I use the ArcHydro Toolbox and ArcGIS 10.4

I ran through the regular steps of Filling Sinks of a DEM, Flow Direction, Flow Accumulation, Stream Definition, Stream segmentation, catchment grid delineation and finally catchment polygon processing. My result looks like the following picture. As you can see the catchments are always a little off. From my understanding they should always cut the segments of a stream nicely. Any idea what might cause this error and what to do about it?


  • 4
    This is normal behavior due to raster nature of Hydrology analysis. – FelixIP Mar 19 '18 at 19:43
  • 3
    It looks quite good considering the coarse raster data. You will never get the watershed delimitation passing through the junction node, the delimitations follow the raster bonduaries and the streams the center – Marco Mar 19 '18 at 21:22
  • I see. That makes sense. Thank you. Is it possible to decrease the size of the rasters to make it a little more accurate? – Canna Mar 19 '18 at 21:34
  • As the above comments indicate this is normal output and as @Marco says will never pass through the node. If it did you open up a whole can of worms with regards to topology. If it did then does the intersection exist in u/s or d/s catchment, well the answer is both! – Hornbydd Oct 27 '19 at 11:27

You need to derive the catchment from a higher resolution DEM raster and preserve the same resolution/cell size. It should be the same resolution that the stream features are based on, that way it can be accurate. Otherwise, I would try smoothing out the catchment polygons by a certain factor to get the streams closer to intersecting them (http://desktop.arcgis.com/en/arcmap/10.6/tools/cartography-toolbox/smooth-polygon.htm).

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