**5. Marun dam**

The Marun dam site is located on the Marun River in the Khuzestan Province approximately 19 km northeast of Behbahan City (**Figures 1** and **14**). The dam was commenced in 1997 and completed in 1999 with a height of 165 m, a crest length of 345 m and reservoir volume of about 1200 million cubic meters. As a rock fill dam, it is the second highest embankment dam in Iran. Its main purpose was flood control, water storage, and a total of 145 MW power generation. It also provides a dependable water resource for irrigation of 55,000 hects of downstream farm lands. The dam site is located on the limestone of the Asmari Formation, of Oligo-Miocene age. The formation is divided into the lower, middle, and upper Asmari formation with a total thickness of 370 m. It consisted of strong limestone partly interbedded with thin layers of shale. The whole formation at the dam site is characterized by karstification evidence.

The Marun dam was built on the northeastern flank of Khaviz anticline in the Zagros fold belt. The foundation of the dam consists of thick-bedded limestone of the Asmari formation Influence of Geological Structure on Dam Behavior and Case Studies http://dx.doi.org/10.5772/intechopen.78742 85

**Figure 14.** Upstream view of Marun dam site before (left) and after (right) construction.

Keyf Malek anticline. This structural feature is very common in the Zagros folds specially in highly deformed and stressed regions such as Izeh fault zone in which the dam is located [36]. High fracturing of the rocks at the dam site is also a sign of the governing role of fault activity in the study area. Successive occurrence of thrust faults cutting the region and overturning of the Lapeh Anticline northeastwards is an indication of extensive tectonic deformation of the region resulted in high and dense fracturing of the Keyf Malek anticline. Additionally, the apparent break in the bedding integrity in the southwest limb of the anticline might be a sign of longitudinal faulting along its strike (**Figure 12**). It should be noted that Doshab Lory fault that runs between the Keyf Malek anticline and Mongasht anticline is a back thrust with a movement in the direction opposite to the general direction of regional tectonic transport. Since, such structures are generally an indication of fault propagation folds, intense fracturing between fore thrust and back thrust is reasonable, which is almost seen for the Karun-3 dam site. As mentioned before, Karun-3 dam site lies in the northern part of Izeh fault (shear) zone that is distinguished by a variety of thrust and dextral strike-slip faults [14] so that their

interaction created a complex highly deformed and sheared geological region.

downstream the dam site might facilitate the occurrence of springs.

and increased to about 2.5 m3

84 Dam Engineering

**5. Marun dam**

Another challenging subject in the dam region is the presence of Abol-Ghasem Spring downstream of the dam site. It is located at about 2.5 km downstream of the dam site, near the right bank of the Karun River (**Figure 9**). Its water was recharged by Lapeh anticline karstic aquifer, before impounding with varying seasonal discharge nearly between 0.5 and 1.5 m3

spring about 70 m downstream of the Abol-Ghasem Spring was changed to a permanent one after the dam impounding. It seems that the both limbs of Keyf Malek anticline are potential paths for seepage equally [34]. Karstification of the northeastern limb of the Keyf Malek anticline along with thrust faulting intensified the seepage at the spring. The presence of an overturned syncline between the two anticlines indicates intense tectonic compression in the region that could result in dense fracturing in the existing two anticlines. Transverse faults cut across the anticline that is evident through sharp and sudden change of Karun River course

The Marun dam site is located on the Marun River in the Khuzestan Province approximately 19 km northeast of Behbahan City (**Figures 1** and **14**). The dam was commenced in 1997 and completed in 1999 with a height of 165 m, a crest length of 345 m and reservoir volume of about 1200 million cubic meters. As a rock fill dam, it is the second highest embankment dam in Iran. Its main purpose was flood control, water storage, and a total of 145 MW power generation. It also provides a dependable water resource for irrigation of 55,000 hects of downstream farm lands. The dam site is located on the limestone of the Asmari Formation, of Oligo-Miocene age. The formation is divided into the lower, middle, and upper Asmari formation with a total thickness of 370 m. It consisted of strong limestone partly interbedded with thin layers of

shale. The whole formation at the dam site is characterized by karstification evidence.

The Marun dam was built on the northeastern flank of Khaviz anticline in the Zagros fold belt. The foundation of the dam consists of thick-bedded limestone of the Asmari formation

/s after reservoir impoundment. Additionally, another seasonal

/s,

with alternation of shale, marlstone gypsum, and anhydrite [38, 39]. The beds strike parallel to the dam axis trending NW-SE and average dip of approximately 35° due NE (**Figure 15**). The rock is regularly well jointed. Although fairly homogenous, the rock shows anisotropic permeability due to karstification of limestone. The rock strata at the site comprise a series of karstic limestones interbedded with water sensitive marls, which dip toward the reservoir. The main geological structures of the region include folds and faults aligned parallel to the main folding axis of NW-SE trend. The reservoir basin is centered mostly along the southwest flank of a broad northwest trending syncline. This feature forms a broad structural basin, approximately 9 km wide and 14 km long. At the dam site, two major joint sets are seen, the first parallel to the bedding, and the second perpendicular to it. However, a special set of

**Figure 15.** A general layout of Marun dam and appurtenant structures [39]. BF is Behbahan thrust fault.

fractures classified as fracture swarms [40] is also recognized here. Fracture swarms are nearly large-scale features, which dissect significant parts of the stratigraphic sequence. In the Khaviz anticline, fracture swarms are represented by faults with displacements of a few meters up to 150 m, and are associated with relative narrow damage zones with locally very high fracture frequency [40]. Three large thrust faults cut the region with a NW-SE general trend. These are named as Behbahan, Arajan, and Tashan faults [14]. A hidden fault cuts the core of Khaviz anticline parallel to Behbahan fault as well. While Karun-3 dam site lies in the northern part of Izeh fault zone, the Marun dam site is located at the southernmost part of it. The dam site is also affected by active faulting as indicated by its seismic activity especially for Tashan Fault.

The remaining flow was from the access tunnel and the grouting adit (2.3 m<sup>3</sup>

amount of water leakage through the left bank of Marun dam was about 10 m3

along the fracture swarms parallel to the second diversion tunnel.

the reservoir reaches a capacity of 4.5 billion m3

**6. Gotvand dam**

entered the fracture system upstream of the plug and passed along the fissures, washed out the marls interbeds forming large cavities. These are master cross joints traversing the dam site rocks from upstream to downstream. Water was leaking into all tunnels and the dam, and all springs received their water from the same fissure as was reported [39]. In fact, these are fracture swarms as was defined above indicating the intense fracturing surrounding faults or narrow zones with a very high frequency of fractures. These major features are major conduits for fluid flow in the subsurface at some stage that is very favorable for karst development. This is almost similar to the karstic features mentioned for Karun-1 dam (abovementioned) although it is almost visible that karstification is developed more and complete at the Marun dam site. Here, the general trend of fracture warms is parallel to the general direction of the maximum compressive stress in the Zagros Fold Belt that produced tension-induced, open fractures resulting in significant secondary permeability to the rock. Intersection of longitudinal fractures (vuggy zone) in the Khaviz anticline with transverse fractures (fracture swarms) amplified permeability of the rock and simplified water leakage through the left abutment during the first reservoir impounding. It is very probable that seepage paths were formed

The second problem in Marun dam site was rock fall occurred along the left abutment recently [41]. Accordingly, stability studies and treatment are being conducted. The variation in shape of the rock blocks obtained from the joint data assessment indicates that the potential for dislodging rock blocks is medium to high. The horizontal joint sets in combination with the very steep slope face on the left bank result in blocks with a high rock fall hazard. The prevailing

The Gotvand or Upper Gotvand dam as the highest rock fill dam in Iran is located in the north of Khuzestan Province (**Figures 1** and **17**). It was constructed across the Karun River in the north of Shushtar city. It is a 178 m high rock fill dam with central clay core and a crest length of 760 m. The normal reservoir level is situated at 232 m above sea level at which

dam has the hydropower plant with the highest energy production capacity in the country. The main purpose of the project is the production of (4250 GWh) hydroelectric energy. The impoundment of the reservoir started in July 2011 and by 2014, the reservoir water level had reached 223 m a.s.l. The main problems in the dam site and reservoir area are instability of the abutments [42] and with a minority, probable seepage potential through the foundation and abutments [43]. The dam foundation and part of the right abutment is underlain by Agha-Jari Formation of Mio-Pliocene Age (**Figures 17** and **18**). Agha-Jari lithology consists of gray, calcareous sandstone with gypsum veins and red marlstone and siltstone. Its rocks contain veins of gypsum usually associated with claystone beds. They are naturally soluble and can lead to excessive seepage. The left abutment of the dam is composed of Bakhtyari

and around 90 km in length. The Gotvand

role of fracture system in rock slope instability at the dam site is again clear [41].

/s). The total

87

Influence of Geological Structure on Dam Behavior and Case Studies

http://dx.doi.org/10.5772/intechopen.78742

/s. The water

The first and prominent problem encountered in Marun dam site was leakage through a diversion tunnel named as second diversion tunnel during the first impounding. Immediately after impoundment, considerable leakage was observed in the pressure tunnel (**Figure 16**) and efforts to open the stop logs failed. At the same time, an embankment was constructed and subsequent grouting controlled the leakage in the pressure tunnel. Old karst channels along a vuggy zone cut by the second diversion tunnel were reactivated and leakage occurred [39]. The total amount of water leakage through the left bank of Marun dam was about 10–15 m3 /s. The unlined second diversion tunnel had a key role in connecting reservoir with karst conduit system.

The embankment was overtopped with increasing water elevation, and considerable leakage of up to 7 m3 /s occurred from weak zones upstream of the plug. The major flow of approximately 4.5 m3 /s was from two large solution channels and leakage around the concrete plug.

**Figure 16.** A general layout of Marun dam and appurtenant structures.

The remaining flow was from the access tunnel and the grouting adit (2.3 m<sup>3</sup> /s). The total amount of water leakage through the left bank of Marun dam was about 10 m3 /s. The water entered the fracture system upstream of the plug and passed along the fissures, washed out the marls interbeds forming large cavities. These are master cross joints traversing the dam site rocks from upstream to downstream. Water was leaking into all tunnels and the dam, and all springs received their water from the same fissure as was reported [39]. In fact, these are fracture swarms as was defined above indicating the intense fracturing surrounding faults or narrow zones with a very high frequency of fractures. These major features are major conduits for fluid flow in the subsurface at some stage that is very favorable for karst development. This is almost similar to the karstic features mentioned for Karun-1 dam (abovementioned) although it is almost visible that karstification is developed more and complete at the Marun dam site. Here, the general trend of fracture warms is parallel to the general direction of the maximum compressive stress in the Zagros Fold Belt that produced tension-induced, open fractures resulting in significant secondary permeability to the rock. Intersection of longitudinal fractures (vuggy zone) in the Khaviz anticline with transverse fractures (fracture swarms) amplified permeability of the rock and simplified water leakage through the left abutment during the first reservoir impounding. It is very probable that seepage paths were formed along the fracture swarms parallel to the second diversion tunnel.

The second problem in Marun dam site was rock fall occurred along the left abutment recently [41]. Accordingly, stability studies and treatment are being conducted. The variation in shape of the rock blocks obtained from the joint data assessment indicates that the potential for dislodging rock blocks is medium to high. The horizontal joint sets in combination with the very steep slope face on the left bank result in blocks with a high rock fall hazard. The prevailing role of fracture system in rock slope instability at the dam site is again clear [41].
