13 January 2022
The Pau Branco landslide – video of the overtopping of the dam
Posted by Dave Petley
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.
A still from the video of the overtopping of the small dam caused by the Pau Branco landslide. Image from a video posted to Youtube.
.
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.
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
Watching the water and debris arrive at the dam in that seemingly slow, but ominous way, reminded me of the videos from the 2011 tsunami in Japan.
Glald you have shared the CCTV footage I got from Bruno Milanez. The “Sterile waste dump” structure that failed was not a dry stack facility. It came into being when Brazil eliminated 50% of Vallourec’s tailings capacity by banning use of natural depressions for any mine wastes. Use of those natural pits ( 26 of them) had been licensed for co disposal of tailings and low grade ores sub economic and not viabe for prrocessing. This faciity apparently included the new depositions for these wastes and the relocation of already deposed materials in the 2 natural depressions. We are still trying to track down the history of design and design approval of that faciity and dpcumenttaion on the 3 years stability review of it just completed in 2019 ( Lindsay Newland Bowker, Executive Director, World Mine Tailings Failures, compiler @worldminetailingsfailures.org)
It reminds me the vibrant day of Italy where a large landslide caused overtoping of dam though dam remained intact. It resulted in great loss . Not sure of deaths if any but this is a classic example of slope failure.
Amazing video. I kept thinking – that’s what could have happened at many other close calls on much larger earthen dams and has not thankfully – such as Swift Reservoir on the south side of Mount St Helens and…so many more. I always wonder how dams will withstand such a landslide induced wave. Thank goodness for excellent engineering designs and preparation. Someone did something right here, although this landslide should have been prevented in the first place. Thanks for sharing. Kudos to the engineers who built that dam. wow.
important point,Mindy. Down stream diversion dams are a very effective way of preventing downstream harm in event of a major failure. That this one worked, I agree is a credit to designers and operators.