Characterizing Density Flow Regimes of Three Rivers with Different Physicochemical Properties in a Run-Of-The-River Reservoir

Round 1

Reviewer 1 Report

The paper showed mixing and circulation characteristics of three rivers with different physicochemical properties in Paldang reservoir, using high-frequency monitoring and three-dimensional (3D) hydrodynamic modeling. I could understand the importance of the paper, and I think the article might be interesting. However, there is little generalization of the characteristics, which makes readers hard to refer this outcome for their research. Also, using a Julian day mixed with normal calendar date in the paper is confusing. Always keeping at least one date system throughout the paper is recommended to understand the paper easily. Moreover, the authors used high-frequency (10-min or 10-s) monitoring data, but high-frequency have little meaning in the paper. So, it might be better to remove the word of the high-frequency from the title to avoid the misunderstanding of the contents. Specific comments are following.

Specific Comments:

1. l. 176: "at depths of 0.2-1 m" should be “at depths of 0.2-1m intervals”.
2. 2.3.1 Why EC at GAC changed much between May and June?
3. l.246: What is the previous data?
4. l.264: Year averaged is confusing because this is monthly average.
5. l.272: Upstream color in blue? (Fig.3 caption said opposite.) Please check.
6. l.329: I cannot understand how the authors compared the data (daily averaged, minute or ...). This is same for other comparisons.

Author Response

Response to Reviewers

Thank you very much for your careful review and suggestions that have helped us improve the quality of our manuscript. Reviewers’ comments/suggestions are in bold text. Author responses are in plain text. All revisions are highlighted in the revised manuscript.

Response to Reviewer #1

• The paper showed mixing and circulation characteristics of three rivers with different physicochemical properties in Paldang reservoir, using high-frequency monitoring and three-dimensional (3D) hydrodynamic modeling. I could understand the importance of the paper, and I think the article might be interesting. However, there is little generalization of the characteristics, which makes readers hard to refer this outcome for their research.

Authors’ response: [overall manuscript]

The characteristics of inflow mixing driven by density currents and relevant water quality problems in stratified reservoirs highlighted in this paper are of common interest among many scholars and reservoir managers around the world. We believe that this paper will be of interest to the readership of Water because the ability to predict the influence of reservoir inflows on water quality is a valuable development that will aid efforts to improve water quality in ROR-type reservoirs. In particular, this paper is of sufficient academic value because it provides important information in interpreting the spatiotemporal occurrence characteristics of harmful algal bloom and hypoxia, which are existing problems in stratified reservoirs, using high-frequency monitoring and three-dimensional (3D) hydrodynamic modeling.

• Using a Julian day mixed with normal calendar date in the paper is confusing. Always keeping at least one date system throughout the paper is recommended to understand the paper easily.

Authors’ response: [overall manuscript]

The date system of all tables and figures except Figure S5 has been changed to Julian day system. Figure S5 is 7-year data from 2012 to 2018; thus, we maintained the Gregorian date system.

• The authors used high-frequency (10-min or 10-s) monitoring data, but high-frequency have little meaning in the paper. So, it might be better to remove the word of the high-frequency from the title to avoid the misunderstanding of the contents.

Authors’ response: [Title]

We have removed the word “high-frequency” from the title. The new title is as follows. “Characterizing Density Flow Regimes of Three Rivers with Different Physicochemical Properties in a Run-of-the-river Reservoir”

• 176: "at depths of 0.2-1 m" should be “at depths of 0.2-1m intervals”.

Authors’ response: [L 175-176]

We have corrected it.

• 3.1 Why EC at GAC changed much between May and June?

Authors’ response: [Table 1]

The total discharge of sewage treatment plants operating in the Gyeongancheon stream basin is about 1.5 m³/s. In June 2016, the drought was severe and the flow of Gyeongancheon stream was cut in half compared to May, resulting in a relatively increased proportion of sewage treatment plant discharges, leading to an increase in EC.

• 246: What is the previous data?

Authors’ response: [L244-247]

The previous data meant the observed 10-year average (2007-2016) inflows into the Paldang reservoir. We have modified the sentence to make it more specific as follows.

“During the 2016 experiment, the ratio of flows from the three rivers into the Paldang reservoir in May was similar to the average ratio over the last decade. However, the proportion of the SH-river flow in June was only 32.8% of the total inflow, which was exceptionally low (Table 2, Figure 2).”

• 264: Year averaged is confusing because this is monthly average.

Authors’ response: [L265-268]

We have modified Figure 2 and changed the caption as follows.

“Figure 2. Discharge trend of Paldang Dam over the past 10 years: (a) average monthly outflow for 2006–2016; (b) average annual outflow for 2006–2016; and (c) hourly variations of discharge for Paldang Dam (PDD), Cheongpyeong Dam (CPD), and Ipo Weir (IPW) from Julian day 122 to 152 (May 2016) and 153 to 182 (June 2016).”

• 272: Upstream color in blue? (Fig.3 caption said opposite.) Please check.

Authors’ response: [L303]

We have modified the caption of Figure 3 as follows.

“The positive (+, red) and negative (-, blue) values of the color bar indicate the upstream and downstream flow, respectively.”

• 329: I cannot understand how the authors compared the data (daily averaged, minute or ...). This is same for other comparisons.

Authors’ response: [L312-317]

We have added a sentence to clearly describe how the error statistics were calculated.

“The error data for the water level was calculated by comparing the simulation values with the observation values in hourly units. In contrast, the errors for flow velocity and water temperature were calculated by averaging the high-frequency observations hourly and comparing these with the simulated values. In the case of EC, the observed value was measured on a weekly basis, and the errors were calculated by comparing this with the simulation value at that time.”

Author Response File: Author Response.docx

Reviewer 2 Report

Thanks to this article.

The topic is interesting and the results are clear.

The english need a revision in my opinion. Some parts are very difficult to read and complex.

I have only some minor comments:

1. line 38. You can add, if you want the following two references. This is to better explain the problems that can occurs with dams and hydropower production in the ecosystem and in the human society.  
   - this for hydropeaking and impact in the ecosystem: Pisaturo, G.R., Righetti, M., Dumbser, M., Noack, M., Schneider, M., Cavedon, V.;
   The role of 3D-hydraulics in habitat modelling of hydropeaking events
   (2017) Science of the Total Environment, 575, pp. 219-230.
   DOI: 10.1016/j.scitotenv.2016.10.046
   - this for the human safet: Pisaturo, G.R., Righetti, M., Castellana, C., Larcher, M., Menapace, A., Premstaller, G.
   A procedure for human safety assessment during hydropeaking events
   (2019) Science of the Total Environment, 661, pp. 294-305. DOI: 10.1016/j.scitotenv.2019.01.158
2. line 39 at the end before the reference [2]. Add "... flood events and during flushing events [2]"
3. line 197: Lagrange
4. line 228-239. Did you performed some mesh dependecy analysis?
5. line 255. Why the sum of the percentage is not 100% but 99.9%?
6. Figure 2. Please increase the font size

Author Response

Response to Reviewers

Thank you very much for your careful review and suggestions that have helped us improve the quality of our manuscript. Reviewers’ comments/suggestions are in bold text. Author responses are in plain text. All revisions are highlighted in the revised manuscript.

Response to Reviewer #2

• The topic is interesting and the results are clear. The English needs a revision in my opinion. Some parts are very difficult to read and complex.

Authors’ response: [overall]

The paper has been edited for language by Editage, a professional editing company, and a certificate is attached (attachment 1)

• line 38. You can add, if you want the following two references. This is to better explain the problems that can occurs with dams and hydropower production in the ecosystem and in the human society. This for hydropeaking and impact in the ecosystem:

Pisaturo, G.R., Righetti, M., Dumbser, M., Noack, M., Schneider, M., Cavedon, V.; The role of 3D-hydraulics in habitat modelling of hydropeaking events (2017) Science of the Total Environment, 575, pp. 219-230. DOI: 10.1016/j.scitotenv.2016.10.046

Pisaturo, G.R., Righetti, M., Castellana, C., Larcher, M., Menapace, A., Premstaller, G. A procedure for human safety assessment during hydropeaking events (2019) Science of the Total Environment, 661, pp. 294-305. DOI: 10.1016/j.scitotenv.2019.01.158

Authors’ response: [L37]

We appreciate your suggestion. Accordingly, we have added the two suggested references to better explain the ecological problems that can arise from dams and hydropower. .

• line 39 at the end before the reference [2]. Add "... flood events and during flushing events [2]"

Authors’ response: [L39]

We have modified the sentence accordingly.

• line 197: Lagrange

Authors’ response: [L196]

This text has been corrected.

• line 228-239. Did you perform some mesh dependency analysis?

Authors’ response: [L228-239]

The sensitivity of the numerical grid was examined for 30 m, 50 m, and 100 m, and the 50 m grid was selected because it could reflect the backflow phenomenon in the bottom layer of the SH-river branch, and the computation time was reasonable. The accuracy of the numerical grid was confirmed by comparison with the measured water level-capacity relationship. The relative error was 3.3%, which can be considered as a good reflection of the reservoir topography.

• line 255. Why the sum of the percentage is not 100% but 99.9%?

Authors’ response: [Table 2]

The values have been revised.

• Figure 2. Please increase the font size

Authors’ response: [Figure 2]

For improved clarity and legibility, we reduced the original four graphs to three and increased the font size.

Attachment 1. Certificate of English Editing

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I appreciate the efforts which authors have done to improve the paper. I think the modified paper is now ready for publishing.