I am attempting to identify a few subwatersheds within a study area; however, the Spatial Analyst Watershed tool has not produced expected results. Apologies if this repeats previous questions, but I did not see any existing discussions that addressed my current situation in enough detail.
I have already used the Fill sinks and Snap Pour Points options to adjust the input datasets, yet the output results of the Watershed tool only creates a very small raster in the immediate vicinity of each pour point. I have used a 30m DEM as well as a resampled 10m version. All of the datasets use the same geographic coordinate system, so I'm not sure what else to consider. There must be some step in the process that I am missing that is not identified or explained in the tool help information.
I have attached a copy of the current Watershed tool result. Any assistance would be appreciated.
Thank you.
UPDATE 04/02/2015 17:15 ET
I started the process again from the beginning using the following steps:
1. New elevation raster with 3m resolution.
2. Fill sinks.
3. Resampled elevation raster to 10m resolution (per a suggestion that 3m might be too fine).
4. Created flow direction raster (with Force edge cells to flow out selected). tested with Force selected and not selected
5. Created flow accumulation raster.
6. Set Snap Pour Points using flow accumulation raster.
7. Ran Watershed tool using the Snap Pour Points.
To clarify, all input datasets use the same projected coordinate system (NAD 1983 HARN State Plane Delaware).
The results still seem to be unreliable. An updated version of the output is attached. The flow accumulation raster appears in the background. The black outline (previously created by a colleague) describes the larger watershed area of interest. My goal is to delineate subwatersheds behind sampling sites that are described by the pour points. Is there something else that I'm missing? Does the specific projection matter? Or is the elevation and flow direction data problematic because it is relatively flat?