Impact of Vegetation Density on the Wake Structure
Round 1
Reviewer 1 Report
This research attempts to experimentally calculate the lateral and longitudinal distribution of erosive and depositional energies in flows around vegetation patches of varying densities. It seems that the primary difference between this experiment and others is that this one attempts to account for varying vegetation densities and a mobile bed simultaneously. But I'm not sure that it does that, which would make this a non-unique research. Overall, I think that the research could have merit, but it is not presented well in this paper.
Primary Suggestions:
The English in this paper is very rough. So rough that it is sometimes difficult to determine what the authors are trying to say. It took me several readings just to understand the experimental setup, for example. If this is to be published in an English-language journal, this must improve drastically.
The Experimental Setup: One of the primary distinctions of this experiment versus others is that use of a mobile bed. Yet, the actual bed load or changes in bed topography are not measured. Also, why use a 1.5 mm gravel as the bed material? How does that scale up to actual river bed material? You don't provide the diameter of the individual fiberglass "vegetation" strands -- how do they compare to the bed material size? If the fiberglass are inflexible, that would suggest they are meant to represent shrubs or trees -- i.e. vegetation diameters that are larger than the bed material. Also, I appreciate the drawings of the experimental setup, but a few actual photos would help out a lot here.
Analysis: In order for this to be really applicable to river science, your results should be presented non-dimensionally. How does a vegetation patch density of 0.5 cm-1 scale up to a floodplain vegetation patch that is 10s of meters in diameter? And if you are distinguishing yourselves from others with a mobile bed, show some analyses of the bed erosion/deposition patterns. Would a changing bed topography affect the turbulent energy patterns you documented? I think this is an important question that is not answered here, but the intro suggests it will be.
Almost all of my line-specific comments have to do with improving the language. I started to keep track of them, but became overwhelmed just after the first page. After the language is improved, a second round of review might yield more line-specific comments.
Author Response
Point1: The English in this paper is very rough. So rough that it is sometimes difficult to determine what the authors are trying to say. It took me several readings just to understand the experimental setup, for example. If this is to be published in an English-language journal, this must improve drastically.
Response 1: We have carefully improved the language according to your Primary Suggestions.
Point2: The Experimental Setup: One of the primary distinctions of this experiment versus others is that use of a mobile bed. Yet, the actual bed load or changes in bed topography are not measured. Also, why use a 1.5 mm gravel as the bed material? How does that scale up to actual river bed material? You don't provide the diameter of the individual fiberglass "vegetation" strands -- how do they compare to the bed material size? If the fiberglass are inflexible, that would suggest they are meant to represent shrubs or trees -- i.e. vegetation diameters that are larger than the bed material. Also, I appreciate the drawings of the experimental setup, but a few actual photos would help out a lot here.
Response 2: We have added some data about flow rate and actual bed topography based on your suggestions. Based on the given parameters of this experiment, we used the shields diagram (Chien, N., and Wan, Z. 1999. Mechanics of sediment transport, ASCE, Reston, Va) to obtain a range of sediment starting sizes, after multiple experiments, we finally found the most suitable particle size is 1.5 mm. This paper designed a (basic) generalization model experiment, and did not use any real river as a prototype for scaling analogy. The cylinder diameter (d) was 4 mm, which falls in the range of real emergent vegetation stems, d=0.1-1 cm (see, Valiela I., Teal J. M., Deuser W. G. The nature of growth forms in the salt marsh grass spartina alterniflora [J], Am Nat, 1978, 112: 461-470. Leonard L. A., Luther M. E. Flow hydrodynamics in tidal marsh canopies [J], Limnol Oceanogr, 1995, 40, 8: 1474-1484.) Since no photos were taken of the experimental layout, relevant photos of the experimental setup could not be provided.
Point3:Analysis: In order for this to be really applicable to river science, your results should be presented non-dimensionally. How does a vegetation patch density of 0.5 cm-1 scale up to a floodplain vegetation patch that is 10s of meters in diameter? And if you are distinguishing yourselves from others with a mobile bed, show some analyses of the bed erosion/deposition patterns. Would a changing bed topography affect the turbulent energy patterns you documented? I think this is an important question that is not answered here, but the intro suggests it will be.
Response 3: Because this paper did not take any actual river as its prototype, the scale between prototype and model was not considered in this experiment. In addition, we mainly exploring the influence of vegetation groups with different densities on flow turbulence, focusing on theoretical research. Therefore, other aspects are not taken into special consideration (actual situation of natural rivers) in the design of vegetation group density. According to your Suggestions, we have added a description of the influence of bed surface morphology on turbulent kinetic energy. However, it is a very complicated problem to study the flow velocity turbulent kinetic energy in moving bed. some of your Suggestions will become the focus of our further research.
Point4: Almost all of my line-specific comments have to do with improving the language. I started to keep track of them, but became overwhelmed just after the first page. After the language is improved, a second round of review might yield more line-specific comments.
Response 4: We have carefully improved the language according to your Primary Suggestions.
Reviewer 2 Report
The paper is well-organized and the flow of the materials is proper. The manuscript could be considered for publication when the authors have responded the comments/suggestions given on the manuscript.
Comments for author File: 
Comments.pdf
Author Response
Point1： The major weakness is that the effect of the flow rate is not presented at all. It is not clarified what are the effect of vegetation, compared to other publications, and there are no any comparative results showing its difference. Therefore, the potential advantages of the present work cannot be evaluated.
Response1：The key point of this paper is to discuss the effect of plant population density change on turbulent kinetic energy. According to your suggestion, we have added the velocity data and the data bed topography. The influence of vegetation on water flow and topographic changes under moving bed conditions is still a very complex problem though, some of your suggestions will be the focus of our further research.
Point2: The English has to be improved in order to match the standards of scientific publication. The practical relevance of the research described in the paper should be better emphasized to better match the typical audience of Water. As a final suggestion, I think the paper and References style has to be checked for consistency.
Response 2: We have carefully improved the language according to your suggestions.
Point3：I don't think this section is explained as clearly as it could be. As far as this section is concerned, I have six issues: It is not clear how the ADV probe is placed. Please improve. As in the wake region the flow usually presents a large velocity variation the grid should be more refined.
Response 3: We have improve the description of the experimental setup. Besides, we also explain our experimental setup about consideration of the large velocity variations in the wake region as “There are seven sections upstream of the model patch and 25 sections downstream of it in velocity measurements and the measuring position is from -4D to 23D. The velocity variation is violent, when it is close to the model patch so that intervals are smaller, when it approaches to the vegetation community. There are seven vertical measuring lines in each section where the lateral values of y from the far left vertical to the far right were 1.75D, 1.17D, 0.58D, 0D, -0.58D, -1.17D, and -1.75D, as well as 8 testing points, which are evenly distributed according to the width and depth. When the vertical distance from the measurement point to the bed was less than 5 mm, the measurement interval was reduced to 1 mm, and when the distance is larger than 5 mm, the measurement intervals are 5 and 10 mm, according to the particular flow depth. ”
Point4：The energy spectrum should be included in the paper.
Response4：In this paper, the turbulent kinetic energy and the change of bed surface under the change of plant population density are discussed. The relationship between energy spectra and LTKE and their relationship with plant populations are relatively complex. Discussion on them will be the focus of our further research.
Point5：An example of measured signal should be presented. Other peer-reviewed journal papers that can be used: Nepf, H.M. (2012b) Flow and transport in regions with aquatic vegetation. Annu Rev Fluid Mech 44:123–142. Tanino, Y., Nepf H.M. (2008) Laboratory investigation of mean drag in a random array of rigid, emergent cylinders. J Hydraul Eng 134:34–41. Ghisalberti, M., Nepf H.M. (2004) The limited growth of vegetated shear layers. Water Resour Res 40:W07502. Kang, H., Choi, S.U. (2006a) Turbulence modeling of compound open-channel flows with and without vegetation on the floodplain using the Reynolds stress model. Adv Water Resour 29(11):1650–1664. Brito, M., Fernandes, J. & Leal, J.B. (2016) "Porous media approach for RANS simulation of compound open-channel flows with submerged vegetated floodplains". Environ Fluid Mech 16:1247–1266. Nepf, H.M. (2012a) Hydrodynamics of vegetated channels. J Hydraul Res 50:262–279. Ghisalberti, M., Nepf, H.M. (2006) The structure of the shear layer in flows over rigid and flexible canopies. Environ Fluid Mech 6:277–301.
Response5：We have added some of the peer-reviewed journal papers you recommended.
Reviewer 3 Report
Why did the authors use only one diameter in simulations?
In the river valley including the main channel and floodplains there is rigid vegetation (trees, large-diameter shrubs) and flexible vegetation (grasses and small-diameter branches).
My question is: why do the simulations cover only one type of vegetation?
The presented simulations apply only to uniform rigid elements that are characterized by a certain roughness. If only this type of vegetation (trees) is assumed, it is characterized by different coefficients of roughness due to the resistance resulting from the porosity of the outer layer.
I suggest extending the literature review by the following publications:
Hajdukiewicz, H., Wyżga, B., Mikuś, P., Zawiejska, J., & Radecki-Pawlik, A. (2016). Impact of a large flood on mountain river habitats, channel morphology, and valley infrastructure. Geomorphology, 272, 55-67.
Mikuś, P., Wyżga, B., Walusiak, E., Radecki-Pawlik, A., Liro, M., Hajdukiewicz, H., & Zawiejska, J. (2019). Island development in a mountain river subjected to passive restoration: The Raba River, Polish Carpathians. Science of The Total Environment, 660, 406-420.
Author Response
Point1: Why did the authors use only one diameter in simulations?
Response 1: The diameter is indeed a crucial element in previous vegetation simulations (e.g. DUNN C , LOPEZ F , GARCIA M H. Mean flow and turbulence in a laboratory channel with simulated vegetation ( HES51 )[ R ] .1996). The fact is if we planned to conduct a series experiments about the diameter, the maximum diameter of vegetation should be 350px or bigger via our trials, only then can we obtain a comparable result. Nevertheless, we cannot get valid and satisfying data in a 750px wide flume due to the effects of side walls and the restriction about the size of probes. So our laboratory is building a wider flume with a width of 2m for further research about vegetation patches.
Point 2: Why do the simulations cover only one type of vegetation?
Response 2: Flexible plants by the lake in nature often appear as submerged plants. The study of the turbulence of submerged plants on mobile bed is very complex and often limited by many factors, such as the sway of the leaves. However, through field investigations, we found that rigid plants often emerged and grew in shallow waters (Such as cattails, sage, reeds and so on). Its roots grow in the soil and have developed aerated tissue. Simulation experiments show that the flow field around the rigid plant is clearer and more regular. Based on this, we can better carry out a series of studies related to flexible vegetation in the future.
Point 3: I suggest extending the literature review by the following publications
Response 3: The literature review by the publications as you mentioned has been added to the article.
Round 2
Reviewer 1 Report
The English is much improved. I see now, with the improved English and based on the authors' comments, that some of my other major recommendations of the methods might have been due to my not understanding what the authors were trying to say. This paper reads much easier now. My primary questions/concerns from before have been addressed -- particularly the influence of the mobile bed.
The way this second version was presented to me was a bit off-putting, with all of the track-changes memorialized on the PDF. I would have liked to have read a clean version. Perhaps because of this, Table 1 was difficult to read for me.
I'm disappointed that you have no photos of the setup. Hopefully lesson learned for next time?
Minor spelling/grammar and other suggestions:
Line 299 -- remove "well"
Line 304 -- replace "It is intended..." with "This study is intended..."
Line 574 -- insert "the" into "Table 1 shows all of THE test..."
Line 575 -- replace "parametes" with "parameters"
Line 577 -- insert: "The INDIVIDUAL PLEXIGLASS cylinder diameter is..."
Line 584 -- insert: "the incipient starting VALUES of..."
Line 585 -- what do you mean by thickness? do you mean vertical depth or horizontal width?
Line 1707 -- remove 'the' so it reads "Through numerical modelling..."
Author Response
The issues about language, missing photos and the track-changes memorialized PDF have really taught us a lesson.
All the minor spelling/grammar have been corrected according to your suggestions.
Thank you for your time and patience.
Reviewer 2 Report
In my opinion the revised version of this manuscript can be accepted, since it has been improved substantially about clarity of contents and aims. Still, the paper is ridden with grammar and syntax errors, mispellings, and the like. A few suggestions:
i) Figures typing should be similar to the text.
ii) It would be better if the authors could save the Figure 4.2 as vector graphs and correct its numbering.
iii) Once again, the references style has to be checked for consistency.
Author Response
According to your suggestions, the issues about pictures, fonts, references style and language have been fixed.
Thank you for your time and patience.
