It is important to have a depressionless DEM for all subsequent hydrological analyses. Areas of internal drainage can cause problems later in the watershed delineation process. Direction of flow must be known for each cell, because it is direction of flow that determines the ultimate destination of water flowing across the surface. You must zoom in quite a way to do this, otherwise your pour point may not be located within a high-flow pathway! If your points are not in a high-flow pathway, move them before proceeding. You have just let ArcGIS automatically generate a series of watersheds. Automatic watershed delineation is easy, but does not give you the control to create basins specifically for pour points of your own selection. For this reason, the manual method is used almost exclusively. Raster data sets can represent drainage networks (e.g., the flow accumulation cells that have at least 5000 upstream cells). When making maps that present the results of watershed delineation you may want to show the grid-based flow network instead of, or in addition to, the vector stream network, especially if the two flow networks do not agree. Source.

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Last Modified: January 25, 2014 @ 12:00 am