Watershed of impoundment pond

[JessicaFein]

Hi,

I'm new at using the watershed tool.  I see that you can use and/or create pour points for stream gauge locations etc...  What if I'm trying to discover the watershed for an upland pond that is a polygon and not a point...should I be looking to find a pour point along the pond or is there a way to use the pond polygon area to use to find the watershed?  I'll ask secondarily, if I do a fill on the DEM will it fill my impoundment pond?

Thanks,

Jessica

[SepheFox]

Hi Jessica, to answer your second question, you can set a z limit for your fill, such that it won't fill your pond. You can try to figure out what that is, or just play around with the z limit until you fill surrounding sinks, but not your pond. As far as the pour point, you might try converting your pond polygon to a raster, so that all the cells of the pond will be used to find the contributing watershed area.

[GabrielUpchurch1]

For the pour points, I would test Sephe's suggestion first to see what you get but I suspect you may get watersheds for each cell in the pond.  I haven't tested this approach so it would be beneficial for you to try it.  Even if you get a bunch of small watersheds, you could post process the data into a single watershed for the whole pond.  Alternatively, if the pond has an outlet, dam, levee, spillway, etc., you could place a point there or if all land around the pond drains into the pond, you could use the pond's centroid.  General knowledge of the slope of the terrain and hydrology for the area will play into where you place a point.

As Sephe pointed out, you will need to experiment with the z limit parameter to avoid having your pond filled.