Sediment Transport of Coastal Region Using Time-Series Unmanned Aerial Vehicle Spatial Data

Round 1

Reviewer 1 Report

Review of:

Sediment Transport of Coastal Region using Time-Series Unmanned Aerial Vehicle Spatial Data

Understanding coastal beach erosion and deposition is highly important to the nature-human coupled environment residing on and in close proximity to the world’s coastlines. This article quantifies geomorphic change derived on the Cheonjin-Bongpo beach, Korean Peninsula derived from aerial surveys during 2020 and 2021. The authors present an article that generally describes the motivation for the study, methods, and its results and conclusions. As a reviewer, I feel this article is not suitable for publication in its present form. The research does include sound scientific methods and results, so with improvements to the article as whole it could contribute to the body of literature using remote sensing applications, specifically UAVs to quantify and monitor coastal beach morphology. The main issues stem from clear communication of the research scope, goals and objectives, result interpretation and its implications to the scientific community, all of which can be addressed. I have generally outlined some of these issues; however, not in totality, below.

The introduction generally describes the issues many of the world’s coastlines are experiencing from coastal development and erosion. The authors could include more detail in describing the natural and anthropogenic drivers of change with citations (lines 41-48). The authors do a good job of describing how Unmanned Aerial Vehicle (UAV) technology can be used to survey coastlines effectively, especially when coupled with high-precision Global Navigation Satellite System (GNSS) technology. However, the authors do not present a clear description of the goals of the study in the introduction section. This is a major flaw as it leaves the reader wondering what the author’s intent of the research. There is a very short description at the end of the introduction describing the basic method used in the study, but they do not give an indication as to what the method used is for, i.e. quantification of beach erosion or deposition. This can be fixed, but describing the research goals is an important aspect to any research article. With the addition of adding research questions and goals, and some detail to the overall problem the introduction will be vastly improved.

The information contained in the site information section describes the study site well and concisely with nice figures, tables, and graphs. The authors may consider adding latitude/longitude text in the Figure 1 map (by the “Study Area” star), for readers not familiar with the Korean Peninsula to see at a quick glance. The information contained in the method section describes acceptable methods well and concisely with figures, tables, and graphs. In addition, the results are generally presented well with figures and graphs.

            The discussion and conclusion describe how using UAV technology in this study was effective at mapping and quantifying change in beach elevation and width through surface modeling. It also generally discusses qualitatively how submerged breakwaters mitigate beach erosion to the study site. However, in its present form, the discussion and conclusion section lack detailed explanations of the results and interpretation of the results relative to the problem and goals of the study. Additionally, there is a lack of discussion relating this particular work to other similar works by other researchers in differing areas. This again is a major issue with the article. This issue can be fixed but is critical to the scientific merit of this article.

            Overall, this article could contribute to the literature as understanding how the human-built environment interacts with the natural environment is critical to planning and managing sustainable and resilient coastal development. However, the communication of this research needs to be vastly improved, mainly in the introduction and discussion and conclusion sections. As a reviewer, I was generally left confused on many things mainly stemming from the authors not fully describing the goals of the study. For example, I am not sure what the authors deem “short” and “long-term”. Is short-term a week or month? Is short-term just pre and post-tropical event. Is long-term just the full year? Two tropical cyclones impacted the study area within the temporal span of the study, examining the effects of just these two storms alone is worthy of publication in itself, if it is presented as such. Beach recovery from tropical cyclone impacts can occur rapidly or on longer time-scales (well over a year) if they even fully recover. Describing these time-scales would be beneficial. Additionally, the authors present a lot of detailed information about the UAVs, methods, storms, wave heights, period, etc., but they do not utilize any of this when examining the results or discussing the interpretation of the results in context of the problem and goals of the study in the discussion.

Final remarks

In consideration of addressing the comments above, this article could add to the literature of using aerial imagery as a tool for quantifying beach morphology. Overall, this manuscript has sound scientific methods, but it suffers from a lack of communication, delivery, and scope. For this reason, I do not recommend acceptance until substantial revisions are made and the article is reconsidered. I did not provide additional comments for individual line numbers since the main scope of the manuscript needs revision. Substantial revisions to include goals and objectives, result interpretation in context of the overall problem and the authors goals and objectives in the discussions and conclusions are needed.

Quality of English language is acceptable

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper deals with a very important and delicate issue. Coastal erosion is certainly a problem that afflicts many countries around the world and deserves studies and effective solutions to ensure the survival of all areas bordering the sea.

The study methodology is not particularly innovative. There are a great many studies using drone photogrammetry. I suggest specifying better at the end of the introduction what is the main purpose of this paper, and its added value compared to other studies using the same methodology. Perhaps adding a few other citations that do not refer only to Korean studies.

 

Detail comments:

Lines 89-90: the sentence on the corruption of the imagery using too many GCPs is not clear to me.

Line 102: the authors write that "the sand is fine", but in lines 107-108 they write that "the median grain size (D50) ranges from approximately 0.70 to 1.13 mm" which is not so fine (see Udden-Wentworth classification).

Lines 110-111: It's not clear to me. The work was done between 2017 and 2019. Why in Figure 2 do the before photos date back to 2007 and 2010?

Lines 123-124: write the acronym shown in Figure 3. I would not put OBS because it could be confused with a turbidimeter (OBS=Optical Backscatter Sensor). Better to write W1, as also reported in the caption.

Table 1: is not mentioned in the text.

Figure 4: the characters of the text, especially in the legends, are illegible.

Lines 144-145: “Table 3 presents the maximum significant wave height, peak period, peak wave direction, and …”, measured by W1 or WINK?

Line 157: It’s not “3 h”, but 4 in table 3.

 

Figure 5: Align the x-axes for easier reading of the 3 graphs. Indicate in the caption what the dotted line is in panel a.

In panel c I would have made a line graph like in the other two panels.

What caused the first peak (hs ~ 5.8 m) before the first blue line?

Line 175: “An aerial survey…” the authors made 13 aerial surveys.

Line 181: “13 aerial photographs..” are 13 aerial surveys or 13 orthophotos.

Line 196: “Five GCPs…” I can see 7 GCPs in the next paragraph.

Lines 251-252: Comment more and better on Figure 10. What is represented by the different colors? What is particularly interesting to see?

Figure 11: red to blue legend represents accumulation and erosion, but beach height or width?

Panel c: this figure is not mentioned in the text. Explain what it represents. In particular, what is reported on the x-axis? What do we infer?

 

Lines 322-324: It would be interesting to see what happened when these dams didn't exist yet. Was the beach under erosion? Are there satellite images?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf