Point delineation watershed output seemingly limited

Question

I have been delineating numerous watersheds worldwide using the point delineation tool. Starting with ASTER DEM and HydroSHEDS streams layers, I have been going through the following sequence of steps, which I understand to be fairly standard: DEM reconditioning, fill sinks, flow direction, flow accumulation, stream definition, stream segmentation, catchment grid delineation, catchment polygon processing, drainage line processing, adjoint catchment processing, drainage point processing, and finally point delineation. When choosing a point for point delineation, I typically look at the flow accumulation layer and choose the point of highest flow accumulation (i.e., the outflow).

I have done this successfully with a large number lakes, but without changing anything in the processing sequence, recently have run into the issue of the watershed output polygon cutting directly through "streams" shown in the flow accumulation layer, and seemingly restricted by something. I can go to the edge of the polygon and create a new "watershed" to include the streams that were cut out to manually get an accurate coverage of the watershed, but this obviously defeats the purpose of the tool.

I have scoured this forum for comparable problems and taken all suggested actions, but none have availed (i.e., checking that the processing extent includes the entire area, etc.). If anyone has any insight on this issue, I would greatly appreciate it! Please let me know if any additional information is needed for understanding.

MarkBoucher · Answer

...  recently have run into the issue of the watershed output polygon cutting directly through "streams" shown in the flow accumulation layer, and seemingly restricted by something. ...

The "restricted by something" statement makes me think to ask you to consider resetting the processing extents. See number 5 on this post: http://forums.arcgis.com/threads/48100-ArcHydro-Problem-Solvers?p=270146&viewfull=1#post270146.

Sometimes the processing extent can be set to one of the layers you are using and the processing results will stop at the "rectangle" limits of that layer. Resetting the processing extent fixes that.

ChristineDartiguenave · Answer

Point Delineation is a 2-step process:

1. Perform a local delineation within the extent of the catchment located under the point.
2. If point is located on a stream grid, find AdjointCatchment feature associated to local Catchment through GridID/GridID relationship and merge with local delineation.

If the GridIDs are out of synch between the Catchment and the AdjointCatchment features, you will end up with a delineation limited to the extent of the local catchment (and missing the upstream adjoint catchment).

Christine Dartiguenave
Esri Water Resources Team