U.S. Ambassador to the United Nations Samantha Power warned that the dam in Mosul is critically unstable and could collapse, sending a 45-foot wall of water coursing through some of the biggest cities in Iraq, including the capital, Baghdad.

AFP:

"It is crucial that all UN member states quickly get informed about the magnitude of the problem and the importance of readiness to prevent a humanitarian catastrophe of epic proportions," said Power.

The ambassador described briefings by technical experts, engineers and representatives from UN aid and development agencies as "chilling."

The dam in northern Iraq was built on an unstable foundation that continuously erodes, and a lapse in required maintenance after the Islamic State jihadist group briefly seized it in 2014 weakened the already flawed structure.

"In the event of a breach, there is the potential in some places for a flood wave up to 14 meters high that could sweep up everything in its path, including people, cars, unexploded ordnance, waste and other hazardous material, further endangering massive population centers that lie in the flood path," said Power in a statement released by the US mission.

Power said repair work must be undertaken as soon as possible and Iraqis must be well informed about the best evacuation routes.

Italian firm Trevi has been selected to carry out crucial repair work on the dam, which is currently protected by Kurdish peshmerga forces.

A UN aid appeal for Iraq has received only eight percent of the $861 million requested, compounding concerns about badly needed assistance.

The warning follows testimony by CENTCOM commander Gen. Lloyd Austin, who told the Senate Armed Services Committee that a catastrophe with much loss of life is possible:

"If the dam fails, it will be catastrophic," Gen. Lloyd Austin III told the Senate Armed Services Committee. "There will be thousands of people donwstream that will either be injured or killed, certainly displaced. And the damage could extend all the way down to -- close to Baghdad, or into Baghdad," which is more than 200 miles downstream.

The U.S. Embassy in Baghdad said as many as 500,000 to 1.47 million Iraqis living along the Tigris River "probably would not survive" the impact of floodwaters that could reach depths greater than 45 feet in some parts of Mosul.

Gen. Austin told Congress, "We have worked with the Iraqis to be sure that they are doing the right things to warn people about this, and in the event that it does fail, what actions they should take to get to safety. And we certainly have measures in place to ensure that U.S. citizens are -- or U.S. personnel -- are accounted for and able to be evacuated in case of the dam's failure."

Austin said when Islamic State terrorists captured the dam for a few months in 2014, the maintenance workers fled, and the work to shore up the dam stopped.

"We have encouraged the Iraqi government, since the dam's been back in the hands of the Iraqis, to make sure that they're doing the right things to go about repairing the dam. They have most recently hired an Italian company to perform maintenance on the dam, but it may be several weeks or months before that company is up and running, so there is a time period that we are concerned about (when) there will be limited to no maintenance performed on the dam," he said.

As the Associated Press reported, the dam on the Tigris River was built in the early 1980s on unstable ground where the earth underneath it is constantly eroded by water. Maintenance crews have continuously poured cement under its foundation in a process known as "grouting."

The situation worsened when ISIS terrorists overran the dam and held it for several weeks in 2014. Since then, efforts to reinforce the dam's foundations have not been adequate, partly because ISIS still controls the factory that produces concrete for the dam.

In 2006, the U.S. Army Corps of Engineers issued a report calling the Mosul Dam "the most dangerous dam in the world."  The situation has only gotten worse over the years.

The U.S. embassy in Iraq issued a warning on February 29 calling the risk of collapse "serious and unprecedented."  And yet the world – and especially the U.S. – have dilly-dallied for months while the possibility of disaster increased. 

Evacuation plans are useless when the water is going to be 50 feet high.  Escaping catastrophe in this case will be a matter of luck.  And Iraq hasn't had much of that lately.