Hydrodynamic Modeling of a Reef-Fringed Pocket Beach Using a Phase-Resolved Non-Hydrostatic Model

Round 1

Reviewer 1 Report

The authors use SWASH to model waves in a 3 dimensionally heterogeneous coastal reef domain at a high resolution (~O(100m)).  The topic presented is relevant to marine science and engineering, especially for reef characterization under various sea level and wave conditions.  The authors do a good job in delineating their contribution to modeling waves in this type of environment, filled with multiple lagoons and channels.  The model and validation descriptions are thorough – The appendix is also appreciated to illustrate the sensitivity to grid size.  The physical description of the reefs’ effects on effectively protecting the shoreline from waves, and their formation of channels is good. The manuscript is clearly written.

Specific Comments on the text:

Line: 134, Table 1: Please use 2 significant figures for the depths of C4 and S9, as the current precision is too high for it to be an approximate depth.

Line 172: “Computationally feasible”

Line 202: Would be useful to show on Figure 1 where the wavemaker was imposed (only along the offshore boundary?)  Does this wavemaker compensate for the fact that only one directional wave spectrum was imposed along the entire length of the offshore boundary?

Line 207: I assume 2 vertical sigma layers were used?

Line 235: The sea surface elevation in Figure 4(a) seems to suggest that the wave directions vary slightly along the offshore boundary.  Then would this be in conflict with the original assumption that the directional spectrum at C0 applies along the whole offshore boundary? However, I can understand that a uniform spectrum be used to help with the cyclic boundary in the lateral boundaries.

Line 400, Figure 10 (also Lines 387-394): I am not clear about the colors – they indicate significant wave heights?  Are we trying to figure out whether stronger waves are biased over smaller waves in both direction and magnitude for the model?

Line 443:  My previous concern of applying one uniform wave spectrum along the entire offshore boundary could be addressed here also.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The authors have modeled the hydrodynamics of a reef-fringed pocket in Western Australia using the non-hydrostatic model SWASH. The manuscript has basically well written and has the potential to be a good paper. However, it suffers from the lack of some key issues which requires major revision to be qualified to published. I could not accept this manuscript to be published unless the revision seriously takes into account these key issues which I have listed below:

Major issues:

What is the reason of using the non-hydrostatic model? How important the non-hydrostatic pressure gradients were important for your study? I do not see anywhere in this manuscript that the authors have explained their reasons of using the non-hydrostatic model and discussed or pointed out the advantages, disadvantages, or differences of the non-hydrostatic models over the hydrostatic models. This seems particularly important when one reads your discussion and conclusion: You point out that refining the model grid did not change the results significantly and your model needs refining the bathymetry to resolve the near-shore hydrodynamics. How would it compare as if you had used a hydrostatic model?? I am aware that for simulating the small scale non-hydrostatic pressure gradients are very important in this kind of modeling as waves play a key role here; and I am not expecting you to do your modeling once again with hydrostatic approximation at this stage to do a one-by-one comparison. But it seems necessary at least to discuss this to show that you are aware of the possible differences between the two approximations. This seems like a big gap here right now and I cannot accept this paper to publish unless these issues are discussed. I would recommend shortly explaining this in your introduction and then adding a paragraph into the discussion answering the questions above and discussing the specific differences between hydrostatic and non-hydrostatic models in simulating coastal ocean, by citing the studies that have compared these two model types.

Introduction: The structure of the introduction should be revised. See my specific comments below.

Discussion, Conclusion: This section seems mostly like a discussion section and, on the other hand, there are some sentences in the discussion section which fit better to conclusions. I would recommend revising both sections or even merging them to have only one “Discussion and Conclusion” section.

Some specific comments:

Line 40: The authors seem to jump directly into the research gap in the very first paragraph, without providing enough basis and background for that. Please consider revising this. The first paragraph should provide a brief background for the research, not the research gap.

Line 70: “especially over the past decade, this has increasingly enabled the application”: what does “this” refer to? It does not make much sense to write “this” in the beginning of the paragraph.

Line 195: Did you check the Rossby radius of your study basin? How does the Coriolis force play a role in your model? What type of waves are generated then?

Line 148-166: What is the numerical scheme of the model? Finite difference? Finite element? Finite volume? Please state within the text.

Line 262: Actually it has been well shown that the 3D hydrodynamic models can mostly be run free of calibration by accepting the standard values in the literature (or their default parameter values). See e.g. (Chung et al. 2009; Marti et al. 2016; Zamani and Koch 2020).

References:

Chung SW, Hipsey MR, Imberger J, 2009. Modelling the propagation of turbid density inflows into a stratified lake: Daecheong Reservoir, Korea. Environmental Modelling & Software, 24 (12) 1467-1482, https://0-doi-org.brum.beds.ac.uk/10.1016/j.envsoft.2009.05.016.

Marti CL, Imberger J, Garibaldi L, Leoni B, 2016. Using time scales to characterize phytoplankton assemblages in a deep subalpine lake during the thermal stratification period: Lake Iseo, Italy, Water Resour. Res., 52, 1762– 1780, doi:10.1002/2015WR017555.

Zamani B, Koch M, 2020. Comparison Between Two Hydrodynamic Models in Simulating Physical Processes of a Reservoir with Complex Morphology: Maroon Reservoir. Water. 2020; 12(3): 814.

Author Response

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Author Response File: Author Response.pdf