Dear authors, dear publisher,

I find the article perfectly within the scope of the journal and of interest to the community. It deals with friction laws and coefficients for compound channels with experimental and theoretical parts.

However, for me, there is too much in common with the article "Kubrak et al., 2019, Apparent topography friction coefficient used for flow calculation in straight compound channels, Water, 11, 745; doi:10.3390/w11040745" that comes under the heading of plagiarism.

That's why I'm suggesting a major revision. The title of the article is too close to the one already published. Some section titles and content are exactly the same as the previously published article. This is not acceptable, so I suggest that the authors completely rewrite the article to eliminate all duplication. 

Furthermore, I think that it is necessary to complete and improve the bibliography, particularly in terms of review of existing resaerchs on the topics, and to clearly highlight the new developments and the scientific obstacles raised in this work and more particularly in relation to their previous work. This will permit to give more in deep feedback.

Best regards

Summary

The manuscript presents findings from laboratory experiments on the effect of trees on the friction coefficient in compound channels. This work is an extension of a previously published work by the same group in 2019 in the Journal Water (Kubrak et al. 2019, https://doi.org/10.3390/w11040745). The effect of different tree configurations was analyzed. The results demonstrated that the presence of trees increase the flow resistance and reduce the flow velocity both in the floodplain and the main channel.

Main comments / Conclusion

I share the opinion of the other reviewer that the paper is well written, and the topic is of interest for this Journal. However, I also agree that multiple parts of the paper are copied from Kubrak et al. (2019) without providing sufficient references. In some parts, the reference is added, but the wording of the sentence is not altered and the use of “…” is missing to highlight that an entire sentence has been copied. I understand that this is an extension of a previous study, and this paper should be readable on its own but there are multiple sections in this current version, where it is not clear if the results are from this or a previous study.

The novelty of this paper is the consideration of trees, but the majority of the conclusions still focus on results that have been presented in Kubrak et al. (2019). The paper needs to be thoroughly revised in order to be suitable for publication.

My main comments are:

1. Introduction: First sentence is copied 1:1, L20-22, and L26-28, Eq. 1, L65 lack reference to Kubrak et al. 2019,
   
   Note that in L29, the paper starts to mention trees. I recommend starting with this right away and also provide context on why the consideration of trees is important. In addition, move L70 with the “main goal” further up and explicitly state what results are used from previous work.
2. Section heading 2 and 3 (this can easily be adapted) are the same as in Kubrak et al. (2019)
3. L107-L115: The first three variants are all included in Kubrak et al. and don’t need to be described in the methods section. The data can be used for comparison in the results section with a brief explanation on the characteristics. This should be removed.
4. Figure 2: Reference to Figure 3 in Kubrak et al. (2019) needed (subfigures a-c are the same as in Water – see comment above, these setups are not needed for this paper)
5. Table 1: Remove tests that have been included in Kubrak et al. (2019): 1.0.14, 2.0.7
6. L146: Remove W 1.0-3.0 or add reference and explicitly state that this stems from another study
7. Figure 4: Reference to Figure 4 in Kubrak et al. (2019) needed (for upper two plots)
8. Figure 5: see comment above (for upper plot)
9. L172-174: Text copied from Kubrak et al. (2019) without any modification; needs to be adapted.
10. Figure 7: Figure legend does not align with parameters used in text; please adapt. Not clear why results for W1.0 are needed, since no trees have been added and the results with respect to the bottom roughness are included in Kubrak et al. (2019). Please revise.
11. L192ff: This entire section is very difficult to follow. I recommend stating the main trend and then adding the relative changes for selected tests.
12. It would be useful to add images from the laboratory experiments. If dye has been added, the exchange processes could be at least discussed. This is mentioned in the abstract but the paper does not include results.
13. I recommend summarizing which average resistance factors result for the different setups (with and without trees). Are these values suitable to estimate the discharge? It would be interesting to show the determined vs. measured discharge for a given scenario.
14. Conclusion: Conclusion points 1, 2 and 4 all contain results from Kubrak et al. (2019) without providing a reference. It seems as these conclusions stem from this paper, which is not correct. The entire conclusions section needs to be revised to focus on the results of this study. I understand that a comparison to the previous paper is important, but the results from the previous work should be identified as such.

Based on my review, I recommend major revision in form and content in order to be considered for publication.