25 years of ground subsidence related to groundwater pumping for breweries in Belgium

Persistent Scatterer Interferometry (PSI) is a valuable technique for studying ground
deformation in Belgium and providing more information on their spatial and temporal
patterns. In this work, about 700 SAR images of different tracks from the European satellites
ERS (1992-2001), ENVISAT (2003-2010), SENTINEL 1 (2014-2018) were processed.
TerraSAR-X data covering the time span 2012-2014 and the area of Brussels were processed
as well. A mapping of the annual average velocity of the PS of the entire period highlighted
already known ground movements discovered during country scale levelling campaigns. But
thanks to its millimetre precision, it permitted to highlight new movements that were not
identified before.
Seven large subsidence or uplifting areas can be spotted from the velocity map. From
north to south, the regions facing ground movements are: The West-Coast, Antwerp and
along the Schelde river and estuary, the Limburg Campine coal mines basin, Merchtem
Londerzeel, the cities of Brussels and Liège as well as a large area related to the Tournai
Mons-Charleroi coal mines basin. The purpose of this work is to make an overview of the
situation (observations, first interpretations) of these ground movements. The highest positive
(uplift), 20 to 25 mm/year and negative (subsidence) -17 to -20 mm/year velocity values are
recorded around the former Limburg coal mines areas. The movements are closely linked to
the groundwater extraction needed during the exploitation time and the recharge of the
mining aquifer occurring at the end of the pumping.
Among the seven highlighted zones, in Merchtem 25 Km NW of Brussels, a ground
subsidence (-3 mm/year on average) is occurring since the beginning of the ERS acquisitions
in 1992. Through the time (ERS, ENVISAT, TerraSAR-X and SENTINEL 1) the subsidence
pattern reduces his extent and is replaced by an uplift due to the raise of the water table.
Piezometers located in the deep Cambro-Silurian aquifer show a clear recharge of this aquifer
since the late 1990’s. The subsidence is finally reduced to a zone where three breweries are
very active and pumping groundwater for the production in the Ledo-Paniselian aquifer and
in the Cambro-Silurian as process water. The Stella Artois brewery located in Leuven 30 Km
E of Brussels is facing a ground subsidence as well clearly visible with the PSI data.