Modeling of Sediment Transportation in Ichkeul Lake for the Estimation of the Influence of the Constructions of the Reservoirs in the Upper Streams

Round 1

Reviewer 1 Report

General comments:

English language correction is needed in whole text, fragments are incomprehensible.

Unfortunately, the manuscript is not well written and the language in many fragments is incomprehensible. The topic and research are interesting, however, and I would be grateful to receive  the manuscript after editorial revision. In addition, the manuscript has a lot of side plots and it is difficult to understand the main aim of the study and contribution to the science. Below are some comments that should be additionally taken into account.

Some specific remarks:

Abstract

The abstract is chaotic and it is difficult to understand the aim of the research. Please rewrite to reflect the main aim, key results and contribution to the science, and to encourage the scholar community to read the Manuscript.

Introduction

I don't know if the fragment about pollution is related to the research in the article. Please explain or edit it. Similarly, the part about birds and plants. The description of the area should be included in the Study Area chapter, and the scientific context of the research should be presented in the Introduction.

Materials and methods

lines 103-104: This is an example of linguistic repetitions in the text "balance .. balanced". The entire manuscript should be re-edited with this in mind. Next sentence has the same problem as many others.

line 115: Why are there no reservoirs on the map?

line 134: Please check the font, because some parts are different, e.g. line 134.

lines 151-161: Calculation unclear, with what data was the approach results compered?

lines 193-196: The next sentence is unfortunately incorrectly written.

lines 229-241: Please check the manuscript if sentences do not start with table/figure number and edit it.

Results and Discussion

The description of the results is not a description of figures or tables. In this chapter each paragraph cannot start with 'Figure represents ..'. The figures are illustration for description, not the other way around.

Providing only R2 and RMSE is not enough to evaluate the modeling. At least one more parameter (NSE, KGE or similar) must be provided.

lines 262-266: Sentence very long and unclear.

lines 310-329: Why is the calibration of the next reservoir here? Please organize the text.

lines 343-352: The description of the experimental methods should be found in the Methods chapter, and the Results chapter should include the results.

Conclusions

The Conclusions are not intended to repeat what was written in the Manuscript in short. It provides additional information for discussion, research limitations and further studies directions. Please adapt the chapter to the guidelines.

Author Response

Dear Reviewer1

Thanks for your helpful comments. That was very helpful for me to revise our manuscript.

English language correction is needed in whole text, fragments are incomprehensible.

Unfortunately, the manuscript is not well written and the language in many fragments is incomprehensible. The topic and research are interesting, however, and I would be grateful to receive  the manuscript after editorial revision. In addition, the manuscript has a lot of side plots and it is difficult to understand the main aim of the study and contribution to the science. Below are some comments that should be additionally taken into account.

Indeed, our first draft was fragmented. As you pointed out, we combined a lot of approch but the aim was not clearly described and the story tended to go aside. I noticed my bad habit of repetitive writing.

Some specific remarks:

Abstract

The abstract is chaotic and it is difficult to understand the aim of the research. Please rewrite to reflect the main aim, key results and contribution to the science, and to encourage the scholar community to read the Manuscript.

We modified the abstract to show the aim clearly. Our study site is very sensitive environmentally but the focus of conservation activities were not comprehensive. We like to create a stir in that.

Introduction

I don't know if the fragment about pollution is related to the research in the article. Please explain or edit it. Similarly, the part about birds and plants. The description of the area should be included in the Study Area chapter, and the scientific context of the research should be presented in the Introduction.

I omitted the description about pollution. Instead, we describe how sensitive estuaries and blackish lakes are and attract scientific interests, with some references. I would appreciate it if you read the revised manuscript.

Materials and methods

lines 103-104: This is an example of linguistic repetitions in the text "balance .. balanced". The entire manuscript should be re-edited with this in mind. Next sentence has the same problem as many others.

Yes, I noticed. I also corrected text similar to such repeating in other parts

line 115: Why are there no reservoirs on the map?

They are shown in the revised manuscript, quite thin. See Figure 1

line 134: Please check the font, because some parts are different, e.g. line 134.

Thanks for your notice. I checked the font

lines 151-161: Calculation unclear, with what data was the approach results compered?

The results of the outflow from Ichkeul to Bizerte Lagoon was not verified with the com parison with observed data. There was no record. We verified this calculation by seeing the reproducibility of the lake water level. We add such description in line 311-313 revised manuscript ver. without track.

In Tinja channel, we installed 2 water level gauge upstream and downstream of tide stop weir. Downstream one is used for calculating the hydraulic gradient. Upper one represent the lake water level. We assumed that the flow rate is the function of the lake water level as shown in Figure 6&7

lines 193-196: The next sentence is unfortunately incorrectly written.

I edit it. I would appreciate it if you read the revised manuscript.

Lines 229-241: Please check the manuscript if sentences do not start with table/figure number and edit it.

I edit it. I would appreciate it if you read the revised manuscript.

Results and Discussion

The description of the results is not a description of figures or tables. In this chapter each paragraph cannot start with 'Figure represents ..'. The figures are illustration for description, not the other way around.

 I edit it, not starting with 'Figure represents ..'. I would appreciate it if you read the revised manuscript .

Providing only R2 and RMSE is not enough to evaluate the modeling. At least one more parameter (NSE, KGE or similar) must be provided.

Thanks for your suggestion. I added NSE as indicator

lines 262-266: Sentence very long and unclear.

First, I moved this paragraph to “Material and Methods”, following toyour next comments.

I edited the sentence to shorten it. Please see Line300 in the revised manuscript without track

lines 310-329: Why is the calibration of the next reservoir here? Please organize the text.

I moved also this paragraph to “Material and Methods”, following to your next comments.

I tried to organize the text. Please see Line272-273 in the revised manuscript without track

lines 343-352: The description of the experimental methods should be found in the Methods chapter, and the Results chapter should include the results.

I moved part of it to the Line375-380 in Material and Methods and remain to Line 474-479 with some change of sentence for result. I would appreciate it if you read the revised manuscript .

Conclusions

The Conclusions are not intended to repeat what was written in the Manuscript in short. It provides additional information for discussion, research limitations and further studies directions. Please adapt the chapter to the guidelines.

Thanks for your advice. I added the limitation of this study and scope for further studies.

Regards.

Author Response File: Author Response.pdf

Reviewer 2 Report

COMMENTS AND SUGGESTIONS FOR AUTHORS

The present work is interesting, is well structured and assessed Modeling of sediment transportation in Lake Ichkeul for the estimation of the influence of the constructions of the reservoirs in the upper streams. The introduction is rather poor, with few bibliographic citations and no presentation of previous work or similar studies. The rest of the paper is well structured, well explained and the results are well represented with plenty of tables and figures.

I give my suggestions for improving the manuscript, which should be done before publication of the paper.

1. Introduction

• The introduction is brief and summarises the interest of the work, although it could be improved.
• The state of the art could be added and previous work could be reported.
• Not too many bibliographical citations.
• The objective of the work is very well defined in the last paragraph.

2. Materials and Methods

• The study site and the two figures are very adequate.
• Estimation of the water balance of the lake part is appropriate.
• In the Figure 3 b, that map is not a geological map, it is a soil map!
• Furthermore, in Figures 3-4, it is understood that the maps are oriented North, but it is necessary to put the North arrow on the map.
• Modeling the sediment resuspension driven by wind part and field observation part are appropriate.

3. Results and discussion

• The text is adequate and the data is well represented with figures and tables.
• In Figure 10, it would be convenient to put a scale and the date of North.
• All other figures including graphs and tables are appropriate.

4. Conclusions

• Are appropriate.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer2

The present work is interesting, is well structured and assessed Modeling of sediment transportation in Lake Ichkeul for the estimation of the influence of the constructions of the reservoirs in the upper streams. The introduction is rather poor, with few bibliographic citations and no presentation of previous work or similar studies. The rest of the paper is well structured, well explained and the results are well represented with plenty of tables and figures.

I give my suggestions for improving the manuscript, which should be done before publication of the paper.

1. Introduction

• The introduction is brief and summarises the interest of the work, although it could be improved.
• The state of the art could be added and previous work could be reported.
• Not too many bibliographical citations.
• The objective of the work is very well defined in the last paragraph.

Thanks for your helpful comments. As you requested, the review of previous study was not sufficient. I added the references related to sediment transportation in estuaries and experimental studies on resuspension. I would appreciate it if you read the revised manuscript

1. Materials and Methods

• The study site and the two figures are very adequate.
• Estimation of the water balance of the lake part is appropriate.
• In the Figure 3 b, that map is not a geological map, it is a soil map!

I changed the caption. That is Soil map indeed.

• Furthermore, in Figures 3-4, it is understood that the maps are oriented North, but it is necessary to put the North arrow on the map.

I add the North Arrow. I moved some paragraphs and figures to Material  and method, following to the comment from other reviewer. Please Figure 4&5 in the revised manuscript

• Modeling the sediment resuspension driven by wind part and field observation part are appropriate.

Thanks for you positive comments to that part. I tried to improve the description. I would appreciate it if you read the revised manuscript

1. Results and discussion

• The text is adequate and the data is well represented with figures and tables.
• In Figure 10, it would be convenient to put a scale and the date of North.
• All other figures including graphs and tables are appropriate.

 Figure 10 was moved to “Study site” in Material and Methods chapter, following to the comments from other reviewer, with North arrow and scale. Thanks for your comments

1. Conclusions

• Are appropriate.

Thank you for all the comments. The order of explanations has been changed to reflect the suggestions from other reviewers, but the results have not changed.

Regards.

Author Response File: Author Response.pdf

Reviewer 3 Report

The topic of the article is interesting, but more information is needed for a final decision.

To understand the validity of the conclusions, it is advisable to supplement the manuscript with answers to questions

1. There is no information about the water balance of the lake: inflow, outflow and evaporation from the water surface. It is advisable to give this information in tabular form and by year.
2. There is no information about water consumption from reservoirs and evaporation. Without this, it is difficult to assess the results of modeling and forecasting inflows.
3. There is no information about the elevations of the bottom of the lake. Were there any bottom observations?
4. Erosion of the bottom should lead to an increase in depth and a decrease (stabilization) of erosion. How is this taken into account in the calculations?
5. Give a table with data on water turbidity: in reservoirs, lake, lagoon and canals.
6. Give a brief description of the reservoir management rules and the rules for the inclusion of the lake protection system against tides.

Author Response

Dear Reviewer 3

Thanks for your helpful comments. I revised my manuscript. Please read it with below replies.

1. There is no information about the water balance of the lake: inflow, outflow and evaporation from the water surface. It is advisable to give this information in tabular form and by year.
2. There is no information about water consumption from reservoirs and evaporation. Without this, it is difficult to assess the results of modeling and forecasting inflows.

Thanks for your suggestion. I added the table 3&4 including the water consumption (intake) and evaporation in the reservoirs in page15. It will help to understand the water budget

1. There is no information about the elevations of the bottom of the lake. Were there any bottom observations?

The values in the bathymetry map of Figure2 is the altitude. That was used for the simulation for the case without the reservoirs. We did not consider the change of the lake bed level for the water budget estimation.

1. Erosion of the bottom should lead to an increase in depth and a decrease (stabilization) of erosion. How is this taken into account in the calculations?

Erosion does not increase the depth. It change the absolute altitude of water surface and bed level parallelly for the same volume of water. The depth was changed due to the volume of water, the decrease of fresh water inflow in winter. However, even with deeper water body, the resuspension in the simulation is same because we assumed the equilibrium state of settlement and resuspension (Eq(3)=0). So that, there is no reflect to the results of the concentration of SS in the lake.

1. Give a table with data on water turbidity: in reservoirs, lake, lagoon and canals.

Unfortunately, we did not obtain the turbidities in lagoon and canal. What we can say is the lagoon is so deep that the resuspension by wind disturbance does not occur. The reverse flow from the lagoon to the lake occurs in summer when the wind in the region is weak. So that the turbidity transportation from lagoon is negligible. I add the explanation in Page 5 from Line202 of revised manuscript.

 On the other hand, Turbidity in reservoirs fluctuate temporally and spatially.　In the reservoirs, bottom density currents occurs in the water body but the discharges over the dam body are overflow of spillway, that is clear water from surface. That was written in Page3 Line100 with the reference [13].

1. Give a brief description of the reservoir management rules and the rules for the inclusion of the lake protection system against tides.

To be honest, Table 3 seems to indicate that water use has been prioritized over environmental protection, especially since it was removed from the list of World Heritage Sites in crisis in 2006. Only the overflow that exceeds the surcharge water level, which is the height of the spillway, flows downstream from the dam. I described that Page7 Line 252 in the revised manuscript.

 On the other hand, the tide stop weir in Tinja channel worked well. Although the fresh water inflow and water level decrease but the increase of the reverse flow was well regulated in table4.

We could make such discussion with the above revision following to your first suggestion. Thanks again for your comment.

However, administrators of the lake and reservoirs in the government are aware that the tidal weir is functioning well, which may be the motivation for prioritizing the use of water in the reservoir. I can't even mention the political inside

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

General comment: The manuscript is significantly improved.

Abstract: The abstract is much better. Interesting and well written.

line 22: double dot and double space.

Introduction: The introduction is really long now. In my opinion a part of information should be placed in Study Area section.

line 52: How this two researches context the manuscript study?

lines 85-95: I think that it is too detailed for the introduction.

line 152: doubled space.

Sub-chapter 1.2: This chapter is important and interesting but the length of the introduction suggest that the whole fragment should be moved to Methods or to Supplementary Material.

Materials and Methods: The chapter is improved.

line 209: unnecessary capital letter.

lines 272-278: This fragment is necessary but please edit the expressions for more professional soundness.

Results and Discussion, Conclusions: I accept changes made in this chapters.  

line 406: doubled dot.

line 515: doubled space.

line 579 double space and line 584 no space

Author Response

Abstract: The abstract is much better. Interesting and well written.

Materials and Methods: The chapter is improved.

Results and Discussion, Conclusions: I accept changes made in this chapters. 

 Thanks for your positive comment on the chapters. I expect it looks interesting to a lot of readers.

Introduction: The introduction is really long now. In my opinion a part of information should be placed in Study Area section.

lines 85-95: I think that it is too detailed for the introduction.

Sub-chapter 1.2: This chapter is important and interesting but the length of the introduction suggest that the whole fragment should be moved to Methods or to Supplementary Material.

Indeed, the manuscript after the 1^st revision had a too long introduction. As you suggested, I moved some parts of the “background” to

2.1. Study site

“Sub-chapter 1.2” was moved to

2.3. Modeling the sediment resuspension driven by wind

line 52: How this two researches context the manuscript study?

I like to list these studies as typical examples that human activities affect estuary environment.

lines 272-278: This fragment is necessary but please edit the expressions for more professional soundness.

I hope the revised turn of phrase of L203-208 in the revised manuscript sounds better.

line 22: double dot and double space.

line 152: doubled space.

line 209: unnecessary capital letter.

line 406: doubled dot.

line 515: doubled space.

line 579 double space and line 584 no space

Thanks for your precise check even for such unarranged writing. I revised my mistakes.

Regards

Reviewer 3 Report

Remarks
1. There is no evaporation in equation (1). This makes a big mistake in the calculations. Evaporation can be accurately calculated by empirical formulas.
2. It is necessary to consider the balance of salts and turbidity in the lake and give the results of calculating the depths (elevations) of water in the lake for 25-50 years.
3. It is necessary to describe the mode of operation of the dam in the connecting channel, and show how it affects the results of calculations.

Author Response

Dear Reviewer 3

Thanks for your various suggestions. In the field measurement in our study site, we have a lot of difficulties regarding data access. We did our best to solve that but there is a limit. I my sense, that is the field study. Perfect setting cannot be expected.

The replies to your comments are as below. I hope you accept my idea.

1. There is no evaporation in equation (1). This makes a big mistake in the calculations. Evaporation can be accurately calculated by empirical formulas.

Thanks for your pointing out the lack of evaporation term in equation 1. I added it.

Regarding the estimation of evaporation, at the beginning of this research, we also planned calculating evaporation from meteorological data with empirical formulas. However, Hours of daylight which is required for Penman formula was not observed at SIDI AHMED AIR BASE. I added the available items of meteorological at that station in L172 of the revised manuscript. Thornthwaite method and Makkink method would be one of the candidates for the estimation but the applicability of that equation is limited. In addition, usually, input data for those equations are monthly mean temperature so that the resolution of that is monthly.

 The most accessible and reliable data for our site was pan evaporation data at dam office. Unfortunately, we could obtain that from 2008 to 2010 only. We compared the 3 years data and confirmed the difference was small.

Limitation of data access was the constraint of our study site, but we are making every effort to get over the obstacle.

2. It is necessary to consider the balance of salts and turbidity in the lake and give the results of calculating the depths (elevations) of water in the lake for 25-50 years.

It is difficult to modeling the consolidation process. We obtained the bulk density on the lake bed and reservoir, but the time series of the inflow of sediment was not simulated because we don’t obtain the turbidity data at the inflow rivers as mentioned in the manuscript. Modeling the sediment discharge from the reservoirs were very difficult due to the complicated behavior of the turbid bottom density current in each reservoirs as shown in the reference[10]. That is the reason why just we compare the outflow of sediment with the annual average of accumulated sediment in the reservoirs.

 Before our study, the environmental conservation of the lake was discussed only from the view point of water balance. Our study suggests the new vison for that issue. Change of sediment budget is "not negligible". We need to stop at that point because we could not obtain the reliable observed data of inflow of sediment and accumulation process. I believe it has a certain scientific contribution even though the change of salinity condition was not shown quantitatively.

3. It is necessary to describe the mode of operation of the dam in the connecting channel, and show how it affects the results of calculations

Honestly, there is no strict record of the operation of the weir. In addition, as I mentioned in the manuscript(Page.7 L224), the additional bypass is the buffer of operation but its precise effect is not countable. On the other hand, the relationships between estimated flow rate and water level with high correlation, shown as Fig 6&7 totally consider such effects.

If the purpose of this study is finding the Best Management Practice, such discussion as you suggested is required. The aim of this study we set is to clarify whether the sedimentation tendency is erosive or cumulative, and not only the water level decrease, also the lake bed depression due to the imbalance of the sedimentation gives a certain negative environmental impact on Ichkeul Lake. I believe this paper can revealed the new vision for the environmental conservation of the World Heritage.

Round 3

Reviewer 3 Report

The manuscript deals mainly with the problem of turbidity in the lake. Water balance and management method are needed to assess environmental impacts.

Water balance data are very approximate, modeling and management are not discussed.Recommendation to authors and editor. I propose, in the title of the article, to leave only a study of the turbidity of the water in the lake.

Author Response

Thank you for your valuable comments from a hydrological point of view. As you pointed out, the water balance shown in this manuscript was not perfect, especially in the evaporation part. However, it is not our intention in this paper to remove the water balance part and show only the increase in turbidity due to wind turbulence. As mentioned in the introduction, the only consideration so far in the management of the World Heritage Site Ichkeul has been to improve the water balance and keep the lake level as high as possible. However, in reality, the height of the bottom laid under the water may have decreased. Only the discussion about resuspension is not enough to express this decline. Without the horizontal movement of solid matter outflowing from the lake, it is impossible to express whether  the bottom of the water is declined. From this point of view, even if the accuracy of the evaluation of evapotranspiration is rather low, the calculation results of water balance in this study, which can reproduce the fluctuations of the lake water level fairly accurately, have a certain degree of reliability. We believe that the sediment transportation discussed with the combination with resuspension modelling will give a new perspective to the environmental conservation measures of the World Heritage Sites, which require appropriate assessment.

To make it easier to check the corrected parts, I will send the pdf of the manuscript with the comments received from the three reviewers and the answers from me attached to each part. I think we responded to all comments except the suggestion that the water balance analysis part is excluded.

Regards

Author Response File: Author Response.pdf