This paper presents an optimal control model for a wind-hydrokinetic powered pumpback operation of a hydropower plant with stringent regulatory requirement on ecological/environmental flows down stream. The objective function is to maximise the energy yield of the hydro reservoir while meeting a contractual and statutory obligation. Three operation models are developed depicting a practical ecological/environmental flows constraints of a power plant under various water management strategies. The results show a potential of this pumpback model in reducing the daily water allocation for hydropower generation by 70% for the given committed load. The last operational scenario shows a decrease in hydrokinetic energy generation by 38.54% and an increase in the daily hydro reservoir energy output by 17%. The later performance is occasioned by an increase in penstock discharge to meet ecological flow requirements. These results underscore that pumpback operation enhances the economic value of water for hydropower generation while ecological flow constraint increases the reservoir yield but derails the benefits of free hydrokinetic energy, which is used in this paper as a measure of the opportunity cost of environmental regulatory policies to the performance of a hydropower system. (C) 2019 Elsevier Ltd. All rights reserved.