How economically and environmentally viable are multiple dams? A hydro-economic analysis using a landscape-based hydrological model at the basin scale

Ekka, Anjana; Jiang, Yong; Pande, Saket; van der Zaag, Pieter

doi:https://doi.org/10.5194/hess-2023-10

Preprints

https://doi.org/10.5194/hess-2023-10

Preprints

15 Feb 2023

| 15 Feb 2023

Status: this discussion paper is a preprint. It has been under review for the journal Hydrology and Earth System Sciences (HESS). The manuscript was not accepted for further review after discussion.

How economically and environmentally viable are multiple dams? A hydro-economic analysis using a landscape-based hydrological model at the basin scale

Anjana Ekka, Yong Jiang, Saket Pande, and Pieter van der Zaag

Abstract. The construction of dams threats the health of watershed ecosystems. To address the health challenge requires a clear understanding of the hydrologic effects of multiple dams with concurrent disturbances at the basin scale and their impact on watershed ecosystems. The purpose of the study is to illustrate how multiple dams in a basin can impact hydrological flow regimes and subsequently aquatic ecosystems that depend on river flows. This study develops a hydro-economic approach to assessing the effects of multiple dams on river ecosystem services under varying scenarios of spatially located reservoirs in the Upper Cauvery River basin, a heavily altered river basin in India. The approach integrates a landscape-based hydrological model with an embedded reservoir operations model to support hydro-economic analysis at the basin scale. The hydrological impacts of different combinations of reservoirs are quantified using Indicators of Hydrologic Alteration (IHA). Further, the production of two major ecosystem services, fish species richness and agricultural production, that depend on flow regimes is estimated, with a production possibility frontier for the two services derived. Results show that smaller reservoirs on lower-order streams that maximize the economic value of water stored are better for the basin economy and the environment than bigger reservoirs. Growing high-value crops in a command area can maximize the value of stored water and, with lower storage, generate similar economic value while reducing hydrological alterations. The proposed approach can help water and river basin managers to understand the provision of ecosystem services in hydrologically altered basins, optimize dam operations, or even prioritize dam removal with the balanced provision of ecosystem services.

Received: 09 Jan 2023 – Discussion started: 15 Feb 2023

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Anjana Ekka et al.

Status: closed

RC1:
'Comment on hess-2023-10', Anonymous Referee #1, 07 Apr 2023

The study investigates impacts of multiple reservoirs in the hydrological regime affecting fish species richness and agricultural productivity in the Upper Cauvery River basin in India. The study is quite relevant as it aims to address tradeoff between economic value and environmental consequences of building multiple reservoirs across the basin. The study seems useful to understand environmental challenges related to the four reservoirs in the Upper Cauvery River basin.
Although the aim and objectives are quite strong, the method and analysis are not, and the discussion seems superficial. The study overlooked several aspects of model assumptions, physical hydrological processes, and several methods are only superficially described, thus the result and conclusion, as of now, is quite limited and do not warrant a novel contribution. The overall quality of current manuscript is fair, and it requires clear articulation of key takeaways and analysis. I do not recommend publication of current manuscript without significant improvements.
General comments
1). The model should be properly described. It lacks basic explanation of what the variables and parameters are? What are the input and output of the model? How is the model simulated? Which parameters are calibrated? The calibration results are not presented. How the flow regime was generated, and which time frame was considered for simulation is unclear.
2). The overall approach is to compare scenarios of current state of 4 reservoirs vs. not having one or more reservoirs. From rather planning perspective, isn’t the more important question is if the smaller multiple reservoirs are better or worse than single or fewer larger reservoirs given all the water demand needs are met? Please mention what are your research questions.
3). The agriculture production and environmental consequences are currently tied to regulated water and scenarios of the number of reservoirs, but it seems like reservoir operations and seasonal influence of streamflow is overlooked in result analysis. As it mentions “embedded reservoir model”, I believe it is incorporated in the model, but it is not clearly described in manuscript.
4). Please define fish species richness. What types of fish species are considered here? Just the number is considered or their migration pattern as well. Is the fish species richness as an indicator enough to describe ecosystem health. Why was the fish species richness only based on the empirical function, and how the equation 3 was adopted and validated for this study basin? Given the size of the basin, does a single FSR value for the whole river networks adequate? Are there any other indexes which was not used in this study due to any limitations? Any such limitations should be mentioned.
Specific comments
5). Section 2.3: Please mention the quality of data obtained. If there are any data gaps, if so, how the data gaps were addressed?
6). Section 2.4: Please provide the parameters that are calibrated. Line 162 mentions it is calibrated based on downstream streamflow, but line 172 mentions target range of metrics with unit as mm/day. Any reason for not using the flow unit here? Why only the downstream flow was compared, is it because inflow was a model input? It is not very clear. Also, please mention the population size, number of generations used, and crossover and mutation probability used and how those parameter values were determined?
7). Line 181-182: What is landscape model? Also, the sentence is confusing to read.
8). Figure 5: It looks like station T. Narasipur is along the same channel upstream of Kollegal as per Figure 3, although reservoir C is on tributary. If it is on tributary, it should be mentioned somewhere to avoid confusion.
9). What is the significance of the hydrological sub-basin watershed delineation in this study with regards to hydrology since it is not a physical based model. How the watersheds are delineated – is it using ArcGIS Hydrology tools, please mention that? Does the line 184 says the sub-basin for reservoir KRS is delineated with Kollegal station as outlet? But it looks like the reservoir is far upstream from this point.
10). Section 2.6: Which indicators are considered, and which are important for this study? Why the IHA was used? It would be useful to mention here.
11). Line 211 – 215: The introduction of PPF can be improved. Currently it seems inadequate, linking it to the objective of this study and why this tool/graph is ideal would be better. How was it generated should be explained in methods? I also think Figure 12 is a great visualization.
12). Section 3.1: The use of term “spatial configuration” is vague. Generally, it could mean configuration in term of location, storage size, total number, or design configuration of reservoirs using an algorithmic approach. Currently it is not the case in this study, as it is just combinations of reservoirs, so it should be rephrased correctly.
13). Section 3.1.1: What is the location in the catchment that the mean annual flow refers to in Figure 6? Line 282 – “The highest mean annual flow was estimated for S₀ followed by S_c and S_b”. This seems to be obvious since the flow in unregulated without any reservoir in S₀ scenario and the contributing areas of the reservoirs in S_cand S_bscenariosmakes up only a small portion of the catchment area. Line 289 – “S_abd has less impact compared to S_acd despite Kabini (C) having less storage capacity compared to the Hemavathi reservoir (B)”. The mean annual flow is not only the function of reservoir volume, but perhaps the contributing area, land use, water use, precipitation pattern (not sure what is the time span considered!) and other properties which was not addressed in the study and the results are poorly presented.
14). Figure 6: It is redundant with Table 2 (Mean annual flow column). Presenting hydrographs would be more informative than Figure 6 since there are only 16 scenarios and expanding the discussion on the role of reservoirs and seasonal streamflow.
15). Section 3.1.2: Line 300-310 – Similar to the above comment, the presentation of the result is very obvious because KRS (D) has the largest capacity and any combination with S_D result is lowest annual extreme flow with the exception for S_C which has comparative higher outflows being the only hydroelectric reservoir.
16). Table 2: It is not clear what are the other hydrological and environmental indicators besides mean annual flow. Perhaps it is better to define it somewhere.
17). Line 306 – 310: A reference to figure would be useful here.
18). Section 3.1.3: Line 324-333 – Residence time is briefly introduced for the first time here without introducing reservoir operations at all. Also, till here the description was based only on the size of reservoirs. It seems there are significant seasonal effects of streamflow and reservoirs operation which is overlooked. Further it describes A is significantly small in capacity than B, A has short residence time than B, and the unregulated flow in B is less than in A, however S_A has higher impact in flow regime than S_B. Does this indicate this larger reservoir is contributing to flow regime? Currently there is not adequate analysis to conclude.
19). Line 351: Again, it is unclear how the economic value for different crops is estimated, and Section 2.7.1 and equation 2 offers very little description.
20). Figure 11: Although the mean annual flow is higher in S_c and S_a, why is FSR lower in Sc compared to S_a and S_b, despite S_c being hydroelectric reservoir? Is it also a function of low flow frequency? I think it require more discussions. And perhaps referring it back to Table 2 would be helpful.
21). Line 395: “The findings show that the scenario without any reservoir (S₀) is advantageous for the diversity of fish species.” This kind of argument does not offer any practical solution, rather what is the optimum FSR, or what is the critical threshold that should not be exceeded would be helpful.
22). Section 4.1: As commented above, the discussion seems rather superficial. Looking into seasonal streamflow effects could be an improvement.
Technical corrections
23). Just a suggestion, it would be easier for readers to visualize the size and contributing area of the reservoirs if Figure 3 and 4 is combined, and even color code the names of the reservoirs in Figure 3 as in Figure 4. Lat/Lon reference in Figure 3 will further improve the figure.
24). Line 182 - 188: It is unclear how the sub-basin is delineated; figure 3 reference would be useful.
25). Table 1: In 1^st row, 4^th column, what is “For individual reservoir”?
26). Line 276: The whole sentence and the meaning of “disentangled” is unclear.
27). Line 294: “However, in combinations with one and no reservoir..”. The sentence is unclear.
28). Line 347: Cite the relevant source.
29). Use of sub-basin name and reservoir name (e.g in Figure 8a and b) and throughout the manuscript is inconsistent. Keeping it consistent would help the readers.
30). Line 363: Generally, instead of saying, “The scenario of 4 dams generates the highest economic value from agricultural production.”, it would be better to write, “Presence of all four dams in the basin generates the highest economic value from agricultural production.”
31). Figure 9: Please keep the range of vertical axes uniform in all figure panels, if possible.

Citation: https://doi.org/10.5194/hess-2023-10-RC1
- AC1: 'Reply on RC1', Anjana Ekka, 11 Jul 2023
  
  Dear reviewer, thank you for your valuable feedback. We have taken into account the insightful suggestions provided, which have allowed us to elaborate further on the content and improve the overall quality of the paper. The responses to the comments are presented in a two-column format and have been submitted as an attachment.
  
  Citation: https://doi.org/10.5194/hess-2023-10-AC1
RC2:
'Comment on hess-2023-10', Anonymous Referee #2, 17 Apr 2023
It's a paper that addresses a relevant issue related to the integrated economic-environmental analysis of infrastructure projects at the basin scale. The paper presents a case study with a series of analyses of different dimensions of impacts (change in flow regimes, fish species richness) and benefits (irrigation/crop production, hydropower) associated with the operation of a series of reservoirs in the Cauvery river basin (India).
While the topic and scope of the work is relevant from a scientific literature perspective, the paper has several important deficiencies, and my suggestion is that the authors go through a major revision process.
The paper's deficiencies fall into two categories. First, those related to how the overall study supports the claims or conclusions presented in the title or the discussion/conclusion sections. Second, those related to the justification/documentation of the specific methodologies used to evaluate each of the proposed environmental or economic components of the proposed framework. Here are my comments on each of these groups:
1. Comments on how the overall study supports the conclusions presented in the title or discussion/conclusion sections.
The title itself suggests that the paper may include a framework that addresses the integrated economic-environmental viability of dams. Indeed, this is a very important issue. However, the paper itself has no actual definition of what a "viable" set of dams is, how the scenarios compared differ in terms of their "viability". The title is therefore misleading. The actual scope is essentially a trade-off analysis between dam implementation scenarios for some of the 4 objectives considered, without offering a critical analysis of the viability of the resulting metrics across scenarios, and simply focusing on comparing values. Is any of the configurations shown in the scenarios economically-environmentally viable, and if so, for whom?
In order to coherently approach the statement in the title, I consider that the authors need to provide:
A definition of what is a viable configuration of dams. There are several possibilities. For example, it could be based on stakeholder preferences and/or, from a purely phenomenological perspective, the identification of boundaries or tipping points in the system that may preclude the functioning of a key component, e.g., fish biodiversity, agriculture, energy production, etc.

Evidence that the proposed components and indicators are relevant in the context of the proposed case study stakeholders, and that these indicators can be quantified with a reasonable degree of certainty. It is not clear in the paper why the 4 selected indicators were chosen and whether they are representative of system processes or priorities. See comment section 2 for some details.

A revised analysis of the interaction between environmental and economic objectives. The current Pareto production frontier analysis only considers the economic component from the perspective of the value of crops, leaving out the monetary value of fisheries, energy, etc.

2. Comments on the specific methodologies used to evaluate each of the proposed environmental or economic components of the proposed framework.
In its current form, the paper describes too succinctly many key components of the analytical framework presented in Figure 1, leaving important gaps in the justification of the selected metrics and the methods used to quantify them. It is understandable that, given the conceptual scope of the work, simplification in the main text may be necessary. However, supplementary materials are required to provide additional details that ensure reproducibility and clarity.
Similarly, there appear to be some important limitations in the proposed analytical components. The four most prevalent are as follows:
Hydrological modelling: It is not clear whether the "landscape hydrological model" is essentially the same as that presented in Ekka et al. (2022), or whether new calibrations were performed for this paper. In any case, the reported performance of the model is relatively low (NSE criteria are considered acceptable in the range of +0.2 to +0.5, and good above +0.5. The reported scores are all negative). There is also no mention of the modeling period (assumed to be the same as in Ekka et al., 2022, is 3 years?) Low performance levels can significantly affect the ability to implement data intensive methods such as IHA.

IHA methodology application is not sufficiently justifies or documented: In the case of freshwater habitat alterations, the paper selected a subset of IHAs. Why the IHA approach and why a subset of IHA indicators? Why not consider other aspects of physical habitat change such as fragmentation, sediment trapping, etc.? Also, can the IHAs be calculated with a reasonable level of confidence given the significant margin of error in several flow components of the hydrologic model?

Fish species richness is not an ecosystem service. It is a metric of biodiversity on evolutionary timescales (i.e., how biophysical processes over thousands to millions of years have produced a particular assemblage of species in a region). More importantly, it does not necessarily explain provision services such as fisheries productivity (for example, aquaculture in reservoirs typically has very high productivity with very low biodiversity).

The estimation of fish species richness was based on a global statistical model developed with the purpose of explaining the global distribution of biodiversity, but NOT of predicting changes in biodiversity based on short term changes in flows. Also, the cited model was developed based on global datasets with no source data in areas such as the case study, and no reference to validation is made. The proposed model is NOT appropriate for this study, as it suggests that by increasing the mean flows over a few years, you’d expect to increase biodiversity in the basin, which is probably not the case.

Therefore, the adoption of the Fish Species richness and model based on flow as a predictor of freshwater ecosystem services is not adequate for the analytical purposes stated in the paper, and must be revised.

The Production Possibility Frontier generalizes far beyond the data point ranges. It is not clear how the authors arrived at the shape of the PPF given the sparse data points of the model output. Also, the PPF is based on a partial analysis of the monetary value of the system's production and is therefore not representative of the production possibilities of the basin, but only of one sector.

Besides the major points mentioned above, it is also worth noting that the formal presentation of contextual data and results, such as maps, tables, and graphs, is sometimes redundant. For example,
Table 2 shows the same information as Figures 9 and 10

The maps/graphs shown in Figures 2, 3, 4, and 5 could be combined into a single figure.

In conclusion, in the opinion of this reviewer, a major revision of the methods and analysis is required for the publication of the paper. Likewise, supplementary materials with descriptions and data are required to illustrate with sufficient detail each of the analytical components developed. Supplementary data sets to allow for reproducibility are strongly encouraged.
Citation: https://doi.org/10.5194/hess-2023-10-RC2
- AC2: 'Reply on RC2', Anjana Ekka, 11 Jul 2023
  
  Dear reviewer, thank you for your valuable feedback. We have taken into account the insightful suggestions provided, which have allowed us to elaborate further on the content and improve the overall quality of the paper. The responses to the comments are presented in a two-column format and have been submitted as an attachment.
  
  Citation: https://doi.org/10.5194/hess-2023-10-AC2

Status: closed

RC1:
'Comment on hess-2023-10', Anonymous Referee #1, 07 Apr 2023

The study investigates impacts of multiple reservoirs in the hydrological regime affecting fish species richness and agricultural productivity in the Upper Cauvery River basin in India. The study is quite relevant as it aims to address tradeoff between economic value and environmental consequences of building multiple reservoirs across the basin. The study seems useful to understand environmental challenges related to the four reservoirs in the Upper Cauvery River basin.
Although the aim and objectives are quite strong, the method and analysis are not, and the discussion seems superficial. The study overlooked several aspects of model assumptions, physical hydrological processes, and several methods are only superficially described, thus the result and conclusion, as of now, is quite limited and do not warrant a novel contribution. The overall quality of current manuscript is fair, and it requires clear articulation of key takeaways and analysis. I do not recommend publication of current manuscript without significant improvements.
General comments
1). The model should be properly described. It lacks basic explanation of what the variables and parameters are? What are the input and output of the model? How is the model simulated? Which parameters are calibrated? The calibration results are not presented. How the flow regime was generated, and which time frame was considered for simulation is unclear.
2). The overall approach is to compare scenarios of current state of 4 reservoirs vs. not having one or more reservoirs. From rather planning perspective, isn’t the more important question is if the smaller multiple reservoirs are better or worse than single or fewer larger reservoirs given all the water demand needs are met? Please mention what are your research questions.
3). The agriculture production and environmental consequences are currently tied to regulated water and scenarios of the number of reservoirs, but it seems like reservoir operations and seasonal influence of streamflow is overlooked in result analysis. As it mentions “embedded reservoir model”, I believe it is incorporated in the model, but it is not clearly described in manuscript.
4). Please define fish species richness. What types of fish species are considered here? Just the number is considered or their migration pattern as well. Is the fish species richness as an indicator enough to describe ecosystem health. Why was the fish species richness only based on the empirical function, and how the equation 3 was adopted and validated for this study basin? Given the size of the basin, does a single FSR value for the whole river networks adequate? Are there any other indexes which was not used in this study due to any limitations? Any such limitations should be mentioned.
Specific comments
5). Section 2.3: Please mention the quality of data obtained. If there are any data gaps, if so, how the data gaps were addressed?
6). Section 2.4: Please provide the parameters that are calibrated. Line 162 mentions it is calibrated based on downstream streamflow, but line 172 mentions target range of metrics with unit as mm/day. Any reason for not using the flow unit here? Why only the downstream flow was compared, is it because inflow was a model input? It is not very clear. Also, please mention the population size, number of generations used, and crossover and mutation probability used and how those parameter values were determined?
7). Line 181-182: What is landscape model? Also, the sentence is confusing to read.
8). Figure 5: It looks like station T. Narasipur is along the same channel upstream of Kollegal as per Figure 3, although reservoir C is on tributary. If it is on tributary, it should be mentioned somewhere to avoid confusion.
9). What is the significance of the hydrological sub-basin watershed delineation in this study with regards to hydrology since it is not a physical based model. How the watersheds are delineated – is it using ArcGIS Hydrology tools, please mention that? Does the line 184 says the sub-basin for reservoir KRS is delineated with Kollegal station as outlet? But it looks like the reservoir is far upstream from this point.
10). Section 2.6: Which indicators are considered, and which are important for this study? Why the IHA was used? It would be useful to mention here.
11). Line 211 – 215: The introduction of PPF can be improved. Currently it seems inadequate, linking it to the objective of this study and why this tool/graph is ideal would be better. How was it generated should be explained in methods? I also think Figure 12 is a great visualization.
12). Section 3.1: The use of term “spatial configuration” is vague. Generally, it could mean configuration in term of location, storage size, total number, or design configuration of reservoirs using an algorithmic approach. Currently it is not the case in this study, as it is just combinations of reservoirs, so it should be rephrased correctly.
13). Section 3.1.1: What is the location in the catchment that the mean annual flow refers to in Figure 6? Line 282 – “The highest mean annual flow was estimated for S₀ followed by S_c and S_b”. This seems to be obvious since the flow in unregulated without any reservoir in S₀ scenario and the contributing areas of the reservoirs in S_cand S_bscenariosmakes up only a small portion of the catchment area. Line 289 – “S_abd has less impact compared to S_acd despite Kabini (C) having less storage capacity compared to the Hemavathi reservoir (B)”. The mean annual flow is not only the function of reservoir volume, but perhaps the contributing area, land use, water use, precipitation pattern (not sure what is the time span considered!) and other properties which was not addressed in the study and the results are poorly presented.
14). Figure 6: It is redundant with Table 2 (Mean annual flow column). Presenting hydrographs would be more informative than Figure 6 since there are only 16 scenarios and expanding the discussion on the role of reservoirs and seasonal streamflow.
15). Section 3.1.2: Line 300-310 – Similar to the above comment, the presentation of the result is very obvious because KRS (D) has the largest capacity and any combination with S_D result is lowest annual extreme flow with the exception for S_C which has comparative higher outflows being the only hydroelectric reservoir.
16). Table 2: It is not clear what are the other hydrological and environmental indicators besides mean annual flow. Perhaps it is better to define it somewhere.
17). Line 306 – 310: A reference to figure would be useful here.
18). Section 3.1.3: Line 324-333 – Residence time is briefly introduced for the first time here without introducing reservoir operations at all. Also, till here the description was based only on the size of reservoirs. It seems there are significant seasonal effects of streamflow and reservoirs operation which is overlooked. Further it describes A is significantly small in capacity than B, A has short residence time than B, and the unregulated flow in B is less than in A, however S_A has higher impact in flow regime than S_B. Does this indicate this larger reservoir is contributing to flow regime? Currently there is not adequate analysis to conclude.
19). Line 351: Again, it is unclear how the economic value for different crops is estimated, and Section 2.7.1 and equation 2 offers very little description.
20). Figure 11: Although the mean annual flow is higher in S_c and S_a, why is FSR lower in Sc compared to S_a and S_b, despite S_c being hydroelectric reservoir? Is it also a function of low flow frequency? I think it require more discussions. And perhaps referring it back to Table 2 would be helpful.
21). Line 395: “The findings show that the scenario without any reservoir (S₀) is advantageous for the diversity of fish species.” This kind of argument does not offer any practical solution, rather what is the optimum FSR, or what is the critical threshold that should not be exceeded would be helpful.
22). Section 4.1: As commented above, the discussion seems rather superficial. Looking into seasonal streamflow effects could be an improvement.
Technical corrections
23). Just a suggestion, it would be easier for readers to visualize the size and contributing area of the reservoirs if Figure 3 and 4 is combined, and even color code the names of the reservoirs in Figure 3 as in Figure 4. Lat/Lon reference in Figure 3 will further improve the figure.
24). Line 182 - 188: It is unclear how the sub-basin is delineated; figure 3 reference would be useful.
25). Table 1: In 1^st row, 4^th column, what is “For individual reservoir”?
26). Line 276: The whole sentence and the meaning of “disentangled” is unclear.
27). Line 294: “However, in combinations with one and no reservoir..”. The sentence is unclear.
28). Line 347: Cite the relevant source.
29). Use of sub-basin name and reservoir name (e.g in Figure 8a and b) and throughout the manuscript is inconsistent. Keeping it consistent would help the readers.
30). Line 363: Generally, instead of saying, “The scenario of 4 dams generates the highest economic value from agricultural production.”, it would be better to write, “Presence of all four dams in the basin generates the highest economic value from agricultural production.”
31). Figure 9: Please keep the range of vertical axes uniform in all figure panels, if possible.

Citation: https://doi.org/10.5194/hess-2023-10-RC1
- AC1: 'Reply on RC1', Anjana Ekka, 11 Jul 2023
  
  Dear reviewer, thank you for your valuable feedback. We have taken into account the insightful suggestions provided, which have allowed us to elaborate further on the content and improve the overall quality of the paper. The responses to the comments are presented in a two-column format and have been submitted as an attachment.
  
  Citation: https://doi.org/10.5194/hess-2023-10-AC1
RC2:
'Comment on hess-2023-10', Anonymous Referee #2, 17 Apr 2023
It's a paper that addresses a relevant issue related to the integrated economic-environmental analysis of infrastructure projects at the basin scale. The paper presents a case study with a series of analyses of different dimensions of impacts (change in flow regimes, fish species richness) and benefits (irrigation/crop production, hydropower) associated with the operation of a series of reservoirs in the Cauvery river basin (India).
While the topic and scope of the work is relevant from a scientific literature perspective, the paper has several important deficiencies, and my suggestion is that the authors go through a major revision process.
The paper's deficiencies fall into two categories. First, those related to how the overall study supports the claims or conclusions presented in the title or the discussion/conclusion sections. Second, those related to the justification/documentation of the specific methodologies used to evaluate each of the proposed environmental or economic components of the proposed framework. Here are my comments on each of these groups:
1. Comments on how the overall study supports the conclusions presented in the title or discussion/conclusion sections.
The title itself suggests that the paper may include a framework that addresses the integrated economic-environmental viability of dams. Indeed, this is a very important issue. However, the paper itself has no actual definition of what a "viable" set of dams is, how the scenarios compared differ in terms of their "viability". The title is therefore misleading. The actual scope is essentially a trade-off analysis between dam implementation scenarios for some of the 4 objectives considered, without offering a critical analysis of the viability of the resulting metrics across scenarios, and simply focusing on comparing values. Is any of the configurations shown in the scenarios economically-environmentally viable, and if so, for whom?
In order to coherently approach the statement in the title, I consider that the authors need to provide:
A definition of what is a viable configuration of dams. There are several possibilities. For example, it could be based on stakeholder preferences and/or, from a purely phenomenological perspective, the identification of boundaries or tipping points in the system that may preclude the functioning of a key component, e.g., fish biodiversity, agriculture, energy production, etc.

Evidence that the proposed components and indicators are relevant in the context of the proposed case study stakeholders, and that these indicators can be quantified with a reasonable degree of certainty. It is not clear in the paper why the 4 selected indicators were chosen and whether they are representative of system processes or priorities. See comment section 2 for some details.

A revised analysis of the interaction between environmental and economic objectives. The current Pareto production frontier analysis only considers the economic component from the perspective of the value of crops, leaving out the monetary value of fisheries, energy, etc.

2. Comments on the specific methodologies used to evaluate each of the proposed environmental or economic components of the proposed framework.
In its current form, the paper describes too succinctly many key components of the analytical framework presented in Figure 1, leaving important gaps in the justification of the selected metrics and the methods used to quantify them. It is understandable that, given the conceptual scope of the work, simplification in the main text may be necessary. However, supplementary materials are required to provide additional details that ensure reproducibility and clarity.
Similarly, there appear to be some important limitations in the proposed analytical components. The four most prevalent are as follows:
Hydrological modelling: It is not clear whether the "landscape hydrological model" is essentially the same as that presented in Ekka et al. (2022), or whether new calibrations were performed for this paper. In any case, the reported performance of the model is relatively low (NSE criteria are considered acceptable in the range of +0.2 to +0.5, and good above +0.5. The reported scores are all negative). There is also no mention of the modeling period (assumed to be the same as in Ekka et al., 2022, is 3 years?) Low performance levels can significantly affect the ability to implement data intensive methods such as IHA.

IHA methodology application is not sufficiently justifies or documented: In the case of freshwater habitat alterations, the paper selected a subset of IHAs. Why the IHA approach and why a subset of IHA indicators? Why not consider other aspects of physical habitat change such as fragmentation, sediment trapping, etc.? Also, can the IHAs be calculated with a reasonable level of confidence given the significant margin of error in several flow components of the hydrologic model?

Fish species richness is not an ecosystem service. It is a metric of biodiversity on evolutionary timescales (i.e., how biophysical processes over thousands to millions of years have produced a particular assemblage of species in a region). More importantly, it does not necessarily explain provision services such as fisheries productivity (for example, aquaculture in reservoirs typically has very high productivity with very low biodiversity).

The estimation of fish species richness was based on a global statistical model developed with the purpose of explaining the global distribution of biodiversity, but NOT of predicting changes in biodiversity based on short term changes in flows. Also, the cited model was developed based on global datasets with no source data in areas such as the case study, and no reference to validation is made. The proposed model is NOT appropriate for this study, as it suggests that by increasing the mean flows over a few years, you’d expect to increase biodiversity in the basin, which is probably not the case.

Therefore, the adoption of the Fish Species richness and model based on flow as a predictor of freshwater ecosystem services is not adequate for the analytical purposes stated in the paper, and must be revised.

The Production Possibility Frontier generalizes far beyond the data point ranges. It is not clear how the authors arrived at the shape of the PPF given the sparse data points of the model output. Also, the PPF is based on a partial analysis of the monetary value of the system's production and is therefore not representative of the production possibilities of the basin, but only of one sector.

Besides the major points mentioned above, it is also worth noting that the formal presentation of contextual data and results, such as maps, tables, and graphs, is sometimes redundant. For example,
Table 2 shows the same information as Figures 9 and 10

The maps/graphs shown in Figures 2, 3, 4, and 5 could be combined into a single figure.

In conclusion, in the opinion of this reviewer, a major revision of the methods and analysis is required for the publication of the paper. Likewise, supplementary materials with descriptions and data are required to illustrate with sufficient detail each of the analytical components developed. Supplementary data sets to allow for reproducibility are strongly encouraged.
Citation: https://doi.org/10.5194/hess-2023-10-RC2
- AC2: 'Reply on RC2', Anjana Ekka, 11 Jul 2023
  
  Dear reviewer, thank you for your valuable feedback. We have taken into account the insightful suggestions provided, which have allowed us to elaborate further on the content and improve the overall quality of the paper. The responses to the comments are presented in a two-column format and have been submitted as an attachment.
  
  Citation: https://doi.org/10.5194/hess-2023-10-AC2

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EndNote: 5

Views and downloads (calculated since 15 Feb 2023)

Month	HTML	PDF	XML	Total
Feb 2023	180	31	3	214
Mar 2023	51	19	1	71
Apr 2023	71	17	5	93
May 2023	18	7	1	26
Jun 2023	10	7	0	17
Jul 2023	63	15	4	82
Aug 2023	39	2	0	41
Sep 2023	20	9	1	30
Oct 2023	13	10	0	23
Nov 2023	12	3	1	16
Dec 2023	0

Cumulative views and downloads (calculated since 15 Feb 2023)

Month	HTML	PDF	XML	Total
Feb 2023	180	31	3	214
Mar 2023	51	19	1	71
Apr 2023	71	17	5	93
May 2023	18	7	1	26
Jun 2023	10	7	0	17
Jul 2023	63	15	4	82
Aug 2023	39	2	0	41
Sep 2023	20	9	1	30
Oct 2023	13	10	0	23
Nov 2023	12	3	1	16
Dec 2023	0

Viewed (geographical distribution)

Total article views: 575 (including HTML, PDF, and XML) Thereof 575 with geography defined and 0 with unknown origin.

Country	#	Views	%

Latest update: 03 Dec 2023

Short summary

The present study offers a hydro-economic method for evaluating the effects of multiple of dams on river ecosystem services under various scenarios of spatially placed reservoirs. Tradeoff analysis between agricultural production and fish species richness is used to examine the economic and environmental feasibility of multiple dams at basin scale. Smaller reservoirs on basin tributaries maximize the value of stored water while benefiting both the economy and the environment.


Total:	0
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