ABSTRACT : The power tunnel, which will convey the water from the Görmel dam to `the proposed hydroelectric power plant on the left slope of the Erik river,, was designed using data from, studies of the geotechnical properties of the rock units along the tunnel alignment. Data were evaluated using the Geomechanic RMR system and the Q system.. Support systems were recommended for the tunnel. The tunnel will be driven, through flysch faci.es of the Eocene Görmel. formation,, and through the matrix (sandstone, greywacke, spilite, diabase, gabbro., basalt) and limestone blocks of the Upper Cretaceous Çamlıca formasion. These limestone Mocks arc the members (Çetincekalesi, Tahtacı, Kükürce» Azıtepe limestone members) of the Çamlıca formation