OHD/HL/DMIP2 - Flow Direction

Flow direction grid files at the 30-m resolution 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)

For the American and Carson basins we downloaded 30-m DEM data from the USGS NED seamless data server for a rectangular box in terms of latitudes and longitudes. We then projected and filled the DEMs and calculated flow directions using ESRI software (ESRI fill and flow direction functions follow the algorithms described by Jenson and Domingue (1988)). The filled DEMs and flow direction grids are provided here. The raw DEMs that we downloaded are available from the DEM page. The processed grids provided here are in an Albers Equal-Area projection and specific projection information is provided in the '.prj' files. The elevation units are meters.

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.

Illinois and Blue River Basins in ABRFC

HRAP and ½ HRAP Resolution

To run the Hydrology Laboratory Research Distributed Hydrologic Model (HL-RDHM) we typically define flow directions for coarse resolution model cells that match or align with the grid of available radar-based forcing data (the HRAP grid). For the American and Carson basins we have derived flow direction grids for HRAP (~ 4 km) and ½ HRAP (~ 2 km) model cells using the algorithm described by Reed (2003). These grids are provided below in HRAP coordinates. Only the pixels we consider inside the basin have values in these grid files.

amer_fd2knclip.asc.gz
amer_fd4knclip.asc.gz
cars_fd2knclip.asc.gz
cars_fd4knclip.asc.gz

References:

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.