Trigger characteristics of torrential flows from high to low alpine regions in Austria.

Torrential processes like fluvial flows (flash floods with or without intensive sediment transport) and debris flows can represent a threat to people and infrastructure in alpine domains. Up to now the hydro-meteorological trigger conditions and their connection with geomorphic watershed characteristics that favor the initiation of either process are largely unknown. Based on modeled wetness states we determined the trigger types (long-lasting rainfall (LLR), short-duration storm (SDS) and intense snow melt (SM)) of 360 observed debris flow and fluvial flood events in six climatically and geomorphologically contrasting watersheds in Austria. Results show that the watershed wetness states play very distinct roles for triggering torrential events across the study regions. Hydro-meteorological variables have little power to explain the occurrence of fluvial flows and debris flows in these regions. Nevertheless, trigger type separation highlighted some geomorphic influences. For example, intense SM triggered more events in sub-watersheds (torrential watersheds in the study region) that are characterized by significantly higher Melton ruggedness numbers than LLR does. In addition, the data show that events triggered by LLRs occur in sub-watersheds of similar exposures (aspects) other than SDS. The results suggest that the consideration of different trigger types provides valuable information for engineering risk assessment.

Debris-flow risk analysis in a managed torrent based on a stochastic life-cycle performance.

Two key factors can affect the functional ability of protection structures in mountains torrents, namely (i) infrastructure maintenance of existing infrastructures (as a majority of existing works is in the second half of their life cycle), and (ii) changes in debris-flow activity as a result of ongoing and expected future climatic changes. Here, we explore the applicability of a stochastic life-cycle performance to assess debris-flow risk in the heavily managed Wartschenbach torrent (Lienz region, Austria) and to quantify associated, expected economic losses. We do so by considering maintenance costs to restore infrastructure in the aftermath of debris-flow events as well as by assessing the probability of check dam failure (e.g., as a result of overload). Our analysis comprises two different management strategies as well as three scenarios defining future changes in debris-flow activity resulting from climatic changes. At the study site, an average debris-flow frequency of 21 events per decade was observed for the period 1950-2000; activity at the site is projected to change by +38% to -33%, according to the climate scenario used. Comparison of the different management alternatives suggests that the current mitigation strategy will allow to reduce expected damage to infrastructure and population almost fully (89%). However, to guarantee a comparable level of safety, maintenance costs is expected to increase by 57-63%, with an increase of maintenance costs by ca. 50% for each intervention. Our analysis therefore also highlights the importance of taking maintenance costs into account for risk assessments realized in managed torrent systems, as they result both from progressive and event-related deteriorations. We conclude that the stochastic life-cycle performance adopted in this study represents indeed an integrated approach to assess the long-term effects and costs of prevention structures in managed torrents.

Quantitative surface analysis by total electron yield.

When the surface of a solid sample is irradiated under vacuum by x-rays an electron emission, owing to photoabsorption, can be measured. As the electrons are detected under neglection of their kinetic energies the total electron yield (TEY) is determined. With a tuneable x-ray monochromator the TEY is measured below and above of one of the absorption edges of a given element. A jumplike increase of the TEY signal, due to the additional photoabsorptions in the corresponding atomic level, can be observed - qualitative analysis. The height of this jump can be correlateted to the concentration - quantitative analysis. It can be shown by a fundamental parameter approach for primary and secondary excitations how to use TEY for a quantitative analysis. The information depth lambda of this new method is approximately 2-400 nm depending on the chemical elements and on the original kinetic energies of Auger and photoelectrons. Thus, TEY is located between photoelectron spectrometry and x-ray fluorescence analysis.