Miet Van Den Eeckhaut

Assessment of groundwater quality using multivariate statistical techniques in Hashtgerd Plain, Iran

Multivariate statistical techniques, such as cluster analysis (CA), factor analysis (FA), principal component analysis (PCA), and discriminant analysis (DA), were applied for the evaluation of variations and the interpretation of a large complex groundwater quality data set of the Hashtgerd Plain. In view of this, 13 parameters were measured in groundwater of 26 different wells for two periods. Hierarchical CA grouped the 26 sampling sites into two clusters based on the similarity of groundwater quality characteristics. FA based on PCA, was applied to the data sets of the two different groups obtained from CA, and resulted in three and five effective factors explaining 79.56 and 81.57% of the total variance in groundwater quality data sets of the two clusters, respectively. The main factors obtained from FA indicate that the parameters influencing groundwater quality are mainly related to natural (dissolution of soil and rock), point source (domestic wastewater) and non-point source pollution (agriculture and orchard practices) in the sampling sites of Hashtgerd Plain. DA provided an important data reduction as it uses only three parameters, i.e., electrical conductivity (EC), magnesium (Mg2+) and pH, affording more than 98% correct assignations, to discriminate between the two clusters of groundwater wells in the plain. Overall, the results of this study present the effectiveness of the combined use of multivariate statistical techniques for interpretation and reduction of a large data set and for identification of sources for effective groundwater quality management.

Tier-based approaches for landslide susceptibility assessment in Europe

In the framework of the European Soil Thematic Strategy and the associated proposal of a Framework Directive on the protection and sustainable use of soil, landslides were recognised as a soil threat requiring specific strategies for priority area identification, spatial hazard assessment and management. This contribution outlines the general specifications for nested, Tier-based geographical landslide zonings at small spatial scales to identify priority areas susceptible to landslides (Tier 1) and to perform quantitative susceptibility evaluations within these (Tier 2). A heuristic, synoptic-scale Tier 1 assessment exploiting a reduced set of geoenvironmental factors derived from common pan-European data sources is proposed for the European Union and adjacent countries. Evaluation of the susceptibility estimate with national-level landslide inventory data suggests that a zonation of Europe according to, e.g. morphology and climate, and performing separate susceptibility assessments per zone could give more reliable results. To improve the Tier 1 assessment, a geomorphological terrain zoning and landslide typology differentiation are then applied for France. A multivariate landslide susceptibility assessment using additional information on landslide conditioning and triggering factors, together with a historical catalogue of landslides, is proposed for Tier 2 analysis. An approach is tested for priority areas in Italy using small administrative mapping units, allowing for relating socioeconomic census data with landslide susceptibility, which is mandatory for decision making regarding the adoption of landslide prevention and mitigation measures. The paper concludes with recommendations on further work to harmonise European landslide susceptibility assessments in the context of the European Soil Thematic Strategy.

Economic valuation of landslide damage in hilly regions: A case study from Flanders, Belgium

Several regions around the globe are at risk of incurring damage from landslides, but only few studies have concentrated on a quantitative estimate of the overall damage caused by landslides at a regional scale. This study therefore starts with a quantitative economic assessment of the direct and indirect damage caused by landslides in a 2,910 km study area located west of Brussels, a low-relief region susceptible to landslides. Based on focus interviews as well as on semi-structured interviews with homeowners, civil servants and the owners and providers of lifelines such as electricity and sewage, a quantitative damage assessment is provided. For private properties (houses, forest and pasture land) we estimate the real estate and production value losses for different damage scenarios, while for public infrastructure the costs of measures to repair and prevent landslide induced damage are estimated. In addition, the increase in amenity value of forests and grasslands due to the occurrence of landslides is also calculated. The study illustrates that a minority of land (only 2.3%) within the study area is used for dwellings, roads and railway lines, but that these land use types are responsible for the vast majority of the economic damage due to the occurrence of landslides. The annual cost of direct damage due to landsliding amounts to 688,148 €/year out of which 550,740 €/year for direct damage to houses, while the annual indirect damage augments to 3,020,049 €/year out of which 2,007,375 €/year for indirect damage to real estate. Next, the study illustrates that the increase of the amenity value of forests and grasslands outweighs the production value loss. As such the study does not only provide quantitative input data for the estimation of future risks, but also important information for government officials as it clearly informs about the costs associated with certain land use types in landslide areas.

Moderate seismic activity affects contemporary sediment yields

Current models aiming to simulate contemporary sediment yield (SY) implicitly assume that tectonic effects are either irrelevant or are reflected by catchment topography. In this study we analyse the relation between SY and seismic activity, a component of tectonic processes. Results show a spatial correlation between SY and seismic activity expressed as the estimated peak ground acceleration (PGA) with a 10% exceedance probability in 50 years. PGA has a significant impact on the spatial variation of SY, even after correcting for cross-correlations with topography, lithology or other factors that may influence SY. Based on three distinct data sets, we demonstrate that this effect is significant both for small catchments in Europe (0.3–3940 km2) and for large river systems worldwide (1580–6.15×106 km2) and that seismic activity may be even more important for explaining regional variation in SY than land use or many other commonly considered factors (e.g. catchment area, climate). We show that explicitly considering seismic activity may lead to SY-estimates that easily deviate a factor 2 or more compared to estimates that do not consider seismic activity. This is not only the case for highly seismically active regions: also in regions with a weak to moderate seismic regime seismic activity helps explaining regional patterns in SY. We argue that these findings have important implications for a better understanding of SY and its sensitivity to human impacts, as well as for our comprehension of sediment fluxes at longer timescales.

Assessment of Soil Erodibility in Taleghan Drainage Basin, Iran, Using Multivariate Statistics

Soil erosion has been recognized as one of the major forms of human-induced soil degradation. Due to land use changes in Iran, erosion has increased 800% between 1951 and 2002, calling for urgent action. But erosion research and policy development are hampered by a lack of information on the underlying factors controlling erosion. Soil types vary in their inherent susceptibility to erosion; but, like most countries, Iran lacks a network of field plots where erodibility is measured. A proxy for erodibility based on existing data and supplemented by an easily measured minimum data set is therefore needed. In this study, we use geological mapping and cluster, principal component, and factor analysis to group soils in the Taleghan Drainage Basin in Iran and subsequently determine their erodibility. First, a geological map of the area was prepared by photogeological methods and on-the-ground verification. Then, three soil profiles were investigated within similar landform units of each geological formation, and soil samples were taken. Physical and chemical properties that might impact soil erodibility (soil texture, pH, electrical conductivity, CaCO3, and soil organic matter) were used to create a matrix of soil properties and parent material. Application of cluster analysis and factor analysis to the data allowed identification of three geological (parent material) clusters. To investigate the mutual effect of land use and parent material on soil erodibility, a soil erodibility factor was obtained for three land use types in each cluster: rangeland, cropland (irrigated), and dry-land farming (nonirrigated). Geological cluster 1, consisting of marl, gypsum, and gypsiferous mudstone, was the most erodible; geological cluster 2, consisting of recent alluvium, alluvial fan, and landslip deposits, was of intermediate erodibility; and geological cluster 3, consisting of igneous rocks, dolomite, and conglomerate, was the least erodible. Within each geological cluster, dry-land farming was the most erodible, cropland was medium erodible, and rangeland was least erodible. The study suggests that geological and land use maps provide a useful framework for assessing soil erodibility. This work can guide future soil erosion studies and direct soil conservation policy to areas most susceptible to erosion.

New Developments in Harmonized Landslide Susceptibility Mapping over Europe in the Framework of the European Soil Thematic Strategy

In the context of the European Soil Thematic Strategy, and the formulation of a draft of a European framework directive devoted to the sustainable use of soil, landslides are recognized as one of the eight soil threats requiring harmonized spatial hazard assessments over the EU territory. The general framework for such assessments consists of a nested geographical approach based on “Tiers”, where a low-resolution (1:1 Million) evaluation (“Tier 1”) using already available pan-European datasets should enable the delineation of priority areas requiring more detailed assessments with additional data (“Tier 2”). In this contribution, we present new developments in the elaboration of a “Tier 1” generic landslide susceptibility evaluation based on a heuristic modelling approach exploiting the most important landslide conditioning factors. Extensive landslide locations available at small spatial scales have been collected and harmonized over the EU territory to be used for input parameter specification and model calibration, evaluation and classification. Since the analyzed area is highly complex in terms of climato-physiographic conditions controlling landslide occurrences, a preliminary landslide terrain differentiation is proposed consisting of eight calibration zones where specific predictor class weights have been allocated through a heuristic indexing approach. The spatially combined preliminary pan-European susceptibility estimate classifies 13 % of the EU territory as prone to landslides, thus requiring more detailed, quantitative inventory-based susceptibility evaluations (“Tier 2”).

Integrating Spatial Multi-criteria Evaluation and Expert Knowledge for Country-Scale Landslide Susceptibility Analysis: Application to France

Information on landslide susceptibility and hazard at the national scale is of fundamental importance for the design and implementation of risk management policies and the prioritarization of the allocation of resources. Lack of such information in Europe and the implementation of the European Union’s Thematic Strategy for Soil Protection (Commission of the European Communities, Thematic strategy for soil protection. COM(2006)231 final. Brussels, 2006a; Commission of the European Communities, Proposal for a Directive of the European Parliament and of the Council establishing a framework for the protection of soil and amending directive 2004/35/EC. COM(2006)232 final. Brussels, 2006b) let to an initiative of JRC (Joint Research Centre, European Commission) to setup a European Landslide Expert Group in order to identify the areas in Europe where landslides are likely to occur. In this context, this work presents the method developed for the creation of the ‘Tier 1’ landslide susceptibility map for France at a 1:1M scale, where susceptibility is defined as the spatial probability of occurrence of an event. The method is applied by differentiating three categories of landslide types, namely slides, falls and flows. More specifically, the method combines a weighting-rating procedure of both factors and classes of factors using a spatial-multi-criteria evaluation technique (SMCE) and an objective calibration of the weights based on statistics on the distribution of observed landslides per slope angle, lithology and landcover classes. The quality of the nation-scale map is evaluated with references (1) to the French landslide inventory map BDMvT, and (2) to regional or local susceptibility maps available in the literature or created for planning purposes.

Decadal-scale analysis of ground movements in old landslides in western Belgium

Summary. More than 150 large deep-seated landslides have been mapped in the Flemish Ardennes. Slope instabilities that have occurred in this hilly area of western Belgium during the last decades correspond to ground movements within these pre-existing landslides. In order to identify the mechanisms and controlling factors of these ground movements, a good knowledge of their spatial and temporal distribution is critical. 13 landslides affecting two hills were investigated based on several DTMs extracted by aerial stereophotogrammetry and spanning the 1952–1996 period. Vertical ground displacements were measured at each pixel by DTM subtraction with a confidence value of 0.70 m. Horizontal displacements were also estimated within the landslides and along the head scarps through topographical profiles. Most observed movements displayed patterns typical of rotational landslides. Vertical and horizontal displacements vary in magnitude both spatially and temporally, with respective ranges – 7.4 m–+ 3.8 m and 0–14 m. Many displacements are materialized in the field. We distinguished two kinds of slope processes, corresponding to either reactivation at a deeper level or shallower motion. The former re-uses pre-exiting surfaces of rupture located at depths of ~ 15– 20 m and is associated with the largest subsidence and uplift. They are also smaller reactivations confined at the landslide head. The other displacements consist in (1) earth flows occurring in the zone of accumulation sometimes as a consequence of large upslope reactivations, and (2) small failures occurring randomly. While most movements were triggered by intense rainfall, their spatial and temporal distribution is strongly related with the nature of the vegetation cover and the human activity.

Index-Oriented Methodologies for Landslide Consequence Analysis: An Application to a Mountain Community in the French Alps

Consequence analysis is a key aspect of anchoring assessment of landslide impacts to present and long-term development planning. Although several approaches have been developed over the last decade, some of them are difficult to apply in practice, mainly because of the lack of valuable data on historical damages or on damage functions. In this paper, two possible consequence indicators based on a combination of descriptors of the exposure of the elements at risk are proposed in order to map the potential impacts of landslides and highlight the most vulnerable areas. The first index maps the physical vulnerability due to landslide; the second index maps both direct damage (physical, structural, functional) and indirect damage (socio-economic impacts) of landslide hazards. The indexes have been computed for the 200 km2 area of the Barcelonnette Basin (South French Alps), and their potential applications are discussed.

Landslide Databases in Europe: Analysis and Recommendations for Interoperability and Harmonisation

Landslide inventories, usually including digital inventory maps and linked alphanumeric attributes, are the most important input for further landslide zoning. However, to allow landslide susceptibility, hazard and risk assessment the inventory databases should contain information on the location of landslide phenomena, types, history, state of activity, magnitude or size, causal factors and the damage caused. Yet, in Europe it is not known which national (or regional) landslide databases contain all this information, and thus allow landslide risk assessment. Therefore this study presents a review of existing national landslide databases in Europe together with a number of regional databases, and proposes improvements in agreement with the EU Soil Thematic Strategy, and with INSPIRE Directive.