Doğançay HEPP, which we commissioned in 2017 and has an installed capacity of 62 MW, is located on Doğançay Çay in Adana Seyhan Basin. Doğançay HEPP, one of the two projects opened with a tunnel boring machine (TBM) by going beyond the traditional methods, was built underground with all its units except for the regulator area. It consists of a regulator structure with a height of 30 meters from the foundation, a 6.9-kilometer-long energy tunnel opened with a tunnel boring machine, a 273-meter-tall surge tank, a penstock shaft and a 514-meter-long penstock tunnel. In the project, which has a Cavern (underground power plant) type power plant, which can be reached through a 70-meter-long tunnel, unlike other projects, the control of the water released from the spillway is carried out with an inflatable flume made of a special membrane, instead of steel covers, facilitating the construction and operation.