Characterization of a landslide-triggered debris flow at a rainforest-covered mountain region in Brazil

Victor Carvalho Cabral,Claudia Vanessa Dos Santos Corrêa,Vinicius Veloso,Fernando Mazo D’Affonseca,Felipe Vemado,Ana Lucía,Marcelo Fischer Gramani,Andrea Fregolente Lazaretti,Christiane Zarfl,Lis Maria Reoni Rabaco,Lucilia Do Carmo Giordano,Augusto José Pereira Filho,Eymar Silva Sampaio Lopes,Claudia Cristina Dos Santos,Fábio Augusto Gomes Vieira Reis,Agostinho Tadashi Ogura

doi:10.1007/s11069-021-04811-9

Abstract

Debris flows represent great hazard to humans due to their high destructive power. Understanding their hydrogeomorphic dynamics is fundamental in hazard assessment studies, especially in subtropical and tropical regions where debris flows have scarcely been studied when compared to other mass-wasting processes. Thus, this study aims at systematically analyzing the meteorological and geomorphological factors that characterize a landslide-triggered debris flow at the Pedra Branca catchment (Serra do Mar, Brazil), to quantify the debris flow’s magnitude, peak discharge and velocity. A magnitude comparison with empirical equations (Italian Alps, Taiwan, Serra do Mar) is also conducted. The meteorological analysis is based on satellite data and rain gauge measurements, while the geomorphological characterization is based on terrestrial and aerial investigations, with high spatial resolution. The results indicate that it was a large-sized stony debris flow, with a total magnitude of 120,195 m3, a peak discharge of 2146.7 m3 s−1 and a peak velocity of 26.5 m s−1. The debris flow was triggered by a 188-mm rainfall in 3 h (maximum intensity of 128 mm h−1), with an estimated return period of 15 to 20 years, which, combined with the intense accumulation of on-channel debris (ca. 37,000 m3), indicates that new high-magnitude debris flows in the catchment and the region are likely to occur within the next two decades. The knowledge of the potential frequency and magnitude (F–M) can support the creation of F–M relationships for Serra do Mar, a prerequisite for reliable hazard management and monitoring programs.

Highlights

Debris flows pose great threat to human life and infrastructure, especially in mountain regions, due to their sudden occurrence, high mobility, volume, impact energy and large run-out distance (Iverson 2000; Begueria et al 2009; Luna et al 2012)
Precipitation recorded by the rain gauges integrated to the Brazilian pluviometer network (Fig. 4) is notably lower than what the nearest rain gauge documented, suggesting that the extreme rainfall rates were mainly concentrated near the hillslopes of Pedra Branca as a result of orographic effect
This study characterized a debris flow that occurred at Serra do Mar in February 2017

Summary

Introduction

Debris flows pose great threat to human life and infrastructure, especially in mountain regions, due to their sudden occurrence, high mobility, volume, impact energy and large run-out distance (Iverson 2000; Begueria et al 2009; Luna et al 2012). These phenomena occur when a mixture of earth material, water and air very rapidly surges down steep drainage paths (Varnes 1978; Takahashi 2006; Hungr et al 2014) and their primary triggering factor is high-intensity rainfall (Milne et al 2008). Despite their highly destructive potential, debris flows are still poorly studied when compared to other mass-wasting processes in Brazil, mainly due to insufficient monitoring (Borga et al 2014; Kobiyama et al 2015; Gregoretti et al 2018)

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Discussion

Conclusion