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Worries grow over Mosul Dam

Catastrophic failure of a major Iraqi dam and the resultant loss of life must be avoided through more reinstatement work, according to a US report published in October.

In the quarterly report to US Congress, the Special Inspector General for Iraq Reconstruction (SIGIR), Stuart W Bowen Jr said the $27M (18.4M) reconstruction project on the Mosul Dam – the country's largest – has lacked any "significant progress", two years after it began.

The Office of SIGIR reports to the US Secretaries of State and Defense.

The US government is funding the project to improve basic grouting facilities needed to tackle problems with the dam foundation, while the Iraqi Ministry of Water Resources seeks a longer-term solution.

The document said improvements to concrete-mixing units had not been completed: "Three mixing plants currently provide no usable benefit to the ministry. Because the contract required delivery of five grout-mixing plants by July 2006, the massive grouting and enhance grouting programmes are now more than one year behind schedule."

The dangerous security situation in Iraq hampered the SIGIR inspection team and meant it could only conduct site visits for three hours at a time – it made two of these in September.

The dam is located on the River Tigris, about 50km north west of Mosul, and is built on soluble soils that are subject to erosion. Soil movement creates cavities beneath the dam and its banks that must be grouted.

The geology comprises layers of marls, chalky limestone, gypsum, anhydrite, clays and severely fractured limestone, most of which are subject to dissolution and karst features.

The day before the quarterly report, the Office of SIGIR published Relief and Reconstruction Funded Work at Mosul Dam, Mosul, Iraq. The report cites a letter sent in May to Iraqi prime minister Nouri al-Maliki from the US ambassador in Baghdad warning that an instantaneous failure of the dam when at its maximum operating level would be catastrophic.

At its highest level of 330m the dam's storage capacity is 11.1bnm3, which the letter said could cause a flood wave 20m deep to hit Mosul, with significant loss of life among its 1.7M inhabitants.

In April last year, the ministry restricted the reservoir operating level to 319m – 11m below its maximum – to try and reduce the risk to life and property.

THE HISTORY OF THE DAM

The dam was built between 1980 and 1984 under the rule of Saddam Hussein. The report: Relief and Reconstruction Funded Work at Mosul Dam, Mosul, Iraq said that to save construction time, the dam was built without the grouting work needed to control seepage through the dam foundations.

It adds that as an alternative, the designer chose to build a grouting gallery that would allow grouting to continue after the dam began operating. The reservoir was filled for the first time in the spring of
1985.

The dam features a 3.4km long earth fill embankment, power house, bottom outlet, concrete lined spillway and fuse plug secondary spillway. The embankment has a volume of 37.7M.m3 and is 113m high. Its crest is 343m high and 10m wide.

It is built on a foundation of soluble soils that are continuously dissolving. The resulting voids have placed the dam under sustained threat from failure over the past 25 years.

Until a long-term solution is found grouting needs to be done to mitigate the risks.

A $27M (!18.4M) short-term project funded by the US government focuses on providing replacement parts and a grouting facilities upgrade to assist the Iraq Ministry of Water Resources with its grouting programme.

Alexandra Wynne

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