Dariali hydropower plant

The site is located about 160 km north of Tbilisi and characterized by high mountains and deep valleys, typical of the Caucasus region. The capacity of the project is set at 108 MW and annual energy generation is estimated 500 million kWh.

The Tergi river is dammed at elevation about 1729 m with a low concrete dam spillway structure. Three sand sluices are provided also acting as a gated spillway in case of floods. A fish ladder is provided between the spillway and the sand sluices. From the intake structure, two 2,4 m diameter steel pipes convey the water to a sand basin. A 110 m long and up to 33 m wide sand basin is on the head race canal route, some 228 m from the intake structure. From the sand basin the water is conveyed through two buried steel pipes of diameter 2,4 m and 2184 m long to the tunnel entrance. The head race tunnel is about 5040 m long from the tunnel intake to the pressure shaft. It is constructed with a 5,5 m diameter tunnel boring machine (TBM). The head race tunnel conveys the water from the diversion pipe to the pressure shaft feeding the power units in an underground powerhouse. A surge tunnel contributes to reducing water hammer in the head race tunnel system and to facilitating grid regulation by the power units.

The powerhouse is a 71 m long, 13,5 m wide and about 28 m high conventional underground cavern supported with rock bolts and shotcrete, housing three Pelton units on vertical axis. Each unit is about 36 MW at rated load. The top of the powerhouse is about 110 m below the overlying ground surface. The tail race tunnel runs from the powerhouse to the Dariali valley conveying the tail water into the headworks of Larsi HPP. It was excavated by drill and blast technique from outside towards the powerhouse. The tail race tunnel is 500 m long, 5 m high and 5 m wide and conveys the tail water to a short tail race concrete culvert entering the Larsi project headworks pond in the Tergi river. The switchyard will be located outside on the right Tergi riverbank near the head race tunnel exit, and guarded by a safety fence. The substation consist of the unit power transformers, intermediate station transformers, air insulated (AIS) switchgear with circuit breakers and disconnecting switches, instrument transformers, surge arresters and steel structure.