Lab 8: Morphometric Analysis

In this lab I used a DEM to create delineate a watershed in Big Cottonwood Canyon, Utah, using a DEM created from 2m lidar data and a defined pour point. Once the watershed boundaries were calculated, I identified a drainage network using a flow accumulation raster and classified the network using a Strahler stream order classification. Also within the delineated watershed, I performed a series of morphometric analyses to get a stronger understanding of the physical characteristics in Big Cottonwood Canyon. Using a 2 meter DEM provided for more fine scale data analysis, but its precision had some unexpected outcomes.

Location

Located south of Salt Lake City, this watershed was the location for Labs 6 & 7.

Task 1: Watershed Delineation

The two methods differ by .26 sq km, with .10 sq km of the difference explained by the area shown in detail at the mouth. For the mouth, the differing areas may be a result of different pour points or DEM resolution differences.

Task 2: Strahler Stream Order  

I ended with a more detailed stream network compared to the NHD dataset due to my use of the 2 meter lidar. The detail shows the NHD stream network compared to my identified stream order dataset. Max flow accumulation was 32,241,148 and the cutoff I used was 15,000. The most unique result from using the 2 meter data came at the valley bottom. The high resolution data was able to pick up drainage ditches as well as Big Cottonwood Creek, identifying channels running parallel to each other (on either side of a road) for much of the network. This outcome is shown in the detail above; periodically, the ditch on the north side of the valley joins the larger 5th order stream. For this reason, I would advise against using the 2 meter lidar data, it's resolution is just too fine. A stream network, at least for this lab, does not need to include small scale features such as ditches. 

Task 3: Other Morphometric Analyses     

Detail for each of the watershed scale maps above - click on the image to enlarge it.

Zonal Statistics for each watershed characteristic. 

Zonal statistics are calculated on all values of a raster within the zones of another user-specified dataset. In this lab, I used the watershed boundary as the zone and performed statistics on three different rasters: percent slope, planform curvature and profile curvature. Slope is calculated as a percent rise which uses the formula (rise/run)*100. Values range from 0 to very high numbers, essentially infinity. A 45 degree slope is a 100 percent slope. Curvature is the second derivative of a surface ('the slope of the slope'), for planform curvature, a positive number means the surface is convex up at that point, a negative number means a concave up surface at the cell. For profile curvature the opposite is true. A negative value indicates a convex up surface at that cell and a positive value indicates a cell which is concave up. Curvature values can be used to identify areas where drainage initiate as well as tracking locations of high potential erosion.

References

Joe Wheaton & Shannon Belmont Lab 08A - Morphometric Analysis. 2015. gis.joewheaton.org. Web. 18 March 2015. http://gis.joewheaton.org/assignments/labs/lab-8---choice/lab08a

Joe Wheaton & Shannon Belmont Lab 08A - Morphometric Analysis - Task 1 - Watershed Delineation. 2015. gis.joewheaton.org. Web. 18 March 2015. http://gis.joewheaton.org/assignments/labs/lab-8---choice/lab08a/task-1---watershed-delineation

Joe Wheaton & Shannon Belmont Lab 08A - Morphometric Analysis - Task 2 - Drainage Network Definition. 2015. gis.joewheaton.org. Web. 18 March 2015. http://gis.joewheaton.org/assignments/labs/lab-8---choice/lab08a/task-2---drainage-networkd-defnition

Joe Wheaton & Shannon Belmont Lab 08A - Morphometric Analysis - Task 3 - Morphometric Analyses. 2015. gis.joewheaton.org. Web. 18 March 2015. http://gis.joewheaton.org/assignments/labs/lab-8---choice/lab08a/task-3---morphometric-analyses

The table in this assignment was created using the HTML Table Generator