Characteristics of Large-Scale Coherent Structures on Irregularly Arranged Rough-Bed Open-Channel Flows

Round 1

Reviewer 1 Report

The authors report the results of experimental measurements performed using PIV for the statistical analysis of velocity profiles in a peebles-covered channel, with particular reference to the identification of large-scale coherent structures. They then identify the energy contribution of such structures.
The topic is of interest but the paper is severely limited by a number of flaws.
First, the introductory part is an almost incomprehensible sequence of acronyms, which seems unnecessary.
Secondly, the methodological approach appears incorrect: it is almost exclusively experimental without specifying the uncertainty of the measurements and without the diagrams showing error bars and confidence bands. Even the test parameters, such as, for example, the stated Reynolds number from 1785 to 4110, appear to be expressed without taking into account the uncertainty of the variables involved: presumably Re=1785 should be expressed as Re=1800, since an accuracy on the fourth digit appears unrealistic. The description of the tests and experimental apparatus appears too verbose and also unnecessary: the authors should focus more on the results of the experiments, leaving the details to an appendix.
There are also a number of minor flaws: the list of references should be complete, without et al.

Author Response

Please refer to the attachment "Cover letter3.docx"

Author Response File: Author Response.docx

Reviewer 2 Report

Paper needs to be improved in following manners, this is a nice study however, following

questions are necessary to be answered before further processing

a. This would be beneficial if authors could provide more details at the end of introduction

specifically stating the objective of the paper, although this is explained but needs a little more

clarity.

b. Authors need to update the survey of literature for more recent papers specifically published in

the recent years 2022 etc.

The authors should elaborate on their new findings that are worthy of consideration for publication in a journal, below some proposed work:

https://doi.org/10.1016/j.enganabound.2022.12.020

https://doi.org/10.1016/j.csite.2023.102767

https://doi.org/10.1016/j.enganabound.2022.11.033

https://doi.org/10.1016/j.enganabound.2022.10.034

https://doi.org/10.1142/S0217979223501473

https://doi.org/10.1016/j.advengsoft.2022.103267

https://doi.org/10.1016/j.seta.2022.102408

https://doi.org/10.1016/j.ijhydene.2022.07.140

https://doi.org/10.1016/j.jics.2022.100617

https://doi.org/10.1016/j.jobe.2022.104328

c. Language of the paper needs professional touch ups as there are typos and errors in some parts

of paper and they need to be reduced.

d. In the conclusion section, authors need to focus on the outcomes of their study with salient

findings only, keep them brief, as more explanation is already added in the results and

discussion section.

e. Results and discussion section is well explained, please try to look at figures in this section they might need more explanation if needed.

f. Altogether after these improvements are properly made, paper would be in a decent shape and

can be considered for publication if revised well.

g. Please give a bird eye view picture of your finding in abstract.

Author Response

Please refer to the attachment "Cover letter1.docx"

Author Response File: Author Response.docx

Reviewer 3 Report

It is with pleasure that I have read this very interesting study by the authors. This presents new experimental results that are of interest given they use both time resolved PIV and SfM for characterising the bed surface. 

However I am a bit baffled overall by the way the results are presented as there may have been an apparent mismatch between the authors claim and results. Specifically it’s not clear how this research fills the gap between regular vs “random” bed surfaces. How is this randomness specified and quantified? Does a metric exist that allows for doing that eg from the SfM statistics? Does the bed surface remain unchanged and if so, can the authors really assess the effect of “random” rough bed surface? 

For detailed comments please see below: 

avoid use of spoken English, for example Line 60: “hot topic” eg can say received increased attention. It may also be important to specify some subfields where this research has implications as well, for example for the start and sustaining of sediment transport (eg see the Science paper by Diplas et al 2008). 

Not many recent specific references to the topic are given early in the manuscript to substantiate the existence of the literature gap the authors present here. This is important to be offered early so that the reader can better appreciate the novelty’s d importance of this study. For example Lines 72-73: Add relevant literature for smooth and rough bed surfaces. 

The manuscript is well written overall but there still exist some minor typos that remove from the quality of presentation and might distract the reader. For example line 122: “can reaches”

Table 1: the columns that state parameters that remain fixed should be mentioned in the text and/or table caption but don’t need be in the table columns. 

Table 2: check column 6 header

In this section and earlier in the text as well as in table 1, a metric the authors can use to quantify the bed surface “randomness” should be introduced and referenced onward. 

Also if in The pertinent literature hydraulic roughness is used to refer to the bed surface conditions, it may be useful to include this parameter in table 1 to facilitate potential comparisons with other studies. 

Line 150: j?

Lines 196-202: are these orthophotos or just topographic? Also what are the specifications of the image stills taken (resolution, field of view, focal length of camera lens) and at what spatial intervals the images were taken? Regarding the image taking routine: where the images taken at regularly spaced intervals or irregular eg more densely following any abrupt variabilities of the bed surface?

Before that can more information be offered over the calibration feature eg the relative depth of placement and clarify if this feature was only used for the bed surface measurements and then removed for the flow experiments?

Also it will be important to detail any additional parameters used for the software so that other readers can feel the reported results are reproducible. 

Lines 210-211: what is the expected error in these metrics? is there any meaning in reporting submillimiter accuracy eg 0.4286 cm (!)

Line 212-214: this needs be written again to match the style of the manuscript 

It is extremely important to offer the means and quantifiable metrics by which the authors aim to define the “randomness” & irregularities of the bed surface. The authors need to add emphasis on this early in the manuscript from the abstract and extend this emphasis to the methods section and section 3.1.

Also in terms of comparing the regular vs random surface how can this be achieved with what has been published in the literature where the standard reference terms for the bed surface condition are focused to what the flow “feels” eg hydraulically smooth and rough bed surfaces? Is it worth that the authors consider such existing metrics in the literature and try to expand them eg for the same hydraulic roughness but distinct bed surface variabilities assessed with new metrics the authors choose to define the bed surface?

Author Response

Please refer to the attachment "Cover letter2.docx"

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

After reading the authors' answers and the revised version, I found no trace of the uncertainty analysis absolutely necessary to validate the experimental data. See, for example, Experimentation, Validation, and Uncertainty Analysis for Engineers by Coleman & Steele; or DOI: 10.1016/j.jnnfm.2013.07.008.
This is not just a matter of form, but of substance.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

The authors have presented a rebuttal to this review. This is sufficient but I would encourage that the authors try offer as much as information and details possible for the benefit of the reader. 

I also have a couple more points:

1. The authors omitted addressing the part where I mentioned that the literature review can be expanded, where the applications of this research are considered, specifically in the area of sediment entrainment (I mentioned Diplas et al 2008 in Science, but if the authors wish they can also consider the following which clearly establishes a need for knowing the spectral scales and energy content of coherent flow structures that may lead to the destabilisation of the river bed surface:  Entrainment of coarse particles in turbulent flows: An energy approach, M Valyrakis, P Diplas, CL Dancey Journal of Geophysical Research: Earth Surface 118 (1), 42-53

2. The authors now use "irregular pebble-rough-bed surface" which is perhaps a bit difficult to relate in a technical sense in a first glance. As I understand it, irregular refers here to the arrangement of the sediment not being regular and its a property of the bed surface. However some readers may take it to mean that it refers to the pebbles being irregularly sized or shaped. While both are not wrong in context there may be ambiguity and lack of clarity to what it refers. There are many options once can choose considering the criteria above. One suggestion could be to remove the word "pebbles" (which is technically covered by the use of "rough") and add a specification to the word "irregular", resulting in: "irregularly arranged rough-bed surface" or a slightly more wordy version: "irregularly arranged pebble roughened bed surface".

Thank you for your consideration!

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 3

Reviewer 3 Report

Thanks to the authors for making required edits.