Iraqi dam burst 'would drown 500,000'

A catastrophic failure of the largest dam in Iraq would send a wave 65ft high hurtling down the valley of the river Tigris, killing up to 500,000 people, US engineers warned yesterday.

The dam, which is near Mosul in the north of the country, was built in 1984 on a bed of water-soluble rock and is in imminent danger of collapse. "In terms of the internal erosion potential of the foundation, Mosul Dam is the most dangerous dam in the world," said a report by the US Army Corps of Engineers. "If a small problem [at] Mosul dam occurs, failure is likely." The collapse of the two-mile long, earth-filled dam would release eight billion cubic metres of water in the lake behind it in a giant wave which would flood Mosul – a city of 1.7 million people 20 miles downstream – to a depth of 60ft.

"A catastrophic failure of the Mosul Dam would result in flooding along the Tigris river all the way to Baghdad," the US military commander General David Petraeus and the US ambassador Ryan Crocker warned the Iraqi prime minister, Nouri al-Maliki, in a letter on 3 May this year. "Assuming a worst-case scenario, an instantaneous failure of Mosul Dam filled to its maximum operating level could result in a flood wave 20m deep at the city of Mosul, which would result in a significant loss of life and property."

The frantic debate within the US and Iraqi governments over the failing dam was kept secret for months to avoid public panic and attracting the attention of insurgents. The US Army Corps of Engineers has tried to monitor the deterioration and undertake remedial action.

The state of the dam and the experts' belief that it is on the verge of collapse was first revealed by The Independent on 8 August. "It could go at any minute," a senior aid worker, who knew of the struggle by American and Iraqi engineers to save the dam, told this newspaper. "The potential for disaster is very great."

The Independent's storywas confirmed yesterday with the release of a report by the US Special Inspector for Iraq Reconstruction, which said that the dam's foundations could give away at any moment. It spells out publicly the degree of alarm felt by the Corps of Engineers, which has directed that American military equipment on the Tigris flood plain should be moved to higher ground. The main problem is that the dam was "built in the wrong place", according to Khasro Goran, the deputy governor of Nineveh province, of which Mosul is the capital. Construction of the dam, initially known as the Saddam Dam, began in 1980 and was completed four years later when the lake behind it began to fill.

"The dam was constructed on a foundation of marls, soluble gypsum, anhydrite and karstic limestone that is continuously dissolving," said a specialist at the US embassy in Baghdad. "The dissolution creates an increased risk of dam failure."

The flat, Mesopotamian plain was the site of the biblical flood where Noah launched his ark to escape the rising waters. Much of the story was drawn from the legend of Gilgamesh, the ancient Mesopotamian hero, which recounts the tale of a great inundation with details strikingly similar to those in Genesis.

For millennia,Iraq was prone to floods as melting winter snows in the mountains of Turkey filled the Tigris and Euphrates rivers. In the 20th century, flooding was brought under control by an elaborate system of dams and dykes. But these would be unable to cope with the vast quantities of water which would be released if the Mosul Dam bursts.

The Independent was first told of the impending disaster by a senior aid worker who feared that no one was doing much to prevent a disaster. "It is a time bomb waiting to go off," he said. "Everybody knows about the threat but they have other preoccupations and, in the case of foreigners, it is now conveniently in Iraqi hands." He added that some military radios issued to US personnel had panic buttons to press when the dam began to give way.

The failings of the dam became clear soon after it was built and, since the late 1980s, the main method used to strengthen the foundations has been to pump liquid cement into them, or grouting.Since May this year, the water level in the reservoir behind the dam has been lowered on the advice of an international committee of experts appointed by the Iraqi Ministry of Water Resources, which is now responsible for the project.

Latif Rashid, the minister in charge, continues to believe that disaster can be averted. But, if the dam does break, there is nothing to stop a 65ft wall of water drowning hundreds of thousands of people between Mosul and Baghdad.