Numerical Study of Discharge Adjustment Effects on Reservoir Morphodynamics and Flushing Efficiency: An Outlook for the Unazuki Reservoir, Japan

The Unazuki Reservoir is located on the Kurobe River, which influenced by a catchment with one of highest sediment yields in Japan. Due to sufficiently available discharge during flood events, annual flushing full water-level drawdown (i.e., free-flow flushing) conducted preserve effective storage capacity reservoir. Nevertheless, upstream half reservoir study segment) suffers from excessive deposition coarser sediments. Remobilization these materials and their transportation further downstream priority owners for sustainable functions, such as flood-risk management hydroelectric energy generation. In this paper, an already sediment-flushing operation simulated, its effects scouring segment together changes bed morphodynamics are presented. A fully 3D numerical model using finite volume approach combination wetting/drying algorithm was utilized reproduce hydrodynamics onsite data. Afterwards, adjustment morphological efficiency were analysed additional single-discharge pulse supplied reservoirs. Simulation results showed that approximately 75% increase average stage changed dominant process into erosive mode segment. If reaches up 100%, flushed sediments target can 2.9 times compared initiation mode.