the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Building a Bimodal Landscape with Varying Bed Thicknesses in Last Chance Canyon, New Mexico
Samuel Anderson
Nicole Gasparini
Joel Johnson
Abstract. We explore how rock properties and channel morphology vary with rock type in Last Chance canyon, Guadalupe mountains, New Mexico, USA. The rocks here are composed of horizontally to near horizontally interbedded carbonate and sandstone. This study focuses on first and second order channel sections where the streams have a lower channel steepness index (ksn) upstream and transition to a higher ksn downstream. We hypothesize that differences in bed thickness and rock strength influence ksn values, both directly by influencing bulk bedrock strength but also indirectly through the production of coarse sediment. We collected discontinuity intensity data (the length of bedding planes and fractures per unit area), Schmidt hammer rebound measurements, and measured the largest boulder at every 40-foot elevation contour to test this hypothesis. Bedrock and boulder minerology was determined using a lab-based carbonate dissolution method. High resolution orthomosaics and DEMs were generated from drone photos. The orthomosaics were used to map channel sections with exposed bedrock. The high-resolution DEMs were used to measure channel slope and hillslope relief. We find that discontinuity intensity is negatively correlated with Schmidt hammer rebound values. Channel steepness is higher where reaches are primarily incising through more thickly bedded carbonate bedrock. Where there is more thinly bedded sandstone rock exposed, channel steepness tends to be lower. Furthermore, the effect that rock properties have on channel morphology is confounded by sediment input from hillslopes. Thickly bedded rock units on surrounding hillslopes contribute larger sized colluvial sediment to the channels, and these reaches have higher ksn. Larger and more competent carbonate sediment armors both the carbonate and the more erodible sandstone and dampens the negative effect sandstone bedrock has on channel steepness. We believe that in the relatively steep, high ksn downstream channel sections slope is primarily controlled by the coarse alluvial cover. We further posit that the upstream low ksn reaches have a baselevel that is essentially fixed by the steep downstream reaches, resulting in a stable configuration where channel slopes have adjusted to lithologic differences and/or sediment armor.
Samuel Anderson et al.
Status: final response (author comments only)
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RC1: 'Comment on egusphere-2022-1285', Anonymous Referee #1, 24 Jan 2023
1. general comments
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Overall, this manuscript deals with and disusses a relavant and well-set study topic fitting the current state of research on landscape development based on lithological setting. There is a good and clear hypothesis, though, there are several issues to be faced in the current version of the paper:
- the introduction needs a distinct backing-up and reasoning by more literature; the discussion needs to be straigthlined
- there is need of more discussion why the one outlier (L3.2) is valid as it is basic for some results/interpretations
- the outcomes developed in the discussion need to be more streamlined and several controdictions need to be cleared
- several figure panels should be combined to ease the interpretations
Thus, this study findings would generally be worth publishing after adressing the above mentioned tasks - below there are several detailed hints/notes/suggestions on how to address them - both scientificaly and technically.2. specific comments
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L1 use a more expressive statement
L23 abstract: we believe?
INTRO
L27 (only) little debate?
L35 also Shobe++2021, GSA Bulletin
L37 needs definition what the ksn actually is (physically) or general description of channel profile descriptors (as they are more defined in the methods)
L45 needs info on the geochemical methods and data as background, there is no info yet
L47-L49 why inverse (physical explanation)?
L54 also Scott&Wohl2019, ESPL
L56 cf. Bursztyn++2015, EPSL
L57 to fluvial geomorphologists, too!
L58 intro of sediment availability, sediment size, btools and cover, and discharge variability is missing, also channel width vs. steepness is not mentioned - these topics are fundamental in this context!
L59 reason, why foirst-order channels (aslo, what are these)
L61 too colloquial text - e.g., "find rock mineralogy" ...
L65 landscape or river channels?
L68ff higher elevation in this scanario!
L70 is this for a ~steady state case the weaker erodibility may be deducted even? (cf. Mitchel&Yanites2021, ESURF)
FIELD
L71 climate (so Kc) is assumably constant, i.e. can be ignored for this analysis?
L85 how about the sediment (size distribution, lithological partition) in the investigated reaches?
METHODS
L105 Xi needs references
L109f which DEM; why 75m?
L112 are the San Gabriel Mountains reasonably comparable to your site (concerning chanel geometry, lithology, grainsizes, climate etc.)?
L117 a metric interval would be more tangible for the community
L118 why (only) the largest boulder - is this significant of anything (e.g., cover)? What is the relation to / meaning for smaller grainsizes?
L121 which unit
L133 define what plucking is, and why it is important here
L142 posting? you mean resolution?
fig4b end of caption is unclear; line colors in c and d are hard to differentiate - take a color-blind friendly range; indicate the Sitting Bull Falls in 4a (is this at L3.2?); also having notes on which channel holds which lithology (refer to fig.2) would be very helpful to get the point
fig5 how does a plot of discontinuity vs. Schmidt Hammer Rebound look like? What do the results tell you?
RESULTS
L187f the carbonate values are not much dfferent between steep and shallower sections
L201 how does the pattern look like if you clipp the actual in-channel boulders from the 500m window
L208ff I assume you refer to fig.7 - you state there "all boulders", but these are 'only' the largest boulders per reach, right? So, at least your result is not generally valid?
DISCUSSION
L221ff for the 5 points refer back to the figures, respectively!
L226 Shobe++2016, GRL
L229 didn't you measure larger Schmidt hammer values in the shallower sections above attesting them harder rock?
L231 that may be valid for you lithologies, but not generally
L236 I don't get this reasoning ...
L238 you mean there only is one data point for steep slopes that determines your whole interpretation above - correct; you say here you ignore it - so what about all the results?; why is this outlier there (is it an transient knickpoint? this would contradict L227ff)
L244ff several repetitions, reduce
L252 so why are there steep vs. shallow carbonate sections
L261 so erosion is focusing on the steep sections (until they are shallow enough to hold cover?) - both on carbonate and sandstone? Though, you say the opposite in L296ff
L267 not by fracture distance?
L272 so then - how is the correlation between bedding thickness with local rock dimensions
L272ff several repetitions, shorten; though you could repeat the bedding thickness values/orders for better evaluation of your discussions!
L283ff this section is missplaced and also repeats a lot; have this earlier in the interpretation - also fig9 partly repeats fig.4cd and should not show up here in the discussion; coul go to the supplement (or maybe show one example of the rock exposure as a panel in fig.4)
L296 contradicts L304f (and L261) - confusing and circular these two last paragraphs; solve for a reasonable, streamlined and consitent interpretation at one place in the text
CONLCUSIONS
L318 need to mention Carbonates here?3. technical corrections
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L39 not necessary
L86/88 repetition
fig1/2 combine into panels
L146 why 40 foot and not [m]?
L189 for on
L209 combine fig.6 and the panels of fig.8 into 4 panels; fig.7 is wrong-placed
fig8 the caption indicates fig6 is added as a panel - do that
fig9 caption: left is right ...; what are the dots?; what are "high-order alluviated channels"; rock-coloring is hard to differentiateCitation: https://doi.org/10.5194/egusphere-2022-1285-RC1 -
RC2: 'Comment on egusphere-2022-1285', Anonymous Referee #2, 10 Feb 2023
General comments:
Building a Bimodal Landscape with Varying Bed Thicknesses in Last Chance Canyon, New Mexico by Anderson et al. presents a detailed analysis of 5 catchments in the Guadalupe Mountains in southern New Mexico, USA. The authors used digital elevation model analysis, field topographic surveys, and field derived estimates of bedrock properties to interrogate how lithology influences bedrock river morphology via its dual roles on setting coarse sediment delivery to channels and the bedrock erodibility coefficient. In this setting, which is dominated by horizontally stratified carbonates and sandstones, the authors find that: 1. Thick carbonates are less erodible than sandstones due to fewer discontinuities and 2. simple interpretations of bedrock erodibility in the channels are confounded by the delivery of coarse, carbonate sediment that armors more erodible sandstone reaches downstream. These two observations lead the authors to conclude that steeper, armored reaches downstream have evolved towards a relatively stable morphology such that slowly eroding upstream reaches are experiencing a constant base level. The fine resolution mapping of rock strength, topography, and coarse sediment are both hard to obtain and immensely valuable to testing our understanding for how rivers incise (or not) into bedrock. As such, this analysis is very much suited to Earth Surface Dynamics community and will provide a useful empirical dataset to the geomorphology literature as a whole. That said, there are two modest sets of revisions I think will help improve the impact of this analysis and manuscript:
1. A broader context for how field sites fit into the landscape.
2. Some tightening of the text to clarify major claims and implications.I do not think there is a need for any major new analysis and thus believe this manuscript will be ready for publication pending minor to moderate revisions. Below, I briefly expand on these two main points and then provide a list of specific line-by-line comments that may help during revisions.
Broader Context
There is always a trade-off between resolution and coverage, whereby this study is an important contribution on the resolution side. The hard-won field data reported in this study merits publication alone by providing very detailed observations for how first order channels erode into sedimentary rock with large erodibility contrasts. That said, I found myself wanting to know more about why they picked the channels they did and how representative the patterns they observed are to the Guadalupe Mountains as whole. Are any of the reach-scale patterns in rock erodibility and coarse sediment production encoded in the geologic units such that it makes predictions for other first order stream in the landscape? Given the relatively small scale of the watersheds analyzed (based on Google Earth they seem to be of order 20 km2; please add table with watershed characteristics), I think it will be useful to see how patterns in channel steepness and lithology translate to rivers more broadly in this landscape. Though it might be beyond the scope to analyze regional data, I think it is still important to show this broader context in mapview in the Introduction.Tighter narrative
While the overall structure of the manuscript is strong and the writing is relatively clear, I think this manuscript could benefit from one more round of careful editing. In particular, the Introduction could use a bit of expansion and the Discussion could benefit from some re-structuring. For the Introduction, I think perhaps framing the problem more centrally around the work of Forte et al. (2016) and Thaler & Covington (2016) could be useful, as elements of this study reiterate findings from both prior studies. By addressing the quadruple challenges of horizontal rock units, complex rock strength assessment, strong erodibility contrasts, and complex interactions with coarse sediment supply, I think it is important to communicate how important the high-resolution data these authors are collecting is. The Discussion currently contains lots of good insights, though I found it a bit wandering in places and redundant in others. As currently structured, L218-230 is an overview. L231-261 attempts to explain how the reach-scale patterns are linked to rock strength and coarse sediment cover. L265-279 explains differences in boulder production between rock types. L283-291 revisits the role of coarse sediment armoring for each of the surveyed channels. L296-315 builds on this to articulate why steepness may not be correlated with incision and why this whole system may be relatively static. Perhaps adding a couple of subheadings could aid in organizing this part of the narrative (e.g., 5.1 Lithology and coarse sediment production and 5.2 Implications for landscape stability).Line-item edits
L15 and throughout: Consider replacing the acronym DEM with DSM. I do not mean to be too picky here, but as I understand it, the authors are generating digital surface models (DSMs) since they are not filtering vegetation. Flying around Google Earth makes me think this is a pretty minor source of uncertainty in either derived hillslope or river metrics. That said, it is worth being precise in the language around this so that the authors can make that point.L15: Consider replacing ‘drone photos’ with ‘drone and ground-based photogrammetry.’ This might require tweaking some of the sentences following, but it seems to me the authors would want to highlight the GoPro data for mapping bedrock discontinuities.
L22: Consider replacing ‘…dampens…channel steepness.’ with ‘…dampens steepness contrasts across rock types.’
L24: Delete ‘essentially’
L44-45: ‘…we could estimate...’ I didn’t quite understand what the latter part of this sentence was getting at. Kc is undoubtedly an important piece of the puzzle but independently constraining it wouldn’t be enough to predict incision from topography for many reasons, including some of the sediment dynamics ones the authors argue for here.
L46: Akward phrasing. Not sure what is meant by empirical definition of eq. 1.
L53: Consider replacing ‘variables that must’ with ‘bedrock properties that should’.
L61: Replace ‘carbonite’ with ‘carbonate’
L62: Check use of commas here and throughout.
L68: Forte et al. (2016) is a good citation here, but I think also a good place to bring in Thaler & Convington (2016). I also think the authors could better elaborate on the ideas gleaned from these prior studies. Forte et al. (2016) had no sediment. Thaler & Covington (2016) argue for the fundamental importance of coarse sediment in armoring channels (funnily enough the hard rock at their site was sandstone and the weak rock was carbonate). These two prior studies are complementary though in that a key ingredient was horizontal rock units. The authors here have presented detailed field measurements for one scenario (i.e., hard over weak), and see elements of both models. In my view, this last paragraph of the introduction could use some re-framing around these ideas to help setup later interpretations of their data.
L71: The field area is awesome, and I understand the focus on where data was collected. That said, this section could use a figure that shows the regional geomorphic context. Ideally, I would love to see this regional context carried through the manuscript by introducing the broader river network here and then relating geology to channel steepness below. I recognize that this may be beyond the scope of this study. As such, I suggest at least putting a regional map figure in this section showing the study area, geology, topography, and river network.
L89: Please capitalize ‘Figure.’ This is the first example I noticed, but it appears throughout the manuscript.
L89-90: Awkward sentence. Perhaps something like ‘Rock unit descriptions from published geologic maps are not at the scale needed for us to constrain rock strength.’
L97: Lat and long for LC3.2 is also in the Figure 3 caption so I don’t think it is needed here. Also, it seems the authors have a naming convention for the GoPro5 imagery LCx.y where x is the channel number and y is the site along the channel. It might be useful to provide a summary table that explains this naming convention and points to where the datasets can be accessed.
L105: Suggest deleting ‘like ksn’. Also, the authors may want to explain in a bit more depth what chi is for the uninitiated.
L111: I think this choice of 500 m (is this the radius or diameter?) to calculate hillslope relief is fine, though I was bit puzzled by the citation of DiBiase et al. (2010). That prior study argued that a 2.5-km radius tracked with channel steepness (and thus fluvial relief) and that <~1-km radius was retaining the threshold behavior observed in mean hillslope angle. I suggest removing this citation, clearly articulating what you mean by hillslope relief, and perhaps simply justifying your choice based on where you think channelized flow begins in your landscape. Depending on how the heads of channels were chosen, the authors could simply use those field-based observations as justification.
L117: Very nice to see all this detailed and systematic approach towards mapping!
L129: I’m sure Agisoft handled all of the lens distortion, and using video is a clever way to get many frames rapidly. Any insight to offer how much overlap between extracted images you needed to get good alignment?
L129-144: It would be nice to see more details regarding the processing of the GoPro5 and Mavic2 data in Agisoft to: 1. Aid reproducibility and 2. Help others learn from these authors experience. Will these datasets and/or some of the derivatives generated be archived somewhere?
L151: I think ‘overnight’ should be one word here.
L155: Should ‘less than 60% quartz’ be ‘more than 60% quartz.’?
L161: Headers for 4.1 – 4.3 could be simplified to something like ‘Morphometric Analysis,’ ‘Bedrock Properties,’ and ‘Boulder Analysis.’ Also, some of the text is hard to follow in the Results sections, which may be easier to digest in tables.
L167: Replace ‘different’ with ‘significantly different’
L173: I wonder if one way to bolster the argument for regressions in Fig 5b would be to elaborate on this geometric argument. On the one hand, the lack of steep, sandstone sites to map discontinuities is an important observation, albeit one that is at odds for building regressions of discontinuity intensity versus slope! What if instead of regressing the data in Figure 5b, could geometric relationships be derived for how slope and bedding discontinuities vary for an assumed bedding thickness? Then, that ‘outlier’ becomes the exception that demonstrates the rule.
L180: I am assuming that splitting of the data into steep versus shallow is based on the elevation bins reported in section 4.1. It might be helpful to use contrasting symbols for these classifications in Figures 5 and 6 to aid interpretation and evaluate sub-population sample sizes.
L193: I assume that ‘only test of the four’ means the authors did a t test comparing low sloping carbonates and low sloping sandstones, and that they were not significantly different?
L214: A lot of this paragraph could be put in a table (and there appears to be some confusion with figure numbering between Figs. 7 and 8). Nevertheless, I think this shape factor result should be moved up as it explains both the prior results and the regressions shown in Figure 8.
L227-230: I think this is one claim that would be strengthened if we had a broader context for the patterns in channel steepness and lithology for this landscape. Could this analysis be used to predict where channels are running through carbonate versus being armored by carbonate clasts?
L231: Remove ‘and’ and add a comma between ‘local slope’ and ‘bedding plane amount.’
L235: Suggest replacing ‘less weak’ with ‘stronger.’
L240: Comma needed after ‘At low slopes’
L242: Delete ‘more’
L245: Suggest replacing ‘less thickly’ with ‘thinly.’
L255: This discussion has me thinking about how useful it would be to have a strip map or even just the survey locations color coded by rock type so that the reader can see how where the sandstone and carbonate members fall in the landscape. It’s all in Figure 9, but hard to map onto the rock units in Figure 2.
L266: Also, Sklar et al. (2017) and Shobe et al. (2021) set up this challenge nicely.
L272: Relation between bedding planes and boulder shape in this setting is really cool!
L287: The distinction between LC1-2 and LC3-5 morphology is interesting and seems to be one of the major findings. The authors could perhaps expand this part of the discussion to consider why this difference occurs and use it to motivate future work? What’s going on with the abrupt offset in chi-elevation space for LC1-2? It almost seems that the mainstem these tributaries are draining to are hung up.
L296-305: Very interesting discussion in context of what is known about erosion rates elsewhere. Have others speculated that these were migrating knickpoints? How fast were these erosion rates and do you think they make sense with your study area?
L314-315: I agree in general, but I think the emphasis may be off. Coarse sediment delivery is clearly important and where you have stronger material in the landscape you expect a strong lithologic imprint in channel steepness patterns. Your discussion here makes me curious about the distinction between stable geometry and erosional steady state (is there one?)
Figure 1: Are channel heads based on a certain critical area? Slope-area break? Could be useful to report this somewhere to help readers interpret the network.
Figure 2: There appears to be a sixth transect only mentioned in the figure caption. Can you clarify how/whether this data was included in the analysis.
Figure 4: Are these kernel density estimates or smoothed histograms in panel b? Also, labeling was a bit hard to read in this figure.
Figure 5b: It seems to me that the discontinuity intensity differences as a function of slope are not all that different between the carbonates and sandstone except for at LC3.2. I suspect this is the most important observation (see comment on L173).
Figures 6-8: These all have the same caption. Please revise to better reflect what is being shown.
Figure 7: This figure seems like it better belongs near the methods (i.e., earlier).
Figure 9: Lots of important observations here that I did not appreciate my first couple times through the manuscript.
References
DiBiase, R. A., Whipple, K. X., Heimsath, A. M., & Ouimet, W. B. (2010). Landscape form and millennial erosion rates in the San Gabriel Mountains, CA. Earth and Planetary Science Letters, 289(1-2), 134-144.Forte, A. M., Yanites, B. J., & Whipple, K. X. (2016). Complexities of landscape evolution during incision through layered stratigraphy with contrasts in rock strength. Earth Surface Processes and Landforms, 41(12), 1736-1757.
Shobe, C. M., Turowski, J. M., Nativ, R., Glade, R. C., Bennett, G. L., & Dini, B. (2021). The role of infrequently mobile boulders in modulating landscape evolution and geomorphic hazards. Earth-Science Reviews, 220, 103717.
Sklar, L. S., Riebe, C. S., Marshall, J. A., Genetti, J., Leclere, S., Lukens, C. L., & Merces, V. (2017). The problem of predicting the size distribution of sediment supplied by hillslopes to rivers. Geomorphology, 277, 31-49.
Thaler, E. A., & Covington, M. D. (2016). The influence of sandstone caprock material on bedrock channel steepness within a tectonically passive setting: Buffalo National River Basin, Arkansas, USA. Journal of Geophysical Research: Earth Surface, 121(9), 1635-1650.
Citation: https://doi.org/10.5194/egusphere-2022-1285-RC2 -
EC1: 'Comment on egusphere-2022-1285', Jens Turowski, 14 Feb 2023
Dear authors,
We have received two reviews now. Both reviewers see the value of the paper, but ask for clarifications, specifically on the scientific narrative and reasoning. This agrees with my impression of the manuscript, adding that the method descriptions lack some details that would be necessary to reproduce your work. I think the paper can be improved by clarifying the objectives and approach at the end of the discussion, as well as the methods, and by making the underlying concepts and connections to current understanding of channel dynamics explicit. Both reviewers give numerous suggestions of how this could be achieved. You can find further suggestions from me below.
I hope this helps. Please feel free to contact me if you need further clarifications or pointers for the revision. I am looking forward very much to reading your revised manuscript.
With best wishes,
Jens Turowski
Handling AE
28 Wohl et al.
29 remove comma after Dietrich
29 maybe ‘scale inversely with rock tensile strength’, the squared relationship has since been challenged (e.g., Mueller-Hagmann, M., Albayrak, I., Auel, C., and Boes, R. M. (2020). “Field investigation on 256 hydroabrasion in high-speed sediment-laden flows at sediment bypass tunnels.” Water, 12, 469).
36 I guess you are referring to the stream power paradigm here; please make the context explicit.
42 The channel steepness index…
43 It would maybe be better to acknowledge the methods here, rather than a particular implementation.
51 add ‘e.g.’ to the citations here, there is considerably more literature on these points.
59-70 the paragraph gives a summary of what has been done and of the outcome, but not of the objective, hypotheses and approach of the paper.
65 The connection to previous literature is better placed in the discussion (see also comment on line 310).
130 Please add citations for the software here.
131 Please explain how you recognized discontinuities in this step.
133 Please describe your criteria for choosing these discontinuities. Currently, the method and decisions cannot be reproduced.
134 Please describe the statistical method used in this step and add a reference for Fraqpac.
141 Please add information about the methods, such as software settings and decision criteria.
143 Please describe your procedure and decision criteria here to make them reproducible.
146 Why 40 feet?
151 Please add information on the typical weight that was considered and on the precision of the scale.
151 Why five times? What was the decision criterion to rinse more often? What was the average and maximum number of rinsing steps?
155 Why? Would that not bias the results?
156 Unclear. What does the word ‘sample’ refer to here? Did you work on different aliquots or did you repeat the analysis on the same sample to check whether the weight would remain constant? How did you make sure that ‘all’ carbonate was dissolved? Please describe the methods and decision criteria, rather than the interpretation.
158 What does the std refer to here?
159 ‘giving credence to our methodology’ – subjective judgement, unnecessary. Let the reader decide by themselves. I suggest to delete.
164 The formulation ‘we find’ suggests an interpretation, which should probably be moved to the discussion. Here, please describe the observations on which this interpretation rests.
165 ‘more subtle’ is vague and subjective. Please describe the observation.
166 Please report the statistical outcome of the test. Please state hypothesis and null hypothesis. Please state the significance criterion you used to reject or accept the hypothesis. The verification is an interpretation of these statistics. Maybe this would be better placed in the method section.
172 ‘were treated as discontinuities’ seems to be an information of the methods, rather than results. Consider moving.
172 Maybe at readings of dip here?
173 Which slope is this? Bedding slope (dip) or channel slope or topographic slope?
177 Which slope is this?
180-188 When using a comparative (‘more’, ‘larger’), please state both items that are compared.
181 more than what?
181 -1 as superscript, also elsewhere.
182 more than what?
189 Unclear, please add information on the purpose and construction of these tests.
192 Consider adding a small table with the outcomes of the statistical tests.
193 what was the null hypothesis?
194 Interpretation, move to discussion.
201-202 Unclear. Please provide the reasoning behind this analysis. Might be good to move this to the method section.
203 Smaller than what?
204 Smaller than what?
205 What does ‘large’ mean in this context? Can you make this quantitative?
206 What do you mean by ‘dramatically’ here?
206 How representative is this for the overall boulder population? What fraction of boulders of the entire population was analyzed? In the methods, you state that you sampled the largest boulder in each reach. Could there be a bias due to size selection?
208 …the lengths… increase…
208 How did you determine the similarity of slopes?
209 What does ‘relatively high’ mean here? What are these values? Add quantitative information, e.g., R2 > 0.9.
209 I do not see where the judgement of conversely comes from. In the preceding sentence, you have not given any contradicting information.
210 Thanks for the quantitative information! :o)
210 What is the parameter m? What kind of relationship did you fit?
210 Capitalize ‘the’. Replace ‘demonstrates’ with ‘shows’ or something similar.
212 better than what? Is a ‘better fit’ a good criterion for choosing one regression model or another?
214 I neither understand what you mean by ‘slightly more’ nor by ‘equidimensional’ in this sentence. The quantitative information in the second half of the sentence is sufficient; consider deleting the first half.
219 Be specific, there are many more rock properties than you have measured!
220 positive or negative correlation?
220 In the list, make clear what is interpretation and what is the observation that the interpretation rests on. For example, under (1), the second half of the sentence refers to an observation.
221 higher than what?
222 (2) is just the corollary of (1), the point does not give an interpretation.
223 (3) Please provide an argument to justify the interpretation.
228 Is this an interpretation (as announced in line 220) or a hypothesis?
240-252 Here, my impression is that there is a mixture of observations, interpretations, and hypotheses, which are not clearly labelled and / or separated, and some of the reasoning behind it is implicit. Please rewrite to clarify and make reasoning explicit.
243 What is the difference in the carbonate and sandstone ways of anisotropy?
258-261 not sure whether I follow the reasoning here. This could be connected to current theoretical understanding of how the channels work (e.g., graded stream paradigm, channel morphology evolves to match erosion to uplift). The recent publication by Nativ et al. may be helpful to make this connection (doi: 10.1029/2021JF006537).
259 In my understanding, the causal relationship would be the other way round. I.e., the stream has a need for erosion, because of uplift or baselevel drop. It adjusts its morphological state – e.g., slope and cover – to match this need. Of course, this works only if the observed situation reflects a steady state. Yet, if it is not in a steady state, why would any observed relations be informative?
260 What is a “potential for erosion”? How would you measure it? This seems to me to be a theoretically-laden concept disconnected from the underlying theory. Can you make the concept behind it explicit?
265 How do you know? Maybe the causality is the other way round.
275 Reference?
273 and following: are the differences significant? What does the word ‘subtle’ (line 274) mean in this context?
277 The relative fractions should be controlled by delivery, transportability and size reduction. The latter two determine average residence times. The argument presented here seems plausible, but also incomplete.
279 the underlying concept behind this reasoning seems to be that boulders diminish in size mainly by fracture. What about abrasion?
287 Interpretation or hypothesis? If the latter, how will you test it?
290-291 Can you make your observation, reasoning and interpretation explicit here?
296 interpretation or hypothesis?
310 The connection to the modelling papers is not clear and needs more detail. This connection has been highlighted in the final paragraph of the introduction, indicating that the authors find it particularly important, and the level of the discussion here should reflect and reason this importance.
313 I think this statement is an important assumption driving both the way you present the data and their interpretation. Maybe you can move this to an earlier point in the article?
Citation: https://doi.org/10.5194/egusphere-2022-1285-EC1
Samuel Anderson et al.
Samuel Anderson et al.
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