A Hundred Thousand Tons of Cement

I mentioned it about a year ago, and it’s since become possibly the most famous dam in the world—and not in a good way. The Mosul Dam in Iraq is poised to give way, flooding the city of Mosul downstream and threatening its 2 million residents. The problem, in part, is caused by erosion, but not in the way you might think.

As this article points out, the dam was designed to withstand an aerial bombardment—and it has. It stretches about 2 miles across the Tigris River and rises 370 feet from the riverbed. The problem is that it’s resting on soluble gypsum. The engineers who built the dam in 1984 realized this, but, acting at the direction of Saddam Hussein’s government, they didn’t have much choice in the location; all the possible sites for the dam had the same type of substrate.

The dam was built quickly, and Swiss consultants involved in the project believed the “gypsum problem” could be managed. (Soviet and French companies also bidding on the project wanted further geological surveys, which were not carried out). Almost immediately after the reservoir behind the dam was filled, in 1985, engineers began noticing sinkholes around the dam and finding underground fractures. The government began a program—which still continues—of filling the cracks and voids with cement. In the three decades since the dam was built, about a hundred thousand tons of cement have been pumped into the ground in this effort. The article provides a more detailed description of the process, but the engineers involved admit they’re working blind—they can’t actually tell where the grout they’re pumping is going. “It could be a single spacious cavity, requiring mounds of grout, or it could be an octopus-like tangle, with winding sub-caverns, or a hairline fracture…. ‘You stop grouting when you can’t put any more grout in a hole,’ says one engineer. ‘It doesn’t mean the hole is gone.’”

A second dam was started to help control flooding if the Mosul Dam failed, but it was abandoned during the Gulf War and never completed. Nearly two years ago, ISIS fighters captured the Mosul Dam; it was recaptured 10 days later, but the interruption in the pumping of cement and the sporadic work since that time—hindered by fighting in the area—is thought to have further weakened it. A breach could occur because underground sinkholes beneath the dam increase in size, or because parts of the dam slowly settle and tilt—which has been happening for more than a year—and finally cause the entire structure to fail. An Italian firm is now bringing in newer equipment in an attempt to fill the underground spaces more efficiently and accurately.

The most dangerous season for the dam is spring, when the Tigris receives runoff from snowmelt. A civil engineer working on the dam believes there will be little or no warning when it finally fails. As the article describes, “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.”