Three-Dimensional Numerical Study of Free-Flow Sediment Flushing to Increase the Flushing Efficiency: A Case-Study Reservoir in Japan

Abstract

Abstract:The catchment of the Dashidaira reservoir located on the Kurobe River has high sediment yield. Because of the sufficient available amount of water in the catchment during flood events, the free-flow sediment flushing operation with full water-level drawdown is employed every year to preserve the effective storage capacity of the Dashidaira reservoir. This paper focuses first on the numerical simulation of a previously conducted free-flow flushing operation in the Dashidaira reservoir using the available in situ obtained data. Afterwards, to improve the flushing efficiency, the effects of water and discharge manipulation and the construction of an auxiliary channel on the total volume of the flushed sediment were studied. A fully 3D numerical model using the finite volume approach in combination with a wetting/drying algorithm was utilized to reproduce the flow velocity field and simulate the movable bed variations. The outcomes revealed that increasing the average free-flow discharge during the free-flow stage by approximately 56%, in the form of multiple discharge pulses, can enhance the flushing efficiency by up to 13%, and the construction of an auxiliary channel in the wide midstream of the reservoir can locally increase the sediment erosion from this area.

Numerical modelling of bank failures during reservoir draw-down

“…Erosion of sediments from reservoirs can also be an important process to consider in decommissioning of dams [1]. The current article describes bank failure algorithms that have been included in a fully 3D numerical model for modelling the sediment movement during the flushing [2][3][4][5][6]. The novel approach is an incorporation of a soil slide algorithm based on geotechnical theory.…”

Spatio‐temporal variability of suspended sediments in rivers and ecological implications of reservoir flushing operations

“…In this context, the method of modelling exchange processes with the riverbed using an equilibrium SSC after Van Van Rijn () is dependent on the actual grain size distribution of the riverbed material, which had to be estimated from the prevailing flow conditions in parts of the modelling domain for reasons of inaccessibility. The same modelling approach is used by Esmaeili et al (), whereas in Hostache et al (), the formula by Zyserman and Fredsoe () is employed. Particularly for cohesive material, which is likely to be mobilized during flushing operations, Hostache et al () used the erosion/deposition flux calculation by Partheniades () instead.…”

“…This simplification, however, disregards the vertical variability over the cross‐section area. Hence, three‐dimensional formulations gained increased importance and have already been applied successfully to estuaries (e.g., Bai, Wang, & Shen, ) and reservoirs (Esmaeili et al, ; Fang & Rodi, ; Khosronejad, Rennie, Neyshabouri, & Gholami, ; Tritthart, ). However, applications of modelling and interpreting the three‐dimensional variability of suspended sediment concentrations (SSCs) within a river reach continuum downstream of a reservoir have not been reported so far.…”

A Computational Fluid Dynamics Simulation Model of Sediment Deposition in a Storage Reservoir Subject to Water Withdrawal

“…A reasonable result for the comparison between the measured and simulated values was obtained for both the suspended load concentration and the bed level variation. The SSIIM model has been applied for modelling the sediment deposition and flushing process in different reservoirs [14][15][16][17]. For a long simulation period of the sedimentation in the reservoir (11 years), the SSIIM model was applied to predict the bed changes due to sedimentation and dredging [18].…”