The root cause of the tailings dam failure in Brazil on Jan. 25 can perhaps be found a century ago, in southern California.
In the first two decades of the 20th century, farmer co-ops and irrigation colonies formed to privately fund the building of dams and reservoirs in California. The low bidder was often John Eastwood and his multiply arched concrete dams.
When the time came to develop bigger dams requiring New York investors, John R. Freeman was brought in as a consulting engineer. Trained as a civil engineer, he made his living in the fire insurance business.
As detailed by the historian D.C. Jackson in his book, “Building the Ultimate Dam,” Freeman quickly established relationships with financiers and state officials, making an argument not on technical but rather on “psychological” grounds: that the public would never approve a thin-walled multiply arched dam, that only a massive earthen or concrete gravity dam could inspire public confidence.
Freeman’s arguments found traction with a technically uninformed financier decision maker, causing the cancellation of the half-completed Eastwood Big Meadows dam and replacing it with a massive gravity dam, despite its inferiority in terms of material efficiency, public safety and cost.
Freeman’s far-ranging influence effectively banished Eastwood from building California and Bureau of Reclamation dams. Of dams built for municipal water systems, he was to build just one more: the Mountain Dell Dam, its graceful arches, buttresses and braces still visible to eastbound traffic up Parleys Canyon above Salt Lake Valley. The site and size of the dam was similar to Big Meadows, including a less-than-ideal shale bedrock that was not watertight.
The Salt Lake City engineer Sylvester Q. Cannon (an MIT mining engineer graduate) drafted a technical review that is a model of analysis, concluding that the multiple arched design provided for “the practical elimination of upward pressure, the practical impossibility of overturning or sliding on its base and the ready facilities for the inspection of the dam at any time.”
The Mountain Dell Dam, designed and built by Eastwood, was completed in 1917 and was quickly followed by the Malad (1917) and the 2,000-foot-long Fish Creek Dam (1920) in Idaho. These dams were critical to the metropolitan and agricultural development of the Intermountain West.
Eastwood died in 1924, after building 17 multiply arched dams, mostly in California, none of which failed. Following the 1928 failure of the Saint Francis Dam, killing over 400 people in southern California, blame was placed on the lack of oversight of its designer, William Mulholland, rather than on its massive concrete gravity design. The California statute drafted following this disaster inexplicably prohibited the further construction of multiply arched dams in the state, specifying instead massive gravity dams of concrete, earth fill, or rockfill, and this became a standard throughout the west and internationally.
So strong were the pressures for consensus around gravity dams set in motion by Freeman, and so rare is the experience, independent thinking, and fact-based analysis demonstrated by John Eastwood and Sylvester Cannon, that despite the perfect safety record of multiply arched dams and the repeated failures of massive gravity dams, gravity dams have been the standard for 75 years.
On Jan. 25, more than 200 people died following the catastrophic failure of a 42-year-old earthen gravity dam in Brazil. Perhaps it is time to try to recover the iconoclastic thinking of Salt Lake City’s City cngineer Sylvester Cannon and have a fresh look at the multiply arched dams of John Eastwood.
Dan McGraw is a Utah physicist and engineer.