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Introduction:
For this weeks lab I did a topographic change analysis on the River Feshie Scotland. I completed two topographic change detections from the years 2003-2004 and 2004-2005. Additionally I identified potential sites of the following four processes; Bank Erosion, Channel Bed Lowering, Channel Bed Rising, and Bar Development
Methods:
To carry out the topographic change detection I downloaded the GCD standalone software. The GCD standalone was used to create the graphs of total elevation change (erosion vs deposition) at a 80% probability threshold. To visualize the change I uploaded the DEMs of the River Feshie from Riverscapes Consortium from 2003-2005 to ArcGIS and used the change detection software to visualize the different processes during this time period. To compute a budget segregation I had create a new shape file in ArcGIS to use as a mask to identify examples of the four different processes and get the net change for the specific areas of interest.
Topographic change from 2003-2004
From 2003-2004 the net river change was degradation with elevation lowering being responsible for 69.75 percent of the change (thresholded value). The total thresholded volume of surface lowering was 2502.96 m^3 and 1085.45 m^3 surface raising.
Figure 1: Table of the topographic change values
2003-2004 Graphs:
Figure 2a (left) and 2b (right): Two graphs showing the topographic change from 2003-2004. Erosion is shown in red and deposition in blue. Figure 2a shows by volume and 2.b shows area.
Topographic change from 2004-2005:
From 2004 to 2005 the river was almost in a state of equilibrium with net degradation being about the same as net aggregation. The total thresholded volume for surface lowering was 6553.93 m^3 and raising was 5286.09 m^3.
2004-2005 Graphs
Figure 3a (left) and 3b (right): Two graphs showing the topographic change from 2004-2005. Erosion is shown in red and deposition in blue. Figure 3.a shows by volume and 3.b shows area.
Budget Segregation and Processes Identification:
To identify the different processes that were occurring from 2004-2005 I uploaded DEMs for the relevant years to ArcGIS pro. I then was able to use the change detection software built into ArcGIS pro to visualize the change. Once the change detection software was ran I looked for areas with the highest values as this would often indicate that something had occurred. To classify the different processes I looked at where in relation to the river it had occured. Bank erosion was the easiest to identify as it was shown in areas that had a lot of erosion near the banks. To find bed erosion I looked for areas of erosion centered in the middle channel. I used the same reasoning for channel bed raising but looked for deposition instead of erosion. I identified bar formation as portions of river that had high values of deposition either on the inside bend of the channel forming point bars or in the middle of the channel forming mid channel bars. Next I created a mask by creating a polygon shape file over the areas I identified as belonging to one of these four processes. By using this new shapefile I was able to carryout a budget segregation using the GCD standalone software.
Maps of Process Identification:
Figure 4.a and 4.b: The visualized change detection between 2004-2005. Figures 4.a and 4.b both show red being aggradation and blue being degradation. Figure 4.b shows the the different processes I attributed to the change.
Budget Segregation Graph:
Figure 5:
Shows the volume m^3 of change that the four processes were responsible for.
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