Impact of Large Reservoirs on Runoff and Sediment Load in the Jinsha River Basin

Round 1

Reviewer 1 Report

This topic of the manuscript falls within the scope of Water Journal, and the proposed methodology is interesting. However, it is noted that investigating the temporal and spatial variation trend of sediment transport has been discussed widely for decades (using different approach and methods). Besides, this manuscript can be improved with regards to the formulation of the proposed methodology, the gaps relevant to study case and data source, detailed discussion on results and scientific findings, the organization of the manuscript as well as grammatical errors. It is for sure that the authors can benefit from the valuable comments and suggestions provided by reviewers while revising the manuscript. Thus, a rejection with invitation to re-submit is recommended for the manuscript in its present form.

*Authors should be informed about the results of studies which they cited in this section. It's not enough to just cite the works. In addition, what the "problem statement" is exactly must be explained via the scientific way. 

* "MATERIALS AND METHODS " section should explain what has been done with a much more "clear and simple" sentences. Too much redundant sentence is written consecutively and the purpose is not fully understood.

* The concept of "hydrology" seems to be completely forgotten in this article, while the importance of hydrology and related sciences must be addressed in the proposed and applied approaches. 

* I think the results are presented without physical interpretation of the problem

Moderate editing of English language required

Author Response

This topic of the manuscript falls within the scope of Water Journal, and the proposed methodology is interesting. However, it is noted that investigating the temporal and spatial variation trend of sediment transport has been discussed widely for decades (using different approach and methods). Besides, this manuscript can be improved with regards to the formulation of the proposed methodology, the gaps relevant to study case and data source, detailed discussion on results and scientific findings, the organization of the manuscript as well as grammatical errors. It is for sure that the authors can benefit from the valuable comments and suggestions provided by reviewers while revising the manuscript. Thus, a rejection with invitation to re-submit is recommended for the manuscript in its present form.

Reply: The manuscript has been thoroughly revised according to the reviewer's suggestions. I hope the revised manuscript can meet the publishing requirements.

*Authors should be informed about the results of studies which they cited in this section. It's not enough to just cite the works. In addition, what the "problem statement" is exactly must be explained via the scientific way. 

Reply: Based on these suggestions, corresponding revisions have been made to the manuscript. The main modification is in lines 67-79; 117-127.

* "MATERIALS AND METHODS " section should explain what has been done with a much more "clear and simple" sentences. Too much redundant sentence is written consecutively and the purpose is not fully understood.

Reply: The explanation in the Methods section has been revised as much as possible based on the reviewer's comments. Meanwhile, the Mann-Kendall method has been fully supplemented. The main modification is in lines 205-213; 236-265.

* The concept of "hydrology" seems to be completely forgotten in this article, while the importance of hydrology and related sciences must be addressed in the proposed and applied approaches. 

Reply: The main purpose of this study is to reveal the trend, spatial differences, and the impact of dam construction on water and sediment changes in the study area. Therefore, the selected method is basically appropriate.

* I think the results are presented without physical interpretation of the problem

Reply: I agree with this view. I have attempted to make modifications. Perhaps there are still shortcomings, and we hope to expand this research work in the future from aspects such as hydrodynamics, sediment sorting, and the proportion of sediment with different particle sizes.

Reviewer 2 Report

My specific comments are in the attached pdf. 

A pleasure to read about sediment impacts in China. My complements to the others for making the effort to make this information available in English. This accounting of the impacts of large reservoirs on runoff and sediment is a valuable contribution to global literature on this subject. Research is clearly organized and explained. Might consider putting information about dam construction in site description not discussion. Explanation of mutation analysis and Mann Kendall should be improved. Focusing on annual data is a necessary first step, but I encourage authors to follow up with more fine grained look at rainfall and discharge relationships at a monthly scale. Examination of why trends are occurring - particularly in the period before large dams installed needs to be improved. 

Comments for author File: Comments.pdf

Fine. A few points in text are marked in attached pdf, where meaning of sentence was unclear. Not sure 'mutation' is the right word to use for the change point detection analysis.

Author Response

Comments and Suggestions for Authors

My specific comments are in the attached pdf. 

A pleasure to read about sediment impacts in China. My complements to the others for making the effort to make this information available in English. This accounting of the impacts of large reservoirs on runoff and sediment is a valuable contribution to global literature on this subject. Research is clearly organized and explained. Might consider putting information about dam construction in site description not discussion. Explanation of mutation analysis and Mann Kendall should be improved. Focusing on annual data is a necessary first step, but I encourage authors to follow up with more fine grained look at rainfall and discharge relationships at a monthly scale. Examination of why trends are occurring - particularly in the period before large dams installed needs to be improved. 

Reply: 1) Thank you for your overall recognition and valuable suggestions for this work! According to the suggestion, relevant information on the 24 large dams built in different years in the study area is supplemented in the form of a table in the Study area section. 2) Improvements have been made to address the issues in sudden change analysis and Mann-Kendall's explanation. 3) It is necessary to conduct more detailed research on the relationship between rainfall and flow on a monthly scale. Given that the manuscript mainly studies the interannual variation characteristics of water and sediment, it is expected that further in-depth research on this aspect will be conducted in the future.

Comments on the Quality of English Language

Fine. A few points in text are marked in attached pdf, where meaning of sentence was unclear. Not sure 'mutation' is the right word to use for the change point detection analysis.

Reply: Thank you for providing a series of annotations in the text of the attachment! We have carefully revised or elaborated more clearly based on all annotations. All modifications are marked in red font.

We have deleted all words 'mutation' that appear in the text and replaced them with ' sudden change' or 'inflection point' as needed.

Reviewer 3 Report

The presented article is an interesting case study on the relationship between trends in water flows and sediment transport in the Jinsha River catchment in the context of the impact of large dam reservoirs. The authors presented the results in an exhaustive way, using a number of analytical and statistical methods. I think that the study was planned in a thoughtful way in the context of the assumed goals. An undoubted advantage is the reference to monitoring data from many years, which allowed for more advanced analyzes and drawing more accurate conclusions. Despite these advantages, the manuscript needs improvement, especially in the context of internationalization of the issues described, clearer formulation of goals, details of the data obtained and information contained in the conclusions. After these major revisions, the paper will be suitable for publication in the Water journal.

1. The introduction is quite short, please extend it to the issue of the impact of hydropower plants and large reservoirs on the environment, society and economy, as well as the situation of hydropower and reservoirs in the world (e.g. in the context of individual national or international policies, e.g. applicable in the European Union). Please cite more literature giving examples outside of China.

2. Please highlight the clear goals of the article. Currently, they are marked in a descriptive form, but quite generally.

3. Figure 1: please add an arrow indicating the direction of water flow in the watercourses. This will make it much easier to orientate yourself in the Jinsha River catchment shown.

4. How was the data obtained from Xiangjiaba and Pingshan Stations consistent with each other? Why was Xiangjaba station chosen to replace Pingshan after 2012? I think that such a change may affect the presented results and, without proper data transfer, may lead to erroneous conclusions. Please refer to this issue both in the description of the methods and in the analysis of the results.

5. Have you considered densifying the grid of points for which multi-year data would be available? The presented division in the context of the course of the river seems justified, however, it covers large catchment areas, so the presented results, discussion of results and conclusions may be too general in the context of spatial variability due to the potential large number of variables in such large areas. Please indicate the number of stations for which there would be similar availability on flow variability and sediment transport.

6. How often were parameters measured in the monitoring of sediment flows and transport? Is it daily data?

7. The presented literature requires internationalization. Looking at the bibliography, the authors referred in most cases to examples from Asia regarding the issues of flow variability and sediment load. Please correct it.

8. I think that the full names of all parameters should be preserved in the captions of tables and figures - while in the main text it is actually better to give the full name and abbreviation at the beginning, and then use the abbreviation, but in the case of captions such checking is a hindrance.

10. Figure 4: what do the abbreviations UF(k) and UB(k) mean? Is a = 0.05 a significance level of 0.05?

11. Please verify the styles used in the text - e.g. in lines 348-355 there is bold, which is unnecessary.

12. In the conclusions, please provide possible future directions of research, the potential significance of the presented results (cognitive and/or application, e.g. recommendations for rational management of water and bottom sediments in reservoirs or within hydropower plants) and provide limitations as to the presented results in context of their universality.

Author Response

Comments and Suggestions for Authors

The presented article is an interesting case study on the relationship between trends in water flows and sediment transport in the Jinsha River catchment in the context of the impact of large dam reservoirs. The authors presented the results in an exhaustive way, using a number of analytical and statistical methods. I think that the study was planned in a thoughtful way in the context of the assumed goals. An undoubted advantage is the reference to monitoring data from many years, which allowed for more advanced analyzes and drawing more accurate conclusions. Despite these advantages, the manuscript needs improvement, especially in the context of internationalization of the issues described, clearer formulation of goals, details of the data obtained and information contained in the conclusions. After these major revisions, the paper will be suitable for publication in the Water journal.

Reply: The manuscript has been thoroughly revised based on the suggestions of the editor and three reviewers.

1. The introduction is quite short, please extend it to the issue of the impact of hydropower plants and large reservoirs on the environment, society and economy, as well as the situation of hydropower and reservoirs in the world (e.g. in the context of individual national or international policies, e.g. applicable in the European Union). Please cite more literature giving examples outside of China.

Reply: Based on this suggestion, we have expanded the introduction, including adding some missing citations and adding various impacts of dam construction on river systems in Europe and America. All these modifications are presented in red in the introduction section.

2. Please highlight the clear goals of the article. Currently, they are marked in a descriptive form, but quite generally.

Reply: This suggestion is very important as it points out serious omissions in the original manuscript. The modifications in this regard are listed on lines 116-127.

3. Figure 1: please add an arrow indicating the direction of water flow in the watercourses. This will make it much easier to orientate yourself in the Jinsha River catchment shown.

Reply: The flow direction is added in Figure 1.

4. How was the data obtained from Xiangjiaba and Pingshan Stations consistent with each other? Why was Xiangjaba station chosen to replace Pingshan after 2012? I think that such a change may affect the presented results and, without proper data transfer, may lead to erroneous conclusions. Please refer to this issue both in the description of the methods and in the analysis of the results.

Reply: The distance between Xiangjiaba Station and Pingshan Station is only 30 km, and the control area of Xiangjiaba Station is only 0.045% more than that of Pingshan Station. The annual runoff and sediment transport values of the two stations are almost equal and can be completely replaced by each other.

A detailed explanation of this aspect can be found in the first paragraph of the dataset section (at lines of 178-185, in red font).

5. Have you considered densifying the grid of points for which multi-year data would be available? The presented division in the context of the course of the river seems justified, however, it covers large catchment areas, so the presented results, discussion of results and conclusions may be too general in the context of spatial variability due to the potential large number of variables in such large areas. Please indicate the number of stations for which there would be similar availability on flow variability and sediment transport.

Reply: The water and sediment data of these hydrological stations actually include the inflow and sediment of the mainstream and all tributaries above their observation sections. It is not contradictory to use this data to analyze the process of water and sediment changes at the location of the hydrological station and discuss the impact of the dam.

The hydrological stations for long-term observation on the main river channel below Shigu are basically these three hydrological stations. There are also some hydrological stations with only about ten years of data, which is not convenient to compare with the water and sediment processes of the aforementioned hydrological stations.

6. How often were parameters measured in the monitoring of sediment flows and transport? Is it daily data?

Reply: The annual data used in the article is calculated based on the daily average observed data. This is the daily work of a professional organization under the Ministry of Water Resources of China, with high data accuracy and observation density.

The explanation on the frequency and accuracy of data observation is supplemented in lines 191-197.

7. The presented literature requires internationalization. Looking at the bibliography, the authors referred in most cases to examples from Asia regarding the issues of flow variability and sediment load. Please correct it.

Reply: Based on this suggestion, some research progresses In Europe and the Americas have been supplemented and cited, and the common impacts of dam construction on water and sediment have been further elaborated. The modifications in this regard are presented in red font on lines 67-92.

8. I think that the full names of all parameters should be preserved in the captions of tables and figures - while in the main text it is actually better to give the full name and abbreviation at the beginning, and then use the abbreviation, but in the case of captions such checking is a hindrance.

Reply: According to this suggestion, all relevant deficiencies have been comprehensively revised.

10. Figure 4: what do the abbreviations UF(k) and UB(k) mean? Is a = 0.05 a significance level of 0.05?

Reply: In response to this suggestion, additional formulas for calculating these parameters were introduced (on lines 236-265).

Yes, ɑ=0.05 is a significance level of 0.05. It was corrected the conceptual errors in the original text.

11. Please verify the styles used in the text - e.g. in lines 348-355 there is bold, which is unnecessary.

Reply: This has been corrected.

12. In the conclusions, please provide possible future directions of research, the potential significance of the presented results (cognitive and/or application, e.g. recommendations for rational management of water and bottom sediments in reservoirs or within hydropower plants) and provide limitations as to the presented results in context of their universality.

Reply: This is a very important suggestion. Based on this suggestion, future research directions that can be focused on have been added (on lines 668-674).

Round 2

Reviewer 1 Report

The revised version has high potential to be accepted; I listed some suggestions and comments to improve the manuscript:

1. Focus on your novelty in abstract and mention it with more details in last paragraph of Introduction

2. Moderate editing English language required

3. Please discuss more about your results

4. Please compare your results with previous studies.

_{Moderate editing of English language required}

Author Response

Dear Reviewer,

Thank you very much for your valuable suggestions.

We have made corresponding revisions to the manuscript in response to these comments. The specific modifications are listed below. We hope the revised manuscript can meet the publishing requirements.

Yours sincerely,

Suiji Wang

The revised version has high potential to be accepted; I listed some suggestions and comments to improve the manuscript:

1. Focus on your novelty in abstract and mention it with more details in last paragraph of Introduction

Reply: The modifications have been made according to the suggestion. Please refer to lines 119-121 for details.

2. Moderate editing English language required

Reply: The manuscript has undergone English language editing by MDPI.

3. Please discuss more about your results

Reply: Based on this suggestion, the discussion of the results has been expanded. Please refer to lines 480-487,592-598,604-606, and 620-642 (highlighted statements).

4. Please compare your results with previous studies.

Reply: According to this suggestion, the supplementary comparison of this study results with those of previous studies is listed in lines 654-662.

Reviewer 3 Report

The Authors took into account all my comments and addressed them exhaustively. Thank you for that and good luck with the further processing of the manuscript.

Author Response

Dear Reviewer,

Thank you for your detailed and valuable suggestions during the previous round of review. Your suggestions are of great significance for manuscript revision and quality improvement. Thank you also for your approval of the revised manuscript!

Yours sincerely,

Suiji Wang