With monitoring of dynamic properties of dams we can continuously observe the ageing process of the structure, while by vibration monitoring we can estimate the condition of the built-in material. Every structure has unique modal characteristics and its unique vibrational signature that change only in case when the structure's mass, stiffness, or geometry is altered. Therefore, if the structural damage causes a decrease in stiffness, the vibration patterns as well as modal properties of the structure will change. Dams represent an important infrastructure and the ageing of dams and preservation of their structural health is rapidly becoming one of the major challenges of the entire dam engineering community. This research focuses on the analysis of operational loads and their effect on the ageing process of a hydropower dam. Shortly after the construction of the Brežice dam and during the start-up tests of hydro-mechanical equipment, we performed vibration monitoring, using state-of-the-art non-contact measurement techniques in combination with traditional contact technologies. The thesis is divided into two parts. In the first part, the motivation and fundamentals of structural health monitoring, vibration based monitoring, dam surveillance, and Laser Doppler Vibrometry (LDV) are presented, followed by the review of peer literature. Experimental work lies at the core of this research. In the second part of the thesis we present the experimental site, the equipment, the procedure and the numerical models of the powerhouse and its overspilling section. Our research confirmed the susceptibility of the concrete dam structure to the effect of operational loads, which is supported also with numerical results in experimental findings. With the beginning of our work during the construction of the dam we were able to capture the initial reference state of the dam, which will serve as a baseline for future diagnostic work. Furthermore, by adopting a corrective procedure of the LDV output, we are now able to use the LDV during regular operation of the powerhouse, when the instrument is placed inside the structure under observation and excited as well. LDV can be used as part of regular vibration monitoring activities on dams during operation.