Hydraulic Flushing of Sediment in Reservoirs: Best Practices of Numerical Modeling

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors present a very interesting and highly relevant review paper on numerical modelling of reservoir sediment management techniques (flushing, venting). The paper is well written and comprehensible.

A few corrections of relatively minor nature should be applied before the paper can be recommended for publication:

1. Unit system: While the text consequently uses the metric system (m, m³/s), a number of Figures show content in US customary units (feet, cfs). The units should be consistent throughout the paper and therefore the following Figures need to be changed into the metric system: 7, 8, 10, 11, 12, 16, 17, 18.

2. Conclusions / concluding remarks: I would expect here a few sentences on the main findings/outcomes of the study, which are currently missing.

3. Literature review: The authors are referred to an early study which combined physical modelling, 3D numerical modelling (using SSIIM) and comparison of empirical relationships for pressure flushing, by Scheuerlein et al. (2004): Numerical and physical modelling concerning the removal of sediment deposits from reservoirs.
This paper has some of the same findings as the present study. It is therefore recommended to include this in the literature review. The article is available on ResearchGate: https://www.researchgate.net/publication/320335691_Numerical_and_physical_modelling_concerning_the_removal_of_sediment_deposits_from_reservoirs

4. Structure: The text on the "Nested Approach" is a methodological one and would fit much better to section 3 of the manuscript, e.g. as new subsection 3.5.

5. Others:

Line 307: Please define h_b0 used in this equation. Also I recommend to remove the rightmost part of the equation (=1/F_bo²) because it is not further used and may confuse readers.

Line 742: A flushing event lasting more than two years (2013-2015)? There is likely to be a typo in one of the years mentioned here.

Line 918 / Table 1: Needs a major layout overhaul.

Comments on the Quality of English Language

While the English language is mostly fine, there are a few typos and missing articles in the text. A quick language-check is therefore recommended.

Author Response

The authors present a very interesting and highly relevant review paper on numerical modelling of reservoir sediment management techniques (flushing, venting). The paper is well written and comprehensible.

A few corrections of relatively minor nature should be applied before the paper can be recommended for publication:

1. Unit system: While the text consequently uses the metric system (m, m³/s), a number of Figures show content in US customary units (feet, cfs). The units should be consistent throughout the paper and therefore the following Figures need to be changed into the metric system: 7, 8, 10, 11, 12, 16, 17, 18.

Reply: Thanks for catching our mixed use of the unit. We have replotted all the mentioned figures and the SI unit is used; new figures are included in the revised manuscript. We have also checked the unit consistency again during the revision.

2. Conclusions / concluding remarks: I would expect here a few sentences on the main findings/outcomes of the study, which are currently missing.

Reply: I added a section near the end of the Concluding Remarks to describe more on the main outcomes.

3. Literature review: The authors are referred to an early study which combined physical modelling, 3D numerical modelling (using SSIIM) and comparison of empirical relationships for pressure flushing, by Scheuerlein et al. (2004): Numerical and physical modelling concerning the removal of sediment deposits from reservoirs.
   This paper has some of the same findings as the present study. It is therefore recommended to include this in the literature review. The article is available on ResearchGate: https://www.researchgate.net/publication/320335691_Numerical_and_physical_modelling_concerning_the_removal_of_sediment_deposits_from_reservoirs

Reply: Thank the reviewer for bringing to our attention the study of Scheuerlein et al. (2004). This paper is included and mentioned in our revised manuscript now.

4. Structure: The text on the "Nested Approach" is a methodological one and would fit much better to section 3 of the manuscript, e.g. as new subsection 3.5.

Reply: As suggested, the “Nested Approach” paragraphs at the end of Section 4.1 have been moved up and designated as Section 3.5.

5. Others:

Line 307: Please define h_b0 used in this equation. Also I recommend to remove the rightmost part of the equation (=1/F_bo²) because it is not further used and may confuse readers.

Reply: Modifications have been made to incorporate the suggestions; thanks.

 

Line 742: A flushing event lasting more than two years (2013-2015)? There is likely to be a typo in one of the years mentioned here.

Reply: Thanks for catching this. The modeling was for two years but the reservoir lower-down was not. So the sentence was modified to avoid confusion.

 

Line 918 / Table 1: Needs a major layout overhaul.

Reply: Thanks; the table layout is fixed in the revised manuscript (we believe it was due to the reformatting process after the submission).

6. Comments on the Quality of English Language

While the English language is mostly fine, there are a few typos and missing articles in the text. A quick language-check is therefore recommended.

Reply: Authors have taken effort to make another round of checking on the English language and hope most typos and minor issues are fixed with the revised manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

This is a good paper on best practices numerically simulating hydraulic reservoir sediment transport. It can be published, however some changes need to be made and some points clarified. The authors should refer to the following comments for revison:

- The reviewer is at a loss as to why the article is classed review paper, given the authors have presented CFD studies applying the guidelines proposed. 

- What is the triangular mesh domain area in Fig. 17a. It is rather confusing as no results are presented outside the rectangular region

- Yes, the results show a good agreement with measurements, however, the computational mesh was not optimised. Could the authors comment why this is the case?

- The governing equations have not been shown and the type of simulation carried out. Was the mixture model used to model the sediments or Eulerian? This detail is missing and can obfuscate the reader's understanding of the work carried out, indeed more so if they intend to replicate it. 

- Turbulence model used and other settings are also needed. 

- General note: which of the figures are literature and which are your results should be clarified. Right now it is difficult to know and hence gauge the actual quality of the paper. 

Author Response

1. This is a good paper on best practices numerically simulating hydraulic reservoir sediment transport. It can be published, however some changes need to be made and some points clarified. The authors should refer to the following comments for revision:

Reply: Thanks for the positive review comments.

2. - The reviewer is at a loss as to why the article is classed review paper, given the authors have presented CFD studies applying the guidelines proposed. 

Reply: The article is intended to be used as a document for general guidelines on how to carry out hydraulic flushing modeling, not to report a new research. Therefore, it belongs to the “General Review” category, as there is no “Guideline” category with the journal. As it is not a Research Article, we do not attempt to provide new research findings.

3. - What is the triangular mesh domain area in Fig. 17a. It is rather confusing as no results are presented outside the rectangular region

Reply: In the manuscript, it is stated that “The 3D mesh has a horizontal size of 9,855 mixed quadrilateral and triangle cells.” Basically, in the horizontal plane, the quad 2D cells are used within the intake tower, but triangular 2D cells are used in the reservoir outside the intake. The results outside the intake are not interesting and the focus, as no sediment was eroded; however, outside zone is needed for the numerical modeling in order to set up the proper far-field conditions for simulating the flows and sediment inside the intake.

4. - Yes, the results show a good agreement with measurements, however, the computational mesh was not optimised. Could the authors comment why this is the case?

Reply: We are unclear about the comment of “the computational mesh was not optimised.” If it refers to that the mesh refinement, we can assure that the mesh refinement study was carried out at the initial stage of the 3D numerical modeling effort, and we did find that the mesh we used was fine enough so that the results were not impacted by the mesh.

5. - The governing equations have not been shown and the type of simulation carried out. Was the mixture model used to model the sediments or Eulerian? This detail is missing and can obfuscate the reader's understanding of the work carried out, indeed more so if they intend to replicate it. 

Reply: The manuscript is of the Review category with modeling guidelines presented. Therefore, we decided that the presentation of governing equations was not critical. In lieu of the comments, we have revised the manuscript in the presentation of case studies so that the particular models used are mentioned – this way, readers may refer to the relevant User’s Manuals or papers of the models for the knowledge of the governing equations. For the 3D modeling of the pressure flushing, we mentioned specifically that the non-hydrostatic Navier-Stokes (NS) equations are solved (The NS equations are the standard in any fluid mechanics textbooks.)

6. - Turbulence model used and other settings are also needed. 

Reply: The same replies above apply to this comment. In the revised manuscript, the specific  turbulence model used for the pressure flushing modeling is added.

7. - General note: which of the figures are literature and which are your results should be clarified. Right now it is difficult to know and hence gauge the actual quality of the paper. 

Reply: We checked all figure again; the sources are provided in the figure caption if a figure is from a literation along with the references.