22 May 2020
Edenville Dam breach: interpreting the failure
Many thanks to all of those who contributed to the discussion yesterday about the catastrophic Edenville Dam breach in Michigan. I thought it would be helpful to summarise views expressed, many of which have come from experts in the field.
First, it is clear that this was not an engineered failure – in other words, it was not planned. There was some discussion on Twitter and in the comments that this was the failure of a fuse plug – i.e. a designed failure point that would release water to prevent overtopping. I can find no evidence that Edenville Dam had a fuse plug, and I do not think that a fuse plug failure would behave in the way shown in the video.
Planet Labs have a wonderful high resolution image of the aftermath of the failure; I wpould be surprised if a fuse plug is intended to leave this type of catastrophic breach:-
The style of failure implies that the dam had become saturated in this area. A key question is going to be why this happened. One suggestion is that the water level exceeded the impermeable barrier, allowing water to flow into the structure. An alternative is that the dam was suffering from seepage prior to the floods. The Google Earth imagery is interesting – this image is from 2018:-
Is there an indication here that there was deformation in the dam? Or that works had been undertaken? I’m not sure. It will be interesting to see both the monitoring records for the dam and the maintenance that had been undertaken, as well as the design cross-sections.
The mechanism of failure is undoubtedly a rotational slip. It is possible that this started as a smaller failure at the crest of the dam, which then drove a larger failure in the main face. However, I favour the interpretation that high pore water pressures, and a loss of unsaturated conditions, through the dam volume drove the failure. There are some indications in the video that high pore water conditions were present in the lower part of the structure.
Readers have rightly pointed out that earthfill embankment dams are not unusual and, when well designed and maintained, they are not unsafe. This dam was completed in 1924. However, these structures do require maintenance – would you expect a train built in 1924 to still work without extensive restoration – and they were designed for a time when rainfall levels were different. Climate change – global heating – is driving increases in rainfall intensities and durations, meaning that the Probable Maximum Flood is increasing in very many places.
I always get howls of protest when I say that climate change is important, but it is the case. These structures, worldwide, are going to need a substantial upgrade to cope with that increase in rainfall, and that’s going to be very expensive. In the interim we will see more failures of this type.
There is also some interesting analysis of the performance of the dam prior to failure online, using INSAR data. It is astonishing that such an interpretation can be generated so quickly. At present I find it hard to interpret this data though – the results seem to indicate deformation across much of the structure, and the section that failed seems to show uplift not, as I would expect, subsidence. This needs further work, but INSAR remains an exceptionally exciting area of work for these types of investigations, and for pre-failure monitoring.
The failure of the dam is a catastrophe for people living in this area. Planet Labs have an online gallery of high resolution images of the impacts. The Planet Labs image below shows some of the downstream flooding for example:
But we must not forget that the effects lie upstream as well. There are numerous houses located around the lakes whose value will have been based upon the proximity to the water. The failure of the dam will have a profound impact, and of course the ecology of the lakes will also have been destroyed.
On reflection 1: my most successful blog day
The past 24 hours have been my most successful day in the 12 years of this blog, with almost 50,000 individual visits. Thank you.
On reflection 2: Controversy over the protection of the Great Western Railway in Devon from landslides
In Teignmouth in Devon in SW England there is controversy over plans by Network Rail to change the alignment of Isambard Kingdom-Brunel’s wonderful Great Western Railway to protect it against landslides. The article claims that the cost of these works is £500 million.
Planet Team (2020). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/