the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Accounting for the effect of forest and fragmentation in probabilistic rockfall hazard
Camilla Lanfranconi
Paolo Frattini
Gianluca Sala
Davide Bertolo
Juanjuan Sun
Giovanni Battista Crosta
Abstract. The presence of trees along the slope and block fragmentation at impact strongly affect rockfall dynamics, and hazard as a consequence. However, these phenomena are rarely simulated explicitly in rockfall studies. We performed rockfall simulations by using the 3D rockfall simulator Hy-Stone, modelling both the presence of trees and fragmentation through specific algorithms implemented in the code. By comparing these simulations with a more classical approach that attempt to account implicitly for such phenomena in the model parameters, and by using a new probabilistic rockfall hazard analysis (PRHA) method, we were able to quantify the impact of these phenomena on the design of countermeasures and on hazard.
We demonstrate that hazard changes significantly when accounting explicitly for these phenomena, and that a classical implicit approach usually overestimates both the hazard level and the 95th percentile of kinetic energy, leading to an oversizing of mitigation measures.
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Camilla Lanfranconi et al.
Status: open (until 14 Apr 2023)
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RC1: 'Comment on egusphere-2022-1521', Anonymous Referee #1, 06 Mar 2023
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This manuscript is very interesting and worth to be published. The effect of fragmentation and forest interaction in rockfall hazard estimation are hot topics on the subject, and this contribution elegantly clarifies and quantifies the effect of both phenomena using the well-established rockfall simulation code Hy-Stone.
I suggest a few improvements before publication.
First, and regarding the fragmentation algorithm described in section 2.1.3, I suggest a more in detail explanation of each section of the algorithm. Even though some details on how fragmentation works on Hy-Stone can be found in Frattini et al. (2012), some parts of the process are not clear. Being the quantification of fragmentation effect one of the goals of this article I suggest a more technical description of the algorithm, including an explanation of how the Yashima et al. (1987) criterion is adapted for the fragmentation threshold and the criteria used to determine the post fragmentation directions (since this may control the spreading of the model).
Second, in the analysis of Roisan event, where fragmentation played a significant role as detailed in the manuscript, it would be very interesting to show the volume distribution of the deposited fragments in the field and compare it with the volumetric distribution obtained by the model during the calibration. If the model results correspond to the field measurements, the model calibration would be more complete regarding fragmentation. In this sense, it would also be convenient to explain what initial volumes are simulated to represent the event and how that initial distribution was determined. These suggestions could be included in section 3.1 if appropriate.
Some minor comments:
Pag 5 line 133. For the calculation of the transit relative frequency when considering fragmentation, the total number of simulated paths include all generated fragments during propagation? When no fragmentation occurs this calculation looks trivial, but increasing the number of blocks during the propagation may lead to misuse of the classic approach.
Pag 7 line 214: Typo: «Figure 2Figure 2»
Pag 12 line 359: Is the sentence «From the results of hazard computation with and without fragmentation algorithm, which the hazard decreases.» correct? Can’t get the meaning.
Pag 13 line 391: Possible bullet missing.
Congratulations for this outstanding work.
Citation: https://doi.org/10.5194/egusphere-2022-1521-RC1 -
RC2: 'Comment on egusphere-2022-1521', Anonymous Referee #2, 25 Mar 2023
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The manuscript represents a very interesting contribution to the understanding of the effect of forest and fragmentation in probabilistic 3D rockfall modelling. The rockfall model HY-STONE and the applied rockfall hazard methodology are valid and outlined clearly. However, the manuscript still lacks a bit of a clear structure, with in particular a sharp distinction between methods, results, and discussion. Furthermore, please check the required reference formatting and reference completeness text/list.
Some comments:
Line 80: please add if block volume & form are considered in Hy-STONE and how the forest/trees are included/considered in the model
Line 155: HY-STONE is capable of simulating such large volumes?
Line 214: typo “Figure 2Figure2”
line 286: typo "Rockfall Hazard"
Figures: please add the resolution of the data/simulations
Citation: https://doi.org/10.5194/egusphere-2022-1521-RC2
Camilla Lanfranconi et al.
Camilla Lanfranconi et al.
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