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Teaching about watersheds and river systems has long been a major theme of physical geography, earth science, and environmental science instruction.  ArcGIS Online now provides capabilities for educators and students to create watersheds, trace downstream, and create viewsheds, all of which can serve as an effective means to foster understanding of watersheds and river systems, how they are connected geographically and temporally, and why they are important.

Boulder, Colorado, like many mountain-front communities, is prone to periodic devastating floods.  To supplement a lesson that I wrote about floods in Boulder, I used the watershed tool in ArcGIS Online to create the watershed that is drained in Boulder Creek through the mouth of Boulder Canyon.  The area is 130.12 square miles, giving a clear reason why any major rapid snowmelt or any major rain event anywhere in that large area creates flood hazards for the city of Boulder.

Watershed upstream from Boulder Colorado.

Where does that water flow once it reaches Boulder?  To find out, I used the new Trace Downstream tool with a 15 mile limit.  The result makes it clear that the areas east and northeast of the city also bear the effects of potential floodwaters.

Trace 15 miles downstream from the mouth of Boulder Canyon, Colorado.

Using the same tool, I ran another Trace Downstream analysis and extended the distance to 3,000 miles.  The result, shown below, fits in well with the lesson but also in any lesson that asks students, "where does a cup of water flowing from my location flow through before it reaches the ocean?"

Trace from Boulder Colorado to the Gulf of Mexico.

Finally, to get a sense for how the terrain in Boulder is mountainous to the west of the mouth of the canyon but flattens to the Great Plains to the east, I used the new Create Viewsheds tool from a point on top of Green Mountain, above the famous Boulder Flatiron rock formations.  The viewshed, as the name implies, indicates the land viewable from a specific point, and in my case, I specified nine miles for the extent. The result of viewshed analysis can foster understanding of the terrain and how the terrain impacts streamflow and flooding.

Nine-mile Viewshed from Green Mountain.

These activities require an ArcGIS Online organizational subscription and to generate the analysis layers such as the ones I did above, you need to have publishing rights in that organization.  With your organizational subscription, examine the map I created above, and try these tools yourself for your own area!

You'll be amazed at how easy it is, and yet how powerful, because these tools can foster understanding of how streams, watersheds, and terrain are connected spatially and temporally.

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