Instream Geomorphic Units from GUT
North Fork Asotin Creek
For this exercise, we examined two sites on North Fork Asotin Creek in the Asotin Watershed in Southeastern Washington. We will use the GUT program to compare the outputs between a site that is relatively simple and one that is far more complex.
2 North Fork Asotin F4
2.1: The in-channel geomorphology of this reach is very simple and straight. It is a single-channel stream and there is not much interesting going on.
2.2: I chose to compare the years 2011 and 2013 because I wanted there to be at least a 2-year difference between the years I analyzed.
2.3: There are similar Tier 2 units between 2011 and 2013. Each have bowl and mound transitions, bowls, mounds, planes, troughs, and walls present
2.4: Troughs and concave features seem to be dominant in each year surveyed and this seems to remain the same through time.
2.5: In both years, glide-run is by far the most common Tier 3 Unit.
2.6: The arrangement of the geomorphic units makes sense for the most part. However, one issue I am seeing is that there are fairly quick transitions from one feature to another.
2.7A Pool
GU Forcing: By Bar/Structure
GU Orientation: Streamwise
GU Position: Mid-Channel
Low Flow WS Slope: Moderate
Low Flow Relative Roughness: Low
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This would be considered a structurally forced pool and the key determining factor for this would be the geomorphic forcing unit. However, GUT is not able to capture the entire pool because it is not able to differentiate between the pool and the surrounding units.
2.7B Bar
GU Forcing: Planform
GU Orientation: Streamwise
GU Position: Bank attached
Low Flow WS Slope: Low
Low Flow Relative Roughness: Moderate
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This would be considered a point bar and the key determining factors for this would be geomorphic forcing, position, and orientation. However, GUT is not able to capture the entire bar and therefore classifies it as a margin-attached bar when it is actually a bank-attached bar.
2.7CÂ Planar
GU Forcing: Not forced
GU Orientation: Streamwise
GU Position: Mid-Channel
Low Flow WS Slope: Shallow
Low Flow Relative Roughness: Low
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This would be considered a glide and the key determining factor for this would be the low relative roughness. However, GUT is not able to differentiate between glides and runs so this could be either.
2.8
A: According to the topo lines this is a pool because it is located in a bowl.Â
B: GUT made the pool appear smaller than it actually is.
C: The pool I identified was larger than what GUT had classified as the pool.
3 North Fork Asotin F6
3.1: The in-channel geomorphology of this reach is a starch contrast to the previous reach. It is significantly more complex and sinuous and even has multiple threads.
3.2: I chose to compare the years 2011 and 2013 because I wanted there to be at least a 2-year difference between the years I analyzed.
3.3: There are similar Tier 2 units between 2011 and 2013. Each has bowl and mound transitions, bowls, mounds, planes, troughs, and walls present
3.4: This reach is better mixed, but from 2011 to 2013 there was more mount transition.
3.5: As with the Tier 2 Units, the Tier 3 Units are well mixed. However, in each year there are mid-channel and bank attached bars that shifted from 2011 to 2013.
3.6: The arrangement of the geomorphic units makes sense for the most part. However, one issue I am seeing is that there are fairly quick transitions from one feature to another.
3.7AÂ Pool
GU Forcing: Planform
GU Orientation: Streamwise
GU Position: Margin attached
Low Flow WS Slope: Low
Low Flow Relative Roughness: Low
​
This would be considered a structurally forced pool and the key determining factor for this would be geomorphic forcing. However, GUT is not able to capture the entire shape of the pool.
3.7B Bar
GU Forcing: Planform
GU Orientation: Streamwise
GU Position: Bank attached
Low Flow WS Slope: Low
Low Flow Relative Roughness: Moderate
​
This would be considered a point bar and the key determining factors for this would be geomorphic forcing, position, and orientation. However, GUT is not able to capture the entire bar and therefore classifies it as multiple bars.
3.7C Planar
GU Forcing: Not forced
GU Orientation: Streamwise
GU Position: Mid-Channel
Low Flow WS Slope: Shallow
Low Flow Relative Roughness: Low
​
This would be considered a glide and the key determining factor for this would be the low relative roughness. However, GUT is not able to differentiate between glides and runs so this could be either.
3.8
A: According to the thalweg and imagery below this is a pool because it is elevated.Â
B: GUT made the bar appear smaller than it actually is. by breaking it into several smaller bars.
C: The bar I identified was larger than what GUT had classified as the bar.
Differences between F4 & F6
4.1: The geomorphic units for reach 4 were not as evenly dispersed as they are in reach 6. Site 6 was significantly more complex in structure and therefore created more complex features.
4.2: Reach 6 is far from a boring straight stream and has multiple channels. It also has more mid-channel bars and is generally more sinuous than reach 4.
4.3: It may still be feasible to grasp the general trends within the stream, but the detail and clarity would be lost without as much data. It would be impossible to see how things have changed through times and therefore it would be impossible to determine if a unit is simply a fluke.
Synthesis
5.1: In the field we did not talk much about transition zones and this was a common unit that GUT assigned to many features. Also, it appears that GUT classifies things at a much finer scale than we did in our field trip.
5.2: When we discussed different Tier 3 Units in the field we did not talk about pocket pools and GUT has that as a unit. Also, it appears that GUT lumps a lot of mid-channel units into the glide-run category where we may have classified things differently.
- 5.3: In order to determine Tier 4 Units we must have vegetation and substrate data. We are not given substrate data so we cannot find the Tier 4 Units simply from the data we are given.
5.4: Personally, I prefer identifying units in the field versus using GUT. However, in the case where field identification is not feasible, it is still possible to determine geomorphic units using GUT. I am fairly confident in my ability to use GUT to differentiate between different geomorphic units.