Assessing different imaging velocimetry techniques to measure shallow runoff velocities during rain events using an urban drainage physical model

Naves, Juan; García, Juan T.; Puertas, Jerónimo; Anta, Jose

doi:https://doi.org/10.5194/hess-25-885-2021

Articles | Volume 25, issue 2

https://doi.org/10.5194/hess-25-885-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/hess-25-885-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 25, issue 2

Research article

|

24 Feb 2021

Research article |

| 24 Feb 2021

Assessing different imaging velocimetry techniques to measure shallow runoff velocities during rain events using an urban drainage physical model

Juan Naves, Juan T. García, Jerónimo Puertas, and Jose Anta

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Final revised paper (published on 24 Feb 2021)
Supplement to the final revised paper
Preprint (discussion started on 06 May 2020)
Supplement to the preprint

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of Naves et al HESS 2020', Anonymous Referee #1, 08 Jun 2020
- AC1: 'Response to Anonymous Referee #1', Juan Naves, 20 Jul 2020
RC2: 'Review of “Assessing different imaging velocimetry techniques to measure shallow runoff velocities during rain events using an urban drainage physical model” by Naves et. al. Review by Rolf Hut', Rolf Hut, 07 Jul 2020
- AC2: 'Response to Referee #2 (Rolf Hut)', Juan Naves, 20 Jul 2020

Peer-review completion

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

ED: Publish subject to revisions (further review by editor and referees) (06 Aug 2020) by Genevieve Ali

AR by Juan Naves on behalf of the Authors (14 Sep 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (08 Oct 2020) by Genevieve Ali

RR by Anonymous Referee #3 (29 Nov 2020)

Suggestions for revision or reasons for rejection

The review relates to the revised version of the manuscript, and it considers the answers that had been given to the previous review.

The well-prepared manuscript compares the performance of different imaging velocimetry techniques for overland flow velocity estimation under the influence of raindrops by means of controlled pilot-scale experiments. It represents a valuable scientific contribution in the field, in particular as the study comes with a comprehensive data set, i.e. findings that are based on solid experimental research. Well-done and very appreciated!

*Two major issues:
1. revised manuscript follows a classical structure, provides (considering references to other publications of the group) sufficient insights in the design of the experiments, presents illustrative results, followed by a discussion slightly biased towards the benefits, avoiding the challenges. The “all-too-positive” tenor, that had been criticized by a previous reviewer (which I agree with), was only partially addressed in the first review.

This is a major point, and it needs to be addressed before final publication. To be more precise: the discussion of the ability of the techniques to correctly measure under real-life conditions (line 388 ff) is essential, but still too optimistic. For instance (cf. line 390 ff.), it is obvious that the results achieved for unseeded techniques show severe deficiencies for rain intensities higher than 30 mmh-1. This aspect however is qualified by underlining the advantages of the technique, e.g. not having to rely on artificial particles to be added to the flow, etc. The doubtlessly existing advantages of unseeded techniques cannot hide the fact that overland flow velocities for higher rainfall intensities cannot be estimated accurately. On the other hand, statements like the one in line 394 is rather wishful thinking, relating to other studies which may show the potential under real-life conditions, but for single events and without the interference of raindrops. IMO the study here provides evidence that the evaluated techniques have limitations, and this should be unambiguously stated.

In a similar fashion, in the Conclusions (line 444, ff) it should be made clearer which method can potentially be applied under which conditions (shallow flows, events of low intensity, influence of raindrops for different intensities). In the current version of the manuscript, I am missing clear sentences like “seeded techniques are not able to measure velocities in areas with extreme shallow flows” which are included in the answer to previous reviews. I think making these aspects crystal-clear (e.g. like “method xy is suitable for rain intensities below a threshold of yz mm h-1”) does not diminish the value of this excellent work, but it helps to do further research or to apply techniques under real-life conditions.

-> line 19: replace “feasibility” with “potential”. The study illustrates the feasibility for controlled experiments but not for real-life applications!

2. Abstract as well as Conclusion: despite it is mentioned in the Conclusion, that further research in real urban catchments should be done: it must be emphasized that the usefulness, i.e. the robustness of the techniques for real-life applications yet remains to be proven by means of further studies in non-controlled environments. With this respect, tangible recommendations on how to approach a validation under real-life conditions should be made to facilitate future research. What about the influence of different surfaces/surface roughness in real-life catchments, or the influence of wind, similarly occurring as raindrops, etc.
*Some minor issues:
- line 120: replace “rugosity” with “roughness”. Plus, it would be very helpful to know the roughness value of the concrete slab in the physical model to put results into context, e.g. when considering other surfaces.

- line 288: “To do this and following the previous results“. Awkward formulation. Consider rewriting.

- The English should be checked again prior final publication!

- Sentences are partially very long, i.e. complex (e.g. line 301 ff). Along with the language check, the authors may want to simplify the text at a few occasions in order to improve readability.

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RR by Anonymous Referee #1 (16 Dec 2020)

ED: Publish subject to minor revisions (review by editor) (18 Dec 2020) by Genevieve Ali

AR by Juan Naves on behalf of the Authors (03 Jan 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (19 Jan 2021) by Genevieve Ali

AR by Juan Naves on behalf of the Authors (21 Jan 2021)

Short summary

Surface water velocities are key in the calibration of physically based urban drainage models, but the shallow depths developed during non-extreme rainfall and the risks during floods limit the availability of this type of data. This study proves the potential of different imaging velocimetry techniques to measure water runoff velocities in urban catchments during rain events, highlighting the importance of considering rain properties to interpret and assess the results obtained.