GUT

I utilized an the ArcGIS extension Geomorphic Unit Tool(GUT) to evaluate two sites on the Asotin Creek in Washington State.

North Fork Asotin F4

• 2.1 in-channel geomorphology

  • The channel is comprised primarily of concave and planar in-channel features, with bank attached convex bar features. There are minimal in channel bar features.

• 2.2 Comparing temporal morphology between 2011-2012

  • I selected 2011 and 2012 as two years to compare the morphology between. I selected two consecutive years to get the greatest gage of how much morphology could be shifting within a year, rather than dramatic net change with no understanding of what might have occurred between, for example 5 years. Additionally, generally speaking the two years shared in-channel geomorphology.

• 2.3 Tier 2 forms

Red: convexities

Dark Blue: Concavities

Light Blue/Teal: Planar

Yellow: Transition

Teal:

• • 2011; In-channel bowls, troughs and planar features are present. Bank attached convex features are present like mounds and walls.

  • 2012; Similar features are present as in 2011. Most notable there are longer stretches of bank attached mounds/convexities.

• 2.7

GUT designates the largest unit a transition zones with some spanning a majority of the channel or encompassing long stretches of longitudinal parts of the stream. I would expect a similar result is sketching a reach by hand, but perhaps not this consuming. Some transition zones stretch near 1/3 of the bank-full channel and I would be curious if there are multiple smaller units that GUT does not quantify as a singular geomorphic unit or if it could be classified as a planar unit. Additionally, using any sub categories is not a useful feature as it generally classifies everything as other as a sub category so it is best to use the unit layer.

• 2.7A Pool- Magenta X

  • Forcing: Flow-width constriction causing incision

  • Orientation: Stream-wise

  • Position: Bank Attached

  • Low Flow Slope: Shallow

  • Low flow relative roughness: low(Z0/h)

  • Tier 3 Name: Bar-forced pool

  • There were no discriminating factors prior to the pool which eliminated most pool geomorphic units . The bank attached bar on the outer bend and constricting flow made for an easy identification

• 2.7B Bar- Teal unit with red X

  • Forcing: By Planform and width

  • Orientation: Stream-wise

  • Position: Bank Attached

  • Low Flow Slope: Flat or N/A

  • Low Flow relative roughness: N/A

  • Tier 3 name: Lateral Bar

  • The bit of sinuosity and flow restriction helped discriminate the feature, as well as its shape and position in the channel

• 2.7C Planar- Blue with X

  • Forcing: Not Forced

  • Orientation: Stream-wise

  • Position: Mid-channel

  • Low Flow Slope: Shallow to moderate

  • Tier 3 name: Run-glide

  • GUT was more successful in designating planar features so this one was not as difficult to identify but the position in channel assisted.

North Fork Asotin F6

• 3.1 In-channel Geomorphology

This reach on the North Fork Asotin reach has a lot more sinuosity which had generated more interesting in-channel geomorphology comparatively to the downstream reach. There are many emerged/ convex units that are emphasized through the bends in the stream

• 3.2 2011-2012

I compared 2011 and 2012 as survey years in order to have a greater understanding of the flow regime on the North Fork Asotin between 2011 and 2012, given I selected the same survey years for F4.

• 3.3 Tier 2 forms

-Orange, convexities

-Blue, concavities

-Yellow, planar

-Green, transition

• • Fig. 5.1 2011; primarily convex and and planar features

  • Fig 5.2 2012; similar location of convexities with a smaller proportion of planar features. Additionally, concavities are more present in this survey year

• 3.4 Trends in Tier 2 Forms

Following bends in the channel convexities emerge on the inside bend, and when the channel allows for flow to diverge mid-channel attached bars form. Additionally, a low proportion of units are planar with much of the space be designated a transition

• 3.7

The most obvious short falling of the GUT for this reach is the bars, shown in fig 6.2 with the margin attached bar, where there are undesignated units. I might think this to be a flood plane units but being that they are located within the channel, and in some examples not present in the previous year survey(2011) I would just come to believe they are a part of the bar.

Another discrepancy I noticed was that the line where a pool drawn did not seem to be a consistent depth with the F4 surveys, this could be due to the presence of pocket-pools and the threshold could be more stark than can is designated a pool

• 4.1 Primary differences when exploring GUT

The primary differences I noticed between the F4 and F6 reach was the sinuosity which leads to a a plethora of features. The straighter reach(F4) produced a much more diverse range of planar features like rapids and a few cascade, this could potentially be attributed to a straighter reach producing higher intensity flows and a quicker loss of elevation. Versus F6 where flow energy was being depilated through the bends in the rivers, contributing to sediment depositing and producing many more convex features.

• 4.2 Inferences about reaches and processes

Going off my conclusions in 4.1 I believe when flow is dissipated over curves in the channel lower energy features are generated as flow has a more difficult time caring sediment through.

• 4.3 Differences in surveys given being data poor, as opposed to data rich given the number of surveys and surveyed reaches

In large part I think I would have came to different conclusions on what that reach is capable of forming under normal flow conditions. For example, if I would have only surveyed 2011 many high energy features like pocket pools and cascades would not have been observed.

• 5.1 Differences in Tier 2 forms between F4 and F6 and what was found in the field

Comparing Tier 2 forms between the reaches it was apparent of the role sinuosity was playing. F6 had consistent(linked) planar units throughout with many more convexities dominating the reach and concavities that had a tendency to be larger than those found in F4 but more sparse. While F4 had discontinuous planar features, short bank attached convexities and small concave features that were more abundant than F6.

The location of the units felt consistent with what was discussed in the field, and when we couldn't label a feature with a unit it could be classified as a transition, this seems to be what GUT denotes as a transition.

• 5.2 Tier 3 GUT vs. field

Any inconsistencies with GUT and what we would label in the field is the detail in which GUT would label a feature. All the distinguished features that GUT identified were generally broad labels. It felt as if GUT was simplifying what tier 3 geomorphic units are possible but it just requires further synthesizing of form, location, and shape to channel to fulling understand a potential unit.

• 5.3 Tier 4?

Given the riverscape context layers some inferences could be made of out of channel features of vegetation in which it is proving cohesion for the banks. But the vegetation surveys would need to accompany each surveyed year in order to help contextualize whether bars and banks are in their vegetation process to infer how active the space is.

I do not believe there was enough information to determine relative roughness. The surveys accounted for bed elevation and slope to determine planar features but actual grain size doesn't seem like a feasible option through remote sensing.

• 5.4 Confidence in applying fluvial taxonomy off of topography

Having a clear planar view of the reach was really helpful in distinguishing features from one another and that gave me confidence in placing a label on the unit. But going off of a detrended DEM(topo) and other topography contexts provided I missed many of the features GUT was able to identify. In particular convexities were hard to pick up on and many planar features will have the same elevation but without relative roughness it is a shot in the dark. Although I do believe that you could have a good understanding of processes at a reach given only topography information.