Measures to mitigate torrential hazards in a typical alpine catchment area in Slovenia

Various sediment-related disasters such as flash floods, debris flows and landslides can occur in an alpine torrential catchment area. To protect infrastructure and human life, various structural and non-structural (grey, green and hybrid infrastructure) protection measures can be used to mitigate torrential risks. An overview is given of the protective measures constructed near the Krvavec ski resort in north-western Slovenia (Central Europe). In May 2018, an extreme debris flood occurred in this area, causing considerable economic damage. After the event in May 2018, various field investigations (e.g. geological and topographical surveys) and modeling applications (e.g. hydrological modeling, debris flow) were carried out to prepare the necessary input data for the design of protective measures against such disasters in the future — due to climate change, further disasters are expected in this torrential catchment area. Compensatory measures include the engineering works of local streams, the construction of a large silt check dam for sediment retention, the construction of several smaller retention dams and the construction of 16 flexible net barriers with an estimated retention volume of ~8000 m3 to control erosion. A comprehensive monitoring system was also set up in the study area to observe and monitor potential future extreme events. This monitoring system includes measurements of corrosion of flexible nets, estimation of concrete abrasion on retention dams, regular geodetic surveys with small drones (UAV) and hydro-meteorological measurements with rain gauges and water level sensors. The recent extreme floods of August 2023 also hit this part of Slovenia, and this combination of technical countermeasures withstood the event and prevented large amounts of coarse debris from being transported to the downstream section and destroying infrastructure, as was the case in a less extreme event in May 2018. Therefore, such mitigation measures can also be used in other torrential catchment areas in the alpine environment.