Three-dimensional numerical modeling of sediment flushing: case study of Dashidaira reservoir, Japan

Taymaz Esmaeili, Tetsuya Sumi, Sameh A Kantoush, Yoji Kubota, Stefan Haun

Tuesday 30 june 2015

12:15 - 12:30h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 5A. Sediment - Erosion

Because of the high sedimentation rate in reservoirs located across the Kurobe River in Japan (e.g. Dashidaira reservoir), sediment flushing with full water level drawdown is used to preserve the effective storage capacity. During a flushing operation with full drawdown, the incoming flood erodes a flushing channel into the deposited sediment. The sediment transportation process during the flushing operation is a complex phenomenon especially in steep reservoirs due to the dynamic interaction between the unsteady flow field and varying bed levels. In this study, the sediment flushing processes was investigated in the steep and meandering channel of Dashidaira reservoir using a 3D numerical model. Measured bed levels before and after the flushing operation were used for model verification purpose. A sensitivity analysis was carried out by employing different bed load transport formulas. Outcomes showed that both Meyer-Peter-Müller and Van Rijn’s formula have a reasonable performance to predict the bed variations in specific zones of the reservoir. It was also found that introducing an additional inflow discharge during the free-flow condition of the flushing operation enhances the total volume of flushed out sediment by increasing the sediment erosion mainly in the lower half of the reservoir.