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I am conducting a hydrologic analysis of DEMs. Suppose that I have the following basins in an area as shown below:enter image description here.
I need to get the cascading order of each of the basins. In other words, I need to know the next downstream basin for each one of those basins. Is there a function that can do this in QGIS, Whiteboxtools, or R.
I am aware of the trace downstream function but it gives the flow line to the outlet, not the next downstream basin.

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    You have some notable artifacts in your basins so, starting over would be prudent. Software such as, TauDEM, SAGA, GRASS or whitebox should all return the Strahler stream order which, in turn, defines the watershed order. TauDEM returns basins with the order as the raster value (you can then vectorize). The artifacts (linear boundaries) are likely a result of not preprocessing you DEM, age effect or using the D8 algorithm for deriving flow direction. An advantage of TauDEM or SAGA is that the D-infinity algorithm is avalible for flow direction.
    – Jeffrey Evans
    Commented Feb 14, 2021 at 19:06

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When the Hydro routines generated the different areas, it also created polygons and 'pour points' (if I remember correctly). The pour points have elevation associated. Maybe ordering from highest to lowest pour point is the answer you want.

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  • Which function? I cannot recall any function that generates pour points for each subbasin.
    – Mohamed Ismaiel Ahmed
    Commented May 15, 2020 at 21:42
  • It's been a long time since I used these tools, but I used GRASS GIS (grass.osgeo.org/grass78/manuals/addons/v.stream.inbasin.html ) and/or Map Windows GIS (hydrology.usu.edu/taudem/taudem5/index.html) that both generated pour points. If you have the polygons, you might find the lowest point with QGIS's routine Zonal Statistics (where you use the DEM as raster and your new polygons for the vector layer); the trouble with this is that maybe you filled some holes to do the hydro modeling and you'll need to use the DEM with the filled holes or your lowest point will just be a hole.
    – Geocurious
    Commented May 19, 2020 at 13:26

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