Using Quinine as a Fluorescent Tracer to Estimate Overland Flow Velocities on Bare Soil: Proof of Concept under Controlled Laboratory Conditions

Round 1

Reviewer 1 Report

The presented manuscript describes a laboratory experiment investigating the estimation of overland flow velocities on bare soil using quinine as a fluorescent tracer. The paper suits the journal, however, before the acceptance it needs some clarifications and changes. Below, you can find some comments helping the improvement of your work. Moreover, authors could spend more time to prepare a proper manuscript in the term of formating (blank pages, double numbering, wrong references formating...).

1) L. 23-24 - this sentence is rather an introduction, not for the abstract, where you should provide specific outcomes of your research.

2) The entire abstract would benefit and would be more attractive by adding some crucial, strong outcome of your research.

3) The English needs polishing by a native speaker.

4) Many sentences lack of proper references to the literature, e.g. the first paragraph of the Introduction.

5) The manuscript is not prepared according to the MDPI author's guidance, e.g. references and their list.

6) L. 45-47 - Please, present some examples for the potential readers. This needs references! Based on the literature, describe these examples. Edit. I saw listed techniques, but without any details. Please, describe them. Show their differences, explain, which should be used to specific measurements, etc. 

7) The list of references is vaque. Most of the papers are selfcitation. It doesn't look good. Can you refer to other researchers?

8) L. 69 - if they were widely used, show more examples.

9) L. 75-79 - this is not clear. Please, rephrase it in more clearly way.

10) Fig. 1 - figure is okay, but the quality is not. This is mostly visible on the text.

11) Table 1 - please, remove it. It's enough to present model of UVA, no necessary to give the entire table with lamp specification.

12) Table 2 - This also is unnecessary space use. It's better to provide this information in the text as 1-2 sentences.

13) Delete unnecessary blank pages.

14) Page 6, L.4 - Did they dry in room temp. or in the oven? How long?

15) Figure 2 should be provided before subsection 2.3 as it was cited in previous subsection!

16) L. 13 - provide more important information like discharge, velocity, etc.

17) Table 4 - Again, this can be provided in the text. Please, use tables for more important data and information, e.g. comparison or so, not for specification of lamp or colour.

18) L. 30-33 - please, delete it, it provides nothing to this research

19) Tables 5-6 - no need to provide this. For reader it's enough to give the used model. Such info can be found in the manufacturer site. This is unnecessary space usage. You can also provide such information as appendix to the manuscript. Here, please, focus more on results and their discussion.

20) L. 118 - please, describe your results and then, refer to proper figure, table in the bracket. Do not describe what is shown on the figure. This is presented in the figure caption.

21) L.129-130 - see my previous comment. Please, refer to this comment throughout the entire paper.

22) 168-170 - are there any advantages od using your new method? Which method is the best and why? What about the costs of these three methods? How about using this in natural river conditions in the field?

23) The paper is vague if it comes to the discussion. I don't see here any discussion, only results description, and comparison between them. This needs to be improved. Also, you should compare and refer to some literature findings, discuss with them.

Author Response

Point-by-point response to the reviewer:

Reviewer 1

The presented manuscript describes a laboratory experiment investigating the estimation of overland flow velocities on bare soil using quinine as a fluorescent tracer. The paper suits the journal, however, before the acceptance it needs some clarifications and changes. Below, you can find some comments helping the improvement of your work. Moreover, authors could spend more time to prepare a proper manuscript in the term of formating (blank pages, double numbering, wrong references formating...).

REPLY:

Manuscript was improved accordingly. Formatting was improved.

1) L. 23-24 - this sentence is rather an introduction, not for the abstract, where you should provide specific outcomes of your research.

REPLY 1:

Sentence was removed

2) The entire abstract would benefit and would be more attractive by adding some crucial, strong outcome of your research.

REPLY 2:

Abstract was improved.

3) The English needs polishing by a native speaker.

REPLY 3:

Parts of the manuscript were checked by a native speaker.

4) Many sentences lack of proper references to the literature, e.g. the first paragraph of the Introduction.

REPLY 4:

References were added. See reply 7.

5) The manuscript is not prepared according to the MDPI author's guidance, e.g. references and their list.

REPLY 5:

Formatting was improved.

6) L. 45-47 - Please, present some examples for the potential readers. This needs references! Based on the literature, describe these examples. Edit. I saw listed techniques, but without any details. Please, describe them. Show their differences, explain, which should be used to specific measurements, etc. 

REPLY 6:

Manuscript was improved. Citations were added. See reply 7.

7) The list of references is vaque. Most of the papers are selfcitation. It doesn't look good. Can you refer to other researchers?

REPLY 7:

Other researchers were cited, namely:

Singh, V.P., editor, Handbook of Applied Hydrology, McGraw-Hill Education, New York, 1440 pp., 2017.

Tauro, F., C. Pagano, M. Porfiri, S. Grimaldi Tracing of shallow water flows through buoyant fluorescent particles. Flow Measurement and Instrumentation 26 (2012) 93–101

Tauro F, Aureli M, Porfiri M, Grimaldi S. Characterization of buoyant

fluorescent particles for field observations of water flows. Sensors 2010;

10(12):11512–29.

Chow V.T, Maidment DR, Mays LW. Applied hydrology. New York: McGraw-Hill; 1988.

Jodeau M, Hauet A, Paquier A, Le Coz J, Dramais G. Application and evaluation

of LS-PIV technique for the monitoring of river surface velocities in high flow

conditions. Flow Measurement and Instrumentation 2008;19(2):117–27.

8) L. 69 - if they were widely used, show more examples.

REPLY 8:

Many examples are given in the next phrase.

9) L. 75-79 - this is not clear. Please, rephrase it in more clearly way.

REPLY 9:

The paragraph was revised by a native speaker.

10) Fig. 1 - figure is okay, but the quality is not. This is mostly visible on the text.

REPLY 10:

Better quality is prepared and will be provided in TIFF for accepted version.

11) Table 1 - please, remove it. It's enough to present model of UVA, no necessary to give the entire table with lamp specification.

REPLY 11:

Table 1 was removed. Information added to the text.

12) Table 2 - This also is unnecessary space use. It's better to provide this information in the text as 1-2 sentences.

REPLY 12:

Table 2 was removed. Information added to the text.

13) Delete unnecessary blank pages.

REPLY 13:

This will be prepared for accepted final version.

14) Page 6, L.4 - Did they dry in room temp. or in the oven? How long?

REPLY 14:

Soil surface was allowed to dry for > 1 week at room temperature. Information added to the text.

15) Figure 2 should be provided before subsection 2.3 as it was cited in previous subsection!

REPLY 15:

Done.

16) L. 13 - provide more important information like discharge, velocity, etc.

REPLY 16:

All available measured data was presented in the tables.

17) Table 4 - Again, this can be provided in the text. Please, use tables for more important data and information, e.g. comparison or so, not for specification of lamp or colour.

REPLY 17:

Table 4 was removed. Information added to the text.

18) L. 30-33 – please, delete it, it provides nothing to this research.

REPLY 18:

These lines were revised: The main advantage of using quinine tracer is the higher visibility of the injected tracer under ultraviolet A (UVA) light for low luminosity conditions.

19) Tables 5-6 - no need to provide this. For reader it's enough to give the used model. Such info can be found in the manufacturer site. This is unnecessary space usage. You can also provide such information as appendix to the manuscript. Here, please, focus more on results and their discussion.

REPLY 19:

Table 5 and 6 were removed. Information added to the text.

20) L. 118 - please, describe your results and then, refer to proper figure, table in the bracket. Do not describe what is shown on the figure. This is presented in the figure caption.

REPLY 20:

Text was improved taking in consideration the suggestions.

21) L.129-130 - see my previous comment. Please, refer to this comment throughout the entire paper.

REPLY 21:

Text was improved taking in consideration the suggestions.

22) 168-170 - are there any advantages od using your new method? Which method is the best and why? What about the costs of these three methods? How about using this in natural river conditions in the field?

REPLY 22:

Advantages are clearly stated in the second paragraph of the conclusions, which was improved. The application of these techniques in rivers was not within the objectives of this paper.

23) The paper is vague if it comes to the discussion. I don't see here any discussion, only results description, and comparison between them. This needs to be improved. Also, you should compare and refer to some literature findings, discuss with them.

REPLY 23:

This technique is not found in the literature and, therefore, comparison between results with other tracers was believed to be the correct approach.

Reviewer 2 Report

Because the equation in the comments cannot appear, please refer to the attached pdf file.

Comments for author File: Comments.pdf

Author Response

Reviewer 2

The following comments are provided for the author as a reference to improve the manuscript.

1. The measured front velocity of overland flow is the maximum velocity of flow, not vertically mean velocity. However, the authors mistook the front velocity for the vertically mean velocity, and they cannot identify the vertical location of the cross section of the max. velocity of the water flow. Moreover, the water depth of the flow over the soil surface is spatially different, could the authors plot the contour lines of water depth for each case?

REPLY 1:

We did not mistook the front velocity for the vertically mean velocity. The objective of this study was to compare quinine with dye and thermal tracer techniques. Therefore, no attempt was made to estimate the mean flow velocity for the cross-sectional area (across the flume). We measured leading-edge velocities and used these measurements to compare the two techniques. The objective of the paper was not focused on determining the real flow velocity.

We agree that the water depth of the flow over the soil surface is spatially different. However, it is not possible to plot the contour lines of water depth because we have depths less than 2-3 mm.

2. Table 2 is referred to the work of Aguas de Coimbra (2020), why? The water source of the present study might be different from that of Aguas de Coimbra (2020).

REPLY 2:

Water used has implication on the fluorescence of quinine, especially regarding pH. It is considered important to inform the reader of these characteristics. Aguas de Coimbra is the entity responsible for the public local water supply, the water source for the present study.

3. Similar to Table 2, Table 3 is also referred to de Lima et al. (2003), why? The soil characteristics might be different.

REPLY 3:

The soil was the same, obtained from the same container that was filled after thorough mixing the soil.

4. Page 6 line 1: The paved material of the flume used in this study is soil, so that the soil properties need to be considered. Why was a small amount of hydraulic cement applied to keep no suffering any type of erosion? If so, the authors need not to use soil as the paved material.

REPLY 4:

The three techniques were tested with exactly the same conditions (same soil surface morphology, discharge, flow depths and velocities). The flow was kept in steady state. The cement was used to avoid erosion, which would change the surface morphology during the experiments.

5. Page 6 lines 12~14:

How were the three techniques tested with “exactly the same” condition? The water flow was not easily kept in really steady state. When different techniques are performed, the conditions might have been changed.

REPLY 5:

It is easy to keep steady state with a constant head tank. All experiments with the different tracers were conducted for steady state conditions. Only then, discharge was changed.

6. In Figure 3: It is ??� = ∑ ∆???? ∆?? ?? ??=1 ?? not ??� = ∑ ∆???? ∆?? ?? ??=1 .

REPLY 6:

Corrected.

7. Page 9 lines 105 and 109: Are the “measuring section” and “scanned section” the same as “scanned area”? If not, show them on Figure 1.

REPLY 7:

All terms mean the same. “scanned section” was eliminated (it only appeared once in the text). Use was made of scanned area, sometimes in combination with measuring section, for clarity: measuring section (video scanned area)

8. What kind of tested surface is used for Figure 5? Please explain it on the figure caption.

REPLY 8:

Information added to the caption.

9. According to Tables 7 to 9, why is the velocity of rill flow lower than that on the flat surface? To my knowledge, the rill flow is more similar to “channel flow”, and the velocity of rill flow is supposed to be faster.

REPLY 9:

The reviewer comment is correct for the same discharges. However, the discharges were much smaller for the rill (much smaller cross section). This is why velocities are smaller.

10. In Table 10, why is there no intercept for the regression equations? It is not consistent with the result of Figure 7.

REPLY 10:

Attention: the axes are not at the origin (0,0)… If they were, all lines would go through (0,0).

Information was added to figure caption.

11. Why is the figure about the brightness intensity distribution in Figure 9 different from that in Figure 8? Please give the different conditions for each figure.

REPLY 11:

Information was added to figure captions.

Round 2

Reviewer 1 Report

The paper has bee improved by the authors and in my opinion, it can be accepted for the publication.

Reviewer 2 Report

I am not satisfied with the authors' reply to comments 1, 4, 5, 9, 10, and 11. The authors didn't catch my points and didn't give good and detailed responses to most comments. For example, in the reply to comment 1, "The objective of the paper was not focused on determining the real flow velocity." If the presented technique cannot measure the real flow velocity, what's the contribution of presenting such a new measurement technique? Then, such a study will become useless.