30 METER DIGITAL ELEVATION MODEL ================================== COVERAGE NAME: Battle Creek Slopes FEATURE TYPE: RASTER -Arc/Info GRID format SOURCE: USGS 30 Meter Digital Elevation Models MINIMUM MAPPING UNIT: 30 meters (spatial resolution) AREAL EXTENT: Battle Creek Hydrologic Unit Dr. Paul Trichilo of Kier Associates and the KRIS project used 30 M USGS DEM data with queries in ArcInfo to define slope areas over 35% in the Battle Creek watershed. The USFS uses slope as an indicator of erosion risk with elevated risk beginning at 35% and slopes over 65% having high or extreme erosion risk. Bedrock types in steep areas are also very important in determining erosion risk. KIER ASSOC DATA QUALITY NOTE 30 M DEM data are not highly accurate at specific locations and are less useful in analysis than 10 M DEM data. DATE OF LAST UPDATE: 3/6/2003 INFO ITEMS: INPUT OUTPUT DATA DECI DESCRIPTION ITEM NAME WIDTH WIDTH TYPE MALS ---------- ----- ------ ---- ---- ------------------------------------ VALUE 4 10 B the elevation in meters (z=10) COUNT 4 10 B the number of cells with that value METHODS: 30 meter DEMs were merged together from Quads. Seamlines were then filtered out and sinks were filled. The Z Value is 30. These are decimeter precision DEMs, so to save space, the elevations were mulitplied by 30 to create an integer GRID that would preserve the precision of the data. ADDITIONAL PROCESSING NOTES: Although the USGS DEM specification indicates that each posting is a floating point number, in most cases these have been rounded to the nearest integer. Therefore these lattices are stored as integers rather than floats, reducing storage requirements significantly. The DEMs were imported with the INT option. Because changing the projection of a grid requires resampling that can cause edge-matching problems, the DEMs have been left in their original projection, which is UTM zone 10 (west of longitude -120) or 11 (east of longitude -120). The best procedure for changing the projection is to merge adjacent grids first, then re-project. The most appropriate re-sampling methods are either bilinear interpolation or cubic convolution. Don't use the default nearest neighbor. DOCUMENTATION DATES: January, 2003: Reprojected to UTM NAD27 (no shift), and clipped to KRIS Project study area. Contact Name: P. J. Trichilo Institute for Fisheries Resources (IFR) 791 Eighth Street Arcata, CA 95521 Contact's Phone: (707) 822-9428