21 May 2020
Edenville Dam failure: the astonishing video of the collapse sequence
Yesterday I posted about the remarkable and devastating failure of the Edenville Dam in Michigan on Tuesday 19 May 2020. There are now heartbreaking images online showing the damage that the resulting flood has caused downstream. Given the known weakness of the dam, this is an unacceptable situation.
From a technical perspective, the most remarkable aspect of this failure is that the sequence of events that induced the breach is caught on video. I tweeted about this yesterday, but it turns out that the landslide that initiated the collapse was also captured, by Lynn Coleman, and posted to Youtube by MLive. This video is astonishing:-
As always we should crowdsource an interpretation of this sequence of events, but allow me to give an initial (and not definitive) interpretation. At the start of the video a small amount of water is seen to have overtopped the dam:-
It would be tempting to surmise that this was a simple overtopping, but I don’t think that is correct. I think the video shows that the crest of the dam has deformed and dipped, creating a depression through which water has started to flow. In other words, the video starts with the dam wall undergoing the early stages of failure, which in turn has allowed a small amount of overtopping.
The Edenville Dam failure then develops apace. The slope fails rapidly, initially forming a large toe bulge and there is major deformation at the crest:-
The failure is rapid and mobile – the still below is only two or so seconds later. Note the blurring of the toe of the landslide due to the rapidity of motion. there is also a hint of some dust or vapour in this area, and above the main body of the slide, which is interesting too:-
The landslide has clearly not failed through the full width of the dam as there is no sign of water pouring through. However, it is likely to have left only a very slender thickness of dam in place. I would hypothesise that this rapidly collapsed under the pressure of the reservoir water as a few seconds later water appears on the landslide deposit:-
The full breach rapidly develops after this.
This video is going to be a classic in the teaching of geotechnical failures, but it also clarifies the events that led to the Edenville Dam failure. It would have been simple to ascribe this to a simple overtopping event that occurred when the capacity of the spillway was exceeded. But in reality the events are are more worrying than that – the dam appears to have undergone a slope failure; a failure of its integrity. This should never occur, and to me it suggests that the problems at the Edenville Dam went further than known issues with the spillway.
Comments and thoughts welcome please. Please also read my follow-up post to understand this event.
On reflection 1: Cyclone Amphan
Cyclone Amphan made landfall on Wednesday and is now bringing heavy rainfall to NE India and Bangladesh. There are some early indications of landslides; we await to see the full impact, probably tomorrow or on Saturday.
On reflection 2: landslide damage to a chairlift in Alberta
A landslide on Tuesday 19 May 2020 damaged a chairlift at Nitehawk Adventure Park, a small ski field located in Grande Prairie, Alberta. From the images the damage is serious.