**3. Karun-1 dam**

Karun-1 (also known as Shahid Abbaspour) is a 200 m high concrete arch dam (**Figures 1** and **3**) at nearly 52 km to the northeast of Masjid-I-Solaiman City in the Khuzestan Province. It was constructed on the Karun River with a reservoir capacity of 3139 MCM to produce electrical energy, to control flood, and to regulate water. The first impounding of the dam reservoir was in December 1976. The presence of two springs downstream the right abutment of the dam site and construction of a new power plant besides recent rock sliding on the dam abutments are the main points of discussion. Since the completion of the dam, seepage problem was a key challenging subject regarding the right abutment shear zone and downstream springs [16–18].

**Figure 3.** Upstream view of Karun-1 dam site before (left) and after (right) construction.

Some studies were later done regarding the construction of a new second powerhouse in the left abutment of the dam [19–21] and recently, rock fall on the right abutment [22, 23].

In fact, most part of the study area, that is, Khuzestan Province and the aforementioned dams

Iran can be generally divided into five major seismotectonic zones (**Figure 2**) that are subjected to destructive earthquakes excluding one (Central Iran characterized by low seismicity). It is considered as a broad seismic zone over 1000 km width that extends from the Turanian platform (southern Eurasia) in the northeast to the Arabian plate in the southwest. The Iranian plateau is characterized by active faulting, recent volcanic activity, and high density of active and recent faults. Reverse faulting dominates the tectonic mechanism of the region. Southwest of Iran, where the studied large dams are located, belongs to the Zagros Active Fold Belt from the seismotectonic point of view [14]. Seismicity in this belt correlates well with topographic elevations greater than 1.5 km. Fault plane solutions for several earthquakes consistently show high angle (40°–50°) reverse faulting and the estimated depths range from 8 to 13 km with magnitudes that range from 4 to 6. The rate of seismicity in this zone is higher than the others, but the type of seismicity is mostly between small to moderate and seldom large. Due to its particular tectonic condition, the large earthquakes have rarely been accompanied by surface rupture in the SFB. Based on the available fault plane mechanisms of the regional events, the maximum

are almost located in the Dezful Embayment, which is a structural unit of the SFB.

principal stress, which is due to regional tectonic forces, strikes N30°± 5° (NE–SW) [15].

**Figure 3.** Upstream view of Karun-1 dam site before (left) and after (right) construction.

Karun-1 (also known as Shahid Abbaspour) is a 200 m high concrete arch dam (**Figures 1** and **3**) at nearly 52 km to the northeast of Masjid-I-Solaiman City in the Khuzestan Province. It was constructed on the Karun River with a reservoir capacity of 3139 MCM to produce electrical energy, to control flood, and to regulate water. The first impounding of the dam reservoir was in December 1976. The presence of two springs downstream the right abutment of the dam site and construction of a new power plant besides recent rock sliding on the dam abutments are the main points of discussion. Since the completion of the dam, seepage problem was a key challenging subject regarding the right abutment shear zone and downstream springs [16–18].

**3. Karun-1 dam**

76 Dam Engineering

Karun-1 dam site is located on the southwestern limb of Kamarun anticline (**Figure 4**) with average bedding dip of 35° toward SW. The anticline is composed of Asmari Limestone of Olig-Miocene age. Asmari formation limestone is a suitable rock foundation for dams regarding its relatively exclusive characteristics such as rigidity and morphology. This formation constitutes a series of double plunging, asymmetrical folds with northwest-southeast trend having steeper southern flanks than the northern ones. The Asmari limestone forms the entire foundation of the Karun-1 dam. It is divided into three parts at the dam site namely, lower, middle, and upper Asmari. The dam is situated on low-karstified middle Asmari that consists of a relatively permeable zone, which in turn is overlain by an impervious shale layer. The upper Asmari limestone exposed just downstream the dam, is highly karstified [16, 18]. The anticline shows some axial plane rotation along its southeast plunge, however, its general trend is northwest-southeast as is common in the whole belt.

The region is seismotectonically very active regarding its location in the Zagros active foldthrust belt [14]. The main faults in the region are of thrust types of which Izeh fault zone cutting across east of the region is a very known feature due to its right lateral component of movement. The Andeka Fault is the main active fault close to the dam site that is characterized by very recent activity [24, 25]. Although no major fault exists at the dam site, recent investigations for excavation of a new powerhouse identified a fault with a general NW-SE trend [20], accompanied by high fracture density. This is most probably a hidden blind fault that is expected to cut the anticline core. The geologic structure of the dam site includes bedding, joint sets, and a spectacular shear zone in the right abutment. Recent study indicated a tectonic lineament with a NE-SW trend that passes through the right abutment, which could

**Figure 4.** 1/100000 Geological map of the Karun-1 dam region [23].

be the main cause of shearing and fracturing in the right abutment [23]. The bedding plane has an average attitude of 32.5/210 (dip/dip direction) in the southwest limb (**Figure 5**) on which the dam is located and is expected to be the major discontinuity at the dam site. The southwest limb has a larger dip than the northeast one, which is characteristic of the southwestern limbs of the Zagros anticlines. It shows high degree of separation with less favorable shear signature. Three joint sets are identified at the dam site with 24/253, 21/166, and 47/038 attitudes. The joints are filled with calcite or clay and partly show slicken-lines. Their spacing is mostly dependent on strike and dip, but small changes can be seen in the joint opening of the left abutment after the excavation of the new powerhouse (No. 2 powerhouse) possibly due to blasting operation. Big or Sabz (meaning green) and Powerhouse Springs are the most significant and spectacular hydrogeological features at the dam site [18]. They demonstrate a widespread karst system in the Asmari limestone. The Zagros anticlines, particularly in the Asmari Formation, contain tension-induced, open fracturing, which has introduced significant secondary permeability to the rock. In this regard, the right abutment shear zone trend strikes along this direction that corresponds to the main regional extensional fractures and is very favorite for ground water flow. The Big Spring flows through a large karst cavern with an average discharge of 4–5 m3 /s (**Figure 4**). The Powerhouse Spring discharge averaged about 0.25 m3 /s. After reservoir impounding, the estimated discharge of Big Spring increased from 10 to 16 m3 /s [26]. Few researches on the springs and reservoir water level fluctuations and sedimentology suggest that the springs' water passing under the foundation is independent of reservoir water elevation and depends on tail water elevation although some suggestions are against this conclusion [18].

pre or synchronous to folding [27]. The existing karst channel shows parallelism to the joint walls. The vertical dip of joint system on the right abutment could be another factor to support

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Another case of problem in the dam site is related to the construction of a new underground powerhouse regarding its time as the reservoir was impounded nearly 25 years before it. The newly designed structure (No. 2 powerhouse) was situated in the left bank of the dam and was excavated in the middle Asmari formation. Rock exposures displayed some signs of karstification such as open or filled cavities and small solution channels along the structural elements. Fortunately, no direct connection with tectonic elements was found in the left abutment. However, some inflow increase was observed in the newly excavated power house

As it was assumed basically that bedding planes were the major discontinuities of the site, the orientation of the No. 2 powerhouse was set perpendicular to the strike of bedding [20]. Fracture system in the left abutment was characterized with very wide to moderate spacing with the evidence of karstification along the joint planes. Some of the solution openings were filled with crystalline calcite and gypsum. All of this evidence supports increase of water inflow through the fractures system. The surface rock at the powerhouse slope belongs to the higher part of the Middle Asmari Formation. Based on the observations, joint sets were the main potential cause of rock instabilities of the cavern [28]. The measured permeability of rock strata was moderate to very high according to various available data with some signature of karstification. Although, Lugeon tests carried out in the geotechnical boreholes were limited to 4 LU, calculations showed a water inflow to the cavern up to 1500 l/min that necessitated creation of a gout curtain between cavern and reservoir. The last challenge related to the existing geologic structure was the potential for the mechanical initiation of a rock fall or slide during and after the dam construction. The construction phase is probably be one or two orders of magnitude higher than with natural causes [29], however, during the operation

spring recharge through the reservoir area by very far upstream sources.

**Figure 6.** A close view of Big Spring (left) and existing joint cavity (right).

period, the phenomenon is possible as is the case for Karun-1 dam.

cavern [28], which lasted to the present.

The location of the two springs is aligned with a tectonic lineament trend SW-NE. Besides, the joint sets at the Big Spring location (**Figure 6**) shows the same general trend. This direction is parallel to the average direction of regional compressive stress in the Zagros Belt and indicates the general trend of extensional fractures forming normal to anticlinal structures

**Figure 5.** General layout of the dam site (left) and downstream view of Big Spring (right). The numbers in the left picture stand for: 1—Karun river, 2—reservoir, 3—Big Spring, and 4—cutoff wall.

**Figure 6.** A close view of Big Spring (left) and existing joint cavity (right).

be the main cause of shearing and fracturing in the right abutment [23]. The bedding plane has an average attitude of 32.5/210 (dip/dip direction) in the southwest limb (**Figure 5**) on which the dam is located and is expected to be the major discontinuity at the dam site. The southwest limb has a larger dip than the northeast one, which is characteristic of the southwestern limbs of the Zagros anticlines. It shows high degree of separation with less favorable shear signature. Three joint sets are identified at the dam site with 24/253, 21/166, and 47/038 attitudes. The joints are filled with calcite or clay and partly show slicken-lines. Their spacing is mostly dependent on strike and dip, but small changes can be seen in the joint opening of the left abutment after the excavation of the new powerhouse (No. 2 powerhouse) possibly due to blasting operation. Big or Sabz (meaning green) and Powerhouse Springs are the most significant and spectacular hydrogeological features at the dam site [18]. They demonstrate a widespread karst system in the Asmari limestone. The Zagros anticlines, particularly in the Asmari Formation, contain tension-induced, open fracturing, which has introduced significant secondary permeability to the rock. In this regard, the right abutment shear zone trend strikes along this direction that corresponds to the main regional extensional fractures and is very favorite for ground water flow. The Big Spring flows through a large karst cavern with an

/s (**Figure 4**). The Powerhouse Spring discharge averaged about

/s. After reservoir impounding, the estimated discharge of Big Spring increased from

sedimentology suggest that the springs' water passing under the foundation is independent of reservoir water elevation and depends on tail water elevation although some suggestions are

The location of the two springs is aligned with a tectonic lineament trend SW-NE. Besides, the joint sets at the Big Spring location (**Figure 6**) shows the same general trend. This direction is parallel to the average direction of regional compressive stress in the Zagros Belt and indicates the general trend of extensional fractures forming normal to anticlinal structures

**Figure 5.** General layout of the dam site (left) and downstream view of Big Spring (right). The numbers in the left picture

stand for: 1—Karun river, 2—reservoir, 3—Big Spring, and 4—cutoff wall.

/s [26]. Few researches on the springs and reservoir water level fluctuations and

average discharge of 4–5 m3

against this conclusion [18].

0.25 m3

78 Dam Engineering

10 to 16 m3

pre or synchronous to folding [27]. The existing karst channel shows parallelism to the joint walls. The vertical dip of joint system on the right abutment could be another factor to support spring recharge through the reservoir area by very far upstream sources.

Another case of problem in the dam site is related to the construction of a new underground powerhouse regarding its time as the reservoir was impounded nearly 25 years before it. The newly designed structure (No. 2 powerhouse) was situated in the left bank of the dam and was excavated in the middle Asmari formation. Rock exposures displayed some signs of karstification such as open or filled cavities and small solution channels along the structural elements. Fortunately, no direct connection with tectonic elements was found in the left abutment. However, some inflow increase was observed in the newly excavated power house cavern [28], which lasted to the present.

As it was assumed basically that bedding planes were the major discontinuities of the site, the orientation of the No. 2 powerhouse was set perpendicular to the strike of bedding [20]. Fracture system in the left abutment was characterized with very wide to moderate spacing with the evidence of karstification along the joint planes. Some of the solution openings were filled with crystalline calcite and gypsum. All of this evidence supports increase of water inflow through the fractures system. The surface rock at the powerhouse slope belongs to the higher part of the Middle Asmari Formation. Based on the observations, joint sets were the main potential cause of rock instabilities of the cavern [28]. The measured permeability of rock strata was moderate to very high according to various available data with some signature of karstification. Although, Lugeon tests carried out in the geotechnical boreholes were limited to 4 LU, calculations showed a water inflow to the cavern up to 1500 l/min that necessitated creation of a gout curtain between cavern and reservoir. The last challenge related to the existing geologic structure was the potential for the mechanical initiation of a rock fall or slide during and after the dam construction. The construction phase is probably be one or two orders of magnitude higher than with natural causes [29], however, during the operation period, the phenomenon is possible as is the case for Karun-1 dam.

long with storage volume of 3 × 109

Abol-Ghasem Spring is of the main concern here.

m3

the dam lies, is mainly consisted of lower Asmari outcrops (**Figure 9**).

faults cut the anticline parallel and normal to its axial trend.

**Figure 9.** Geological map of the dam site area. Red star is the location of Abol-Ghasem Spring [36].

of a hazardous slope named G2M above takeoff yard and a big downstream spring named as

The dam body was constructed on Asmari formation on the southwest limb of Keyf Malek Anticline that is surrounded by elevated anticlines including Lapeh (in the northeast) and Monghast (on the southwest) [32, 34]. The reservoir area is underlain by Pabdeh, Asmari, Gachsaran, and Agha-Jari formations. The Asmari formation limestone is the main waterbearing formation at the dam site and reservoir area with a potential for karst development similar to that discussed previously (part1) and is reported for other dam sites in the Zagros Fold Belt and in this chapter (Karun-1 and Marun dams). The Keyf Malek anticline, on which

It is made up of interbedded limestone and marly limestone with porosity values between 1 and 15.7% that imply medium to extremely porous rocks. The limestone is generally light gray to light brownish gray, fine to medium grained, strong to very strong [32]. The bedding strikes NW-SE with low dip at the anticline crest. On the southwestern limb, the dip of layers is very steep up to 80° due SW (**Figure 10**). The northeastern limb of the anticline has a dip of about 70°–80°. The fold axis shows a slight plunge toward the southeast (141°/06°). Regular joint sets are developed and these have consistent orientations across the project area. A major NW-SE trending fault named as Doshab Lori Fault passes within 500 m to the southwest of the dam site. Another major thrust fault cuts the northeastern limb of the anticline creating an overturned syncline between the Keyf Malek and Lapeh anticlines (**Figures 9** and **10**). The major seismically active faults in the study area [35] are presented in **Figure 11**. Some small

. The dam was impounded in November 2004. The presence

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**Figure 7.** Rock sliding (in yellow) at right abutment of the dam.

Here, due to the downstream dip of bedding, which is unfavorable for a dam site, a natural potential for rock fall and slide on the dam abutments was predictable (**Figure 7**). This geological condition is of key importance since the southwestern (downstream side) limbs of the Zagros anticlines are usually very steeper than the northeastern limb due to the action of thrust faulting that affect the southwestern anticlinal limbs [30, 31]. New observations proved the subject and some rock slide and fall happened especially on the right abutment. There seems to be some flexuring along the bedding plane as well. The vertical tensional joints on the right abutment could amplify rock falling.
