The output of delineate watershed using Arc Hydro looks shrinked.

[hanakohinonn]

Hello,

 I'm trying to delineate watershed and sub watershed using Arc Hydro.

I  created watershed in the following procedure.

1. Dem Manipulation (Fill Sinks)　
2. Flow Direction　
3. Flow Accumulation　
4. Stream Definition　
5. Stream Segmentation
6. Catchment Grid Delineation　
7. Catchment Polygon Processing
8. Drainage Line Processing
9. Adjoint Catchment Processing
10. Drainage Point Processing

However, the output of Catchment Polygon Processing different from the shape of DEM .(Please Look at the picture. The red line is the out put of catchment polygon process, and the background picture is DEM.)

I don't know how to get the output in Catchment Polygon Processing which is the same shape of DEM.

Can someone please help me how I can do this?

Thank you.

[DeanDjokic · Accepted solution]

This is expected behavior.  The areas not covered by the catchments drain "out" of the DEM along DEM fringes.  They do not drain into the drainage lines generated using the terrain preprocessing steps (and stream definition threshold) you described.  Standard catchments exist only for areas draining into the drainage lines.  To test that, you can use the Arc Hydro flow path tracing tool.  Click on any point in those non-catchment-covered areas and you will notice that the flow path trace will "leave" the DEM without flowing into the streams.  If you want to cover those "fringe" areas, you can use Arc Hydro "Append Coastal Catchments" tool (in "Terrain Preprocessing" toolset).  That will create catchments over those areas, but note that they will not have drainage lines and will not be connected to the existing drainage lines.  This step is optional and is needed only if you have large "coastal" areas that might impact performance of other Arc Hydro tools if point of interest is those areas.  Based on your figure, that is not necessary.