Flood control across hydropower dams: The value of safety

Hydropower reservoirs inherently serving as major flood protection infrastructures, are commonly occupied with gated spillways, to increase both their storage capacity and head. From an operational viewpoint, during severe flood events, this feature raises challenging conflicts with respect to combined management of turbines and gates. From the perception of safety, a fully conservative policy that aims to diminish the possibility of dam overtopping, imposes to operate the turbines in their maximum capacity and, simultaneously, opening the gates to allow uncontrolled flow over the spillway. Yet, this practice may have negative economic impacts from three aspects. First, significant amounts of water that could be stored for generating energy and also fulfilling other uses, are lost. Second, the activation of turbines may be in contrast with the associated hydropower scheduling (e.g., generation of firm energy only during peak hours, when the market value of electricity is high). Last, the flood wave through the spillway may cause unnecessary damages to downstream areas. In this vein, this paper aims to reveal the problem of ensuring a best-compromise equilibrium between the overall objective of maximizing the benefits from hydropower production and minimizing flood risk. In order to explore the multiple methodological and practical challenges from a real-world perspective, we take as example one of the largest hydroelectric dams of Greece, i.e., Pournari at Arachthos River, Epirus (useful storage 310 hm³, power capacity 300 MW). Interestingly, this dam is located just upstream of the city of Arta, thus its control is absolutely crucial for about 25 000 residents. Based on historical flood events, as well as hypothetical floods (e.g., used within spillway design), we seek for a generic flood management policy, to fulfill the two aforementioned objectives. The proposed policy is contrasted with established rules and actual manipulations by the dam operators.