Assessment of Baseflow Separation Methods Used in the Estimations of Design-Related Storm Hydrographs Across Various Return Periods

Round 1

Reviewer 1 Report (Previous Reviewer 1)

Comments and Suggestions for Authors

I am of the opinion that it can be accepted.

Author Response

Dear reviewer:

Please see the enclosed file.

Kind regards,

The authors

Author Response File: Author Response.docx

Reviewer 2 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

I reviewed the new version of the article, but since there was no red response file from the authors, I could not understand how the changes were made. However, my thoughts did not change:

1) I still do not think the references are sufficient.
2) I suggested a comparison with a second station. That was not done either.
3) I requested that discussions and suggestions be added to the findings and results. That was not done either.
4) I still have the same thoughts about the working language. It resembles a technical note rather than a scientific article.

Author Response

Dear reviewer:

Please see the enclosed file.

Kind regards,

The authors

Author Response File: Author Response.docx

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

The manuscript deals with the estimation of design storm hydrographs. A method is proposed to derive storm hydrographs for different return periods based on hydrological station data, adopting five different baseflow separation methods.

The manuscript is an original contribution. It addresses the aims of Hydrology and the topic is of interest for the readership of the Journal. The analysis on a real case study (i.e.,

the Lengupá River watershed in Colombia) strengthens the research.

English language is clear, and the presentation is satisfactory; anyway, I have detected some criticisms in the text that should be properly addressed.

The Authors can benefit from the comments below to improve their paper. These have to be accomplished before manuscript acceptance.

 

 

Abstract

The abstract is concise and reflects the content of the article. It summarizes the main outcomes of the study.

 

 

Keywords

Ok, the provided four keywords are informative and useful for indexing purposes.

 

 

Introduction

The Section is well arranged; aims of the study are properly clarified and relevant references are included.

Lines 32-34: Concerning the importance of proper estimation of storm hydrographs, in addition to the mentioned design and development of engineering projects such as dams, diversion structures, urban drainage systems, and channels, Authors are recommended to include the importance of an accurate estimate of the flood hydrograph also for the purposes of a reliable estimate of the pollutant load in stormwater runoff. In this regards, Authors should consider to include the following references to enhance the introductory discussion:

• New optimization strategies for SWMM modeling of stormwater quality applications in urban area. Journal of Environmental Management 361:121244, https://doi.org/10.1016/j.jenvman.2024.121244.
• Stormwater quality models: performance and sensitivity analysis. Water Sci. Technol. 62, 837–843, https://doi.org/10.2166/wst.2010.325.

 

Lines 54-56: Authors are recommended to include EPA-SWMM to the list of software packages used for rainfall-runoff modelling.

 

 

Methodology

This section is clear and adequately detailed. The provided figures are clear and necessary for the presentation. Authors may consider including some relevant references to highlight the advantages and the most appropriate application context of each of the presented baseflow methods.

In figure 3 panel b) “t_e” is not indicated. Please, check equation (4).

Lines 201: Please specify that “Annex 1” is or provide a proper reference.

 

 

Practical application

This section is presented in a logical sequence. It is quite clear even if some improvement is recommended.

Authors are recommended to add some information on the watershed upstream of the Páez hydrological station, i.e. surface area, average slope.

Line 253-254: cells are highlighted with green and grey colors; blue is not used.

Authors should better justify why the storm hydrographs from 1996, 1997, and 1998 have been used to apply the methods proposed in this study.

Line 313: Table 3 can be eliminated since its contents are also indicated in the text.

 

 

Discussion

Discussion is interesting. Advantages and limitations of the study are properly highlighted.

 

 

Conclusions

Conclusions seem reasonable and supported by the results.

 

 

References

Two reference are recommended in the “Introduction” section regarding the importance of an accurate estimate of the flood hydrograph also for the purposes of a reliable estimate of the pollutant load in stormwater runoff. Some references are suggested in the “Methodology” section to highlight the advantages and the most appropriate application context of each of the presented baseflow methods. Apart from these references, based on my knowledge, no important reference is missing.

Author Response

Dear reviewer:

Please see the enclosed file.

Kind regards,

The authors

Author Response File: Author Response.docx

Reviewer 4 Report (New Reviewer)

Comments and Suggestions for Authors

The expression “using the constant, linear, and master recession curve methods” appears repeatedly in the manuscript (e.g., Lines 75, 87, 133, and 277). This phrasing should be revised for improved readability and consistency. Additionally, other methods—such as the Boussinesq and isotopic methods—are introduced in parts of the text (including Figure 1), though they are not clearly utilized in the analysis. The manuscript should clearly state how many methods are actually applied in the present study and remove any unnecessary or unused methods to avoid confusion.

The authors have non-dimensionalized the hydrograph in Figure 2b. However, the methodology used for this process is not explained in the main text. While an equation is provided in the figure caption, a clear and concise explanation should also be included in the text to ensure reader comprehension.

In several instances, the use of symbols for different parameters is inconsistent and potentially confusing. For example, the symbol “q” represents non-dimensional discharge in Figure 2b but is later used to denote instantaneous discharge in Figure 3. To improve clarity and consistency, the authors are advised to provide a list of symbols and notations and ensure uniform usage throughout the manuscript.

To reduce redundancy, it is recommended that Section 2.3 be merged into Section 2.2.

In Table 6, five stations are listed, but it is unclear why some are included despite not being used in the study. All stations actually used in the analysis should be clearly described in the Methods section, or alternatively in Section 3.1 where the main station is discussed.

Finally, the Discussion section would benefit from improvement by including comparisons of the findings with those of similar studies. This would help contextualize the results and strengthen the scientific contribution of the work.

Author Response

Dear reviewer:

Please see the enclosed file.

Kind regards,

The authors

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

The manuscript has been significantly improved following the recommendations of the Reviewers; all my concerns have been addressed and convincingly justified.

Author Response

Thank you so much

Reviewer 4 Report (New Reviewer)

Comments and Suggestions for Authors

The Authors have revised their manuscript according to the comments. I have just one minor comment:

In table 7, the Authors have compared the "computed" against "measured" values.  I do not have access to the mentioned reference (oronado-Hernández 2010) that the authors have used for this comparison, but it seems to me that it does not include 200 years of flow recording to be be considered as "measured" value in the studied rivers. The authors should revise the titles in this table or add an explanation in the text to clarify this issue.

Author Response

Dear Reviewer:

Please see the enclosed file.

Kind regards,

The authors

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I would like to congratulate the authors for their work. I have evaluated article “Assessment of Baseflow Separation Methods for Estimating Design Storm Hydrographs Across Various Return Periods ” and my suggestions are below.

This study comparatively analyzes five different baseflow separation methods for the estimation of the design storm hydrograph, which is critical for the design of hydraulic structures against heavy rainfall events. The research is based on data from the Páez hydrological station on the Lengupá River in Colombia. The methods include constant baseflow, linear separation, master recession curve, Boussinesq-based physical approach and isotope-based chemical approach. The results show that the linear method in particular gives the most successful predictions with low error rates (RMSE: 0.45%).

I am of the opinion that it can be accepted after the following major revision.

Recommendations:

 

• The abstract outlines the methodology and findings, but numerical findings such as RMSE should be clearly highlighted at the end of the abstract
• Some formulas contain complex expressions. Equation references (e.g. Eq. 2, Eq. 7) should be better linked in the text.
• The parameter calibration process should be explained more clearly. For example, how was the K (recession constant) value determined?
• The sub-explanations of the graphs are insufficient. It should be more clearly stated what is shown by which method in each graph.
• There are some typos and should be revised, e.g:

Page 13 “To generate the strom hydrograph...” storm hydrograph

Page 6 “Constat baseflow” Constant baseflow

Page 15 “the recession constant (𝐾 )” the recession constant (𝐾) (space should be deleted)

 

• The finding that the linear method gives the best results with low RMSE is quite strong. However, why this method performs better (in a physical sense) needs to be discussed.
• The discussion on the applicability of the Boussinesq and isotope methods is only mentioned in the conclusion with a suggestion for “future work”. Possible field challenges or data requirements should be mentioned.
• The Practical Application section has a strong emphasis on the integration of the work into field applications. However, the section should be more balanced, addressing limitations and uncertainties as well as advantages. It should also provide more concrete examples of where the methods can directly contribute to engineering or policy processes.
• There is no general comment on how valid the method is in different climatic and geographical regions. For example, the applicability in tropical, semi-arid or mountainous regions is not questioned.
• The application section is only at the engineering level; it could be linked to decision-making processes such as water management policies, basin planning, etc.

Reviewer 2 Report

Comments and Suggestions for Authors

In this study, a hydrological method was developed based on flow data obtained from a limnigraph on a Colombian stream and base flow was determined according to five basic flow separation techniques.

After deciding on the base flow separation method, frequency analysis was performed at various repetition times of the design hydrographs.

The method and equations used in the study are sufficient.
The tables and figures created are suitable for the study.
As a result, the linear base flow separation method found according to the low RMSE value was determined and frequency analysis was performed according to this method.

I would like to suggest short additions to the study and ask a number of questions..
1) Could a comparison be made using more than one flow observation station data?
2) Could a regional frequency analysis be considered by selecting not only the station at the basin outlet but also some flow observation stations in the upper regions?
3) The findings obtained should be discussed in more detail.
4) Comprehensive information should be added to the results section of the study regarding what the research will contribute to science and what kind of problems it will solve in practice.

Comments on the Quality of English Language

The English could be improved to more clearly express the research.

The written language of the study is not sufficient. It should be enriched with fluent and detailed expressions.

Reviewer 3 Report

Comments and Suggestions for Authors

This paper deals with baseflow separation methods. The primary objective is to enhance the modelling of design storm hydrographs for various return periods, where new formulations for computing storm hydrographs for different return periods are proposed. However, the new formulations are based on equation (1), which is, in my opinion, incorrect. The last term (integral) looks odd, and it cannot produce VM,R. I assume that the correct form of the last term implies integral of only q(t), which is multiplied then by QB,R(tp). Consequently, all remaining calculations are pointless.