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HYDROGEOLOGICAL OF MOSUL

DAM SITE

By

Issa Elias Issa

A report submitted as partial fulfilment of requirements for

geology of Iraq course

Department of Civil, Environmental and Natural Resources

Engineering

Luleå University of Technology

September 2011

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Contents Figures and Tables

1- Introduction………………………………………………………. 1

2- Description of Mosul dam …………………………………... 3

3- Hydrological Mosul dam ……………………………………. 5

1- Climate …………………………………………………………… 6

Precipitation ………………………………………………….. 6

Temperatures ………………………………………………… 8

Relative humidity …………………………………………… 10

Winds …………………………………………………………. 11

Evaporation …………………………………………………... 13

2- Main characteristics for Tigris river basin ………………. 14

3- Sedimentation …………………………………………………... 17

4- Geological Mosul dam ……………………………………….. 19

5- Summary …………………………………………………………. 26

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Figures and Tables

Figures

Figure 1. Map of Iraq …………………………………………………………………. 2

Figure 2. Mosul dam …………………………………………………………………... 3

Figure 3. Schematic diagram of Mosul dam cross ………………………………….. 4

Figure 4. Spillway, Radial gate and stilling basin …………………………………... 5

Figure 5. The percentage of rainy and dry days in year at the Mosul dam station . 6

Figure 6. The percentage of effective and not effective rain in the year at Mosul dam

station ………………………………………………………………………………….. 7

Figure 7. Maximum daily rain depth in year ……………………………………….. 7

Figure 8. The relative distribution for Max. temperatures in the year at Mosul dam

site ……………………………………………………………………………………... 9

Figure 9. The relative distribution for Min. temperatures in the year at Mosul dam

site …………………………………………………………………………………….. 9

Figure 10. Relative distribution for Max. humidity ………………………………. 10

Figure 11. Relative distribution for Min. Humidity in the year …………………. 11

Figure 12. Percentage distribution for winds direction in year ………………….. 12

Figure 13. Percentage distribution for winds velocities in year ………………...... 12

Figure 14. Relative distribution of daily evaporation depth in the dam site …..... 13

Figure 15. Discharge elevation curve at paish-khabure ………………………….. 15

Figure 16. Reservoir area and volume at indicated elevation ……………………. 16

Figure 17. variation of the Suspended load with flow rate in Tigris river ……… 18

Figure 18. Geological map of Mosul city ………………………………………….. 20

Figure 19. Geological map of Mosul reservoir ………………………………….… 21

Figure 20. Geological map of Mosul dam site …………………………………….. 22

Figure 21. Small cave was found in March 2002 within a gypsum / anhydrite

layer …………………………………………………………………………………... 24

Figure 22. Karst phenomenon cause spring in bedrock ………………………...… 25

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Figure 23. Collapse in the top layer ………………………………………………… 26

Tables Table 1: Max. Rain depth for years (1994-2008) at Mosul dam meteorological station ………………………………………………………………………………… 8 Table 2: Lithostratigraphic table of Mosul dam area ……………………………. 23

1- Introduction. The Iraq is located in Asia between longitudes (40.7 to 48) and latitude

(29 to 37), with a total area ( 425,320 km2 ) is bordered by Islamic

Republic of Iran to the east, the Arab gulf to the south east, Saudi Arabia a

and Kuwait to the south, Jordan and Syria to the west and Turkey to the

north. Shown in fig.(1). Topographically, Iraq is shaped like a basin

consisting of the great Mesopotamian alluvial plain of the Tigris and

Euphrates rivers this plain is surrounded by mountains in the north and the

east which can reach altitudes of (3350m) above the sea level, and desert

areas in the south and west which account for (40 %) of the total area.

The climate in Iraq is mainly of continental subtropical semi-arid type,

with the north and north-eastern mountains regions having a Mediterranean

climate. Rainfall is very seasonal and occurs in the winter from December

to February, expect in the north and northeast of country, where the rainy

season is from to April. Average annual rain is estimated at (216mm), but

ranges from (1200mm)in the northeast to less (100mm) over (60%)of the

country in the south. Temperatures about (16Cº ) dropping at night to (2Cº)

with possibility of frost in winter, but summers are dry and hot to extremely

hot with temperature of over (45Cº) during July and August, dropping at

night to (26Cº).

Iraq passes from the two rivers Tigris and Euphrates, originating in the

Turkey. Before their confluence, the Euphrates flows for about (1000km)

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and Tigris for about (1718 km) within the territory of Iraq, the average

annual runoff for Tigris is estimated about (35.458 km3) and of the

Euphrates is (11.227 km3). Flows into the Tigris River seven tributaries are

on the left bank. Unlike the Tigris, the Euphrates not receives tributaries

during its passage in Iraq. See fig.(-1-).

Figure 1: Map of Iraq

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2- Description of Mosul dam.

Mosul dam is one of the biggest hydraulic structures in Iraq which has

been built since 1986 on the Tigris River in north of Iraq approximately

(50km) northwest from Mosul city. Shown in fig.(2)

River

Mosul dam Main Spillway

Figure 2: Mosul dam

It is rock fill dam with mud core, high (113 m), its length with the

spillway is (3650 m), top width (10 m). The surface area of its reservoir is

(380 km2) with a storage capacity of (11.11 billion m3) at operation level

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(330 m) above sea level, including (8.16 billion) live storage and (2.95

billion) dead storage. Shown fig.(-3-).

Figure 3: Schematic diagram of Mosul dam cross section

The dam has spillway contains of (5) radial gates with dimension (13.5m

x 13.5m) giving a discharge of (5370 m3/sec) at the operation level. Fig. (4 )

as shown. This dam was constructed for hydroelectric power generating,

flood control for Mosul city and water storage for the agricultural purpose

and tourist.

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Figure 4: Spillway, Radial gate and stilling basin

3- Hydrological Mosul dam. The catchments area for Tigris River geographically divided into three

regions mountainous, foot hills and the plain region. The climate of

catchments area may be regarded similar to the Mediterranean climate,

except some differences due to the presence of mountainous region, which is

located within the Turkish territory. The climate of this region is hot-dry

summers and cold rainy winters, while the second region is hot-dry summers

and cold-dry winters, which is located in northern of Iraq. The plains region

extends from Balad town north Baghdad city to Arab gulf. This is hot-dry

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summers but semi-cold and became relatively wet. In this case can regarded

the climate of Mosul and Mosul dam region are similar.

3.1- Climate.

- Precipitation.

The Precipitation in the Tigris river basin occurs between (Octobers –

May). In the mountainous region most precipitation is snow, but in the foot-

hills and plains is usually rain. The annual rate of precipitation over the

Tigris basin ranges between ranges (450-1500mm) annually in the Turkey

site, while is ranging between (200-600mm) annually in Mosul city. The

biggest depth of the rain is recorded in 24 hour is (71.6mm) at the dam site.

Fig.(-5-) show the percentage of rainy days in the year, but Fig. (-6-) show

the ratio of effective rainfall to total that causes runoff.

Figure 5: The percentage of rainy and dry days in year at the Mosul dam

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Figure 6: The percentage of effective and not effective rain in the year at Mosul dam

From data recorded in station that previously mentioned have been

identified maximum rain storm for each year as shown in table (1) which is

shows the maximum rain depth for years (1994-2008). Also Fig.(-7-)

illustrated time series for maximum depth to this period.

Max

. Rai

n d

epth

(mm

)

Year

Figure 7: Maximum daily rain depth in year

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Table (1) Max. Rain depth for years (1994-2008) at Mosul dam meteorological station.

year Max. rain depth (mm) in 24 hour

1994 41 1995 35 1996 51.5 1997 22 1998 35 1999 21 2000 27 2001 36.5 2002 42 2003 29 2004 20 2005 50 2006 35 2007 35 2008 15.5

- Temperatures. The average monthly temperatures in Mosul city range between (6Cº) in

the January to reach maximum level in July (34Cº), but the maximum

temperature recorded is (51.1Cº) in July (1977) and the lowest temperature is

(-11.1Cº) in January (1925), the relative distribution for Max. and Min.

temperatures in the year at Mosul dam site are illustrated in fig.(-8-) and fig.

(-9-)., during the period (1994-2004).

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Figure 8: The relative distribution for Max. temperatures in the year at Mosul dam site

Figure 9: The relative distribution for Min. temperatures in the year at Mosul dam site

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- Relative humidity. The average monthly of relative humidity at Mosul city ranging between

(80%) in January, to less than (30%) in July, fig. (-10-) and fig.(-11-) shows

respectively the relative distribution for Max. and Min humidity in the year

for the same site.

Figure 10: Relative distribution for Max.

humidity in the year.

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Figure 11: Relative distribution for Min.

humidity in the year.

- Winds. The prevailing winds in the Mosul dam site are blowing mostly from the

west to east during the summer while the prevalent winds are eastern winds

monthly January and February. The annual average speed about (3.6m/sec),

the range of these velocities between (2-3) m/sec in cold season to rise

(5m/sec) in warm season. Fig.(-11-) shows the percentage of winds direction

during the year which are measured between (1994-2006), but the fig. (-12-)

explain the percentage wind velocities in the year for the same place and

period.

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Figure 12: Percentage distribution for winds direction in year

Wind velocity

Figure 13: Percentage distribution for

winds velocities in year

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- Evaporation.

The amount of annual evaporation is estimated about (2.1m) depth from

the reservoir surface. The seasonal variation of evaporation is relatively

large range between (40mm) in January to (400mm)in July. Fig.(13)

summarize relative distribution of daily evaporation depth in the dam site.

Figure 14: Relative distribution of daily evaporation depth in the dam site

3.2- Main characteristics for Tigris river basin.

The main resources for Tigris river is Hazar lake, which is located in the

south east Turkey, with level about (1200m) above sea level, surrounded by

mountain reach height (3000m). The basin is determined from east and north

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sides by mountain chains common to both Turkey, Iraq and Iran. Flows into

the river north Mosul city many tributaries Batman, Kazan, Botan and

Alkhabur, that sources of these is the same mountain region all these

converge with Tigris river from left bank. The river is shallow wide in the

Diyarbakir but after reach with Batman become Narrow deep river with

height velocity and entirely within Iraqi borders in paish-khabur. The wide

river valley (flood plain) range between (2-10) km north Mosul city to paish-

khabur. The slop river in this reach is (0.65m/km). The catchments area

estimated up Mosul city is (52200 km2 ) including (23500 km2 ) in Iraq. The

rain in the basin concentrated between January to February but the snow is

melting in April and May therefore the flood period is between February to

May, after this the flow rate reduce where the lower rates occur during the

August to October.

From data of flow rate for (76) year for Mosul station we get.

Minimum annual discharge (280 m3/sec).

Annual discharge (653 m3/sec).

Maximum annual discharge (1395 m3/sec).

The peak highest daily discharge is registered up to (9200 m3/sec), which

occurred on the (15 April 1988). Fig.(14) gives relation between discharge

and elevation, Fig. (15) Variation between reservoir volume and area with

stage.

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Figure 15: Discharge elevation curve at paish-khabure.

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Figure 16: Reservoir area and volume at indicated elevation

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3.3- Sedimentation.

Rate of sedimentation in the Tigris River especially in Mosul dam site

has been estimated from many group Iraqi and foreign companies, since the

fifties of the last century. In (1951) Irrigation development commission

provided under supervision F.F.Huag study entitled “ Control of the Iraqi

rivers and use of waters” as estimated the annual rate of sediment in the

Tigris river up the Mosul dam site about (356m3/year per Km2 from

catchments area). Also Advisory committee under the supervision of Sir

Alexender in (1953) estimated the Sediment amount (400m3/year per Km2

from catchments area).

Then provided Harza engineering company, Binnie and Partners in (1963)

report volume II about “Hydrological survey of Iraq” investigated the

amount of suspended load during period (8 October 1958 to 28 June 1962),

when the discharge ranged (97- 1321) m3/sec. The samples were taken from

the region expected Mosul dam lake covered. Fig (16) shows the relation

between discharge and suspended sediment rate for (Mosul, Tusan and

Zakho stations).

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Mosul Tusan Zakho

Figure 17: variation of the Suspended load

with flow rate in Tigris river

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4. Geological Mosul dam. The geology of the area surrounding the dam site consists of Pleistocene

to Recent age alluvial deposits overlying rocks of the Lower to Middle

Miocene age Lower Fars Group (the principal foundation rocks below the

dam causing the major concerns) and the Oligocene to Lower Miocene age

Jeribe formation. Fig.(17,18 and 19) are show the geological map formation

for Mosul city, Mosul Reservoir area and dam site respectively. The lower

terraces along the river have sandy, clayey silt up to 20m thick which was

used for constructing the core of the dam. Some alluvium is present at

elevations over 80 m above the present valley floor, indicative of major

climatic variations. The lithostratigraphic column of the formations is shown

in Table (2).

The foundation geology of the dam comprises of a layered sequence of

rocks including marls, chalky limestone, gypsum, anhydrite, and limestone.

A feature of the geology is the occurrence of karstic limestone and the

development of solution cavities within the gypsum and anhydrite layers.

Four significant gypsum units were identified during design and construction

varying in thickness from (8 to 16m).

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20

Figu

re 18: Geological m

ap of M

osul city

Figu

re 19: Geological m

ap of M

osul reservoir

21

22

Figu

re 20: Geological m

ap of M

osul d

am site

Table (2) Lithostratigraphic table of Mosul dam area

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The dissolution and erosion of gypsum by water seeping under the dam is

believed to be the main cause of the development of voids requiring

continuous grouting fig.(20) shows the cave due to the dissolution. The

erosion and dissolution rates in gypsum are related to the seepage velocities

and hydraulic gradient.

Figure 21: Small cave was found in March 2002 within a gypsum/anhydrite layer

A review of case histories dealing with gypsum show that gypsum

dissolution occurs until seepage water reaches a calcium sulfate saturation of

approximately 2,000 ppm. The dissolution zone moves downstream as

greater quantities of unsaturated water attack a gypsum bed. At Mosul major

dissolution occurs at the “karstic line”, the inferred boundary where

anhydrite converts to gypsum and this unit is subsequently dissolved and

eroded by seepage. The development of karst leads to high permeability

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conduits that can convey substantial quantities of water at varying velocities

fig.(21) shows this within the bedrock. The karst development is deep and

extends to a depth of about 100m below the dam foundation.

Figure 22: Karsts phenomenon cause spring

in bedrock

The dissolution by groundwater is a common phenomenon and the void is

generally filled with collapse breccias from the overlying beds fig.(22)

shows the earth collapse due to dissolution. Also the conglomerate beds in

the terrace deposits raise a problem of water seepage through open cracks

and possibly of piping by internal erosion of the silty layers in contact with

water paths. All these points that have been referred to previously deserve

special attention.

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Figure 23: Collapse in the top layer near the

Mosul dam site

5- Summery. Generally Mosul dam is the large hydraulic structure in Iraq which is

located northern Mosul city. It is one of the important strategic projects for

storage water, power generation and flood protection, so that should be study

and analysis any information that related to it.

- Hydrological information is useful to know the amount of water

storage and release to determine the best method of operation,

estimate the amount of water possible to reach the lake from the

catchments area up dam site and know the quantity of sediment that

could enter to the reservoir consequently their influence on the

storage capacity of reservoir.

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- Geological structure for dam site and surrounding area is essential

to know the dam state and know the main problems that may be

occurs before or after construction. The geology of the Mosul dam

site area is superficial deposits overlying rocks of the Upper and

Lower Fars Groups above the Jeribe formation. The Jeribe

formation rocks are of Oligocene to Lower Miocene age, while the

rocks of the overlying Fars groups are of Lower to Middle Miocene

age. The foundation geology of the dam comprises a layered

sequence of rocks including marls, chalky limestones, gypsum,

anhydrite, clays and limestones. A feature of the geology is the

development of karst or solution weathering within the limestones

and the anhydrite and gypsum layers. The presence of gypsum and

anhydrite in the marl would be particularly detrimental in zones

where high seepage flows could develop, i.e mainly at the contact

with the cavernous limestone. This will require a special attention

in avoiding high velocities, induced by high hydraulic gradients.

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References

College of Engineering, 2011, Sediment Study Upstream Pump

Station Al-Jezera Project, Final Report, Consultancy Bureau,

College Engineering, Mosul University, 103p.

Imatran Voima Osakeyhtio, 1968,Geologe Map Reservoir Are,

Scale 1:100 000, Republic of Iraq, Ministry of Agrarian Reform.

Imatran Voima Osakeyhtio, 1968,Geologe Map of Dam Site,

Scale 1:100 000, Republic of Iraq, Ministry of Agrarian Reform.

Harza Engineering Company, Binnie and Parteners, 1963,

Hydrological Survy of Iraq, Final Report, Vol. III, Government of

Iraq, Ministry of Agriculture, 146p.

Kelley, J.R.,Wakeley, L.D., Broadfoot, S.W., Pearson, M.L.,

McGrath, C.J., McGill, T.E., Jorgeson, J.D., and Talbot, C.A.,

Geologic Setting of Mosul Dam and Its Engineering Implications,

U. S. Army Crops of Engineers, Engineer Research and

Development Center, 50p.