topic Re: Watershed Area for Random Point in ArcGIS Spatial Analyst Questions

Watershed Area for Random Point

LenDesson — Thu, 15 Aug 2013 18:12:23 GMT

I took a DEM and made a Flow Direction waster from it, ran Sink, there were some, and ran Fill. Re-ran Flow Direction.
What I am trying to do is find the Watershed for a random point (not necessarily a pour point). If I locate my random point and then run the Watershed tool, the tool gives me a very small area which does not seem to represent all the upstream cells that drain to it.

I found this really helpful link and though the processing extents were my problem, but I made sure to set those properly and I am stillgetting the small area result.

http://forums.arcgis.com/threads/78317-Watershed-tool-returns-only-immediate-catchment-not-entire-upstream-catchment-extent?highlight=watershed

Any ideas or other ways to go about it?

Re: Watershed Area for Random Point

NeilAyres — Fri, 16 Aug 2013 08:06:30 GMT

You need to use the snappour command / tool to snap your "random" pour point to a cell of highest accumulation within a certain radius.
If you just input any "random" point its likely that you will get many that have a quite tiny "watershed".
You will not see the small imperfections in your dem that are causing this.
N

Re: Watershed Area for Random Point

LenDesson — Fri, 16 Aug 2013 13:33:16 GMT

You need to use the snappour command / tool to snap your "random" pour point to a cell of highest accumulation within a certain radius.
If you just input any "random" point its likely that you will get many that have a quite tiny "watershed".
You will not see the small imperfections in your dem that are causing this.
N

Yep, this was the step I was missing... the Snap Pour Points tool snapped my random point to the closest high accumulation flow line, returned a raster which I was able to feed in to the Watershed tool to delineate the real watershed.