Effectiveness and limits of scale independence in the depositional signatures of an experimental alluvial fan
DOI:
https://doi.org/10.17735/cyg.v39i1-2.105207Keywords:
alluvial fan, scale independence, physical modelling, geomorphological experimentsAbstract
Alluvial fans constitute attractive environments for human settlements in mountainous areas, however, their dynamic evolution entails a significant risk to the surrounding population and infrastructure. In recent decades there has been a remarkable development in the study of these landforms from an experimental approach, nevertheless, there are fundamental limitations in applying the principles of classical dynamical scaling to represent these systems. Therefore, it is necessary to assess how capable models are of capturing the dynamics of natural landscapes and to advance towards a quantitative understanding of the effectiveness and limits of natural scale independence in morphodynamics. To this aim, we performed a series of experiments with sediment-laden flows on a physical model of alluvial fan replicated at two different scales (1:1 and 3:4). The exposed areas associated with each experiment were quantified and mapped in a GIS. Exposure probability maps, descriptive and inferential statistical analysis of exposure percentages, and spatial statistical analysis of the exposure probability distribution were then conducted to evaluate the degree of statistical similarity of the patterns as the scale of the model was varied. The results obtained showed significant statistical variations in the distributary dynamics of both models, reflecting a dissimilarity in the kinematics of the processes occurring in the fan, which leads to the conclusion that, at least for a model under unconfined flow conditions similar to the one used in this study, scale independence does not fully apply. This implies that small-scale models should be used with caution, especially for the study of hazards in real alluvial fans, since the response in statistical terms on the indication of the hazard presents significant discrepancies when varying the scale of the model used.
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