GCD topographic of Feshie River

Map of the Feshie River with Budget Segregation mask

The map shows the Feshie river in Scotland with the budget segregation mask I created between years 2006 and 2005 based on a DEM of Difference and interpretation. It is useful to see how I identified the changes in the river over time to understand where the results came from. Interpretation of the results is below.

I chose Bank erosion on high magnitude changes at the edge of significant elevation differences. Bed lowering was based around low magnitude changes in an area that looked to be the channel (steep sides around a lower area inferred to be the banks of a channel). Bed raising was attempted to be based around an inferred channel (so looking for steep sides around a lower area) and bar development was based either on deposition near the side of a channel or notably higher above the channel (so a central bar)

Interpretation

Bank Erosion

The total volume of surface lowering for suspected bank erosion was 285±106 m^3, the graph showcases how bank erosion was typically occuring in the higher elevation changes which is consistent with bank failures.

Bar Development

The total volume of surface raising was 107±51 m^3 with vertical raising of 0.19±0.09m. The graph above and those data show that suspected bar development was occurring in the shorter change fraction which is consistent with the flat splats of deposition that occur in the development of bars.

Bed Lowering

The total volume of suspected bed lowering was 423±44 m^3 and vertical average lowering of 0.28±0.10 m. Coupled with the graph above, bed lowering is primarily occurring in the lower fraction of elevation change which makes sense since bed lowering is typically either scouring or other processes such as deflation that are relatively low magnitude vs erosion which typically involves bank failure, a high magnitude change.

Bed Raising

The total volume of suspected bed raising was 579±179 m^3 with a vertical average of 0.29±0.09 m. Coupled with the graph above, bed raising was occurring predominantly in the moderate vertical change fraction. This is consistent with the forces that drive bed raising: uplift, aggradation, and rebound. One conundrum is differentiating bed raising with bar development since they occur through very similar processes and with a DEM and DoD it is not clear where exactly the bars and the active channel are. This is likely where I'm the most uncertain

General conclusions

The budget segregations gave relatively expected results, but definitely demonstrate the subjectivity and uncertainty in developing the masks. I briefly compared my masks to the ones provided in the GCD folder and the biggest discrepancies were with the raising processes. It is discussed in the bed raising section why I believe the raising geomorphic interpretations are more inaccurate. I am confident that the high magnitude lowering areas were bank erosion based on the characteristic pattern of bank erosion following that pattern. Bed lowering is the second most confident, and that's mainly just because it was relatively easy to tell the difference between a large steep bank compared to a low gradient bed that lowered. The big uncertainty for me is deciding whether there was proper erosion or if there was some other effect. The bank erosion is likely true erosion due to how high magnitude it was, but were bed changes due to actual sediment entrainment/deposition or from another process? Ultimately, these are things that definitely come with time, familiarity, and practice. It is extremely cool to see how we can use simple elevation differences to hypothesize the processes occurring within a system. I see why a career was made off of this, on the face of it, simple analysis.

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