The Effect of Wave-Induced Current and Coastal Structure on Sediment Transport at the Zengwen River Mouth^†

Round 1

Reviewer 1 Report

The manuscript submitted for review presents the problem of model research in the field of water circulation in the nearshore zone in conjunction with a field experiment on the example of the Zengwen River Mouth.

I believe that the article is written clearly but can be published after minor revision. Below I present a short description of individual chapters with an indication of gaps that should be filled/corrected.

In the introduction, the authors review the literature of the studied subject, both in relation to the modeling in the nearshore zone and the situation of the Zengwen River estuary. The authors also provide information on the tested mouth of the Zengwen River and general information on the model used. Literature review contains items from 1967 to the latest ones from 2018 (items 1-25 of 48). Selective but sufficient selection of literature. The reviewer has no comments.

In Chapter 2, the authors present numerical model. A model from the NearCoM-TVD group is presented. The reviewer has no comments. Authors must analyze that all newly appearing symbols in the equations are defined.

In Chapter 3, the authors present model configuration. This chapter describes details of the model used and the range of input data used. The reviewer has no comments.

In Chapter 4 Model Validation and Statistic Error Analysis, the authors present the calibration of the model on time series and the statistical criteria functions used. The accepted data for model validation / calibration are data from the studied region. Acquiring this data and the responsibility for it lies with the Authors. From the publication point of view, it is properly prepared. The reviewer only has a technical note regarding the drawings (Figures 5 and 6). The time courses are hardly visible. They should be enlarged.

In Chapter 5, the authors present Model Result and Discussion. The authors presented the results in the field of wave and flow field under different tidal hours, seasonal variations of wave and flow field and residual sediment transport and morphological evolution. The reviewer assumes that these are the correct results that have been analyzed in accordance with the proposed methodology. Therefore, the reviewer has one comment as to the content of the chapter - the discussion should be based on the literature cited. The authors in this chapter cited only 1 item !!! This needs to be changed. Technical note: it is necessary to enlarge drawings (Figs. 7 -12).

At the end of the manuscript in chapter 6, the authors present the conclusions from the work. The reviewer has no comments. Conclusions appropriate.

References: 46 literature items, selected selectively but properly.

Author Response

The manuscript submitted for review presents the problem of model research in the field of water circulation in the nearshore zone in conjunction with a field experiment on the example of the Zengwen River Mouth.

I believe that the article is written clearly but can be published after minor revision. Below I present a short description of individual chapters with an indication of gaps that should be filled/corrected.

In the introduction, the authors review the literature of the studied subject, both in relation to the modeling in the nearshore zone and the situation of the Zengwen River estuary. The authors also provide information on the tested mouth of the Zengwen River and general information on the model used. Literature review contains items from 1967 to the latest ones from 2018 (items 1-25 of 48). Selective but sufficient selection of literature. The reviewer has no comments.

In Chapter 2, the authors present numerical model. A model from the NearCoM-TVD group is presented. The reviewer has no comments. Authors must analyze that all newly appearing symbols in the equations are defined.

In Chapter 3, the authors present model configuration. This chapter describes details of the model used and the range of input data used. The reviewer has no comments.

In Chapter 4 Model Validation and Statistic Error Analysis, the authors present the calibration of the model on time series and the statistical criteria functions used. The accepted data for model validation / calibration are data from the studied region. Acquiring this data and the responsibility for it lies with the Authors. From the publication point of view, it is properly prepared. The reviewer only has a technical note regarding the drawings (Figures 5 and 6). The time courses are hardly visible. They should be enlarged.

Response: we thank for reviewer’s suggestions. The time courses of Figure 5 and 6 are revised. 

In Chapter 5, the authors present Model Result and Discussion. The authors presented the results in the field of wave and flow field under different tidal hours, seasonal variations of wave and flow field and residual sediment transport and morphological evolution. The reviewer assumes that these are the correct results that have been analyzed in accordance with the proposed methodology. Therefore, the reviewer has one comment as to the content of the chapter - the discussion should be based on the literature cited. The authors in this chapter cited only 1 item !!! This needs to be changed. Technical note: it is necessary to enlarge drawings (Figs. 7 -12).

Response: we thank for reviewer’s suggestions. The time courses of Figure 7-12 are revised. 

We also cite more item to improve the discussion “The circulation patterns at the mouth of ZhenWen River may differ from prior model simulations of New River Inlet, NC [10-12], Ria de Ribadeo, Spain [49] and Willapa Bay Inlet, WA [50] owing to differences in the river mouth geometries and the complex channel-shoal bathymetries. However, similar to the condition in those ebb dominant tidal inlets, tidally averaged flows on the ebb shoal were seaward directed owing to this asymmetry in flood versus ebb. The ebb-dominant tidal jet results in offshore transport in the main section of the river channel, whereas the circulation patterns resulting from waves and wave-current-bathymetry interactions may carry sediment landward on the ebb tidal delta.”

At the end of the manuscript in chapter 6, the authors present the conclusions from the work. The reviewer has no comments. Conclusions appropriate.

References: 46 literature items, selected selectively but properly.

Author Response File: Author Response.pdf

Reviewer 2 Report

I enjoyed reading this study, which was of local interest only in its present form. More could have been made of the improvements of the new modelling methods, e.g. by comparing against other models. Also ways to generalise the results to other systems, or to at least discuss this, would be welcomed. Finally the sediment transport simulations were not validated and an attempt to validate or to quantify the uncertainties is needed I think.

Abstract - Not sure if second sentence is referring to Taiwan or is a general statement (if the latter, consider swapping first two sentences around). Not clear if the sediment transport simulations were validated. L29: 'a coastal structure', or 'coastal structures'. Otherwise clear and well written.

1. Introduction - L54: 'Waves can...'. L80: 'current speeds...'. L77: In this paragraph it would be useful to read information about mean/extreme river flows, tidal velocities, wave heights, sediment and morphology characteristics. L92: Much of the information in this paragraph should be presented in the Methods section.

2. Numerical Model - No comments here

3. Model Configuration - L214: Need to make clear whether the model boundary was at or near the Hsin-Chung Station and also what the forcing frequency was (e.g. daily-mean data?) and whether this is sufficient to capture the effects of variations in the hydrograph. Also were any rain events captured in this period, and what is the hydrological climate of the river?

4, Model validation - Could you calculate the normalised RMSE (as a percentage)? Model validation of sediment transport is missing. This needs to be stated as a major assumption in this paper, since sediment transport is a function of velocity cubed, your uncertainty in max and net velocities needs to be set within the expected implications for sediment transport. 

5. Results and Discussion - Sediment transport simulations: What coefficient of bed friction was used, and was this spatially and temporally fixed? (when in reality this is not fixed and should be discussed). How does the D50 represent the realistic range of sediment size classes? Are there many different sizes or is it well sorted? Since there is no validation to back-up these results, this is a very weak part of the paper. If there are bathymetry data from different times, then one method of validation would be to simulate the bed evolution from one older data set to the newer one. Or are there a set of sensitivity simulations that you can perform to argue that some of the erosion/accretion patterns presented are in fact robust with respect to uncertainties in model parameterisation? Implementing some of these ideas would greatly improve the paper.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

Overall, a very well-written and interesting manuscript. The numerical investigation with a field experiment is well-considered and assists in developing the evidence presented in the study. I have only minor observations regarding the introduction and conclusion.

The authors mentioned local anthropogenic change but nothing more than that. I would recommend including a brief section explaining the change in terms of local context and how coastal and estuarine modeling is connected to anthropogenic influences or changes over time. I appreciate the way you end the introduction, which is helpful for the readers.

I also believe it could strengthen the manuscript by adding a conclusive remark/discussion that how your methods can improve reproducibility in the modeling of physical processes in the coastal ocean.  

No further comments I appreciate the opportunity to review this manuscript.

Specific comments:

Line 454: I think there is a typo. It will be deltas, right?

Author Response

Please see the attachment

Author Response File: Author Response.pdf