Landslides mapped from LIDAR imagery, Kitsap County, Washington By Jonathan P. McKenna, David J. Lidke, and Jeffrey A. Coe 2008 ABSTRACT: Landslides are a recurring problem on hillslopes throughout the Puget Lowland, Washington but can be difficult to identify in the densely forested terrain. However, digital terrain models of the bare-earth surface derived from LIght Detection And Ranging (LIDAR) data express topographic details sufficiently well to identify landslides. Landslides and escarpments were mapped using LIDAR imagery and field checked (when permissible and accessible) throughout Kitsap County. We relied almost entirely on derivatives of LIDAR data for our mapping, including topographic-contour, slope, and hill-shaded relief maps. Each mapped landslide was assigned a level of “high” or “moderate” confidence based on the LIDAR characteristics and on field observations. A total of 231 landslides were identified representing 0.8 percent of the land area of Kitsap County. Shallow debris topples along the coastal bluffs and large (>10,000 m2) landslide complexes are the most common types of landslides. The smallest deposit mapped covers an area of 252 m2, while the largest covers 0.5 km2. Previous mapping efforts relying solely on field and photo-grammetric methods identified only 57 percent of the landslides mapped by LIDAR (61 percent high confidence and 39 percent moderate confidence) although nine landslides previously identified were not mapped during this study. The remaining 43 percent identified using LIDAR have 12 percent high confidence and 88 percent moderate confidence. Coastal areas are especially susceptible to landsliding; 67 percent of the landslide area that we mapped lies within 500 m of the present coastline. The remaining 33 percent are located along drainages farther inland. The LIDAR data we used for mapping have some limitations including: 1) rounding of the interface area between low slope surfaces and vertical faces (that is, along the edges of steep escarpments) which results in scarps being mapped too far headward (one or two meters), 2) incorrect laser-distance measurements resulting in inaccurate elevation values, 3) removal of valid ground elevations, 4) false ground roughness, and 5) faceted surface texture. Several of these limitations are introduced by algorithms in the processing software that are designed to remove non-ground elevations from LIDAR data. Despite these limitations, the algorithm-enhanced LIDAR imagery does effectively “remove” vegetation that obscures many landslides, and is therefore a valuable tool for landslide inventories and investigations in heavily vegetated regions such as the Puget Lowland. 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CONTENTS This report (OF08-1292.pdf) is accompanied by a map (OF08-1292_map.pdf)two geographic information systems (GIS) shapefiles (deposits and scarps), and one hillshade relief image of Kitsap County. Hillshade.zip contains a subfolder called "ShadedRelief" which contains two subfolders called "hillshade" and "info" (when extracting the individual files from the zip file, the directory structure must be maintained in order for the files to open properly, for example, when extracting files in WinZip, the box "Use folder names" must be checked). The shapefiles are called "deposits" and "scarps" and are delineations of the deposits and headscarps, respectively, that were mapped using the LIDAR data. Both shapefiles contain attribute information. The "deposits" shapefile contains three attributes labeled (1) "Confidence", (2) "ID" and (3) "Area". The attribute "Confidence" is the certainty of the deposit which is populated as either "Moderate" or "High" confidence. The "ID" attribute is the identification number of each landslide deposit and corresponds to values shown on Sheet 1. The "Area" attribute is the square footage of each landslide deposit. The "scarps" shapefile contains two attributes labeled (1) "Confidence", and (2) "Length". The attribute "Confidence" is the certainty of the deposit which is populated as either "Moderate" or "High" confidence. The "length" attribute is the linear distance of each scarp in units of feet. The hillshade relief image was derived from the LIDAR DEM with a sun angle 45 degrees above the horizon and a sun azimuth of 315 degrees. SPATIAL INFORMATION: The spatial reference information for the "deposits" shapefile is as follows: Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Planar: Map_Projection: Map_Projection_Name: Lambert Conformal Conic Lambert_Conformal_Conic: Standard_Parallel: 47.500000 Standard_Parallel: 48.733333 Longitude_of_Central_Meridian: -120.833333 Latitude_of_Projection_Origin: 47.000000 False_Easting: 1640416.666667 False_Northing: 0.000000 Planar_Coordinate_Information: Planar_Coordinate_Encoding_Method: coordinate pair Coordinate_Representation: Abscissa_Resolution: 0.000000 Ordinate_Resolution: 0.000000 Planar_Distance_Units: survey feet Geodetic_Model: Horizontal_Datum_Name: North American Datum of 1983 Ellipsoid_Name: Geodetic Reference System 80 Semi-major_Axis: 6378137.000000 Denominator_of_Flattening_Ratio: 298.257222 Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -123.003095 East_Bounding_Coordinate: -122.459975 North_Bounding_Coordinate: 47.942779 South_Bounding_Coordinate: 47.394309 The spatitial reference information for the "scarps" shapefile is as follows: Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Planar: Map_Projection: Map_Projection_Name: Lambert Conformal Conic Lambert_Conformal_Conic: Standard_Parallel: 47.500000 Standard_Parallel: 48.733333 Longitude_of_Central_Meridian: -120.833333 Latitude_of_Projection_Origin: 47.000000 False_Easting: 1640416.666667 False_Northing: 0.000000 Planar_Coordinate_Information: Planar_Coordinate_Encoding_Method: coordinate pair Coordinate_Representation: Abscissa_Resolution: 0.000000 Ordinate_Resolution: 0.000000 Planar_Distance_Units: survey feet Geodetic_Model: Horizontal_Datum_Name: North American Datum of 1983 Ellipsoid_Name: Geodetic Reference System 80 Semi-major_Axis: 6378137.000000 Denominator_of_Flattening_Ratio: 298.257222 Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -123.001852 East_Bounding_Coordinate: -122.461147 North_Bounding_Coordinate: 47.942502 South_Bounding_Coordinate: 47.425610 The database contact is: Jonathan P. McKenna 303-273-8619 jmckenna@usgs.gov U.G. Geological Survey Denver Federal Center Box 25046 Mail Stop 966 Denver, CO 80225 CONTENTS: OF08-1292.pdf OF08-1292_map.pdf 00Readme.txt hillshade.zip ShadedRelief hillshade info data_files include: Deposits.dbf Deposits.prj Deposits.sbn Deposits.sbx Deposits.shp Deposits.shx Scarps.dbf Scarps.prj Scarps.sbn Scarps.sbx Scarps.shp Scarps.shx Metadata include: Deposits.shp.xml Depositsmetadata.txt.xml scarps.shp.xml Scarpsmetadata.txt.xml VI. INSTRUCTIONS AND DOCUMENTATION FOR U.S. GEOLOGICAL SURVEY OPEN-FILE REPORT 2008-1292 To access the data: The data files can be downloaded via the web from http://pubs.usgs.gov/of/2008/1292. The main product is a Portable Document Format (.pdf) map, which requires Adobe Acrobat for viewing. Acrobat software runs on a variety of systems, and is available for download free of charge from Adobe at http://www.adobe.com. Software Required: Adobe Acrobat (6.x, 7.x, or 8.x), or Adobe Acrobat Pro (6.x, 7.x, or 8.x), or the free Adobe Reader (6.x, 7.x, or 8.x) - 8.x is preferred ArcGIS 9.1 or later preferred, older versions may also work