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Watershed tool problem

Question asked by dazzasmith on Feb 28, 2011
Latest reply on Mar 2, 2011 by geonetadmin
Hi,

I'm having issues with the Spatial Analyst (Hydrology) Watershed tool. I'm using a D8 flow direction grid (clipped to area of interest) and a point feature class (in FGDB) for my pour point data (in ArcGIS 9.3.1). The issue is that the results that I'm getting don't extend upstream as far as they should according to the flow direction grid cells. For example, why doesn't the grid cell directly above the pour point not get included in the watershed when its flow direction is 4 (i.e. straight down)? Has anyone else had similar issues with this? Please see attached screenshots:

ClippedD8andPourpoint.png - inputs and contextual stream network.
ProblematicWatershed(Green).png - output (light green area), which should extend upstream to include the rest of the catchment.

Please see attached link to make sense of the D8 symbology used:

http://www.ce.utexas.edu/prof/maidment/visual/dallas/david2/sld017.htm

Cheers,

Darren

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