Wits School of Civil and Environmental Engineering senior lecturer and corresponding author Dr Luis Torres-Cruz
Civil engineers at the University of the Witwatersrand (Wits) in Johannesburg have used public satellite and aerial imagery in a study to investigate the history of the infamous Jagersfontein waste storage facility in the Free State.
The study, which was authored by Wits School of Civil and Environmental Engineering senior lecturer and corresponding author Dr Luis Torres-Cruz and co-author and Wits master’s candidate Christopher O'Donovan, was published in the journal Scientific Reports on April 5.
The publication of the study comes six months after the catastrophic failure of a diamond tailings storage facility in Jagersfontein, on September 11 last year, resulting in the death of one person and the destruction of multiple homes. It also caused significant damage to the surrounding environment.
Sources of public satellite images used in the study included Google Earth Pro, and the Sentinel-2 and Landsat 8 satellite missions. Additionally, some of the immediate consequences of the failure were assessed using commercial satellite images.
The study found that the history of the Jagersfontein dam deviated from best engineering practice. These deviations included mine waste deposition from predominantly one side of the dam, erosion gullies on the dam wall and significant amounts of ponded water – at times positioned against the retaining structure.
Based on the analysed images, the study hypothesises that the percolation of water through the dam, followed by external erosion, ultimately triggered instability.
“We expect our paper to be useful to those interested in understanding how this tragic event came to be and also to help prevent future failures,” tailings dams geotechnical specialist Torres-Cruz said at the release of the findings.
“The fact that our study relies on publicly available data to investigate the history of the dam implies that anyone can independently verify our observations,” O’Donovan added.
To assess the impact and consequences of the dam failure, Torres-Cruz and O’Donovan captured two high-resolution satellite images that illustrate the damage inflicted on the surrounding residential areas.
Based on a three-dimensional reconstruction of the failed dam, the authors estimate that between four-million and six-million cubic metres of mine waste were released.
The study also includes an animation that illustrates the post-failure geometry. Additional satellite imagery shows that the mine waste travelled 7 km over dry land and 56 km along streams and rivers to reach the reservoir of the Kalkfontein dam.
The paper notes that some of the satellite imagery viewing platforms used in the analysis are free for non-commercial purposes and relatively easy to use.
Accordingly, when coupled with an understanding of tailings dams, these platforms can empower stakeholders to adopt public satellite imagery as a starting point to proactively monitor tailings dams.
Moreover, the study suggests that greater awareness of the capabilities of public satellite imagery can encourage greater adherence to good construction practices.
The study also emphasises that a robust monitoring strategy of tailings dams should focus on their adequate construction and operation.
It also draws attention to the importance of conducting an official and independent site investigation to better understand the failure sequence and the conditions that led to it.