Supervisor: Johannes HÜBL

Project assigned to: Tobias SCHÖFFL

Debris flows represent a considerable natural hazard in alpine settlement areas. A central aspect of protection against such events is a deeper insight into the process. The flow velocity is an important physical quantity which is used, for example, in the dimensioning of mitigation structures, for technical building protection and for early warning systems. The measurement of the surface velocity which is regarded as the maximum velocity occurring within a debris flow is therefore an essential link in the chain of fundamental process research and applied protection against natural hazards.

As a result of further development of various technologies such as video technology and high-frequency radar technology, the non-contact measurement of the velocity of a debris flow has improved significantly in recent years. The pulsed Doppler high-frequency radar (HF-radar) provides a wide aspect of applications in alpine mass movements such as debris-flows, avalanches and rockfall and is able to detect such processes.

The Institute of Mountain Risk Engineering (IAN) currently has three HF-radar units in operation. In addition to the debris-flow monitoring station in Lattenbach (Pians, Tyrol), the HF-radar has been in use since 2011, and since 2018 at the Gadria creek monitoring station (South Tyrol, Italy). The third and mobile version of the HF-radar was installed in July 2020 as part of a debris-flow early warning system at the Dawinbach creek (Strengen, Tyrol) and is now being used in a similar way for protection against rockfall in Weißwald (St. Leonhard, Tyrol). In this project, following research questions will be addressed:

  1. What is the surface velocity distribution of a debris-flow? What statistical velocity values of the Doppler spectra are best suited for calculating discharge, total volume and impact forces?
  2. Is there a correlation between surface velocities and other or measured parameters such as flow height?  Can further quantitative statements about dynamic flow characteristics be obtained from this?
  3. Is it possible to improve the early warning thresholds based on the measured events?

Based on a successful validation of the HF-radar, precise discharge and volume calculations of debris-flows will be performed. Furthermore, improved early warning thresholds for the HF-radar will be developed. With the results of the data analysis in this study we aim for deeper insights into the physics and dynamics of debris flows. 

Figure 1: Incoming boulder debris-flow front at the Gadria creek monitoring site on August 10, 2020.

Figure 2: Data visualization of the debris-flow event on August 10, 2020. Here, the dynamics of the pulsating high-velocity surges can be observed.