Analysis of triggering factors of debris flows and conditions for possible reactivation: Case study of the Lemešná Mountain in the Javorníky Range, Czech Republic

Abstract

On 2nd June 2010, heavy rainfall triggered a significant debris flow on the southern slope of Lemešná Mountain in the Javorníky Range (Outer Western Carpathians), Czech Republic. Multidisciplinary research was carried out there, including geomorphological survey, electrical resistivity tomography, laser scanning, soil and rainfall analysis. The debris flow occurred after the prolonged convective and intense rainfall. The antecedent precipitation index calculated for the previous 30 days reached 134.1 mm and the daily rainfall 37.4 mm, 13 times higher than the long-term average daily rainfall. The debris flow occurred in unconsolidated flysch sediments and caused minor damages. The locality was affected by slope movements in the past, as evidenced by two debris flow deposit cones in the valley. Electrical resistivity tomography revealed a sliding surface at a depth of 5 m and another at 15-20 m. However, according to local residents and the forest manager, no mass movement has been recorded in there in the last 40 years. Human intervention, particularly artificial drainage and deforestation, could also have contributed to the debris-flow triggering. The aim of this work was a complex analysis of the triggering conditions of the debris flow and a risk assessment of new events in this area.