Round 1

Reviewer 1 Report

see attached review report

Comments for author File: Comments.pdf

Author Response

Comments and Suggestions for Authors

 

1. I have read with interest your paper on Evaluation of Travel Time for Different Density of Floatable Litter Influenced by River Flow Velocity. The manuscript deals with the interesting problem, however, I have a few comments. Unfortunately, applied manuscript does not contain numbered lines, so I will have to indicate just pages and paragraphs.

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript.

• Number lines is added.

 

2. Page 3, paragraph 2 – what distance is taken for travel time (T) estimation? It must be revealed in introduction as well as in abstract.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration.

• The distance used for FL migration in ToT method is explained in Abstract section, but not in Introduction section because previous paragraph is excluded. Please see line 22 on page 1 for further information.

 

3. Page 12, paragraph 1 – equation referred in the paragraph as (4) should appear under this paragraph directly

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration.

• We decided to simplify the explanation by focusing on volume calculation method first and not relating to density equation in this section yet. Thus, the paragraph is excluded and replaced with paragraph 1 on page 4. Please see line 96-98 on page 4 for further information.

 

4. Page 13 – I understand the idea of flow velocity estimation on the base of float method and its application for this problem is reasonable. However, using Youtube instruction for students is good for ... students, not for scientific investigation, because there is much more than an idea of measurement. You need to interpret environmental results in a reliable way. Please, read any guidebook for hydrometry, there are plenty, for example: W. Boiten, 2003, Hydrometry, A.A. Balkema Publishers (Taylor & Francis e-Library, ISBN 0-203-97109-4 Master e-book, ISBN 90 5410 423 6 (paperback edition) or any other.

 

The basic problems of your measurement are as follows:

5. the measurement reach should be as straight as possible, without significant turbulences, and its length is related to width of the channel. In the photo (Fig. 5 – left) we can see channel bend,

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript.

• For your information, both Figure 3 - left and right - are taken at other river sections. They are not representing/showing the river section where simulation was conducted. The river section chosen for simulation has straight channel. The picture of the exact river section is updated as in Figure 6 on page 7.

 

6. you mentioned 3 measurements and average value. You need to explain if float started 3 times in the same place (middle of channel or along main current) or it was left, right and central part of the cross-section. It is very important for results interpretation.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration and corrected accordingly.

 

• For the particular correction, please refer line 224 – 227 on page 8.

 

7. correction factor is not a constant. Its value depends on bottom material (roughness and friction), water depth and level of float immersion.

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript. I agree that correction factor is not a constant.

• However, using the method and formula for measuring river flow velocity which is sourced from Arizona (2018), none of this parameter is included in the formula. The 0.85 correction factor is acquired from this source. Moreover, the river bottom (roughness and friction) and level of float immersion are not in the scope of study. Only water depth parameter was measured as the adding information for future improvement of this study.

 

8. Moreover, your modification of Time of Travel (ToT) Method is the surface float method practically. Please explain why you calculated average cross-section velocity whereas Time of Travel refers to surface velocity only. It is also interesting, how the particular FL objects travelled during ToT experiment in matter of movement obstructions (shape and dimensions) – temporary contacts with bottom, branches etc.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration.

• It is admitted that Figure 6 does not explain float method clearly and confusing. River cross-section is not needed for measuring river surface velocity. Moreover, ToT method only consider river surface velocity, not average river cross-section velocity. Thus, the previous Figure 6 is excluded. However, reader can refer to Figure 7 on page 8 for reference to conduct float method because it is almost the same with ToT method.

 

9. In my opinion you should revise and improve the paragraphs relating to measurement and result interpretation. In my opinion some reversing results in ToT for B and C velocity conditions are mostly determined by measurement conditions.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration. The manuscript as a whole has been updated and improved.

 

10. Section 3.6 (Data Analysis) needs serious improvement in matter of methods description. Presented text is absolutely insufficient.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration. The manuscript as a whole has been updated and improved. Please refer to line 238 – 241 and 244 – 246 on page 8 for further information.

 

11. Chapter Results and Discussion is expected to start with number 4. In this section you have described your results data in great detail. However, you should also pay more attention to synthetic comments, if there are some regularities or some expected did not exist and why? You should assess the influence of measurement conditions on gathered data as well.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration.

• There are additional points in Discussion section. Please refer to line 421 – 424 on page 13.

 

12. Finally, the manuscript needs also language correction because in many paragraphs it is hard to follow the author’s ideas.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration and corrected accordingly.

• We read the whole manuscript and adjusted the coherence and cohesion and term use to make it clearer and scientific.

 

 

 

 

 

 

 

 

 

 

Author Response File: Author Response.docx

Reviewer 2 Report

I have read with interest your paper on Evaluation of Travel Time for Different Density of Floatable Litter Influenced by River Flow Velocity. The manuscript deals with the interesting problem, however, I have a few comments. Unfortunately, applied manuscript does not contain numbered lines, so I will have to indicate just pages and paragraphs.

Page 3, paragraph 2 – what distance is taken for travel time (T) estimation? It must be revealed in introduction as well as in abstract

Page 12, paragraph 1 – equation referred in the paragraph as (4) should appear under this paragraph directly

Page 13 – I understand the idea of flow velocity estimation on the base of float method and its application for this problem is reasonable. However, using Youtube instruction for students is good for ... students, not for scientific investigation, because there is much more than an idea of measurement. You need to interpret environmental results in a reliable way. Please, read any guidebook for hydrometry, there are plenty, for example: W. Boiten, 2003, Hydrometry, A.A. Balkema Publishers (Taylor & Francis e-Library, ISBN 0-203-97109-4 Master e-book, ISBN 90 5410 423 6 (paperback edition) or any other. The basic problems of your measurement are as follows:
- the measurement reach should be as straight as possible, without significant turbulences, and its length is related to width of the channel. In the photo (Fig. 5 – left) we can see channel bend,
- you mentioned 3 measurements and average value. You need to explain if float started 3 times in the same place (middle of channel or along main current) or it was left, right and central part of the cross-section. It is very important for results interpretation.
- correction factor is not a constant. Its value depends on bottom material (roughness and friction), water depth and level of float immersion.
Moreover, your modification of Time of Travel (ToT) Method is the surface float method practically. Please explain why you calculated average cross-section velocity whereas Time of Travel refers to surface velocity only. It is also interesting, how the particular FL objects travelled during ToT experiment in matter of movement obstructions (shape and dimensions) – temporary contacts with bottom, branches etc.
In my opinion you should revise and improve the paragraphs relating to measurement and result interpretation. In my opinion some reversing results in ToT for B and C velocity conditions are mostly determined by measurement conditions.

Section 3.6 needs serious improvement in matter of methods description. Presented text is absolutely insufficient.

Chapter Results and Discussion is expected to start with number 4. In this section you have described your results data in great detail. However you should also pay more attention to synthetic comments, if there are some regularities or some expected did not exist and why? You should assess the influence of measurement conditions on gathered data as well.

Finally, the manuscript needs also language correction because in many paragraphs it is hard to follow the author’s ideas.

Author Response

Reviewer 2 (R2)

 

The paper describes an attempt to evaluate travel times of different types of litter in a fluvial environment. It is, however, far too long, too longwinded, unbalanced, poorly written and methodologically wrong.

 

Relevance

1. The subject, if properly treated, is of practical relevance.

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript

 

Title

2. The title reflects the content of the paper, but is rather long. It could just as well read something like:

‘Travel time of floatable litter in rivers’.

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript.

• The title is corrected to ‘The Travel Time of Floatable Litter Density Influenced by River Flow Velocity’.

 

Abstract

3. The abstract adequately reflects the content of the paper.

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript

 

Introduction

4. The introduction is far too long and long-winded. It is a broad literature review on the worldwide

problem of litter in water bodies, rather than a to-the-point introduction to the rather narrow subject of

the paper. Some parts – like those stating that knowledge is insufficient – are repeated several times.

Halfway p. 4 starts a section numbered 1.1 with a heading in italic, suggesting this to be a subsection

on the Introduction (title printed in boldface). The content is still very broad, so in that sense it fits into

the introduction.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration and corrected accordingly.

• Introduction section is simplified to a shorter explanation and more narrow topics being discussed. Together, the part of ‘knowledge gap’ fact is removed to not make it repetitive anymore.
• Subsections are removed. All the paragraphs are combined in one text.

 

 

 

5. Similarly, section 1.2 on the potential sources of riverine litter and section 1.3 on the pathway to the

ocean are very broad and large parts of them could just as well be omitted from this paper.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration and corrected accordingly.

• Section 1.2 and 1.3 are omitted from the manuscript. Refer to page 1 & 2.

 

6. Section 1.4 starts with a very confusing description of what happens in tidal rivers, whereas the case considered in this paper is to my knowledge non-tidal. The case-description later on in the paper

leaves the reader in the dark about this.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration and corrected accordingly.

• The part explaining the effect of river tides toward migration and accumulation of riverine litter is removed. Please refer page 1 and 2.

 

 

Materials and methods

7. Only after 10 pages of introduction the paper comes to the point.

 

Author’s Response: Thank you for your time and consideration in leaving a remark.

• Introduction section is adjusted accordingly; which the total page of Introduction is lesser. Please refer to page 1 and 2.

 

8. The flow chart in Figure 3 is not in balance, in that it contains the objectives as well as the actions to

achieve them. Suggestion to leave out the top box and integrate the second box into the one at the

bottom.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration and corrected accordingly.

• A new research design framework is created as in Figure 1. Please refer to page 3 for further information.

 

9. The symbol P in the second box is not defined and should probably read ρ (that is the symbol used for

density in Eq. 4).

 

Author’s Response: Thank you for your time and consideration in leaving a remark.

• The symbol P for density in research design framework is removed. Please refer Figure 1 on page 3. While the density, ρ symbol is used properly. Please refer to line 138 on page 5.

 

10. The numbering of the subsections is not in order (2.1 is followed by 3.2).

 

On the basis of this framework, one would expect a balanced description of the methods used in each of them. Unfortunately, this is not the case. The determination of mass etc. of litter elements (section 3.3) and ‘the’ flow velocity in the river (section 3.4) are described in a level of detail up to triviality,

whereas the more interesting determination of the travel time (section 3.5) and the correlation analysis

(section 3.6) receive hardly any attention and cannot possibly be reproduced by the reader.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration

• All Material & Method subsections are adjusted accordingly to balance their length. Please refer to page 3 and 8 for detail information.
• Data analysis section is improved. Please refer to line 244 – 246 on page 8 for further information.

 

11. The case description is insufficient1. I mis a map of the river section where the measuring station is

located. Moreover, it does not become clear whether the river is tidal (given the text on tidal rivers in

the introduction). The photographs in Figure 3 suggest that the river is by no means a uniform channel

of constant width and depth. This means that there will be lateral velocity gradients and probably even

deadwater zones. In such an environment one cannot speak about travel times in deterministic terms:

dispersion and lingering back will lead to a wide statistical distribution, of which the travel time as

evaluated in the paper will estimate the minimum, whereas the mean will be significantly larger and the

maximum very much larger. I consider this as a major methodological flaw.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration.

 

The comments here are:

 

1. Missed map of river section

 

Author’s Response: Add map of Sg. Berkelah location. Please refer to page 6. Please check Figure 5 in the revised manuscript.

 

1. The relevance of the river tides the effect of river tides toward migration and accumulation of riverine litter point in Introduction section

 

Author’s Response: Sg. Berkelah is not a tidal river. As solution, the explanation regarding the effect of river tidal on the accumulation of riverine litter is excluded. Please refer to page 1 and 2.

 

1. Wrong picture of river section

 

Author’s Response: Include the photo of exact river section as Figure 6; which has straight and non-wandering channel

 

1. Non-uniform channel (in depth & width) cause the possibility of lateral velocity gradients and deadwater zones. This results the dispersion and lingering back; which lead to a wide statistical distribution.

 

Author’s Response: Many thanks for your kind comment. We have revised and discussed further regarding this.

• Here goes the reasoning. The non-uniform depth & width of river channel should not be an issue because the aim is to assess how FL ToT is affected by surface river velocity. The correlation is between ToT and the value of velocity – in this case, the river velocity. The river depth & width were measured in order to determine average velocity of the river section using float method. Moreover, river depth & width were taken three times at the middle and both ends of river section during every condition. The approach of using float method is due to the lack of and inaccessible flowmeter during world COVID-19 pandemic lockdown 2020. It is undeniable that FL ToT still affected by other factors such as underwater turbulence, water inlet into FL cavity etc. However, these factors are not in the scope of study. Please refer to line 539 – 548 on page 16 in Disclaimer section.

 

Discussion

12. I miss a discussion, critically considering the approach taken and the conclusions drawn.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration and corrected accordingly. The discussion has been highlighted in the revised manuscript. Please refer to page 10, 11, 13 and 15 for the action taken.

 

Conclusion

13. The conclusions are supposed to give the conclusions from the work done, not a reiteration of

objectives and approach. The first two paragraphs can therefore be omitted.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration.

• The first two paragraphs are omitted. Please refer to page 15 for the action taken.

 

14. References

Due to the very wide area covered in the introduction, the reference list is very long (almost 4 pages in

small font).

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration.

• The Reference list is shortened as the Introduction section is adjusted.

 

Figures

15. The figures are clear and with readable annotations.

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript.

 

 

 

English

16. The English is generally OK, except a few misprints, missing words and non-running sentences

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript.

 

Recommendation

17. I recommend rejection, mainly because of the methodological flaw.

 

Author’s Response: We appreciate your kind concern about the primary version of the manuscript and giving us opportunities to revised the manuscript. We revised the manuscript based on your constructive comments. The methodological flaw of the manuscript has been appropriately revised. We believe that the revised version of the manuscript is readable scientifically meaningful. 

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Something must have gone wrong with my review of the original manuscript. This is probably the reason why there is no response to my rather fundamental critque. I therefore send my report, once again and maintain my advice.

Author Response

Applied Sciences MDPI

 

Manuscripts Title: Evaluation of Travel Time for Different Density of Floatable Litter Influenced

                                 by River Flow Velocity

 

Manuscript ID: applies-2178263

 

 

Dear Editor: Ann Xu

 

We are grateful for the chance to revise the text that you have provided us. The reviewers deserve special thanks for paying close attention to an earlier version of the work.

We worked hard to update, edit, and rewrite the document to increase the quality of the study and its presentation in the updated version. We've made changes to the manuscript based on the reviewer's comments, and the full list of changes is below:

 

Reviewer 2 (R2)

 

p/s: The correction in manuscript for R2 was highlighted with green colour

 

The paper describes an attempt to evaluate the travel times of different types of litter in a fluvial environment. It is, however, far too long, too longwinded, unbalanced, poorly written, and methodologically wrong.

 

Relevance

1. The subject, if properly treated, is of practical relevance.

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript

 

Title

2. The title reflects the content of the paper but is rather long. It could just as well read something like:

‘Travel time of floatable litter in rivers’.

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript.

• The title is corrected to ‘The Travel Time of Floatable Litter Density Influenced by River Flow Velocity’.

 

Abstract

3. The abstract adequately reflect the content of the paper.

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript

 

Introduction

4. The introduction is far too long and long-winded. It is a broad literature review on the worldwide

problem of litter in water bodies, rather than a to-the-point introduction to the rather narrow subject of

the paper. Some parts – like those stating that knowledge is insufficient – are repeated several times.

Halfway p. 4 starts a section numbered 1.1 with a heading in italics, suggesting this to be a subsection

on the Introduction (title printed in boldface). The content is still very broad, so in that sense, it fits into

the introduction.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration and corrected accordingly.

• The introduction section is simplified to a shorter explanation and more narrow topics being discussed. Together, the part of the ‘knowledge gap’ fact is removed to not make it repetitive anymore.

 

• Please refer to the Introduction section on pages 1 and 2

 

 

• Subsections are removed in the Introduction section. All the paragraphs are combined in one text.

 

 

5. Similarly, section 1.2 on the potential sources of riverine litter and section 1.3 on the pathway to the

Ocean is very broad and large parts of them could just as well be omitted from this paper.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration and corrected accordingly.

 

• Sections 1.2 and 1.3 are omitted from the Introduction section.

 

• Refer to pages 1 and 2.

 

6. Section 1.4 starts with a very confusing description of what happens in tidal rivers, whereas the case considered in this paper is to my knowledge non-tidal. The case description later on in the paper

leaves the reader in the dark about this.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration and corrected accordingly.

 

• The part explaining the effect of river tides on migration and accumulation of riverine litter is removed from the Introduction section.

 

• Please refer pages 1 and 2.

 

 

Materials and methods

7. Only after 10 pages of introduction the paper comes to the point.

 

Author’s Response: Thank you for your time and consideration in leaving a remark.

• The introduction section is adjusted accordingly; the total page of the Introduction is lesser.

 

• Please refer to pages 1 and 2.

 

8. The flow chart in Figure 3 is not in balance, in that it contains the objectives as well as the actions to

achieve them. Suggestion to leave out the top box and integrate the second box into the one at the

bottom.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration and corrected accordingly.

• A new research design framework is created as in Figure 1.

 

• Please refer to page 3 for further information.

 

9. The symbol P in the second box is not defined and should probably read ρ (that is the symbol used for

density in Eq. 4).

 

Author’s Response: Thank you for your time and consideration in leaving a remark.

• The symbol P for density in the research design framework is removed.
• Please refer to Figure 1 on page 3.

 

• While the density, ρ symbol is used properly.
• Please refer to line 202 on page 7.

 

10. The numbering of the subsections is not in order (2.1 is followed by 3.2).

 

On the basis of this framework, one would expect a balanced description of the methods used in each of them. Unfortunately, this is not the case. The determination of mass etc. of litter elements (section 3.3) and ‘the’ flow velocity in the river (section 3.4) are described in a level of detail up to triviality,

whereas the more interesting determination of the travel time (section 3.5) and the correlation analysis

(section 3.6) receive hardly any attention and cannot possibly be reproduced by the reader.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration

• All Material & Method subsections are adjusted accordingly to balance their length.
• Please refer to lines 217 – 225 on pages 8 - 9 to see some of the changes made.

 

• Data analysis section is improved.
• Please refer to line 316 - 319 on page 10 for further information.

 

11. The case description is insufficient1. I miss a map of the river section where the measuring station is

located. Moreover, it does not become clear whether the river is tidal (given the text on tidal rivers in

the introduction). The photographs in Figure 3 suggest that the river is by no means a uniform channel

of constant width and depth. This means that there will be lateral velocity gradients and probably even

dead water zones. In such an environment one cannot speak about travel times in deterministic terms:

dispersion and lingering back will lead to a wide statistical distribution, of which the travel time as

evaluated in the paper will estimate the minimum, whereas the mean will be significantly larger and the

maximum very much larger. I consider this a major methodological flaw.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration.

 

I list out the comments first. The comments here are:

 

1. Missed map of the river section

 

Author’s Response:

• Add a map of Sg. Berkelah location.
• Please refer to page 7 and check Figure 3, Figure 4, and Figure 5 for the map of the exact Sg. Berkelah location.

 

1. The relevance of the river tides and the effect of river tides toward migration and accumulation of riverine litter point in the Introduction section

 

Author’s Response:

• Berkelah is not a tidal river. As a solution, the explanation regarding the effect of river tidal on the accumulation of riverine litter in the Introduction section is excluded.
• Please refer to pages 1 and 2

 

 

1. Wrong picture of the river section

 

Author’s Response:

• Include the photo of the exact river section as Figure 6; which has a straight and non-wandering channel
• Please refer to page 8 to check on Figure 6.

 

 

1. Non-uniform channels (in-depth & width) cause the possibility of lateral velocity gradients and dead water zones. This results in the dispersion and lingering back; which leads to a wide statistical distribution.

 

Author’s Response: Many thanks for your kind comment. We have revised and discussed further regarding this.

• Here goes the reasoning. The non-uniform depth & width of river channel should not be an issue because the aim is to assess how FL ToT is affected by surface river velocity. The correlation is between ToT and the value of velocity – in this case, the river velocity. The river depth & width were measured in order to determine the average velocity of the river section using the float method. Moreover, river depth & width were taken three times at the middle and both ends of the river section during every condition. The approach of using the float method is due to the lack of an inaccessible flowmeter during world COVID-19 pandemic lockdown in 2020. It is undeniable that FL ToT is still affected by other factors such as underwater turbulence, water inlet into the FL cavity, etc. The possibility of these factors influencing FL travel time is discussed in the Result and Discussion sections. However, these factors are not in the scope of the study.

 

• Please refer to lines 693 - 6095 on page 21 in the Disclaimer section.

 

Discussion

12. I miss a discussion, critically considering the approach taken and the conclusions drawn.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration and corrected accordingly.

 

• The result and Discussion section is separated into two different sections and more explanation is added in the Discussion section.

 

• Please refer to lines 582 – 588 on page 19 to see some of the changes made.

 

Conclusion

13. The conclusions are supposed to give the conclusions from the work done, not a reiteration of

objectives and approaches. The first two paragraphs can therefore be omitted.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration.

• The first two paragraphs are omitted.
• Please refer to page 20 for the action taken.

 

14. References

Due to the very wide area covered in the introduction, the reference list is very long (almost 4 pages in

small font).

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration.

• The Reference list is shortened as the Introduction section is adjusted.
• Refer to pages 1 – 2 to check on the Introduction section and pages 22 – 23 for the Reference section.

 

Figures

15. The figures are clear and with readable annotations.

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript.

 

 

 

English

16. The English are generally OK, except for a few misprints, missing words, and non-running sentences

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript.

 

Recommendation

17. I recommend rejection, mainly because of the methodological flaw.

 

Author’s Response:

• We appreciate your kind concern about the primary version of the manuscript and giving us opportunities to revise the manuscript. We revised the manuscript based on your constructive comments. The methodological flaw of the manuscript has been appropriately revised. We believe that the revised version of the manuscript is reliable even though it is less scientific.

 

• I understand the point here. However, I really hope your consideration to accept the method used together with the results obtained. This is because I believe that the method and results obtained are reliable, as it is suggested by the Arizona Department of Environmental Quality (ADEQ). Plus, it is published on YouTube. I hope you also can consider the materials, tools, and space limitations I faced during this study was conducted. The limitation was due to the global COVID-19 lockdown that cause the inaccessible to my university. Thus, using more scientific methods might be impossible for me. Anyways, thank you for your suggestion to read more on the guidebook list you share with me. I will surely take it into consideration for future reference.

 

Thus, I appeal for this method to be accepted. I appreciate your consideration.

Reviewer 2 Report

I accept the manuscript in present form

Author Response

Applied Sciences MDPI

 

Manuscripts Title: Evaluation of Travel Time for Different Density of Floatable Litter Influenced

 

                                 by River Flow Velocity

 

Manuscript ID: applies-2178263

 

Dear Editor: Ann Xu

 

We are grateful for the chance to revise the text that you have provided us. The reviewers deserve special thanks for paying close attention to an earlier version of the work.

 

We worked hard to update, edit, and rewrite the document to increase the quality of the study and its presentation in the updated version. We've made changes to the manuscript based on the reviewer's comments, and the full list of changes is below:

 

Reviewer 1 (R1):

 

p/s: the correction in manuscript for R1 was highlighted with blue color

 

Comments and Suggestions for Authors

 

    I have read with interest your paper on the Evaluation of Travel Time for Different Density of Floatable Litter Influenced by River Flow Velocity. The manuscript deals with an interesting problem, however, I have a few comments. Unfortunately, the applied manuscript does not contain numbered lines, so I will have to indicate just pages and paragraphs.

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript.

 

    Number lines are added.

 

    Page 3, paragraph 2 – what distance is taken for travel time (T) estimation? It must be revealed in the introduction as well as in the abstract.

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration.

 

    The distance used for FL migration in the ToT method is explained in the Abstract section, but not in the Introduction section because the explanation of the FL travel time method is previously excluded from the introduction.

 

 

 

    Please see line 30 on page 1 in the Introduction section

 

 

 

    Page 12, paragraph 1 – equation referred to in the paragraph as (4) should appear under this paragraph directly

 

 

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration.

 

    We decided to simplify the explanation by focusing on the volume calculation method first and not relating to the density equation in this section yet. Thus, the paragraph is excluded and replaced with paragraph 1 on page 4.

 

 

 

    Please see lines 153 - 155 on page 5 for further information.

 

 

 

    Page 13 – I understand the idea of flow velocity estimation on the base of the float method and its application for this problem is reasonable. However, using Youtube instruction for students is good for ... students, not for scientific investigation, because there is much more than an idea of measurement. You need to interpret environmental results in a reliable way. Please, read any guidebook for hydrometry, there are plenty, for example, W. Boiten, 2003, Hydrometry, A.A. Balkema Publishers (Taylor & Francis e-Library, ISBN 0-203-97109-4 Master e-book, ISBN 90 5410 423 6 (paperback edition) or any other.

 

 

 

The basic problems of your measurement are as follows:

 

    the measurement reach should be as straight as possible, without significant turbulences, and its length is related to the width of the channel. In the photo (Fig. 5 – left) we can see a channel bend,

 

 

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript.

 

 

 

    Regarding your comment using the float method is less scientific, I also understand your point here. However, I really hope your consideration to accept the method used together with the results obtained. This is because I believe that the method and results obtained are reliable, as it is suggested by the Arizona Department of Environmental Quality (ADEQ). Plus, it is published on YouTube. I hope you also can consider the materials, tools, and space limitations I faced during this study was conducted. The limitation was due to the global COVID-19 lockdown that cause the inaccessible to my university. Thus, using more scientific methods might be impossible for me. Anyways, thank you for your suggestion to read more on the guidebook list you share with me. I will surely take it into consideration for future reference.

 

 

 

Thus, I appeal for this method to be accepted. I appreciate your consideration.

 

 

 

    For your information, both Figure 3 - left and right - are taken at other river sections. They are not representing/showing the river section where the simulation was conducted. The river section chosen for simulation has a straight channel.

 

 

 

    Please refer to page 7 for the picture of the exact river section as in Figure 5 and page 8 for Figure 6

 

 

 

    you mentioned 3 measurements and an average value. You need to explain if the float started 3 times in the same place (middle of the channel or along the main current) or if it was left, right, and central part of the cross-section. It is very important for results interpretation.

 

 

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration and corrected accordingly.

 

 

 

    For the particular correction, please refer to lines 250 - 254 on page 8.

 

 

 

    the correction factor is not a constant. Its value depends on the bottom material (roughness and friction), water depth, and level of float immersion.

 

 

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript. I agree that the correction factor is not a constant.

 

    However, using the method and formula for measuring river flow velocity which is sourced from Arizona (2018), none of these parameters is included in the formula. The 0.85 correction factor is acquired from this source. Moreover, the river bottom (roughness and friction) and level of float immersion are not in the scope of the study. Only the water depth parameter was measured as the adding information for future improvement of this study.

 

 

 

    This is my reason for using this method, in this case specifically for the correction factor.

 

Thus, I appeal and I really hope for this method to be accepted. I appreciate your consideration.

 

 

 

 

 

    Moreover, your modification of the Time of Travel (ToT) Method is the surface float method practically. Please explain why you calculated average cross-section velocity whereas Time of Travel refers to surface velocity only. It is also interesting, how the particular FL objects traveled during the ToT experiment in a matter of movement obstructions (shape and dimensions) – temporary contacts with the bottom, branches, etc.

 

 

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration.

 

    It is admitted that the figure does not explain the float method clearly and is confusing. A river cross-section is not needed for measuring river surface velocity. Moreover, the ToT method only considers river surface velocity, not average river cross-section velocity.

    

    Thus, the previous Figure 6 is excluded. However, the reader can refer to Figure 7 on page 10 for reference to the conduct float method because it is almost the same as the ToT method.

 

 

 

    In my opinion, you should revise and improve the paragraphs relating to measurement and result interpretation. In my opinion, some reversing results in ToT for B and C velocity conditions are mostly determined by measurement conditions.

 

 

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration. The manuscript as a whole has been updated and improved.

 

 

 

    Please refer to lines 505 – 508 on page 17

 

 

 

    Section 3.6 (Data Analysis) needs serious improvement regarding the description of the method. The presented text is absolutely insufficient.

 

 

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration. The manuscript as a whole has been updated and improved.

 

 

 

    More explanation about statistical analysis is added.

 

 

 

    Please refer to lines 305 – 307 and 316 – 319 on page 10

 

 

 

    Chapter Results and Discussion is expected to start with number 4. In this section, you have described your results data in great detail. However, you should also pay more attention to synthetic comments, if there are some regularities or some expected did not exist and why? You should assess the influence of measurement conditions on gathered data as well.

 

 

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration.

 

    There are additional points in the Discussion section.

 

 

 

    Please refer to lines 503 - 506 on page 17.

 

 

 

    Finally, the manuscript needs also language correction because in many paragraphs it is hard to follow the author’s ideas.

 

 

 

Author’s Response: Thank you for your time and consideration in leaving a remark. Your comment was taken into consideration and corrected accordingly.

 

 

 

    We read the whole manuscript and adjusted the coherence and cohesion and term used to make it clearer and more scientific.

 

Round 3

Reviewer 1 Report

See attached review report

Comments for author File: Comments.pdf

Author Response

Recommendation: minor revision

 

p/s: the correction in manuscript for R1 was highlighted with yellow color

 

Brief summary

The paper has improved a lot with respect to the first version. Yet it leaves some points to be improved. Therefore, I recommend minor revision.

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript

 

 

Relevance

The subject, if properly treated and clearly presented, is of practical relevance.

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript

 

 

Title

The adjusted title does not make sense. Please consider: “Travel time of floatable litter as a function of river flow velocity”.

Author’s Response:

• Thank you for your thoughtful comment and inquiry regarding the manuscript
• If I may explain, the term ‘density’ is important to include in the title to explain clearly of us studying how different density of floatable litter and river flow velocity affecting FL travel time.
• Some suggestions for the manuscript title, considering your latest comment are

“The Travel Time of Floatable Litter as a Function of its Different Density and River Flow Velocity” or “The Travel Time of Different Floatable Litter Density Influenced by River Flow Velocity”.

 

• Thus, the previous title is not updated yet
• However, we believe in your knowledge and judgement for changing the title to “Travel time of floatable litter as a function of river flow velocity” as the best option.

 

 

 

Numbers

1. Mentioning the ToT-distance clarifies a The first version could be read as if it concerned a much larger distance. At the same time, it raises the question about numbers. How can the litter move significantly faster than the velocity of a float: according to the numbers mentioned in lines 53 and 54, the fastest object moved with a speed of 30/43.93 = 0.68 m/s while the flow velocity was only 0.23 m/s.

Also, when considering average speeds over all FL in Table 4 and Figure 9, litter speeds are well above the river flow velocity in all three cases. This needs explanation or correction.

2. I also noted something strange in Table 3. If I multiply the time taken by the float by the river flow velocity, the result is only 5 m in case B. In cases A and C, it is 26 and 3.67 m, respectively. This, too, needs explanation or correction.

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript

1. Fastest object (FL14) moved faster than river flow velocity because of the different object/FL density. The density of float bottle was bigger than FL 14. Higher density results in longer travel time and lower velocity at the same time. River flow velocity value is not to be compared directly to FL speed and travel time because the river flow velocity value is only as the baseline to assess the velocity and FL travel time during different river flow velocity. In which, it is proven that the higher river flow velocity - in overall - results in shorter FL travel time.

 

The float bottle travel time is faster than the fastest travelled FL 14 because the travel time is recorded in 5 m distance. Assuming the distance travelled by float bottle is 30 m, the travel time is slower than average FL travel time during Condition A. For example:

Float bottle travel time in 5 m distance during Condition A = 14.307 s

Float bottle travel time in 30 m distance during Condition A = 14.307 s x (5 m x 6)

                                                                                                           = 85.842 s

 

Comparing average FL travel time and float bottle travel time in 30 m distance, FL travel time is far faster (t = 43.93 – 82.00 s) than float bottle travel time (t = 85.842 s). This explains the situation of FL higher speed above river flow velocity.

 

2. There is some mistake for river flow velocity calculation in Condition A, thus the calculation is redone and corrected.

The time taken for float bottle to travel between 2 points was somehow interchangeable and not the actual value of float bottle travel time respective to Condition B and Condition C. Thus, the value is exchanged between Condition B and Condition C accordingly.

 

 

 

Symbols

1. The symbol V is used for velocity (e.g. lines 53 and 54) and for volume (e.g. in 1, Eq. 4 and lines 336-337).
2. The mass density is sometimes indicated by the symbol ρ (e.g. in 4), but in most instances by the symbol p. This symbol, however, is also used to indicate a statistical property (e.g. line 441).

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript

 

1. The V symbol is distinguished to volume, V and velocity, v. For example, please refer to Equation (1) on page 5 and Equation (5) on page 8.

 

2. The p symbol is uniformly used for all density values stated in manuscript. For some examples, please refer to Equation (4) on page 7 and line 354 on page 11.

 

 

English

The English is generally OK, except a few misprints, missing words and non-running sentences.

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript

 

 

Recommendation

I recommend minor revision.

 

Author’s Response: Thank you for your thoughtful comment and inquiry regarding the manuscript

 

 

 

Author Response File: Author Response.docx