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I have a reasonably accurate steam network for a watershed. This network includes the main channel, major forks, and tributaries. Each channel, fork, and tributary are individual records with single part geometries. The lines are topologically connected such that each tributary is snapped to its downstream geometry. Each line's geometry equals the flow direction of the watercourse it represents (lines point downhill). I also have a surface model with the same extent as the overall watershed. While these data currently exist in a vector datatype I can transform them into a raster datatype if needed.

I would like to create a new dataset such that each division delineates the (approximate) drainage for each tributary, fork, or main channel.

@WhiteboxDev states that Several [QGIS processing tools ] take stream network inputs and map subbasins in Creating catchment from point using DTM raster in QGIS? but I am unaware of what tool those would be.

Using ArcGIS Desktop, how do I create areas around my existing stream features where each area approximates the drainage around each stream feature?

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With available stream network, it is a very basic procedure in ArcGIS terms:

# CONVERT STREAMS TO RASTER
PolylineToRaster_conversion("STREAMS", "FID", "TARGET")
# CREATE VOID UNDER STREAMS
RasterCalculator_sa('Con(IsNull("TARGET"),"DEM")', "HOLES")
# FILL OUTPUT OF ABOVE
Fill_sa("HOLES", "FILLED")
# COMPUTE FLOW DIRECTION
FlowDirection_sa("FILLED", "FLOWDIR", "NORMAL", "")
# DELINEATE SUBCATCHMENTS
Watershed_sa("FLOWDIR", "TARGET", "WSHEDS", "VALUE")

Output: enter image description here

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  • Yes, thanks again @FelixIP! Your post is the most concise explanation of the hydrology tool set in ArcGIS. This was the exact path I followed earlier but the confusion was on my part. My problem was that I was comparing the resulting watershed boundaries against the vector version of my stream network. The vector lines were crossing over the watershed boundaries and that appeared to me an error with the algorithms which was untrue. Converting the rasterized version of the stream network back to vector data returned stream lines that did not cross basin boundary lines.
    – GBG
    Commented Sep 26, 2018 at 4:35

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