Round 1

Reviewer 1 Report

Author Response

General comment: The study applied the hydrological modeling and sediment monitoring methods for a typical intermittent mediterranean river, aiming at investigating the flood events and sediment transport. The data and method are convincible, and the results are most clear. I think the paper could be accepted once the author considers my comments in below.

Answer to reviewer 1: Thank you very much for your comments and suggestions concerning our manuscript. All the requested revisions have been incorporated into the manuscript and a comment to each requested revision has been reported bellow.

General Comment 1:  1. The discussion part is too long and covers two much parts in study area, method, and the results. The readers may get lost in the discussion part. Authors should consider to subset the discussion part into 2-3 sub sections.

Answer 1: The authors agreed with the reviewer comment about the discussion, therefore, the discussion part was refined into a smaller section discussing three key points : the first one is regarding the hydrological modeling using the SWAT model, the second one is about the use of the optical images to establish the relationship between the simulated flow and river plumes and the third section is a proposed methodology using the swat sediment yield output to validate quantitatively the plumes linked to the high flow events and detected by the images and a concise summary of the principal implications of the findings and some limitations of the study.

Please refer to the discussion from line 474 to line 545.

General Comment 2:  2. In the discussion or conclusion part, author could consider to formulate clearly the wider implications of the main findings – of relevance for a wide international readership.

Answer 2:
The reviewer comment was taken into consideration, the main findings of this research were highlighted better both in the discussion and the conclusion, for example: 

• Line: 538-541, “This technique could be furthermore enhanced if information of sediment concentration is available, in order to validate the SWAT projections. The latter will provide a quantitative estimate of the suspended sediment forming the plumes and outflows to the sea.”
• Line: 566-570“Furthermore, RGB analysis of the optical datasets coupled with the SWAT output are not only able to provide accurate hydrological projections, but also estimates of the sediment volume/yield transported during the plumes. The latter is of great importance when examining sediment dynamics and coastal morphodynamics. “

Specific Comment 1:  what is the Title 1, Title 2 … mean in Table 2

Answer 3: The titles in table 2 were corrected and replaced.

• Title 1: File
• Title 2: Parameter name
• Title 3: Description
• Title 4 : Range

Specific Comment 1:  2. The font size in most of the figures (especially Figures 3 and 4, 9) should be larger. They are too small to see.

Answer 4: The figures have been improved according to the reviewer comments, the font of  figures 3, 4 and 9 was increased as suggested.

Additional clarifications:

In addition to the above comments, all spelling and grammatical errors have been corrected. We look forward to hearing from you and to respond to any further questions and comments you may have.

Sincerely

Author Response File: Author Response.docx

Reviewer 2 Report

General Comments

This paper is trying to investigate the river plume process in Xiropotamos basin, based on optical monitoring system. This research is very interesting and of important significance. However, the current manuscript is not well constructed, and the contribution or novelty is not very clear. Therefore, Major revision is suggested

Specific Comments

(1) The most outstanding contribution of the current research would be the processing of the optical images to quantify the river plume (such as sediment amount). However, few description could be found in the current paper on this technique. The authors need to give more explanation how to process these images and how to relate the characteristics of images with those of the river plume.  

(2) The discrepancy between the simulated and measured flow in Fig.5 is high. The authors need to address this problem.

(3)In section 3.2, the image analysis is too simple. I suggest the authors to further clarify the relationship between the RGB histogram and the river plume characteristics. Considering that the sampling rate of the optical monitoring system is high, investigating the dynamic process of river plume and its relations with the RGB histogram change will be possible.

(4) In section 4, the discussion reads like another version of introduction, which is inappropriate. The authors could discuss more on the mechanisms of river plume based on their obtained data from the optical monitoring system, or on the unfilled technical gaps and possible solutions of extracting the river plume characteristic from the images etc. These discussions will be much more attractive to broad readers.

Author Response

Response to reviewer 2:

General comment:  This paper is trying to investigate the river plume process in Xiropotamos basin, based on optical monitoring system. This research is very interesting and of important significance. However, the current manuscript is not well constructed, and the contribution or novelty is not very clear. Therefore, Major revision is suggested

Answer to reviewer 2:

Thank you for the insights regarding the paper and its further improvement opportunities. All the recommended revisions have been taken into consideration and comments from the authors are presented below.

Comment 1:  The most outstanding contribution of the current research would be the processing of the optical images to quantify the river plume (such as sediment amount). However, few descriptions could be found in the current paper on this technique. The authors need to give more explanation how to process these images and how to relate the characteristics of images with those of the river plume.

Answer 1:

The aim of this paper is to validate the flood events using the TIMEX images. Therefore, the RGB colors property of optical images was used to qualitatively assess the plumes that are driven by the high discharge of Xiropotamos river. By using the RGB color density and intensity in the area where the river plumes happen (the outlet of the river) before, during and after the selected flood events, we were able to clearly link the discharge to the occurrence of sediment plumes. We assume that the RGB color density during the event has a direct relationship with the turbidity of the water which technically would indicate the presence of sediments (plumes).

More explanation was provided in the manuscript accordingly in the methodology and results section.

• Line “304-314”, 309-472”

Comment 2:  The discrepancy between the simulated and measured flow in Fig.5 is high. The authors need to address this problem

Answer 2: The reviewer comments have been addressed in the manuscript accordingly:

• Line “373-382”: “The overestimation of some high peaks in the validation period might be explained by the scarcity of the meteorological stations, meaning that the spatial distribution of the precipitation over the watershed is not perfectly accounted for, which could explain the incomplete agreement between the observed and simulated flow with the rainfall events. Furthermore, the results of PBIAS show a gradual overestimation of the streamflow discharge for the validation period (1995-1996) (Figure 4. b). The Nash-Sutcliffe results were acceptable for both the calibration and validation periods (> 0.5) and overall statistical results we within the acceptable range. “

Comment 3:  In section 3.2, the image analysis is too simple. I suggest the authors to further clarify the relationship between the RGB histogram and the river plume characteristics. Considering that the sampling rate of the optical monitoring system is high, investigating the dynamic process of river plume and its relations with the RGB histogram change will be possible.

Answer 3: As requested by the reviewer, the relationship between the  RGB histogram and the river plumes have  been investigated and explained better in the results section, from line 309 to 472.

Comment 4:  In section 4, the discussion reads like another version of introduction, which is inappropriate. The authors could discuss more on the mechanisms of river plume based on their obtained data from the optical monitoring system, or on the unfilled technical gaps and possible solutions of extracting the river plume characteristic from the images etc. These discussions will be much more attractive to broad readers.

Answer 4: Thank you for pointing this out, we agree with the reviewer's comment. We have, accordingly, modified the discussion part to avoid another version of the introduction and also to emphasize on the applicability of this method in a data scarce river.

Additional clarifications:

In addition to the above comments, all spelling and grammatical errors have been corrected. We look forward to hearing from you and to respond to any further questions and comments you may have.

Sincerely

Author Response File: Author Response.docx

Reviewer 3 Report

I appreciate the opportunity to review “A qualitative assessment of river plumes coupling SWAT model simulations and a Beach Optical Monitoring System.”  The paper provides an examination of the sediment transported via ephemeral streams to a beach.  The authors use a coupled approach of SWAT modeling and an optical monitoring system.

1. What is the main question addressed by the research?

The authors state that the purpose of the paper is to “…investigate the relationship between plumes and flush floods during intense precipitation events.”  This is a viable objective, but the paper fails to deliver the analysis.  The authors provide the results of the development, calibration, and the validation of the SWAT model; however, the is no analysis from this that is coupled with the optical monitoring system.  The SWAT results are an isolated outcome. 

The first three paragraphs of the discussion read as literature review and do not draw from the results provided.  I expected to see an interpretation as to how the pre-, during, and post- sediment plumes were similar or different and what this means to the system.  Additionally, the results of the SWAT model were no integrated at all with the optical monitoring system results. 

AS for the results, why were the storms in March and April presented?  The SWAT data (figure 6) would indicate that neither was a significant storm event.  The August 2014 or November 2014 storm events would seem to be higher magnitude events. 

In the end, the objective is not addressed through the results and discussion. While results are presented, the paper has a deficit from there, lacking analysis and interpretation of the data.  No relations between plumes and flash floods is provided.

Rather than reject, I recommend a major revision that would include a fully  updated discussion that speaks to the data presented and provides analysis of the the SWAT model and the optical systems data, effectively creating the proposed relationship.  In the absence of a revised/new discussion, I would recommend reject as the paper does not provide anything other than a calibrated/validated model and random data.

2. Do you consider the topic original or relevant in the field, and if so, why?

Potentially.  The use of the optical monitoring system is novel and could provide added insight into sediment transport processes in beach systems as well as other systems.  However, the paper provides no insight, analysis, of discussion of the results.  How are the results useful for this area?  Could these results be applicable to others?

3. What does it add to the subject area compared with other published material?

4. What specific improvements could the authors consider regarding the methodology?

I am comfortable with the methodology and do not have and specific comments here.

5. Are the conclusions consistent with the evidence and arguments presented and do they address the main question posed?

The conclusions do not draw from the discussion because the discussion is lacking.  See comment addressing 1. and 2. above.

6. Are the references appropriate?

7. Please include any additional comments on the tables and figures.

Please see annotated copy for additional notes.

Comments for author File: Comments.pdf

Author Response

Response to reviewer 3:

General comment:  I appreciate the opportunity to review “A qualitative assessment of river plumes coupling SWAT model simulations and a Beach Optical Monitoring System.”  The paper provides an examination of the sediment transported via ephemeral streams to a beach.  The authors use a coupled approach of SWAT modeling and an optical monitoring system.

Answer to reviewer 3: Authors are thankful for your valuable remarks regarding this work and the improvement chance given. All the recommended revisions have been taken into consideration and comments from the authors are presented below.

Comment 1:  1. What is the main question addressed by the research?

The authors state that the purpose of the paper is to “…investigate the relationship between plumes and flush floods during intense precipitation events.”  This is a viable objective, but the paper fails to deliver the analysis.  The authors provide the results of the development, calibration, and the validation of the SWAT model; however, the is no analysis from this that is coupled with the optical monitoring system.  The SWAT results are an isolated outcome.

The first three paragraphs of the discussion read as literature review and do not draw from the results provided.  I expected to see an interpretation as to how the pre-, during, and post- sediment plumes were similar or different and what this means to the system.  Additionally, the results of the SWAT model were no integrated at all with the optical monitoring system results.

AS for the results, why were the storms in March and April presented?  The SWAT data (figure 6) would indicate that neither was a significant storm event.  The August 2014 or November 2014 storm events would seem to be higher magnitude events.

In the end, the objective is not addressed through the results and discussion. While results are presented, the paper has a deficit from there, lacking analysis and interpretation of the data.  No relations between plumes and flash floods is provided.

Rather than reject, I recommend a major revision that would include a fully updated discussion that speaks to the data presented and provides analysis of the  SWAT model and the optical systems data, effectively creating the proposed relationship.  In the absence of a revised/new discussion, I would recommend reject as the paper does not provide anything other than a calibrated/validated model and random data.

Answer 1: Following the reviewer comments a major revision has been conducted,

The main question addressed by the research is: are coastal imaging with high spatiotemporal resolution of importance in order to validate the flood event simulated with a SWAT model?

The relationship between the SWAT results and the coastal TIMEX images is now better explained in both the methodology, results and discussion sections.

The March events were presented, because although they don't have high peaks compared to the fall-winter season, the spring season tends to have frequent successive floods that generate important plumes according to our results and a research done previously "Hydrometeorological impact of climate change in two Mediterranean basins" (Vozinaki et al., 2018) . We explained this in the manuscript in line “503-510”

The august event was investigated too and added to the results in line “439-449”, However the November event due to downtime of the camera the optical data is not available for that period the TIMEX data is available for 10 months of the year 2014, from January until first week of November.

Comment 2:  2. Do you consider the topic original or relevant in the field, and if so, why?

Potentially.  The use of the optical monitoring system is novel and could provide added insight into sediment transport processes in beach systems as well as other systems.  However, the paper provides no insight, analysis, of discussion of the results.  How are the results useful for this area?  Could these results be applicable to others?

Answer 2: We have highlighted the novelty of this research in the manuscript and incorporated all suggestions made. The results were improved and a more detailed description of the findings was provided with better analysis and added events. We also improved the discussion to answer the main questions.

The importance and usefulness of these results were discussed as well as the applicability of the results is mentioned in line 537-538. Also in the conclusion: “547-570”

Comment 5:  5. Are the conclusions consistent with the evidence and arguments presented and do they address the main question posed?

The conclusions do not draw from the discussion because the discussion is lacking.  See comment addressing 1. and 2. above.

Answer 5:

The conclusion was updated accordingly.

Additional clarifications:

In addition to the above comments, all spelling and grammatical errors have been corrected. We look forward to hearing from you and to respond to any further questions and comments you may have.

Sincerely

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

My comments have been addressed.

My only suggestion is a thorough review of grammar and punctuation.  Within the revised/added text there are multiple errors.

Author Response

Response to reviewer 3:

General comment:  My only suggestion is a thorough review of grammar and punctuation.  Within the revised/added text there are multiple errors.

Answer to reviewer 3: Authors are thankful for your valuable remarks regarding this work and the improvement chance given. The grammar and the structure of the text throughout the entire article was updated as recommended.

Author Response File: Author Response.docx