the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 02 Nov 2023
Assessment of the impact of dam reservoirs on river ice cover – an example from the Carpathians (central Europe)
Maksymilian Fukś
Abstract. This paper presents a method for determining the impact of dam reservoirs on the ice cover of rivers below their locations based on a long measurement period (1950–2020) and synthetic-aperture radar (SAR) data. Two rivers and two sets of dam reservoirs located in the Carpathian Mountains (central Europe) were selected for this study. In order to estimate the influence of their reservoirs, a logistic regression model was built to describe the relationship between the course of air temperature and the occurrence of ice cover (i.e., total ice cover and border ice) at water gauge cross sections above and below the reservoirs. The influence of reservoirs was then defined as the differences between the values predicted from air temperature and those observed at the water gauge cross sections. Additionally, the extent of the impact of the reservoirs was estimated based on SAR data (Sentinel-1) by identifying river sections below the reservoirs on which total ice cover did not form despite the persistence of very low air temperatures. This study demonstrates that dam reservoirs are an important factor in transforming the ice regime of rivers. We found that decreases in the incidence of ice cover as a result of their operation could exceed 80 % in the sections immediately below their location, and that this reduction decreased as the distance from the reservoir increases. According to SAR data, it was estimated that total ice cover did not form in sections 26–60 kilometers below the reservoirs, despite the presence of favorable thermal conditions. Based on the research results presented here, it is reasonable to assume that the rapid increase in the number of dam reservoirs worldwide in the second half of the 20th century is an important factor transforming the ice regime of rivers. This study also demonstrates that the logistic regression model and SAR data are useful tools for assessing the impact of dam reservoirs on river ice cover.
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Maksymilian Fukś
Status: open (until 06 Jan 2024)
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RC1: 'Comment on tc-2023-151', Andrew Newton, 30 Nov 2023
reply
Dear Editor,
The manuscript by Maksymilian Fukś investigates the impact of dam construction on the ice regime of two rivers in central Europe. The author is able to demonstrate clear changes in the ice regimes before and after dam construction. Overall, the paper is well written, and I find little issue with the main result. My main concern is about the implications of what this result means, with concerns also about whether the available data have been used as effectively as possible to make the argument. I also have a concern about the methodology. On my pdf there are some annotations of minor edits that would be required to improve clarity in some places, but these are relatively simple. Overall, I do believe this paper is publishable, but major revision is needed in order to account for the issues presented below. I am very happy for the author to contact me if they have any questions about this feedback or if I have been unclear. If these issues are successfully revised, this paper will be a good contribution to the study topic.
Best wishes,
Andrew Newton – Queen’s University Belfast
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Major issues:
1) In the discussion I am not convinced it has explained what the dam has changed in the ice regime itself. Yes, the ice season has reduced, and it does appear that this might be associated with construction of the dams, but that in itself does not do enough in my view, particularly given the scale of impact that you state this paper might have. I think there needs to be a greater investigation into the potential causality of these changes. You outline some theoretical ideas, such as changes in discharge, but provide no evidence from the study site that could help to back this up. I strongly suspect you are correct in your hypothesis about what caused the impact, but it would make the paper significantly stronger if you could demonstrate some of this. Perhaps these data do not exist, but if they do, then I would encourage using these data to help make your point. If you have data such as Figure 9 for other time periods, then this would be a good place to start.
2) There is clearly a difference in the ice cover trend before and after the dam construction (Figure 2 shows that), but these trends have been derived from just two time periods – before and after. I would like to see you try some moving averages of that trend, perhaps a moving window of ~10-15 years within the before and after time periods. I suspect this would help to demonstrate that it was not a gradual change, but a rather blunt one. This would help to make your point of the dam influence, though it still does not explain the causal mechanism.
3) I would also like to see some greater statistical analyses of the climate change signal. This need not be complicated – e.g., some work can clearly be done on investigating the climatological trends in the weather station data and how these trends might relate to your ice regime changes. If there is no, or only a small, climate change signal in your weather stations, then this helps to make your point that it must have been the dam construction that impacted the ice regimes. This would be especially useful if data are not available to address point (1) above.
4) I would like to see a table that provides the geographical characteristics of the different water and weather stations, such as elevation. It would also be helpful to provide a comment on which weather stations are used to infer the air temperature at which water gauges – this is not currently as clear as it could be. This will provide a stronger link between the datasets.
5) I would like to see greater discussion in the text about how reflective the author feels the weather stations are of the temperature that is likely to have been observed at the water gauges. For example, the lack of geographical information about the different data sites – e.g., elevation – means that I cannot be sure what elevation difference there might be between them, and this will certainly impact how representative those observations are likely to be. Maybe there is little difference in elevation, but this needs to be explained in more detail, and if there are major differences in elevation between the weather stations and the associated water gauges, then I would think that this needs to be taken into account when drawing up the correlations between temperature and ice presence. The strong correlations do suggest this might not be a significant factor, but I still think this needs to be properly accounted for, or at least discussed.
6) The impact of the work needs to be developed further. The start of your concluding point (1) is very important but given the above issues I am not sure you have presented a strong enough case to robustly make this argument. If you can make the above revisions, then you certainly will have. There also needs to be some extra information on what this result would also mean for climate change studies – essentially that the trends of a declining river ice cover are not a de facto proof of climate change, and the wider hydrological setting needs to be taken into account in such settings. If you are able to make the revisions above you will be able to: 1) prove the dam influence is the case, and 2) prove that climate is not the main driver. This is a key selling point of the paper and if that case can be made more strongly, it will provide a good contribution to the literature.
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Minor issues:
1) In a large number of places in the text it is not always clear what is being referred to. The reader can often infer it, but it is better to be specific and unambiguous – e.g., instead of saying “their”, “this” etc., state what it is you are referring to.
2) I would encourage rewording of the locations from above/below the dam to upstream/downstream of the dam. This is much clearer language. I highlighted some instances, but not all of them.
Maksymilian Fukś
Maksymilian Fukś
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