HOW TO
Creating a watershed requires computing the flow direction across a Digital Elevation Model (DEM) as well as defining the locations used to determine the catchment area. A point feature class is often used as the ‘feature pour point data;’ however, the Watershed geoprocessing (GP) tool also accepts a flow accumulation threshold raster. Using a threshold raster is particularly useful when pour points do not exist and watersheds need to be generated for the entire DEM based on the junctions of a stream network that has been derived from flow accumulation.
Note:
This workflow requires a license for the Spatial Analyst extension.
Note:
This workflow assumes that all preparatory work on the input elevation surface, the DEM, has already been performed. For more information, refer to the following links:
• Creating a depressionless DEM
• Understanding drainage systems
Note:
For more information about these tools, refer to the following links:
• Flow Direction (Spatial Analyst)
• Flow Accumulation (Spatial Analyst)
Note:
Manual manipulation of the symbology on the flow accumulation raster shows the cells where water is prone to accumulate, which correlates with large cell values.
Code:
SetNull("RASTER_NAME" < 1800, 1)
Note:
This statement contains a hypothetical threshold value.
Note:
For more information, refer to the following links:
• Overview of the rules for Map Algebra
• Set Null (Spatial Analyst)
Note:
For more information, refer to the following link:
• Stream Link (Spatial Analyst)
Note:
For more information, refer to the following links:
• How Watershed works
• Watershed (Spatial Analyst)
Article ID: 000011964
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