Pumped-storage hydropower is one of the most viable large-scale energy storage options. When managed optimally, pumped-storage hydropower may also bring monetary benefits due to price variations in the electricity market. Two main concerns are the lack of suitable sites and potential environmental impacts, which can be alleviated by using already existing, closely situated reservoirs. The goal of this study is to develop operating strategies for cascade pumped-storage hydropower systems composed of already existing hydropower plants. Main challenges are the treatment of the stochastic behavior of inflows and hourly electricity price variations. In this study, monthly historical inflows are used as inputs to generate operating rule curves. Based on past electricity prices, a scenario-based approach is developed to reflect the uncertainty in electricity price variations. Combining the two approaches, nonlinear mathematical models are constructed to obtain average annual revenues for cascade hydropower plants and the pumped-storage hydropower systems. The models are solved for the cascade multi-reservoir system in Coruh Basin of Turkey for five different scenarios based on electricity prices for years 2013-2017. The revenue gain ranged between 2.9% and 10.4%. It is concluded that operation of the cascade hydropower plant system in the pumped-storage mode brings additional revenue. (C) 2019 Elsevier Ltd. All rights reserved.