A modeling methodology to study the tributary-junction  alluvial fan connectivity during a debris flow event

Garcés, Alex; Zegers, Gerardo; Cabré, Albert; Aguilar, Germán; Tamburrino, Aldo; Montserrat, Santiago

doi:https://doi.org/10.5194/nhess-22-377-2022

Articles | Volume 22, issue 2

https://doi.org/10.5194/nhess-22-377-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/nhess-22-377-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 22, issue 2

Research article

|

10 Feb 2022

Research article |

| 10 Feb 2022

A modeling methodology to study the tributary-junction alluvial fan connectivity during a debris flow event

Alex Garcés, Gerardo Zegers, Albert Cabré, Germán Aguilar, Aldo Tamburrino, and Santiago Montserrat

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Final revised paper (published on 10 Feb 2022)
Preprint (discussion started on 17 Sep 2021)

Interactive discussion

Status: closed

RC1:
'Comment on nhess-2021-266', Anonymous Referee #1, 05 Oct 2021

Dear Authors

I read your paper with great interest and I think that the topic is perfectly within the scope of the journal. Your approach tackles a very important problem regarding the design of countermeasure work for flow processes characterized by higher uncertainties. You propose a very honest and straightforward procedure which is well described in the paper that can be applied in other contexts and also for landscape evolution analysis. Having said that, I have only some open questions regarding your work that should be addressed before publication.

Broad comments:

Debris flow or debris flood? Please address the terminology issue also in the light of this new paper Church, Michael; Jakob, Matthias (2020). . Water Resources Research, doi:10.1029/2020WR027144

L75: the Crucecita Alta deposit is described in bulk with other fans in paper (Cabrè 2020a). Figure 6 of that paper shows the inferred sediment concentrations during the event but, since we are focusing on this test site now, I would advise you to provide a paragraph discussing how you estimated the sediment concentrations for each surge. Moreover, in Cabrè 2020a it is stated that the maximum thickness of the deposits is 100 cm while your simulations of the viscous debris flow show larger thickness of deposits for Surge 1. Is the remoulding of the subsequent floods that reduces the deposit thickness in the upper part of the fan? Is it possible to add a map showing the deposit thickness inferred from the geomorphological survey? The model calibration of debris flows just on the basis of the impacted area instead of deposits can lead to errors. In case it is not possible, please insert two sentences in the text highlighting this potential problem.

L259: I completely agree with you that for modelling calibration is sometimes difficult or not robust to rely only on a automatic algorithms to select the best fit parameters; it is in fact usually best to incorporate the expert knowledge euristic to select the best fit parameters and call the algorithm a Decision Support System rather than a automatic calibration algorithm. To better explain this to the readers you can provide a figure with the cloud points of your optimization indexes to show how clustered or nonclustered your 100 simulations were, so as to also understand how arbitrary is your “five runs” threshold.

Specific comments:

L10: if a channel is wide enough

L50: citation missing (?)

Figure 1: it is not clear what do the black lines represent in part b. Can you show in a less stylized way where exactly the element at risk (roads and buildings) are located in fig b?

L386: to design mitigation works

L389: the broad flow typology

L398: are deviated and forced to deposit

L399: With surge 4 avulsion is present, inundating the southern portion of the fan

Figure 8: please explain why the deposition pattern in surge 4 is so rectified, it seems a little bit unrealistic - did you experience problems with DTM interpolation? Can you show the contour lines of your model DTM topography?

L435: buffer?

L441-446: please revise this paragraph as the concepts expressed are clear but their formulation is not so

L484: incide

Citation: https://doi.org/10.5194/nhess-2021-266-RC1
- AC1: 'Reply on RC1', Alex Garces, 09 Nov 2021
  
  Dear Referee 1
  We thank you for your time in commenting on our paper. We found your appreciation of our manuscript motivating, and your comments were constructive for us. In the supplement, we reply to each broad and specific comments.
  Kind regards,
  
  Citation: https://doi.org/10.5194/nhess-2021-266-AC1
RC2:
'Comment on nhess-2021-266', Eric Barefoot, 28 Oct 2021

I enjoyed reading this manuscript from Garcés and coäuthors. Overall I found this manuscript to be reasonably clear, well-structured, and sound in its methods. I am not a frequent reader of NHESS, but from checking a few recently-published articles, this manuscript appears to be a very good fit for the mission of the journal, and describes a clever approach to predicting impacts of debris flows in mountainous settings. The modeling approach the authors outline requires substantial tuning, user input, local knowledge, and has a limited ability to etrapolate beyond the location being evaluated. As a result, quite a bit of data would be required to use this modeling approach for hazard mapping or analyzing a proposed mitigation approach. That said, the authors have done a good job of describing and clearly outlining when their model is applicable and when it is not, which I think is an especially strong aspect of this paper. I came away with a good sense of where and when an approach like theirs would be applicable, and what data I would need to collect in advance to use their methods.

I see no major obstacles to publication, and have enumerated a few minor comments in the attached document that I think would improve the manuscript’s clarity.

Citation: https://doi.org/10.5194/nhess-2021-266-RC2
- AC2: 'Reply on RC2', Alex Garces, 20 Nov 2021
  
  Dear Eric
  We thank you for your time in reviewing our manuscript. We also thank you for constructive feedback, especially on how to improve our figures. We hope that our changes are in line with your expectations. In the supplement, you will find our reply to each comment.
  Kind regards,
  
  Citation: https://doi.org/10.5194/nhess-2021-266-AC2

Peer review completion

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

ED: Publish subject to minor revisions (review by editor) (30 Nov 2021) by Paola Reichenbach

AR by Alex Garces on behalf of the Authors (10 Dec 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (15 Dec 2021) by Paola Reichenbach

Short summary

We propose a workflow to model the response of an alluvial fan located in the Atacama Desert during an extreme storm event. For this alluvial fan, five different deposits were identified and associated with different debris flow surges. Using a commercial software program, our workflow concatenates these surges into one model. This study depicts the significance of the mechanical classification of debris flows to reproduce how an alluvial fan controls the tributary–river junction connectivity.