the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Scenario building and runout modelling for debris flow hazards in pro-/periglacial catchments with scarce past event data: application of a multi-methods approach for the Dar catchment (western Swiss Alps)
Mario Kummert
Reto Aeschbacher
Christoph Graf
Alexis Rüeger
Philippe Schoeneich
Markus Zimmermann
Margreth Keiler
Abstract. In high mountain areas, the disposition (susceptibility of occurrence) for debris flows is increasing in steep terrain, as – due to climate change – rapid glacier retreat and permafrost degradation is favouring higher availability of loose sediments. The probability of occurrence and magnitude of pro- and periglacial debris flows is increasing, too, as triggering events such as heavy thunderstorms, long-lasting rainfalls, intense snow melt or rain-on-snow events are likely to occur more often and more intensely in future decades. Hazard assessment for debris flows originating from pro- and periglacial areas is thus crucial but remains challenging, as records of past events on which local magnitude-frequency relationships and debris flow scenarios can be based on are often scarce or inexistent. In this study, we present a multi-methods approach for debris flow hazard scenario building and runout modelling in pro- and periglacial catchments with scarce past event data. Scenario building for the debris flow initiation zone reposes on (i) the definition of meteorological and hydrological triggering scenarios using data on extreme point rainfall and precipitation-runoff modelling, and (ii) the definition of bed load scenarios from empirical approaches and field surveys. Numerical runout modelling and hazard assessment for the resulting debris flow scenarios is carried out using RAMMS-DF, which was calibrated to the studied catchment (Le Dar, western Swiss Alps) based on the area of debris flow deposits from the single major event recorded there in summer 2005. The developed approach is among the first to propose systematic scenario building for pro- and periglacial debris flows triggered by precipitation dependent events.
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Mauro Fischer et al.
Status: open (until 08 Oct 2023)
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RC1: 'Comment on egusphere-2023-1190', Stefan Hergarten, 06 Sep 2023
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This paper provides an hazard assessment with regard to debris flows for a small catchment in the Alps. The results are finally obtained from simulations with the debris flow version of the model RAMMS. Focus is on simulating different scenarios, defined by different amounts of precipitation and available sediment.
The manuscript is very long. I often had the feeling that it reads like a thesis rather than like a scientific paper. I guess that it is indeed a shortened version of the M.Sc.-thesis of the third author (Reto Aeschbacher). I am quite sure that the thesis was excellent and that the supervisors were delighted about it. But on the other hand, it is not concise and not to the point. Each step is expanded in great detail, which is fine in a thesis, but not in a scientific paper.
As a main point, however, I feel that the results are a bit trivial. If there is more rainfall and more sediment available, the debris flow will be faster and reach a longer runout. And if we separate one big event into two smaller subsequent events, the debris flow will be weaker. For practical purposes (planning etc.), it is undoubtedly useful to have such scenarios available. For an operational application, however, the effort seems to be quite high and the uncertainties are also high.
Scientifically, the interplay of precipitation and sediment availability would be the most interesting aspect of debris flows. So what defines the intensity of the debris flow finally? Under which conditions is precipitation the limiting factor and under which conditions sediment availability? Unfortunately, the results presented here are restricted to a line in this 2-D parameter space since sediment availability is assumed to be a function of precipitation. As far as I can see, a single-phase flow model such as RAMMS would not be suitable for going deeper here.
In sum, I am not convinced that the manuscript in its present form provides sufficient new scientific insights, in particular in relation to its length. Sorry that I cannot be more positive at this occasion since I feel that the student's work behind was really a nice piece of work.
Best regards,
Stefan HergartenCitation: https://doi.org/10.5194/egusphere-2023-1190-RC1
Mauro Fischer et al.
Mauro Fischer et al.
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