Dexter Filkins spins a frightening tale of Iraq's Mosul Dam, which a US Army Corps of Engineers report called "the most dangerous dam in the world:"
Completed in 1984, the dam sits on a foundation of soluble rock. To keep it stable, hundreds of employees have to work around the clock, pumping a cement mixture into the earth below. Without continuous maintenance, the rock beneath would wash away, causing the dam to sink and then break apart. But Iraq's recent history has not been conducive to that kind of vigilance. [...]
In February, the U.S. Embassy in Baghdad issued a warning of the consequences of a breach in the dam. For a statement written by diplomats, it is extraordinarily blunt. "Mosul Dam faces a serious and unprecedented risk of catastrophic failure with little warning," it said. Soon afterward, the United Nations released its own warning, predicting that "hundreds of thousands of people could be killed" if the dam failed. [...]
If the dam ruptured, it would likely cause a catastrophe of Biblical proportions, loosing a wave as high as a hundred feet that would roll down the Tigris, swallowing everything in its path for more than a hundred miles. Large parts of Mosul would be submerged in less than three hours. Along the riverbanks, towns and cities containing the heart of Iraq's population would be flooded; in four days, a wave as high as sixteen feet would crash into Baghdad, a city of six million people.
The description of the potential catastrophe predicts that "An inland tidal wave could displace the 1.2 million refugees now living in tents and temporary quarters in northern Iraq, adding to the chaos:"
The wave, the Embassy's report predicted, would move rapidly through the cities of Bayji, Tikrit, and Samarra, wiping out roads, power stations, and oil refineries; damage to the electrical grid would probably leave the entire country without power. At least two-thirds of Iraq's wheat fields would be flooded. [...] To control the erosion, the government began a crash program of filling the voids with cement, a process called "grouting."
Grouting work had been running "Every day, nonstop" until recent years:
When ISIS fighters took the dam, in 2014, they drove away the overwhelming majority of the dam's workers, and also captured the main grout-manufacturing plant in Mosul. Much of the dam's equipment was destroyed, some by ISIS and some by American air strikes. The grouting came to a standstill--but the passage of water underneath the dam did not.
Estimates of the lost time range from "less than three weeks" to "about four months" to a former official's estimate that "The grouting work stopped for eighteen months."
According to a U.S. Army Corps of Engineers report, numerous voids had opened up below the dam--as much as twenty-three thousand cubic metres' worth. "The consensus was that the dam could break at any moment," John Schnittker, an economist who has been working on water issues in Iraq for more than a decade, said.
A subsequent report "that water downstream contained high concentrations of dissolved gypsum--evidence of large voids" makes one worry about the potential closeness of this catastrophe.