Impact of flexible net barriers on torrential processes under different hydrological conditions, including the extreme flood of August 2023 in Slovenia

Climate change is expected to increase the magnitude and frequency of water-related hazards such as debris flows and other types of mass movements. Therefore, mitigation measures need to be carefully planned to protect infrastructures and communities. In this study, the effects of flexible net barriers on erosion and sediment transport processes, as well as geomorphological changes in two typical alpine torrents are investigated. Special attention is paid to the extreme flood event of August 2023 in Slovenia. The results show that the flexible net barriers were able to retain large amounts of sediment and protect downstream infrastructure despite the extreme rainfall with a return period of over 250 years. During the extreme event in August, high impacts were detected by monitoring devices at several locations withing the investigated area. During the extreme event, around 2000 m3 of material was trapped behind the flexible net barriers in the Brezovški graben, while between the barriers, there were also sections where erosion processes took place. The amount of net erosion due to the August 2023 event was estimated at around 1500 m3 in the investigated area (i.e., 0.063 km2) of the Brezovški graben. The flexible net barriers proved to be an effective solution for mitigating the torrential hazards since the sediment transport dynamic after the August 2023 event decreased. Data acquisition using remote sensing methods enables us to enhance the understanding of torrential processes.