192-210, 2011 Issn 1816-9112

192 Research Journal of Fisheries and Hydrobiology, 6(3): 192-210, 2011 ISSN 1816-9112

ORIGINAL ARTICLES

The Probability Of Zagros Mountains Environmental Pollution Due To Seismic Response Of Bakhtiari Dam

Zaniar Tokmechi

Department of Civil Engineering, Mahabad Branch, Islamic Azad University, Mahabad, Iran.

ABSTRACT

The Bakhtiari Dam is a planned arch dam on the Bakhtiari River within the Zagros Mountains in Lorestan Province, Iran. At a planned height of 315 meters (1,033 ft), it will be the world's tallest dam once completed and withhold the largest reservoir in Iran. The Zagros Mountains are the largest mountain range in Iran and Iraq. With a total length of 1,500 km (932 mi), from northwestern Iran, and roughly correlating with Iran's western border, the Zagros range spans the whole length of the western and southwestern Iranian plateau and ends at the Straits of Hormuz. In this paper, the probability of environmental pollution due to heavy metals caused by Bakhtiari dam failure is studied. Finite Element and ZENGAR methods are used to analyze the probability of pollution at dam downstream. Different dam cross sections and various loading conditions are considered to study the effects of these factors on the seismic behavior of the dam. Results show that the effect of the highest cross section is not the most significant for heavy metals pollution at the dam down stream. Pollution coefficient due to stress along Y axis (Sy) is always the determinant pollution. While, in all sections Sx and Sy are the determinant parameter affecting downstream heavy metal pollution and normally are bigger than Sz. And, Sz which can never be a determinant. According to results, when the earthquake accelerations are bigger, maximum pollution coefficient due to tensile stress at dam basement is increased. While, the pollution due the maximum compressive stress at dam basement depends on both earthquake acceleration and loading condition.

Key words: Environmental pollution, Seismic Response, Bakhtiari dam, ZENGAR, FEM

Introduction

The main purpose of the Bakhtiari dam is hydroelectric power production and it will support a 1,500 MW power station. By trapping sediment, the dam is also expected to extend the life of the Dez Dam 50 km (31 mi) downstream. The Zagros fold and thrust belt was formed by collision of two tectonic plates — the Eurasian and Arabian Plates. Recent GPS measurements in Iran have shown that this collision is still active and the resulting deformation is distributed non-uniformly in the country, mainly taken up in the major mountain belts like Alborz and Zagros The seismic action on dams is the most important to be considered in dams safety studies and its effects on the environmental pollution (United States Army Corps of Engineers, 1990). In 21st century, hydraulic power exploitation and hydraulic engineering construction have been improved in many countries. Some high dams over 200m, even 300m in height, have been built in many areas of the world (Jianping et al., 2006). Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms (Mohsenifar et al., 2011; Allahyaripur et al., 2011). Pollution can take the form of chemical substances or energy, such as noise, heat, or light. Pollutants, the elements of pollution, can be foreign substances or energies (Arabian and Entezarei, 2011), or naturally occurring; when naturally occurring, they are considered contaminants when they exceed natural levels (Arbabian et al., 2011; Hosseini and Sabouri, 2011). Pollution is often classed as point source or no point source pollution. Pollution has always been with us. According to articles in different journals soot found on ceilings of prehistoric caves provides ample evidence of the high levels of pollution that was associated with inadequate ventilation of open fires. The forging of metals appears to be a key turning point in the creation of significant air pollution levels outside the home. Core samples of glaciers in Greenland indicate increases in pollution associated with Greek, Roman and Chinese metal production. According to the statistics, the construction regions in many areas, are notable for their high environmental pollution (Wang and Li, 2006; Qasim et al., 2010 a; Qasim et al., 2010 b). Therefore, environmental studies affected by the seismic safety of large dams is one of the key problems that need to be solved in the design of Corresponding Author: Zaniar Tokmechi, Department of Civil Engineering, Mahabad Branch, Islamic Azad University, Mahabad, Iran. Tel: +98-918-873-1933, Fax: +98-871-3229437, E-mail: [email protected] 193 Res. J. Fish & Hydrobiol., 6(3): 192-210, 2011 dams. While, difficulties exist in determining the seismic response of dams (United States Army Corps of Engineers, 1995). The most important difficulty is dams complex geometry and forms, motivated by the topography and geotechnical character of the implantation zone and controlling the project pollution effects. According to the previous studies, usually 2D models corresponding to the higher section the dam have been used in the structural seismic analyses of the dams (Fenves and Chopra, 1984). While, normally there is a lot of variation in the dam foundation geometry which can be extremely make the study of the dam downstream pollution difficult. In this paper, the probability of environmental pollution caused by Bakhtiari dam failure is studied. Finite Element and ZENGAR methods are used to analyze the probability of pollution at dam downstream. Different dam cross sections and various loading conditions are considered to study the effects of these factors on the probability of environmental pollution due to seismic behavior of the dam.

Materials And Methods

Bakhtiari Dam:

Background:

Preliminary studies for the dam began in 1996 and were carried out by Mahab Qods Consulting Engineers. The studies were carried out over a period of 33 months and in March 2000, the results were given to Iran Water & Power Resources Development Co (IWPCO). In May of 2005, IWPCO awarded consultation services for the project to Moshanir Consulting Engineers, Dezab Consulting Engineers, Econo-Electrowatt/Boyri and Stucky Pars Consulting Engineers. On April 30, 2007 the construction contract was awarded to China's Sinohydro Corporation who is also working with Farab Co. of Iran. The contract is worth $2 billion and is being funded with direct investment from China. Sinohydro signed the 118 month contract on March 15, 2011 and will be working with Iran's Farab.

Construction:

During construction, a total of six bridges will be built to support workers, vehicles and equipment in addition to various access roads. To divert the river, two tunnels, 1,151 m (3,776 ft) and 1,180 m (3,871 ft) in length will be constructed at the dam's left abutment. They will have discharge capacities of 2,090 m (6,857 ft) and 1,680 m (5,512 ft) respectively. To divert the water, two roller-compacted concrete cofferdams will be constructed. The upstream cofferdam will be 51 m (167 ft) high and the downstream 25 m (82 ft). Material to construct the dam including aggregate will come from the actual excavation of the dam site along with three quarries in the area.

Design:

The Bakhtiari will be a 315 m (1,033 ft) tall and 434 m (1,424 ft) long variable-radius arch dam. It will be 10 m (33 ft) wide at its crest and 30 m (98 ft) wide at its base while being composed of 3,100,000 m3 (109,475,467 cu ft) of concrete. The dam's reservoir will have a normal capacity of 4,845,000,000 m3 (3,927,905 acre·ft) and an active or "useful" capacity of 3,070,000,000 m3 (2,488,890 acre·ft). At a normal elevation of 830 m (2,723 ft) above sea level, the reservoir will have a surface area of 58.7 km2 (23 sq mi), maximum width of 1 km (1 mi) and length of 59 km (37 mi). Its catchment area will be 6,288 km2 (2,428 sq mi). The dam will contain two spillways. The main service spillway will be an 11 m (36 ft) diameter tunnel in the right abutment with two flood gates. The discharge capacity of this spillway will be 5,830 m3/s (205,885 cu ft/s). The second spillway will be two radial gates on the dam's orifice with a discharge capacity of 1,510 m3/s (53,325 cu ft/s). The dam's powerhouse will be located underground at the left abutment. It will be 161 m (528 ft) long, 64 m (210 ft) high and 24 m (79 ft) wide; containing 6 x 250 MW vertical Francis turbine- generators. Before reaching the power station, water will be transferred by six 51 m (167 ft) long penstocks. Feeding water to the penstocks is a 504 m (1,654 ft) long headrace tunnel with a three gate intake structure. Figure 1 shows the dam place.

194 Res. J. Fish & Hydrobiol., 6(3): 192-210, 2011

Fig. 1: Bakhtiari dam place

Zagros Mountains:

The Zagros Mountains are the largest mountain range in Iran and Iraq. With a total length of 1,500 km (932 mi), from northwestern Iran, and roughly correlating with Iran's western border, the Zagros range spans the whole length of the western and southwestern Iranian plateau and ends at the Straits of Hormuz. The highest points in the Zagros Mountains are Zard Kuh (4,548 m) and Mt. Dena (4,359 m). The Hazaran massif in the Kerman province of Iran forms an eastern outlier of the range, the Jebal Barez reaching into Sistan. Figure 2 to 4 show some pics from Zagros mountain.

Fig. 2: Zagros mountain 1

Fig. 3: Zagros mountain place 195 Res. J. Fish & Hydrobiol., 6(3): 192-210, 2011

Fig. 4: Valey in Zagros mountain

Geology:

A relatively dense GPS network which covered the Zagros in the Iranian part. Also proves a high rate of deformation within the Zagros. The GPS results show that the current rate of shortening in SE Zagros is ~10 mm/yr and ~5mm/yr in the NW Zagros. The NS strike-slip Kazerun fault divides the Zagros into two distinct zones of deformation. The GPS results also show different shortening directions along the belt, i.e. normal shortening in the South-East and oblique shortening in the NW Zagros. The sedimentary cover in the SE Zagros is deforming above a layer of rock salt (acting as a ductile decollement with a low basal friction) whereas in the NW Zagros the salt layer is missing or is very thin. This different basal friction partly made different topographies in either sides of Kazerun fault. Higher topography and narrower zone of deformation in the NW Zagros is observed whereas in the SE, deformation was spread more and wider zone of deformation with lower topography was formed. Stresses induced in the Earth's crust by the collision caused extensive folding of the preexisting layered sedimentary rocks. Subsequent erosion removed softer rocks, such as mudstone (rock formed by consolidated mud) and siltstone (a slightly coarser-grained mudstone) while leaving harder rocks, such as limestone (calcium-rich rock consisting of the remains of marine organisms) and dolomite (rocks similar to limestone containing calcium and magnesium). This differential erosion formed the linear ridges of the Zagros Mountains. The depositional environment and tectonic history of the rocks were conducive to the formation and trapping of petroleum, and the Zagros region is an important part of Persian Gulf oil production. Salt domes and salt glaciers are a common feature of the Zagros Mountains. Salt domes are an important target for oil exploration, as the impermeable salt frequently traps petroleum beneath other rock layers.

Type And Age Of Rock:

The mountains are divided into many parallel sub-ranges (up to 10, or 250 km wide), and have the same age as the Alps. Iran's main oilfields lie in the western central foothills of the Zagros mountain range. The southern ranges of the Fars Province have somewhat lower summits, reaching 4000 metres. They contain some limestone rocks showing abundant marine fossils. The Kuhrud Mountains form one of the parallel ranges at a distance of approx. 300 km to the east. The area between these two impressive mountain chains is home to a dense human population that lives in the intermediate valleys which are quite high in altitude with a temperate climate. Their rivers, which eventually reach salt lakes, create fertile environments for agriculture and commerce.

Ecology:

The Zagros Mountains contain several ecosystems. Prominent among them are the forest and steppe forest areas (PA0446), which have a semi-arid temperate climate. The annual precipitation there ranges from 400 mm to 800 mm, and falls mostly in the winter and spring. The winters are severe, with winter low temperatures often below −25 degrees C. The summer and autumn are very dry. They are the home to the Zagros Mountains Mouse-like Hamster.

History:

196 Res. J. Fish & Hydrobiol., 6(3): 192-210, 2011

Signs of early agriculture date back as far as 9000 BC to the foothills of the Zagros Mountains, in cities later named Anshan and Susa. Jarmo is one archaeological site in this area. Shanidar, where the ancient skeletal remains of Neanderthals have been found, is another. Some of the earliest evidence of production has been discovered in the Zagros Mountains; both the settlements of Hajji Firuz Tepe and Godin Tepe have given evidence of wine storage dating between 3500 and 5400 BC. During early ancient times, the Zagros was the home of peoples such as the Kassites, Guti, Assyrians, Elamites and Mitanni, who periodically invaded the Sumerian and/or Akkadian cities of Mesopotamia. The mountains create a geographic barrier between the flatlands of Mesopotamia, which is in Iraq, and the Iranian plateau. A small archive of clay tablets detailing the complex interactions of these groups in the early second millennium BC has been found at Tell Shemshara along the Little Zab. Tell Bazmusian, near Shemshara, was occupied between the sixth millennium BCE and the ninth century CE, although not continuously.

Earthquake and ZENGAR method:

Earthquake as a special and challengeable load condition is one of the most significant loads that is considered in the dam designing and its effects could not be negligible. In this paper, ZENGAR method is used to model the earthquake loading condition (Omran and Tokmechi, 2008). According to this method, hydrodynamic pressure of water can be derived by the equation 1. P  C. . H (1) h w where αh is the maximum horizontal acceleration of the earthquake, γw is water mass density , H is the water depth and C is a coefficient which is given by C Z Z Z Z C  m ( (2  )  (2  ) (2) 2 H H H H where Z is the depth of the point from the water surface and Cm is a coefficient which is given by 90   Cm  0.73( ) (3) 90 where is the upstream slope. The inertia load due to the vertical acceleration of the earthquake can be also given by E  v.W (4) where αv is the maximum vertical acceleration of the earthquake and W is the weight of the dam. In this study, a sample earthquake condition properties have been taken as shown in Table 1 (Omran and Tokmechi, 2008). Also, eight different loading conditions, mentioned in Table 2, have been considered to study the seismic response of the dam (Omran and Tokmechi, 2008).

Table 1. Earthquake Condition

Earthquake Level Maximum Horizontal Acc. (g) Maximum Vertical Acc. (g)

DBL 0.28 0.20 MDL 0.34 0.25 MCL 0.67 0.55

Table 2. Loading Conditions Uplift Loading Condition Body Weight Hydrostatic Pressure Earthquake Pressure LC1 * - * - LC2 * * * - LC3 * * * DBL (1st mode I) LC4 * * * DBL (2nd mode II) LC5 * * * MDL (1st mode) LC6 * * * MDL (2nd mode) LC7 * * * MCL (1st mode) LC8 * * * MCL (2nd mode)

I: Earthquake inertia loading and dam body weight act in the same direction II: Earthquake inertia loading and dam body weight act in the apposite direction 197 Res. J. Fish & Hydrobiol., 6(3): 192-210, 2011

Finite Element Method:

In this study, Constant Strain Triangle element is used (Chandrupatla, 1997). Equation 5 is used to calculate the element stresses. The calculated stress is used as the value at the center of each element.   DBq (5) Where D is material property matrix, B is element strain displacement matrix, and q is element nodal displacement from the global displacements vector Q. For plane strain conditions, the material property matrix is given by Equation 6. 1  0  E   D    1 0  (6) (1 )(1 2 )  0 0 1 2   2 Element strain-displacement matrix is given by Equation 7.

y23 0 y31 0 y12 0  1   B  0 x 0 x 0 x (7) det J  32 13 21  x32 y23 x13 y31 x21 y12  In which, J is Jacobian matrix, and the points 5, 6, and 7 are ordered in a counterclockwise manner. Jacobian matrix is given by Equation 8.

x13 y13  J  (8) x y   23 23  Global displacements vector Q is given by Equation 9. KQ  F (9) In which, K and F are modified stiffness matrix and force vector, respectively. The global stiffness matrix K is formed using element stiffness matrix ke which is given by Equation 10. e T (10) k  te Ae B DB In which, te and Ae are element thickness and element area, respectively.

Results And Discusion

Seismic Response:

Using Finite Element, ZENGAR and probability studies methods, study of the probability of environmental pollution due to Bakhtiari dam failure has been done and different loading conditions were considered. Fig. 5 to Fig. 15 show the probability of environmental pollution due to failure (Named PEP) caused by maximum compressive stress values in different cross sections. The PEP due to maximum tensile stress values are also shown in Fig. 16 to Fig. 26. The PEP due to vertical stress distribution across dam basement due to different loading conditions are the other key factors for controlling dam safety, and they are shown in Fig. 27 to Fig. 37. In all Figures Sx, Sy and Sz are stand for PEP due to stress along X, Y, and Z axis, respectively.

PEP Due To Maximum compressive stress (1st section) 120

100 80

60 40

20 Sx 0 Sy 12345678Sz LC

Fig. 5: PEP Due To Maximum compressive stress (1st section) 198 Res. J. Fish & Hydrobiol., 6(3): 192-210, 2011

PEP Due To Maximum compressive stress (2nd section) 60 50 40

20 Sx 10 Sy 0 Sz 12345678 LC

Fig. 6: PEP Due To Maximum compressive stress (2nd section)

PEP Due To Maximum compressive stress (3rd section) 100

20 Sx Sy 0 Sz 12345678 LC

Fig. 7: PEP Due To Maximum compressive stress (3rd section)

PEP Due To Maximum compressive stress (4th section) 100

20 Sx Sy 0 Sz 12345678 LC

Fig. 8: PEP Due To Maximum compressive stress (4th section) 199 Res. J. Fish & Hydrobiol., 6(3): 192-210, 2011

PEP Due To Maximum compressive stress (5th section) 100.00

80.00

60.00

40.00

20.00 Sx Sy 0.00 Sz 12345678 LC

Fig. 9: PEP Due To Maximum compressive stress (5th section)

PEP Due To Maximum compressive stress (6th section) 100

20 Sx Sy 0 Sz 12345678 LC

Fig. 10: PEP Due To Maximum compressive stress (6th section)

PEP Due To Maximum compressive stress (7th section) 60

40 30

20 Sx 10 Sy 0 Sz 12345678 LC

Fig. 11: PEP Due To Maximum compressive stress (7th section) 200 Res. J. Fish & Hydrobiol., 6(3): 192-210, 2011

PEP Due To Maximum compressive stress (8th section) 60 50

40 30 20 10 Sx 0 Sy 12345678Sz LC

Fig. 12: PEP Due To Maximum compressive stress (8th section)

PEP Due To Maximum compressive stress (9thsection) 100

40 Sx 20 Sy 0 Sz 12345678 LC

Fig. 13: PEP Due To Maximum compressive stress (9th section)

PEP Due To Maximum compressive stress (10th section) 90 80 70 60 50 40 30 20 Sx 10 Sy 0 Sz 12345678 LC

Fig. 14: PEP Due To Maximum compressive stress (10th section) 201 Res. J. Fish & Hydrobiol., 6(3): 192-210, 2011

PEP Due To Maximum compressive stress (11th section) 100

20 Sx Sy 0 Sz 12345678 LC

Fig. 15: PEP Due To Maximum compressive stress (11th section)

PEP Due To Maximum tensie stress (1st section)