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Mosul Dam

As of August 2014 Daesh [ISIL, etc] had control of the Mosul Dam. Thus, Daesh had the ability to open the dam and flood many urban areas connected by the Tigris River. Iraqi and Kurdish ground forces retook the Mosul Dam in August 2014 with the help of US air strikes - an achievement that was under threat by January 2015. Kurdish peshmerga fighters launched a new offensive to secure areas southeast and southwest of the dam.

On 28 February 2016 the US Embassy in Baghdad stated: "Mosul Dam faces a serious and unprecedented risk of catastrophic failure with little warning. A catastrophic breach of Iraq’s Mosul Dam would result in severe loss of life, mass population displacement, and destruction of the majority of the infrastructure within the path of the projected floodwave. The floodwave would resemble an in-land tidal wave between Mosul and Samarra’, and would sweep downstream anything in its path, including bodies, buildings, cars, unexploded ordinances, hazardous chemicals, and waste..."

Flood waters could reach depths greater than 15 meters in some parts of Mosul city in as little as one to four hours, giving residents little time to flee. In three to four days, the water would reach Baghdad, swelling the river that dissects the city by some 10 meters, and likely forcing the closure of the capital's international airport. The 500-kilometer flood path would also damage or destroy large sections of infrastructure, and knock power plants offline, causing the entire Iraqi electricity grid to shut down. Farmland would also be severely damaged.

Mosul Dam (formerly known as Saddam Dam) was constructed in the 1980s on the Tigris River near the city of Mosul, Iraq, for irrigation, flood control, water supply, and hydropower. Mosul Dam, located 50 km north of Mosul city, was built on the Tigris Riverby an Italian –German joint company. It has a length of 3.2 kilometers and a height of 131 meters. It is the largest dam in Iraq and the fourth largest dam in the Middle East.

The site was chosen for reasons other than geologic or engineering merit. One of the reasons for the insistence of the Iraqi regime to build a dam in its current location was that Saddam Hussein wanted to make a natural barrier to the movement of Kurdish Peshmerga rebels and obstruct supplies to them. The lake would cut off the Bahdinan area in Kurdistan, which had been a center of revolutions and opposition movements against the former Iraqi regime.

Sinkholes, caves, and cracks appeared in and around the dam foundation during construction and reservoir impoundment in 1984. In 2010 the Mosul Dam continued to require a half million dollars per year to repair cracks that threaten its integrity and reduce its effective hydropower potential.

From a geologic standpoint, the foundation is very poor, and the site geology is the principal cause of continuing intense concern about the safety of the structure. Specifically, the dam was constructed on alternating and highly variable units of gypsum, anhydrite, marl, and limestone, each of which is soluble in water under certain conditions.

The Arabian Plate was part of the supercontinent of Gondwana throughout much of geologic time. Two episodes of rifting, from the Permian Period (286 to 245 million years ago (Ma)) to the Jurassic Period (206 to 144 Ma), formed the Neo-Tethys Ocean and were followed by periods of subsidence and sediment accumulation. Tectonic activity of the Neo-Tethys Ocean area along with fluctuations in sea level influenced the type and amount of sedimentation on the Arabian Plate. At times, the plate was inundated with ocean water, resulting in the deposition of limestone. Similarly, in the plate area that is now Iraq, shallow marine shelf and near-shore zones accumulated carbonate and evaporite sediments.

Rock layers near and under Mosul Dam are subject to dissolution and the development of karst features. Karst topography is characterized by landforms that result from subsurface dissolution of water-soluble geologic materials and is often surficially manifested as dolines (sinkholes). Dolines are closed circular to elliptical hollows or depressions, often funnel shaped, with diameters ranging from a few meters to a few kilometers and depths ranging from a meter to hundreds of meters.

The visual portion of a sinkhole represents a very small percentage of the loss of material in the subsurface. Surface expression of a sinkhole may not occur until the visually obscured portion of the feature is well developed and very large.

A large sinkhole developed in February 2003, east of the emergency spillway when the pool elevation was at 325 m. The Mosul Dam staff filled the sinkhole the next day, with 1200 cu m of soil. The pool was dropped and then raised again, and the sinkhole reopened, meaning the fill from February sank into deeper parts of the dissolution feature. In June, it was refilled with another 2000 cu m of material, with the pool at 315 m. The pool was raised to 320 m and the sinkhole reopened, requiring another 1000 cu m of fill.

Impoundment of a large freshwater reservoir in contact with such unstable geologic materials promotes continuous dissolution in the foundation and abutments, with preferential and rapid dissolution of gypsum and anhydrite layers. This condition creates a situation demanding extraordinary engineering measures to maintain the structural integrity and operating capability of the dam. The requisite engineering measures have included maintenance grouting of the structure continuously since construction. The purpose of maintenance grouting is to close water-flow pathways that open by rapid dissolution of geologic materials in the foundation and abutments.

The consensus among various expert panels and engineers and scientists who have studied or worked directly on Mosul Dam is that the embankment was constructed well and is not the cause for concern. However, without continuous maintenance grouting of the foundation and abutments, the dam would fail.

The US Army Engineer Division, Gulf Region (GRD), became increasingly concerned about the safety of the dam as their tenure in-country lengthened. An international panel of experts (IPE) had recommended that the structural integrity of Mosul Dam could be improved by transitioning the grouting program from 1980s practices to the best available 21st-century techniques and equipment. Further, the IPE recommended that a 3-D geologic model and hydrogeologic or groundwater flow model should be developed to support the transition to enhanced grouting.

Annual reports of grouting over the several years up to 2007 showed large and rapid changes in grout-curtain efficiency (described in Annual Reports of Dam Operations provided by Ayoub or included in the LOD). That is, formation permeability or effectiveness of the grout curtain at a certain location can change quickly, in weeks to months rather than the centuries to millennia expected in less dramatic geologic processes. These changes and other published and unpublished data indicate vertical and lateral changes with time on a fairly small scale (meters or submeter) within a single rock unit.

The Gannett Fleming, Inc., IntelliGrout® system is a comprehensive integration of data collection, real-time data display, database functions, real-time analytical capabilities, and computer-aided design to manage large-scale seepage-control and other grouting projects. Gannett Fleming, Inc., working in partnership with Advanced Construction Techniques, Ltd., developed IntelliGrout® for managing and accomplishing seepage control and stabilization of large earthen and concrete dams, and reconstruction of underground structures such as subways, tunnels, railway, water supply aqueducts, mines, and penstocks.

Mineralogic variability within rock units resulted from original depositional processes that created interfaces and zones of weakness within individual beds. These natural zones of weakness now function as ingress points for seep water and allow dissolution zones to move vertically and horizontally.

By 2007 dissolution was occurring at a faster rate than natural geologic processes. Sinkholes that had reached the surface recently on the east abutment indicated large-scale dissolution in the subsurface. Rock quality, grout-curtain efficiency as related to piezometer data, sinkhole development, sinkhole retreatment, dissolution rates of rock material, and water chemistry (total dissolved solids) collectively indicate that the dissolution front is moving to the east and downstream. The rate of subsurface dissolution has been increased by the presence of the reservoir.

The pattern of regrouting in and between recently grouted sections of the dam [as of 2007] showed that grouting at one location causes the flow path (seepage) of subsurface water to move to another location, but does not stop the seepage. At or above a pool depth of 318 m above sea level, the rate of subsurface dissolution increases markedly, leading to the recommendation that the pool not be raised above 318 m.

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Page last modified: 04-03-2016 17:45:50 ZULU