# Torrential Hazards' Mitigation Measures in a Typical Alpine Catchment in Slovenia
## 4 Conclusions  
This study presents an overview of torrential hazard mitigation measures used to mitigate the torrential hazards in a typical Alpine catchment in Slovenia based on post-extreme-event surveys and modeling results. The implementation of countermeasures was divided into three phases: (i) channel regulation work in the downstream part of the watershed, (ii) the construction of a large slit check dam with a retention volume of approximately 14,000 m\({}^{3}\) for sediment retention, and (iii) the implementation of 16 flexible net barriers with an estimated retention volume of 8000 m\({}^{3}\) in both torrents in the upstream part of the watershed. It should be noted that phase (ii) is currently ongoing, while phases (i) and (iii) have already been completed. In the scope of the conducted measures, an extensive monitoring system has also been established that will enable us to explore characteristics of torrential hazards in the future. The monitoring system includes a rain gauge, a video recording system, periodical UAV surveys, Guards(r), and a field test site to measure concrete abrasion. The preliminary results have indicated that activity detected by Guards(r) was caused either by strong wind or heavy rainfall. However, not all thunderstorms caused any torrential erosion activities. Hence, further research is needed to better evaluate the triggering factors of torrential hazards. Field abrasion experiments need more time to be effective since, so far, flexible net barriers have substantially reduced sediment transport over the concrete plates--this will be a rather long-term experiment. The main scientific and applied contribution of this study is to clearly present and show examples of good practices in sediment management in a typical Alpine catchment that could also be used in other parts of the country. The recent August 2023 flood event has shown that the executed structural (grey) mitigation measures effectively limited excessive sediment erosion and transport from steep torrential channels to downstream areas; they withstood high dynamic loads and, as such, are able to cope with extreme hydro-meteorological events above design discharges determined for a 100-year return period [28]. After the August 2023 event, there was no significant damage to the Krvavec cabin car ski lift (Figure 13)--contrary to substantial damages during the less intense May 2018 event [23]. Also, the rainfall erosivity for the 2023 event was larger than the one for the 2018 event, when there was significant damage at the Krvavec cabin car ski lift ([23]). Therefore, such structural (grey) measures (e.g., flexible net barriers) could be applied in steep torrential catchments in similar geological settings and those that are difficult to access with heavy machinery and hence the construction of torrential concrete check-dams is more challenging. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app132011136/s1](https://www.mdpi.com/article/10.3390/app132011136/s1)]([https://www.mdpi.com/article/10.3390/app132011136/s1](https://www.mdpi.com/article/10.3390/app132011136/s1)), Figure S1: Torrential unstable conditions in the Brezovski torrent; Figure S2: Drilling process (left) and steel anchors (right); Figure S3: Construction site in the Brezovski graben torrent; Figure S4: Series of flexible barriers on the Brezovski torrent; Figure S5: Series of flexible barriers on the Brezovski torrent; Figure S6: Maximum 30-m wind speed and rainfall rate for the period of Guard@operation and identification of days when the Guards@detected some activity. Wind speed and rainfall data are obtained from the nearby Krvavec station; Figure S7: Some additional parameters measured by the Guards(r) during the one-month period; Table S1: Main characteristics of events detected by Guards(r).