This tool will perform a watershedding operation based on a group of specified pour points, i.e. outlets or target cells. The user must specify the name of a flow pointer (flow direction) raster, a pour point file (raster or vector), and the output raster. If a vector pour point file is specified, it must be of a Point ShapeType (i.e. Point, PointZ, PointM, MultiPoint, MultiPointZ, MultiPointM). Watersheds will be assigned the input pour point ID value. If a raster pour point file is specified, pour point, or target, cells are denoted in the input pour-point image as any non-zero, non-NoData value. The flow pointer raster should be generated using the D8 algorithm.
Pour point vectors can be developed by creating a new point-type shapefile (Create New Shapefile) and using on-screen digitizing to designate pour point locations. It may help to have either a stream network image or a flow accumulation raster displayed in the background. it is recommended that you use the Jenson's Snap Pour Point method to ensure the digitized outlets are coincident with the digital stream contained within the DEM flowpaths.
To create a pour point raster, use the New Raster From Base Raster tool to create a blank image. The newly created raster image should have a background value of either zero or NoData. Display a stream network image or a contributing area image (bottom layer) and the newly created blank image (top layer). (Notice that if you filled the newly created blank image with zeros instead of NoData values, you will need to set the transparency of the displayed blank image as something greater than 0%, such that you can see the underlying base image.) Select the Modify Pixel Values in Image button or from the Tools menu. Zoom into and select the pixels associated with the features of interest and modify the value to some non-zero positive value. If you do not manage to get the outlet on the correct cell coincident with the stream, you can post-process the outlets raster using Jenson's Snap Pour Point method.
The following is an example of a Python script that uses this tool:
wd = pluginHost.getWorkingDirectory()
pointerFile = wd + "D8 pointer.dep"
outletsFile = wd + "pour points.shp"
outputFile = wd + "output.dep"
args = [pointerFile, outletsFile, outputFile]
pluginHost.runPlugin("Watershed", args, False)
This is a Groovy script also using this tool:
def wd = pluginHost.getWorkingDirectory()
def pointerFile = wd + "D8 pointer.dep"
def outletsFile = wd + "pour points.dep"
def outputFile = wd + "output.dep"
String[] args = [pointerFile, outletsFile, outputFile]
pluginHost.runPlugin("Watershed", args, false)