Punchiná Dam

The Punchiná Dam is an embankment dam on the Guatapé River 17 km east of San Carlos in Antioquia Department, Colombia. The dam creates Punchiná Reservoir which is part of the 1240 MW San Carlos Hydroelectric Power Plant. The power plant was completed in two 620 MW stages, the first was completed in 1984 and the second in 1987. It is the largest power station in Colombia.

Background
The project was initiated by Interconexion Electrica S.A. in 1973 and appraised in 1978. In May 1978, a World Bank loan was approved to help fund the dam and both stages of the power plant. Construction began in 1979, the dam was completed in 1983 and the last generator of stage one was operational in 1984. Stage two's final generator was operational in December 1987. The commissioning of stage two was originally slated for 1984 and stage one for 1983 but was delayed due to financial problems and redesigns. The total cost of stage one was US$443.7 million and stage two US$166.3 million.

Design and operation
The Punchiná Dam is a 70 m tall and 800 m long embankment-type dam with 6000000 m3 of fill and a crest elevation of 785 m.

Punchiná Reservoir
The reservoir created by the dam has a capacity of 72 e6m3, of which 52.23 e6m3 is active capacity. The surface area of the reservoir is 3.4 km2.

San Carlos Hydroelectric Power Plant
Initiating the flow of water towards the power station are two 54 m tall intake towers behind the dam in the reservoir. Each tower provides water to a respective stage of the power plant via tunnels. The two tunnels are each about 4.5 km long and to protect against water hammer, each tunnel is equipped with a surge tank. The underground power house is 400 m below the surface, 203 m long, 19.65 m wide and 27.5 m high. Adjacent to the power house is another cavern that holds the transformers and is of similar dimensions. Once the water reaches the power house, each tunnel supplies the four 155 MW Pelton turbines of its respective stage. Once the water leaves the turbines, each stage releases it into their own 1.5 km long tailrace tunnel where the water is discharged into the Samaná Norte River. The tunnels have a combined maximum discharge of 330 m3/s.