Delineate Watershed for a Polygon?

[ThomasBurley]

Hi,
I'm trying to determine how to delineate a wateshed for a polygon (example: lake polygon) so I can automate using Python scripting. ArcHydro has a "Batch Watershed Delineation from Polygons" tool that works well, but I don't believe the Watershed Processing tools of ArcHydro have been ported into geoprocessing like the ArcHydro Terrain Preprocessing tools have.

I don't want to use pour points for the lakes to delineate because the data I'm dealing with are sediment cores taken in the actual lake itself, so I need to use a polygon of the lake.


How could one do this using the Spatial Analyst hydrology tools and/or the ArcHydro Terrain Preproccessing tools available in the Spatial Analyst toolbox? I'm sure it's possible, I just haven't figured out how to do this...

thanks

Tom Burley
USGS, Austin TX

[DonovanCameron]

How Watershed Works

Watershed (Spatial Analyst)


Those two explain the watershed tools built into ArcGIS.


The watershed tool will require you to indicate 'pour points' and flow direction. Flow direction can be generated using the Flow Direction (Spatial Analyst) tool.

[ChrisSnyder]

Note that is entirely correct to rasterize your lake, and use the lake raster as input to the Watershed tool (along with your flow direction raster). Then the output watershed will represent all the cells that contribute flow to the lake as a whole (not just a "pour point" or "outlet" point of the lake). Using the rasterized lake is much easier and probably more correct. Also, while maybe more glitzy and seemingly user-friendly, the ArcHydro tools are all based on the existing Hydro toolset in Spatial Analyst. Nothing new - just repackaging.