Since I last wrote about the Mosul Dam two months ago, no concrete progress has been made in stemming the structure’s deterioration. Italian contractors seem to be closing in on a deal with the Iraqi government, but no plans are set in stone. Exactly how the Italian team would repair the dam remains unclear- the operation could be a full facelift or simply a continuation of the original grouting process. Meanwhile, Mosul remains as unstable as ever, and day by day water still seeps under the dam. From a bystander’s perspective, the slow speed of action and bureaucracy is worrying, and raises the question of whether Iraqi officials are unconvinced of the situation’s urgency. If there are truly people who remain dubious of the possibility of a total, catastrophic collapse, their view may be swayed by looking back to a dam that, before its failure, bore a great number of parallels with Mosul’s: the Saint Francis Dam, which collapsed nearly ninety years ago in Los Angeles.
The remains of the St. Francis Dam
In the classic noir drama Chinatown, Jack Nicholson’s private-eye protagonist stumbles across a conflict between small-time farming landowners and corporate developers throwing together an immense water system for the expanding city (and their own expanding land holdings). In real life, the most prominent agent of these developers was self-trained engineer William Mulholland who, for a decade and a half, undertook a massive infrastructure program which was technically remarkable but ethically nebulous. The epicenters of his operations were the rugged Owens and San Fernando Valleys, where, from 1913 to 1925, with his extraordinary gifts of speed and organization, he built a 233-mile aqueduct and eight dammed reservoirs. While fostering urban growth, these projects diverted water from farmers, who responded with protests and sometimes violence. On several occasions activists dynamited the public works; the risk of the water supply being cut off greatly worried the city government.
Chinatown depicts violent effects of Los Angeles’s thirst
Tensions were high in 1925, when two of the largest dams yet were under construction closer to the city proper: the Mulholland Dam in Hollywood and the St. Francis Dam in San Francisquito canyon. Unlike Mulholland’s earlier earthwork dams, the new structures were built with concrete due to a lack of clay-based soil in the area; concrete which, though stronger by the pound than soil, was more porous and water-permeable.
The St. Francis Dam was a hybrid design with an arched element (like, for instance, the Hoover Dam) but relied mainly on its gravity dam elements- just as the Mosul Dam is today. Its construction was rushed due to the threat of violence- just as at Mosul. Like those at Mosul, the Angeleno engineers conducted minimal investigations into the site’s geology. This geology just happened to be rich in soft gypsum.
The Dam before its collapse
Water hemmed in by the dam quickly eroded the gypsum to create large fissures under the structure, issuing a one-two punch to the dam: the foundations settled into the cracked rock unevenly, and water buoyed the unstable structure upwards. Some may be confused as to how concrete, being two and a half times as dense as water, is forced upwards in these situations. This phenomenon is not due simply to floatation; rather, the pressure of the water behind the dam, forcing fluid through the fissures, is acting on the underside as well as the reservoir face of the dam.
On March 12, 1928, Mulholland was called to St. Francis Dam to inspect a leak of “dirty water”, whose brown coloration hinted that loam was being washed out from underneath the dam. For some reason- some have cited hubris on Mulholland’s part, others have hypothesized that clear water washing over the top diluted the brown water- the engineer declared the dam fully safe. That night the dam crumbled and water surged from the reservoir, carrying huge chunks of concrete hundreds of meters. The flood rushed downstream. A minimum of 430 people were killed.
Part of the dam, resting on the valley floor
Overnight, Mulholland’s career was snuffed. Whether he is fully culpable is still under debate; perhaps he was doomed to failure by his businessman and politician clients’ demands for speed. He is a clear inspiration for the engineer Mulwray in Chinatown, who, having refused to keep building dams after one’s collapse, is murdered by a water magnate. Today, the St. Francis Dam disaster has been largely forgotten in Los Angeles, so he is remembered more for giving his name to Mulholland Dam and Mulholland Drive.
Like all structural failures, the dam’s led to greater safety measures in future construction. Many dams built since at sites similar to the San Francisquito Canyon now have such devices as permanent grout curtains, directed drainage systems, and uplift relief wells. Mosul Dam, however, is at risk because it was built without any of these protective measures. It is entirely reasonable to assume that its fate if untreated will mirror that of the St. Francis Dam- and the urban areas downstream will pay the price.
Workers construct a grout curtain for a modern Pennsylvania dam
Total Views: 1291 ,