Flow direction grid files at several resolutions are provided for the convenience of any participants who wish to use them. In
these grids, each cell contains an integer indicating one of eight possible flow directions. The ESRI code conventions are use in
the files provided: E=1, SE=2, S=4, SW=8, W=16, NW=32, N=64, NE=128. 'Filled' DEMs at the 30-m resolution are also made available
from this page.
30-m Resolution (~ 1 arc-second)
The 30-m DEM flow direction grids were produced by the National Severe Storms Laboratory (NSSL) (Documentation available at
http://www.nssl.noaa.gov/teams/western/basins/) using the Jenson and Domingue (1988) algorithms implemented via ESRI software.
NSSL's production of these DEM derivatives contributed to the Elevation Derivatives for National Applications (EDNA) project
(Documentation available from the EROS Data Center at
http://edna.usgs.gov/). NSSL processed 30-m DEM data ned-h for each USGS hydrologic unit (identified by a unique
hydrologic unit code (HUC)) including a surrounding buffer area.
From this site, the filled DEM and derived flow direction grids are provided for HUCs covering the DMIP2 Oklahoma basins. Note
that the DEMs on this page differ from those on the DMIP2 DEM page (
http://www.nws.noaa.gov/oh/hrl/dmip/2/dem.html) because they are filled and because they were processed in 2001 while the
data on the DMIP2 DEM page were recently obtained from the NED website (August, 2005). The 30-m DEM files are the same as those
described on the DMIP1 DEM page (http://www.nws.noaa.gov/oh/hrl/dmip//dem.html).
These grids are in an Albers-Equal Area Projection and the elevation units are centimeters. See the .prj files for details.
See (DEM page) for a description of the header format.
400-m Resolution (~15 arc-seconds)
Although 30-m flow directions are more accurate and we use them to derive the basin boundaries provided on this web site, we also provide 400-m flow directions. The 400-m flow directions were derived using the 400-m DEMs and digitized streamline files. Click here for a description of flow direction derivation procedures.
DEM (projected, 400-m, covers the entire RFC):
Flow directions (projected, 400-m, covers the entire RFC):
HRAP Resolution (~ 4 km)
Flow directions for the HRAP grid cells used to map multi-sensor precipitation data were derived using 400-m DEM data and DEM derivatives using the method described by Reed (2003). To be more GIS-compatible, the grid headers are provided in the polar Stereographic coordinates which is a simple transformation from the HRAP system. See Reed and Maidment (1997), http://www.nws.noaa.gov/oh/hrl/distmodel/hrap.htm, and http://www.nws.noaa.gov/oh/hrl/dmip/nexrad.html for more information on polar Stereographic coordinates.
abhrapfd.asc.gz: Flow directions for HRAP grid cells over the ABRFC domain. (For the Illinois R. and Blue River areas, the flow directions were actually derived from a 30-m resolution DEM while a 400-m DEM was used to derive flow directions for the rest of ABRFC).
Half-HRAP Resolution (~ 2 km)
illinois2kfd.asc.gz: half-HRAP flow directions for Elk R. basin
elk2kfd.asc.gz: half-HRAP flow directions for Elk R. basin
Jenson, S.K., and J.O. Domingue, Extracting topographic structure from digital elevation data for geographic information system analysis, Photogrammetric Engineering and Remote Sensing, 54, 1593-1600, 1988.
Reed, S., Deriving Flow Directions for Coarse Resolution (1 - 4 km) Gridded Hydrologic Modeling, Water Resources Research, 39, 9, 4-1-4-11, 2003.
Reed, S.M., and D.R. Maidment, Coordinate Transformations for Using Nexrad Data in GIS-based Hydrologic Modeling, Journal of Hydrologic Engineering, 174-182, Nov. 1997.