Debris-flow hazard investigation with Kanako-2D in a rural basin, Alto Feliz municipality (Brazil)

Abstract

Mountainous regions of Brazil, especially where rural families live, need to be assessed for debris flow. Though debris flows rarely occur in this country, they have caused serious damages including human losses. Computational modeling of debris flows is an important tool to develop hazard maps and to improve the understanding of debris-flow mechanisms, since observed occurrences are rare. Therefore, the objective of the present study was to evaluate the potential for debris flows in a small rural basin (0.712 km²), in the municipality of Alto Feliz, Rio Grande do Sul state (Brazil), by using the Kanako-2D model which was calibrated with another debris flow in the same region. We simulated three scenarios by altering the debris volume and consequently the hydrograph (peak flow and peak time). All the scenarios show that debris flows would impact an existing rural house, even with the smallest potential debris volume. The modeled erosion and deposition areas along the debris flow are similar, with the magnitudes (depths) of erosion and deposition being different among the scenarios. In general, in each transversal section, the most pronounced point of erosion or deposition is almost always at the thalweg location. Along the stream channel, deposition was greatest upstream of an abrupt reduction in slope. The formation of a natural dam is observed at the channel junctions where erosion and deposition alternatively took place. Because of the investigation of the potential of debris flows, the simulation results were not compared with the actual occurrence in the present study. However, the present study could show that computational modeling of debris flow is very important for localities where debris flow occurs and that the debris-flow hazard map is useful for land-use planning.