Riverbed Changes of the Uppermost Atchafalaya River, USA—A Case Study of Channel Dynamics in Large Man-Controlled Alluvial River Confluences

Round 1

Reviewer 1 Report

Paper submitted for review „Riverbed changes of the uppermost Atchafalaya River, USA – A case study of channel dynamics in large man-controlled alluvial river confluences” investigated river hydraulic changes from 1935 to 2016 and riverbed changes from 1998 to 2006 in the channel of one of the world’s largest man-controlled river confluence, the Mississippi-Red- Atchafalaya River confluences. It is an interesting topic considering the fact that the papers related to the impact of human activities on the dynamics of changes taking place in the canals are relatively scarce. The papers should be published after incorporating several amendments.

other comments:

1. The unit should be corrected – e.g. line 102 – it should be km³, not km3. Similarly, line 172 (m², not m2), 198 (m m^-1, not m m -1), line 377 (km², not km2). In addition, in line 357 units should be uniformized - once there is mg/L, another time mg L^-1.
2. The caption under the figure reads Atchafalaya River (right) and the Lowermost Mississippi River (left), it seems there should be Atchafalaya River (left) and the Lowermost Mississippi River (right).
3. Delete unnecessary spaces in sentences – e.g. in lines 183, 250, 264 etc.

Author Response

Comments and Suggestions for Authors

Paper submitted for review „Riverbed changes of the uppermost Atchafalaya River, USA – A case study of channel dynamics in large man-controlled alluvial river confluences” investigated river hydraulic changes from 1935 to 2016 and riverbed changes from 1998 to 2006 in the channel of one of the world’s largest man-controlled river confluence, the Mississippi-Red- Atchafalaya River confluences. It is an interesting topic considering the fact that the papers related to the impact of human activities on the dynamics of changes taking place in the canals are relatively scarce. The papers should be published after incorporating several amendments.

Authors’ response: Thank you very much for your support and for taking time to review our manuscript. We greatly appreciate your comments and suggestions, all of which have been taken into account in this revised manuscript.

other comments:

1. The unit should be corrected – e.g. line 102 – it should be km³, not km3. Similarly, line 172 (m², not m2), 198 (m m^-1, not m m -1), line 377 (km², not km2). In addition, in line 357 units should be uniformized - once there is mg/L, another time mg L^-1.

Authors’ response: Thank you for pointing these out. We have carefully checked the units and have changed accordingly.

2. The caption under the figure reads Atchafalaya River (right) and the Lowermost Mississippi River (left), it seems there should be Atchafalaya River (left) and the Lowermost Mississippi River (right).

Authors’ response: Thank you. The suggested change has been made.

3. Delete unnecessary spaces in sentences – e.g. in lines 183, 250, 264 etc.

Authors’ response: Done.

Author Response File: Author Response.pdf

Reviewer 2 Report

Reviewed paper is devoted to the riverbed changes of the uppermost Atchafalaya River, USA – A case study of channel dynamics in large man-controlled alluvial river confluences. The subject of the paper well fits the scope of Water. The paper could be considered for publication in Water after substantial revision taking into account the following comments.

The stability of the channels is one of the most important indicators of the state of water bodies, the possibility and stability of their economic use. The reviewed paper is devoted to the analysis of stability of a complex channel system of Red - Mississippi – Atchafalaya rivers. It examines the geographical aspects of the problem based on materials for a sufficiently long observation period from 1935 to 2016.

1. The work is based on a comparison of materials from two bathymetric surveys performed in 1998 and 2006, by assessing changes in raster relief models for the period under consideration. In this case, a grid spacing of 10 m was used with a distance between measuring sections of 200-400 m causing doubt on the quality of the data obtained. From Figure 2 it is clearly seen that the interpolation between the measuring sections was carried out in automatic mode, which significantly reduces the quality of the initial information, leading to significant errors.
2. The paper mentions the processes of ridge motion along the flow, however, this process is not taken into account in assessing the volume of reformation.
3. In order for the results of this work to be used for other similar objects, the authors should consider the mechanisms of the formation of channel processes themselves.
4. In the present work, the global Reynolds number Re=(V*H)/ν is used as the main hydrodynamic parameter. However, in channel flows with very large Reynolds numbers Re, the main hydrodynamic characteristics of the flow become completely self-similar with respect to Re, i.e. they cease to depend on it. Of much greater interest are the values of the local Reynolds number Re*=(V* *d)/ν, where V* is the dynamic flow velocity, the d-characteristic diameter of particles of bottom sediments, and also the values of global and local Froude numbers Fr = V²/g*H, Fr*=(V*)²/(g*d). Unfortunately, the assessment of these parameters in the paper is not carried out.
5. In assessing the stability of bottom sediments, the ratio of flow rate and particle size and cohesion of bottom sediments plays a decisive role. Unfortunately, the relationship between the average watercourse velocity and water flow rate, and the role of granular and ridge roughness in its formation are not considered in the work. The dispersion composition of bottom sediments is not presented (only the range of variation is indicated, which is not sufficient). Of considerable interest for solving the problem under consideration is the analysis of changes in the dispersion composition of bottom sediments over the observation period.
6. The sediment runoff is used in the paper as one of the main indicators. At the same time, however, it is not indicated which sediments are considered: weighted, entrained or their total characteristic.
7. How was sediment runoff estimated - by field measurements or by calculations? If field measurements were carried out, it is necessary to indicate the technology of measurements and their frequency. If by calculations, then on the basis of what calculation relationships?
8. It should be noted that sediment flow estimates are typically characterized by errors. In this regard, it was very interesting to compare sediment flows with a change in the morphometry of the considered water bodies.
9. Currently, there are many software products for modeling channel processes, in particular: Delft3D-FLOW Simulation of multi-dimensional hydrodynamic 6. flows and transport phenomena, including sediments User Manual January 12, 2011 Delft Deltares. 672 p .; Berger R.C., Tate J.N., Brown G. L., Savant G. “Adaptive Hydraulics (AdH) Version 4.5. Hydrodynamic User Manual. " January. 2015; Reference Manual "RiverFlow2D Two-Dimensional River Dynamics Model." August 2016. Hydronia LLC. In this regard, the work would have acquired a completely different significance if the modeling of this channel system and its comparison with the observed dynamics were carried out.

In general, the paper in the present form has a purely descriptive character and is not of significant interest.

Author Response

Comments and Suggestions for Authors

Reviewed paper is devoted to the riverbed changes of the uppermost Atchafalaya River, USA – A case study of channel dynamics in large man-controlled alluvial river confluences. The subject of the paper well fits the scope of Water. The paper could be considered for publication in Water after substantial revision taking into account the following comments.

[Authors’ response:] We would like to thank you for taking the time to review our manuscript. We greatly appreciate your comments and suggestions, all of which have been taken into account in this revised manuscript.

The stability of the channels is one of the most important indicators of the state of water bodies, the possibility and stability of their economic use. The reviewed paper is devoted to the analysis of stability of a complex channel system of Red - Mississippi – Atchafalaya rivers. It examines the geographical aspects of the problem based on materials for a sufficiently long observation period from 1935 to 2016.

1. The work is based on a comparison of materials from two bathymetric surveys performed in 1998 and 2006, by assessing changes in raster relief models for the period under consideration. In this case, a grid spacing of 10 m was used with a distance between measuring sections of 200-400 m causing doubt on the quality of the data obtained. From Figure 2 it is clearly seen that the interpolation between the measuring sections was carried out in automatic mode, which significantly reduces the quality of the initial information, leading to significant errors.

[Authors’ response:] Thank you for your comments. Yes, the 10-m resolution is relatively large for the area between two cross-sections. However, our purpose in this study is comparing the volume changes of riverbed deformation using two sets of DEM. We tried different resolutions (10 to 50 meters) in such calculation and found that the resolution has little effects on estimated results in volume changes. The calculation error of comparing two repeated bathymetric measurements was normally less than 5% showing in our software -  “Geomorphic Change Detection" – an add-in software in ArcGIS developed by Wheaton etc. (Wheaton et al., 2013; Wheaton et al., 2010).

2. The paper mentions the processes of ridge motion along the flow, however, this process is not taken into account in assessing the volume of reformation.

[Authors’ response:] Thank you for pointing this out. We aimed to estimate long-term channel bed deformation using river stage data and decadal bathymetric data. Therefore, we neglected the ridge motion between the periods. Although the detailed study on bedform evolution can help understanding bedload transport and bed dynamics, such study is a little out of the scope of current manuscript.

3. In order for the results of this work to be used for other similar objects, the authors should consider the mechanisms of the formation of channel processes themselves.

[Authors’ response:] Thank you. Based the study, we found that the increased discharge ratio between the tributary and main channels between 1855 and 2016 could be the main reasons for the observed bed deformation. Other factors, such as large floods and river engineering may also have impacts on the channel formation.

4. In the present work, the global Reynolds number Re=(V*H)/ν is used as the main hydrodynamic parameter. However, in channel flows with very large Reynolds numbers Re, the main hydrodynamic characteristics of the flow become completely self-similar with respect to Re, i.e. they cease to depend on it. Of much greater interest are the values of the local Reynolds number Re*=(V* *d)/ν, where V* is the dynamic flow velocity, the d-characteristic diameter of particles of bottom sediments, and also the values of global and local Froude numbers Fr = V²/g*H, Fr*=(V*)²/(g*d). Unfortunately, the assessment of these parameters in the paper is not carried out.

[Authors’ response:] Thank you for the suggestions. As you suggested, we now have calculated both local Reynolds number and global/local Froude numbers. Please see the revised Table 3.

5. In assessing the stability of bottom sediments, the ratio of flow rate and particle size and cohesion of bottom sediments plays a decisive role. Unfortunately, the relationship between the average watercourse velocity and water flow rate, and the role of granular and ridge roughness in its formation are not considered in the work. The dispersion composition of bottom sediments is not presented (only the range of variation is indicated, which is not sufficient). Of considerable interest for solving the problem under consideration is the analysis of changes in the dispersion composition of bottom sediments over the observation period.

[Authors’ response:] Thank you for your suggestions. We totally agree with you. The factors such as discharge, particle size, and bed slope are critical for understanding the stability of channel bed. Actually, we are working on another manuscript focusing on the bed deformation using 1-D and 2-D modeling, which is comprehensive and beyond the scope of this present study. The main objective of the current paper is to study the long-term bed deformation along the channel, we believe that presenting our modeling effort and the findings in a separate paper is more suitable.

6. The sediment runoff is used in the paper as one of the main indicators. At the same time, however, it is not indicated which sediments are considered: weighted, entrained or their total characteristic.

[Authors’ response:] Thank you. For making it clear, we have added related information in the Discussion. For example, suspended sediment – particle diameter smaller than 0.0625 mm, bed material load - sediment comprising the bed that travels either as bedload or suspended load.

7. How was sediment runoff estimated - by field measurements or by calculations? If field measurements were carried out, it is necessary to indicate the technology of measurements and their frequency. If by calculations, then on the basis of what calculation relationships?

[Authors’ response:] The sediment data were gathered from the U.S. Geological Survey. Based on the USGS, sediment samples were collected two to three times per month using a depth-integrated sampler, normally US D-99, from a survey boat. We have added the into the revised manuscript (see lines 413-415). 

8. It should be noted that sediment flow estimates are typically characterized by errors. In this regard, it was very interesting to compare sediment flows with a change in the morphometry of the considered water bodies.

[Authors’ response:] Thank you for the comments. We wish we could make the comparison; however, it is difficult to directly compare our estimated bed erosion with sediment flows because the previously published work only looked at suspended sediment transport of the Atchafalaya River (Mize et al., 2018), in which separate sand transport was not included.

9. Currently, there are many software products for modeling channel processes, in particular: Delft3D-FLOW Simulation of multi-dimensional hydrodynamic 6. flows and transport phenomena, including sediments User Manual January 12, 2011 Delft Deltares. 672 p .; Berger R.C., Tate J.N., Brown G. L., Savant G. “Adaptive Hydraulics (AdH) Version 4.5. Hydrodynamic User Manual. " January. 2015; Reference Manual "RiverFlow2D Two-Dimensional River Dynamics Model." August 2016. Hydronia LLC. In this regard, the work would have acquired a completely different significance if the modeling of this channel system and its comparison with the observed dynamics were carried out.

[Authors’ response:] This is a very good point and we appreciate for the literature citations. As explained above, a modeling work for the river reach is comprehensive and is beyond the scope of this paper. But we have included the citations in the revised manuscript, please see lines 488-492.

In general, the paper in the present form has a purely descriptive character and is not of significant interest.

[Authors’ response:] Thank you for taking some of your valuable time to review our manuscript. We obviously disagree with your assessment and we are positive that descriptive character has its own merit and modeling work does not always provide scientific significance. In return we analyzed all your comments and suggestions carefully and we have been used them to substantially improve the paper accordingly. We hope the revisions meet your expectations and are convincing enough to reverse your initial decision and thus recommend the publication of the paper.

 

References:

Mize, S.V., Murphy, J.C., Diehl, T.H., Demcheck, D.K., 2018. Suspended-sediment concentrations and loads in the lower Mississippi and Atchafalaya rivers decreased by half between 1980 and 2015. Journal of Hydrology, 564, 1-11.

Wheaton, J.M., Brasington, J., Darby, S.E., Kasprak, A., Sear, D., Vericat, D., 2013. Morphodynamic signatures of braiding mechanisms as expressed through change in sediment storage in a gravel-bed river. Journal of Geophysical Research: Earth Surface, 118(2), 759-779.

Wheaton, J.M., Brasington, J., Darby, S.E., Sear, D.A., 2010. Accounting for uncertainty in DEMs from repeat topographic surveys: improved sediment budgets. Earth Surface Processes and Landforms, 35(2), 136-156.

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript focuses on an absolutely relevant issue about the possible geomorphological consequences of channel changes and discharge variations of engineered river confluences. It was clearly found as a research gap that the former studies on bed morphology were focusing on the thalweg erosion without giving more emphasis on bank to bank changes. The authors found that the flow increase resulted in significant bed degradation of the upper Atchafalaya River and the scouring continued. The study serves as a valuable additional for a better understanding of downstream hydromorphologic effects of engineered river confluences.

I have only the following issues for the authors to be discussed:

• Figure 1. I suggest to redesign the figure in order to highlight the Atchafalaya River in a more visible way. In this version it is hardly possible to see it. What is the background layer by the way? It should be also mentioned in the captions or on the map with small letters.
• Lines 121-129. Is there any reference to support this paragraph?
• Lines 152-154. How was the single-beam data collected? What kind of instrument and settings was applied? 
• Figure 2. Why those raw points are extending the channel edges? Aren't these in-channel survey points? Please clarify these things.
• Figure 3-4. Why to plot a decimal place on y-axis?
•  

Author Response

Comments and Suggestions for Authors

The manuscript focuses on an absolutely relevant issue about the possible geomorphological consequences of channel changes and discharge variations of engineered river confluences. It was clearly found as a research gap that the former studies on bed morphology were focusing on the thalweg erosion without giving more emphasis on bank to bank changes. The authors found that the flow increase resulted in significant bed degradation of the upper Atchafalaya River and the scouring continued. The study serves as a valuable additional for a better understanding of downstream hydromorphologic effects of engineered river confluences.

Authors’ response: First of all, we would like to sincerely thank you for your support and for taking your valuabletime to review our manuscript. We greatly appreciate your comments and suggestions, all of which have been taken into account in this revised manuscript, and they have been very helpful in improving the quality of our manuscript.

I have only the following issues for the authors to be discussed:

Figure 1. I suggest to redesign the figure in order to highlight the Atchafalaya River in a more visible way. In this version it is hardly possible to see it. What is the background layer by the way? It should be also mentioned in the captions or on the map with small letters.

Authors’ response: Thank you for the comments. The background image is the Landsat imagery (Band742), which has been added to the caption. For this figure, we tried to redesign. But if we zoom in to highlight the Atchalaya River, we lost information about the Old River Control Complex (ORCC). Showing detailed information of the ORCC are critical for our interpolation of the riverbed deformation in the Discussion section. Therefore, we would like to keep the figure in its current format and hope this is acceptable.

Lines 121-129. Is there any reference to support this paragraph?

Authors’ response: Thank you for pointing this out. We have added the following reference in the paragraph, “Mossa, J. 2016. The changing geomorphology of the Atchafalaya Rriver, Louisiana: A historical perspective. Geomorphology, 252, 112-127. 

Lines 152-154. How was the single-beam data collected? What kind of instrument and settings was applied? 

Authors’ response: The data was collected by the USACE and they can be found https://www.mvn.usace.army.mil/Missions/Engineering/Geospatial-Section/ARHB_2006/ARHB_2006_PDF/. Unfortunately, there is no information about instrument and parameter settings in the document, but we provided the link to it in the revised manuscript.

Figure 2. Why those raw points are extending the channel edges? Aren't these in-channel survey points? Please clarify these things.

Authors’ response: Thank you for pointing this out. The original single-beam data cover the entire channel from bank to bank and part of the floodplain. We have added this information in the revised manuscript.

Figure 3-4. Why to plot a decimal place on y-axis?

Authors’ response: We use a decimal place on y-axis because the reported data have a one-decimal place accuracy. We would like to keep consistency with the orriginal data.

Author Response File: Author Response.pdf

Reviewer 4 Report

Dear Authors,

your research on the evolution of the Atchafalaya River is interesting, but the manuscript needs improvement before the next stage. In the following, I have suggested some changes, mainly related to the need for providing more details on the used methods and data.

In general, please double-check the language involving a native English speaker.

Please use SI units (m³s^-1 and not cms).

Be consistent in using the Journal style for the references (e.g., check line 290).

 

Abstract

The abstract should be rephrased, pointing out the main hypotheses, the used methods, the results and the conclusions. In the present version, these parts are somehow present, but described in a very bad and confused manner, which prevents the readers from understanding what the paper is about.

At the end of the abstract, you claimed: “The findings strongly suggest that confluence zones of large alluvial rivers can experience extensive, long-lasting channel erosion”. Maybe this is true for this specific case study, but I have some doubts that this can be applied to all large rivers worldwide. I suggest rephrasing such conclusions.

 

1. Introduction

From this Introduction, the novelty is not so clear to me. Can you please review also works made on the Atchafalaya River, to better point out what is your contribution in studying this specific environment? Maybe you can move here some of the text reported in Section 2.

Here you claimed that the investigated period is 1935-2016, while in the Abstract you said 1936-2016. Please, be consistent.

lines 61-63: what do you mean?

 

2. Geomorphological settings

Please change the title of this section is a more common “Case study”.

 

3. Material and Methods

Please add more details on the used data. Section 3.1 is too short for understanding the quality/quantity of such data.

Additional details could be added to this section to allow for the study reproducibility. Indeed, reading the text is not completely clear what you made. Maybe adding a flowchart for section 3.2 could be helpful, as well as providing some graphs for Section 3.3

 

4. Results

In addition to Figures 3 and 4, please provide the net difference between the two surveyed years, aiming to emphasize the areas with significant erosion/deposition.

Section 4.4: what is the need for computing the Reynolds number? To me, it is quite obvious that, in a river, the flow is always turbulent…

Similarly, as you observed sediment transport and erosion/deposition, what is the need for computing the bed shear stress? For sure it will be higher than the critical one.

I suggest expanding the research looking at the changes of the bankfull width. This could suggest some planar changes that could be also correlated to the transient hydrology, in addition to the elevation changes already reported.

 

5. Discussion

In Section 4.1 you showed the comparison between the thalweg elevation in 1998 and 2006, while in Section 5.1 you are discussing the elevation changes in other periods. I think that more details on the sources of the used data are needed, aiming to provide the readers with a clearer picture of the kind of dataset that you have.

Figure 9: supposing a linear trend between two points is the simplest assumption, but maybe it could be not the right one. Can you please provide a few more details on how you computed (assumed) such a trend?

lines 371-372: what do you mean?

Author Response

Comments and Suggestions for Authors

Dear Authors,

your research on the evolution of the Atchafalaya River is interesting, but the manuscript needs improvement before the next stage. In the following, I have suggested some changes, mainly related to the need for providing more details on the used methods and data.

Authors’ response: Dear Reviewer, first of all, we would like sincerely to thank you for your support and for taking the time to review our manuscript. We greatly appreciate your helpful comments and suggestions, all of which have been taken into account in this revised manuscript as described below.

In general, please double-check the language involving a native English speaker.

Authors’ response: Thank you. The manuscript has been carefully revised and hthe final version has been checked by a native English speaker.

Please use SI units (m³s^-1 and not cms).

Authors’ response: Thank you. All units have been checked and have been changed to SI units throughout the manuscript.

Be consistent in using the Journal style for the references (e.g., check line 290).

Authors’ response: Thank you. The references have been double-checked and corrected.

Abstract

The abstract should be rephrased, pointing out the main hypotheses, the used methods, the results and the conclusions. In the present version, these parts are somehow present, but described in a very bad and confused manner, which prevents the readers from understanding what the paper is about.

Authors’ response: Your point is well taken. We have done our best to revise the abstract as you suggested. We hope the changes made meet your expectation.

At the end of the abstract, you claimed: “The findings strongly suggest that confluence zones of large alluvial rivers can experience extensive, long-lasting channel erosion”. Maybe this is true for this specific case study, but I have some doubts that this can be applied to all large rivers worldwide. I suggest rephrasing such conclusions.

 Authors’ response: We agree with you, and have rephrased the sentence to “The findings suggest that confluence zones of large alluvial rivers under controlled flow and confined levee conditions can experience extensive, long-lasting channel erosion.” We hope the change meets your expectations.

1. Introduction

From this Introduction, the novelty is not so clear to me. Can you please review also works made on the Atchafalaya River, to better point out what is your contribution in studying this specific environment? Maybe you can move here some of the text reported in Section 2.

Authors’ response: Thank you for the suggestion. There were two studies focusing on channel geometry in the Atchafalaya Rivers. We have moved part of them from Section 2 to the Introduction. Please see Lines 86-90.

Here you claimed that the investigated period is 1935-2016, while in the Abstract you said 1936-2016. Please, be consistent.

Authors’ response: The period is “1935-2016”. The one in the Abstract has been corrected.

lines 61-63: what do you mean?

 Authors’ response: For making it clear, we have rephrased to sentence to “...The scour depth was reported that can be as high as six times the ambient depths in the anabranches. Although scour depth was well studied, little attention has been given to scour length under significantly varied tributary discharge ratio”. 

1. Geomorphological settings

Please change the title of this section is a more common “Case study”.

 Authors’ response: The title has been changed.

1. Material and Methods

Please add more details on the used data. Section 3.1 is too short for understanding the quality/quantity of such data.

Authors’ response: Thank you for the suggestion. More details about the data have been added to the revised Section 3.1.

Additional details could be added to this section to allow for the study reproducibility. Indeed, reading the text is not completely clear what you made. Maybe adding a flowchart for section 3.2 could be helpful, as well as providing some graphs for Section 3.3

Authors’ response: As suggested, a new figure (Figure 3) was added to show the flowchart of the analysis of riverbed deformation.

 

1. Results

In addition to Figures 3 and 4, please provide the net difference between the two surveyed years, aiming to emphasize the areas with significant erosion/deposition.

Authors’ response: Thank you for the good suggestion. We have added a new figure (Figure 6) to show the net difference of the two DEM datasets.

Section 4.4: what is the need for computing the Reynolds number? To me, it is quite obvious that, in a river, the flow is always turbulent…

Authors’ response: Thank you for your comments. One of the other reviewers also pointed this out and he suggested to calculate local Reynolds number, global and local Froude number. Therefore, we added the calculation of these numbers. We think they are helpful for readers to understand hydrodynamic characteristics of the flow.

Similarly, as you observed sediment transport and erosion/deposition, what is the need for computing the bed shear stress? For sure it will be higher than the critical one.

Authors’ response: Thank you, please see the previous response.

I suggest expanding the research looking at the changes of the bankfull width. This could suggest some planar changes that could be also correlated to the transient hydrology, in addition to the elevation changes already reported.

Authors’ response: Thank you for the suggestion. Actually, there is little changes in bankfull width through the studied period because the studied channel is completely constrained by levee and revetment.

1. Discussion

In Section 4.1 you showed the comparison between the thalweg elevation in 1998 and 2006, while in Section 5.1 you are discussing the elevation changes in other periods. I think that more details on the sources of the used data are needed, aiming to provide the readers with a clearer picture of the kind of dataset that you have.

Authors’ response: Thank you. Section 5.1 discussed long-term river stage variation along the uppermost Atchafalaya River. This is a further interpolation of Section 4.3. We consider that it is important to show readers a big picture before we discussed short-term details on the riverbed deformation (i.e., the changes between 1998 and 2006, Section 5.2).

Figure 9: supposing a linear trend between two points is the simplest assumption, but maybe it could be not the right one. Can you please provide a few more details on how you computed (assumed) such a trend?

Authors’ response: Yes, Figure 9 (now Figure 11) shows possible linear discharge ratio change between the period of 1855-1880 and the period of 1963-2016. It came from the gradual increase of river flow in the Atchafalaya River after 1930 (Figure 12). However, there are no available discharge data before 1930 and therefore, we could not retrieve the trend before that. For making it clearer, we added more explanation in the caption of Figure 11.

lines 371-372: what do you mean?

Authors’ response: There are some studies using the variations of thalweg elevation to estimate riverbed deformation (deposition/erosion). But it the present study, we found the variations between thalweg and overall bed deformation are inconsistent. For example, the increased thalweg (from -11.7 m to -11.4 m) shows deposition occurred during 1998-2006 (Figure 4). However, the DEM analysis (Figure 5) shows extensive erosion occurred in the channel.

 

Thank you so much again for taking your valuable time to review our manuscript. Your careful reading and helpful comments and suggestions have allowed us to improve the manuscript.

Author Response File: Author Response.pdf

Round 2

Reviewer 4 Report

Dear Authors,

thank you for having addressed my concerns. The present version is more clear and, in my opinion, ready for the publication.