A complex multi-reservoir hydropower development (HPD) was studied from the point of view of energy production. The Gâlceag HPD system consists of three reservoirs, a high head hydropower plant (HPP) powered by two Francis turbines of 75 MW each, and a pumping station (PS) equipped with two centrifugal pumps of 10 MW each. The hydraulic system configuration is unusual: the PS discharge pipe conveys the water directly into HPP's penstock. Three operation scenarios were investigated: ① normal operation (with PS shutdown and HPP operational, as a conventional HPP), ② simultaneous operation (with both HPP and PS operational), and ③ pumped storage (with HPP shutdown and PS operational). Primarily, a numerical model was set up in EPANET to investigate the influence that the variation in the initial level of the HPP upstream reservoir has on the production of energy. In the sequel, a numerical model was derived and solved in GNU Octave to investigate the influence on the energy production of HPD due to initial levels of both the HPP upstream and downstream reservoirs. The results can be used in a decision support system to assess the overall operation of Gâlceag HPD based on water availability.