Birgit Jochum

Geoelectrical monitoring: an innovative method to supplement landslide surveillance and early warning

Permanent geoelectrical monitoring, using the GEOMON4D instrumentation in combination with high resolution displacement monitoring by means of the D.M.S. system, was performed at two active landslide areas: Ampflwang/Hausruck in Austria, and Bagnaschino in Italy. These sites are part of the Austrian geoelectrical monitoring network, which currently comprises six permanently monitored landslides in Europe. Within the observation intervals, several displacement events, triggered by intense precipitation, were monitored and analysed. All of these events were preceded by a decrease of electric resistivity. The application of an innovative 4D inversion algorithm made it possible to investigate the potential processes which led to the triggering of these events. We conclude that resistivity monitoring can significantly help in the investigation of the causes of landslide reactivation. Since the results also contribute to the extrapolation of local displacement monitoring data to a larger scale, resistivity monitoring can definitely support decision-finding in emergencies.

Geoelectrical monitoring of frozen ground and permafrost in alpine areas: field studies and considerations towards an improved measuring technology

Processes that control permafrost warming in Alpine regions are still not completely understood. Recently, geoelectrical monitoring has emerged as a useful tool to investigate thawing and freezing processes. However, high resistive environments and harsh environmental conditions pose very unfavourable conditions for automated resistivity measurements. Based on the results of several test studies, an improved data acquisition system for geoelectrical monitoring of frozen soils was developed. Furthermore, the implementation of algorithms for statistical analysis of raw data time series led to a significant improvement in the reliability of inversion results. At two Alpine sites, namely Molltaler Glacier and Magnetkopfl/Kitzsteinhorn, the adapted system was tested at soil temperature conditions between 0°C and –12°C. Data was continuously collected at both locations over nearly a full seasonal cycle. The results showed an almost linear dependency of resistivity and temperature at values above –0.5°C. At lower temperatures, the relation was non-linear, indicating that the reduction of porosity due to the shrinking of connected brine channels was the dominating process that determined the value of resistivity. Based on the derived results, further improvements were suggested, especially for measurements at soil temperatures below –4.5°C as low injection currents make it extremely challenging to gather these.

Airborne geophysical mapping as an innovative methodology for landslide investigation: evaluation of results from the Gschliefgraben landslide, Austria

Abstract. In September 2009, a complex airborne geophysical survey was performed in the large landslide affected area of the Gschliefgraben valley, Upper Austria, in order to evaluate the applicability of this method for landslide detection and mapping. An evaluation of the results, including different remote-sensing and ground-based methods, proved that airborne geophysics, especially the airborne electromagnetic method, has a high potential for landslide investigation. This is due to its sensitivity to fluid and clay content and porosity, which are parameters showing characteristic values in landslide prone structures. Resistivity distributions in different depth levels as well as depth slices along selected profiles are presented and compared with ground geoelectrical profiles for the test area of Gschliefgraben. Further interesting results can be derived from the radiometric survey, whereas the naturally occurring radioisotopes 40K and 232Th, as well as the man-made nuclide 137Cs have been considered. While the content of potassium and thorium in the shallow subsurface layer is expressively related to the lithological composition, the distribution of caesium is mainly determined by mass wasting processes.

Numerical Modelling of Hydrological Parameters for an Enhanced Interpretation of ERT Monitoring Data

Open image in new window Electrical Resistivity Tomography (ERT) has become a standard application for evaluation of structural and hydraulic properties of landslides. The technical improvement during the last few years made the method of ERT also attractive for long-term monitoring in term of regularly repeated measurements as newly developed 4-D inversion routines can assure the comparability of different ERT measurements. The interpretation of the achieved data is typically carried out qualitatively on a visual basis. In the framework of the LAMOND project (Long-Term Landslide Monitoring for Understanding of Underlying Dynamic Processes as Basis for an End-User Focused Early Warning) the abilities of numerical optimization and finite element modeling are conducted to close the gap between ERT observations and a dynamic, hydrological process model. So far, only one site could be examined and a workflow for numerical optimization of Archies law has been developed. These results will be the basis for a finite element process model which will deliver basic insights and help in decision-making for early warning systems.

Assessment of Shallow Interflow Velocities in Alpine Catchments for the Improvement of Hydrological Modelling

Advective long-duration rain events play an important role in the development of floods. A realistic depiction of interflow processes is not possible with the most customary precipitation/runoff (P/R) models. To increase knowledge about interflow processes in long-term rainfall events and improve the data situation for hydrological modelling, field experiments were performed in five Austrian catchments. These catchments differ from one another in precipitation characteristics, land cover, land use, pedological and geological situation. Long-term irrigation experiments on large plots combined with the insertion of a salt tracer (LiCl or NaCl) on smaller plots and geoelectrical measurements were used to assess the water movement in the soil and underlying substrate. This study has made significant contributions to (i) improving the design of measuring interflow on the plot and the hillslope-scale, (ii) improving the knowledge of bandwidths of shallow interflow velocities for typical substrates in the Eastern Alps and (iii) facilitating the regionalisation of data acquired at the local level, to the catchment or the regional scale.

Airborne Geophysical Survey and Innovative Landslide Monitoring at Gschliefgraben, Austria

New geophysical approaches for landslide investigation and monitoring were tested in the site of Gschliefgraben by the end of September 2009. Multiparameter airborne geophysics is a promising method for landslide investigation which could quickly determine the most susceptible areas to mass wasting (electromagnetics) and areas with active shallow mass movements (passive microwave); the content of radioactive elements could contribute to studying displacement or weathering degree. The introduced new techniques for mass movement monitoring and early warning (GEOMON4D and D.M.S. automated monitoring systems) proved, that such a combination of high-accuracy monitoring of displacement, ground-water level and ground temperature together with monitoring of the ground resistivity and self-potential temporal changes could definitely be an effective approach for early warning.

Pechgraben Landslide: Evaluation of Geophysical/Geotechnical Methods in Terms of Remediation Support

Information from the application of geophysical and geotechnical methods are essential for decision makers to initiate appropriate emergency or remediation measures in case of a catastrophic landslide event. This paper summarizes all the applied measuring and monitoring methods that accompanied the catastrophic landslide event of Pechgraben (Upper Austria) in 2013 as well as the three years after the completion of major parts of the remediation work. Beside scientific aspects, the focus of the geophysical/geotechnical investigations was put on the support of decision makers. To improve the efficiency of the support for future similar landslide events, it is necessary to evaluate the applied methods in terms of their information content concerning the emergency and remediation strategy. We ended up with the conclusion that there are a few key methods providing essential information for decision makers during different time phases of the landslide event. However, for a detailed understanding of the landslide behavior and the ongoing subsurface processes, a combination of different methods is required.

Monitoring im Bereich der Rutschung Pechgraben (Oberösterreich): Methodik und Ergebnisse

ZusammenfassungDer folgende Artikel beinhaltet eine Zusammenfassung der Monitoring-Methoden, die während der Reaktivierung der Rutschung Pechgraben (OÖ) angewandt wurden bzw. nach wie vor angewandt werden. Die Methoden umfassen die regelmäßige Einmessung eines dichten Punktnetzes mittels GNSS, wiederholte Befliegungen mittels Laserscan zur Bestimmung des Massenverlustes bzw. -zuwachses, Oktokopterbefliegungen für die photogrammetrische Bilddatenauswertung sowie verschiedene geophysikalische Methoden (Geoelektrik, Inklinometer, Bodenfeuchte und Bodentemperatur). Der Schwerpunkt des Artikels liegt auf der exemplarischen Darstellung einzelner Ergebnisse, um die Anwendungsmöglichkeiten der jeweiligen Monitoring-Methode im Bereich von Hangrutschungen zu zeigen.AbstractThis article summarises the application of different monitoring methods during the reactivation of the Pechgraben landslide (Upper Austria). The applied methods (some of them are still acquiring data) incorporated repeated GNSS measurements of several defined benchmarks, repeated laser scan flights for the determination of mass losses or accumulation, octocopter flights for photogrammetric data analysis as well as several geophysical methods (geoelectrics, inclinometer, soil moisture and soil temperature). The focus in this article is put on exemplary evaluation of particular results to demonstrate the application spectrum of the respective monitoring methods in landslide areas.

Geophysics in the Context of Disaster Mitigation: Results from the Landslide at Pechgraben, Austria

In early June 2013 a large landslide was triggered at the area of Pechgraben, situated in a mountainous area of Upper Austria. Only several hours after the onset of the first movements, a geophysical investigation program was started to support the planning of the disaster response actions as well as the design of a follow up early warning system. The geophysical methods included geoelectric profiling, geoelectrical monitoring, borehole logging, GPS, inclinometric, piezometric, soil humidity and optical monitoring as well as airborne geophysics. Within this paper results of different methods are given and evaluated on their role within disaster mitigation.

Results of Geoelectrical Monitoring of Landslides Collected by the SafeLand/TEMPEL Network

Based on the promising results from a pilot monitoring project the GEOMON4D geoelectrical monitoring system was applied to several landslide monitoring tests sites, where also permanent monitoring data of displacement and hydrology are available to investigate the correlation of electrical parameters with other data. This monitoring network was set up in frame of the FP7 project SafeLand and the project TEMPEL (Austrian Science Fund) starting from October 2009 on. Analysis of the first monitoring results confirmed the potential of geoelectrical parameters as additional indicators to be applied within future early warning systems of landslides.