Figure 3.12: The D-∞ Model (Tarboton, 1997)
The D-∞ Model assigns a flow direction based on steepest slope on a triangular facet (Tarboton, 1997). The automated methods covered in this report do not use the D-∞ approach, and so this method of watershed delineation is not further investigated.
Before computing filling pits and computing flow direction, the user may want to “burn-in” streams. This process raises the land surface cells off the stream cells by an arbitrary elevation so that streams delineated from the DEM match those produced in the National Hydrography Dataset (NHD) produced by the USGS. This step is not necessary for high resolution DEMs (Olivera et al., 1999).
Once flow direction has been calculated, a flow accumulation grid is computed. This is done by counting the number of contributing cells to each cell