Post Mining Ground Deformations Transition Related to Coal Mines Closure in the Campine Coal Basin, Belgium, Evidenced by Three Decades of MT-InSAR Data

Abstract

Spatio-temporal ground-movement measurements and mappings have been carried out in the Campine coalfield in Belgian Limburg since the closure of the mines to document post-mining effects. MT-InSAR measurements are compared to groundwater head changes in the overburden and to height data from the closest GNSS stations. Radar interferometry is used to estimate the extension and the velocity of ground movements. In particular, the MT-InSAR technique has been applied to SAR acquisitions of the satellites ERS-1/2 (1991–2005), ENVISAT (2003–2010), COSMO-SkyMed (2011–2014), and Sentinel-1A (2014–2022). The images were processed and used to highlight a switch from subsidence to uplift conditions in the western part of the coal basin, while the eastern part had already been affected by a rebound since the beginning of the ERS-1/2 acquisitions. Following the closure of the last active colliery of Zolder in 1992 and the subsequent cease of mine-water pumping, a recharge of mine-water aquifers occurred in the western part of the basin. This process provoked the change from subsidence to uplift conditions that was recorded during the ENVISAT period. In the center of the coal-mining area, measured uplift velocities reached a maximum of 18 mm/year during the ENVISAT period, while they subsided at -12 mm/year during the ERS-1/2 period. Mean velocities in the western and eastern parts of the coalfield area have decreased since the last MT-InSAR measurements were performed using Sentinel-1A, while the Zolder coal mine continues to rise at a faster-than-average rate of a maximum of 16 mm/year. The eastern part of the coalfield is still uplifting, while its rate has been reduced from 18 mm/year (ERS-1/2) to 9 mm/year (Sentinel-1A) since the beginning of the radar–satellite observations. Time-series data from the two GNSS stations present in the study area were used for a local comparison with the evolution of ground movements observed by MT-InSAR. Two leveling campaigns (2000, 2013) were also used to make comparisons with the MT-InSAR data. The station’s measurements and the leveling data were in line with the MT-InSAR data. Overall, major ground movements are obviously limited to an extension of the actual underground-mining works and rapidly diminish outside of them.

Review on the Use of Satellite-Based Radar Interferometry for Monitoring Mining Subsidence in Urban Areas and Demographic Indicators Assessment

“…Year 1992 represents the starting moment of long multi-temporal SAR analyses, as the first satellite mission including an imaging Synthetic Aperture Radar (SAR), which provided enough suitable data for interferometry was the ERS-1 (European Remote Sensing) satellite [15], launched in July 1991. The longest time evolution of mining subsidence monitoring using InSAR was made in Belgium, for three decades [16].…”

“…The evolution of the InSAR techniques could be revealed by the reviewed scientific literature, articles on the topic of InSAR methods used for monitoring mining subsidence being available from 1997 [17] until today [16].…”

“…Unlike the previous methods, for PSI the atmospheric phase contributions are removed, all available radar data can be used regardless the geometrical baseline, good phase coherence can be achieved using the available data [42], and accuracies of millimetric level are obtained [18]. PSI technique was used for mining subsidence monitoring in [13,14,16,25,26,33,39,[43][44][45][46][47][48][49][50][51][52].…”

“…In the subsidence study from Athens Basin, Greece, the type of mining is not specified [51]. Considering the exploitation mode, some of the scientific contributions refers to underground mining [14,16,24,25,28,35,46], or open pit [36,39,52,59,60]. Meanwhile, there are some mining areas where both underground and open pit exploitation are found, e.g.El Teniente, Chile [39,44].…”

“… historical sites (e.g. iron mining in Rancourt, Lorraine, France [43], coal mining in Witbank Coalfields, South Africa [32], Athens Basin [51], South Limburg, Netherlands [50],  closed mines in the 1990s (e.g.Inowroclaw, Poland [47], South Derbyshire and Leicestershire, UK [62], Nord/Pas-e-Calais, France [25], Ocnele Mari, Romania [35], Campine Coal Basin, Belgium [16]),  closed mines after 2000 (e.g. salt mine in Poland [11][12][13]),  active mining sites (e.g.…”