Slovenian Case Study On Forest Roads Affected By Last Year's Torrential Floods

In July and August 2023, Slovenia was hit by a large number of intense torrential storms, which together resulted in the largest natural disaster in Slovenia. In many places in northern Slovenia, local precipitation and river flows far exceeded the 100-year return periods. The Slovenia Forest Service reported that the storms damaged more than 2,000 km of forest roads, making the management of around 15% of Slovenia's forests temporarily impossible. The forest roads were damaged by debris flows, landslides or windbreak fallen trees. In the Koroška region, we investigated 10 cases of destruction of forest roads at the junctions with torrential streams and studied the possible causes. The size of the catchment areas of the observed bridging objects ranged from 2 to 72 ha. The common characteristics of the damaged roads were: (1) all were built before the year 2000; (2) in all cases, pipe culverts or bridges were clogged with debris or woody material; (3) in one case, a newly built filled slope of skid trail colapsed into the torrent, resulting in a masive debris flow downstream. Some cases could be solved by proper maintenance and larger dimensioning of the transverse structures, while others would only survive if they were reconstructed into dips or by slowing erosion processes upstream.