Tracking landslide displacements by multi-temporal DTMs: A combined aerial stereophotogrammetric and LIDAR approach in western Belgium

The study of small and/or slow reactivations of landslides requires describing their displacements over decades, which may be done with accurate multi-temporal digital terrain models (DTMs). We applied aerial stereophotogrammetry to build the historical topographies of old deep-seated landslides close to Oudenaarde in the Flemish Ardennes (West Belgium) at different dates. Three precise aerotriangulations (1996,1973,1952) were carried out. After capturing the ground data manually from the stereomodels, 2 m-resolution DTMs were interpolated by kriging, with a final accuracy ranging between similar to 45 cm and similar to 65 cm. Another DTM was interpolated with an accuracy of similar to 30 cm from airborne LIDAR data acquired in 2002. Differential DTMs were produced to identify vertical and horizontal ground displacements over the 1952-2002 period. We describe here the kinematics of a particularly active landslide with a well-documented recent activity. Until the first half of the 90 s, little activity of the landslide was detected. In February 1995 a reactivation event caused vertical displacements of up to -7 m along the main scarp and up to +4 m in the accumulation zone. Horizontal movements of 4 to 10 m are also inferred. These topographic changes correspond to reactivated slip along the rotational basal shear surface. In the same time, the main scarp retreated by up to 20 m. The reactivation, favoured by several anthropogenic factors (e.g. loading, impeded drainage), was triggered by intense rainfall. Between 1996 and 2002, the observed displacements correspond to limited scarp retreat (<= 4 m) and compaction of the slipped mass, partly enhanced by artificial drainage. (c) 2008 Elsevier B.V. All rights reserved.