Debris Flow Occurrences In Rio Dos Cedros,
Southern Brazil: Meteorological And
Geomorphic Aspects
Author(s)
M. Kobiyama, R. F. Goerl, G. P. Corrêa & G. P. Michel
Abstract
In Santa Catarina State (Brazil), Rio dos Cedros is one of the cities that suffered
from natural disasters triggered by very intense rainfall in November 2008.
According to the Municipal Civil Defense, this event caused economic losses of
US$2.1 million and 96 homeless, directly affecting 90% of the municipal
population. The principal phenomenon responsible for these disasters was the
debris flow. In this context, field surveys were conducted throughout the city in
order to investigate the possibility for houses to be affected by landslides and
debris flows. After the preliminary evaluation, two cases of debris flow whose
extensions were over 1 km were chosen for a more detailed survey. The
objective of the present study was to analyze the meteorological and geomorphic
aspects of these cases. The total rainfall in Rio dos Cedros in November 2008
and the entire year of 2008 were 644 mm and 2509 mm, respectively. An
analysis of the daily rainfall during October and November 2008 and the debris
flow occurrence time indicates that the factor triggering debris flows in Rio dos
Cedros in 2008 was the accumulated rainfall, not its intensity. Two debris flows
analyzed in the present study had different geomorphic conditions, one being
confined in the channel and showing ordinal debris flow (Debris A), and the
other unconfined, presenting the debris avalanche feature (Debris B). The larger
density of clastic blocks was observed at the depositional area of Debris B. Both
the localities are characterized with migmatite. Topographic analysis showed that
the volume of the mass movement is related with topographic parameters
(elevation difference and travel distance). This relationship implies that the two
cases of Rio dos Cedros had similar behavior to other cases reported in temperate
and cold regions. It is, therefore, concluded that there is geomorphic control on
Keywords
debris flow, volume of mass movement, topographic survey, rainfall, woody vegetation, Brazil
Related Book
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