Abstract
Abstract. Traditionally, interactions between tributary alluvial fans and the main river have been studied in the field and in the laboratory, giving rise to different conceptual models that explain their role in the sediment cascade. On the other hand, numerical modeling of these complex interactions is still limited because the broad debris flow transport regimes are associated with different sediment transport models. Even though sophisticated models capable of simulating many transport mechanisms simultaneously exist, they are restricted to research purposes due to their high computational cost. In this article, we propose a workflow to model the response of the Crucecita Alta alluvial fan in the Huasco Valley, located in the Atacama Desert, Chile, during an extreme storm event. Five different deposits were identified and associated with four debris flow surges for this alluvial fan. Using a commercial software application, 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. Once our model is calibrated, we use our workflow to test if a channel is large enough to mitigate the impacts of these flows and the effects on the tributary–river junction connectivity.
Highlights
In arid and semi-arid regions, extreme storm events commonly trigger debris flows with high potential to modify the landscape (Mather and Hartley, 2005; Michaelides and Singer, 2014)
We analyze if the proposed workflow can reproduce the debris flow event and the geomorphological adjustments that this alluvial fan experienced
The new scoured channel on the alluvial fan is wider than the channel observed in the field possibly due to the numerical model resolution. These results show that the fan–river interactions become important for surges 3 and 4 because the tributary sediment discharge experiences a complete coupling with the main river through alluvial fan trenching and progradation
Summary
In arid and semi-arid regions, extreme storm events commonly trigger debris flows with high potential to modify the landscape (Mather and Hartley, 2005; Michaelides and Singer, 2014). The sediment stored in the catchments is transported towards tributary-junction alluvial fans and main rivers during these events. Tributary-junction alluvial fans play a crucial role in the transference of sediment from source areas to the main river (Fryirs, 2013; Aguilar et al, 2020). Understanding the fan dynamics and fan–river interactions is necessary to comprehend the sediment cascade during debris flow events. These processes are still not properly modeled in hazard assessment projects (Savi et al, 2020)
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