I was surprised to read of a disaster waiting to happen on the Tigris River in Iraq.
A lethal threat sits in Iraq right now, one that could kill hundreds of thousands of civilians with little notice. The weapon briefly fell into the jihadis’ hands last summer, and still poses a destructive risk to much of the country.
The 750-megawatt Mosul Dam is the country’s largest, and one of the most productive in the Middle East. But its proximity to Mosul, ISIS’s biggest Iraqi city, has caused nightmares in both Baghdad and Washington.
Built during the Saddam era on a weak foundation of gypsum, the dam requires continuous maintenance and reinforcement with fresh concrete. Without these efforts, some ten billion tons of water threaten to sweep down the Tigris, flooding towns and villages hundreds of miles downriver. Baghdad could see flooding of more than fifteen feet, according to one report. A U.S. Army Corps of Engineers study in 2006 called it “the most dangerous dam in the world” and estimates of the potential civilian death toll reach as many as half a million.
There's more at the link.
I couldn't figure out why any dam would be built to such shoddy specifications, or how it could 'require continuous maintenance and reinforcement'. Further investigation revealed:
Construction on the Mosul Dam began in 1980 by a German-Italian consortium that was led by Hochtief Aktiengesellschaft. Because the dam was constructed on a foundation of soluble gypsum, the engineers recommended the implementation grout curtain within the foundation before the superstructure was built. Instead, to speed construction of the dam, engineers installed a grouting gallery that would allow continuous grouting of the dam's foundation in order to promote stability. Construction was complete in 1984 and in the spring of 1985, the Mosul Dam began to inundate the Tigris River, filling the reservoir which submerged many archaeological sites in the region. Because of significant structural stability issues associated with the Mosul Dam, grouting and additional construction and repairs are constant.
The earthen embankment dam is located on top of gypsum, a soft mineral which dissolves in contact with water. Continuous maintenance is required to plug, or "grout", new leaks with a liquefied slurry of cement and other additives. More than 50,000 tonnes (49,000 long tons; 55,000 short tons) of material have been injected into the dam since leaks began forming shortly after the reservoir was filled in 1986, and 24 machines currently continuously pump grout into the dam base.
. . .
Iraqi officials maintain that the U.S. government is overstating the risk. The Army Corps of Engineers has proposed that the Badush Dam under construction downstream be expanded to obstruct the large wave which would result if the Mosul Dam collapsed. This has been resisted by Iraqi officials, who note that the current plan for the Badush Dam is US$300 million to provide hydroelectric power and help irrigation while the proposed expansion would cost $10 billion.
Again, more at the link.
So Saddam Hussein built a dam on a soluble foundation, not a solid one; and it's basically been under repair ever since, to stop Mother Nature doing what she does so well and punishing human hubris by bringing inevitable nemesis. All this in a country where the USA has spent, by some accounts, as much as $60 billion in US currency and $146 billion in Iraqi currency on rebuilding its infrastructure. A mere one to two per cent of that money would have sufficed to completely rebuild this dam (or replace it with one in a more suitable location) and make sure it wouldn't need ongoing maintenance, or fall prey to natural decay. Seems to me that would have been a much better way to spend it than allow so many billions to be frittered away on graft, corruption and sleaze.