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Large Wood And Flash Floods: Evidence From The 2007 Event In The Davča Basin (Slovenia)


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173 - 182




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F. Comiti, L. Mao, E. Preciso, L. Picco, L. Marchi & M. Borga


This paper presents the evidence gathered during a post-flood survey in a Slovenian mountain basin (Davča basin, drainage area of 32 km2) following the catastrophic flood of September 2007. Channel avulsion, debris flows and landslides delivered large volumes of wood into the channel, and massive wood accumulations were found at the basin outlet. Wood-induced dam-break flows were therefore hypothesised to be responsible for most of the damages. Field observations and approximate discharge estimations indicate that the damages suffered in the Davča basin can be attributed to excessive wood load only to a limited extent, and that the critical factors were narrow road crossings which acted as traps for sediment and wood. Keywords: woody debris, flash floods, mountain rivers, Slovenia. 1 Flood hazards due to natural dams and large wood Mountain valleys are subject to several natural hazards, which include mass wasting, debris flow and fluvial processes. However, some of the most hazardous phenomena occur when the three phenomena interact, as in the case of temporary damming of stream channels by landslides [6, 7, 12] or debris-flow deposits which often include large wood (LW) [1, 8, 10]. In fact, the subsequent breaching and collapse of these dams release destructive dam-break waves which can attain extremely high flow discharges, unpredictable from a mere hydrological perspective [9]. As a consequence, such events are thought to


woody debris, flash floods, mountain rivers, Slovenia.