Geomorphology and Watersheds

For our first project I decided to create two watersheds using ArcGIS 10.6 and compare the stream average gradient and sinuosity of all the streams in each watershed. Initially I wanted to see if urban land cover might be a driving factor in increasing stream gradient and sinuosity. 

Since we are here in Auburn, Alabama I created a watershed around Auburn, and for comparison created one just to the east where, from the map, I could see far less development. I used Arc’s Hydrology tools to trace out streams and delineate watersheds. I created a file geodatabase with the features classes, one for each watershed, and traced streams I wanted to compare.

I found a Python toolbox called Calculate Sinuosity which conveniently can iterate through a shapefile or feature class of streams, calculate the sinuosity, and adds that to a newly created field in the attribute table. I spent a lot of time trying to figure out how to make ArcGIS calculate stream gradient before re-discovering Tom Dilts’ custom toolbox Stream Gradient & Sinuosity Toolbox for ArcGISv10. It didn’t like my streams in the feature class, so I decided to use Stream to Feature to convert my streams raster (which I had clipped to each watershed) into polylines, and fed that to the tool - success. I then used the statistics function to find average gradient/slope, sinuosity, and length.

I found that the two watersheds were nearly identical. Chewacla Creek Watershed, which Auburn is in, has 20% urban cover compared to 1.77% in the Little Uchee watershed, and yet sinuosity and gradient were very similar. There was greater relief in the Little Uchee, but more urban cover in Chewacla. I suspect these two might balance one another. Or other factors are at work; more work needs to be done.

Attribute	Chewacla Creek Watershed	Little Uchee Watershed
Area	162.22 km2	165.92 km2
Streams	377	376
Relief (meters)	120.082	148.025
Average slope	0.033°	0.041°
Average sinuosity	0.907	0.897
Average length	991 meters	962 meters
Urban cover	20.89 %	1.77 %
Forest Cover	65.08 %	92.38 %
Agricultural cover	7.56 %	3.42 %
Open water	6.44 %	2.44 %