Lidar-Derived Decadal Change in Barrier Morphology: A Case Study of Waisanding, Taiwan

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Based on the article reviewed, I observed that the manuscript titled ‘Lidar-Derived Decadal Change in Barrier Morphology: A Case Study of Waisanding, Taiwan’ could be considered for publication/acceptance after considering all minor revisions.

Comments for author File: Comments.pdf

Author Response

The authors gratefully acknowledge the comments for the Geosciences-3269378 MS, “Lidar-Derived Decadal Change in Barrier Morphology: A Case Study of Waisanding, Taiwan”.

Modifications are marked in blue in the revised version. The replies to the comments are as follows:

 

1. Please add full term of DEM and LiDER in abstract as the first use in the manuscript (P1, L14-15).

Response: (L15) Corrected.

 

2. What is LV drop? Please give elaborative term of LV drop in abstract and it was also not found in the other part of the manuscript. Please check it (P1, L19).

Response: (Line 19-20) The corresponding average land volume (LV) decrease in elevation can be estimated to be -0.0286 m/year.

 

3. Please add some references based on traditional shoreline datasets. I recommend [1– 2]:

Response: Some recommended references and others are added, as followed

• Shamsuzzoha, M.; Ahamed, T. Shoreline Change Assessment in the Coastal Region of Bangladesh Delta Using Tasseled Cap Transformation from Satellite Remote Sensing Dataset. Remote Sens (Basel) 2023, 15, doi:10.3390/rs15020295.
• Natarajan, L.; Sivagnanam, N.; Usha, T.; Chokkalingam, L.; Sundar, S.; Gowrappan, M.; Roy, P.D. Shoreline Changes over Last Five Decades and Predictions for 2030 and 2040: A Case Study from Cuddalore, Southeast Coast of India. Earth Sci Inform 2021, 14, 1315–1325, doi:10.1007/s12145-02100668-5.
• Mujabar, S.; Chandrasekar, N. A Shoreline Change Analysis along the Coast between Kanyakumari and Tuticorin, India Using Remote Sensing and GIS. Arab J. Geosci. 2013, 6, 6647–6664.
• Almonacid-Caballer, J.; Sánchez-García, E.; Pardo-Pascual, J.E.; Balaguer-Beser, A.A.; Palomar-Vázquez, J. Evaluation of annual mean shoreline position deduced from Landsat imagery as a mid-term coastal evolution indicator. Geol. 2016, 372, 79–88. [CrossRef]
• Liu, Q.; Trinder, J.; Turner, I.L. Automatic super-resolution shoreline change monitoring using Landsat archival data: A case study at Narrabeen–Collaroy Beach, Australia. Appl. Remote Sens. 2017, 11, 016036. [CrossRef]

 

• Alzubaidi, L.; Zhang, J.; Humaidi, A.J.; Al-Dujaili, A.; Duan, Y.; Al-Shamma, O.; Santamaría, J.; Fadhel, M.A.; Al-Amidie, M.; Farhan, L. Review of deep learning: Concepts, CNN architectures, challenges, applications, future directions. Big Data 2021, 8, 1–74. [CrossRef]

 

4. Please add a high-resolution map including latitude and longitude information (Figure 1, P3, L92-94).

 Response: (Line 117) Both latitude and longitude are included.

 

5. Please add a stared note (*) of the month at the bottom of the table to enhance the readability as 1 to 12 ~ January to December (Table 1, P4, L131-132).

 Response: (Line 151) We use the abbreviation of the month directly instead of the number.

 

6. Please add a reference (P4, L133) to the statement 'the waves are the primary force on the beach.

Response: The sentence of “The waves are the primary force on the beach.”  is replaced with a paragraph and added citations.

 

7. Please check the trademarks (^TM) symbol or registered (^®) sign, country of origin information after the used camera's name or model name (P5, L154-156).

Response: Thank you for your advice. After checking and asking about the measurement unit, "Leica ALS70-500HP" and "PHASE-ONE IXA180" are just product names and models, without trademark (™) or registration (®) symbols. Additionally, we have now added the country of origin of these devices based on your suggestion. The correction is as follows:

(Line 167-172) The DEM data collected in this study come primarily from surveys conducted using an airborne LiDAR system. It includes an Airborne LiDAR Leica ALS70-500HP and an aerial survey digital camera, PHASE-ONE IXA180, which is produced in Switzerland and Denmark, respectively.

 

8. Please mention the source of the Figure 3 (P6, L196-197).

Response: This figure is drawn by the author with reference to Barrineau et al. (2015) and has been explained in the Lines 179-180 in the original version. 

(Line 229) Figure 2. A typical cross-section of a barrier island modified from Barrineau et al. [31].

 

9. Please give the reference of the equation 1's origin and an example of the equation for applying in another research/manuscript to compute the harmonic series (P6, L201205).

Response: We describe the method and application of Harmonic analysis in section 2.3.3 (Line 245-269) associated with its references.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

General impressions:

The paper addresses morphometric aspects of the WSDB in a very direct and technical manner, based on data obtained by remote sensing, aiming to understand the recent morphogenetic evolution and to know the factors responsible for the erosion and migration of the WSDB.

 

As the author himself says, this is a case study, in this sense it would be interesting to advance a little further in the literature that addresses barrier islands, bringing paleoenvironmental and geochronological studies in the introduction and discussions, to expand possible correlations. Suggestions:

https://onlinelibrary.wiley.com/doi/abs/10.1111/sed.12418

https://onlinelibrary.wiley.com/doi/10.1002/esp.5989

 

Introduction

It can be expanded to include more references on barrier islands and include paleoenvironmental dynamics associated with coastal and barriers island changes.

 

Materials and Methods

Some results are presented in this topic, change them to the results.

 

Results

In results, data selection criteria are presented specifically, which should be included in the Materials and Methods, readjust.

 

Discussions

They are very focused only on the study area, and should present more correlations with other areas, where subsidence occurred and where the variation in relative sea level affected barrier islands or coastal sectors to demonstrate that this is a process perceived in WSDB, but that it can be replicated in other locations if a similar methodology is used.

Comments for author File: Comments.pdf

Author Response

The authors gratefully acknowledge the comments for the Geosciences-3269378 MS, “Lidar-Derived Decadal Change in Barrier Morphology: A Case Study of Waisanding, Taiwan”.

Modifications are marked in green in the revised version. The replies to the comments are as follows:

 

1. As the author himself says, this is a case study, in this sense it would be interesting to advance a little further in the literature that addresses barrier islands, bringing paleoenvironmental and geochronological studies in the introduction and discussions, to expand possible correlations. Suggestions:

https://onlinelibrary.wiley.com/doi/abs/10.1111/sed.12418 and

https://onlinelibrary.wiley.com/doi/10.1002/esp.5989

Response: We add a paragraph about paleoenvironmental study on coasts in the introduction and the 4.3 section of “ Paleoenvironmental Reconstruction” in the discussion, including literature review and study suggestion in the future. (Line 89-95, 106-108, and 680-721)

2. It can be expanded to include more references on barrier islands and include paleoenvironmental dynamics associated with coastal and barriers island changes.

Response: We add the 4.3 section of “ Paleoenvironmental Reconstruction” in the discussion, including literature review and study suggestion in the future. (Line 89-95, 106-108, and 680-721)

3. Some results are presented in this topic, change them to the results.

Response: The result about computed waves is moved to the section 4.2. Line 634-646).

4. In results, data selection criteria are presented specifically, which should be included in the Materials and Methods, readjust.

Response: The paragraph on section selection has been moved to Section 2.3.2 in Methods. (Line 230-244).

5. They are very focused only on the study area, and should present more correlations with other areas, where subsidence occurred and where the variation in relative sea level affected barrier islands or coastal sectors to demonstrate that this is a process perceived in WSDB, but that it can be replicated in other locations if a similar methodology is used.

Response: The morphological evolution of each barrier island has its own uniqueness and commonalities. If there is a decrease in the LA of a barrier island next to other areas of LS and SLR, the methodology of this case study can effectively capture and reasonably explain its morphological changes. (Line 623-626)

Currently, there is no well-bore data from geological drilling to conduct research. If there are sufficient research funds in the future, it would be a good academic study to establish the well-bore data at some locations of WSDB and to describe paleoenvironmental elements and stratigraphic architecture. Both subsidence analysis and paleogeographic investigation can be carried out at the same time to obtain the LS amount and sedimentation process of WSDB. (Line 716-721).

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Abstract - This is clear and concise and summarises the findings of the paper

Introduction -This provides a clear introduction to barrier beaches, their importance and evolution. It places the study into context. It could be improved with a brief section that outlines historical changes (last 100-200 years) in the barrier system. Much of the final paragraph, which describes the structure of the paper is not required.

Materials and Methods - A very clear outline of a variety of background information and its source which is relevant to the study. Also good to see that the source of the LIDAR data is described in detail. Is there any data available that indicates the accuracy of each LIDAR data set?

Results - In general a very detailed description of the data sets. Very good to see that a variety of parameters have been used and detailed description of different sections of the barrier system. The text should also mention that two of the LIDAR data sets were collected in April/early May (start of summer season) whilst the others were largely from July/September (summer season) There are two sections that need modification

Section 3.1.3 - At lines 283-284 it states that the change in barrier elevation is the result of overwash. This is an over simplification. The elevation changes due to overwash (elevation reduction) and dune formation (elevation increase). It is the balance of these two processes that determine how high the dunes reach. The text needs to be altered to reflect the dune formation process. It should also be noted that waves do not form dunes, it is wind blowing over exposed beach surfaces that transport sand to build up the dunes. A wide foreshore promotes wind transport.

Section 3.2 - Time Changes

Lines 352-354 - The text clearly indicates that there is no significant correlation between time and width of the barrier. It is thus inappropriate to outline the 0.755 m/yr rate of change, since it draws attention to a possible trend that is not statistically supported. This section needs to be redrafted.

Discussion - This largely focuses on the possible impact of land subsidence, sea level rise and typhoons. There is no reference to sediment supply or to long term evolution of the system. A paragraph that places the current results into the context of longer term evolution, if it is available, would be helpful. Similarly some assessment of activities that may have altered the sediment dynamics of the system would be helpful (e.g. dredging for beach nourishment, reduced sediment supply from rivers or due to coastal structures). In addition the following section needs to be revised 

Section 4.2 - Large Wave Effects

Lines 588-590 - I do not understand why the 5 typhons between 2004-2009 are then linked to a decrease in volume in 2016, given there are a further 8 typhoons between 2010 and 2015. There is a lack of data between 2006-2011 to justify the statement. The section needs to be reviewed and revised. The impact of a single event could be significant but the following period of standard coastal processes could be building up the dunes again. It is noteworthy that during the later period when there were no typhoons the volume did not significantly change. This might be a better starting point. The impact of the typhoons in terms of severity and distance from site needs to be assessed but the current text does not do this effectively.

Conclusions - A clear summary of the main findings.  

Minor Proposed Changes

Lines 11, 20, 81 - the comma before and is not required and should be removed. The rest of the text should be checked and further commas removed as required.

Line 30 - Change to   .... The Waisanding Barrier (WSDB) is a...

Line 31 - Change to ...island, located on the west coast of Taiwan (Fig. 1).

Line 33 - Change to ... for oyster farming in Taiwan.

Lines 72-73 - Change to ....different organisations, in all 13 DEM datasets collected over a 30 year period were identified and assessed for their data quality.

Lines 73-74 - Change to ...These LiDAR datasets provided a opportunity to determine the recent evolution of a barrier island and to assess the factors that produced the changes. 

Lines 74-83 - The final section of this paragraph can be removed. I do not think it is necessary to outline the content of the following sections.

 

Author Response

The authors gratefully acknowledge the reviewers' comments for the Geosciences-3269378 MS, “Lidar-Derived Decadal Change in Barrier Morphology: A Case Study of Waisanding, Taiwan”.

Modifications are marked in red in the revised version. The replies to the comments are as follows:

 

1. Introduction -This provides a clear introduction to barrier beaches, their importance and evolution. It places the study into context. It could be improved with a brief section that outlines historical changes (last 100-200 years) in the barrier system. Much of the final paragraph, which describes the structure of the paper is not required.

Response: The part of describing the structure of the paper is delimited.

 

2. Materials and Methods - A very clear outline of a variety of background information and its source which is relevant to the study. Also good to see that the source of the LIDAR data is described in detail. Is there any data available that indicates the accuracy of each LIDAR data set?

Response: Since the lagoon between WSDB and Taiwan is a shallow water area and covered with oyster shelves, it is impossible to carry out underwater surveying for marine bathymetry. In the early days, offshore marine bathymetry in the sea side and onshore elevation measurements of WSDB were carried out several times. However, these measurements do not provide comprehensive elevations of detailed morphology and are no longer available. It is therefore impossible to indicate the accuracy of LiDAR data sets. We search a new document about the quantitative assessment of LIDAR data accuracy and add the statement as follows: (Line 175-182) The average discrepancy of the LiDAR elevations is verified to be 0.12 m and the RMSE of the horizontal offsets is approximately 0.50 m [47] Elaksher et al., 2023]. The surveying company once used e-GNSS (e-Global Navigation Satellite System) to measure the elevation of two control points to verify that the LIDAR elevation accu-racy was about 0.1 m. Most of the DEM data were measured by the same company, and its equipment underwent calibration and inspection by the National Standards Bureau each time. Therefore, the dense and accurate data from LiDAR technology are suitable for analyzing morphological changes across the entire WSDB.

3. Results - In general a very detailed description of the data sets. Very good to see that a variety of parameters have been used and detailed description of different sections of the barrier system. The text should also mention that two of the LIDAR data sets were collected in April/early May (start of summer season) whilst the others were largely from July/September (summer season) There are two sections that need modification.

Response: We correct the wrong statement.

(Line 185-187) Three LiDAR data sets were collected in April/early June, the beginning of summer, whilst eight data sets were largely from July/September during the summer season. The earlier two data sets were measured in November.

(Line 196-199) We obtained seven-year data from the Tainan Hydraulics Laboratory at National Cheng Kung University (NCKU). Two measurements were carried out by the 5th River Management Office of the Water Resources Department in 2018 and 2019. The National Academy of Marine Research implemented LiDAR measurements in 2020. These LiDAR data belong to the research commissioning unit.

4. Section 3.1.3 - At lines 283-284 it states that the change in barrier elevation is the result of overwash. This is an over simplification. The elevation changes due to overwash (elevation reduction) and dune formation (elevation increase). It is the balance of these two processes that determine how high the dunes reach. The text needs to be altered to reflect the dune formation process. It should also be noted that waves do not form dunes, it is wind blowing over exposed beach surfaces that transport sand to build up the dunes. A wide foreshore promotes wind transport.

Response: T This paragraph has been significantly modified as follows.

(Line 336-345) From the topography of all sections, it can be seen that the foreshore beach is narrower and steeper than the backbarrier. The change in topographic level of these sections is the result of breaching the dunes and depositing sediment in the backbarrier in the form of washover fans and terraces [60]. Overwash typically occurs during severe storms and may extend to the backbarrier bay or lagoon. At the same time, the beach face generally retreats landward [61]. The primary source of dune deposits is aeolian sand transport from the subaerial beachface, particularly from dissipative beaches. [62]. Run-up overwash occurs when wave run-up heights exceed the dune height. The extent of sedimentation during an extreme storm and the rate of island transgression depends on the height and alongshore continuity of the foredunes. [60, 63].  

 

5. Section 3.2 - Time Changes. Lines 352-354 - The text clearly indicates that there is no significant correlation between time and width of the barrier. It is thus inappropriate to outline the 0.755 m/yr rate of change, since it draws attention to a possible trend that is not statistically supported. This section needs to be redrafted.

Response: We change the paragraph to “The coefficient of determination for width is 0.004. This value is extremely low relative to the length, indicating that there is no obvious linear change trend in the width. The rate of change from linear regression is not statistically significant.”

 

6. Discussion - This largely focuses on the possible impact of land subsidence, sea level rise and typhoons. There is no reference to sediment supply or to long term evolution of the system. A paragraph that places the current results into the context of longer term evolution, if it is available, would be helpful. Similarly some assessment of activities that may have altered the sediment dynamics of the system would be helpful (e.g. dredging for beach nourishment, reduced sediment supply from rivers or due to coastal structures). In addition the following section needs to be revised

Response: We indicate the factors affecting the morphological evolution of an island. Some factors are discussed in the section 4.1 and 4.2. However, there is no data available of river sediment sources and winds related to the morphological evolution of WSDB.

   The statement is written in Lines 703-715.

7. Section 4.2 - Large Wave Effects. Lines 588-590 - I do not understand why the 5 typhons between 2004-2009 are then linked to a decrease in volume in 2016, given there are a further 8 typhoons between 2010 and 2015. There is a lack of data between 2006-2011 to justify the statement. The section needs to be reviewed and revised. The impact of a single event could be significant but the following period of standard coastal processes could be building up the dunes again. It is noteworthy that during the later period when there were no typhoons the volume did not significantly change. This might be a better starting point. The impact of the typhoons in terms of severity and distance from site needs to be assessed but the current text does not do this effectively.

Response: The part of Large Wave Effects has major correction to reasonably explain the LV changes in Figure 12 by accumulated excess wave energy per year. (Line 647-671)

  

  

Minor Proposed Changes:

8. Lines 11, 20, 81 - the comma before and is not required and should be removed. The rest of the text should be checked and further commas removed as required.

Response: All the commas before and in the original draft have been deleted.

9. Line 30 - Change to   .... The Waisanding Barrier (WSDB) is a...

Response: In the previous summary, Waisanding Barrier has been abbreviated to WSDB, so we will use WSDB directly here. “The WSDB is a typical sandy barrier island,”

10. Line 31 - Change to ...island, located on the west coast of Taiwan (Fig. 1).

Response: Corrected.

11. Line 33 - Change to ... for oyster farming in Taiwan.

Response: Corrected.

12. Lines 72-73 - Change to ....different organisations, in all 13 DEM datasets collected over a 30 year period were identified and assessed for their data quality.

Response: Corrected.

13. Lines 73-74 - Change to ...These LiDAR datasets provided a opportunity to determine the recent evolution of a barrier island and to assess the factors that produced the changes.

Response: Corrected.

14. Lines 74-83 - The final section of this paragraph can be removed. I do not think it is necessary to outline the content of the following sections.

Response: The final section of this paragraph has been removed.

Author Response File: Author Response.docx