Riverine Sediment Changes and Channel Pattern of a Gravel-Bed Mountain Torrent

Round 1

Reviewer 1 Report

Congratulations on this successful work. The scientific quality is excellent. The structure corresponds to the journal requirements. I recognize the good methodical knowledge as well as the good local knowledge of the authors. I would just like to make two points:

(1) Perhaps the manuscript is a bit too long. Here I ask the editor to compare it with the journal requirements.

(2) The image quality of some graphics could be improved.

Depending on these two points I "accept in present form" resp. "accept after minor revision".

Author Response

Dear reviewer,

Thank you very much for your appreciative comments.

Concerning your two points:

(1) According to the Instructions for Authors, the journal requirements do not limit the page count. Therefore, we suggest not to shorten the text.

(2) Figure 10 was slightly modified. Apart from that, we carefully checked the graphics’ quality and assessed the quality as appropriate. However, if specific changes are necessary, please indicate that by mentioning the figure’s number.

Gernot Seier, on behalf of the authors

Author Response File: Author Response.pdf

Reviewer 2 Report

The data the authors collected seem to be useful, but the current draft does not utilize them effectively. Although the main words of the title are "sediment changes and channel pattern", relevant discussion is given only seven lines of Section 5.2. Other discussion materials are found in Section 5.1, and they focus on data error and quality issues. Overall,  the authors put emphasis on technical issues, whereas truly scientific contents are very limited in the current draft. A related problem is that the way this paper is written is of local interest. Except for Introduction, the authors wrote only about their small study area in Austria almost always. Note that detection of temporal changes in channel location and sedimentation/erosion based on high-resolution DEMs is not a new topic. Using drones etc, many geomorphologists have already conducted such studies. I do not understand why the authors did not cite such papers in the Discussion section and write scientific implications of their work in comparison with previous publications. Without this, the paper is not internationally meaningful in a scientific sense. 

One advantage of this work over previous studies using high-resolution multi-temporal DEMs is the collection of ERT data. This is not often made in DEM-related studies. However, in the Discussion section, the authors did not utilize the ERT results to make general geomorphological interpretations. So it is hard to understand why the ERT measurement was conducted.

Other issues:

• The English is readable but there are some grammatical errors and awkward expressions. For example, the authors often write like "which enable (or allow) to quantify...". The grammatically correct expression is "which enable (or allow) us to quantify...". Another example can be seen in L154 - it is rather redundant because the authors wrote "overlap was overlap". The heading of 4.1.3 does not make sense grammatically.  These are only a few examples of existing problems.
• The reason for the choice of the study area (Langgriesgraben) should be more clearly stated. There is a very brief reason-alike in L45, but there are many other places in the world where the same thing is applicable. 
• Putting many text phrases in a figure is not good. For example, in Fig. 1, info about the projection, datum, etc. can be written in the caption, not inside the figure. 
• Please do not begin a figure caption with "a)". A general title of the whole figure should be written first.  
• All values in Table 4 begin with "~". This is very unusual. It is also strange that the value like "11053" is approximate. A value like 10000 or 11000 can be approximate. 
• In Table 4 "d-1" is used like a word, but this way should be used only for a unit.  

Author Response

Dear reviewer,

Thank you very much for your comments. A precondition for any geomorphological interpretation is a detailed description of the methods used, which is in particular relevant in quantitative approaches. Even though already more or less established in geosciences, due to the fact that SfM photogrammetry and relating methodological limitations are in many cases not adequately described or considered, a description of the techniques used is essential in order to support any morphological interpretation. In other words: imagine a case, the results would have been presented without this detailed information – in such a case, morphological interpretations and implications would not be meaningful. Therefore, we fail to understand your opinion concerning the ‘technical issues’. These are not only minor issues, but are essential for the description of the methods used. In addition, we fail to understand your opinion concerning ‘truly scientific’ content. Also, the size of a study area does not influence the scientific quality. In this regard, we have to absolutely disagree. Moreover, the study focuses on a mountain torrent and consequently, the text mainly deals with the investigated area and the methods applied, the quality of the data, the results and interpretations, which means that throughout the manuscript there are also other topics addressed (e.g., methodological considerations etc.). As SfM-based studies using terrestrial or UAS-based imagery are necessarily conducted in local environments, of course, and hopefully, the study is also of local importance. However, as shown with the literature cited in the Introduction and throughout the whole manuscript, the high importance of SfM-based (terrestrial and using UAS) studies for fluvial geomorphic questions becomes obvious. With our study we contribute to this current field of science. Also, the literature cited throughout the manuscript is both relevant and ample (64 citations in the first draft). In sum, we fail to see any subject-specific argument for your opinions. However, the discussion section was slightly expanded according to your suggestion.

We agree, it would be interesting to expand the ERT-related subsurface interpretations. However, without further and in-depth investigations, we would not recommend to discuss the subsurface conditions in more detail. We think it becomes clear that in this study we focus on the results based on UAS-based SfM photogrammetry. And the additionally conducted subsurface investigations are enabling a rough idea about the interplay of the surface and subsurface conditions.

Some sentences were modified according to your suggestion. Please see the highlighted text in the current version of our manuscript.

We disagree. We think it is very clearly presented why we chose the study area. Of course, there are also other areas that could be studied – we fail to understand your opinion.

As it is also not recommendable to have large text blocks in the figure captions, and as this information makes the figure useful as data basis for other studies, from our point of view, it is important to let the reader see that the presented data is georeferenced. Therefore, we suggest to show the information in the figure.

According to your suggestion, the figure captions were modified by placing the subfigures’ labels to the end of the particular sentence.

We think the `~`-sign is very indicative of the fact that all the respective values are rounded. Therefore, we suggest to use this sign to concisely highlight this fact. Concerning the objection of whether the values could be approximate: as the calculations are based on data with accuracies in the centimeter or low decimeter range, we think it is arguable to highlight that the integer values (in the range of meters, which is at least one order of magnitude above the data basis’ accuracy and precision) are approximate. To make this clearer, the table heading was expanded with the note ‘[…] (numbers rounded to integer) […]’.

Modified. As the related values are in a similar version also presented in the graph (Figure 10), both lines were deleted.

Please see the attached PDF that includes your points and our relating responses.

Gernot Seier, on behalf of the authors

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Authors,

your manuscript is interesting and generally well-written. Both the research goals and the used methods are described in detail, and the discussion on the uncertainties correlated to use UASs for estimating erosion/deposition in fluvial systems is a very good point, which is generally not addressed by similar articles.

In my opinion, your work needs only minor changes, as you can see in the attachment. Besides what I wrote there, please consider expanding the text discussing the applicability of your methodology to other contexts, aiming to attract more readers.

Comments for author File: Comments.pdf

Author Response

Dear reviewer,

Thank you very much for your insightful comments and your detailed notes on the text and the respective suggestions. Also, we would like to thank you for the questions, please find my direct response to each of the questions in the PDF. With only one exception (please see explanations in the PDF), all of your suggestions were considered and accordingly, the text was amended.

Gernot Seier, on behalf of the authors

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors did not seriously deal with my previous review comments. There have already been numerous similar publications in geomorphological journals using multi-temporal high-resolution DEMs to discuss changes in fluvial landforms, and I believe scientific advantages of the present work over such previous studies must be presented clearly if the authors like to publish this paper in a high-quality journal like Remote Sensing.  Concerning this issue, the authors added only some sentences at the end of discussion this time, but they are nothing more than general remarks, and did not show the advantages of the current work as compared to previous similar studies. In summary, the authors did not seriously consider the important knowledge of fluvial geomorphology accumulated based on similar approaches, and only presented what they did and described how the accuracy of their work was. I do not think this way of writing is suitable for a good scientific journal. 

Author Response

Dear reviewer,

Thank you very much for your comments.
Please acknowledge that point-by-point we responded to your previous comments, which we carefully considered and appreciated. In any such cases where we did not agree with your point of view, we clearly explained and reasoned why changes are not necessary. Concerning your current review comments: the literature cited in the manuscript already comprises numerous and relevant examples of high-resolution DEM-based studies in fluvial geomorphology. As we showed and discussed with the cited and up-to-date literature, the influence of methodological characteristics on DEM uncertainties and for estimating erosion and deposition in fluvial systems (resulting from UAS-based SfM photogrammetry) are not widely discussed yet. Our study contributes to this current topic by indicating that considering methodological and technical information in fluvial morphological studies could lead to completely different morphological interpretations. In other words: fluvial geomorphological interpretations based on UAS and SfM photogrammetry are more reliable and meaningful, if the technique’s details are considered, which is often not the case yet. Therefore, it is of great importance to present and discuss the details of remote sensing technology and its applications, which is the journal’s scope and which is addressed with our study. If, in your opinion, any further literature should be cited, please mention the reference.

Gernot Seier, on behalf of the authors

Author Response File: Author Response.pdf