Temporal dynamics of short-term regulation in run-of-river hydropower cascades

Hydrological alterations caused by hydropower dams significantly impact river ecosystems. In Nordic rivers where regulation of rivers for hydropower dominates flow alterations, the hydropower operations often introduce more frequent flow fluctuations directly linked to energy demand. In cascaded run-of-river hydropower plants (ROR-HPPs), upstream regulation directly affects downstream flow characteristics, leading to complex interactions between upstream and downstream regulation dynamics. Although free-flowing tributaries downstream of the hydropower plants dampen the flow pulsations due to regulation, cascading ROR-HPPs amplify the hydrological alterations in the regulated river. This study investigates the temporal dynamics of hydrological alterations in cascaded ROR-HPPs, analysing the interdependencies between upstream flow regulation and downstream flow patterns. Through hydrological modelling and flow routing, the study examines the downstream propagation of regulated flows from one hydropower plant to another in a cascade, and the changes in hydrological alterations introduced by the successive ROR-HPPs. By analysing the temporal dynamics of flow regulation between hydropower dams in a cascade, the study highlights the need for integrated hydropower management strategies that account for cascading effects and balancing energy production with ecological sustainability.