Rainfall Thresholds of the 2014 Smutná Valley Debris Flow in Western Tatra Mountains, Carpathians, Slovakia

Abstract

An extensive debris flow occurred, in the Smutná valley, Western Tatra Mts. in Slovakia on 15 May 2014. The aim of this study is to describe the morphology of the observed debris flow and to evaluate the conditions that preceded its formation as well as the previous activity of debris flows on this path. The observed debris flow is among the most extensive ones in terms of morphometric characteristics in the Roháčská valley and its tributaries (e.g., the length of the erosion-accumulation zone of ~600 m, volume >1200 m3). However, compared to previous studies from the Western Tatra Mts., it belongs to the average sized debris flows, or a minor event in terms of the general size classification based on the volume of debris flows. A similarly extensive debris flow was recorded on this track in the early 1970s after which only two additional minor events have been recorded there until 2014. The monthly precipitation totals in the 2013/2014 winter season were low compared to the long-term average. The main triggering factor for debris flow initiation was continuous rainfall that lasted 29 hours resulting in ~120–135 mm of precipitation. Most of the derived global empirical thresholds for debris flow initiation were exceeded as well as rainfall thresholds suggested by the published studies for the Western Tatra Mts.