Channel Incising and Sandbar Growth in the Upper Yangtze River Estuary During 1994–2019, China
, Shuo Chen 1,2, Mengjie Zhao 3, Wen Liu 4, Yijun Xu 2,*, Zijun Li 1, Jinkuo Lin 1 and Shuwei Zheng 1,*Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsPlease see the attachment
Comments for author File: 
Comments.pdf
Author Response
Reviewer comments:
Reviewer #1:
In present study, authors used historical bathymetric data to assess channel and bar development in the Yangtze River estuary. Along with this, authors also analyzed the influence of anthropogenic activities and climate changes on the branching channel-bar system of the upper YRE.
Concept of paper is good and also written in well manner.
[Authors’ response] We would like to sincerely thank you for taking your valuable time to review our manuscript. All your comments and suggestions have been taken into account while revising our manuscript, and they have been very helpful for us to improve the quality of our manuscript.
- The title "Channel incising--------Yangtze River-------" should be considered including the temporal period. For example, "-------during 1994–2019".
[Authors’ response] Thanks for your suggestion. We have modified the title to: Channel incising and sandbar growth in the upper Yangtze River Estuary during 1994−2019, China.
(2) The description of "Topography deformation" in the keywords is not very appropriate, which can be modified to "Topography changes".
[Authors’ response] We agree and have changed it to “Channel topographic changes.”
(3) There are several "Error! Reference source not found." warning in the paper, please revise or add it. The specific picture number could not be found in the results and analysis of the paper.
[Authors’ response] Thank you for catching this. We have checked reference source and verified citation numbers throughout the revised version.
(4) The format of the formula in the paper are also confused, for example, there are not placed in the middle position.
[Authors’ response] Sorry for the confusion. Modified.
(5) The three formulas in the Methods section of 2.3 are a bit confusing. The sediment mass change (M) of the first formula does not appear in the results and is not directly related to the second and third formulas. It is not clear how these three formulas relate to each other. Please re-describe the above three formulas in detail.
[Authors’ response] Sorry for the confusing. The three formulas in the Methods section were re-describe in detail. Please see lines 166-171.
Moreover, we have added the results about sediment mass change (M) in section of 3.1. “Based on the bulk density of riverbed material of 1.30 t/m3 (Guo et al. 2021), a total of 12.48×108 t of sediment has been eroded from the study area, with an annual erosion of 0.49×108 t/a over the past 25 years.” Please see lines 187-192.We hope that these changes/additions meet your expectation.
(6) In section 3.3, what data or methods are used to determine the boundary of the sandbars? Please describe it in detail in your paper.
[Authors’ response] Thank you for your careful review. In this study, the boundary of sandbars was extracted from historical bathymetric maps (Table 1). Because the datum of these maps is theoretical lowest tide level, we selected the 0 m isobath as the sandbar boundary. Thus, the area of Xinliuhe Shoal increased from 6.1 km2 (1994) to 16.15 km2 (2018) with an average increase of 0.42 km2/a (Figure 4). Please see lines 215-219.
(7) The numerical value of net erosion volume in the YRE (Lines 350-351) has an uncertainty, but how is this uncertainty calculated? No specific explanation was given in this paper.
[Authors’ response] Sorry for the confusing. We have added related discussion in section 4.4 (see lines 345-351).
In this study, 3.74×107 m3 channel volume of the results may have been due to sea level rise, making the estimate likely larger than the actual change. Therefore, the channel volume change caused by erosion may be smaller than our estimate based solely on bathymetric map changes. This means that considering the effect of the sea level rise, the net erosion volume in the YRE from 1994 to 2019 is more than 9.58×108-3.74×107 m3 (or 9.58-0.37×108 m3).
(8) There are some mistakes in the Figure 8. For example, 1) the text (Line 323) does not match the picture in 2007, 2) there are two “subgraph C” in Figure 8, 3) the numerical range of the legend is “-25 to 0” which is clearly less than that in the sub-figures. Additionally, the instruction for the Figure 8 results is too little to explain clearly.
[Authors’ response] Thank you for your careful review. We have modified Figure 8 and added more information about sub-figures.
Figure 8. Scour pit at the head of Xinliuhe Shoal. Map A shows locations of Xinliuhe Shoal, Xinliuhe Shoal Protection Project and scour pit. B-G maps show the deepest point of the scour pit in 2007, 2009, 2011, 2015, 2018, and 2022, respectively. Red closed lines in D-G maps show the -20 m isobath.
(9) In Section 4.4, how is the result of channel volume caused by sea level rise calculated? Please explain in detail.
[Authors’ response] Thank you for your careful review. According to the 2022 Chinese Sea Level Bulletin, taking the average sea level change rate (3.49 mm/a) from 1994 to 2019, the total change over this period is calculated to be 8.73 cm.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis paper addresses the impact of anthropogenic activities on the geomorphic dynamics of estuaries, focusing specifically on the upper Yangtze River Estuary over a period from 1994 to 2019. The study assesses the topographic evolution of the estuary focusing on the shifting dynamics of channels and sandbars. The paper provides valuable data, contributing to the scientific literature on estuarine dynamics, especially regarding the interactions between human interference and erosion of estuarine channels. However, the readability is difficult due to formatting issues with errors in all references to figures in the text and the excessive use of acronyms. Some acronyms are not defined immediately at their first appearance, which create confusion for the reader. Additionally, the overuse of acronyms may reduce the clarity of the text in certain sections.
Furthermore, the following comments must be taken into account and revisions should be made where necessary.
Specific comments
- More information about the water and sediment discharge data should be provided (line 150)
- How is the measurement uncertainty calculated? (line 189)
- In Figure 2F, how is the net change for the fifth bar (1994-2019) calculated? It seems that some information is missing
- Verify the accuracy of the annual increase of the XLHS (line 217)
- Verify the total area of sand bodies (line 218)
- Why is there no analysis or comment on the downstream migration of the DF-BDS (par. 3.3.2)?
- References to publications by the Intergovernmental Panel on Climate Change should also be provided, given the global significance of this organization (line 331).
- The relationship between wave propagation speed and the square root of water depth is valid only in shallow water. As sea levels rise, the dynamics of waves in the estuary may change and the impact could be complex. It depends on several factors such as wave energy and changes in the coastline. The sentence needs clarification, as it is oversimplified (line 339).
Technical comments
- Using “changing water and sediment dynamics” is more appropriate (line 57)
- It is suggested to repeat for the first time the acronymous YRE as it first appears in the text beyond the abstract
- Define the acronym XLHS (line 113)
- TGD should be defined in the text beyond caption Figure 1 (line 146)
- BDS must be defined (line 149)
- Specify if you are referring to GIS software (line 168)
- In order to better clarify equation (1), (2) and (3) a schematic representation of the vertical section of the channel must be provided
- Better define P1, etc. It is unclear due to errors in the references
- Verify statement (line 247)
- It was initially specified that the available data for SS and SSC covered the period from 2000 to 2021, but now it is reported from 1986. Please clarify (line 283)
- Verify statement (line 287-288)
Comments on the Quality of English Language The English language used in the article is sometimes unclear. It would benefit from improvement in terms of clarity and overall readabilityAuthor Response
Reviewer comments:
Reviewer #2:
This paper addresses the impact of anthropogenic activities on the geomorphic dynamics of estuaries, focusing specifically on the upper Yangtze River Estuary over a period from 1994 to 2019. The study assesses the topographic evolution of the estuary focusing on the shifting dynamics of channels and sandbars. The paper provides valuable data, contributing to the scientific literature on estuarine dynamics, especially regarding the interactions between human interference and erosion of estuarine channels. However, the readability is difficult due to formatting issues with errors in all references to figures in the text and the excessive use of acronyms. Some acronyms are not defined immediately at their first appearance, which create confusion for the reader. Additionally, the overuse of acronyms may reduce the clarity of the text in certain sections.
[Authors’ response] We greatly appreciate you for your support and your valuable time in reviewing our paper. All of your comments and suggestions have been taken into account in our paper, and they have been very helpful for us to improve the quality of our manuscript.
Specific comments
- More information about the water and sediment discharge data should be provided (line 150).
[Authors’ response] Your point is well taken. To address this, we have added the website about these data. “Water and sediment discharge data from the Datong Hydrological Station were collected from 1960 to 2021. The data includes annual and monthly averages (http://www.cjw.gov.cn/zwzc/zjgb/cjnsgb/).”
We hope that these changes/additions meet your expectation.
- How is the measurement uncertainty calculated? (Line189)
[Authors’ response] Sorry for the confusion. We have re-write this part.
From 1994 to 2019, the riverbeds experienced strong erosion with an erosion volume of 13.00×108 m3 and a deposition volume of 3.41×108 m3 (Figure 2). As a result, the channel eroded a net volume of 9.59×108 m3 with an average erosion thickness of 2.17 m or an average annual erosion rate of 8.67 cm (Figure 2E and 2F). Based on the bulk density of riverbed material of 1.30 t/m3 (Guo et al. 2021), a total of 12.48×108 t of sediment has been eroded from the study area, with an annual erosion of 0.49×108 t/a over the past 25 years. Specifically, major erosion occurred in water depths between -5 and -20 m (76.65 %), while water depths between 0 and -5 m and > -20 m accounted for 1.10% and 10.48%, respectively. Notably, the area between -5 and -10 m was eroded by 3.10×108 m3 (accounting for 29. 35 %), and the -10−-20 m was eroded 5.01×108 m3 (47.29%).
We hope that these changes/additions meet your expectation.
3) In Figure 2F, how is the net change for the fifth bar (1994-2019) calculated? It seems that some information is missing
[Authors’ response] Sorry for the confusion. We have changed the bar and added some illustration in Figure 2 to explain these results.
Figure 2. Erosion and deposition of total volume between years. (Erosion: Volume of erosion in the river channel within the specified period. Deposition: Volume of deposition in the river channel within the specified period. Net change: Absolute value of deposition minus erosion. Positive axis on the coordinate represents sedimentation; negative axis represents scour.)
4) Verify the accuracy of the annual increase of the XLHS (line 217).
[Authors’ response] Thank you for your suggestion. Upon verification, the rate calculations in line 271 are accurate; however, wrongs are noted in the data at line 213 and the year cited at line 218.
5) Verify the total area of sand bodies (line 218).
[Authors’ response] Thank you for your suggestion. We have confirmed the numerical value of the area and denoted it in the figure title as the area of the 0m isobath of the sand bodies.
6) Why is there no analysis or comment on the downstream migration of the DF-BDS (par. 3.3.2)?
[Authors’ response] Thank you for your suggestion. Firstly, we have added a description of the migration of the center of gravity of sand particles in lines 224-229: Between 1994 and 2003, the sand body migrated at an average annual rate of 485.06 meters, marking the fastest period of migration. From 2003 to 2011, migration slowed, with an average annual downstream movement of 148.49 meters. Between 2011 and 2015, rapid sedimentation at the sand tail resulted in a swift repositioning of the sand body's centroid, averaging 414.15 meters per year (Figure 4F). Subsequently, from 2015 to 2018, the migration rate further decreased, averaging 62.45 meters annually.
7) References to publications by the Intergovernmental Panel on Climate Change should also be provided, given the global significance of this organization (line 331).
[Authors’ response] Thank you for your suggestion. We have added the " AR6 Synthesis Report: Climate Change 2023 " report published by the IPCC in 2023 as a reference in line 448-450.
8) The relationship between wave propagation speed and the square root of water depth is valid only in shallow water. As sea levels rise, the dynamics of waves in the estuary may change and the impact could be complex. It depends on several factors such as wave energy and changes in the coastline. The sentence needs clarification, as it is oversimplified (line 339).
[Authors’ response] Thank you for your suggestion. Firstly, we specifically rephrased this sentence as: In addition, the greater water depth due to sea level rise will intensify fluctuations in maximum storm surges and wave heights. Nearshore wave heights are more susceptible to the impacts of sea-level rise compared to those in the open ocean. (Kai et al., 2017; Shen et al., 2019) with an updated reference.
Technical comments
9) Using “changing water and sediment dynamics” is more appropriate (line 57).
[Authors’ response] Revised.
10) It is suggested to repeat for the first time the acronymous YRE as it first appears in the text beyond the abstract.
[Authors’ response] Thank you for your suggestion. Revised.
11) Define the acronym XLHS (line 113).
[Authors’ response] Done.
12) TGD should be defined in the text beyond caption Figure 1 (line 146).
[Authors’ response] Done.
13) BDS must be defined (line 149).
[Authors’ response] Thank you for your suggestion. Modified.
14) Specify if you are referring to GIS software (line 168).
[Authors’ response] Yes, added the information.
15) In order to better clarify equation (1), (2) and (3) a schematic representation of the vertical section of the channel must be provided.
[Authors’ response] Thank you for your suggestion. Revised.
16) Better define P1, etc. It is unclear due to errors in the references.
[Authors’ response] Sorry for the confusion. Done.
17) Verify statement (line 247).
[Authors’ response] Thank you for your suggestion. Revised.
18) It was initially specified that the available data for SS and SSC covered the period from 2000 to 2021, but now it is reported from 1986. Please clarify (line 283).
[Authors’ response] Sorry for the confusion. Revised. Please see lines 294-295.
19) Verify statement (line 287-288).
[Authors’ response] Modified.
20) Comments on the Quality of English Language.
The English language used in the article is sometimes unclear. It would benefit from improvement in terms of clarity and overall readability.
[Authors’ response] Thank you for your careful review. We have checked the paper again and modified some misspellings and old language. We have invited native English experts to polish this paper. Please see the revised version.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsDuring my previous review of the manuscript, I highlighted issues with errors in cross-references (Error! Reference source not found.). Unfortunately, these errors are still present in the current version.
Accurate cross-references are crucial for evaluating the manuscript effectively and ensuring its coherence and quality. As the issue persists, I kindly suggest that all cross-references be thoroughly corrected before proceeding with further reviews. Furthermore, it is necessary to provide at the beginning of the article a Nomenclature table with all acronymous used in the text.
Author Response
Reviewer comments:
During my previous review of the manuscript, I highlighted issues with errors in cross-references (Error! Reference source not found.). Unfortunately, these errors are still present in the current version.
Accurate cross-references are crucial for evaluating the manuscript effectively and ensuring its coherence and quality. As the issue persists, I kindly suggest that all cross-references be thoroughly corrected before proceeding with further reviews. Furthermore, it is necessary to provide at the beginning of the article a Nomenclature table with all acronymous used in the text.
[Authors’ response] We greatly appreciate you for your support and your valuable time in reviewing our paper. We have cross-referenced the bibliographic citations in our paper. Regarding the use of acronyms, we have checked the acronyms used in the text and modified those that are unnecessary. At the same time, the full forms of all acronyms have been used at their first occurrence. All your suggestions have been very helpful for us to improve the quality of our manuscript.
Author Response File: Author Response.pdf
