413, and 429 Times portions of the motor road, from just south of Linville Falls to south of Buck Creek Gap at NC 80 near Marion.
Henderson County Henderson County Henderson County Henderson County Henderson County, Near Hendersonville Henderson County Jackson County
McDowell County, Near Old Fort
SR-1710 Both Directions, Bald Rock Rd. SR-1799 Both Directions, Deep Gap Rd. SR-1194 Both Directions, Patterson Rd. SR-1613 Both Directions, Slick Rock Rd. SR-1706 Both Directions, Little Creek Rd. Shepard Street portion of N.C. 191 NC-281 (Mile Marker 13 to 17) Both Directions, Little Canada I-40 (Mile Marker 72 to 67or 69-67) Both Directions
9/10/2004 9/10/2004 17:06 NCDOT 9/8/2004
NCDOT
Trees down and Mudslide, Mudslide, Road has collapsed collapsed along along with a mudslide near waterfall. Deep Gap has many landslides blocking the road
9/8/2004
NCDOT
Two mudslides into road
9/8/2004
NCDOT
Road is washed out. Mudslide covering entire road
NCDOT
Sinkhole - road washed away about 1 mile off Sugarloaf Mountain Road (SR 1868). One lane closed closed due to mudslide mudslide
9/8/04 9/8/04 11:00AM 11:00AM NCDOT 9/8/2004
NCDOT
Road is closed due to slide from SR 1140 (Fanny Mae Brown Road) to Rock Bridge near near Tannassee Gap. Detour is signed. Detour distance is 41 miles.
early morning, 9/8/04
NCDOT
A slide on I-40 at Old Fort Mountain has blocked 2 of 3 lanes on westbound I-40 as well as 2 of the 3 eastbound lanes. Emergency crews are working to reopen the rest of the lanes as quickly as possible. Expect delays.
148
McDowell County, Near Woodlawn
US-221 Both Directions
Polk County Polk County
Pearson Falls Rd., near Saluda U.S. 176
Polk County
U.S. 176
Transylvania County
Old Highway 64/ N.C. 281N White Laurel subdivision, 9/8/2004 near Boone
Watauga County
NCDOT
9/9/2004
Asheville CitizenTimes 9/9/2004 Asheville CitizenTimes 9/9/2004 Asheville CitizenTimes 9/8/04 11:00AM NCDOT Rick Wooten, personal communication
There are several mudslides and dangerous areas at the top of US 221 North (Linville (Linville Mtn.). The road is closed and will be reopened as soon as the crews can complete the work and make the road passable again. US 221 North (Linville Mtn.) is closed due to Hurricane Frances. Approximately 70 feet of the road is washed away at the Mountain Paradise Campground. It will take a couple of months to rebuild rebuild this portion. A mudslide closed Pearson Falls Road near Saluda. between Saluda and Tryon, one lane closed from mudslides Temporarily closed Tuesday near the Henderson-Polk County line when mud and trees slide down a bank Portion of road closed due to mudslides near the Jackson County line This appears to have been an embankment failure. One home was destroyed, and eight condemned for occupancy
HURRICANE IVAN - SEPTEMBER 16-18, 2004 County Avery County
Location N.C. 184 and 194
Date Reported
Source Asheville Citizen Times
Description There was so much rain that high water and mudslides covered N.C. 184 and 194, shutting Banner Elk off from the rest of the region.
Buncombe County
Mink Farm Road
9/18/2004
mudslide
Buncombe County
Hookers Gap
9/18/2004
Buncombe County
Gibbs Road
9/18/2004
Buncombe County
Freedom Farm Road
9/18/2004
Buncombe County
Newfound Rd
9/18/2004
Asheville Citizen Times Asheville Citizen Times Asheville Citizen Times Asheville Citizen Times Asheville Citizen
149
mudslide mudslide mudslide mudslide
Buncombe County Buncombe County Buncombe County Buncombe County Haywood County Haywood County Haywood County Haywood County
Haywood County
Times Asheville Citizen Times Sluder Branch Road - #99 9/18/2004 Asheville Citizen Times N.C. 151 Asheville Citizen Times Arrowood Rd. near 9/17/2004 2:00 Asheville Citizen Starnes Cove Rd. Times I-40 mudslide in the 9/17/2004 13:44 NCDOT westbound lane at MM 35 U.S. 19-23 9/17/2004 0:00 Asheville Citizen Times Dutch Cove at Turnpike 9/17/2004 Asheville Citizen Times I-40, between the TN state 9/17/2004 NCDOT line and MM 20 North Turkey Creek Rd
U.S.276
Henderson County
Middle Fork (one lane closed) Jackson County, Near Cashiers NC-107 (Mile Marker 18 to 18) Both Directions
9/18/2004
9/17/2004
Asheville Citizen Times 9/17/2004 Asheville Citizen Times 9/16/2004 23:02 NCDOT
Mudslide at Early's Mtn. Road Mudslide & Pvt. Bridge damaged Closed due to major slide near Blue Ridge Parkway access debris flow occurred on side of mountain near the town of Enka-Candler, destroyed at least one home Interstate 40 is closed in Haywood County from Exit 451 in Tennessee to Exit 20 in North Carolina due to a slope failure. mudslides mudslide I-40 is closed in Haywood County between the Tennessee State Line and mile marker 20 due to the road being washed away. rockslide south of Waynesville mudslide mudslide - N.C. 107 is closed form the Thorpe Power Plant south to Cashiers. Downed trees, boulders and mudslides are blocking the road, the main access the area.
Jackson County, Near Cashiers US-64 Both Directions
9/16/2004 23:19 NCDOT
US 64 is closed between Cashiers and the Transylvania Co. Line due to slides and debris. US 64 is closed between Cashiers and the Macon Co. Line due to slides and debris. Hwy 64 at Spring Forest Road, three-fourths of highway has slid off
Macon, near Franklin McDowell County, Near Woodlawn Swain, Near Bryson City
9/17/2004 7:46 9/17/2004 6:21
NCDOT NCDOT
Down Trees and Slides Rockslide on NC226-A will probably take all day to move.
9/17/2004 8:02
NCDOT
Mud Slide and shoulder broke off
SR-1310, Wayah Rd. NC-226 ALT Both Directions SR-1195, Hwy 19a
150
Transylvania County, near Brevard Watauga, near Boone
SR-1540, Wilson Rd.
9/18/2004 3:35
NCDOT
SR-1130, Lee Gualtney Rd.
9/17/2004 9/17/2004 17:16 NCDOT
151
Due to high water, trees, power lines, and slides road is closed. Slide blocking blocking road
Appendix D: Debris Flow Inventory MATERIAL
DATA SOURCE
NCDOT Cv
Rd
Scot Scott, t, R NCG NCGS S Pomero Pomeroy y NCDOT
Rd
NCDOT
Cv Rd
Pomero Pomeroy y NCDOT NCDOT NCDOT
Rd Rd
Cv Rd
NCDOT NCDOT NCDOT NCDOT NCDOT Lam Lambe NCDOT NCDOT NCDO NCDOT T Pomero Pomeroy y NCDOT Dockal FS
Cv? Cv?
Rd
NCGS NCGS Dockal Pome Pomero roy y NCDOT NCDOT
REMARKS
SR 1607, .5mi S of Madison County line Brev Brevar ard d slid slidee BRP BRP Mile Mile 357. 357.7 7 MP 17.6, E of SR 1336 WBL Intersection of BRP, 694, SR 2053 .6 mi E of SR 1130 1130 WBL .2mi N of Buncombe County line, US 25-70 Balsam Balsam Gap Landsl Landslide ide Rt. 206 NBL NC 226, .6mi S of 1253 Bals Balsam am Gap Gap II Land Landsl slid idee 600 ft. S of SR 1319 1319 Fine Finess Cree Creek k Slid Slidee NC 262, 1.8mi S of TN line Off FR475, W of Davidson River, elev. 2500 feet Possible landslide Richland Ridge Rd. Magg Maggie ie Vall Valley ey debr debris is flow flow Cove Creek Slide Slide Num Number ber 50 N-side N-side of NC19 NC19
LAT
LONG
35.73 35.7300 00 82.7 82.700 000 0
COUN OUNTY
Bunc Buncom ombe be
YEAR
1990 1990
TYPE
Slum Slump p
GEO GEO UNIT SOIL SOIL UNIT SLOP SLOPE E ASPE SPECT
Ymg Ymg
NC090 NC090
10
N
35.1 35.190 900 0 82.8 82.870 700 0 Tran Transy sylv lvan ania ia 1970 1970 Debr Debris is Flow Flow Dqd Dqd 35.7 35.730 305 5 82.3 82.308 082 2 Bunc Buncom ombe be 1995 1995 Debr Debris is Flow Flow Zatw Zatw 35.480 35.4800 0 82.650 82.6500 0 Buncom Buncombe be 1977 1977 Slump Slump Zatm Zatm 35.63 .6300 82.9900 Hay Haywoo wood 1968 Debris Flow Zch
NC093 NC093 11 NC09 NC098 8 11 NC093 NC093 13 NC0 NC006 13
SE
35.650 35.6500 0 82.490 82.4900 0
Buncom Buncombe be
1982 1982
Zatm Zatm
NC095 NC095
13
N
35.480 35.4800 0 82.670 82.6700 0 35.470 35.4700 0 82.950 82.9500 0 35.76 .7600 82.6100
Buncom Buncombe be Haywoo Haywood d Madison
1977 1977 Slump Slump 1990 1990 Slump Slump 1989 Deb Debris Flow
Zatm Zatm ZYbn Ybg Ybgg
NC093 NC093 NC090 NC090 NC10 C100
15 15 16
E SW NW
35.440 35.4400 0 83.0800 83.0800 35.600 35.6000 0 82.940 82.9400 0 35.99 35.9900 00 82.1 82.160 600 0
Haywoo Haywood d Haywoo Haywood d Mitc Mitche hell ll
1989 1989 1996 1996 1990 1990
ZYbn ZYbn Zatm Zatm
NC095 NC095 NC006 NC006 NC093 NC093
17 17 17
E W SW
35.4 35.450 500 0 83.0 83.070 700 0 35.890 35.8900 0 82.750 82.7500 0 35.6 35.670 700 0 82.9 82.990 900 0 35.480 35.4800 0 82.650 82.6500 0 36.0 36.090 900 0 82.0 82.090 900 0
Hayw Haywoo ood d Madiso Madison n Hayw Haywoo ood d Buncom Buncombe be Mitc Mitche hell ll
Debr Debris is Flow Flow 1986 1986 Slump Slump 1978 1978 Debr Debris is Flow Flow 1977 1977 Slump Slump Slum Slump p
ZYbn ZYbn Zsr Ybgg Ybgg Zatm Zatm Ymg Ymg
NC10 NC103 3 NC092 NC092 NC00 NC006 6 NC093 NC093 NC09 NC098 8
18 18 19 19 19
NE W N S S
Dqd
NC094 NC094
20 20
S
Slump Slump
Slump Slump Slump Slump Slum Slump p
35.280 35.2800 0 82.810 82.8100 0 Transy Transylva lvania nia
1993 1993
35.1 35.180 800 0 82.8 82.890 900 0 Tran Transy sylv lvan ania ia
2003 2003 Debr Debris is Flow Flow
Zata Zata
NC00 NC006 6
20
S
35.5 35.501 014 4 35.2800 35.2800 35.4 35.450 500 0 35.920 35.9200 0
Debr Debris is Flow Flow Slump Slump 1977 1977 Debr Debris is Flow Flow 1976 1976 Slump Slump
Zgs Zgs Zatb Zatm Zatm Zabg Zabg
NC10 NC103 3 NC094 NC09 NC095 5 NC093 NC093
21 21 21 21
NE SE E N
83.0 83.094 944 4 Hayw Haywoo ood d 82.8100 82.8100 Transylvan Transylvania ia 82.6 82.660 600 0 Hend Hender erso son n 82.0600 82.0600 Mitch Mitchell ell
152
Slump Slump
SW E SE
Cv? Rd
Rd Rd
Rd rk Cv?
Rd
USFS
Microburst; dual slides near 35.77 .7700 83.0400 Hay Haywoo wood Dry Branch Pome Pomero roy y Num Numbe berr 24 35.4 35.470 700 0 82.6 82.660 600 0 Bunc Buncom ombe be Pome Pomero roy y Num Number ber 49 35.4 35.440 400 0 82.6 82.660 600 0 Hend Hender erso son n Lam Lambe Wate Waterv rvil ille le Land Landsl slid idee 35.6 35.690 900 0 83.0 83.010 100 0 Hayw Haywoo ood d NCDOT SBL NC 25-70, S of NC 35.91 35.9100 00 82.7 82.750 500 0 Madi Madiso son n 208 NCGS Deadly debris flow (12/11) 35.50 .5048 83.8500 Hay Haywood ood - Maggie Valley Debris Pome Pomero roy y Num Number ber 15 35.5 35.500 000 0 82.6 82.650 500 0 Bunc Buncom ombe be Pome Pomero roy y Num Number ber 6 35.4 35.480 800 0 82.6 82.690 900 0 Bunc Buncom ombe be Pome Pomero roy y Num Number ber 41 35.4 35.430 300 0 82.6 82.610 100 0 Hend Hender erso son n Pome Pomero roy y Num Number ber 43 35.4 35.430 300 0 82.6 82.640 400 0 Hend Hender erso son n Pome Pomero roy y Num Number ber 35 35.4 35.460 600 0 82.6 82.640 400 0 Bunc Buncom ombe be Pome Pomero roy y Debr Debris is Torr Torren entt 35.4 35.480 800 0 82.6 82.680 800 0 Bunc Buncom ombe be Dockal Near Maxwell Cove, east of 35.320 35.3200 0 82.740 82.7400 0 Transy Transylva lvania nia drainage Dockal Cove Creek Slide Slide 35.2800 35.2800 82.8100 82.8100 Transylvan Transylvania ia NCDOT SBL NC 215, 200' N of SR 35.40 .4000 82.9400 Hay Haywoo wood 1216, approximate NCDOT NCDOT I-40, I-40, World' World'ss Fair Fair Slide Slide 35.77 35.7700 00 83.090 83.0900 0 Haywoo Haywood d NRCS Several debris flows 35.7647 82.2656 Yancey triggered by trop. depression Pome Pomero roy y Num Number ber 36 35.4 35.470 700 0 82.6 82.620 200 0 Bunc Buncom ombe be Pome Pomero roy y Num Number ber 37 35.4 35.470 700 0 82.6 82.610 100 0 Bunc Buncom ombe be NCDOT NCDOT SBL SR 1137 1137 35.930 35.9300 0 82.5000 82.5000 Mitche Mitchell ll NCDOT SR 1318, .55mi W of SR 35.92 .9200 82.6700 Madison 1334 Pome Pomero roy y Num Number ber 16 35.4 35.496 966 6 82.6 82.650 504 4 Bunc Buncom ombe be Pomero Pomeroy y 35.480 35.4800 0 82.680 82.6800 0 Buncom Buncombe be Pome Pomero roy y Num Number ber 34 35.4 35.450 500 0 82.6 82.650 500 0 Bunc Buncom ombe be Pomero Pomeroy y 35.480 35.4800 0 82.650 82.6500 0 Buncom Buncombe be Dockal Cove Creek Slide Slide 35.2800 35.2800 82.8100 82.8100 Transylvan Transylvania ia NCDOT WBL SR 1334, 0.2 mi NW 35.91 .9100 82.6900 Madison of SR 1425
153
1994 Debris Flow
Zsl
NC1 NC103
22
SE
1977 1977 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow Debr Debris is Flow Flow 1986 1986 Slum Slump p
Zatm Zatm Zatm Zatm Ybgg Ybgg Zsr Zsr
NC09 NC093 3 NC09 NC093 3 NC10 NC102 2 NC092 NC092
22 22 22 23 23
SE E SW SW
2003 Debris Flow
Ybg Ybgg
NC1 NC103
23
NE
197 1977 7 1977 1977 1977 1977 1977 1977 197 1977 7 1977 1977 1996 1996
Debr Debris is Flow Flow Debr Debris is Flow Flow Debr Debris is Flow Flow Debr Debris is Flow Flow Debr Debris is Flow Flow Debr Debris is Flow Flow Slump Slump
Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatb Zatb
NC09 NC093 3 NC09 NC093 3 NC09 NC093 3 NC09 NC093 3 NC09 NC093 3 NC09 NC093 3 NC095 NC095
23 23 23 23 23 23 24
NE NE SE S SE W SW
Slump Slump 1989 Debris Flow
Zatb Zatm
NC094 NC0 NC095
24 24
SE E
1982 1982 Slump Slump 1977 Debris Flow
Zsp Zatw
NC102 NC102 NC098
24 25
SW W
197 1977 7 Debr Debris is Flow Flow Zatm Zatm NC09 NC093 3 25 1977 1977 Debr Debris is Flow Flow Zatm Zatm NC09 NC093 3 25 1990 1990 Slump Slump Zabg Zabg NC093 NC093 1990 Deb Debris Flow Ybg Ybgg NC0 NC093 25
SE S
1977 1977 Debr Debris is Flow Flow 1977 1977 Slump Slump 197 1977 7 Debr Debris is Flow Flow 1977 1977 Slump Slump Slump Slump 1990 Deb Debris Flow
Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatb Ybg Ybgg
NC093 NC093 NC093 NC093 NC09 NC095 5 NC093 NC093 NC094 NC094 NC0 NC093
26 26 27 27 27 27
25
SW W E SW NE S E N
Rd wr Cv Cv Cv Rd
Pome Pomero roy y Pome Pomero roy y Pome Pomero roy y Pome Pomero roy y Pome Pomero roy y Pom Pomeroy eroy NCDOT NCDOT Pome Pomero roy y NCDOT NCDOT NCDOT NCDOT NCD NCDOT OT NCGS NCGS NCGS NCGS Pomeroy Pome Pomero roy y Pome Pomero roy y Pome Pomero roy y NCGS Pome Pomero roy y Pomeroy
Rd Cv
Rd/Cv
Pome Pomero roy y Pome Pomero roy y NCDO NCDOT T Pome Pomero roy y Pome Pomero roy y Pome Pomero roy y NCDOT Pome Pomero roy y Witt Pome Pomero roy y Pome Pomero roy y
Num Number ber 17 Num Number ber 39 Num Number ber 51 Num Number ber 34
35.5 35.520 200 0 82.6 82.640 400 0 Bunc Buncom ombe be 35.4 35.440 400 0 82.6 82.640 400 0 Bunc Buncom ombe be 35.4 35.450 500 0 82.6 82.660 600 0 Hend Hender erso son n 35.4 35.450 500 0 82.6 82.650 500 0 Bunc Buncom ombe be 35.4 35.480 800 0 82.6 82.670 700 0 Bunc Buncom ombe be 35.4 35.49 900 82.6 82.660 600 0 Bunc Buncom ombe be W of SR 1395 1395 35.890 35.8900 0 82.660 82.6600 0 Madiso Madison n Num Number ber 16 35.5 35.520 200 0 82.6 82.640 400 0 Bunc Buncom ombe be 35.54 35.5400 00 82.8 82.810 100 0 Hayw Haywoo ood d MP 8.8, 8.8, E of Harmon Harmon Den 35.7200 35.7200 83.040 83.0400 0 Haywoo Haywood d NC 1318 1318,, .25 .25 W of 1334 1334 35.9 35.920 200 0 82.6 82.670 700 0 Madi Madiso son n Hick Hickey ey Fork Fork Debr Debris is Flow Flow 36.0 36.006 068 8 82.6 82.697 977 7 Madi Madiso son n Alle Allen n Stan Stand d Debr Debris is Flow Flow 35.9 35.986 865 5 82.7 82.761 611 1 Madi Madiso son n No. 23, Runnout length of 35.4 35.47 700 82.6 82.660 600 0 Bunc Buncom ombe be 2820 ft. 35.4 35.480 800 0 82.6 82.650 500 0 Bunc Buncom ombe be Num Number ber 14 35.4 35.490 900 0 82.6 82.660 600 0 Bunc Buncom ombe be Num Number ber 7 35.4 35.480 800 0 82.6 82.690 900 0 Bunc Buncom ombe be Blackstone Knob West 35.7 35.73 353 82.3 82.317 174 4 Bunc Buncom ombe be Slide Num Number ber 4 35.4 35.478 788 8 82.6 82.686 863 3 Bunc Buncom ombe be No. 31, Chute 1800 ft. long, 35.4 35.46 600 82.6 82.650 500 0 Bunc Buncom ombe be into Laurel Branch Num Numbe berr 30 35.4 35.460 600 0 82.6 82.670 700 0 Bunc Buncom ombe be Num Number ber 25 35.4 35.480 800 0 82.6 82.670 700 0 Bunc Buncom ombe be MP 1.0, 1.0, I-40 I-40 35.7 35.77 700 83.0 83.080 800 0 Hay Haywoo wood Num Number ber 10 35.4 35.490 900 0 82.6 82.680 800 0 Bunc Buncom ombe be Num Number ber 48 35.4 35.430 300 0 82.6 82.660 600 0 Hend Hender erso son n Num Number ber 12 35.4 35.490 900 0 82.6 82.660 600 0 Bunc Buncom ombe be MP 7.95 EBL, N of single 35.7200 83.0300 Haywood tunnel 35.4 35.490 900 0 82.6 82.650 500 0 Bunc Buncom ombe be Rt. 215 35.2900 35.2900 82.9100 82.9100 Transylvan Transylvania ia Numbe Numberr 2 35.4 35.470 700 0 82.7 82.700 000 0 Bunc Buncom ombe be Num Number ber 40 35.4 35.440 400 0 82.6 82.620 200 0 Bunc Buncom ombe be
154
1977 1977 Debr Debris is Flow Flow 197 1977 7 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow 197 1977 7 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow 197 1977 Debr Debris is Flow Flow 1980 1980 Slump Slump 1977 1977 Debr Debris is Flow Flow 1984 1984 Slum Slump p 1979 1979 Slump Slump 1990 1990 Debr Debris is Flow Flow 1999 1999 Debr Debris is Flow Flow 1999 1999 Debr Debris is Flow Flow 197 1977 Debr Debris is Flow Flow
Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Ybgg Ybgg Zatm Zatm ZYbn ZYbn Zsl Ybgg Ybgg Zwc Zwc Zwc Zwc Zatm Zatm
NC09 NC093 3 NC09 NC093 3 NC09 NC095 5 NC09 NC095 5 NC09 NC095 5 NC09 NC095 5 NC095 NC095 NC09 NC093 3 NC006 NC006 NC102 NC102 NC09 NC093 3 NC09 NC092 2 NC09 NC092 2 NC09 NC090 0
27 27 27 28 28 28 28 28 28 28 28 28 29
S N E NE SE S E S S SW N SE E S
1977 1977 197 1977 7 1977 1977 200 2004
Debr Debris is Flow Flow Debr Debris is Flow Flow Debr Debris is Flow Flow Debr Debris is Flow Flow
Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm
NC09 NC093 3 NC09 NC095 5 NC09 NC093 3 NC09 NC095 5
29 29 29 29
SE NE NE S
1977 1977 Debr Debris is Flow Flow 197 1977 Deb Debris ris Flow Flow
Zatm Zatm Zatm Zatm
NC09 NC093 3 NC09 NC095 5
29 30
NE E
1977 1977 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow 1973 Debris Flow
Zatm Zatm Zatm Zatm Zsr Zsr Zatm Zatm Zatm Zatm Zatm Zatm Zsl
NC09 NC095 5 NC09 NC095 5 NC10 NC102 2 NC09 NC093 3 NC09 NC093 3 NC09 NC095 5 NC102
30 30 30 30 30 30 30 30
NE E SW SW E S N
1977 1977 Debr Debris is Flow Flow Slump Slump 1977 1977 Debr Debris is Flow Flow 197 1977 7 Debr Debris is Flow Flow
Zatm Zatm Zatm Zatm Zatm Zatm Zatm
NC09 NC093 3 NC095 NC09 NC095 5 NC09 NC093 3
31 31 31 31
SW E E NE
28
Rd
Pome Pomero roy y Pome Pomero roy y NCDOT
Num Number ber 44 No. No. 8, Debr Debris is Torr Torren entt NC 63, 5.1mi N of Buncombe County line
Rd Cv?
Otte Ottema man n USFS
35.4 35.496 967 7 82.6 82.643 431 1 Bunc Buncom ombe be Microburst; dual slides near 35.77 .7700 83.0400 Hay Haywoo wood Dry Branch Num Number ber 32 35.4 35.450 500 0 82.6 82.650 500 0 Bunc Buncom ombe be Num Number ber 29 35.4 35.460 600 0 82.6 82.680 800 0 Bunc Buncom ombe be 35.4 35.49 900 82.6 82.650 500 0 Bunc Buncom ombe be identi identifie fied d in 3D Analys Analystt 35.7200 35.7200 86.040 86.0400 0 Haywood Haywood Numbe Numberr 28/2 28/29 9 35.4 35.470 700 0 82.6 82.660 600 0 Bunc Buncom ombe be identi identifie fied d from from DOQQ DOQQ 35.770 35.7700 0 83.090 83.0900 0 Haywood Haywood Num Number ber 11 35.4 35.490 900 0 82.6 82.670 700 0 Bunc Buncom ombe be Num Number ber 42 35.4 35.420 200 0 82.6 82.620 200 0 Hend Hender erso son n Num Number ber 42 35.4 35.420 200 0 82.6 82.620 200 0 Hend Hender erso son n Num Number ber 38 35.4 35.440 400 0 82.6 82.630 300 0 Bunc Buncom ombe be Blac Blacks ksto tone ne Knob Knob East East Slid Slidee 35.7 35.733 338 8 82.3 82.315 154 4 Bunc Buncom ombe be 35.4 35.470 700 0 82.6 82.660 600 0 Bunc Buncom ombe be Numbe Numberr 14 (sec (secon ond d head head)) 35.4 35.490 900 0 82.6 82.660 600 0 Bunc Buncom ombe be Numbe Numberr 5 35.4 35.480 800 0 82.6 82.690 900 0 Bunc Buncom ombe be I-40, I-40, East East of Twin Twin Tunnel Tunnelss 35.7600 35.7600 83.040 83.0400 0 Haywoo Haywood d Poun Poundi ding ng Mill Mill Bran Branch ch Slid Slidee 35.9 35.995 951 1 82.7 82.732 325 5 Madi Madiso son n Num Number ber 33 35.4 35.460 600 0 82.6 82.650 500 0 Bunc Buncom ombe be Chute 920 ft. long, debris 35.4 35.46 600 82.6 82.650 500 0 Bunc Buncom ombe be torrent Num Number ber 28/2 28/29 9 35.4 35.470 700 0 82.6 82.660 600 0 Bunc Buncom ombe be Mt. Mt. Mitc Mitche hell ll Slid Slidee 35.7 35.730 300 0 82.3 82.300 000 0 Bunc Buncom ombe be SBL NC 25-70, 250 ft. N of 35.8 35.890 900 0 82.7 82.750 500 0 Madi Madiso son n SR 1319 Numbe Numberr 3 35.4 35.480 800 0 82.6 82.690 900 0 Bunc Buncom ombe be Debr Debris is Torr Torren entt 35.4 35.490 900 0 82.6 82.680 800 0 Bunc Buncom ombe be Lesser Lesser Fines Fines Creek Creek Slide Slide 35.670 35.6700 0 82.990 82.9900 0 Haywood Haywood Num Number ber 33 35.4 35.460 600 0 82.6 82.650 500 0 Bunc Buncom ombe be Rt. 215 35.2900 35.2900 82.9100 82.9100 Transylvan Transylvania ia
Rd
Rd rk
Cv
rk
Cv MGW MGW Rd
wr
Pome Pomero roy y Otte Ottema man n Pom Pomeroy eroy Witt Witt Pome Pomero roy y DOQQ DOQQ Pome Pomero roy y Pome Pomero roy y Pome Pomero roy y Pome Pomero roy y NCGS NCGS Pome Pomero roy y Pome Pomero roy y Pome Pomero roy y NCDOT NCDOT NCG NCGS S Pome Pomero roy y Pomeroy Pome Pomero roy y Woot Wooten en NCDOT Pome Pomero roy y Pome Pomero roy y NCDOT NCDOT Pome Pomero roy y Witt
35.4 35.430 300 0 82.6 82.640 400 0 35.4 35.480 800 0 82.6 82.680 800 0 35.70 35.7000 00 82.8 82.820 200 0
Hend Hender erso son n Bunc Buncom ombe be Madi Madiso son n
155
1977 1977 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow 1980 1980 Slum Slump p
Zatm Zatm Zatm Zatm Ybgg Ybgg
NC09 NC093 3 NC09 NC093 3 NC095 NC095
31 31 31
S SW NE
1977 1977 Debr Debris is Flow Flow 1994 Debris Flow
Zatm Zatm Zsl
NC09 NC093 3 NC1 NC102
31 32
S SE
1977 1977 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow 197 1977 Debr Debris is Flow Flow Slump Slump 1977 1977 Debr Debris is Flow Flow Slump Slump 1977 1977 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow 2004 2004 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow 1985 1985 Slump Slump 2001 2001 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow 197 1977 Deb Debris ris Flow Flow
Zatm Zatm Zatm Zatm Zatm Zatm Zsl Zatm Zatm Zsp Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zsl Zwc Zwc Zatm Zatm Zatm Zatm
NC09 NC095 5 NC09 NC095 5 NC09 NC095 5 NC102 NC102 NC09 NC095 5 NC102 NC102 NC09 NC095 5 NC09 NC093 3 NC09 NC093 3 NC09 NC093 3 NC09 NC095 5 NC09 NC093 3 NC09 NC095 5 NC09 NC093 3 NC102 NC102 NC09 NC092 2 NC09 NC095 5 NC09 NC095 5
32 32 32 32 32 33 33 33 33 33 33 33 34 34 34 34
E NE S W E SW E E SE E SW SE NE E SE
35 35
E SE
1977 1977 Debr Debris is Flow Flow 2003 2003 Debr Debris is Flow Flow 1986 1986 Slum Slump p
Zatm Zatm Zatw Zatw Zsr Zsr
NC09 NC095 5 NC09 NC098 8 NC092 NC092
35 35 35
E S W
1977 1977 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow 1950 1950 Slump Slump 1977 1977 Debr Debris is Flow Flow Slump Slump
Zatm Zatm Zatm Zatm Zbgg Zbgg Zatm Zatm Zatm
NC09 NC095 5 NC09 NC095 5 NC006 NC006 NC09 NC095 5 NC095
35 35 35 36 36
E W S E E
34
S
Cv Rd
Pome Pomero roy y Pome Pomero roy y NCDOT NCDOT Pome Pomero roy y Otte Ottema man n Pome Pomero roy y NCDO NCDOT T Pome Pomero roy y Pome Pomero roy y Otte Ottema man n NCDOT
Cv
Pome Pomero roy y Pome Pomero roy y Pome Pomero roy y Witt NCDOT
wr Rd Rd
NCDOT NCDOT Pome Pomero roy y Pomeroy
Rk
Cv
Pome Pomero roy y Pome Pomero roy y Pome Pomero roy y Pome Pomero roy y Pome Pomero roy y Pom Pomeroy eroy Pome Pomero roy y Pome Pomero roy y Pome Pomero roy y Pom Pomeroy eroy Pome Pomero roy y
Num Number ber 8 Debr Debris is Torr Torren entt MP 0.4, I-40 I-40 numb number er 27 Num Number ber 27 SBL SBL NC 261 261 Debr Debris is Torr Torren entt Debr Debris is Torr Torren entt numbe numberr 28 NBL NC 25-70, S of NC 208 Num Number ber 46 Num Number ber 45 Num Number ber 13 Rt. 215 I-40, may have been rockfall, not sure NC 215 debr debris is torr torren entt Ext. rock rubble at toe, multi-headed flow, No. 28 Num Number ber 29 Num Number ber 27 Numbe Numberr 9 Num Number ber 9 Debr Debris is Torr Torren entt Num Number ber 26 Num Number ber 1 Num Number ber 47 Num Number ber 22
35.4 35.480 800 0 82.6 82.680 800 0 35.4 35.490 900 0 82.6 82.660 600 0 35.770 35.7700 0 83.090 83.0900 0 35.4 35.446 468 8 82.6 82.647 474 4 35.4 35.460 600 0 82.6 82.670 700 0 35.4 35.480 800 0 82.6 82.670 700 0 36.1 36.100 000 0 82.1 82.100 000 0 35.4 35.490 900 0 82.6 82.660 600 0 35.4 35.490 900 0 82.6 82.660 600 0 35.4 35.460 600 0 82.6 82.670 700 0 35.91 35.9100 00 82.7 82.750 500 0 35.4 35.440 400 0 35.4 35.440 400 0 35.4 35.490 900 0 35.2900 35.2900 35.78 35.7800 00
Bunc Buncom ombe be Bunc Buncom ombe be Haywood Haywood Hend Hender erso son n Bunc Buncom ombe be Bunc Buncom ombe be Mit Mitchel chelll Bunc Buncom ombe be Bunc Buncom ombe be Bunc Buncom ombe be Madi Madiso son n
82.6 82.650 500 0 Hend Hender erso son n 82.6 82.650 500 0 Hend Hender erso son n 82.6 82.670 700 0 Bunc Buncom ombe be 82.9100 82.9100 Transylvan Transylvania ia 83.1 83.100 000 0 Haywo Haywood od
197 1977 7 1977 1977 1997 1997 1977 1977 1977 1977 197 1977 7 197 1977 1977 1977 1977 1977 1977 1977 1989 1989
Debr Debris is Flow Flow Debr Debris is Flow Flow Slump Slump Debr Debris is Flow Flow Debr Debris is Flow Flow Debr Debris is Flow Flow Debr Debris is Flow Flow Debr Debris is Flow Flow Debr Debris is Flow Flow Debr Debris is Flow Flow Slum Slump p
Zatm Zatm Zatm Zatm Zsp Zatm Zatm Zatm Zatm Zatm Zatm Ymg Ymg Zatm Zatm Zatm Zatm Zatm Zatm Zsr Zsr
NC09 NC093 3 NC09 NC095 5 NC102 NC102 NC09 NC095 5 NC09 NC095 5 NC09 NC095 5 NC0 NC098 NC09 NC095 5 NC09 NC095 5 NC095 NC095 NC09 NC092 2
36 36 36 36 37 37 37 37 37 38 38
NW SW S S E NE SW SW SW NE NW
1977 1977 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow 1977 1977 Debr Debris is Flow Flow Slump Slump 1989 1989 Slum Slump p
Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zsp Zsp
NC09 NC093 3 NC09 NC093 3 NC09 NC095 5 NC095 NC102 NC102
38 38 38 39 39
SE SE SW E S
35.350 35.3500 0 82.910 82.9100 0 35.46 35.4600 00 82.6 82.670 700 0 35.4 35.46 600 82.6 82.670 700 0
Haywoo Haywood d Bunc Buncom ombe be Bunc Buncom ombe be
1988 1988 Slump Slump 1977 1977 Debri Debriss Flow Flow 197 1977 Deb Debris ris Flow Flow
Zatm Zatm Zatm Zatm Zatm Zatm
NC095 NC095 NC09 NC095 5 NC09 NC095 5
39 40 40
NE SE SE
35.4 35.460 600 0 82.6 82.670 700 0 35.4 35.480 800 0 82.6 82.670 700 0 35.4 35.490 900 0 82.6 82.680 800 0 35.4 35.490 900 0 82.6 82.680 800 0 35.4 35.490 900 0 82.6 82.670 700 0 35.5 35.50 000 82.6 82.670 700 0 35.4 35.480 800 0 82.6 82.670 700 0 35.4 35.470 700 0 82.7 82.700 000 0 35.4 35.440 400 0 82.6 82.650 500 0 35.4 35.49 900 82.6 82.660 600 0 35.4 35.480 800 0 82.6 82.660 600 0
Bunc Buncom ombe be Bunc Buncom ombe be Bunc Buncom ombe be Bunc Buncom ombe be Bunc Buncom ombe be Bunc Buncom ombe be Bunc Buncom ombe be Bunc Buncom ombe be Hend Hender erso son n Bunc Buncom ombe be Bunc Buncom ombe be
1977 1977 1977 1977 1977 1977 1977 1977 1977 1977 197 1977 197 1977 7 197 1977 7 1977 1977 197 1977 1977 1977
Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm Zatm
NC09 NC095 5 NC09 NC095 5 NC09 NC093 3 NC09 NC093 3 NC09 NC093 3 NC09 NC095 5 NC09 NC095 5 NC09 NC095 5 NC09 NC093 3 NC09 NC095 5 NC09 NC095 5
41 41 41 41 41 41 42 42 46 46 1977 1977
E E W SW W E SE NW SE E SE
156
Debr Debris is Flow Flow Debr Debris is Flow Flow Debr Debris is Flow Flow Debr Debris is Flow Flow Debr Debris is Flow Flow Deb Debris ris Flow Flow Debr Debris is Flow Flow Debr Debris is Flow Flow Debr Debris is Flow Flow Deb Debris ris Flow Flow Debr Debris is Flow Flow
Appendix E: SINMAP Results
Stable Area (km²) % of Region # of Landslides % of Slides LS Density
3796.6 53.5 12 8.6 0.003
Stable Area (km²) % of Region # of Landslides % of Slides LS Density
1735.2 24.5 2 1.4 0.001
Stable Area (km²) % of Region # of Landslides % of Slides LS Density
1735.2 24.5 2 1.4 0.001
Stable Area (km²)
1735.2
Moderately Stable
Default Parameters - 30m DEM Quasi-Stable Lower Threshold
949.2 13.4 14 10.0 0.015
Moderately Stable
544.1 7.7 5 3.6 0.009
3112.1 44.0 46 32.9 0.015
Recharge 125mm – 30mDEM Quasi-Stable Lower Threshold
358.0 5.1 2 1.4 0.006
Moderately Stable
1114.8 15.7 73 52.1 0.065
Recharge 50mm – 30m DEM Quasi-Stable Lower Threshold
358.0 5.1 2 1.4 0.006
Moderately Stable
1216.3 17.1 41 29.3 0.034
544.1 7.7 5 3.6 0.009
3103.3 44.0 46 32.9 0.015
Recharge 250mm – 30m DEM Quasi-Stable Lower Threshold
358.0
544.1
157
3102.1
Upper Threshold
15.3 0.2 0 0.0 0.000
Upper Threshold
1315.9 18.6 84 60.0 0.064
Upper Threshold
1286.7 18.2 81 57.9 0.063
Upper Threshold
1278.7
Defended
0.1 0.0 0 0.0 0.000
Defended
3.8 0.1 1 0.7 0.263
Defended
28.1 0.4 4 2.9 0.142
Defended
53.6
Total
7092.3 100.0 140 100.0
Total
7069.1 100.0 140 100.0
Total
7055.4 99.9 140 100.1
Total
7071.7
% of Region # of Landslides % of Slides LS Density
24.5 2 1.4 0.001
Stable Area (km²) % of Region # of Landslides % of Slides LS Density
1735.2 24.5 2 1.4 0.001
Stable Area (km²) % of Region # of Landslides % of Slides LS Density
2524.7 35.7 8 5.7 0.003
Stable Area (km²) % of Region # of Landslides % of Slides LS Density
3673.9 53.0 14 11.5 0.004
Stable
5.1 2 1.4 0.006
Moderately Stable
7.7 5 3.6 0.009
43.9 46 32.9 0.015
Recharge 375mm – 30m DEM Quasi-Stable Lower Threshold
358.0 5.1 2 1.4 0.006
544.1 7.7 5 3.6 0.009
3102.1 43.8 46 32.9 0.015
18.1 78 55.7 0.061
Upper Threshold
1278.7 18.1 77 55.0 0.060
Recharge 125mm, C = .1-.25 – 30m DEM Moderately Quasi-Stable Lower Upper Stable Threshold Threshold
535.7 7.6 4 2.9 0.007
Defended
61.4 0.9 8 5.7 0.130
Defended
2355.6 33.3 63 45.0 0.027
811.2 11.5 60 42.9 0.074
Default Parameters - 10m DEM Moderately Quasi-Stable Lower Stable Threshold 868.0 1120.2 1229.4 12.5 16.1 17.7 11 24 69 9.0 19.7 56.6 0.013 0.021 0.056
Upper Threshold 44.3 0.6 4 3.3 0.090
Defended
Upper Threshold
Defended
Moderately Stable
844.5 11.9 4 2.9 0.005
0.8 7 5.0 0.131
Recharge 50mm- 10m DEM Quasi-Stable Lower Threshold
158
3.8 0.1 1 0.7 0.263
0.6 0.0 0 0.0 0.000
100.1 140 100.0
Total
7079.5 100.1 140 100.0
Total
7075.5 100.1 140 100.1
Total
6936.4 100.0 122.0 100.0
Total
Area (km²) % of Region # of Landslides % of Slides LS Density
1591.9 23.1 0.0 0.0 0.000
Stable Area (km²) % of Region # of Landslides % of Slides LS Density
1591.9 23.2 0.0 0.0 0.000
Stable Area (km²) % of Region # of Landslides % of Slides LS Density
1591.9 23.1 0.0 0.0 0.000
Stable Area (km²) % of Region # of Landslides % of Slides LS Density
1591.9 23.0 0.0 0.0 0.000
Stable Area (km²)
2306.1
322.7 4.7 2.0 1.6 0.006
494.4 7.2 5.0 4.1 0.010
2944.9 42.7 33.0 27.0 0.011
1514.0 22.0 82.0 67.2 0.054
Recharge 125mm - 10m DEM Moderately Quasi-Stable Lower Stable Threshold 322.7 494.4 2932.5 4.7 7.2 42.7 2.0 5.0 33.0 1.6 4.1 27.0 0.006 0.010 0.011
Upper Threshold 1455.2 21.2 74.0 60.7 0.051
Defended
Recharge 250mm - 10m DEM Moderately Quasi-Stable Lower Stable Threshold 322.7 494.4 2930.9 4.7 7.2 42.5 2.0 5.0 33.0 1.6 4.1 27.0 0.006 0.010 0.011
Upper Threshold 1434.2 20.8 70.0 57.4 0.049
Defended
Recharge 375mm -10m DEM Moderately Quasi-Stable Lower Stable Threshold 322.7 494.4 2930.8 4.7 7.2 42.4 2.0 5.0 33.0 1.6 4.1 27.0 0.006 0.010 0.011
Upper Threshold 1432.4 20.7 70.0 57.4 0.049
Defended
Recharge 125mm, C = .1-.25 – 10m DEM Moderately Quasi-Stable Lower Upper Stable Threshold Threshold 495.1 789.9 2269.2 959.3
159
24.8 0.4 0.0 0.0 0.000
70.8 1.0 8.0 6.6 0.113
126.4 1.8 12.0 9.8 0.095
138.8 2.0 12.0 9.8 0.086
Defended
50.2
6892.7 100.0 122.0 100.0
Total
6867.5 100.0 122.0 100.0
Total
6900.5 100.0 122.0 100.0
Total
6911.0 100.0 122.0 100.0
Total
6869.8
% of Region # of Landslides % of Slides LS Density
33.6 5.0 4.1 0.002
7.2 4.0 3.3 0.008
11.5 5.0 4.1 0.006
160
33.0 45.0 36.9 0.020
14.0 56.0 45.9 0.058
0.7 7.0 5.7 0.139
100.0 122.0 100.0
Appendix F: SHALSTAB Results
PERCENT CUMPERCENT CUMPERCENT INSTABILI INSTABILITY TY 14.87 14.87 Ch C hronic Instability 20.50 35.37 < -3.1 11.40 46.76 -3 -3.1 - -2.8 10.55 57.32 -2 -2.8 - -2.5 6.40 63.72 -2 -2.5 - -2.2 0.81 64.53 > -2.2 35.47 100.00 S Sttable
Cohesion 2000, SFA 26 – 30m DEM NUMSLIDES NUMSLIDES PERSLIDES CUMSLIDES CUMSLIDES 10 45.45 45.45 5 22.73 68.18 2 9.09 77.27 2 9.09 86.36 0 0.00 86.36 1 4.55 90.91 2 9.09 100.00
Area km² CUMAREA LS DEN 243.8 243.8 0.041 336.2 580.0 0.015 186.9 766.9 0.011 173.1 940.0 0.012 105.0 1044.9 0.000 13.3 1058.2 0.075 581.8 1639.9 0.003
PERCENT CUMPERCENT CUMPERCENT INSTABILI INSTABILITY TY 0.04 0.04 Ch Chronic Instability 2.00 2.04 < -3.1 4.19 6.23 -3 -3.1 - -2.8 9.63 15.85 -2 -2.8 - -2.5 9.20 25.05 -2 -2.5 - -2.2 1.99 27.04 > -2.2 72.96 100.00 St Stable
Cohesion 2000, SFA 45 – 30m DEM NUMSLIDES NUMSLIDES PERSLIDES CUMSLIDES CUMSLIDES 0 0.00 0.00 3 13.64 13.64 2 9.09 22.73 5 22.73 45.45 1 4.55 50.00 0 0.00 50.00 11 50.00 100.00
Area km² CUMAREA LS DEN 0.7 0.7 0.000 32.8 33.5 0.092 68.7 102.2 0.029 157.8 260.0 0.032 150.8 410.8 0.007 32.6 443.4 0.000 1196.6 1639.9 0.009
Cohesion 9427.41, SFA 45 (SINMAP Upper Bound) – 30m DEM PERCENT CUMPERCENT CUMPERCENT INSTABILI INSTABILITY TY NUMSLIDES NUMSLIDES PERSLIDES CUMSLIDES CUMSLIDES Area km² CUMAREA LS DEN 0.00 0.00 Ch Chronic Instability 0 0.00 0.00 0.0 0.0 0.000 0.00 0.00 < -3.1 0 0.00 0.00 0.0 0.0 0.000 0.00 0.00 -3.1 - -2.8 0 0.00 0 .0 0 0.0 0.0 0.000 0.01 0.01 -2.8 - -2.5 0 0.00 0 .0 0 0.2 0.2 0.000 0.04 0.05 -2.5 - -2.2 0 0.00 0 .0 0 0.6 0.8 0.000 0.03 0.08 > -2.2 0 0.00 0.00 0.5 1.3 0.000 99.92 100.00 S Sttable 22 100.00 100.00 1638.7 1639.9 0.013
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Default Results – 30m DEM NUMSLI NUMSLIDES DES PERSLID PERSLIDES ES CUMSLI CUMSLIDES DES 0 0.00 0.00 3 13.64 13.64 4 18.18 31.82 6 27.27 59.09 2 9.09 68.18 0 0.00 68.18 7 31.82 100.00
Area Area km² CUMAREA LS DEN 0.7 0.7 0.000 68.3 69.0 0.044 117.7 186.7 0.034 235.1 421.8 0.026 201.8 623.6 0.010 41.4 665.0 0.000 974.9 1639.9 0.007
Cohesion 0, SFA 26 (SINMAP Lower Bound) – 30m DEM PERCENT CUMPERCENT CUMPERCENT INSTABILI INSTABILITY TY NUMSLIDES NUMSLIDES PERSLIDES CUMSLIDES CUMSLIDES 25.59 25.59 Ch C hronic Instability 11 50.00 50.00 24.52 50.11 < -3.1 6 27.27 77.27 9.60 59.71 -3 -3.1 - -2.8 3 13.64 90.91 8.72 68.43 -2 -2.8 - -2.5 0 0.00 90.91 5.20 73.63 -2 -2.5 - -2.2 2 9.09 100.00 0.38 74.01 > -2.2 0 0.00 100.00 25.99 100.00 S Sttable 0 0.00 100.00
Area km² CUMAREA LS DEN 419.7 419.7 0.026 402.1 821.8 0.015 157.5 979.3 0.019 143.0 1122.2 0.000 85.2 1207.5 0.023 6.3 1213.8 0 .0 0 0 426.2 1639.9 0.000
PERCENT CUMPERCENT CUMPERCENT INSTABILIT INSTABILIT 0.04 0.04 Ch Chronic Instability 2.00 2.04 < -3.1 4.19 6.23 -3 -3.1 - -2.8 9.63 15.85 -2 -2.8 - -2.5 9.20 25.05 -2 -2.5 - -2.2 1.99 27.04 > -2.2 72.96 100.00 St Stable
Cohesion 0, SFA 45 – 30m DEM NUMSLIDES NUMSLIDES PERSLID PERSLIDES ES CUMSLIDES CUMSLIDES 0 0.00 0.00 3 13.64 13.64 2 9.09 22.73 5 22.73 45.45 1 4.55 50.00 0 0.00 50.00 11 50.00 100.00
Area km² CUMAREA LS DEN 0.7 0.7 0.000 32.8 33.5 0.092 68.7 102.2 0.029 157.8 260.0 0.032 150.8 410.8 0.007 32.6 443.4 0.000 1196.6 1639.9 0.009
PERCENT CUMPERCENT CUMPERCENT INSTABILIT INSTABILIT 1.08 1.08 Ch Chronic Instability 7.55 8. 8 .62 < -3.1 9.66 18.28 -3 -3.1 - -2.8
Cohesion 2000, STA 35 – 30m DEM NUMSLIDES NUMSLIDES PERSLID PERSLIDES ES CUMSLIDES CUMSLIDES 3 13.64 13.64 4 18.18 31.82 5 22.73 54.55
Area km² CUMAREA LS DEN 17.6 17.6 0.170 123.8 141.4 0.032 158.4 299.8 0.032
PERCENT PERCENT CUMPERC CUMPERCENT ENT INSTABIL INSTABILITY ITY 0.04 0.04 Ch Chronic Instability 4.17 4.21 < -3.1 7.18 11.39 -3 -3.1 - -2.8 14.33 25.72 -2 -2.8 - -2.5 12.31 38.03 -2 -2.5 - -2.2 2.53 40.55 > -2.2 59.45 100.00 St Stable
162
13.97 9.61 1.73 56.40
32.25 41.86 43.60 100.00
-2 -2.8 - -2.5 -2 -2.5 - -2.2 > -2.2 St Stable
PERCENT CUMPERCENT CUMPERCENT INSTABILIT INSTABILIT 3.34 3.34 Ch Chronic Instability 14.04 17.38 < -3.1 13.00 30.38 -3 -3.1 - -2.8 14.94 45.31 -2 -2.8 - -2.5 9.42 54.73 -2 -2.5 - -2.2 1.49 56.23 > -2.2 43.77 100.00 St Stable
2 2 0 6
9.09 9.09 0.00 27.27
63.64 72.73 72.73 100.00
Cohesion 0, STA 35 – 30m DEM NUMSLIDES NUMSLIDES PERSLID PERSLIDES ES CUMSLIDES CUMSLIDES 3 13.64 13.64 9 40.91 54.55 2 9.09 63.64 3 13.64 77.27 1 4.55 81.82 0 0.00 81.82 4 18.18 100.00
229.1 157.6 28.4 925.0
528.9 686.6 715.0 1639.9
0.009 0.013 0.000 0.006
Area km² CUMAREA LS DEN 54.8 54.8 0.055 230.2 285.1 0.039 213.1 498.2 0.009 244.9 743.1 0.012 154.5 897.6 0.006 24.5 922.1 0.000 717.8 1639.9 0.006
Total 10m DEM Haywood - 26 1922 0 2 PERCENT CUMPERCENT INSTABILIT NUMSLIDES PERSLIDES CUMSLIDES Area km² CUMAREA LS DEN 32.57 32.57 Ch C hronic Instability 20.0 86.96 86.96 534.8 534.8 0.037 17.09 49.66 < -3.1 0.0 0.00 86.96 280.7 815.5 0.000 8.52 58.18 -3 -3.1 - -2.8 3.0 13.04 100.00 139.9 955.4 0.021 9.14 67.32 -2 -2.8 - -2.5 0.0 0.00 100.00 150.1 1105.5 0.000 6.60 73.92 -2 -2.5 - -2.2 0.0 0.00 100.00 108.3 1213.8 0.000 3.05 76 76.97 > -2.2 0.0 0.00 100.00 50.2 1264.0 0.000 23.04 100.01 St Stable 0.0 0.00 100.00 378.3 1642.3 0.000 Total 10m DEM Haywood - 26 1922 2000 2 PERCENT CUMPERCENT INSTABILIT NUMSLIDES PERSLIDES CUMSLIDES Area km² CUMAREA LS DEN 21.35 21.35 Ch C hronic Instability 13.0 56.52 56.52 350.6 350.6 0.037 14.85 36.20 < -3.1 5.0 21.74 78.26 243.7 594.3 0.021 9.28 45.48 -3 -3.1 - -2.8 2.0 8.70 86.96 152.4 746.7 0.013 10.92 56.40 -2 -2.8 - -2.5 2.0 8.70 95 9 5.65 179.3 926.0 0.011 8.33 64.73 -2 -2.5 - -2.2 0.0 0.00 95.65 136.8 1062.8 0.000 4.02 68.75 > -2.2 0.0 0.00 95.65 66.0 1128.8 0.000 31.26 100.01 St Stable 1.0 4.35 100.00 513.3 1642.1 0.002
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Total 10m DEM Haywood - 35 1922 2000 2 PERCENT CUMPERCENT INSTABILIT NUMSLIDES PERSLIDES CUMSLIDES Area km² CUMAREA LS DEN 3.16 3.16 Ch Chronic Instability 6.0 26.09 26.09 51.9 51.9 0.116 6.85 10.01 < -3.1 7.0 30.43 56.52 112.6 164.5 0.062 7.26 17.27 -3 -3.1 - -2.8 1.0 4.35 60.87 119.2 283.7 0.008 12.95 30.22 -2 -2.8 - -2.5 4.0 17.39 78.26 212.7 496.4 0.019 12.78 43.00 -2 -2.5 - -2.2 3.0 13.04 91.30 209.9 706.3 0.014 6.83 49.83 > -2.2 0.0 0.00 91.30 112.1 818.4 0.000 50.17 100.00 St Stable 2.0 8.70 100.00 823.9 1642.3 0.002
PERCENT 7.02 11.20 9.83 14.55 12.46 6.27 38.67
Total 10m DEM Haywood - 35 1922 0 2 CUMPERCENT INSTABILIT NUMSLIDES PERSLIDES CUMSLIDES Area km² CUMAREA LS DEN 7.02 Ch C hronic Instability 10.0 43.48 43.48 115.2 115.2 0.087 18.22 < -3.1 5.0 21.74 65.22 183.9 299.1 0.027 28.05 -3 -3.1 - -2.8 1.0 4.35 69.57 161.4 460.5 0.006 42.60 -2 -2.8 - -2.5 5.0 21.74 91.30 239.0 699.5 0.021 55.06 -2 -2.5 - -2.2 1.0 4.35 95 9 5.65 204.7 904.2 0.005 61.33 > -2.2 0.0 0.00 95.65 103.0 1007.2 0.000 100.00 St Stable 1.0 4.35 100.00 635.0 1642.2 0.002
PERCENT 0.00 0.11 0.24 0.92 2.40 2.59 93.74
Total 10m DEM Haywood - 35 1922 9427.41 2 CUMPERCENT INSTABILIT NUMSLIDES PERSLIDES CUMSLIDES Area km² CUMAREA LS DEN 0.00 Ch Chronic Instability 0.0 0.00 0.00 0.0 0.0 0.000 0.11 < -3.1 2.0 8.70 8.70 1.8 1.9 1.111 0.35 -3.1 - -2.8 1.0 4.35 13 13.04 3.9 5.8 0.256 1.27 -2 -2.8 - -2.5 2.0 8.70 21.74 15.1 20.9 0.132 3.67 -2 -2.5 - -2.2 3.0 13.04 34 34.78 39.4 60.3 0.076 6.26 > -2.2 2.0 8.70 43.48 42.6 102.9 0.047 100.00 S Sttable 13.0 56.52 100.00 1539.3 1642.2 0.008
Total 10m DEM Haywood - 45 1922 0 2 PERCENT CUMPERCENT INSTABILIT NUMSLIDES PERSLIDES CUMSLIDES Area km² CUMAREA LS DEN 0.34 0.34 Ch Chronic Instability 0.0 0.00 0.00 5.6 5.6 0.000 2.29 2.63 < -3.1 8.0 34.78 34.78 37.6 43.2 0.213 3.37 6.00 -3 -3.1 - -2.8 2.0 8.70 43.48 55.4 98.6 0.036
164
8.46 11.85 7.70 65.99
14.46 -2 -2.8 - -2.5 26.31 -2 -2.5 - -2.2 34.02 > -2.2 100.00 S Sttable
3.0 7.0 0.0 3.0
13.04 30.43 0.00 13.04
56.52 86.96 86.96 100.00
139.0 194.6 126.5 1083.6
237.5 432.1 558.6 1642.2
0.022 0.036 0.000 0.003
Total 10m DEM Haywood - 45 1922 2000 2 PERCENT CUMPERCENT INSTABILIT NUMSLIDES PERSLIDES CUMSLIDES Area km² CUMAREA LS DEN 0.09 0.09 Ch Chronic Instability 0.0 0.00 0.00 1.6 1.6 0.000 0.99 1.09 < -3.1 5.0 21.74 21.74 16.3 17.9 0.307 1.69 2.78 -3 -3.1 - -2.8 2.0 8.70 30.43 27.8 45.7 0.072 4.92 7.70 -2 -2.8 - -2.5 3.0 13.04 43 43.48 80.8 126.5 0.037 8.50 16.20 -2 -2.5 - -2.2 4.0 17.39 60.87 139.5 266.0 0.029 6.39 22.59 > -2.2 2.0 8.70 69.57 104.9 370.9 0.019 77.41 100.00 S Sttable 7.0 30.43 100.00 1271.3 1642.2 0.006 Total 10m DEM Haywood - 45 1922 9427.41 2 PERCENT CUMPERCENT INSTABILIT NUMSLIDES PERSLIDES CUMSLIDES Area km² CUMAREA LS DEN 0.00 0.00 Ch Chronic Instability 0.0 0.00 0.00 0.0 0.0 0.000 0.00 0.00 < -3.1 0.0 0.00 0.00 0.1 0.1 0.000 0.01 0.01 -3.1 - -2.8 1.0 4.35 4.35 0.1 0.2 8.598 0.03 0.04 -2.8 - -2.5 0.0 0.00 4.35 0.5 0.7 0.000 0.15 0.19 -2.5 - -2.2 1.0 4.35 8.70 2.4 3.1 0.417 0.33 0.52 > -2.2 0.0 0.00 8.70 5.4 8.5 0.000 99.48 100.00 S Sttable 21.0 91.30 100.00 1633.7 1642.2 0.013 Total Default Values - 10m DEM Haywood PERCENT CUMPERCENT INSTABILIT NUMSLIDES PERSLIDES CUMSLIDES Area km² CUMAREA LS DEN 0.34 0.34 Ch Chronic Instability 0 0.00 0.00 5.6 5.6 0.000 3.96 4.30 < -3.1 8 34.78 34.78 65.0 70.6 0.123 5.21 9.51 -3 -3.1 - -2.8 2 8.70 43.48 85.5 156.1 0.023 12.38 21.89 -2 -2.8 - -2.5 5 21.74 65 65.22 203.2 359.3 0.025 15.61 37.50 -2 -2.5 - -2.2 6 26.09 91 91.30 256.3 615.6 0.023 9.52 47.02 > -2.2 0 0.00 91.30 156.4 772.0 0.000 52.98 100.00 S Sttable 2 8.70 100.00 870.1 1642.1 0.002
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