13 January 2022
The Pau Branco landslide – video of the overtopping of the dam
A video has now emerged online that shows the overtopping of the dam immediately downstream of the Pau Branco landslide in Brazil on 8 January 2022. This video was apparently collected by CCTV at the site:-
At the start of the video it is clear that the rainfall was heavy, and the dam was full with water cascading down the spillway on the far side. As the landslide becomes visible on the left side of the footage a displacement wave races across the lagoon and causes an initial overtopping event. This quickly develops as the volume of the lagoon is filled with landslide debris.
Initially most of the overtopping is water from within the lagoon, and this is reflected by the videos from the road below the dam. Later in the video solid material overtops the structure – this may be a combination of landslide debris and silt from within the pond.
The video demonstrates the power of such an event – the speed and relentless nature of the overtopping are stark. It is fortunate that the structure was in place – it has retained a large proportion of the mine waste, probably preventing a much more powerful and destructive flow from reaching the road and from a greater volume of mine waste being unretained now.
And of course it is fortunate that the retaining structure was able to stand up to the flow. If it had collapsed rapidly then the impact would have been much more serious.
Meanwhile the fallout from the Pau Branco landslide continues. Inevitably, further questions are being asked about the stability of the huge numbers of mine waste piles in Brazil (this should not be confined to Brazil of course). Reports also indicate that a licence was granted in January 2021 for an expansion of the
dry stack mine waste pile that failed. It will be interesting to know how much of this expansion had occurred at the time of the collapse.
Finally, of course, there are many similar slopes associated with this mine waste pile. Urgent work is needed to determine the stability of these slopes.