27 May 2020
The aftermath of the Sanford dam failure in Michigan
The catastrophic failure of the Edenville Dam in Michigan last week was not the only dam failure that day. About 16 km downstream from Edenville lay the smaller Sanford Dam, which also failed. In a sense this is an understandable collapse – the dam would not have been constructed to withstand the flows associated with the failure of the Edenville Dam. It would perhaps have been surprising if the structure had withstood such an event.
Planet Labs have collected images of the aftermath of the failure of the Sanford Dam. This is a Google Earth image, collected in November 2018, which shows the site of the dam:-
Note that the fuse plug, designed to allow an emergency increase in flow to prevent dam failure, is clearly visible. This is the Planet Labs high resolution SkySat image of the aftermath of the failure:-
The terrible flood damage downstream of the breach is all too evident. The dam itself has been almost completely removed.
Rebuilding these sites is going to be a long and expensive process.
An early failure similar to the Edenville Dam?
Meanwhile, in the comments on my earlier posts about the Edenville Dam, Bruce Feinberg has noted the similarity with the failure of the Kelly Barnes Dam on 6 November 1977 at Toccoa in Georgia, USA. This was another earthen dam that breached during heavy rainfall, killing 39 people. The USGS investigated this failure, and the report is online. The report makes shocking reading – the dam was poorly documented and in a very poor state of repair at the time of failure. Photographs from 1973 show that a slope failure in the face of the dam had already occurred. The USGS report hypothesises that the breach may have been caused by a further slope failure in the downstream face of the dam:
[Slope failure] appears to be a distinct possibility, particularly on the downstream slope when the previous slope failure is considered along with the possibility of the development of tension cracks upslope of the previous failure together with a computed factor of safety that is marginal. The long period of rain would have saturated tension cracks, if they existed, and the entire downstream slope would have become essentially saturated and even more susceptible to failure. A local downstream slope failure similar to that observed in 1973 could have caused limited breaching allowing localized overtopping. This concept would corroborate the hydraulic computations.
This proposed mechanism of failure is indeed similar to that of the Edenville Dam.
On reflection 1: no resting place
A landslide has disturbed Vicksburg National Cemetery in Mississippi, requiring archeologists to relocate the remains of the Civil War Union soldiers. Work will now be undertaken to stabilise the slope.
On reflection 2: A landslide video from Colombia
A nice landslide video was captured on the Florencia – Neiva highway in Colombia:-
La vía Florencia – Neiva permanece cerrada desde la madrugada de este martes. En video quedó registrado uno de los derrumbes en el kilómetro 40, entre Suaza-Florencia, que impiden el tránsito vehicular #VocesySonidos pic.twitter.com/JrEV5AR1H7
— BluRadio Colombia (@BluRadioCo) May 27, 2020