Land Subsidence Observed in the Merchtem Area (Flanders) – 30 Years of SAR Data Associated to Groundwater Withdrawal?

A land subsidence affecting several towns at the joining limits of the Belgian Provinces of East Flanders, Antwerp and Flemish Brabant is followed during the last three decades. ERS 1–2, ENVISAT, TerraSAR-X and Sentinel-1A satellites SAR scenes were processed from 1992 till October 2020 to map the land subsidence evolution. The subsidence corresponds to a surface area of 220 km 2 during the ERS 1/2 time interval distributed over three distinct subsidence bowls. During the ENVISAT and TerraSAR-X time interval, only one residual subsidence bowl was mapped affecting a surface area of about 70 km 2 . Several towns (Londerzeel and Steenhuffel) remained in the center of the subsidence bowl. The annual average negative velocity values range between −5.99 and −0.5 mm/year. During the Sentinel-1A period, the subsidence bowl has lost half of its surface reaching 36 km 2 . The LOS velocity values have also decreased during the period 2016–2020.

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