Review Reports - Hydraulic Planning in Insular Urban Territories: The Case of Madeira Island—Ribeira Brava

Round 1

Reviewer 1 Report

I only have a few minor comments:

The assessed work is very interesting and is based on a properly adopted methodology with the use of real data resources from the region under consideration, which is a particularly valuable value.
Due to the fact that the work uses impressive databases (e.g. The Regional Civil Engineering Laboratory of the Autonomous Region of Madeira and The National Water Resources Information System), the text should provides more detailed information about them.
There is only one oversight: there is no reference to Figure 1 in the text.
The study considers analyze the flood propensity and the optimization of counteracting the effects of typical (hydrological) floods caused by rainfall. It happens that they are accompanied by other delayed effects, resulting from a different type of flood, the so-called hydrogeological flood, which can change the soil-water relationship and affect local buildings and infrastructure. This is in particular true for areas of river valleys with a very low slope, where water spills beyond the river or canal and lingers for a long time. Especially, that it was found that the river mouth of the Ribeira Brava watershed doesn't have the capacity ti drain the rain flow for the return period. If there is a possibility of such a risk in the analyzed area, attention should be paid to it in the text (omit the comment if the discussed risk doesn't exist).

Author Response

Dear reviewer, I will now send you my responses to all suggestions for revisions. If any adjustments are needed, please do not hesitate to contact me.

Reviewer 1:

I only have a few minor comments:

The assessed work is very interesting and is based on a properly adopted methodology with the use of real data resources from the region under consideration, which is a particularly valuable value. – Only informative!
Due to the fact that the work uses impressive databases (e.g. The Regional Civil Engineering Laboratory of the Autonomous Region of Madeira and The National Water Resources Information System), the text should provides more detailed information about them. – Page 5, Page 7 and Page 13, I put this information. This institution only send to me the files with the respective data.
There is only one oversight: there is no reference to Figure 1 in the text. – Done.
The study considers analyze the flood propensity and the optimization of counteracting the effects of typical (hydrological) floods caused by rainfall. It happens that they are accompanied by other delayed effects, resulting from a different type of flood, the so-called hydrogeological flood, which can change the soil-water relationship and affect local buildings and infrastructure. This is in particular true for areas of river valleys with a very low slope, where water spills beyond the river or canal and lingers for a long time. Especially, that it was found that the river mouth of the Ribeira Brava watershed doesn't have the capacity ti drain the rain flow for the return period. If there is a possibility of such a risk in the analyzed area, attention should be paid to it in the text (omit the comment if the discussed risk doesn't exist). - With the information that I has write indifferent pages, is clear this point – In page 9 – I write this: … in case the runoff capacity of the river mouth is insufficient to drain the rain flow in the watershed and guarantee the established safety margin, it becomes necessary to size mitigation mechanisms, such as detention basins. – In page 16 – I write this: Since the primary objective of this research was to verify the need to implement simplified measures to mitigate the impacts of floods in the Ribeira Brava watershed, the use of the detention basin proved to be effective in controlling the flow at the river mouth, which can be characterized as a structural measure [32]. Initially, the Fill Rate values were 94%, 99% and 93% for the Rational, Giandotti and Mockus methodology, respectively, passing to 56% after the implementation of the measure. Therefore, it is evidenced that the chosen mitigation measure allows the river mouth to work below the 85% threshold, as indicated earlier. Furthermore, this study corroborates the flood risk analysis prepared by the Regional Directorate for Territorial Ordering and Environment (DROTA), Table 11, indicating an acceptable accuracy for the present study. – In page 16 – I write this: The results obtained in this study denote that the Ribeira Brava watershed is susceptible to floods during an extreme precipitation event, which is reinforced by the Flood Risk Report prepared by DROTA.

Author Response File: Author Response.pdf

Reviewer 2 Report

The article HYDRAULIC PLANNING IN INSULAR URBAN TERRITORIES: THE CASE OF MADEIRA ISLAND – RIBEIRA BRAVA fits thematically into the submitted journal. The aim was to study is to analyze the flood propensity of the main watercourse to suggest two methodologies to mitigate the impacts. For results the geomorphological data obtained from tthe SIG ArcGIS software. It was verified through the Manning-Strickler equation. The results correspond to the analyses performed, the authors propose appropriate recommendations.

I denote in my reading an extreme and demanding work, as well as the handling of various software.

An article that in itself values a true paradise - Madeira Island.

Author Response

Dear reviewer, I will now send you my responses to all suggestions for revisions. If any adjustments are needed, please do not hesitate to contact me.

Reviewer 2:

I denote in my reading an extreme and demanding work, as well as the handling of various software.

An article that in itself values a true paradise - Madeira Island. – Only informative!

Reviewer 3 Report

Please see the comments (word version).

Comments for author File: Comments.pdf

Author Response

Dear reviewer,

As described in the abstract, “The main objective of this study is to analyze the flood propensity of the main watercourse of Ribeira Brava drainage basin and, if necessary, to suggest two methodologies to mitigate the impacts - i.e. detention basin sizing and riverbed roughness coefficient adjustment”. Furthermore, this study corroborates the flood risk analysis prepared by the Regional Directorate for Territorial Ordering and Environment (DROTA) - Flood Risk Report prepared by DROTA.

This study, which I developed, intends to provide the watershed with a set of measures (detention basin and roughness coefficient adjustment), in order to maximize the capacity to drain the rain flow.

Therefore, the innovation of this study is associated with mitigation measures for this problem.

I will then answer each of the problems you identified, in front of it after the "-".

Manuscript Number: water-1387607

Title: HYDRAULIC PLANNING IN INSULAR URBAN TERRITORIES: THE CASE OF MADEIRA ISLAND – RIBEIRA BRAVA

The present study aims to undertake the hydrological analysis of the region, in order to verify the expected peak flow rate for a recurrence time of 100 years and then compare it with the drainage capacity of the stream mouth of the Ribeira Brava watershed. The results obtained in this study denote that the Ribeira Brava watershed is susceptible to floods during an extreme precipitation event, which is reinforced by the Flood Risk Report prepared by DROTA.

In general, the authors have done a lot of work for this study. However, this manuscript still needs some editing and revision.

Concretely, my main issues with this paper are the following:

In the Abstract section, the authors need to emphasize the innovation or discovery of this study in this part. In the current content, I did not find the innovation of this research. Therefore, I suggest that the author rewrite this part of the content. - As I described in my introduction, I intend to analyze the need for mitigation measures for this watershed.

In the Introduction section, the author needs to write clearly what are the deficiencies in previous studies. - As I described in my introduction, I was able to validate the information of the Flood Risk Report prepared by DROTA, however, I proposed effective mitigation measures. Page 2, where I put the following information:

Furthermore, mountainous regions are more prone to the occurrence of flash floods, since steep slopes allow a greater gravitational energy and, consequently, a greater destructive force for surface flows [12, 14]. Therefore, it is possible to ascertain that high-altitude volcanic islands such as Hawaii, Gran Canaria, Reunion and Madeira have geomorphological and lithological features that make them more susceptible and vulnerable to flooding [13 – 15].

With the increase of this problem globally and especially in tropical regions, it has become necessary to develop measures and devices to mitigate the impacts of floods [3 - 5]. Initially, the main guideline to urban drainage was the conventional principle of rapid removal of the cause of the problem, i.e., redirecting the excess flow from its origin to another location [5]. However, the principle of rapid removal of the problem, even if it is efficient for upstream regions, causes flooding to worsen in downstream areas. In this sense, there is only the convenient transfer of the problem from one area to another, without actually solving the problem at its source, which is established through anthropic actions, geomorphological and hydrological characteristics of the watershed. Therefore, it is verified that there is a need to use practices with the greatest capacity to mitigate the effects of floods, in other words, to establish effective procedures at the source of the problem, without redirecting the destructive effects from one zone to another [4, 5, 14, 16].

In the Autonomous Region of Madeira, there is no study of this kind, my intention is in the near future to develop the same for the 27 watersheds in the region.

Also in the Introduction section, in the last paragraph, the author emphasizes the purpose of this research. I suggest that the author sort out the possible innovations or discoveries in this research and reflect them in this paragraph. - Page 2, I think that with the following description I demonstrate the innovation of the study: … this study also aims to indicate a structural intervention for the stream mouth, with significantly reduced urban impacts. This intervention refers to changing the physical characteristics of the walls and riverbed of the stream, namely the roughness coefficient. Therefore, it will be verified the minimum characteristics of the stream in order to increase the drainage capacity, without the need for dimensional changes.

In Materials and Methods section, Figure 1 needs to add the latitude and longitude coordinate system. It is recommended to add a map showing the location of the study area. In page 2 – I write this: … the Ribeira Brava watershed - is located on the southern slope of Madeira Island, between latitudes 30º 01' N and 33º 08' N and longitudes 15º 51' W and 17º 30' W [17, 18].

Also in Materials and Methods section, the flowchart shown in Figure 3 is too simple. It is recommended that the author change this picture. The Figure should reflect the purpose, content, and methods of this research to make it a complete system. - I processed a new version of the flowchart, according to the methodology developed in the article.

Also in Materials and Methods section (Precipitation Analysis part), the data used in this analysis were obtained through public sources such as the National Water Resources Information System (SNIRH). It is recommended that the author add a detailed data URL link. - In page 7 – I write this: … The analysis of precipitation was based on data provided by the National Information System on Water Resources (SNIRH) [29]. The bibliographic reference 29 has the following description: 29. SNIRH (2021). Sistema Nacional de Informação de Recursos Hídricos. Disponível em: https://snirh.apambiente.pt/index.php?idMain=2&idItem=1&objCover=920123704&objSite=920685506; Acesso em: 20 de Junho de 2021.

Also in Materials and Methods section (Precipitation Analysis part), the authors mention that the Gumbel Distribution was chosen for precipitation. Why choose this probabilistic distribution? Do authors use multiple distributions and perform the fitting optimization process? - In page 7 – I write this: … Regarding the probabilistic methodology adopted, the Gumbel Distribution was chosen, since it showed a better fit with the data obtained and the expected projection for watersheds on the island of Madeira [25].

In carrying out this analysis I used different laws, such as: log-normal law or Galton's, Gumbel's, Pearson's III and normal law.

In the Results section, Figure 5 also needs to add the latitude and longitude coordinate system. In page 2 – I write this: … the Ribeira Brava watershed - is located on the southern slope of Madeira Island, between latitudes 30º 01' N and 33º 08' N and longitudes 15º 51' W and 17º 30' W [17, 18]. - Thus avoiding the repetition of information.

Also in the Results section, Figure 6 also needs to add the latitude and longitude coordinate system. In page 2 – I write this: … the Ribeira Brava watershed - is located on the southern slope of Madeira Island, between latitudes 30º 01' N and 33º 08' N and longitudes 15º 51' W and 17º 30' W [17, 18]. - Thus avoiding the repetition of information.

Also in the Results section, the author's analysis of the results is not in-depth, and it is only a simple explanation of the results at present. It is recommended that the author re-analyze this part in-depth and put the non-important results in the appendix. - In the results section, I placed the information (values of different parameters), necessary for the correct perception and development of the problem. If I put all the tables resulting from the calculation, the work will be too extensive, however I can send the Microsoft Excel files for a correct analysis and future definition.

In the Conclusions section, in this part, the author has shown too much the results of this research, and it is recommended that the author emphasize the innovations and discoveries of this research. - As I described in my introduction, I was able to validate the information of the Flood Risk Report prepared by DROTA, however, I proposed effective mitigation measures. Page 17, where I put the following information: This occurs because the stream bed has characteristics that are very unfavorable to surface runoff, as it has a surface with a significant presence of stones and vegetation. These characteristics of the riverbed reduce the velocity of the water flow and, consequently, reduce the drainage capacity, especially in areas with very low slope, such as the river mouth. Furthermore, the insufficient drainage capacity of the river mouth was demonstrated by 3/4 of the methodologies employed: Rational, Giandotti and Mockus.

Regarding the proposed simplified solutions, the Dutch Method did not present an applicability coherent with the pre-established urban premises, because it suggests very high lengths for the detention basin, higher than the length of the main watercourse. On the other hand, the Simplified Triangular Hydrograph Method presents satisfactory results, because it allows the implementation of the detention basin without changing the height or width of the stream.

Lastly, the change in the roughness coefficient also presented satisfactory and effective results for the mitigation of flood impacts, because it is a relatively simple measure to be proceeded and still meets the demand of the watershed under study.

I did not find any innovations in this research. Therefore, I emphasize again that the author needs to make a thorough summary of the innovations in this study. - As I described in my introduction, I was able to validate the information of the Flood Risk Report prepared by DROTA, however, I proposed effective mitigation measures.

If it is necessary to process any adjustments or want any further clarification, I will be fully available. Thank you very much for your insight and analysis of this study.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Accept in present form.

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

The paper is very interesting and well written.

- Literature review could be strengthened.

Conclusions should reinforce the association with similar studies and findings.

Reviewer 2 Report

Broad comments:

In my opinion, this manuscript does not present enough novelty and has several methodological major flaws. The duration of the daily rainfall data series is not enough to extrapolate the results of a return period of 100 years, which compromises all the results.

Specific comments:

The following are more specific/detailed comments and advices that should be considered:

- Page 2, line 52: a flood corresponds to fluvial flooding. In this sentence it is incorrect to mention floods and for this reason, floods should be replaced by flooding. In this specific context, floods correspond to urban flooding. Please verify throughout the document the different types of flooding.

- Page 2, line 55-56: probably flash floods.

- Page 2, lines 55-60: the concepts of susceptibility, hazard, propensity, proneness, severity, magnitude, damage, etc. are not clear in this manuscript. Please verify throughout the document. I suggest you read some hazard literature to clarify these terms. Suggestions: 1) Varnes (1984) Landslide hazard zonation: a review of principles and practice; 2) Julião et al (2009) Guia metodológico para a produção de cartografia municipal de risco e para a criação de sistemas de informação geográfica (SIG) de base municipal.

- Page 2, line 59: not only geomorphological, but also lithological. Not only susceptible, but also vulnerable.

- Page 2, line 61: “With the increase of this problem globally and especially in tropical regions”. References?

- Section 2.1: the presentation of the study area (Ribeira Brava watershed) must be more detailed. The physical features of Madeira should be more detailed too. There are no references to elevations, lithology, area/surface of the watershed (despite it is presented later on the text), the built-up areas in this watershed (through the SCS curve number, for example), etc. More references to the flooding history of Madeira/Ribeira Brava and to the extreme events would be helpful.

- Section 2.3: these parameters and formulas are well-known in this research field. So, it would be enough if you mention what were the used parameters, the references, and the respective justifications.

- Page 6, lines 223-225: the Gumbel distribution frequently generates an overestimation of the return periods. more data would be useful, in addition to the reference to a master's thesis. Additionally, the time of concentration of this drainage basin is much lower than the daily scale.

- Page 7, lines 260-264: “since the duration of precipitation is equal to the time of concentration of the watershed, using the total amount of daily precipitation in the hydrologic analysis would cause oversizing of hydraulic structures”. This is what I mentioned in my previous comment. You have identified the problem, but a solution is not presented.

- Section 2.5: it is not necessary to present all these formulas. Why was the Soil Conservation Service method not used? Nevertheless, both the rational method and SCS method present much lower results when compared to the reality.

Reviewer 3 Report

This manuscript is focused on the flood issues. The research contents in it are of great significance to defend people's lives, property and infrastructures. As a good case illustration, they involve assessment of flood propensity and measures for flood impacts mitigation. Two measures were analyzed, i.e. detention basin and roughness coefficient adjustment. Detention basin can be seen as a more eco-friendly and sustainable measure than engineering ones such as construction of a dam for flood prevention and control. And roughness coefficient adjustment is another alternative, which is easy to be implemented in practice. Generally, this manuscript has clear thinking and useful results. However, it still has several problems need to be solved.

(1) This manuscript is submitted to the section: Oceans and Coastal Zones, Port Structures, Maritime Transport and Tourism. But little relative descriptions can be found in it.

(2) In the title: “Insular Urban” means that Madeira is a special city. Regarding hydraulic planning, what makes it different from other cities? Is this specialty will affect the hydraulic planning? To what extent? And how? These did not showed in the text.

(3) It is better to clearly explain the novelty of this study, for example the progress of this study in terms of detention basin design compared with previous relevant studies.

(4) In the manuscript the detention basin and the roughness coefficient are assessed separately. I think it is necessary to explore their interactions and combined effects.

(5) It is suggested to write down the advantages of the two measures. For example, compared with reservoir, flood retention basins have been used widely (Yu et al., 2020) and may have less negative impact on the environment. Operation of reservoir can affect river water salinity and ground-water salinity (Xie et al., 2020).

Xie, W.P., Yang, J.S., Yao, R.J. and Wang, X.P., 2020. Impact Study of Impoundment of the Three Gorges Reservoir on Salt-Water Dynamics and Soil Salinity in the Yangtze River Estuary. Journal of Environmental Informatics, 36(1), 11-23.

Yu, B.Y., Wu, P., Sui, J., Ni, J. and Whitcombe, T., 2020. Variation of Runoff and Sediment Transport in the Huai River–A Case Study. Journal of Environmental Informatics, 35(2), 138-147.

(6) Is climate change are affecting flood in the studied area? To discuss it is necessary for ensuring the study is systematic. Therefore climate change relevant papers such as the following ones are suggested to be cited.

Shrestha, N.K. and Wang, J., 2020. Water Quality Management of a Cold Climate Region Watershed in Changing Climate. Journal of Environmental Informatics, 35(1), 56-80.

Li, Z., Li, J.J. and Shi, X.P., 2020. A Two-Stage Multisite and Multivariate Weather Generator. Journal of Environmental Informatics, 35(2), 148-159.

P. Fu, G. H. Huang, L. R. Liu, and M. Y. Zhai, A factorial CGE model for analyzing the impacts of stepped carbon tax on Chinese economy and carbon emission, Science of the Total Environment (Elsevier), 759, Article 143512 (2021). (SCI IF = 6.551)

(7) Other problems.

In line 110 in Figure 3: I wonder if “Basis” in “Detention Basis” is a typo. It should be “Basin”?

In line 112: To ensure the repeatability of the study, which database did the authors use for the “extensive literature review”? It is suggested to explicitly mention it.

In line 120: Please place the references where they are actually cited.

In line 105: As for the statement of “which can be easily verified in situ”, it is better to provide a panorama of the river to enhance persuasion.

In line 215: “A = Watershed area, km²;”, I've already seen this symbol in line 152. It is unnecessary to repeat it in the following paragraphs. The similar problem appeared in line 312 and 320: “t_C = Concentration time, hours”. And in lines relevant to Qp.

In line 122-123: To be consistent and to avoid confusion, it is better to change rainfall into precipitation.

In line 240: n’ should be the number of samples minus 1, since S’ denotes sample standard deviation.

In line 341: Use “if” instead of “since”?

In line 471-472: “Simplified Triangular Hydrograph” should be “STH” because the acronym of it has already been mentioned in the previous paragraph.