The automatic detection and identification of alpine mass movements such as debris flows, debris floods, or landslides have been of increasing importance for devising mitigation measures in densely populated and intensively used alpine regions. Since these mass movements emit characteristic seismic and acoustic waves in the low-frequency range (<30 Hz), several approaches have already been developed for detection and warning systems based on these signals. However, a combination of the two methods, for improving detection probability and reducing false alarms, is still applied rarely. This paper presents an update and extension of a previously published approach for a detection and identification system based on a combination of seismic and infrasound sensors. Furthermore, this work evaluates the possible early warning times at several test sites and aims to analyze the seismic and infrasound spectral signature produced by different sediment-related mass movements to identify the process type and estimate the magnitude of the event. Thus, this study presents an initial method for estimating the peak discharge and total volume of debris flows based on infrasound data. Tests on several catchments show that this system can detect and identify mass movements in real time directly at the sensor site with high accuracy and a low false alarm ratio.

International and national laws promote stakeholder collaboration and the inclusion of the community in flood risk management (FRM). Currently, relocation as a mitigation strategy against river floods in Central Europe is rarely applied. FRM needs sufficient preparation and engagement for successful implementation of household relocation. This case study deals with the extreme flood event in June 2016 at the Simbach torrent in Bavaria (Germany). The focus lies on the planning process of structural flood defense measures and the small-scale relocation of 11 households. The adaptive planning process started right after the damaging event and was executed in collaboration with authorities and stakeholders of various levels and disciplines while at the same time including the local citizens. Residents were informed early, and personal communication, as well as trust in actors, enhanced the acceptance of decisions. Although technical knowledge was shared and concerns discussed, resident participation in the planning process was restricted. However, the given pre-conditions were found beneficial. In addition, a compensation payment contributed to a successful process. Thus, the study illustrates a positive image of the implementation of the alleviation scheme. Furthermore, preliminary planning activities and precautionary behavior (e.g., natural hazard insurance) were noted as significant factors to enable effective integrated flood risk management (IFRM).

As a consequence of their natural occurrence and the frequent formation of multiple surges with high sediment loads, debris flows are considered one of the most hazardous gravity‐driven mass movements in mountain regions. Field measurements of surge dynamics are an essential link in the chain of understanding fundamental process dynamics and engineering protection against debris flows. However, continuous information on the velocities of multiple consecutive surges within a single debris‐flow event with high temporal resolution is rare. In this study, we present a new pulse‐Doppler radar (PD radar) for high‐resolution real‐time debris‐flow monitoring. We analyze PD radar data sets over a torrent length of 250 m for two debris flows that occurred at the Gadria creek (IT), on 26 July 2019 and 10 August 2020. The radar data were validated with independently derived data from particle image velocimetry and manually tracked velocities. We observe that between surges, the flow frequently comes to a complete halt and is re‐mobilized by subsequent surges, resembling erosion‐deposition waves in granular flows. In addition, our data confirm that surges can superimpose and merge. We anticipate that the outcomes of this work serve as a blueprint for future high‐resolution observations of debris‐flow surge dynamics with PD radar and that our findings provide new insights into the physical principles of natural debris flows.

Torrential catchments are complex systems showing a huge diversity of sediment and flow regime reactions. Therefore, it seems reasonable to decrease the complexity by introducing a conceptual framework to obtain a general idea of the torrential system’s behavior. The aim of the manuscript is to provide a conceptual framework and a stepwise procedure to develop a reproducible sediment management concept. This involves starting with a definition of torrential process types. These processes are then routed through the drainage system, which is divided into homogeneous reaches. Each reach transfers a flow process from the upstream node to the adjacent downstream reach, based on driving geomorphic factors of sediment mobilization and deposition. Additionally, a sediment budget, derived from cumulative erosion and deposition volumes, is calculated. The estimated flow process together with the sediment budget enables the selection of a sediment management strategy. The implementation of the strategy is based upon the selection of functions, which define the desired modification with regard to the torrential system. Ultimately, the sum of each function’s performance must lead to the fulfilment of the overall protection objective.