AnsweredAssumed Answered

Watershed tool returns only immediate catchment, not entire upstream catchment extent

Question asked by dwilcoxars on Feb 22, 2013
Latest reply on Aug 5, 2016 by cbrailo
I have a 1m DEM derived from LiDAR.

I wish to determine the watershed catchment above a specific pour point.  The Pour Point is in a shapefile.

I am working with the tools in Spatial Analyst Tools > Hydrology.

I did a FlowDirection, then I did a Sink, and yes, there were some, so I did a Fill.  I then repeated the FlowDirection. 

I also did FlowAccumulation and FlowLength, as well as a SnapPourPoint to make sure my Pour Points were appropriately located.  I selected a search of 3 cells, and the point moved down three cells, so I moved it UP three cells from my original location, and my original location was selected, so I know it is an acceptable pour point.

With the Flow Length (using the Upstream option and making high values dark) I can see a beautiful representation of the flow.  I want to capture the entire extent of the flow into that point.  The FlowAccumulation at that point is over 65000, and the upward FlowLength is nearly 600.

However, when I try to define the Watershed using the Pour Point, I get just this small catchment immediately above the Pour Point, about 100 grid cell count, NOT the entire catchment.  Using the FlowDirection I moved one cell downstream, and got a smaller adjacent catchment of only 40 cells -- so it didn't even include the original try's extent, let alone ALL the upstream extent!

How does one set thresholds to say give me the whole thing, not just the immediate little bit.

Thanks.  I'm attaching a graphic to show what I mean.