Mitigation of large landslides and debris flows in Slovenia, Europe

Mikoš, Matjaž (author), Majes, Bojan (author)

In Slovenia, a small central European country, in the second half of the 20th century minor landslides of different forms (shallow landslides, slides, slumps – average volume of 1000 m3, rarely 10,000 m3) were prevailing, mainly triggered during short and intense rainfall events or after prolonged rainfall periods of moderate intensities. Unfavorable geological conditions are the main causes for a high slide density (≈ 0.4 slide per 1 km2) in Slovenia, despite good vegetation conditions (more than 60% covered by forests). Experiences with mitigation of large landslides were rare until the last decade, when four large landslides (Stože, Slano Blato, Strug, and Macesnik) with volumes of the order of 1 million m3 were triggered and urged for fast mitigation. They can be placed in the category of rainfall-induced landslides that became active in unfavorable geological conditions. The Stože Landslide with a volume of around 1.5 million m3 was initiated in November 2000 as a debris landslide on the Stože slope in morainic material above the village of Log pod Mangartom in W Slovenia after a wet autumn period with no snow accumulation but rising runoff coefficients. It turned from a debris landslide on a hill slope into a catastrophic debris flow due to low inertial shear stress caused by high water content. The Slano Blato Landslide also formed in fossil landslide masses on a contact of calcareous and flysch formations during wet autumn period in November 2000. It is ever since progressively enlarging behind the main scarp via retrogressive slumping of new and freshly weathered material that due to high water pore pressures turns into a viscous earth flow. The Strug Landslide is a very good example of a complex slope movement, which started in December 2001 as a rockslide with a consequent rock fall that triggered secondary landslides and caused occasional debris flows. In 2002 over 20 debris flows were registered in the village of Koseč below the Strug Landslide, mainly on days with a daily rainfall accumulation of 20 to 30 mm. In 2003 and 2004 no further debris flows could be observed, therefore these events in the Strug landslide area were defined as material and not rainfall driven events. The Macesnik Landslide above the village of Solčava in N Slovenia near the border with Austria was triggered in autumn 1989. Till 1994 there were no activities on the landslide. In the period between 1994 and 1998 the advancement of the landslide on the slope was utmost intense. Firstly, the landslide destroyed state road, and a new pontoon bridge had to be built instead. In 1996, the landslide advanced and destroyed a turn on the same state road. In 1999, a large rock outcrop stopped the advancement of the landslide. Further advancement would possibly destroy several farmhouses on its way down the valley towards the Savinja River. Possible damming of this alpine river would cause a catastrophic flooding. The ongoing mitigation of these landslides is subjected to a special law adopted in 2002 (revised in 2005). The final mitigation is planned to be finished before the end of 2010, with estimated costs of 60.5 Mio € for all activities planned. These costs should be added to the estimated sum of 83.5 Mio € as the final remediation costs for all other registered active small-sized landslides in Slovenia. Practical experiences in Slovenia with large landslides up to now show that only strict and insightful co-ordination, interdisciplinary approach and adequate financial support may lead to a successful mitigation.

• Language: Unknown
• Keywords: landslides, debris flows, Slovenia, mitigation, legislation, hydrology, engineering geology, geotechnical engineering
• Work type: Not categorized
• Organization: FGG - Faculty of Civil and Geodetic Engineering
• Publisher: Nova Science Publishers
• Year: 2010
• Number of pages: 105-131
• PID: 20.500.12556/RUL-73250
• Publication date in RUL: 30.10.2015