Abstract
Mosul Dam is an earth fill dam located on the Tigris River in North Western part of Iraq. It is 113 m in height, 3.4 km in length, 10 m wide in its crest and has a storage capacity of 11.11 billion cubic meters. It is, constructed on bedrocks which consist of gypsum beds alternated with marl and limestone, in cyclic nature. The thickness of the gypsum beds attains 18 m; they are intensely karstified even in foundation rocks. This has created number of problems during construction, impounding and operation of the dam. Construction work in Mosul Dam started on January 25th, 1981 and started operating on 24th July, 1986. After impounding in 1986, seepage locations were recognized. The cause of seepage is mainly due to: 1) The karsts prevailing in the dam site and in the reservoir area. 2) The existence of gypsum/anhydrite rock formations in the dam foundation alternating with soft marl layers and weathered and cavernous limestone beddings. 3) The presence of an extensive ground water aquifer called Wadi Malleh aquifer, which affects considerably the ground water regime in the right bank. The dissolution intensity of the gypsum/anhydrite ranged from 42 to 80 t/day which was followed by a noticeable increase in the permeability and leakages through the foundation. Inspection of the dam situation in 2014 and 2015 indicates that the dam is in a state of extreme unprecedentedly high relative risk. In this work, possible solutions to the problem are to be discussed. It is believed that grouting operations will elongate the span life of the dam but do not solve the problem. Building another dam downstream Mosul Dam will be the best protective measures due to the possible failure of Mosul Dam, to secure the safety of the downstream area and its’ population.
Highlights
Mosul Dam is located on the Tigris River in North Western part of Iraq; approximately 60 km northwest of Mosul city [1] (Figure 1)
The seepage due to the dissolution of gypsum and anhydrite beds raised a big concern for the safety of the dam and its possible failure. This problem was kept in a small closed circle within the Iraqi Ministry of Water Resources till the US Army Corps of Engineers conducted a study on Mosul Dam for the period June, 2004 to July, 2006 and highlighted the possibility of the dam failure
The Upper Member, as the Lower Member of the Fatha Formation consists of cyclic sediments, marls, clay stone, limestone and gypsum; in the uppermost part the clay stone ratio increases as compared with the lower part
Summary
In the vicinity of Mosul Dam, the exposed formation is Lower Fars (Fatha). It is composed of alternating beds of limestone, marl and gypsum [2]. The Upper Member, as the Lower Member of the Fatha Formation consists of cyclic sediments, marls, clay stone, limestone and gypsum; in the uppermost part the clay stone ratio increases as compared with the lower part. These inhomogeneous rocks; in their mechanical behavior, will certainly behave differently when are loaded. The other fault is trending N NE-S SW along the right bank of the River Tigris This fault is not clear on the surface and it was detected using Landsat images. The area of the dam site almost doesn’t suffer from active tectonic disturbances; this is confirmed by Kelly et al [22], when they stated that the dam body does not suffer from any problem
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