No abstract

No abstract

Shallow landslide processes in geologically prone areas are recognised to pose threat to both human life and property. As precipitation is one of the main triggers for landslides, hydro-meteorological interrelationships and related future changes regarding frequency and magnitude of landslide processes in particular are of major interest. Long-term monitoring investigations of active landslide sites can provide a better understanding of the kinematic behaviour and triggering conditions of slope instabilities induced by hydrometeorological patterns. In this study, we present the installation and first results of a long-term monitoring setup in the Flysch Zone of Lower Austria equipped with a large variety of combined hydrological and geotechnical measuring techniques. The geological unit of the Flysch Zone, characterised by high contents of clay and the corresponding weathering products, is exceptionally prone to earth and debris slides which are mostly triggered by heavy precipitation events or snow melting. The landslide under investigation is situated in the heterogeneous lithology of Flysch deposits, surrounded by private property and without any agricultural usage. There is evidence of landslide activity since the 1950s. As it is showing only moderate displacement velocities (max. 20 cm in 2009), it represents a predestined study site for a long-term monitoring and the testing of new monitoring techniques. One of the main aims of this study is to characterise the internal structure, assess the current landslide dynamics and to analyse recent process activity by means of surface and subsurface monitoring installations. Surface methods currently include terrestrial laser scanning, GNSS and total station measurements. With these, surface movement rates of approx. 12 cm/6 months have been detected in the most active part of the landslide. Inclinometer measurements together with results from core drillings and penetrations tests suggest a complex, rotational landslide system with different shear zones, consisting of a more active part in the upper 3 m underlain by a less active part down to 9-m depth. As this monitoring site is designed to be operated for at least 10 years, information about its structure and high-resolution, multi-temporal data about its dynamics can be correlated with hydrological cause variables in the future. These insights and the exemplary nature of the study site regarding shallow landslide processes in Flysch deposits will be useful for the development of novel analysis methods for both Lower Austria as well as study sites with similar initial conditions.

No abstract

<p>Many examples of regional scale statistical landslide susceptibility assessments can be found in scientific literature. A real-life application of these maps for spatial planning decisions is less common. As result of the MoNOE research project (Method development for landslide susceptibility modelling in Lower Austria), a landslide susceptibility map has been created. Since 2014, this map is constantly used by provincial spatial planners and geologists to guide strategic settlement development in Lower Austria (approx. 19200 km²). Resulting from a multi-temporal inventory of 12,889 slides, a generalized additive model (GAM) was applied to predict the landslide susceptibility using a variety of meaningful morphological and geo-environmental predictors. These easily-applicable, local-scale (1:25,000) landslide susceptibility maps consist of three susceptibility classes. The three classes correspond to low landslide susceptibility (covering 78% of all pixels within the study area), moderate (16% of all pixels) and high (6% of all pixels). Although well accepted by the stakeholders, a few important questions recently arise: a) Is this map able to correctly predict new landslide events that occurred after the implementation of this map? b) With the inclusion of these new samples, is the terrain susceptibility still the same? c) If the terrain susceptibility has changed with the inclusion of the unused (partly recently mapped) samples, why and to what extent?</p><p>By aiming to answer these questions, a review project named MoNEW is currently in place, which has the overall objective to quantify the accuracy of the MoNOE spatial predictions. The new landslides were obtained from two main different sources: 1) recently occurred damage related landslides from a cadaster of landslide events (in German: “Baugrundkataster"), and 2) landslides mapped from hillshades of a high-resolution LiDAR DTM. Based on these new landslides, the final quality of MoNOE will be explored and the landslide susceptibility recalculated to identify potential differences. Therefore, the identical MoNOE methodological design will be applied to ensure comparability and quality control. Changes in the spatial prediction will be quantified and deeply explored.</p><p>First exploratory analysis has demonstrated that most of the new landslides occurred within the highest landslide susceptibility class, indicating an apparent good ability of the past MoNOE susceptibility model to predict these landslides. Depending on the inventory source, 34 to 64% of the landslides occurred within the higher susceptibility class (this percentage was 70% by design in the original <em>MoNOE </em>project). This variation might be explained by the positional accuracy and mapping methodologies of the new landslides. Additionally, it was observed that most of the new landslides occurring in other less susceptible classes (i.e., “low” and “moderate”) were actually located in close proximity to the highest susceptibility class. Given the applicability scale of the MoNOE landslide susceptibility map (1:25,000), these (mostly very low) quantified distances between the landslide locations and the high susceptibility pixels might be inside of the new landslide mapping accuracy. However, how much the landslide susceptibility of the terrain might change with the addition of these new samples is currently under analysis.</p>