Small dams alter thermal regimes of downstream water

Chandesris, André; Van Looy, Kris; Diamond, Jacob S.; Souchon, Yves

doi:https://doi.org/10.5194/hess-23-4509-2019

Articles | Volume 23, issue 11

https://doi.org/10.5194/hess-23-4509-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/hess-23-4509-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 23, issue 11

Research article

|

05 Nov 2019

Research article |

| 05 Nov 2019

Small dams alter thermal regimes of downstream water

André Chandesris, Kris Van Looy, Jacob S. Diamond, and Yves Souchon

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Final revised paper (published on 05 Nov 2019)
Preprint (discussion started on 09 Apr 2019)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review of "Determinants of thermal regime influence of small dams"', Anonymous Referee #1, 02 May 2019
- AC1: 'responses to the comments of referee #1 following the discussion of article hess-2019-136 : Determinants of thermal regime influence of small dams', André Chandesris, 15 Jul 2019
RC2: 'reviewer comment', Anonymous Referee #2, 11 May 2019
- AC2: ''responses to the comments of referee #2 following the discussion of article hess-2019-136 : Determinants of thermal regime influence of small dams'', André Chandesris, 15 Jul 2019
RC3: 'Interactive comment on “Determinants of thermal regime influence of small dams” by André Chandesris et al.', Anonymous Referee #3, 14 May 2019
- AC3: ''responses to the comments of referee #3 following the discussion of article hess-2019-136 : Determinants of thermal regime influence of small dams',', André Chandesris, 15 Jul 2019

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (further review by editor and referees) (16 Jul 2019) by Anas Ghadouani

AR by André Chandesris on behalf of the Authors (22 Jul 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (23 Jul 2019) by Anas Ghadouani

RR by Anonymous Referee #2 (30 Aug 2019)

Suggestions for revision or reasons for rejection

Thanks for the careful revision; I agree that the article improved notably.

All line numbers refer to the revised manuscript

Line 28: “that these effects can be accurately predicted” – these are bold words, given the limited variability of sites and environmental conditions within your dataset, and the limited number of explanatory variables you actually tested.

Line 194 ff: I would also characterize a fourth pattern in the temperature development, which is a period of progressively decreasing Tmin and Tmax (but not as a sharp drop), e.g. from 13/8/2014 to 18/8/2014 in Figure 2. Such a characteristic likely is related to relatively cool weather, maybe with moderate precipitation, or what do you assume?

Section 3.4 / Figure 5: I do not quite understand why you talk about correlation between air temperature and the upstream-downstream difference in stream temperature. It is not strong; I assume you have thought of why you looked into it (besides it being requested by a reviewer), but it does not become clear to the reader why. Either explain this, or maybe leave out Figure 5 as it does not seem to add much information, and just mention the results of a simple correlation analysis.

Figure 6: The cluster dendrogram should relate to your group names. I assume that gp 12-13 is group B2, group 8-11 is group B1, and gp 1-7 is group A. However, if this is the case, why do you refer to the two more distinct groups (according to your cluster analysis) with names B1 and B2? Also, intuitively, group B2 is most distinct, whereas B1 and A are more similar, as only B2 has both uniquely high delta Tmin and delta Tmax. Your distinction probably originates from group A being considered less problematic ecologically (low increase in Tmax), whereas both group B1 and B2 show a higher increase in Tmax, but this choice should be discussed, also wrt. the cluster analysis.

Line 245 ff: For my understanding, you describe the two different timeseries in an unnecessarily complicated manner. Isn’t the whole point of your distinction between group A and B, that group A does NOT show a siginificant/consistent increase in Tmax, whereas group B does? Then I suggest mentioning this directly instead of saying that “the downstream temperature is generally warmer than the upstream temperature […] except for a few hours”. So, the point is not only that “the duration above the thermal threshold is short” (line 250 f.), but more that group A does not show a consistent increase in Tmax, which usually is the ecologically problematic temperature?

Line 257 ff: This is hard to understand, please reformulate. Plus, can you state this based on only the three days from two example sites?

Line 330ff: “Group A is characterised by a residence time less than 0.7 days […] In group A, we suggest that long residence times reduce cooling effects” – isn’t that formulated confusingly? You mean, that even the short (as in shorter than most in group B) residence time already reduces the nocturnal cooling effect? And why should the large dams from group B with a short residence time (0.2 days) still experience heating from solar radiation? Shouldn’t that be mainly related to the residence time (hence, many of the smaller dams should also experience heating from solar radiation? Or are the smaller dams shaded by vegetation to a larger extent than the larger ones? If so, canopy cover/shading of the reservoir areas should really be considered as another explanatory variable. I assume you do not really know this, but at least try to discuss some of the potentially counter-intuitive results).

Line 410: “For example, a simple model using only small dam residence time and surface area may be able […]” Isn’t this a bold statement, given what I mentioned in the above paragraph regarding line 330 ff.?

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ED: Publish subject to minor revisions (review by editor) (25 Sep 2019) by Anas Ghadouani

AR by André Chandesris on behalf of the Authors (27 Sep 2019) Author's response Manuscript

ED: Publish as is (03 Oct 2019) by Anas Ghadouani

AR by André Chandesris on behalf of the Authors (08 Oct 2019)

Short summary

We found that small dams in rivers alter the thermal regimes of downstream waters in two distinct ways: either only the downstream daily minimum temperatures increase, or both the downstream daily minimum and maximum temperatures increase. We further show that only two physical dam characteristics can explain this difference in temperature response: (1) residence time, and (2) surface area. These results may help managers prioritize efforts to restore the fragmented thermalscapes of rivers.