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I'm using ArcGIS (Hydrology toolbox) for watershed delineation for a number of pour points, and I'm running into problems with very meandering rivers on extremely flat alluvial land (Amazon basin).

When I run the tool I get extremely small watershed rasters, or larger ones that break off at random points. I have used the exact same DEM, Flow Accumulation and Flow Direction raster files to successfully delineate other watersheds in more mountainous areas.

I'm assuming that the flat relief and meandering river path are to blame, but I'm not sure. The raster resolution is 90m, and I'm using a single point shapefile with the pour point manually placed dead centre on the river. (As I've successfully done previously.) I've tried with a raster pour point but there's no difference.

Does anyone have experience delineating watersheds for this type of river, or any suggestions?

This is what a section of the river looks like. This goes on for a few thousand kilometres.

One attempt at delineating a watershed.

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    Place point in the upper part of the catchment. Use flow direction as backlink raster and see if costpath goes through place where you stuck – FelixIP Apr 13 '16 at 18:32
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    Anything, e.g. dem or flow direction. It shows where stream running from source point – FelixIP Apr 13 '16 at 19:29
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    It means that your processing extent is wrong. Use environment settings and set it = flow direction raster, snap to flow direction, and cell size=fdir as well. I should of tell this from the shape of your 'watershed', straight lines is the sign to watch. Check this out gis.stackexchange.com/questions/157767/… – FelixIP Apr 13 '16 at 20:21
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    Great, that worked! I'd looked into that before but somehow didn't figure it out properly. Can you make a proper reply so I can mark it as the solution? Thanks a lot! – carderne Apr 13 '16 at 21:12
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    Glad it works. Just up vote the answer I pointed to in my comments please – FelixIP Apr 13 '16 at 21:14

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