Watershed tool problem

[DarrenSmith]

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

[PatrickTaurman · Accepted solution]

Hi Darren,

In the Environments setting for the Watershed tool, can you set the Extent (under general Settings) to the flow direction raster, and then run the tool again and let me know if this helps.

Patrick

[Anonymous User]

Original User: dazzasmith

Thanks Patrick, that seems to have solved my issue. I was actually setting the extent of the part of the flow direction grid that I clipped out in my python script (i.e. the D8 input to the watershed tool), but it seems that the watershed tool needs the environment variable set otherwise strange results (such as those in the example) are encountered.

On a related but slightly different note: I think that I've actually had a discussion about this on ESRI forums before, which would be worth linking to, if only I could find it. Do you happen to have any idea how to list (only) your own forum posts (i.e. those tied to your ESRI global account), like you could with the old setup before they changed to the new forums?

Thanks again for your help.

Darren

[PatrickTaurman]

Darren,

Click on your name (dazzasmith) and select View Profile.  There is an option there to view all posts by you.

Patrick

[Anonymous User]

Original User: dazzasmith

Sorry, should have been more specific. I was looking for a way at listing all of my posts from the old forums. I hope ESRI haven't made this impossible.