Description and analysis of the debris flows occurred during 2008 in the Eastern Pyrenees 1Department of Geotechnical Engineering and Geosciences, Technical University of Catalonia, Barcelona, Spain
2Geosciences Department – Faculty of Sciences, National University of Colombia, Bogotá, Colombia
3Sediment Transport Research Group, Technical University of Catalonia, Catalonia, Barcelona
Received: 04 Nov 2009 – Revised: 26 Apr 2010 – Accepted: 12 May 2010 – Published: 30 Jul 2010Abstract. Rainfall-triggered landslides taking place in the Spanish Eastern
Pyrenees have usually been analysed on a regional scale. Most
research focussed either on terrain susceptibility or on the
characteristics of the critical rainfall, neglecting a detailed
analysis of individual events. In contrast to other mountainous
regions, research on debris flow has only been performed marginally
and associated hazard has mostly been neglected.
In this study, five debris flows, which occurred in 2008, are
selected; and site specific descriptions and analysis regarding
geology, morphology, rainfall data and runout were performed. The
results are compared with worldwide data and some conclusions on
hazard assessment are presented.
The five events can be divided into two in-channel debris flows and
three landslide-triggered debris flows. The in-channel generated
debris flows exceeded 10 000 m3, which are unusually large mass
movements compared to historic events which occurred in the Eastern
Pyrenees. In contrast, the other events mobilised total volumes less
than 2000 m3. The geomorphologic analysis showed that the
studied events emphasize similar patterns when compared to published
data focussing on slope angle in the initiation zone or catchment
Rainfall data revealed that all debris flows were triggered by high
intensity-short duration rainstorms during the summer season.
Unfortunately, existing rainfall thresholds in the Eastern Pyrenees
consider long-lasting rainfall, usually occurring in autumn/winter.
Therefore, new thresholds should be established taking into account
the rainfall peak intensity in mm/h, which seems to be a much more
relevant factor for summer than the event's total precipitation.
The runout analysis of the 2008 debris flows confirms the trend that larger
volumes generally induce higher mobility. The numerical simulation of the Riu
Runer event shows that its dynamic behaviour is well represented by Voellmy
fluid rheology. A maximum front velocity of 7 m/s was back-analysed for the
transit section and even on the fan velocities larger than 2 m/s were
This preliminary analysis of the major Eastern Pyrenean debris flows
represents the first background for future studies. Additional research on
other events is necessary to support the results presented herein, and to
properly assess and reduce hazard related to debris flows.
Citation: Portilla, M., Chevalier, G., and Hürlimann, M.: Description and analysis of the debris flows occurred during 2008 in the Eastern Pyrenees, Nat. Hazards Earth Syst. Sci., 10, 1635-1645, doi:10.5194/nhess-10-1635-2010, 2010.