Life Stage-Specific Hydropeaking Flow Rules
, Miguel Moreira 3, Isabel Boavida 3, Melanie Haslauer 1, Günther Unfer 1, Bernhard Zeiringer 1, Franz Greimel 1, Stefan Auer 1, Teresa Ferreira 2 and Stefan Schmutz 1Round 1
Reviewer 1 Report
The authors provide a conceptual model to help inform the development of management practices to mitigate the impacts of hydroramping effects on different life stages of fish. The conceptual mode is supported by a review of current literature and describes critical links between fish ecology and the timing of specific impacts associated with changes in flow discharge. The authors provide what seems reasonable, but general, advice on how to manage flows to mitigate impacts. Broader gaps in science and knowledge needs are discussed, as well as limitations of the proposed actions given the science knowledge and where additional science is beneficial.
The MS is well written and provides informative and impressive infographics. The MS does not present new original research, but provides a conceptual framework with clear links to conservation and management implications. It does however seem a surprise to me that this body of work has not previously been aggregated and summarised for presentation in scientific or management articles. While lacking quantitative rigour or specificity, the MS draws upon previous work in a way that provides a clear articulation of the problem and knowledge base, and I am sure would find a warm reception in the appropriate communities and form an important part of ongoing management discussions.
Specific comments:
45. Suggest rewording to ‘fish can be affected by changes in various components…’
51. Providing some general examples here of previous efforts in both structural and operational mitigation methods would be helpful for framing.
51. Why is implementation difficult? Again, some examples here would be useful for identifying the comparative strengths of what you are proposing.
56. Is ‘bottlenecks’ the right word here? In the context of hydropower ramping, you are talking about reducing the negative effects of controls (added flows) to fish ecology? Is what you are saying that hydropower provides a bottleneck to healthy fish populations? (also in conclusion, framing may be better in terms of ‘reducing impact on specific life stages through…’ rather than ‘bottlenecks’ which broadly mean something else in ecology such as a low point in population abundances rather than a threatening process)
66. suggest some clause here about refining the method for other species rather than an ‘as is’
70. Reabsorb vs absorb
72. Sentence is ambiguous. Presumably you are not saying that the generation 1 adults use different habitat, but rather gen 2 when/as they mature
75. Attenuation or alteration?
Figure 1 is pictorially great.
Figure 1 and the conceptual model seems incomplete without a description of the approximate, or guidance on, the temporal widow that each control should operate on. This is essential to inform management.
91. Does not seem on the ‘other hand’. Both examples seem to collaborate the point
95. ‘stop to prepare’ or ‘stop preparing’. The former would imply that this is needed for initiation of redd building.
121. Is this because electricity demand is higher in winter? Is ‘in contrast’ what you mean?
122. it had been discussed numerously that they deposit eggs in the gravel. Why introduce ‘lithophilic’ here?
130. infiltration or deposition?
145. I think these clauses are good, and could similarly apply elsewhere in the MS
159-161. Not sure how these are ‘on other hands’. Are they not two different complementary strategies to get the same outcome?
182. Sensitive or vulnerable? Surely any life stage that is stranded is going to be sensitive to it.
272. This seems to contradict the previous statements about vulnerability of different life stages
383. I would question defining the work as ‘state of the art’. This term is very arbitrary and people have been linking life history processes to environmental conditions for decades, or longer. Albeit it might be novel in the hydropeaking field, it is still catch up to many other fields in where even robust quantitative methods for prediction exist.
A nice piece of work.
Author Response
Response to Reviewer 1 Comments
Point 1:The authors provide a conceptual model to help inform the development of management practices to mitigate the impacts of hydroramping effects on different life stages of fish. The conceptual mode is supported by a review of current literature and describes critical links between fish ecology and the timing of specific impacts associated with changes in flow discharge. The authors provide what seems reasonable, but general, advice on how to manage flows to mitigate impacts. Broader gaps in science and knowledge needs are discussed, as well as limitations of the proposed actions given the science knowledge and where additional science is beneficial.
The MS is well written and provides informative and impressive infographics. The MS does not present new original research, but provides a conceptual framework with clear links to conservation and management implications. It does however seem a surprise to me that this body of work has not previously been aggregated and summarised for presentation in scientific or management articles. While lacking quantitative rigour or specificity, the MS draws upon previous work in a way that provides a clear articulation of the problem and knowledge base, and I am sure would find a warm reception in the appropriate communities and form an important part of ongoing management discussions.
Response 1: Dear reviewer! We appreciate your thorough response and your kind feedback. Please find our responses to your specific comments below.
Point 2: 45. Suggest rewording to ‘fish can be affected by changes in various components…’
Response 2: As suggested, we inserted “…by changes” into the sentence.
Point 3: 51. Providing some general examples here of previous efforts in both structural and operational mitigation methods would be helpful for framing.
Response 3: We inserted examples of both structural (e.g., construction of retention basins) and operational (e.g., reducing flow fluctuation rates) mitigation measures. See lines 51-52.
Point 4: 51. Why is implementation difficult? Again, some examples here would be useful for identifying the comparative strengths of what you are proposing.
Response 4: We inserted a description why implementation is often difficult: “…because of significant reductions in energy yield when setting ecological thresholds.” Also, we changed the following sentence to highlight the need of addressing these difficulties (“to avoid energy losses”) as well as guaranteeing ecological efficiency through targeted mitigation measures.
Point 5: 56. Is ‘bottlenecks’ the right word here? In the context of hydropower ramping, you are talking about reducing the negative effects of controls (added flows) to fish ecology? Is what you are saying that hydropower provides a bottleneck to healthy fish populations? (also in conclusion, framing may be better in terms of ‘reducing impact on specific life stages through…’ rather than ‘bottlenecks’ which broadly mean something else in ecology such as a low point in population abundances rather than a threatening process)
Response 5: We agree and changed the phrasing here (line 59) as well as in the conclusion (line 436) from “bottleneck” to “hydropower-induced bottleneck”.
Point 6: 66. suggest some clause here about refining the method for other species rather than an ‘as is’
Response 6: We changed the sentence to: “Nevertheless, many aspects of the presented mitigation concept can potentially be transferred to or adapted to the requirements of other taxa.”
Point 7: 70. Reabsorb vs absorb
Response 7: Thank you.It should be “absorbed”. We changed it accordingly.
Point 8: 72. Sentence is ambiguous. Presumably you are not saying that the generation 1 adults use different habitat, but rather gen 2 when/as they mature
Response 8: We meant to say that fish use different habitats as they grow in size, e.g. subadult or adult use different habitats than emerging fry. Therefore, we changed this sentence to the following: “As fish increase in size, they use different habitats. Once they reach sexual maturity, their life cycle starts over again.”
Point 9: 75. Attenuation or alteration?
Response 9: We meant “flow restoration” and changed it accordingly.
Point 10: Figure 1 is pictorially great.
Figure 1 and the conceptual model seems incomplete without a description of the approximate, or guidance on, the temporal widow that each control should operate on. This is essential to inform management.
Response 10: Thanks for the compliments on the Figure.
We understand your comment on the temporal windows as we also discussed this point intensively during the development of the conceptual approach. However, there is a large variability in timing of e.g. spawning for a single species only. For example, in some Austrian rivers, grayling spawning only takes 14 days, whereas in other rivers it takes 2-3 months. Similar observations have also been found for the brown trout where spawning in two rivers shows no overlap at all (Unfer, G., Hauer, C., Pinter, K. (2011): Spawning redds of brown trout in geologically different streams. In: American Fisheries Society, New Frontiers in Fisheries Management and Ecology: Leading the Way in a Changing World). This temporal variability in life cycle stages in different rivers is well depicted in Figure 2. Nonetheless, we agree that it is essential to state this and we, therefore, inserted the following sentence in line 307-308: “… the temporal windows must be adapted to the local river conditions.”
Point 11: 91. Does not seem on the ‘other hand’. Both examples seem to collaborate the point
Response 11: We agree and deleted “on the one hand” as well as “on the other hand”.
Point 12: 95. ‘stop to prepare’ or ‘stop preparing’. The former would imply that this is needed for initiation of redd building.
Response 12: We changed it to: “stop preparing”.
Point 13: 121. Is this because electricity demand is higher in winter? Is ‘in contrast’ what you mean?
Response 13: We changed these sentences to better contrast the difference between the hydrological winter situation of unimpacted rivers and hydropeaking rivers: “In the winter, mountainous rivers are characterized by an extended low baseflow period. During this season, hydropeaking rivers, however, often exhibit relatively high flow fluctuations.”
Point 14: 122. it had been discussed numerously that they deposit eggs in the gravel. Why introduce ‘lithophilic’ here?
Response 14: We changed the sentence to: “As salmonids deposit their eggs in the gravel bed siltation may reduce hatching success by affecting interstitial water flow.”
Point 15: 130. infiltration or deposition?
Response 15: “Infiltration” is correct. See Hauer et al. 2018 (DOI: 10.1002/esp.4505).
Point 16: 145. I think these clauses are good, and could similarly apply elsewhere in the MS
Response 16: Thank you. We also went through the rest of the manuscript and applied it where fitting.
Point 17: 159-161. Not sure how these are ‘on other hands’. Are they not two different complementary strategies to get the same outcome?
Response 17: We deleted the first “on the one hand” and changed the second one to “additionally”.
Point 18: 182. Sensitive or vulnerable? Surely any life stage that is stranded is going to be sensitive to it.
Response 18: We changed it to “vulnerable”.
Point 19: 272. This seems to contradict the previous statements about vulnerability of different life stages
Response 19: Different stranding studies agree that fry and early juvenile life stages are the most vulnerable life stage in regards to downramping velocity (see recent review from Moreira et al. 2019 (https://doi.org/10.1016/j.scitotenv.2018.12.107), and chapter 2.3). In this section, we look at stranding by discussing the effects it has at the population level. In this regard, the study from Sauterleute et al. is the first to describe this aspect and the authors suggest that, after the density-dependent recruitment phase, stranding during winter has a very high impact on the population level. Nevertheless, in our opinion, this does not contradict the previous statement, as ramping thresholds must be implemented in both life cycle stages, although, as argued in section 2.3.1, the thresholds might become less stringent over time – but not too stringent to cause detrimental effects on the population level.
Point 20: 383. I would question defining the work as ‘state of the art’. This term is very arbitrary and people have been linking life history processes to environmental conditions for decades, or longer. Albeit it might be novel in the hydropeaking field, it is still catch up to many other fields in where even robust quantitative methods for prediction exist.
Response 20: We agree and changed the wording to: “… such a life cycle stage approach constitutes the most up-to-date framework on hydropeaking mitigation …”
Point 21: A nice piece of work.
Response 21: Thank you for the effort you put into reviewing this manuscript!
Author Response File: 
Author Response.docx
Reviewer 2 Report
This is a thorough review of the work that has been done on hydropeaking effects on salmonid fishes at different life-stages. It provides a valid qualitative framework for addressing the issue (shown in Figure 1). The authors support their inferences, and it is difficult to identify any area where the manuscript is omitting pertinent issues. As such, I would recommend this for publication.
There are a few issues minor issues. Possibly the authors could refer to Air Cushion Reservoir Technology and include a sentence or two on the literature showing different effects in different salmonid species (although neither is essential). The heading for section 2.4.1 could be removed.
Minor issues
1) Maybe the authors could mention Air Cushion Underground Reservoir technology in Section 3.4 (an expensive approach but one that can be used when there is limited space available).
2) Maybe the authors could also add a sentence comparing the relative effects on different salmonid species. For instance, some studies suggest that brown trout populations are more detrimentally affected by hydropeaking than Atlantic salmon populations.
3) I suggest removing the heading “2.4.1. Fish movements, feeding, and growth”. It is a strange only having one level 3 heading in Section 2.4. Also, the levels 3 headings in Section 2.3 (2.3.1. Mitigation thresholds for impact mitigation; 2.3.2. Emergence window establishment) describing mitigation strategies are informative because they relate directly to the manuscript’s title. Why did the authors not continue in this fashion in Section 2.4? If the authors think it is necessary to include level 3 titles in Section 2.4, maybe they could consider following the format of Section 2.3?
The English is generally very good, but there are some instances where it could be improved (see below):
Line 44: “Fish communities, in particular, are…” better than “Especially fish communities are”
Line 49: “it is imperative” better than “it is stringent”
Line 56: “point out the need” (remove “no”)
Line 58: “in rivers affected by hydropeaking” better than “in hydropeaking rivers” (?). A “hydropeaking river” sounds a bit strange.
Line 59: “especially during ecological sensitive periods” better than “and especially ecologically sensitive periods”
Line 68 “many salmonids” is probably better because just “salmonids” would generalize this behaviour to all species, but salmo trutta lacrustis, for example, may spawn in a lake and not perform upstream spawning migrations
Line 70 “after hatching the following spring” better than than “after hatching” (?)
Line 75: “Thus, the key parameters” better than “Thus, also the key parameters”
Line 90: remove comma after “(O. gorbuscha)”
Line 91-92: Suggest removing “on the other hand” – a bit informal
Line 98: “flows have returned” better than “flow returned”
Line 101: suggest just writing “on migrating fish” as the final clause of the sentence just refers to migration periods, not spawning
Line 135: suggest removing “, at the same time,”
Line 139: remove “, therefore,”
Line 142: “also depends” better than “depends also”
Line 144 “were able to substantially” better than “are substantially able”
Line 159: remove ,”it is on the other hand,”
Line 161: “Additionally” better than “On the other hand”
Line 171: should this be “absorbed” rather than “resorbed”?
Line 178: maybe “Thresholds” rather than “Mitigation thresholds” so that mitigation is not repeated in the title
Line 179: maybe “downramping” instead of “turbine stops”
Line 202: “These emergence windows”, not “This…”
Line 203, remove comma before “just before”
Line 205-207: remove “the” before species names for consistency with the rest of the text
Line 250: should this be “They recommend reducing downramping during nighttime hours” (not “to”), if they are suggesting that night-time in winter is a potential problem
Line 252: I don’t see how the following line follows from the previous: “However, this might be because, in the Skagit River case study, daytime flow reduction represented 89% of all events during the peak stranding period”
Line 259: “Only in late winter was fish activity reduced during high flows in the night.” better than “Only in late winter, fish activity was reduced during high flows in the night.”
Line 289: “environmental flows in rivers” rather than “environmental flow rivers”?
Line 290: should it be “it is required” (i.e. the authors are referring to their work in this manuscript rather than Alfredsen’s)
Line 317: suggest removing “likely”
Line 332: Can this sentence be simplified? “Next to river restoration measures, also connectivity to tributaries – enabling recruitment – may play an essential role in supporting fish populations in hydropeaking rivers.” is difficult to read.
Line 380 “In recent years”
Line 391-392: I would suggest merging the final sentence with the preceding sentence, and simplifying a bit: e.g. “Future research will, among others, have to better quantify the effects of hydropeaking on spawning activities and egg incubation phases (especially with regard to scour or siltation, and sub-daily temperature changes), and investigate impacts on the fish population at the community level, including investigating the effects of hydropeaking on the food web (e.g. between nutrients, periphyton, macroinvertebrates and fish).
Author Response
Response to Reviewer 2 Comments
Point a:This is a thorough review of the work that has been done on hydropeaking effects on salmonid fishes at different life-stages. It provides a valid qualitative framework for addressing the issue (shown in Figure 1). The authors support their inferences, and it is difficult to identify any area where the manuscript is omitting pertinent issues. As such, I would recommend this for publication.
There are a few issues minor issues. Possibly the authors could refer to Air Cushion Reservoir Technology and include a sentence or two on the literature showing different effects in different salmonid species (although neither is essential). The heading for section 2.4.1 could be removed.
Response a: Dear reviewer! We thank you for your thorough review of our manuscript and we highly appreciate your comments to further improve the work. Please find our detailed responses below.
Minor issues
Point1) Maybe the authors could mention Air Cushion Underground Reservoir technology in Section 3.4 (an expensive approach but one that can be used when there is limited space available).
Response 1: Thank you for this suggestion. We added a sentence about ACUR technology in section 3.4: “Currently, the feasibility of the air cushion underground reservoir (ACUR) technology to mitigate environmental hydropeaking effects is being tested in the European HydroFlex project (https://h2020hydroflex.eu)” (see lines 389-391).
Point2) Maybe the authors could also add a sentence comparing the relative effects on different salmonid species. For instance, some studies suggest that brown trout populations are more detrimentally affected by hydropeaking than Atlantic salmon populations.
Response 2: In line 197-200, we mention downramping velocity thresholds for Atlantic salmon, European grayling, and brown trout, which highlights that some species are less/more susceptible to stranding caused by hydropeaking. However, despite such research on stranding, we believe it is too early to generalize that a species’ population is more detrimentally affected by hydropeaking than another species’ population.
Point3) I suggest removing the heading “2.4.1. Fish movements, feeding, and growth”. It is a strange only having one level 3 heading in Section 2.4. Also, the levels 3 headings in Section 2.3 (2.3.1. Mitigation thresholds for impact mitigation; 2.3.2. Emergence window establishment) describing mitigation strategies are informative because they relate directly to the manuscript’s title. Why did the authors not continue in this fashion in Section 2.4? If the authors think it is necessary to include level 3 titles in Section 2.4, maybe they could consider following the format of Section 2.3?
Response 3: We agree with the point raised and removed the level 3 heading in Section 2.4.
Point4:The English is generally very good, but there are some instances where it could be improved (see below):
Response 4: Thank you for your feedback on the language and suggestions for further improvement.
Point5: Line 44: “Fish communities, in particular, are…” better than “Especially fish communities are”
Response 5: We changed it to: “Fish communities, in particular, are …”
Point6: Line 49: “it is imperative” better than “it is stringent”
Response 6: We changed it to: “… it is imperative to …”
Point7: Line 56: “point out the need” (remove “no”)
Response 7: We removed the “to”. It now reads: “multiple studies point out the need to …”
Point8: Line 58: “in rivers affected by hydropeaking” better than “in hydropeaking rivers” (?). A “hydropeaking river” sounds a bit strange.
Response 8: We changed it to: “in rivers affected by hydropeaking …”
Point9: Line 59: “especially during ecological sensitive periods” better than “and especially ecologically sensitive periods”
Response 9: We changed it to: “especially during ecologically sensitive periods.”
Point10: Line 68 “many salmonids” is probably better because just “salmonids” would generalize this behaviour to all species, but salmo trutta lacrustis, for example, may spawn in a lake and not perform upstream spawning migrations
Response 10: We agree and changed it to: “many salmonids”.
Point11: Line 70 “after hatching the following spring” better than than “after hatching” (?)
Response 11: Hatching does not necessarily occur in the following spring with all salmonid species. For example, brown trout often hatches in mid-winter. Therefore, we prefer to leave it as it is.
Point12: Line 75: “Thus, the key parameters” better than “Thus, also the key parameters”
Response 12: We deleted “also”.
Point13: Line 90: remove comma after “(O. gorbuscha)”
Response 13: We removed the comma.
Point14: Line 91-92: Suggest removing “on the other hand” – a bit informal
Response 14: We deleted both, “on the one hand” and “on the other hand.”
Point15: Line 98: “flows have returned” better than “flow returned”
Response 15: We changed it to: “flows have returned.”
Point16: Line 101: suggest just writing “on migrating fish” as the final clause of the sentence just refers to migration periods, not spawning
Response 16: We removed “and spawning” to write only “on migrating fish.”
Point17: Line 135: suggest removing “, at the same time,”
Response 17: We removed “, at the same time,”
Point18: Line 139: remove “, therefore,”
Response 18: We removed “,therefore,”
Point19: Line 142: “also depends” better than “depends also”
Response 19: We switched the position of “also”.
Point20: Line 144 “were able to substantially” better than “are substantially able”
Response 20: We changed it to: “were able to substantially…”
Point21: Line 159: remove ,”it is on the other hand,”
Response 21: We deleted it.
Point22: Line 161: “Additionally” better than “On the other hand”
Response 22: We changed it to: “Additionally, …”
Point23: Line 171: should this be “absorbed” rather than “resorbed”?
Response 23: Correct. We changed it to: “absorbed”
Point24: Line 178: maybe “Thresholds” rather than “Mitigation thresholds” so that mitigation is not repeated in the title
Response 24: Thanks! We changed it to: “Thresholds for impact mitigation”
Point25: Line 179: maybe “downramping” instead of “turbine stops”
Response 25: We changed it to “downramping”.
Point26: Line 202: “These emergence windows”, not “This…”
Response 26: We changed it accordingly.
Point27: Line 203, remove comma before “just before”
Response 27: We deleted the comma.
Point28: Line 205-207: remove “the” before species names for consistency with the rest of the text
Response 28: We removed the “the” before the species names.
Point29: Line 250: should this be “They recommend reducing downramping during nighttime hours” (not “to”), if they are suggesting that night-time in winter is a potential problem
Response 29: They are actually suggesting that daytime downramping is a major problem. We, therefore, changed the sentence to: “they recommend limiting downramping to nighttime hours.”
Point30: Line 252: I don’t see how the following line follows from the previous: “However, this might be because, in the Skagit River case study, daytime flow reduction represented 89% of all events during the peak stranding period”
Response 30: As stated in response 29, Connor & Pflug (2004) suggest that downramping during the day causes significant stranding. Hence, instead of daytime downramping, downramping should predominantly occur during the night. However, since most other studies point exactly to the opposite, we suggest that their “focus on daytime mitigation might be because, in the Skagit River case study, daytime flow reduction represented 89% of all events during the peak stranding period.” (We changed the sentence accordingly; see lines 260-261).
Point31: Line 259: “Only in late winter was fish activity reduced during high flows in the night.” better than “Only in late winter, fish activity was reduced during high flows in the night.”
Response 31: We changed it to: “Only in late winter was fish activity reduced during high flows in the night.”
Point32: Line 289: “environmental flows in rivers” rather than “environmental flow rivers”?
Response 32: We added “in”.
Point33: Line 290: should it be “it is required” (i.e. the authors are referring to their work in this manuscript rather than Alfredsen’s)
Response 33: Yes, we are referring to our work and changed it to “it is required.”
Point34: Line 317: suggest removing “likely”
Response 34: We removed “likely”.
Point35: Line 332: Can this sentence be simplified? “Next to river restoration measures, also connectivity to tributaries – enabling recruitment – may play an essential role in supporting fish populations in hydropeaking rivers.” is difficult to read.
Response 35: We simplified this sentence.
Point36: Line 380 “In recent years”
Response 36: We added: “in recent years”.
Point37: Line 391-392: I would suggest merging the final sentence with the preceding sentence, and simplifying a bit: e.g. “Future research will, among others, have to better quantify the effects of hydropeaking on spawning activities and egg incubation phases (especially with regard to scour or siltation, and sub-daily temperature changes), and investigate impacts on the fish population at the community level, including investigating the effects of hydropeaking on the food web (e.g. between nutrients, periphyton, macroinvertebrates and fish).
Response 37: Thank you, we updated the sentence (line 404-410).
Author Response File: Author Response.docx
