The Influence of Hydropower Plant Operational Scenarios on Maintaining the Navigable Depths in an Anthropized River Reach: A Case Study on the Danube River in Slovakia Downstream of the Gabčíkovo Hydropower Plant

The hydropower plant together with its reservoir makes it possible to modify the natural flow regime. These changes can affect sediment transport dynamics and cause morpho-logical changes in the river. If the river is also used as a waterway, the operational scenar-io of the hydropower plant can have a significant impact on sediment deposition, thereby reducing its navigable depths and increasing the risk of vessel–riverbed collisions. In this study, a 2D hydrodynamic model of the Danube River downstream of the Gabčíkovo Hy-dropower Plant (GHP) in Slovakia was developed to evaluate the influence of operational scenarios on maintaining the required navigable depths and to determine the most suita-ble scenario in terms of fairway maintenance costs. The operational scenario of the GHP influences the amount of sediment deposited downstream of the plant. The volume of deposition in the critical ford was approximately 50% smaller under hydropeaking than under run-of-river operation. The increase in riverbed elevation during hydropeaking was 33% to 64% lower than under run-of-river operation. The study results indicate that this reach of Danube can remain navigable for a longer period without intervention (dredging), thanks to sufficient navigable depth maintained by erosion caused by hydropeaking, compared to run-of-river operation.