Watershed Delineation

GEOG 337- GIS II

The goal of this lab was to learn about watersheds and how to delineate them using ArcMap. A watershed is the area of land where all of the water that falls in it and drains off of it goes to a common outlet. They can vary in size, which this lab demonstrates.

First, I transformed the park boundary layer and watershed data to the same projection. To avoid edge issues, I created a 20 kilometer buffer around the park layer. I clipped the watershed layer into the park boundary, added a 30 arc-second DEM from ArcGIS Online, and clipped it to the road buffer layer.

Then, I ran the project raster tool with an output cell size of 60 meters and later 120 meters. A larger cell size generalizes the watershed more. After that, I calculated the flow direction of watershed and removed “sinks”. Sinks need to be filled in because they obstruct water flow. I then filled them in to create a new layer with the raised elevations.

To identify where flow accumulates, I ran the flow accumulation tool with the flow direction tool based on that output. A source layer was then used, which I converted into streams that ArcMap can recognize. Finally, I converted the streams into vectors for watersheds to be delineated. My final step was clipping everything to the park boundary.

Sources

Dr. Caitlin Curtis. University of Wisconsin-Eau Claire. New York State GIS Clearinghouse. CUGIR. ArcGIS online.