Estimation of Boundary Shear Stress Distribution in a Trapezoidal Cross-Section Channel with Composite Roughness

Round 1

Reviewer 1 Report

The manuscript deals at a high scientific level with the problems arising in the study of hydraulic resistance, sediment transfer, environmental loads and wetlands design.. Based on experimental data on the zero shear stress dividing line, the authors have developed a new cross-sectional model for estimating the distribution of boundary shear stresses in a trapezoidal cross-sectional channel with composite roughness.

The research corresponds to the subject of the journal. The topic of the manuscript is relevant, the manuscript contains a good overview and justification of a new, more effective method for solving an urgent problem of applied hydraulics.

The results of solving applied problems using the proposed model and known models are compared (Lines 305-306, 307-308, 327-328, 411-412).

The methodology and results of the study are of interest to many potential readers.

The research material is presented clearly, the manuscript is easy to read.

Conclusions and conclusions are confirmed by scientific results and are justified in detail in section 5 (Lines 340-410).

The manuscript meets the criteria of relevance of the topic, novelty and reliability of the results.

However, the following question arises.

1. There is probably an extra dot in the headings of section 3 and subsection 3.1 (Line 154, 155).

Author Response

We thank the reviewer for the approval. The typo errors pointed out have been revised.

Reviewer 2 Report

The article is very interesting and well prepared. I have no substantive or critical comments.

 

Author Response

We thank the reviewer for the approval.

Reviewer 3 Report

Dear authors,

The research you have presented in the manuscript, development of the new method for boundary shear stress estimation in channels with composite roughness, is very interesting and deserves to be published. Paper has proper structure; it is well written; context within the state-of-the-art research is explained; methods, results and discussion are clearly presented.

Please find below a few remarks that need to be addressed before publishing.

 

General remarks

The main remark I have with the results is that authors base their “equal local-region velocity” method around the assumption that hydraulic radii ratio (η) can be used to represent the relation of partial and total energy slope within the cross-section (S'/S), which is vaguely, if at all, supported by the (presented) data.

The relationship between S'/S and η is given by the Fig.2, which shows high scatter of the data which doesn’t indicate that η would be suitable predictor for S'/S. Even if this could be the case, authors haven’t presented any quantitative values for the correlation. Please support this relationship with the enough quantitative data.

Additionally, from the data presented in the Fig. 2. cross-section characteristics are not distinguishable (bottom width, flow depth, etc.). Since authors haven’t supplied their dataset with the manuscript submission (and it is not planned to be if published, either), authors need to present more specific and detailed data for their underlying assumptions – i.e. cluster the dataset into the identifiable portions using common variables that would provide insight into the relationship (similar clustering as you ).

When results are analyzed, for η, shear stress distribution, and SF, the biggest discrepancy is evident for S90. Can you please elaborate on this in more detail?

 

Specific remarks

In the Introduction “environmental loadings” and “wetland design” are too general, please consider removing them or replacing with more specific applications that directly relate to shear stress.

Reference for “Normal Depth Method” should be added to supplement [Khodashenas] referring to MPM method (and others) – ln36.

Since authors present the concept of flow partitioning, “wall” might not be the best term – this way Pw could be mistaken with total wetted perimeter. Instead, I suggest that you consider substituting with “side wall” which you also interchangeably used throughout the text.

On ln142 the sentence is incomplete.

On ln99 where variables are declared, “H, A0, Pw and Pb0” should be “H, A, Pw and Pb” to keep universality that is explained later on in the sentence with subscripts.

Continuing the preceding remark, variable “k” should be introduced here, where it occurs initially (ln104) instead later on.

Subscripts across the manuscript are not uniform – e.g. for eq. (2) it should be Pb0/Pw0 =…

On ln183, “…these points are located at the dividing line, the water surface and the center line, respectively.” – the order of lines and corresponding points is not consistent.

The reference for zero shear stress at the center line for type 1 needs to be added.

Subscripts describing the zonals and directions of associated flow velocity components is confusing since the same (y, z) component names are used interchangeably between themselves and zonals.

 

S90, S45 and S68 appear on Fig 2 before they have been declared.

Author Response

We would like to thank the two reviewers for their reviews and recommendation on our manuscript. We are pleased with their overall positive evaluation on the quality of the manuscript and constructive comments for further improvement. We also appreciate the reviewers for their careful scrutiny of the presentation of our work. We have revised our manuscript, taking into consideration of all the review comments. All these changes have significantly improved the quality and presentation of the manuscript. Here, we respond to the specific review comments.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Dear authors,

Thank you for addressing all my remarks and revising the manuscript accordingly. Although I still have some issues with presentation of the η suitability as predictor for S'/S, I believe that you have presented enough data that readers can decide for themselves if this approach is suitable.

Author Response

Thanks again very much. Your valuable comments in round 1 are actually helping to improve the manuscript.