Satellite-Derived Shoreline Changes of an Urban Beach and Their Relationship to Coastal Engineering

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper discussing the Satellite-derived shoreline changes of an urban beach and their  relationship to coastal engineering seems technically sound. However, a few potential areas might require clarification and improvement.

    1.Summarize the key findings and conclusions in the abstract.
    2.The introduction provides a good background but can benefit from more recent references and a clearer connection to the research problem.
    3.Clearly identify the research gap that this study addresses.
    4.What is the main question addressed by the research?
    5.Add discussion of previous research methodologies and findings specific to Haikou Beach to better contextualize the current study.
    6.Provide detailed  information about the tools used (e.g., GEE downloader, CASPRS) in the methodology section.
    7.The choice of transect intervals (100-900 m) needs further justification. Are these intervals based on specific criteria or previous studies?
    8.Summarize the data selection and preprocessing process.
    9.The discussion section should include a comparison with previous studies to contextualize the findings.
    10.The discussion could be more critical regarding the limitations of satellite imagery, such as resolution constraints and potential biases in image interpretation.
    11.The conclusion is repetitive and could be more concise. It should focus on summarizing the key findings and their implications briefly.
    12.Provide more specific recommendations for future research based on the findings of this study.
    13."Scaterplots" should be "Scatterplots" (Figure 6 description).
    14."Tansect" should be corrected to "Transect".

The study could be strengthened by addressing the mentioned points, particularly in terms of methodological transparency, statistical analysis, and critical discussion of limitations. With these enhancements, the research could offer even more robust and actionable insights for coastal management and engineering.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

This study focuses on Haikou Beach, where multiple coastal engineering projects have been constructed, including offshore artificial islands, beach nourishment, and other coastal engineering structures. The approach used subpixel image-processing of satellite imagery to map shoreline position from 1986 to 2023. Shoreline positions were corrected using historical water levels, which were simulated using a regional ocean tide model and corrected by the seasonal sea level. Analysis of shoreline changes was conducted along 174 study transects (at 100-900 m intervals) using the CASPRS. Shoreline change results are presented by transect, in relation to the engineering projects, and summarized by key temporal periods. Research results show that coastal structures have driven the erosion and accretion patterns in the study site, which are of magnitudes much greater than those observed during the period before the construction. The discussion describes the observed pattern of shoreline change, the effect of structures and potential changes in the future.

 

The manuscript is well-written and organized. The citations are appropriate for the methods and approaches. The authors have cited some of their publications regarding the subpixel method approach used in this study and other coastal research, although it is not excessive. The study could benefit from additional citations regarding the use of subpixel approaches for coastal research, if possible. Overall the methodology used to map, assess error, and correct shoreline position are appropriate and reproducible. Satellite data is available online and the authors have made their data available from figshare.com. Shoreline change intervals also seem suitable for the study site length. Figures are easy to read, labeled appropriately and use simple design. I am uncertain that the calculations for the development of the tombolo are applicable  given the shape of the islands,  perhaps supplement the discussion with additional observation of other artificial islands. 

 

Comments on the Quality of English Language

I did not have any suggested changes for the use of English language. 

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Review for “Satellite-derived shoreline changes of an urban beach and their relationship to coastal engineering” in Remote Sensing by Hu et al.

This study employed a transect-focused approach and subpixel shoreline recognition technology to investigate the historical shoreline change of Haikou Beach. The authors applied an advanced waterline correction method leading to a random error of only 4.9 m. They revealed the shoreline change characteristics of Haikou Beach and the impact of coastal engineering projects, particularly three offshore artificial islands and five beach nourishments, and shows that the construction of offshore artificial islands exerted a predominantly positive impact on the evolution of Haikou Beach. I’ve enjoyed reading this manuscript, the presented results are very interesting. I can recommend the publication of this paper after a minor revision.

1.       I suggest the authors to detail the method that correct the mean waterline position with the simulated water levels and intertidal beach slope. In Chi et al. (2023), they mentioned that the oscillation generated by waves and tides and the interference of accident events can be limited under the support of vast imagery (Ding et al., 2021). The waterlines in fused images were considered as shorelines at the height of Mean Sea Water Level. Do you use a similar method?

2.       In Fig. 11, it can be found that, as the construction of the artificial island, the sediment volume of accretion and erosion gradually becomes non-conservative. Does this imply that the artificial island promotes shoreline accretion mainly via cross-shore sediment transport? I don't know what the real situation is, but it seems to be possible to estimate the contributions of bulk sediment transport in cross-shore and longshore directions.

3.       The response of shoreline motions to beach nourishment can be instantaneous, however, there might be a morphological hysteresis (or lag) between shoreline response and the construction of the mega artificial island. Could you please provide some comments on this issue?

References

S. Chi, C. Zhang, P. Wang, et al. Morphological evolution of paired sand spits at the Fudu river mouth: Wave effects and anthropogenic factors, Marine Geology 2023 Vol. 456 DOI: 10.1016/j.margeo.2023.106991

Ding, Y., Yang, X., Jin, H., Wang, Z., Liu, Y., Liu, B., Zhang, J., Liu, X., Gao, K., Meng, D., 2021. Monitoring coastline changes of the Malay Islands based on Google Earth Engine and dense time-series remote sensing images. Remote Sens. 13 (19), 3842.

Author Response

Please see the attachment.

Author Response File: Author Response.docx