Coastal Erosion Caused by River Mouth Migration on a Cuspate Delta: An Example from Thanh Hoa, Vietnam

Round 1

Reviewer 1 Report

Major revision is suggested. Please see the attachment.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Review of the paper titled ‘Coastal erosion caused by river mouth migration on cuspate delta: An example from Thanh Hoa, Vietnam’, by Dinh Van Duy , Tran Van Ty, Cao Tan Ngoc Than, Cu Ngoc Thang, Huynh Thi Cam Hong, Nguyen Trung Viet 2 and Hitoshi Tanaka, submitted to HYDROLOGY journal, man. ref. 2564245

The Authors present a study on recent evolution of Ma river delta in Vietnam. They argue that asymmetrical distribution of sediment discharged by the river produces asymmetric evolution of the delta and try to assess the degree of asymmetry of sediment flows using both satellite imagery an analytical solutions based on one line model principles. The subject is quite interesting, but its coverage is somewhat flawed by not including any hydro- and litho-dynamic information. Several major items have been ignored:

1.      From Fig. 1a one can immediately see that the fetch for S and SE winds is much longer than that from NW, N and NE sectors. Thus, wave forcings from S/SE sectors should produce much stronger longshore currents running toward NW.

2.      Fig. 1d identifies a rocky boundary, impermeable to sand. It means that the NW currents should have a rather significant sediment transport potential, but near the rock the amount of longshore sediment transport is close to nil; it is natural that further downstream that potential is gradually saturated, producing a littoral drift at the expense of sediment depletion from delta tip.

3.      Much smaller SE drift driven in limited fetch conditions pushes some sediment in that direction, where it meets the rocky boundary and is probably lost offshore.

The Authors should take into account these morphological aspects, as they seem to be the predominant causes of asymmetrical evolution of the tip of delta lobe. Another intriguing aspect is the sudden seaward transition of the norther tip between 2001 and 2005. It was not mentioned whether such events were observed previously and are known by e.g. local population (in qualitative terms of course). If such events were observed before, they could point to delicate equilibrium of the delta. If, however, this event was driven by human intervention (e.g. closure of a smaller branch that caused a temporary growth of sediment discharge through the main branch) then we could speak about persisting erosion.

In sum, the Authors are asked to explain why they did not include any hydrodynamic information (lack of data?). Then, they should explain why they ignored well known morphological settings (fetch and rocky boundary). Finally, they should explore past river discharges seeking events with rapid seaward advances of the delta. The last element is particularly important, because we could get some insight into possible past human interventions in the area. The review recommendation is major revision of the paper.

At best the language should be inspected by a native English speaker; at least by a local English language expert.

Author Response

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Reviewer 3 Report

Dear Authors,

I have gone through the study and acknowledge that a notable topic was selected. The importance of the topic from the climate change adaptation angle is of great significance. For improving the quality of the manuscript, I have the following suggestions/comments:

1. Global prospect of the problem and techniques to investigate the problem has not been mentioned in the introduction section of the manuscript. By doing so, you'll reach the research gap and it would converge to novelty and contribution of the instant study. A must-do part.

2. What software/modeling tool is employed? Create ease of doing/replication for prospective researchers and readers.

3. There must be a chart of hydrological and sediment yield depicting the fluvial pulses and discuss the oceanographic profile of the coastal area (wave height, historic extreme events storms, etc.), and history of hard/soft measures taken along the coastline.  

4. At line 67 "only cloud-free images were selected," good care is taken for recruiting the satellite images but in the case of the coastal profile, also mention the water/tidal level (in Table 1) exactly at the time of satellite image acquisition. It is necessary to conduct the analysis at equal/comparable water levels.

5. Line 120-122, elaborate on how the sediment rate was converted to sand transport rate? Don't you think sediment reaching the mouth of rivers had sorted and fine sediments (clay component) dominate in the estuarine zones? Substantiate it with the Ma River case. 

6. Some minor corrections are suggested over the body of the attached PDF.

Good luck with the revision and subsequent publication. 

 

Comments for author File: Comments.pdf

Dear Authors,

The manuscript in hand is of good quality from a write-up prospect. However, I have marked a few corrections. Please adhere to the marking for further refinement.

Author Response

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Reviewer 4 Report

The work of Van Duy et all. deals with the very important problem of coastal erosion, showing an example from Thanh Hoa, Vitnam.

Even if the methods and the results are very supportative of the final discussion, in my opinion the work must be written in a better scientific way. I mean, all the paragraphs starts with something like:  "Figure XXX shows ...", instead of discussed first the figure and than relate it with the figure.

However, the work deserve to be published after that changes.

Hereafter I report some minor edits:

Figure 1d: please add a scale bar and north arrow

Line 104 please add a space

Line 250 please add a space

Data Availability Statement: should be modify

Author Response

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Round 2

Reviewer 1 Report

The present version can be accepted.

Minor editing of English language is required.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The Authors have positively addressed most of my concerns. What remains missing is a conclusion pointing to identification of local wind and wave climate studies to continue the research on Ma River delta with more precision in future. 

Line 42 Replace 'threads' with 'threats',

L 103 Add a blank line before the heading of Table 1,

L 106 Replace 'analytical analysis of...' with analytical approach to...',

L 139 Remove redundant 'the',

L 166 Add a blank line before the heading of Table 2,

L 185 Replace '2,065' with '2,650',

L 241 Remove 'the metric unit of',

L 246, Remove 'Moreover, the', replace with 'The',

L 411 Correct 'Staion' with 'Station'.

 

Author Response

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Reviewer 3 Report

Dear Authors,

Thank you for addressing the comments. One of my observation was:

"At line 67 "only cloud-free images were selected," good care is taken for recruiting the satellite images but in the case of the coastal profile, also mention the water/tidal level (in Table 1) exactly at the time of satellite image acquisition. It is necessary to conduct the analysis at equal/comparable water levels."

and your response is:

"It is unfortunate that we do not have the cross-shore beach profile along the Ma River delta’s lobes as well as measured water level at the Ma River mouth so we can not perform the tidal correction for the shoreline positions. However, the error related to the coarse resolution of the Landsat images (30m/pixel) can exceed the tidal effect."

 

Ok, I would recommend that you add the following limitation of the study either at the end of the introduction section or at the end of the conclusions. 

In the absence of a cross-shore beach profile along the Ma River delta’s lobes as well as the measured water level at the river mouth, this study was conducted without taking into the tidal correction for the shoreline positions. Therefore, care must be taken while using the results of this investigation. 

All the best for publication.

 

Author Response

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