Marko Komac

Rainfall thresholds for rainfall-induced landslides in Slovenia

In Slovenia, rainfall-induced landslides lead to considerable damages, even causing human losses. In order to reduce the impact of this kind of landslide, several researchers analyzed rainfall-induced landslides in this country, but to date, no rainfall thresholds have been developed for a landslide warning system at national scale. In this paper, the definition of rainfall thresholds for rainfall-induced landslides in Slovenia is presented. The thresholds have been calculated by collecting approximately 900 landslide data and the relative rainfall amounts, which have been collected from 41 rain gauges. To define the thresholds, an existing procedure characterized by a high degree of objectiveness has been used. This approach is based on a software that was developed for a test site with very different characteristics (Tuscany, central Italy). At first, a single national threshold has been defined; subsequently, the country was divided into four zones, on the basis of the major river basins. The effectiveness of the thresholds has been verified by the use of several statistical parameters and it resulted in quite good performances, even if with some uncertainties, probably due to the quality of the available data. Besides the setting of a threshold system, usable for civil protection purposes at national scale, an additional outcome of this work was the possibility of applying, with good results, a methodology defined for another region, therefore testing its degree of exportability in different settings.

Coupling of GPS/GNSS and radar interferometric data for a 3D surface displacement monitoring of landslides

Persistent scatterer interferometry (PSI) is capable of millimetric measurements of ground deformation phenomena occurring at radar signal reflectors (persistent scatterers, PS) that are phase coherent over a period of time. However, there are also limitations to PSI; significant phase decorrelation can occur between subsequent interferometric radar (InSAR) acquisitions in vegetated and low-density PS areas. Here, artificial amplitude- and phase-stable radar scatterers may have to be introduced. I2GPS was a Galileo project (02/2010–09/2011) that aimed to develop a novel device consisting of a compact active transponder (CAT) with an integrated global positioning system (GPS) antenna to ensure millimetric co-registration and a coherent cross-reference. The advantages are: (1) all advantages of CATs such as small size, light weight, unobtrusiveness and usability with multiple satellites and tracks; (2) absolute calibration for PSI data; (3) high sampling rate of GPS enables detection of abrupt ground motion in 3D; and (4) vertical components of the local velocity field can be derived from single-track InSAR line-of-sight displacements. A field trial was set to test the approach at a potential landslide site in Potoška planina, Slovenia to evaluate the applicability for operational monitoring of natural hazards. Preliminary results from the trial highlight some of the key considerations for operational deployments in the field. Ground motion measurements also allowed an assessment of landslide hazard at the site and demonstrated the synergies between InSAR and GPS measurements for landslide applications. InSAR and GPS measurements were compared to assess the consistency between the methods from the slope mass movement detection aspect.

The ICL Adriatic-Balkan Network: analysis of current state and planned activities

International Consortium on Landslides (ICL) Adriatic-Balkan Network was established in January 2012 as one of eight regional and thematic ICL networks to promote activities of the International Consortium on Landslides and the International Programme on Landslides. This paper presents the annual report of the ICL Adriatic-Balkan Network for the year 2012. The main activity of the regional network was to complete an overview of publicly available data and sources about landslides in the region, scientific and professional practices related to evaluation and mitigation of landslide hazard, as well as related legislative framework. Recommendations for the discussion and endorsement in the course of the ICL Adriatic-Balkan Network activities will be derived from the analysis of strengths, weaknesses, opportunities, and threats related to landslide issues which are present at the national level in Croatia, Slovenia, and Serbia and at the regional level. Discussion and endorsement of the recommendations are planned as a further activity which will be held in March 2013 in Zagreb (Croatia), during the planned first regional symposium on landslides in the Adriatic-Balkan Region.

A National Warning System for Rainfall-Induced Landslides in Slovenia

In Slovenia intense short and less intense long-duration rainfall is a primary cause of shallow landslides that some estimates put at 10,000, or approximately one landslide per two square kilometres. These events impose a huge burden on local and state budgets, occasionally even taking lives. At least part of the damage (and the loss of lives) could be prevented with a reliable near real-time landslide hazard forecast system that would continuously draw from three data/model pillars: the precipitation forecast model, the landslide susceptibility model and the rainfall triggering values for landslide occurrence. Each of the three pillars brings some uncertainty to the landslide hazard forecast. A project was set up to forecast the possible occurrence of rainfall-induced landslides in Slovenia (acronym “Masprem”), tackling all three pillars, but focusing primarily on the rainfall triggering values. With the goal of an automated near real-time landslide hazard forecast that will eventually be promptly available online to the general public, the challenges of precipitation forecast data conversion and transfer between two servers, continuous forecast model development and serving the intermediate forecast results on the web were dealt with. The project set up a challenging task, to model the landslide hazard through time for the whole of Slovenia at a coarser scale and to model the same hazard for selected municipalities at a more detailed scale. The results and lessons learned will be presented in this paper.

Landslides Susceptibility Mapping in Oklahoma State Using GIS-Based Weighted Linear Combination Method

Oklahoma experiences approximately 20 reported landslides per year, which cause damage to transportation corridors and infrastructure. A refined regional hazard map has the potential ability to assist the state with detecting landslide hotspots and prevent future transportation corridor blockages. Combining the Geographic Information System (GIS) and high resolution satellite images, a first-cut landslide susceptibility map over the state of Oklahoma has been generated through the following two steps. The top four key landslide-controlling factors, including slope, soil texture type, land cover and elevation, were derived from a comprehensive geospatial database. After that, GIS-based weighted linear combination (WLC) method was utilized to assign the factor weight for each controlling parameter to generate the landslide susceptibility values, which are classified into five categories. Our study indicates that the entire state can be divided into five levels of susceptibility, namely very low (7.80 %), low (38.32 %), medium (45.15 %), high (8.09 %) and very high (0.64 %). These results match the historical landslide risk map well, especially in the south eastern and north western corner of the state. Further comparison with the landslide inventory data provided by the Oklahoma Department of Transportation (ODOT) and U.S. Geological Survey (USGS) shows that, 17 out of 19 (ODOT) and 60 out of 86 (USGS) events are located in category “high” or “very high”, which demonstrates the ability of WLC method in predicting landslide prone areas.

Landslides at a uranium mill tailing deposit site Boršt (Slovenia) detected by radar interferometry

This paper presents a comparison of persistent scatterer interferometry (PSI) monitoring results with in situ displacement measurements at the November 1990 landslide at the Boršt uranium mill tailing deposit site after heavy rain. Although the landslide did not directly endanger people, site remediation works were undertaken due to the subsequent environmental problems. Additionally, in situ monitoring with benchmarks was established in order to detect the ground motion of the landslide body. PSI campaigning in the Škofjeloško-Cerkljansko area, where the uranium mill tailing is situated, performed for the purpose of measuring displacements of natural targets near the active landslide area, also detected displacements, most probably indicating a creeping process. When comparing the pre- and post-remediation velocities at the benchmarks located on the landslide with persistent scatterers (PSs) located near the landslide, the rates could be regarded as background. The results show that the remediation works in the form of a drainage tunnel were very effective as post-remediation velocities at the landslide closer to the PSs resembled the velocities of the PSs, while the velocities of the landslide mass above the drainage tunnel slowed down, even to below the background velocities. The high correlation values between the movements of the benchmarks and the PSs also confirm that the remediation works were effective as the fluctuations in the displacement values of the landslide were very similar to those of the PSs. Nevertheless, although there are several limitations in comparing the two different datasets, the PSI technique can be complementary to conventional in situ methods.

Rockfall Susceptibility Assessment at the Municipal Scale (Bovec Municipality, Slovenia)

A detailed rockfall susceptibility map of the Bovec municipality at 1:25,000 scale was produced by application of the methodology, developed at the Geological Survey of Slovenia. A Chi-square analysis with a linear weighted sum model approach was used on the basis of selected spatio-temporal factors (lithology, strata dipping, slope angle and distance to faults) for defining the rockfall areas and classifying them according to probability of rockfall occurrence. The final product is a rockfall susceptibility map (only for source areas in this phase), which serves as one of the bases in municipality spatial planning. It is also available through a web application for general public access. The purpose of the latter is in part also raising the public awareness.

Earthquake-Induced Landslides in Slovenia: Historical Evidence and Present Analyses

The paper gives a short overview of the historical earthquakes on the territory of Slovenia since AD 792, with the 1511 Idrija Earthquake (MM = 6.8 ± 0.3) as the strongest earthquake in this record. Firstly, seismotectonic characteristics of Slovenia are presented together with the seismological map of Slovenia. Secondly, a national landslide database and landslide occurrence map (cadastre) is discussed. Furthermore, different (statistical) models are presented that have been used to prepare landslide (also debris flows and rock falls) susceptibility maps of Slovenia at scale 1:250,000. The role of earthquakes as triggering factors in these models is discussed. Moreover, a field case study is discussed; the conclusions reached by the analysis of the numerous rock falls initiated during the 1998 Posocje earthquake (ML = 5.6; the strongest earthquake in the 20th century with the epicenter in the territory of Slovenia) and the 2004 Posocje earthquake (MLV = 4.9) is presented. A short final section on legislative framework in Slovenia with regard to hazard and risk mapping of slope instabilities respectively mass movements (including earthquake-induced landslides) is given.

Comparison of prediction methods for oxygen-18 isotope composition in shallow groundwater

Groundwater is the most important source of drinking water in the world. Therefore, information on the quality and quantity is important, as is new information related to the characteristics of the aquifer and the recharge area. In the present study we focused on the isotope composition of oxygen (δ18O) in groundwater, which is a natural tracer and provides a better understanding of the water cycle, in terms of origin, dynamics and interaction. The groundwater δ18O at 83 locations over the entire Slovenian territory was studied. Each location was sampled twice during the period 2009-2011. Geostatistical tools (such us ordinary kriging, simple and multiple linear regressions, and artificial neural networks were used and compared to select the best tool. Measured values of δ18O in the groundwater were used as the dependent variable, while the spatial characteristics of the territory (elevation, distance from the sea and average annual precipitation) were used as independent variables. Based on validation data sets, the artificial neural network model proved to be the most suitable method for predicting δ18O in the groundwater, since it produced the smallest deviations from the real/measured values in groundwater.

TXT-tool 2.386-2.1 A System to Forecast Rainfall-Induced Landslides in Slovenia

Nowadays, an increasingly important area of work in landslides prediction is the development of tools to generate warnings to potentially affected communities. For the last 20 years many countries and cities have been affected by heavy rainfall leading to landslides and Slovenia is no exception. Therefore, public awareness of extreme events has notably increased across the world in different sectors. In order to provide a solution to the problem a national landslide warning system, Masprem, has been developed based on three main raster datasets: landslide-triggering rainfall threshold values, precipitation forecasts, and landslide susceptibility maps. At the moment, a landslide warning system predicts landslide probability for the area of Slovenia in the scale 1:250,000 twice a day. A Masprem system also calculates landslide predictions on a local level, including maps of exposure of inhabitants, buildings and different types of infrastructures to potential landslide occurrence at a scale of 1:25,000 for five selected municipalities. In the present Teaching Tool a design of the system for modelling a probability of landslide through time in Slovenia is highlighted.