To ensure safe operation of hydropower plant (HPP) in all conditions, every HPP has to have defined operation concept. Operation concept is always defined for starting conditions in which HPP and its reservoir starts to operate. Based on the selected operation concept a set of operating rules is applied. As a result of the selected operating concept and designed set of operation rules a water level pivot point appears in HPP reservoir. Pivot point represents the point in the reservoir, where the water level remains constant, regardless the increase or. decrease of the flow in the river. Pivot point appears only at times, when HPP operates in accordance with designed set of operation rules. But with the construction of HPP, hydraulic conditions of the river are altered. Consequently of that a process of sedimentation begins in the reservoir. In this assignment the impact of sedimentation on the initial location of water level pivot point and thus on starting operation concept is analyzed with methods of hydraulic modeling. Hydraulic calculations are performed for theoretical example of HPP in a reservoir with simplified geometry. Changes in reservoir's bottom and hydraulic roughness are observed and their impact on the starting operating concept is investigated. By performing calculations for this example, we obtaine basic knowledge regarding how the various changes influence the water level pivot point and the level of impact on operation concept. The results are later validated with calculations for the hydraulic model of HPP Boštanj. Based on the results from both calculations, the analysis were made. The analysis explains the impact of sedimentation on the location of water level pivot point, the implications on operation concept and how the effects can be mitigated.