The paper describes the development of a geological and geotechnical model produced for the design of a hydro power plant and its large RCC (roller compacted concrete) dam. Various in situ and laboratory investigation methods and rock mass classification were introduced for the definition of subsurface parameters and rock mass parameters were derived for design purposes. The mechanical parameters of the rock masses were the basic input for different finite element models that were used in order to evaluate the interacting static system of foundations and structures. The insights gained from this work were used to implement appropriate amendments to the design of the hydropower plant.