Leakage at Mosul dam in north Iraq has engineers worried and recent grouting efforts have not been executed effectively, according to a US study. Report by Neil Ford.
Despite sustained investment, attempts to tackle weaknesses in the structure of the Mosul dam on the Tigris river in north Iraq have failed to make much impact to date. This was the main finding of the Relief and Reconstruction Funded Work at Mosul Dam report, which was produced by the US Office of the Special Inspector General for Iraq Reconstruction (SIGIR). The SIGIR inspection team uncovered severe problems with US efforts to help Iraq mitigate risks at the structure, which must be tackled if the long-term future of the hydroelectric and water supply scheme is to be secured.
The earthfill dam, which was completed in 1984, is 3.4km long, 113m high and has a volume of 37.7M m3. There is a concrete-lined gated spillway with a maximum discharge capacity of 12,400m3/s, and a 400m long fuse-plug secondary spillway on the left abutment with a discharge capacity of 4000m3/s with levels reaching within 2m of the dam crest. The power intake structure includes four 7.0m by 10.5m hydraulically operated wheel gates.
The multi-purpose reservoir has a total storage volume of 11.1B m3 while active storage is 8.1B m3. The hydroelectric element of the scheme includes four 187.5 MW turbines, which provide electricity to the 1.7M inhabitants of Mosul. The geology underlying the project comprises layers of clays, severely fractured limestone, gypsum, chalky limestone, marls and anhydrite, which are prone to dissolution and the development of karst features.
The dam was built on soluble soils, says the SIGIR report. Due to the leakage they consequently have been subject to erosion and the movement within their mass, creating cavities and voids beneath the dam. In particular, there is a thin, horizontal layer of non-binding clay, which encourages seepage and places the dam at some risk, the report continues.
In an attempt to finish the original dam project quickly, the structure was completed without all necessary grouting having been done to control seepage through the foundation. Then, in March 1985, seepage became apparent when the reservoir was first impounded and after 12 months the flow rate was more than 800l/s. The Ministry of Water Resources attempted repeatedly to tackle the problem but only met with partial success. Most investment was made into a continuous grouting programme – implemented 24 hours a day, six days a week – in order to fill the cavities. This reduced the volume of seepage but failed to stem it entirely.
Fluctuations in the water level within the regulating reservoir have resulted in the development of sinkholes at the dam, most recently in early 2005 and late 2006. The appearance of the new sinkholes raised fears that cavities beneath the structure could lead to dam failure because they were closer to the dam than existing ones. According to a study of the dam by consultants Washington Group International and black-veatch, “the decision to locate such a major and important dam on the foundation rock mass which exists at the Mosul dam site was fundamentally flawed.”
The scheme’s weaknesses were identified as a major problem in Iraq’s water sector shortly after the fall of the government led by Saddam Hussein. In 2004, concerns were raised over the conditions, long-term stability and safety of Mosul dam. At the time, the main problems listed were the impact of solution and internal erosion, plunge pool erosion and the emergence of the sinkholes.
A panel of experts was set up to assess the extent of the weaknesses and best methods to tackle them. It reported: “The safety of the Mosul dam cannot be assured due to unpredictable and unique foundation conditions.”
The panel recommended the continuation of the grouting programme in the short term but argued that the construction of Badush dam as a backstop would be the best long-term solution.
As a result, the US has provided support to the Iraqi government since 2005 to help establish a lasting solution to the dam’s problems. Studies were undertaken to identify the most serious problems and to develop solutions. While Iraq’s Ministry of Water Resources investigates the long-term answers, in the short term the US government has been funding a series of projects to ensure the safety of the dam.
As a result of the various studies a US$27M grouting programme was established to be administered by the US Army Corps of Engineers (USACE), Gulf Region Division, and funded by the Iraq Relief and Reconstruction Fund. A total of 21 contracts were awarded under the programme, including for procurement and installation of five grout mixing plants and the construction of stationary silos. In addition, an enhanced grouting programme was drawn up to solve the dam’s structural weaknesses in the long term.
In December 2006, the Corps produced a report entitled Hypothetical Dam Failure Scenarios, which argued that the probability of dam failure at Mosul is exceptionally high. This prompted the US Ambassador to Iraq and the Commanding General of the Multinational Force in Iraq to jointly write to the Iraqi prime minister in May 2007, arguing that the dam presented unacceptable risks and did not meet international standards for risk and reliability, so the safety of the dam could not be assured. They concluded that the worst case scenario could be a significant loss of life and property. The Corps believes that dam failure could flood the city of Mosul within four hours to a maximum depth of more than 20m.
A SIGIR team, comprising an engineer and two auditors, inspected work on the dam during the third quarter of 2007, as part of its continuing assessment of reconstruction projects across the entire water sector, and possibly in response to the intense safety fears. The main aim of the assessment was to “determine whether selected sector reconstruction contractors were complying with the terms of their contracts or task orders” and to evaluate the effectiveness of the “monitoring and controls exercised by administrative quality assurance and contract officers”. SIGIR concluded that US efforts have as yet to yield the “significant improvements” desired but it is hoped that the benefits will become apparent in the near future.
The SIGIR report indicates that seepage flows are collected and measured at three plate weirs and water comes from three locations: the access gallery and the right and the left sides of the spillway. It adds: “The water from the left side is the largest flow and appears to emanate from the limestone rocks of the abutment…The flow from the right side is thought to be water passing under the spillway.”
All the flows are believed to be relatively constant, having started since the reservoir was impounded, and remain clean and clear.
The report identified a number of different weakness in the work carried out to date, partly with design drawings and equipment. Drawings for the reconstruction work were inadequate, while there were no comprehensive schematic drawings of the enhanced grouting equipment. The report states: “After a thorough review of all available design drawings, we found the drawings to be deficient, leading to a number of safety concerns.”
For instance, the drawings for the stationary silos lacked significant details, such as bracing support for the entire height of the silos and also for the method of depositing cement into the silos.
In some cases, both construction and efforts to improve construction weaknesses were found to be inadequate. For example, it was “determined that 43 of the 144 foundation bolts were inadequately installed. Further, the installation of the foundation bolts also contradicted the contractor’s own design construction techniques, which required bolt threads to extend higher than the nut.” The inspection team argue that this leaves the dam in a potentially dangerous condition.
Secondly, the quality management programme did not adequately ensure the correct delivery and construction of material and equipment. For example, one contractor supplied pumps with 36m3/hour and 17.5m lift capability. However, the company invoiced for pumps with 54m3/hour capacity and 20m lift capability. The Gulf Region Division passed responsibility for checking deliveries by contractors to the Ministry but this task was not carried out to a high enough standard. Some contractors merely delivered equipment without installing it, although the report argues that “the assembly of the stationary silos and mixing plans obviously required significant construction efforts”.
This resulted in problems with contract sustainability. Contracts required suppliers to provide a large number of spare parts with each delivery, so that equipment could remain operational even if individual parts wore out. No spare parts for some pieces of equipment could be identified during the inspection. However, as contractors’ invoices claimed that they had been delivered and there was little verification of the contents of deliveries, it was impossible to make suppliers accountable for any discrepancies. Overall, the execution of the 21 contracts was not considered “consistent with the original project objectives to provide the Mosul dam and the Ministry personnel with critically needed spare and replacement parts, and also the ability to conduct massive grouting or to fully implement enhanced grouting”.
The Advanced Grouting System (AGS) is proving an area of particular concern. It has two main elements: modified grout batching and delivery equipment for balance stable grout handling, mixing and other functions; plus an Integrated Analytical System (IAS) for automated computer aided grouting monitoring and analysis. However, the three IAS units are not being employed at present, partly because their air conditioning systems are unable to keep them cool enough to operate. In addition, the dam manager told the SIGIR inspection team that the software provided is far too advanced for the IAS units.
In addition, the modified grout batching has been only partly assembled because of the lack of schematic drawings to explain how the various components should be assembled. Crucially, the AGS contract did not require the supplier to provide on site commissioning, training or technical support. An insufficient training course of just seven weeks was given to the Ministry employees on the project. However, a grouting expert with the Corps, who previously worked on the project, commented: “Grouting is highly specialised, using highly specialised equipment; only an expert with years of experience on a wide range of grouting projects involving different operational environments, equipment and staging techniques can readily discern the nuts and bolts of the required equipment and equipment functions on a given project.”
These problems were also highlighted in the SIGIR quarterly report, which was presented to the US Congress at the end of October. The SIGIR report conceded that the programme has yet to significantly improve the basic grouting capability of the Ministry resources at the dam. The Commander of the Multinational Force in Iraq and the US Ambassador have also expressed their concern regarding the lack of progress in improving basic grouting capability.
The work at the Mosul dam is just part of the wider redevelopment of the Iraqi water sector that is required. A joint report by the World Bank and UN in 2003 estimated that the rehabilitation of the water and wastewater sector would cost US$14.4B. However, the latest SIGIR report argues that reconstruction work to date has been impeded by a lack of trained workers, inadequate maintenance and the ongoing violence. Although the total number of insurgent attacks has fallen over recent months, security has become more of a problem in the dam area and SIGIR reports that Mosul is second only to Baghdad with regard to the number of reported attacks. Indeed, SIGIR personnel had to cancel several inspection visits to construction works at Mosul because of concerns over possible attacks.
The main problem with the original Mosul dam project seems clear: the dam structure was not suitable for the underlying geology. At the same time, the SIGIR report appears in no doubt as to why attempts to mitigate the problems at the dam have failed so far. Adequate procurement systems for the grouting programme were not put in place, while there was no strategic overview of the programme as a whole. As a result, the quality and suitability of the equipment and materials employed is deficient and a rather fragmented approach to rehabilitation has been adopted.
Work on the current programme will continue as planned but it is hoped that full implementation of the enhanced grouting operation will build on the work carried out to date. The material and equipment required for the enhanced operations will be supplied under the US Embassy’s Iraq Transition Assistance Office. Staff from the Assistance Office are currently finalising the Post Delivery Support Plan to provide the ministry and the Mosul dam with the materials and equipment needed to improve current grouting operations and to implement in full the enhanced grouting programme.
The Post Delivery Support Plan highlights six key improvements needed as soon as possible:
• Fix the IAS units (Intelligrout) to make them fully operational;
• Procure additional grouting mixing plants with 30m3/hour capacity;
• Provide additional materials required for continuing grouting operations;
• Perform required laboratory testing to establish the design mixes with the desired rheological properties, using water and mix components;
• Conduct two separate field tests, one inside the gallery and one outside; and,
• After completion of the field tests and identifying the desired design mixes, fully implement enhanced grouting.
In addition, a receiving committee, equipped with details of all contracts, will monitor and assess the delivery of all materials and equipment.
The Transition Office is confident that the plan will adequately resolve the outstanding issues and problems and facilitate the ultimate implementation of the enhanced grouting. It remains to be seen whether this will be achieved but SIGIR certainly seems to be putting a great deal of effort and investment into tackling the long-term weaknesses in the Mosul dam. Although the exact timescale for the rehabilitation work has not been set in stone, further SIGIR reports over the next two years are likely to provide updates on progress at the site.