Contribution area in the plateau in watersheds located at passive margin’s escarpments: implications for the analysis of debris flow susceptibility

Abstract

Escarpments’ watersheds are, in general, very susceptible to hydrogeomorphological processes such as debris flows. Furthermore, in escarpments with passive margins, the occurrence of river captures in the escarpment-plateau contact is common, promoting hydrodynamic changes in the river systems. When incorporating terrains with different characteristics, the morphometry of the basin, expressed from a set of parameters, may present values that are not representative of the watersheds’ dynamics in steep reliefs. The objective of this work is to compare the susceptibility to debris flows of watersheds, analyzed with and without the capture area in the plateau, through a semi-quantitative method based on the use of morphometric parameters. Therefore, 59 basins were delimited on the Serra Geral escarpment in the Caminhos dos Cânions do Sul Geopark. There were significant differences in the classes of greater susceptibility: the basins analyzed with the contribution area on the plateau presented 30.5% classified as High susceptibility and 10.1% as Very High, while the basins analyzed without a contribution area on the plateau were 22 % High and 44.1% of Very High. Considering the records of recent debris flow events, the results seem more adjusted to reality when considering the basins without the drainage area on the plateau.