GCD for the River Feshie
Digital Elevation Models
Below are digital elevation models (and hillshades) for the River Feshie in Scotland. When compared, one can see how the braided channel changes over time. Geomorphic change detection (gcd) is applied to the years below.
2003
2006
2007
80% error surfaces
Below are the relative error values measured at 80% confidence. Darker shades indicate greater error.
2003 error
2006 error
2007 error
Change Detection
Change detections were derived by calculating a DEM of difference (DOD) between years of comparison. Above one can see DEM changes going from 2003 to 2007.
2006-2007
The diagram on the left depicts the change of sediment in between 2006 and 2007. Erosion and degradation can be seen in red, while deposition and aggradation can be seen blue. Channel avulsion is apparent as some of the braids are deposited on and others are cut away. The graph below shows the volume of sediment lost and gained based on elevation. There was a net loss of sediment over the course of a year. Sediment was deposited over a larger area more shallowly and was eroded at greater depths over less area.
2003-2007
I chose to compare the whole range of years to the final year to see if erosion and deposition was occurring in different locations and if channel metamorphosis was a slow process or occurred year by year. Volume lowered and raised was less than twice as great between the two, indicating that the channel was not avulsing in a focused direction. Areas that had been eroded were deposited on the following year and vice versa. The proportion of total difference between the two time periods was greater (~3x), demonstrating that the channel, while having varying levels of erosion and deposition was on an overall downward trend in total volume. This makes me believe channel/anabranch adjustments in River Feshie are semi-fluid, but channel aggradation or deposition over a reach is more consistent.
Identified Mechanisms
Geomorphic change mechanisms are identified in the black outlines below. Then change detection (same color scheme as above), the 2003 DEM and 2007 DEM are subsequently shown to help visually explain the classification given. It helps to hover your mouse near each feature as a point of reference.
Bar development occurs in areas where there is deposition Bank erosion can be seen where the bank (darker hillshades) within the main channel. The flow then adjusts around it. laterally adjust, changing the location of the flow vector.
Channel aggradation can be seen in the above video in areas Channel degradation is the opposite, where the areas where the banks don't move, but the z value(elevation) increases. between the banks stay the same, but the elevation within the channel deepens.
Budget Segregations
Total sediment volumes for each geomorphic change detection can be seen on the graph below. While there was greater erosion than deposition between 2003-2007, because of variation in number of features and feature size, these estimates don't accurately represent reach-wide proportions of sediment volumes.
Volumes for each geomorphic change mechanism identified are plotted below based on total elevation change.
Bar Development
Bank Erosion
Channel Aggradation
Channel Degradation
By comparing the distributions (not the volume) of the graphs above, it becomes apparent that bank erosion and bar development cause much greater elevational changes than aggradation and degradation. This concurs with the ease at which I identified bar development and bank erosion.