How to #delineate a #watershed #GIS

How do you #delineate a #watershed using a #DEM.

One of the fun parts of sharing knowledge on #YouTube is entering uncharted waters.  While sharing GIS videos on YouTube, I realized there were insufficient videos to show how to delineate a watershed from scratch using ESRI’s ArcMap.  Actually on a basic search on YouTube, there was nothing.  While going to school is great, there has to be something online that can serve as a quick refreshers for students and professionals alike.

When undertaking this fun challenge, it was a nice refresher on the classic was to do this–especially when I had been delineating watersheds using hydrological model tools.  Reviewing the video, yea its a little rough on the edges, but it represents those fundamental steps in building the layers for delineating a watershed.

To start the watershed delineation process, we first start with the Mosaic step (click here for a video refresher).  After essentially joining raster layers, we start with filling the sinks and determining the flow direction.


After the mosaic, sink filling and flow direction determination, we started the flow accumulation and digitizing pour points.  In this video, we recieved great questions from +Josh McGee and +Gladys Chelangat who asked about the criteria for breaking the classification with “high flow accumulation” in the video comments.  We break the classes to define the difference between high flow and minimal flow.  The flow in channel will be significantly higher than those overland flow paths.


In the final video, we merged the watershed delineation steps to bring the components together.  We received a fundamental and important comment from Nototo on how important it was to have the same raster cells.  I was very happy to see a fellow GIS-er work through a problem.  As with any data you work with, it is important to check the project and in the case of raster with mosaic operations, you want to make sure all cells are the same resolution.


Did you find what you were looking for?  Feel free to share your appreciation in the comments of this blog, on Google+ (teachugis) or on Twitter (  As always, thanks for watching. 🙂





Leave a Reply

Please log in using one of these methods to post your comment: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s