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Article

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

1
Department of Civil Engineering, Gorgan Branch, Islamic Azad University, Gorgan 49147-39975, Iran
2
Disaster Prevention Research Institute (DPRI), Kyoto University, Uji, Kyoto 611-0011, Japan
3
Hydro Technology Institute Co., Ltd., Nakanoshima, Osaka 530-6126, Japan
4
Institute for Modelling Hydraulic and Environmental Systems, University of Stuttgart, 70569 Stuttgart, Germany
5
Department of Civil and Environmental Engineering, Norwegian University of Science and Technology, S.P. Andersens vei 5, 7491 Trondheim, Norway
*
Author to whom correspondence should be addressed.
Academic Editors: Achim A. Beylich and Athanasios Loukas
Water 2021, 13(12), 1624; https://doi.org/10.3390/w13121624
Received: 21 March 2021 / Revised: 27 May 2021 / Accepted: 4 June 2021 / Published: 9 June 2021
(This article belongs to the Special Issue Sediment Transport and River Morphology)
The Unazuki Reservoir is located on the Kurobe River, which is influenced by a catchment with one of the highest sediment yields in Japan. Due to a sufficiently available discharge during flood events, annual sediment flushing with full water-level drawdown (i.e., free-flow sediment flushing) is conducted to preserve the effective storage capacity of the reservoir. Nevertheless, the upstream half of the reservoir (i.e., study segment) suffers from the excessive deposition of coarser sediments. Remobilization of these coarser materials and their transportation further downstream of the reservoir is a priority of reservoir owners for sustainable reservoir functions, such as flood-risk management and hydroelectric energy generation. In this paper, an already conducted sediment-flushing operation in the Unazuki Reservoir is simulated, and its effects on sediment scouring from the study segment of the reservoir together with changes in bed morphodynamics are presented. A fully 3D numerical model using the finite volume approach in combination with a wetting/drying algorithm was utilized to reproduce the hydrodynamics and bed changes using the available onsite data. Afterwards, the effects of discharge adjustment on the morphological bed changes and flushing efficiency were analysed in the study segment using an additional single-discharge pulse supplied from upstream reservoirs. Simulation results showed that an approximately 75% increase in the average discharge during the free-flow stage changed the dominant morphological process from deposition into an erosive mode in the study segment. If the increase in discharge reaches up to 100%, the flushed volume of sediments from the target segment can increase 2.9 times compared with the initiation of the erosive mode. View Full-Text
Keywords: numerical modelling; reservoir flushing; discharge adjustment; flushing efficiency numerical modelling; reservoir flushing; discharge adjustment; flushing efficiency
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MDPI and ACS Style

Esmaeili, T.; Sumi, T.; Kantoush, S.A.; Kubota, Y.; Haun, S.; Rüther, N. Numerical Study of Discharge Adjustment Effects on Reservoir Morphodynamics and Flushing Efficiency: An Outlook for the Unazuki Reservoir, Japan. Water 2021, 13, 1624. https://doi.org/10.3390/w13121624

AMA Style

Esmaeili T, Sumi T, Kantoush SA, Kubota Y, Haun S, Rüther N. Numerical Study of Discharge Adjustment Effects on Reservoir Morphodynamics and Flushing Efficiency: An Outlook for the Unazuki Reservoir, Japan. Water. 2021; 13(12):1624. https://doi.org/10.3390/w13121624

Chicago/Turabian Style

Esmaeili, Taymaz, Tetsuya Sumi, Sameh A. Kantoush, Yoji Kubota, Stefan Haun, and Nils Rüther. 2021. "Numerical Study of Discharge Adjustment Effects on Reservoir Morphodynamics and Flushing Efficiency: An Outlook for the Unazuki Reservoir, Japan" Water 13, no. 12: 1624. https://doi.org/10.3390/w13121624

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