WHATS YOUR ANGLE SLOPE MODELING TERRAIN ANALYSIS Jessica

WHAT’S YOUR ANGLE? SLOPE MODELING & TERRAIN ANALYSIS Jessica Gormont & Rachel Shirley 3 rd Eastern Panhandle, West Virginia GIS Users Group Meeting September 18, 2009

INTRODUCTIONS • Jessica Gormont GIS Technician, Jefferson County • Rachel Shirley GIS Intern, Jefferson County • Project Members: – – Todd Fagan GIS Specialist, Jefferson County Jennie Brockman Planning & Zoning Director, Jefferson County Dr. Edward Snyder Professor, Shepherd University John Maxey Jefferson County Planning Commission

LINEUP • • Background Purpose Definitions Field QA Data Results Future Applications

BACKGROUND Project Culmination: • Planning concerns in the Blue Ridge Mountain Community • GIS Office tasked by County Commission to fill data gaps – slope, 2 ft contours, land cover • Will aid planning staff and public analyze topography

PURPOSE • Purpose: To create an accurate slope model for the entire County, focusing on the Blue Ridge Mountain Area • Slope 2 ft topographic contours, land cover

BLUE RIDGE MOUNTAIN STUDY AREA • “The Mountain”: all land in Jefferson County east of the Shenandoah River • Area = 24. 3 sq mi (11% of County) • Elevation = Approx. 250 ft to 1700 ft (1450 ft change) • Includes Federal, State, County, and privately owned land • Addresses = 3, 285 (13% of County) mostly residential

WHY USE GIS FOR STUDY? • Can generate slope over large areas quickly • Less chance for human error • Combine with other overlays for enhanced understanding of land conditions

DEFINITIONS - SLOPE Slope is “an inclined surface or ground that has a natural incline”. Measured in Percent or Degrees 50% = 26. 5° 100% = 45° 150% = 56. 3° Infinite = 90° Photo Source: Laser. Craft Inc.

DEFINITIONS - LIDAR Li. DAR (Light Detection And Ranging) is an optical remote sensing technology that utilizes light to gather topographic data. DEM Photo Source: Dewberry Hillshade

METHODS/DATA 5 methods compared: • Field calculated slope with laser range finder • 10 -meter Slope Model • 3 -meter Slope Model • 1 -meter Slope Model • Rise/Run using 1 -meter DEM and points obtained from GPS

FIELD CALCULATIONS • 34 locations for field slope verification • Selection Attributes: – Varying levels of slope (gentle, moderate, and steep) – Ownership (public vs. private) – Distribution over study area – Un-modified since 2003

FIELD CALCULATIONS • Equipment: – Contour XLRic Laser Rangefinder (Laser. Craft Inc. ) – Trimble Geo XT handheld GPS receiver

ACCURACY • Laser. Craft Contour XLRic Laser Rangefinder: – Range Accuracy = 0. 10 meter at 85 meters – Inclination = +/- 0. 1 degrees • Trimble Geo XT handheld GPS receiver: – Horizontal Accuracy = < 1 meter (submeter) – Vertical Accuracy = 1. 5 to 2 meters

FIELD WORK • Measured points: 10 ft and 40 ft from basepoint • Slope calculated by internal inclinometer • Gathered GPS points (at basepoint, 10 ft target, and 40 ft target) for mapping purposes Blue Ridge Elementary School Field Slope = 22%

DATA • 10 -meter Slope Model – 2003 USGS 10 -meter DEM (UTM NAD 1983) – Vertical Accuracy = +/- 7 meters • 3 -meter Slope Model – 2003 USGS 3 -meter DEM (UTM NAD 1983) – Vertical Accuracy = +/- 1 meter • 1 -meter Slope Model (Li. DAR) – 2005 USDA-NRCS 1 -meter DEM (UTM NAD 1983) – Vertical Accuracy = 0. 15 meter

DATA GENERATED 1) Drew slope lines between points 2) Used Hawth’s Analysis Tools to calculate slope of line for each DEM 3) Plotted model v. field slopes on graph 4) Obtained R 2 value for each dataset from linear regression model

10 -M NED DEM (USGS)

3 -M NED DEM (USGS)

1 -M LIDAR DEM (USDA-NRCS)

RESOLUTION PROGRESSION 10 -m Slope 3 -m Slope 1 -m Slope

RESULTS • 1 -meter Li. DAR DEM more accurate than other datasets available: – Higher R 2 value – Finer detail allows for more accurate representation of the surface

FINAL MAP • This is the map generated using the best available, most accurate, digital data

ZOOMING IN…

BLUE RIDGE ELEMENTARY SCHOOL Field Slope = 22% Slope Model = 16 – 24%

POTENTIAL FUTURE USES 1. 2 -ft topographic contours 2. Useful for baseline data for future comprehensive plans 3. Data freely accessible by citizens for planning purposes 4. If used, would provide monetary savings to the public 5. Better way to measure average slope for an area 6. Useful for determining amount of necessary remediation on a site 7. Sub-watershed and riparian zone delineation

TRUE 3 D LINE OF SIGHT ANALYSIS

HIGH RESOLUTION LAND COVER

POTENTIAL FUTURE USES CONTD. Land Stability Map: – Would include overlay of soils, geology, land cover, impermeable surfaces, tree canopy, etc – Could be combined with Universal Soil Loss Equation (USLE) to determine potential soil loss – Useful for assessing potential groundmovement and erosion-prone areas

SUMMARY • Most accurate data available • Reasonably represents the terrain in Jefferson County • Provides a good confidence of accuracy for 2 -ft contours • 1 -m Li. DAR can be used for planning purposes and combined with other data layers for the creation of valuable datasets

ACKNOWLEDGEMENTS • • • Jennie Brockman John Maxey Dr. Ed Snyder Mike Schwartz John Young University of Vermont

REFERENCES Aguilar, F. and J. Mills. 2008. Accuracy Assessment of Li. DAR-derived digital elevation models. The Photogrammetric Record 23(122): 148 -169. Beyer, H. L. 2004. Hawth's Analysis Tools for Arc. GIS. Available at: http: //www. spatialecology. com/htools. Laser. Craft Inc. 2009. Contour XLRic Laser Rangefinder. Norcross, GA. FEMA 2003. Federal Emergency Management Agency. Guidelines and Specifications for Flood Hazard Mapping Partners, Appendix A: Guidance for Aerial Mapping and Surveying. Available online at http: //www. fema. gov/library/view. Record. do? id=2206. FGDC 1998. Federal Geographic Data Committee. Geospatial Positioning Accuracy Standards, Part 3: National Standard for Spatial Data Accuracy. FGDC-STD-007. 3 -1998. Available online at http: //www. fgdc. gov/standards/projects/FGDC-standards-projects/accuracy/part 3/chapter 3. NDEP 2004. National Digital Elevation Program. Guidelines for Digital Elevation Data, Version 1. 0. Available online at http: //www. ndep. gov/NDEP_Elevation_Guidelines_Ver 1_10 May 2004. pdf. Trimble Navigation Limited 2009. Trimble Geo. XT Handheld Receiver. Sunnyvale, CA. USDA-NRCS 2005. United States Department of Agriculture-Natural Resources Conservation Service. 1 -m Li. DAR Raster Dataset. 07/31/2005. USGS 2003 a. United States Geological Survey. National Elevation Dataset (NED) 1/9 Arc Second (~ 3 m resolution). Available at: http: //seamless. usgs. gov/products/9 arc. php. USGS 2003 b. United States Geological Survey. National Elevation Dataset (NED) 1/3 Arc Second (~10 m resolution). Available at: http: //seamless. usgs. gov/products/3 arc. php.