Base Information

Topography

Alborz chain mountains region is divided into two southern and northern parts according to the variable and different structure of geology. Siah-Bishe project is located in north of Alborz chain mountains, in the place of original layers of geology. Considering Kandovan fault, the northern part of the Alborz chain mountains is located in Shemshak Structure.
The main components of this project are the upstream dam reservoir and related structures, water tunnels, surging tanks and first part of pressure shafts; which are located within the area of Main Trust Fault. The said parts are all located in Shemshak structure. Generally this part includes shill, sediments and sandstones.
Other parts of the project such as downstream part of the leaning shafts, power house cavern, transformer cavern, bottom outlet tunnels, downstream dam and other related structure are located in continuity of Rootar and Dorood rivers and include limestone with different compositions of sandstones, shill and copper igneous stones.

Meteorology

Siahbishe project is located in northern Alborz mountain area and is situated in 125 kilometers north of Tehran with winter and summery climate. Weather condition of this area is affected by high altitude of the region, seasonal winds and downpours (rain, snow and hail).
Intense winters and snowfalls in second half of the third season of the year causes severe working and transportation conditions in this area. In the following table the maximum and minimum temperature degrees are shown in the upstream and downstream dam areas.

Temperature degree	Downstream dam	Upstream dam
Maximum	+ 25	+ 34.5
Miniimum	- 18	- 27

Average annual temperature in upstream dam area is equal to 7°c and in downstream dam area is equal to 9°c.

Hydrology

With increasing altitude, generally downpours increase. Measuring downpours rate is a hard task due to dispersion of the catchment area and different distances of pluviometer stations.
In project area, maximum amount of downpours happen between February and March to May and June; that is 300 mm.
Average inflow discharge of downstream dam reservoir is estimated 67.1 m3/s. Outflow discharge of upstream dam is divided into two catchment areas. Differences of average downpours between Gramroodbar river (annually 400 mm for downstream part of the catchment area) and north of Kandovan (annually 950 mm for upstream part of the catchment area) would affect the current features.

Average of inflow discharge of upstream and downstream dams’ reservoir

	Area of catchment	Inflow current in 1990 to 1991	Average of inflow current
Downstream reservoir	93.8 hecto m2	23.6 hecto m3 annually	49.2 hecto m3 annually
Upstream reservoir	19.3 hecto m2	6.5 hecto m3 annually	13.5 hecto m3 annually

Flood

The amount of flood for return period of 1000 years
in downstream and upstream reservoir

	Average daily outflow discharge	Maximum outflow discharge
Downstream reservoir	120 m3/s	240 m3/s
Upstream reservoir	38 m3/s	76 m3/s

The amount of flood for return period of 10000 years
in downstream and upstream reservoir

Quarry

Average daily outflow discharge

Maximum outflow discharge

Downstream reservoir
165 m3/s

330 m3/s

Upstream reservoir
53 m3/s

106 m3/s

Flood amount of diversion systems of upstream and downstream dams

Maximum 20 year flood

Maximum 100 year flood

The results of the year 1983 with the return period of 20 years

Downstream reservoir
74 m3/s

1415 m3/s

360 m3/s

Upstream reservoir
24 m3/s

45 m3/s

80 m3/s

Maximum discharge with the return period of 10000 years

PMF/PMP

Ratio

Downstream reservoir
330 m3/s

910 m3/s

2.74

Upstream reservoir
106 m3/s

190 m3/s

1.8

Water quality

Average suspended particles within Alborz mountains area is altering considerably and is within an approximate range of 300 ton/year/km2 to 200 ton/year/km2.
On the basis of carried out measurements near the area of downstream dam (Chalus river in Zoghal bridge and Karaj dam), total amount of sediments are almost 750 ton/Year/Km2.
Carried out estimation by the Lahmeyer-Moshanir J/V shows an amount of 1.09 ton/m3 for dried weight of settled sediments (10% sand, 45% slime, and 45% clay).

Sedimentation

Annual average of sediment erosion in upstream reservoir is 1118 ton/km2 and in downstream reservoir is estimated to be 660 ton/km2. These results show that annual estimated erosion in upstream catchment area is 170% more than downstream catchmnet area.

Planning the water resources

According to the nature of pump storage dams, always a definite volume of water dislocate between upstream and downstream reservoirs. The important issues related to water resource planning in water filling and operation periods of such projects can be generally as follows:

1- Water filling period:
In this period generally the upstream reservoir is filled up to the maximum operation level and it is necessary to fill the downstream reservoir to the minimum operation level. Also the water rights and environmental issues of the mentioned reservoir downstream should be considered.

2- Operation period
In this period, parts of daily outflow of the river which is surplus to the upstream reservoir profitable volume, would be used in power generation system and other parts would be released for the minimum needed water rights of downstream area in the river. Also in downstream reservoirs, releasing the compulsory surplus water which is from upstream reservoir and releasing the inflow of downstream reservoir water from two rivers of Garmrudbar and Chalus for keeping the reservoir at the minimum operation level and preserving needed empty volume of reservoir are among the important issues.
According to the considerable volume of water surplus, which is evacuated daily through the bottom outlet of downstream reservoir, some arrangements can be considered such as turbine installation in the exit of bottom outlet for optimum use of water.

Geology

Siahbishe project is located in north of Iran, between Tehran and Chalus cities and is situated in northern Alborz mountain domain which is part of the parallel anticline and synclines that form the southern boundary of the Caspian puddle. Siahbishe project is located in 4 kilometer distance of Candovan trust fault which is very important in technical structure of Iran geology. It devides Alborz chain mountains into two northern and southern parts. In southern part, Karaj Sazand is expanded with Sansenozoic and in its northern part, where Siah-Bisheh project is located; the Sazands of first and second geology periods are expanded.

Seismicity

Some of the important faults of the Siahbishe dam structures are Candovan, Talaghan, northern Alborz, north of Tehran, Caspian and the main fault of the construction area. The biggest earthquake of this zone has been 7.4 in Richter scale and the biggest earthquake resulted from the nearest fault (Candovan) has been 7.2 in Richter scale.
The biggest earthquake velocity which is sustained into the construction area is about 0.59 g horizontal in downstream dam zone and 0.41 g vertical in upstream dam zone.
Achieved velocity for operation base level is equal to 0.25 g horizontal and for maximum design level is equal to 0.34 g horizontal.

Dam reservoir

Temperature degree	Downstream dam	Upstream dam
Minimum operation level	2376 masl	1885.5 masl
Maximum operation level	2407.6 masl	1905.2 masl
Profitable reservoir volume	3642858 m3	3707105 m3
Length of reservoir	1000 m	1100 m

Siahbishe Project