How to use Watershed tool in ArcPy

Question

I have 40 pour points and want to find out the area upstream of each pour point. I see that I can use the 'Watershed' tool for this. However, I do not want to do this manually. Therefore, I am trying to use ArcPy to delineate the upstream drainage areas in a for loop.

My question is how do I specify the pour point in the Watershed tool? The syntax is:

 outWatershed = Watershed('flowdir', 'pourpoint')

How do I specify the pour points in the for loop? My pour points are contained in a point feature class named 'delineation_points'. I learned that I can use data cursor for this purpose, but I do not understand how? For example,

 cursor = arcpy.da.SearchCursor('delineation_points','*')
 a = cursor.next()

Here, the variable 'a' gives me the field values for the first point in the 'delineation_points' feature class? If I use this as input to the 'Watershed' in place of 'pourpoint', it gives an error:

outWatershed = Watershed('flowdir', a)

I am sure there is something wrong with the way I am giving 'a' as the input.

Answer 1

The watershed tool wants a feature layer as the second input, you are passing a tuple. You could use the MakeFeatureLayer with a where_clause and an iterator to pass the pour points one at a time to the watershed tool.

However you don't have to do it one pour point at a time. Add all the pour points to the watershed tool, make sure you also add the unique numeric field to identify the pourpoint.

Watershed('flowdir', 'delineation_points', 'your Unique numeric pour_point_field')