Assessing the Accuracy of 3D Modeling of Hydrotechnical Structures Using Bathymetric Drones: A Study of the Karatomara Reservoir

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript takes the Karatomar Reservoir in Kazakhstan as an example. The bathymetric survey was carried out using an Apache 3 drone, and the reservoir models were constructed in QGis and Surfe software. The research aimed to investigate the actual situation of the reservoir after 78 years of operation, the accuracy of bathymetric surveys in representing the reservoir topography after interpolation, and to determine the appropriate measurement interval, providing a reference for the accuracy assessment of 3D reservoir modeling and related research. The following comments are for the authors' reference:

1. The measurement was solely conducted using an Apache 3 drone equipped with a single-beam single-frequency echo sounder, resulting in a single measurement device. It is recommended to incorporate other measurement methods such as multi-beam echosounders and LiDAR to obtain data. By comparing the measurement results of different devices, the reliability of the data can be improved.
2. The simple kriging method was chosen as the interpolation algorithm, yet the comparison with other interpolation methods was not in-depth and comprehensive enough. It is necessary to further compare the performances of multiple interpolation methods under different topographic conditions and data densities, so as to more fully illustrate the advantages and applicability of the simple kriging method.
3. When evaluating the measurement interval, the data was mainly based on the "bay" area of the reservoir. However, this area may not fully represent the characteristics of the entire reservoir. It is required to select more diverse measurement points in the main body of the reservoir for the evaluation of the measurement interval and model construction, ensuring that the research results can be generalized to the entire reservoir.
4. Although the drone echo sounder was calibrated, the parameters were only set at specific depths, and no comparison and verification were made with other reliable measurement data. It is advisable to increase the calibration depth points and compare with high-precision measurement data (such as laboratory measurement data or data from other authoritative institutions) to ensure the accuracy of the measurement data.
5. The changes in reservoir parameters were mainly attributed to siltation and vegetation growth, while other possible factors such as climate change and changes in the water quality of upstream inflows were not considered. A comprehensive analysis of the impacts of multiple factors on reservoir parameter changes should be conducted to construct a more complete influencing factor analysis system.
6. The measurement errors and uncertainties in the model construction process were not analyzed. Methods such as error propagation analysis and Monte Carlo simulation should be employed to evaluate the uncertainties and clarify the confidence intervals of the research results.
7. When describing the research methods and results, the explanations of some professional terms were not clear, such as the processes of "digital elevation model processing" and "spatial image quality determination". The specific operations and principles related to these terms should be elaborated in detail to enhance the readability of the paper.
8. Some of the charts (such as some depth measurement result charts) have incomplete axis labels, lacking key information such as units. It is necessary to improve the chart labels so that readers can more intuitively and accurately understand the content of the charts.

Author Response

Thanks for your comments!

Comment 1: 

The measurement was solely conducted using an Apache 3 drone equipped with a single-beam single-frequency echo sounder, resulting in a single measurement device. It is recommended to incorporate other measurement methods such as multi-beam echosounders and LiDAR to obtain data. By comparing the measurement results of different devices, the reliability of the data can be improved.

Response 1:

The echo sounder used in the study, based on the specialized bathymetric drone Apache 3, is designed by the manufacturer for bathymetric studies of large water bodies, has internal equipment to compensate for the influence of waves and was additionally “tied” to GNSS, which made it possible to achieve the stated accuracy of depth measurements of up to 0.01 meters.

The drone's echo sounder has been verified by the state center for verification of measuring equipment, certified for use in Kazakhstan (and additionally calibrated by the authors of the study for the Karatomar reservoir. Accuracy adjustment was made by adjusting the parameters at depths of 1, 3 and 5 meters of this reservoir (reservoir bay), plus an additional 10 and 15 meters for the reservoir itself (information is given in the first edition of the article, lines 147-152, SE line 136-140).

Also, I would like to note that for additional verification of both the measurement results and 3D modeling, the authors manually collected data on the depths of the reservoir control points using a line and a hydrometric rod. The data from our ultrasonic measurements using a bathymetric drone and manual measurement methods coincided with an error of less than 0.1 m. The deviation of the modeling data from manual measurement methods also did not exceed the required 10%. Which confirmed the success of the drone calibration, verified the accuracy and reliability of the measurements/modeling. (correction added to the second edition of the article, line 140-147)

The Karatomar reservoir during the study period (and to date) is filled to more than 90-98% of its maximum volume.

LiDAR technologies allow us to assess the topology of the reservoir bowl only above the water's edge. And they do not allow measuring the depths of the underwater part of the object (this fact is noted by the authors in Table 2 of the article).

Multi-beam echo sounders (compared to single-frequency single-beam type Apache 3) are intended more for obtaining a detailed picture of relatively small underwater submerged objects, and not for measuring depths during bathymetric studies of hydraulic structures (or studying objects with a complex bottom structure). And the economic costs of using multi-beam echo sounders do not make them attractive in bathymetric studies of large hydraulic structures (like the studied reservoir with an area of ​​93.7 km²).

Comment 2: 

The simple kriging method was chosen as the interpolation algorithm, yet the comparison with other interpolation methods was not in-depth and comprehensive enough. It is necessary to further compare the performances of multiple interpolation methods under different topographic conditions and data densities, so as to more fully illustrate the advantages and applicability of the simple kriging method.

Response 2:

The linear interpolation method is the simplest and most frequently used. The method does not depend on the number of nodes (when adding nodes, there is no need to recalculate all the values). Of the obvious advantages, it is worth noting fairly accurate results in cases where the change in the values ​​of the interpolated depths is relatively uniform and predictable.

However, the linear interpolation method has a significant drawback - the function graph is not smooth and often significantly does not coincide with the true depth values.

Compared to the compared methods, kricking gives the best linear unbiased prediction of intermediate values ​​with the correct a priori assumptions.

Kricking also minimizes the variance of the measurement error. (correction added to the second edition of the article, line  271-285)

Comment 3: 

When evaluating the measurement interval, the data was mainly based on the "bay" area of the reservoir. However, this area may not fully represent the characteristics of the entire reservoir. It is required to select more diverse measurement points in the main body of the reservoir for the evaluation of the measurement interval and model construction, ensuring that the research results can be generalized to the entire reservoir.

Response 3:

The Tobol and Ayat rivers (as well as the "bay") in the reservoir zone are characterized by a smooth bottom relief with a slope of 0.5 °/°° - 0.8 °/°°

The authors estimated the correlation of the "bay" dependencies on the Tobol and Ayat river beds based on the Pearson criterion. The dependencies are in medium and highly correlated zones (Table 8 of the article), which confirms the validity of applying the "bay" methods to the entire reservoir.

Additionally, to verify the results, the authors carried out bathymetry of individual polygons of the Ayat River bed in the area of ​​the village of Naberezhnoye with a density of 50, 100, 200, 300, 400 and 500 meters (data from which were not included in the final 3D model of the reservoir). Analysis of the accuracy of the obtained data confirmed the previously obtained conclusions about the minimum required density of measurements with a step of no more than 200 meters. (correction added to the second edition of the article, line 508-516)

Comment 4: 

Although the drone echo sounder was calibrated, the parameters were only set at specific depths, and no comparison and verification were made with other reliable measurement data. It is advisable to increase the calibration depth points and compare with high-precision measurement data (such as laboratory measurement data or data from other authoritative institutions) to ensure the accuracy of the measurement data.

Response 4:

The bathymetric drone and sonar have been verified and certified for use in the Republic of Kazakhstan. Accuracy adjustment was made by setting the parameters at depths of 1, 3 and 5 meters of this reservoir (reservoir bay), plus an additional 10 and 15 meters for the reservoir itself (information is provided in the article). This range of depths adjusted as a result of sonar calibration covers 97% of the reservoir area and 99.99% of the reservoir volume (Table 9 of the article). The maximum depth was recorded as 16 meters.

Although verification should remove the issue of the device accuracy, I repeat, for additional verification of both the measurement results and 3D modeling, the authors manually collected data on the depths of the reservoir control points using a line and a hydrometric rod. The data from our ultrasonic measurements using a bathymetric drone and manual measurement methods coincided with an error of less than 0.1 m. The deviation of the modeling data from manual measurement methods also did not exceed the required 10%. Which confirmed the success of the drone calibration and verified the accuracy and reliability of the measurements/modeling. (correction added to the second edition of the article, line  141-147).

There is no current data from other authoritative institutions, which is why the study was initiated.

Comment 5: 

The changes in reservoir parameters were mainly attributed to siltation and vegetation growth, while other possible factors such as climate change and changes in the water quality of upstream inflows were not considered. A comprehensive analysis of the impacts of multiple factors on reservoir parameter changes should be conducted to construct a more complete influencing factor analysis system.

Response 5:

The question of identifying the nature and reasons for measuring the hydromorphology of the reservoir bottom was not raised in the article. Only questions of assessing the accuracy of bathymetry and determining the real picture of the state of the reservoir with the required accuracy were raised.

As part of the technical assignment for this study, the assessment of the factors you proposed for identifying the nature and reasons for measuring the hydromorphology of the reservoir bottom is also not provided for.

Comment 6: 

The measurement errors and uncertainties in the model construction process were not analyzed. Methods such as error propagation analysis and Monte Carlo simulation should be employed to evaluate the uncertainties and clarify the confidence intervals of the research results.

Response 6:

The drone allows you to receive measurement points with different density along the route. We used measurements with a step of 0.1 meters. The resulting data array was evaluated within the confidence interval.

Points that did not satisfy the 3-sigma rule were removed and were not used in building the model. (correction added to the second edition of the article, line 477-480)

Comment 7: 

When describing the research methods and results, the explanations of some professional terms were not clear, such as the processes of "digital elevation model processing" and "spatial image quality determination". The specific operations and principles related to these terms should be elaborated in detail to enhance the readability of the paper.

Response 7:

In the interpretation you provided, I did not find the terms "digital elevation model processing" and "spatial image quality determination" in the article.

Comment 8: 

Some of the charts (such as some depth measurement result charts) have incomplete axis labels, lacking key information such as units. It is necessary to improve the chart labels so that readers can more intuitively and accurately understand the content of the charts.

Response 8:

The diagrams have been corrected. The depth unit has been added to all diagrams.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The article explores an important topic in water resource management by assessing the accuracy of 3D reservoir modeling using bathymetric data. While the study is based on reliable field measurements and offers useful insights, major revisions are needed to improve the structure, clarify the methods, and strengthen the scientific discussion.

• The introduction (lines 41–94) includes numerous technical details about bathymetric and interpolation methods. While informative, they obscure the primary research objectives. Focus the introduction on the specific context of the Karatomar reservoir, regional hydrological challenges, and the rationale behind the study. Detailed technical explanations can be moved to the Methods section.
• The description of instruments and software is thorough, but the methodology flow could benefit from a visual summary, such as a flowchart or diagram showing the steps from data acquisition to 3D modeling.
• The reported 53% reduction in volume is highly significant. Can you estimate the contribution of sedimentation vs. shoreline overgrowth to this loss?
• There is no mention of external validation for the generated 3D models. Were any manual depth measurements or independent data sources available for validation? What is the acceptable error threshold for reservoir management applications in this context?
• The discussion section remains mostly descriptive. Consider expanding the interpretation of your findings, especially regarding their hydrological, environmental, and socio-economic implications.

Author Response

Thank you for your comments!

Comment 1:

The introduction (lines 41–94) includes numerous technical details about bathymetric and interpolation methods. While informative, they obscure the primary research objectives. Focus the introduction on the specific context of the Karatomar reservoir, regional hydrological challenges, and the rationale behind the study. Detailed technical explanations can be moved to the Methods section.

Response 1:

Introduction has been corrected.

Comment 2:

The description of instruments and software is thorough, but the methodology flow could benefit from a visual summary, such as a flowchart or diagram showing the steps from data acquisition to 3D modeling.

Response 2:

The diagram has been added to the article as figure 1.

Comment 3:

The reported 53% reduction in volume is highly significant. Can you estimate the contribution of sedimentation vs. shoreline overgrowth to this loss?

Response 3:

At this stage of the study, identifying the causes of significant changes in the reservoir volumes was not set as a task. The tasks were to assess the actual state of the hydraulic structure in the context of increased risks of climate change, assess the accuracy of the constructed models and determine the required volumes of bathymetric measurements to achieve the set accuracy of the model.

Perhaps, identifying the causes of changes in the volumes and areas of hydraulic structures may be the next step in the study.

Comment 4:

There is no mention of external validation for the generated 3D models. Were any manual depth measurements or independent data sources available for validation? What is the acceptable error threshold for reservoir management applications in this context?

Response 4:

Yes, for additional verification of both the measurement results and 3D modeling, the authors manually collected reservoir control point depth data using a line and a hydrometric rod. The data from our ultrasonic measurements using a bathymetric drone and manual measurement methods coincided with an error of less than 0.1 m. The deviation of the modeling data from manual measurement methods also did not exceed the required 10%. This confirmed the success of the drone calibration and verified the accuracy and reliability of the measurements/modeling.

(correction added to the second edition of the article, line 147-147).

We found no references to the use of a clear acceptable threshold for inventory estimation error in reservoir management. When using a precautionary approach to inventory management, a 90–95% probability is taken into account that the actual value will not be higher than the corresponding limit value. The acceptable risk in this case may be in the range of 5–10%.

In the study, we used a threshold of 10% (line 532-534 of the first. edition of the article)

When forming the technical assignment for the research, the ministry also defined an error of no more than 10%.

Comment 5:

The discussion section remains mostly descriptive. Consider expanding the interpretation of your findings, especially regarding their hydrological, environmental, and socio-economic implications.

Response 5:

Inaccurate data on the assessment of both fresh water reserves during the dry period and an erroneous idea of ​​the available free volumes of existing reservoirs can lead to significant environmental and socio-economic consequences.

Only in the context of the consequences of the flood in the spring of 2024, according to public sources:

- 3.3 thousand affected families received a one-time social payment for a total of 1.1 billion tenge;

- 1,149 houses were surveyed and assessed. More than 700 of them were recognized as unsuitable for habitation;

- more than 270 families received compensation for the repair and restoration of their houses for a total of 821.1 million tenge.

The environmental consequences have not yet been fully determined, since the flood zone (in addition to crop fields) also included objects posing significant threats.

(correction added to the second edition of the article, line 633-644).

Reviewer 3 Report

Comments and Suggestions for Authors

The authors submitted an interesting manuscript dealing with accuracy assessment of 3D bathymetric modelling of surface water reservoirs. Given current changes in the climate systems, this study would provide an insightful approach for surface water level variations. While the conclusions are supported by the results; the authors should improve the section of material and methods before the manuscript could be considered for publication. Below are some comments and suggestion to improve the overall quality of the manuscript:

 Lines135-183: The authors should improve the section 2. Materials and Methods: First by including the subsection (2.1) containing information related to the description of the Studied area. Second by including the subsection (2.2) of Methodology in which the authors should provide detailed information related to the dataset creation (2.2.1. data acquisition) and the description of the (2.2.2.) methods used to analyse these datasets. Such information would help readers better understand how you proceeded to respond to the research questions indicated in the section of introduction. It would also be easy to understand the novelty and the contribution of this current research study.

 

Lines 187-248, 388-394: as these paragraphs contain information related to the methodology, I think that it would be better to include them in the section of Materials and Methods.

The authors should improve the quality of the Figures as well (such as 5 to 12).

Lines 64-68: it would be interesting to provide references of recent studies conducted dealing with bathymetry and shoreline modelling using modern technologies and advanced methodological approaches. Please refer to (1) Muzirafuti, A.; Crupi, A.; Lanza, S.; Barreca, G.; Randazzo, G. Shallow water bathymetry by satellite image: A case study on the coast of San Vito Lo Capo Peninsula, Northwestern Sicily, Italy. In Proceedings of the 2019 IMEKO TC19 International Workshop on Metrology for the Sea: Learning to Measure Sea Health Parameters, MetroSea 2019, Genoa, Italy, 3–5 October 2019; pp. 129–134.; (2) Gui, R.; Song, W.; Lv, J.; Lu, Y.; Liu, H.; Feng, T.; Linghu, S. Digital Elevation Model-Driven River Channel Boundary Monitoring Using the Natural Breaks (Jenks) Method. Remote Sens. 2025, 17, 1092. https://doi.org/10.3390/rs17061092

 

Author Response

Thank you for your comments!

Comment 1:

Lines135-183: The authors should improve the section 2. Materials and Methods: First by including the subsection (2.1) containing information related to the description of the Studied area. Second by including the subsection (2.2) of Methodology in which the authors should provide detailed information related to the dataset creation (2.2.1. data acquisition) and the description of the (2.2.2.) methods used to analyse these datasets. Such information would help readers better understand how you proceeded to respond to the research questions indicated in the section of introduction. It would also be easy to understand the novelty and the contribution of this current research study.

Response 1:

The section "Materials and Methods" has been structured and corrected.

Comment 2:

Lines 187-248, 388-394: as these paragraphs contain information related to the methodology, I think that it would be better to include them in the section of Materials and Methods

Response 2:

The section "Materials and Methods" has been structured and corrected.

Comment 3:

The authors should improve the quality of the Figures as well (such as 5 to 12).

Response 3:

The figures have been corrected. The depth unit has been added to all diagrams.

Comment 4:

Lines 64-68: it would be interesting to provide references of recent studies conducted dealing with bathymetry and shoreline modelling using modern technologies and advanced methodological approaches. Please refer to (1) Muzirafuti, A.; Crupi, A.; Lanza, S.; Barreca, G.; Randazzo, G. Shallow water bathymetry by satellite image: A case study on the coast of San Vito Lo Capo Peninsula, Northwestern Sicily, Italy. In Proceedings of the 2019 IMEKO TC19 International Workshop on Metrology for the Sea: Learning to Measure Sea Health Parameters, MetroSea 2019, Genoa, Italy, 3–5 October 2019; pp. 129–134.; (2) Gui, R.; Song, W.; Lv, J.; Lu, Y.; Liu, H.; Feng, T.; Linghu, S. Digital Elevation Model-Driven River Channel Boundary Monitoring Using the Natural Breaks (Jenks) Method. Remote Sens. 2025, 17, 1092. https://doi.org/10.3390/rs17061092

Response 4:

Please note that the reservoir was studied when it was more than 97% full. The worst (minimum) reservoir fullness for the entire period of reservoir operation known to me was 54-57% during a period of several consecutive dry years. This was about 20 years ago.

Methodological approaches such as (1) Muzirafuti, A.; Crupi, A.; Lanza, S.; Barreca, G.; Randazzo, G. are a type of remote sensing methods and do not provide any fundamental differences from the methods of space radar altimetry and processing of aerial/space images. They allow us to estimate only the unfilled volume of the reservoir bowl. An analysis of such approaches is presented in Table 2.

We have not found any research results to date with the required accuracy for operating hydraulic structures filled with water. The authors of the methodology themselves refer to the possibility of studying only the above-water relief.

The source (2) Gui, R.; Song, W.; Lv, J.; Lu, Y.; Liu, H.; Feng, T.; Linghu, S., suggested by the respected reviewer, also refers to satellite research methods. Yes, we agree with you that the Jenks method suggested in the article can allow a more accurate assessment of the coastline (added to the article, lines 622-625, and to the literature as source 49).

The processing of photographs from the Sentinel satellite only, performed by the authors, allowed the required accuracy to be achieved.

Reviewer 4 Report

Comments and Suggestions for Authors

The topic of the manuscript is relevant and timely. The issue of monitoring water reservoirs and evaluating bathymetric accuracy is important for sustainable water resource management, especially in the context of climate change and extreme events. The case of the Karatomar Reservoir in Kazakhstan is a good example of regional challenges in this field.

The study uses appropriate methods (bathymetric drone survey, GIS analysis, kriging interpolation), and the authors provide a significant amount of data. However, the paper requires major revisions before it can be considered for publication.

- The title is overly long and vague. The phrase “On the Question of…” is not suitable for a scientific title.“Accuracy Assessment of 3D Reservoir Modeling Using Drone-Based Bathymetry: A Case Study of the Karatomar Reservoir” would be better.

- The introduction lacks a clear research question and is too broad at the beginning. It includes general statements on global water storage, but the connection to the specific case study is delayed. Please make the problem statement and research objectives clearer in the first 2–3 paragraphs.

- the text in the graphs in fig 5-8 and 10 are very small, hard to read. 

- For the discussion, remark the new findings compared to previous bathymetric studies?

Comments on the Quality of English Language

The manuscript contains many grammatical and stylistic issues. For example, in the abstract:

i) “the study of the patterns of modeling accuracy from the frequency of tacks was carried out using crying methods” — likely a mistranslation of kriging.

ii) Sentences are often long, repetitive, or unclear. A full professional English language editing is necessary to meet academic standards.

Author Response

Thank you for your comments!

Comment 1:

The title is overly long and vague. The phrase “On the Question of…” is not suitable for a scientific title.“Accuracy Assessment of 3D Reservoir Modeling Using Drone-Based Bathymetry: A Case Study of the Karatomar Reservoir” would be better.

Response 1:

The title has been corrected to "Assessing the accuracy of 3D modeling of hydraulic structures using bathymetric drones: a study of the Karatomar Reservoir".

Comment 2:

The introduction lacks a clear research question and is too broad at the beginning. It includes general statements on global water storage, but the connection to the specific case study is delayed. Please make the problem statement and research objectives clearer in the first 2–3 paragraphs.

Response 2:

The introduction has been corrected

Comment 3:

the text in the graphs in fig 5-8 and 10 are very small, hard to read.

Response 3:

The figures have been corrected. 

Comment 4:

For the discussion, remark the new findings compared to previous bathymetric studies?

Response 4:

Corrected. Lines 619-626.

Comment 5:

“the study of the patterns of modeling accuracy from the frequency of tacks was carried out using crying methods” — likely a mistranslation of kriging.

Response 5:

The translation typo has been corrected.

Comment 6:

Sentences are often long, repetitive, or unclear. A full professional English language editing is necessary to meet academic standards.

Response 6:

I tried to simplify the sentences as much as possible.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Accept

Author Response

Comment: Accept

Response: Thank you for your high appreciation of my work and your comments, which helped me make it better! Sincerely, M. Zarubin

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have satisfactorily addressed all my questions and have taken into account all of my comments and recommendations. I find their responses clear and appropriate, and I am satisfied with the revisions made to the manuscript.

Author Response

Comment: The authors have satisfactorily addressed all my questions and have taken into account all of my comments and recommendations. I find their responses clear and appropriate, and I am satisfied with the revisions made to the manuscript.

Response: Thank you for your high appreciation of my work and your comments, which helped me make it better! Sincerely, M. Zarubin

Reviewer 3 Report

Comments and Suggestions for Authors This submitted version of the previous manuscript is not sufficiently improved to be considered for publication. The authors should revise the manuscript by including all comments and suggestions provided by Reviewers and Academic Editor. The authors should firstly improve the Quality of English Language. The authors should revise and rephrase the title of the manuscript as well. Based on submitted version of the previous manuscript, they could rephrase it as follow: Drone-derived bathymetry Accuracy Assessment for Hydro-Technical Structures 3D Modeling: A Case Study of The Karatomara Reservoir. However, the content of the manuscript especially Introduction should be improved. The authors should include sufficient references in the section of Introduction; 4 references do not provide comprehensive understanding of the State-of-the Art of this current manuscript. The section 2. Materials and Methods should be revised and improved by including the descriptions of the Study Area (2.1) and the Methodology (2.2). In the Subsection 2.2, the authors should provide details of Data Acquisition, and the Methodological approach adopted to analyze these datasets. The section 3 should be improved as well; by adopting a  better representation of the Results. Lines 426-433: should be in the section of Methodology. The section of References should be improved. The responses provided by the authors are not accurate such as … The authors of the methodology themselves refer to the possibility of studying only the above-water relief (response 4): What do you mean by above-water relief ?.

Author Response

Thank you for your comments!

Comment 1: The authors should revise the manuscript by including all comments and suggestions provided by Reviewers and Academic Editor. 

Response 1: Thank you. I always carefully consider all the comments of the respected academic editor and all four reviewers and make adjustments to the version of the article before submitting it for the next stage of review.

 

Comment 2: The authors should firstly improve the Quality of English Language. 

Response 2: We have tried to correct this remark. I have attached the corrected version (10052025) to the system for this round of review.

 

Comment 3: The authors should revise and rephrase the title of the manuscript as well. Based on submitted version of the previous manuscript, they could rephrase it as follow: Drone-derived bathymetry Accuracy Assessment for Hydro-Technical Structures 3D Modeling: A Case Study of The Karatomara Reservoir. 

Response 3: The original title of the article "On the question of assessing the accuracy of 3D modeling of water reserves using the example of the Karatomar reservoir" was corrected in the first round of reviewing according to the suggestion of reviewer 4.

The title in the current wording ("Assessing the accuracy of 3D modeling of hydrotechnical structures using bathymetric drones: a study of the Karatomar Reservoir") was suggested by reviewer 4.

In my opinion, the wording proposed by you and the current one (proposed by reviewer 4) are very close.

 

Comment 4: However, the content of the manuscript especially Introduction should be improved. The authors should include sufficient references in the section of Introduction; 4 references do not provide comprehensive understanding of the State-of-the Art of this current manuscript. 

Response 4: The introduction has been revised as per the reviewers' requests in Round 1.

In response to your last comment, I have once again tried to revise the introduction and expand the review of articles in it.

 

Comment 5:  The section 2. Materials and Methods should be revised and improved by including the descriptions of the Study Area (2.1) and the Methodology (2.2). In the Subsection 2.2, the authors should provide details of Data Acquisition, and the Methodological approach adopted to analyze these datasets. 

Response 5: Sorry, I didn't understand your comment. After the first stage of reviewing, the "Materials and Methods" section of the article is structurally divided into 3 subsections:

2.1. Object and algorithm of the study;

2.2. Methods of obtaining initial data;

2.3. Methods of processing bathymetric data.

Section (2.1) presents the initial information about the Karatamar reservoir and the algorithm we proposed for conducting its study. In section (2.2), we considered all issues related to conducting instrumental bathymetry (the equipment used and the methods of its additional calibration we used), issues of obtaining the coastline from space images. In section (2.3), we considered methods related to issues of interpreting the obtained data.

 

Comment 7: The section of References should be improved. 

Response 7: The section of References have been corrected.

 

Comment 8: The responses provided by the authors are not accurate such as … The authors of the methodology themselves refer to the possibility of studying only the above-water relief (response 4): What do you mean by above-water relief?.

 

Response 8: The above-water relief of a reservoir is the relief of the slopes of its banks protruding above the water level (the reservoir bowl is above the water level). (In our case, due to the maximum filling of the reservoir, the relief is above the value of the forced backwater level).

 

I did not understand from the comment whether you meant the correctness of the wording or the correctness of the requirement for remote sensing methods.

 

With regard to the correctness of the wording. I agree with you regarding the inaccuracy of the wording we used in Table 2.

 

I have corrected this wording "The possibility of constructing only above-water reliefs" to "The complexity of constructing a model of the underwater part of a water body with high accuracy".

 

With regard to remote sensing methods:

Methods of space sensing of the Earth allow us to obtain measurements of this (above-water) relief with high accuracy. However, in our case, this is not of particular importance for the result obtained due to the maximum filling of the reservoir bowl.

The assessment of underwater relief (relief below the water level) by these methods provides significantly worse results in terms of accuracy.

For example, in the article you recommended Muzirafuti, Anselme & Crupi, Antonio & Lanza, Stefania & Barreca, Giovanni & Randazzo, Giovanni. (2019). “Shallow water bathymetry by satellite image: a case study on the coast of San Vito Lo Capo Peninsula, Northwestern Sicily, Italy.” the authors themselves state the following:

“…Based on the International Hydrographic Organization’s (IHO) S-44 standards [19] which determine the quality of survey methods, the SDB method can be classified as a special order survey method, (Table 1), with horizontal accuracy of about ± 2 m and vertical accuracy of ± 0.25 m to ± 0.75 m where environmental conditions are ideal…”. The conclusions on the error of the order of ±1 m are confirmed by them in Table 3 "Quality assessment of SDB results" of the article.

Although the SDB method is undoubtedly of great interest especially for the analysis of marine shallow water areas, such an initially high error of the method exceeds the maximum permissible error of reservoir studies (10%) by 80.66% of the reservoir surface area.

The SDB method, of course, can be used by us as an alternative method for comparing the results of bathymetry with ultrasonic sonar. But why should we study and use a deliberately less accurate method, if for this reservoir we have already obtained control points, albeit by manual methods, but with a higher measurement accuracy?

 

Reviewer 4 Report

Comments and Suggestions for Authors

• There are still some sentences that should not be placed anywhere in the manuscript such as "As a result of the study conducted by the authors of the article, the following answers to the research questions were obtained." in Discussion. The manuscript must be checked by an English language editor or English academic editing.
• What happened to the Introduction section? As I see, most of the literature reviews are transferred to the Method section. Why did the authors prefer this unusual schema? I strongly recommend transferring back most of the references to the introduction section. 
• The authors claims that they remarked the new findings compared to previous bathymetric studies in Lines 619-626. However, the regarding paragraph seems almost the same as in the previous version. Please make some comparisons of the results in the manuscript with the results previously published in other regarding references. The comparisons will validate and/or support your results. 

Comments on the Quality of English Language

• There are still some sentences that should not be placed anywhere in the manuscript such as "As a result of the study conducted by the authors of the article, the following answers to the research questions were obtained." in Discussion. The manuscript must be checked by an English language editor or English academic editing.

Author Response

Thank you for your comments!

Comment 1: There are still some sentences that should not be placed anywhere in the manuscript such as "As a result of the study conducted by the authors of the article, the following answers to the research questions were obtained." in Discussion. The manuscript must be checked by an English language editor or English academic editing.

Response 1: We have tried to correct this remark.

 

Comment 2: What happened to the Introduction section? As I see, most of the literature reviews are transferred to the Method section. Why did the authors prefer this unusual schema? I strongly recommend transferring back most of the references to the introduction section. 

Response 2: The introduction has been corrected according to the reviewers' requests in Round 1.

In the version of the article submitted for this round of review, I have added paragraphs concerning the state of the research problem and the methods for studying such hydraulic structures.

 

Comment 3: The authors claims that they remarked the new findings compared to previous bathymetric studies in Lines 619-626. However, the regarding paragraph seems almost the same as in the previous version. Please make some comparisons of the results in the manuscript with the results previously published in other regarding references. The comparisons will validate and/or support your results. 

Response 3: Thank you for your comment. I understand you. I understand that it is desirable to verify the instrumental research data for reliability not only by various research methods (for this, we verified the ultrasonic bathymetry by taking control point data using manual measurements), but also to verify it in the context of historical changes.

However, in this case there is a problem...

With regard to the Karatomar reservoir, we found only one article in open sources containing the results of a survey of the reservoir dam in 2013, but not its bathymetry (Zhantayev, Z. Kurmanov, B. Breusov, N. Shigayev, D. and Kirsanov, A. (2013) Ground Penetrating Radar Survey of Dam Structures of Kazakhstan on the example of Aktobe and Karatomar Water Storage Basins, Open Journal of geology , https://api.semanticscholar.org/CorpusID:56336565).

The data from the open encyclopaedia Wikipedia also contains only the final figures for the volume and maximum depth of the reservoir for 1961 and do not differ significantly from the received design plans for the reservoir.

Unfortunately, we have not found and do not have any other historical data for comparative analysis (except for the data of 1961). We tried to reflect the deviations of the obtained results of our studies from the planned data of 1961 in Table 10.

The only thing that can indirectly confirm our conclusions about the Karatomar reservoir is the similar results obtained for the Verkhnetobol (located upstream along the Tobol River, Figure 3) reservoir. There is also a significant decrease in volume there.

Perhaps, identifying the reasons for the change in the volumes and areas of hydraulic structures in Kazakhstan may be the next step in our research.

 

Round 3

Reviewer 4 Report

Comments and Suggestions for Authors

Since the revisions requested are not sufficient (some of them were not applied), I have to reject the manuscript.

-The reviewer strongly suggested academic English editing twice, and the authors prefered to do that job by theirselves. However, the language is not in an academic jargon because of several reasons: for example, the authors used "the authors" word a lot (in lines: 63, 79, 88, 90, 106, 123, 172, 259, ) in the text. We know the authors wrote the paper, they developed the algorithm proposed, and so on. But, refering themselves in the paper again and again is not proper in a journal article. Refering themselves is almost much more than the citations in the Introduction section.

-Also, as I stated before the re-design of the paper is not suitable. Even after the Result section there are new references that did not refered in the Introduction or Method sections. There is no place for the exact literature review in the paper.

Comments on the Quality of English Language

 

The reviewer strongly suggested academic English editing twice, and the authors prefered to do that job by theirselves. However, the language is not in an academic jargon because of several reasons: for example, the authors used "the authors" word a lot (in lines: 63, 79, 88, 90, 106, 123, 172, 259, ) in the text. We know the authors wrote the paper, they developed the algorithm proposed, and so on. But, refering themselves in the paper again and again is not proper in a journal article. Refering themselves is almost much more than the citations in the Introduction section.

 

Author Response

Comment: -The reviewer strongly suggested academic English editing twice, and the authors prefered to do that job by theirselves. However, the language is not in an academic jargon because of several reasons: for example, the authors used "the authors" word a lot (in lines: 63, 79, 88, 90, 106, 123, 172, 259, ) in the text. We know the authors wrote the paper, they developed the algorithm proposed, and so on. But, refering themselves in the paper again and again is not proper in a journal article. Refering themselves is almost much more than the citations in the Introduction section.

-Also, as I stated before the re-design of the paper is not suitable. Even after the Result section there are new references that did not refered in the Introduction or Method sections. There is no place for the exact literature review in the paper.

Response: Thank you for your meticulous work on our article and the comments you have made! We are confident that this work will help make our article much better and more readable. We have tried to remove the word "authors" from the article. We plan to edit the English style by contacting the MDPI language editing service after all the reviewers' comments have been corrected.