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 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 con...
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MDPI AG
2021-06-01
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| author | Taymaz Esmaeili Tetsuya Sumi Sameh A. Kantoush Yoji Kubota Stefan Haun Nils Rüther |
| author_facet | Taymaz Esmaeili Tetsuya Sumi Sameh A. Kantoush Yoji Kubota Stefan Haun Nils Rüther |
| author_sort | Taymaz Esmaeili |
| collection | DOAJ |
| description | 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. |
| first_indexed | 2024-03-10T10:34:43Z |
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| institution | Directory Open Access Journal |
| issn | 2073-4441 |
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| last_indexed | 2024-03-10T10:34:43Z |
| publishDate | 2021-06-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Water |
| spelling | doaj.art-f77c3a0357334ba4960c376798a5af172023-11-21T23:26:45ZengMDPI AGWater2073-44412021-06-011312162410.3390/w13121624Numerical Study of Discharge Adjustment Effects on Reservoir Morphodynamics and Flushing Efficiency: An Outlook for the Unazuki Reservoir, JapanTaymaz Esmaeili0Tetsuya Sumi1Sameh A. Kantoush2Yoji Kubota3Stefan Haun4Nils Rüther5Department of Civil Engineering, Gorgan Branch, Islamic Azad University, Gorgan 49147-39975, IranDisaster Prevention Research Institute (DPRI), Kyoto University, Uji, Kyoto 611-0011, JapanDisaster Prevention Research Institute (DPRI), Kyoto University, Uji, Kyoto 611-0011, JapanHydro Technology Institute Co., Ltd., Nakanoshima, Osaka 530-6126, JapanInstitute for Modelling Hydraulic and Environmental Systems, University of Stuttgart, 70569 Stuttgart, GermanyDepartment of Civil and Environmental Engineering, Norwegian University of Science and Technology, S.P. Andersens vei 5, 7491 Trondheim, NorwayThe 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.https://www.mdpi.com/2073-4441/13/12/1624numerical modellingreservoir flushingdischarge adjustmentflushing efficiency |
| spellingShingle | Taymaz Esmaeili Tetsuya Sumi Sameh A. Kantoush Yoji Kubota Stefan Haun Nils Rüther Numerical Study of Discharge Adjustment Effects on Reservoir Morphodynamics and Flushing Efficiency: An Outlook for the Unazuki Reservoir, Japan Water numerical modelling reservoir flushing discharge adjustment flushing efficiency |
| title | Numerical Study of Discharge Adjustment Effects on Reservoir Morphodynamics and Flushing Efficiency: An Outlook for the Unazuki Reservoir, Japan |
| title_full | Numerical Study of Discharge Adjustment Effects on Reservoir Morphodynamics and Flushing Efficiency: An Outlook for the Unazuki Reservoir, Japan |
| title_fullStr | Numerical Study of Discharge Adjustment Effects on Reservoir Morphodynamics and Flushing Efficiency: An Outlook for the Unazuki Reservoir, Japan |
| title_full_unstemmed | Numerical Study of Discharge Adjustment Effects on Reservoir Morphodynamics and Flushing Efficiency: An Outlook for the Unazuki Reservoir, Japan |
| title_short | Numerical Study of Discharge Adjustment Effects on Reservoir Morphodynamics and Flushing Efficiency: An Outlook for the Unazuki Reservoir, Japan |
| title_sort | numerical study of discharge adjustment effects on reservoir morphodynamics and flushing efficiency an outlook for the unazuki reservoir japan |
| topic | numerical modelling reservoir flushing discharge adjustment flushing efficiency |
| url | https://www.mdpi.com/2073-4441/13/12/1624 |
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