The Mosul Dam in Iraq was built nearly 30 years ago by the Saddam Hussein regime, amid concerns that the bedrock foundation is fundamentally flawed. The bedrock is primarily made up of gypsum and anhydrite which are highly water-soluble. The engineers responsible for the dams construction solved this by constantly grouting the holes which formed.
The job of grouting was carried out by a team of 300 workers working in shifts 24 hours a day. In August of 2014 the dam was captured for a period of almost 11 days by ISIS. When the dam was finally recaptured, only about 30 of the workers returned and much of the equipment used for grouting was looted.
One of the two sluice gates used to regulate pressure is also jammed and must be repaired in order for the system to work properly. In combination with the coming snow melt the water level and pressure will rise to a point that the dam cannot withstand and will result in catastrophic failure. There was supposed to be a failsafe built down river, but due to sanctions against iran in 1991 the project was abandoned.
If the dam fails a 20-metre high wave will overrun the city of Mosul in 4 hours and eventually hit the city of Baghdad in 45 hours. Official estimates say that at least 500,000 people will die as a result, other estimates project more than a million. The official emergency plan of the Iraqi government is for everyone to move 6km from the river, a plan which is heavily criticized as the people who make it will have nothing left to live off of.
On Wednesday the Iraqi government announced they had signed a deal with an Italian construction firm to repair and maintain the dam for 18 months, valued at $296 million (US). Additionally the Italian government will send 450 troops to defend the dam.