A Brief History of Dams in Iraq. The Case of Mosul Dam Presented to Al-Diwan, April 10, 2016 by Mosaid Al-Hussaini, Ph.D, PE

Transcription

1 A Brief History of Dams in Iraq The Case of Mosul Dam Presented to Al-Diwan, April 10, 2016 by Mosaid Al-Hussaini, Ph.D, PE

2 Dams in General Definition of a Dam: A dam is a barrier made of soil, concrete or rock across flowing stream for impounding water. Dam Classifications: Dams may be classified into a number of different categories, depending upon the purpose of the classification with respect to their height, use, hydraulic design, material used in construction and others. Classification According to Height Small (greater than 25 to 40 ft), ( 7.5 to 12.3 m) Intermediate (40 to 100 ft), (12.3 to 31m) Large (greater than 100 ft), (greater than 31 m).

3 Dams in General Classification According to Use Storage Dams: to impound water during period of surplus supply to be used during period of deficient supply. These dams may be used for water supply, Irrigation, Hydroelectric power, Fish and wildlife, Recreation. Detention Dams: They are used to elevate water and allow it to flow to ditches, canals or others for the purpose of irrigation developments. In such dams water store temporarily or held for long time.

4 Dams in General Classification With Respect to Hydraulic design: Overflow Dams, which are design to discharge water over their crest and usually constructed of concrete. Non-overflow Dams, which are design not to overtop the crest such as earth and rockfill dams. Classification of dams by materials: Earthfill Dam, Rockfill Dam Concrete gravity dam, Buttress Dam Concrete arch dam. Composite dam

5 Dams in General Earthfill Dams: They are constructed of locally available materials from the construction site that require no processing. Such dams are the most widely used and materials used in their construction are usually homogeneous. Overflow could severely damage the dam, so spillways are required, as well as filters.

6 Earthfill Dam

7 Rockfill Dam Rockfill Dams: Rockfill dams use rocks of all sizes in the construction to provide stability, they also use impervious core, as well as filters to provide water tightness against seepage through the dam. Such dams require foundations that does not undergo excessive settlements under load. Rocks and/or compacted sands are suitable foundation.

8 Rockfill Dam

9 Concrete Dam Concrete Gravity Dams: They are suitable for sites where there are reasonably sound rock foundations. Concrete dams are well suited for use as overflow spillway, therefore they need no major spillway as in the case of earthfill or rockfill dams.

10 Concrete Gravity Dam

11 Buttress Dam Buttress Dam It is a special type of gravity dam, where the amount of concrete is reduced by watertight slab supported by rectangular slopping buttresses.

12 Concrete Arch Dam Concrete Arch Dam Arch dams are much thinner than gravity dams. They are suitable where the ratio of the width of the dam to its height is not large, and the abutments are solid.

13 Dams in Iraq History of Dams in Iraq From ancient time, Iraq is known for building dams by themselves and not depended on other to build for them. Historically, the most important hydraulic projects are the following: a) Sennacherib ( BC) built a dam across the Khoser River North of Mosul to irrigate The Assyrian capital Ninawa. He also used dams for war and destruction. b) Al-Hur Ibn Yousif (Omayyad governor to Mosul) diverted The Tigris River (726 to 731) from flowing eastward to Ninawa at place called Hawi Al-Chenisa to flow to its existing channel passing by the city of Mosul. c) Hulago in 1258 broke Nahrawan dikes and flooded Baghdad area and made the Abbasid Cavalry immovable before attacking the city.

14 Iraqi Dams d) Al-Kut Regulator built in 1937 for flood control.

15 Iraqi Dams e) Dukan Dam in Sulaymania ( ).

16 Spillway of Dukan Dam Morning Glory

17 Darbandekhan Dam ( )

18 Mosul Dam g) Mosul Dam, Mosul ( ).

19 Mosul Dam, General Information a) The Tigris River is the most important source of water in Iraq, with average yearly flow of 51 Billion Cubic Meters. 92% of the water comes from outside the country and only 8% from inside. b) The Iraqi Board of Developments suggested the building of Mosul Dam in 1950 in Aski Mosul area near the village of Dhaw Al-Qamar. c) The general location of the dam was confirmed by two British consulting firms. Other consulting firms for investigating the site followed. d) The location of the dam changed several times because the Iraqi government was not able to decide on the size of the irrigated area. It changed from 2,500 Sq. Km to 7,500 Sq. Km. In 1974 an initial decision was made to select the present location.

20 Mosul Dam, General Information e) Geotechnical and geological investigations began on the selected location that ended in All consultants agreed that the foundation of the dam is difficult and complicated because of the presence of Gypsums ( CaSO4), Limestone and Marl and other soluble rocks. They considered grouting the foundation as a cure for the problem.

21 Mosul Dam Design Stage: a) Contract was signed with consortium of Swiss Consultants in 1978, they were asked to make the final design and prepare construction contract. b) Seven companies were involved in the construction, three Germans, three Italians, and one Japanese. The Japanese company was hired to design and construct the hydroelectric power stations. c) The project was completed in 1985.

22 Mosul Dam Dam Technical Data: Location: 60 Km. to the north of Mosul

23 Mosul Dam Purpose: Irrigation, flood control, hydropower, and recreation. Reservoir length : about 50 Km. Average Reservoir width : 5 Km. Storage capacity : Maximum Cu. Km. Aver. (from 8 to 3 Cu. Km.).

24 Mosul Dam Dam height : 113 m. Dam length : 3650 m. Width at the crest (Top point): 10 m. at Elevation 341 a.s.l (Sea level).

25 Mosul Dam Major Spillway Technical Data: Concrete spillway on left abutment at crest elevation 330 m. asl. Maximum discharge: 12,600 Cum. per second. Length : 680 m.

26 Mosul Dam Concrete Spillway: Five concrete spillways, each measure 13.5 X13.5m with radial gates Seismicity: (3.6 to 5.3) degrees on Richter scale

27 Mosul Dam Foundation condition of the dam. a) The foundation of the dam consists of several layers of gypsum material that have the ability to dissolve by running water. b) Existence of layers of broken rocks (called bereccia) that allow easy water passages. c) After reservoir filling in 1986 water began to seep (small fountains) in several areas such as abutments and downstream channel. d) The amount of calcium sulfate (CaSO4) showed an increase in downstream water in comparison to the upstream flow.

28 Mosul Dam

29 Mosul Dam Corrective measure Taken a) Grouting program began by constructing grouting curtains beneath the core of the dam deep in the foundation. Grout is a mixture of 1.0 part cement, 3.0 part sand and 4% betonite. b) The high water pressure created holes in the curtain called Windows and render the curtain ineffective. c) The operators use different insoluble grouting materials and continue grouting. Grouting reached an average of 3,000 ton per year. d) In 2004, the US Army Corps of Engineers Contracted Black & Fitch to propose a solution, they suggested to drop upstream water level not to exceed 319 a.s.l. (i.e. lowering the water level by 11 m.)

30 Mosul Dam Sink holes In 1992, sinkholes started to appear at different locations around the dam. They probably existed within the water channel and the reservoir. Four sinkholes appeared on a straight line parallel to the longitudinal axis of the dam. The largest sinkhole is SD6, it was filled twice.

31 Mosul Dam

32 Mosul Dam

33 Mosul Dam Upstream Slope Failure The gentle slopping on the left of the upstream area of the dam is in a state of failure, with average crack width of 1.0 ft (30 cm).

34 Mosul Dam The Aftermath of the Dam Failure The surge wave resulting from the unlikely event of dam failure will travel south and cause great loss of lives and property damages until its energy vanishes. Mathematical and statistical model was used at the time of the dam design (1984) is shown.

35 Mosul Dam

36 Mosul Dam Conclusions The condition of the dam has worsened rather than improved because of war and neglect since my inspections of the dam over a decade ago.

37 Mosul Dam Recommendations a) Start immediately with the construction of a cut-off wall (concrete wall at the upstream toe of the dam to extend to the depth to the unaffected layer of the Foundation). b) Install adequate instrumentations (Piezometers, inclinometers, settlement markers, seismic recording equipment, etc) to monitor the condition of the dam. c) Establish Dam Safety Emergency Plan which include 1. Reservoir dewatering procedure 2. Dam failure inundation maps 3. Emergency repair materials and equipments 4. Prepare list of material suppliers and contractors and all official personnel involved in the evacuation. 5. Establish Notification and Coordination Procedure.

38 Iraqi Dams in General Other Existing Dams in Iraq, For other dams in Iraq, it is important to form serious Dam Safety Inspection Teams consisting of competent and well-trained individuals to perform yearly inspection of each dam. The team should consist but not be limited to the following: a. Geotechnical engineer. b. Structural engineer. c. Mechanical engineer. d. Electrical engineer. e. Hydrology and Hydraulics engineer. f. Environmental engineer. g. Geologist. h. Instrumentation Specialist.