I'm trying to analyse a raster in order to get watersheds at approximate 2 ha size, using flow direction/accumulation.

I've been using the steps outlined below, with initial conditions for cells starting at 2 ha. However whenever I do a raster calculator, I keep getting a raster with only one big black 0.


Flow Direction

Flow Accumulation

Raster Calculator @ 12500 cells

Focal Statistics


Raster to polygon

Am I doing something fundamentally wrong in this build up? Basically I need watersheds as polygons with a size of 2 ha, using a DEM Raster.

Additional information about raster DEM: Raster is about 40 mb, in a projected CRS and a cell size of 0,4 x 0,4 m covering about 420 ha.

X: 5992 Y: 4280

Float32 - Thirty two bit floating point

  • 1
    How big is your raster? Resolution? Is on a projected CRS? We need more details, so please, edit your question
    – aldo_tapia
    Nov 3, 2017 at 10:47
  • After computing flow accumulation use calculator to find cells >=12500. Most upstream cells are you first sinks. Compute their watersheds and erase this area from flow direction raster. Repeat starting with flow accumulation.
    – FelixIP
    Nov 3, 2017 at 18:37
  • Change Pixel depth from 32bit to 16bit and float to signed integer.
    – BBG_GIS
    Nov 4, 2017 at 12:05

1 Answer 1


Try calculating the z value for your fill tool. I would try without raster calculator. Create the polygon from the watershed's and then select the 2 ha areas from the shape area.

There is a good workflow for the z value of the sinks in your raster:

ArcGis desktop help

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