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In this section the project basic information is presented in form of following items:
Topography
Topography and morphological status of Khersan 3 construction valley has provided suitable conditions for construction of an elevated double arc concrete dam in a way that average lateral topography gradient is more than 60° and maximum height from the river bottom to the banks is estimated to be more than 350 m.
Topography
Meteorology
Average annual temperature in dam site is about 17°C. Average annual evaporation from water free level in Dam Lake is about 1674 mm. Average annual comparative humidity is 47% and average amount of annual rainfall in the region of catchment area is estimated to be 645 mm. Due to expansion of the catchment area and existence of high chain mountains of Zagros, climate of this region is changeable in its different parts, in a way that south to north-west of the region is moderate semi-humid to cold semi-humid, slopes and north eastern area of the region is semi-dry and cold and finally upper heights of the region have cold and humid climate.
In order to carry out meteorological studies, psychometric and pluviometer stations (totally 67 stations) of Ministry of Energy and synoptic, climatology and pluviometer stations of Meteorology Organization (totally 32 stations) have been used.
Meteorology
Hydrology
The studied catchment area is located in south-west of the country in an area between geographical latitude of 30°-15¢ to 31°-30¢ and geographical longitude of 50°-55¢ to 52°-00¢. Main part of Khersan catchment area is mountainous and altitude of its highest point in Dena Mountain is 4413 masl. The average height is 2398 masl and the measurement of this area to Khersan 3 recommended dam location is about 7733 km2.
 
Summary of physiographic specifications of Khersan 3 Dam
 
Location
Area
Circumference (km2)
Average height (masl)
Length of river (km)
Average gradient of river
(%)
Khersan 3 axis
7733
570
2398
180
0.9
 
Hydrometric stations status

The most important hydrometric stations located next to the project site are:
  1. Barez hydrometric station:
     this station is located between geographical coordinates of 50°-23¢ to 31°-32¢. Measurement of catchment area of this station is equal to 8941.7 km2 and its height is 815 masl. It is a first grade station that is equipped with scale, poltelfric and liminograph. This station was established in 1958-1959 and now has totally 49 years of statistic records.
  2. Kata hydrometric station (Marbare River):
    this station is located in geographical coordinates of 51°-16¢ to 31°-11¢. Measurement of catchment area of this station is equal to 4060.6 km2 and its height is 1530 masl. It is a first grade station that is equipped with scale, poltelfric and liminograph. This station was established in 1971-1972 and now has totally 33 years of statistic records.
  3. Pataveh hydrometric station:
    this station is located in geographical coordinates of 51°-16¢ to 30°-58¢. Measurement of catchment area of this station is equal to 2714.2 km2 and its height is equal to 1465 masl. It is a first grade station that is equipped with scale, poltelfric and liminograph. This station was established in 1971-1972 and now has totally 33 years of statistic records.
Discharge status of River at Project Site

Khersan River originates from the heights around Yasuj Province which includes Dena Peak with the height of 4413 m. The river has two important branches of Marbareh and Garmrud. These two branches, near a place called Sarsur, join each other and form Khersan River. The area measurement of this river near Barez station is equal to 8941.7 km2. According to the project’s hydrological studies, discharge of Khersan River near the reservoir and power house of Khersan 3 dam is equal to 2971 million m3.
Hydrology
Flood
Regarding the existing statistics of maximum daily flood from hydrometric station of Barez in 1956-1957 and also accessibility of daily maximum flood statistics in hydrometric stations of Kata and Pataveh since 1971-1972, the information of floods with different return periods at the project site are as follows:
 

Return period

2
5
10

20

25

50

100

1000

10000

Maximum discharge (m3/s)

815
1292
1596

2073

1961

2493

2467

3771

4690

 
For determining PMF of Khersan River at the dam site, experts have benefited from estimated PMP on the basis of storm of March 1997 and also rainfall pattern distribution. Maximum probable flood peak on this basis is estimated to be 6799 m3.
Flood
Water quality
According to the Wilcox Curve which is drawn for the selected stations, it is observed that Khersan River water quality at the site of Khorasan 3 Dam is C2-S1 and according to Shuler Diagram drawn for selected stations the quality of water is suitable for drinking.
Water quality
Sedimentation
Average sedimentation amount of Khersan 3 Dam catchment area is equal to 366 tons/year/km2. This volume would give us an amount equal to 2,360,000 m3 of annual sedimentation entry into dam reservoir; therefore 50-year entry sedimentation in dam reservoir would be equal to 118 million m3.
Sedimentation
Planning the water resources
Normal level of Khersan 3 Dam is equal to 1432 masl and minimum level is equal to 1400 masl. Therefore with benefiting from a power station with installation capacity of 400 MW it would generate annually 682 Gwh of secure energy and also 439 Gwh of the secondary energy.
Summary of project’s water resources planning is as follows:
 
Dam crest height (masl)
1440
Maximum normal level of water (masl)
1432
Minimum normal level of water (masl)
1400
River-bed height (masl)
1262
Lake’s volume at normal level (million m3)
1158.4
Lake’s volume at minimum level (million m3)
520.1
50 years sedimentation volume (million m3)
118
Level of sedimentation volume
1355.8
50-year sedimentation level in the vicinity of dam’s body
1308
Installation power (MW)
400
Output coefficient (%)
28
Hours of generating peak energy
6.7
Annual generated secure energy (Gwh)
682
Annual generated secondary energy (Gwh)
439
Total annual generated energy (Gwh)
1121
Planning the water resources
Geology
Dam site and lake are located at the geological zone of Zagros Chain Mountains. The general procedure of geological structures is north-west to south-east and includes a series of compressed synclines and anticlines. Dam site is located on “Laki” north-east anticline whose general lithology consists of lime and lime-maronite stones of Asemary components. Asemary components at the dam site are divided in two upper and lower Asemary.
Layering gradients with the angle of 35° at the dam site is toward upstream, which besides the layering system it has also affected some of stone blocks joints. In the construction boundary beside the mentioned joints, about 35 faults with different lengths are identified.
Permeability in left abutment and central foundation is estimated high and stone blocks in right bank are also considered to be highly permeable.
Geology
Seismicity
Khersan 3 dam site is located in Zagros Mountains. Existence of faults such as Randegy Jalaleh, Ablarun, Shoram, Chirbun, Zeitun, Dalun, Rig, Sefidar and Dena in 200 km distance of construction site indicates the high seismic potential within the boundary of dam site. Naghan earthquake in 1977 in 75 km distance of site with the magnitude of 6.1 MS and with intensity of IV is highly remarkable.
Most important historical earthquakes of the Project domain are: earthquake of Ahwaz in 840, earthquake of Khuzestan in 1052, earthquake of Arajan in 1085 and earthquake of north-east of Shiraz in 1824, which most of their magnitude had been between 5.8-6.8 MS and their distance to the construction site had been within the range of 88 to 211 km.
Powerful land movement’s parameters include horizontal and vertical maximum velocity, which are estimated in three levels of designing base, maximum design and maximum credible, are as followed:
 
Earthquake level in design
Horizontal maximum velocity (g)
Vertical maximum velocity (g)
Design base level (DBL)
0.3
0.21

Maximum design level (MDL)

0.39
0.28
Maximum credible level (MCL)
0.63
0.52
Seismicity
Dam reservoir
Specifications of level, volume and height of Khersan 3 dam reservoir according to plans with the scales of 1:2500 are shown in the following table. According to this table volume of Khersan 3 Dam reservoir at the level of 1432 masl, equal to 172 m of height, is 1158 million m3. Dam reservoir would occupy an area equal to 33.85 km2.
 
Height (meter)
Level (masl)
Surface (km2)
Volume (million m3)

0

1260

0

0

10

1270

0.02

0.1

20

1280

0.2

1.1

30

1290

0.4

1.4

40

1300

0.7

9.8

50

1310

1.1

18.9

60

1320

1.6

32.3

70

1330

2.2

51

80

1340

3

76.8

90

1350

3.8

110.9

100

1360

5

155.1

110

1370

6.6

213

120

1380

8.7

289.7

130

1390

11.4

390.3

140

1400

14.6

520.1

150

1410

17.6

681.3

155

1415

19.2

777.5

158

1418

20.21

835.2

160

1420

20.85

837.7

172

1432

33.85

1158

Dam reservoir

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