Olivier Maquaire

Continuous Monitoring and Near-Real Time Processing of GPS Observations for Landslide Analysis: A Methodological Framework

The objective of this work is to present a methodology for the near-real time characterization of displacements using permanent GPS stations on landslides. In France, several GPS receivers have been installed on active landslides since a few years. These landslides show very different displacement rates and kinematic regimes. For the monitoring of landslides where the required degree of accuracy is millimetric, GPS has been mainly used for repeated measurements, as a complement to conventional geodetic methods. Permanent monitoring is still not usually performed operationally.

Landslide consequence analysis: a region-scale indicator-based methodology

Consequence analysis is, together with hazard evaluation, one of the major steps of landslide risk assessment. However, a significant discrepancy exists between the number of published landslide hazard and landslide consequence studies. While various methodologies for regional-scale hazard assessment have been developed during the last decade, studies for estimating and visualising possible landslide consequences are still limited, and those existing are often difficult to apply in practice mainly because of the lack of data on the historical damage or on landslide damage functions. In this paper, an indicator-based GIS-aided methodology is proposed with an application to regional-scale consequence analysis. The index, called Potential Damage Index, allows describing, quantifying, valuing, totalizing and visualising different types of consequences. The method allows estimating the possible damage caused by landslides by combining weighted indicators reflecting the exposure of the elements at risk. Direct (physical injury, and structural and functional damage) and indirect (socio-economic impacts) consequences are individually analysed and subsequently combined to obtain a map of total consequences due to landsliding. Geographic visualisation of the index allows the delineation of the areas exposed to any type of possible impacts that could be combined with a corresponding map displaying landslide probability of occurrence. The method has been successfully applied to analyse the present consequences in the Barcelonnette Basin (South French Alps). These maps contribute to development of adequate land use and evacuation plans, and thus are important tools for local authorities and insurance companies.

Coastline at Risk: Methods for Multi-Hazard Assessment

ABSTRACT SOLDATI, M., MAQUAIRE, O., ZEZERE, J. L., PIACENTINI, D and LISSAK, C, 2011. Coastline at Risk: Methods for Multi-Hazard Assessment. In: Micallef, A. (ed.), MCRR3–2010 Conference Proceedings, Journal of Coastal Research, Special Issue, No. 61, pp. 335–339. Grosseto, Tuscany, Italy, ISSN 0749-0208. In recent years the interest for coastal hazards has increased significantly due to extreme events, sometimes related to climate change, that frequently occur in different parts of the world, often inducing high risk situations. This paper outlines the objectives, perspectives and preliminary results of a research project entitled “Coastline at risk: Methods for multi-hazard assessment” which aims at providing useful knowledge for the mitigation of coastal instability. The project is managed by the European Centre on Geomorphological Hazards (Centre Européen sur les Risques Geomorphologiques, CERG) and funded by the EUR-OPA Major Hazards Agreement. Investigations are focused on coastal landslides in three different morpho-climatic European environments: Malta (Mediterranean coastline), Lower Normandy (Channel coastline) and Central Portugal (Atlantic coastline). The research outputs are expected to provide a significant opportunity for scientific discussion based on the comparison of data regarding instability situations in the context of multi-hazards assessment. The latter has until now dealt slightly with the coasts of Malta, Normandy and Portugal on which the investigations will be focused, despite significant risk issues present there, as evidenced from a series of accidents and damages recorded after landslide events. The aims of the project will be pursued through multidisciplinary investigations which foresee geomorphological and engineering-geological approaches. Integrated avant-garde research techniques, both traditional and innovative, will be applied with special reference to mapping, monitoring and modelling of coastal instability phenomena. The final objective is to propose a method for coastal multi-hazard assessment that can be used to face and manage coastal hazards.

Identification of Hydro-Meteorological Triggers for Villerville Coastal Landslide

The Villerville–Cricqueboeuf landslide (Normandy, France) is an example of a very well monitored coastal landslide. The long time series goes back to the 1980s initiated after the January 1982 major re-activation of the landslide complex. The combination of translational movement of large blocks of chalk and sandstone and the rotational movement at the cliff’s toe results in a very complex hydrological system. Earlier research showed a qualitative connection of displacement or re-activation with meteorological forcing and inland hydrological circumstances.

Landslide Susceptibility Assessment by EPBM (Expert Physically Based Model): Strategy of Calibration in Complex Environment

Physically based model may be used to assess landslide susceptibility over large areas. However, majority of case studies are applied for complex phenomena for a one event, a little site or over large areas when landslides have simple geometry and environmental conditions are homogeneous. Thus, assessing landslide prone areas for different type of landslides with several geometries and for large areas needs some specific strategies. This work presents an application of a specific procedure based on a physically based model for one complex area with several landslide types. By different steps, it is demonstrated this is possible to improve susceptibility map and take into account of different slope failure with different depths. This first attempt encourages us to continue on this path in order to improve the existing susceptibility maps in this area.

Landslide Consequences and Post Crisis Management Along the Coastal Slopes of Normandy, France

The coastal slopes of the Pays d’Auge plateau (Calvados, Normandy, France) are regularly affected by landslides mainly triggered by rainfall. The study area between Trouville and Honfleur has been subject to slow continuous displacements (5–10 cm.year−1) for several centuries, punctually disturbed by episodes of acceleration with metric displacements. The landslides are located along a very touristic coastal area where increasing land pressure is evident.

Examining high-resolution survey methods for monitoring cliff erosion at an operational scale

This paper aims to compare models from terrestrial laser scanning (TLS), terrestrial photogrammetry (TP), and unmanned aerial vehicle photogrammetry (UAVP) surveys to evaluate their potential in cliff erosion monitoring. TLS has commonly been used to monitor cliff-face erosion (monitoring since 2010 in Normandy) because it guarantees results of high precision. Due to some uncertainties and limitations of TLS, TP and UAVP can be seen as alternative methods. First, the texture quality of the photogrammetry models is better than that of TLS which could be useful for analysis and interpretation. Second, a comparison between the TLS model and UAV or TP models shows that the mean error value is mainly from 0.013 to 0.03 m, which meets the precision requirements for monitoring cliff erosion by rock falls and debris falls. However, TP is more sensitive to roughness than UAVP, which increases the data standard deviation. Thus, UAVP appears to be more reliable in our study and provides a larger spatial coverage, enabling a larger cliff-face section to be monitored with a regular resolution. Nevertheless, the method remains dependent on the weather conditions and the number of operators is not reduced. Third, even though UAVP has more advantages than TP, the methods could be interchangeable when no pilot is available, when weather conditions are bad or when high reactivity is needed.