Subsidence revealed by PSInSAR technique in the Ottignies-Wavre area (Belgium) related to water pumping in urban area
Xavier Devleeschouwer(1) , Pierre-Yves Declercq(1)
, and Franck Pouriel(1)
Royal Belgian Institute of Natural Sciences,
Rue Jenner, 13,
Radar interferometry (PS technique) has been applied in and around Brussels. The total area investigated is equivalent to 900 km². The ERS1/2 data sets covering the time span 1992-2003 have been exploited. Seventy-four scenes were used and around 173000 permanent scatterers (PS) were identified and could be used for time-series analysis. Several ground motion processes have been pointed out for the first time in Belgian urban environment. In particular, a subsidence process has been detected along the Dyle river between Ottignies and Wavre (SO-NE direction). 7186 permanent scatterers (PS) were used in the Dyle basin to interpolate (kriging) the average annual velocity data.
The urban and suburban areas of Wavre affected by the strongest negative ground deformations (average annual velocity displacement from -1,3 to -4,7 mm/yr) correspond to the zone of water-catchments and pumpings in the Cretaceous aquifer. A link seems to exist between the subsidence zone and the Quaternary sediments of the alluvial plain of the Dyle river. In addition to the pumpings effects, the presence of Quaternary peat layers (50 cm to 5,6 m) and the deepness of the Cambrian basement are also important parameters that influence the subsidence process. A progressive decrease of the subsidence values towards the southwest near the village of Ottignies is observed. This is related to the deepness of the Cambrian basement that ranges from 18-22 m in the center of Wavre to 5 m deep near Ottignies.
Field campaigns in the subsidence area reveals millimetre to centimetre cracks in the walls of the buildings attesting active ground motions.