Three-Dimensional Numerical Modelling of Reservoir Flushing to Obtain Long-Term Sediment Equilibrium

Saam, Leon; Mouris, Kilian; Wieprecht, Silke; Haun, Stefan

doi:10.3850/38wc092019-0742

Cited by 7 publications

(6 citation statements)

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“…layer in the assumed 60 m wide flushing channel along the thalweg of Schwarzenbach Reservoir implies a flushed sediment volume of 16.5 × 10 3 m 3 , which agrees well with the study bySaam et al (2019), who assessed the feasibility of reservoir flushing in Schwarzenbach and obtained a flushed sediment volume of 13.6 × 10 3 m 3 in a simulation of a full drawdown flushing scenario. At an erosion depth of 15 cm, the resulting NCH4,FSL are 6.5 kmol CH4, 8.1 kmol CH4, and 12.5 kmol CH4 if the flushing operation is conducted in April, June, and September, respectively.…”

supporting

confidence: 89%

“…In this reservoir, flushed sediment volumes between 60 × 10 3 and 590 × 10 3 m 3 with an average flushed sediment volume of 287 × 10 3 m 3 have been reported (Sumi et al, 2009;Esmaeili et al, 2017). Therefore, the average flushed sediment volume in Dashidaira reservoir is 17-21 times larger than the estimated flushed sediment volumes in the study of Saam et al (2019) and in this study.…”

Section: Significance Of the Potentially Released Amount Of Ch4 Due T...contrasting

confidence: 43%

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Methane emissions due to reservoir flushing: a significant emission pathway?

Lessmann

Fernández

Martínez-Cruz

et al. 2023

Preprint

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Abstract. Reservoirs can emit substantial amounts of the greenhouse gas methane (CH4) via different emission pathways. In some reservoirs, reservoir flushing is employed as a sediment management strategy to counteract growing sediment deposits that threaten reservoir capacity. Reservoir flushing utilizes the eroding force of water currents during water level drawdown to mobilize and transport sediment deposits through the dam outlet into the downstream river. During this process, CH4 that is stored in the sediment can be released into the water and degas to the atmosphere resulting in CH4 emissions. Here, we assess the significance of this CH4 emission pathway and compare it to other CH4 emission pathways from reservoirs. We measured seasonal and spatial CH4 concentrations in the sediment of Schwarzenbach Reservoir, providing one of the largest datasets on CH4 pore water concentrations in freshwater systems. Based on this dataset we determined CH4 fluxes from the sediment and estimated potential CH4 emissions due to reservoir flushing. CH4 emissions due to one flushing operation can constitute 7–14 % of the typical annual CH4 emissions from Schwarzenbach Reservoir, whereby the amount of released CH4 depends on the timing of the flushing operation within the season. The larger the thickness of the sediment layer mobilized during the flushing operation the larger the average CH4 concentration per unit volume of flushed sediment. This suggests that regular flushing of smaller sediment layers releases less CH4 than removal of the same sediment volume in fewer flushing events of thicker sediment layers. In other reservoirs with higher sediment loadings than Schwarzenbach Reservoir, reservoir flushing could cause substantial CH4 emissions, especially when flushing operations are conducted frequently. Therefore, CH4 emissions due to reservoir flushing must be included in estimates of annual overall greenhouse gas emissions from reservoirs that are subject to regular flushing operations.

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supporting

confidence: 89%

Section: Significance Of the Potentially Released Amount Of Ch4 Due T...contrasting

confidence: 43%

Methane emissions due to reservoir flushing: a significant emission pathway?

Lessmann

Fernández

Martínez-Cruz

et al. 2023

Preprint

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“…In addition, hydrological variability as a result of climate change [61][62][63] and human interactions such as land clearance may also increase soil erosion and subsequently sediment loads in rivers, leading to increased reservoir sedimentation. Therefore, development and implementation of sustainable sediment management techniques to maintain sufficient reservoir storage on a long term has become increasingly important in meeting rising water and energy demands (e.g., [2,64]). Traditionally, reservoirs are designed for a lifetime of 50 to 100 years [41,65], leading to societal, environmental and economical problems beyond the designed lifetime.…”

Section: Sedimentsmentioning

confidence: 99%

“…In addition to guiding documents, containing empirical and analytical approaches, also physical models are employed to simulate management strategies. Recently, numerical models have been frequently employed to evaluate the success of sediment management strategies [40,48,64,[72][73][74][75][76]. Sediment management strategies to reduce reservoir sedimentation and maintain reservoir volume can be summarized under three main approaches [67]:…”

Section: Sedimentsmentioning

confidence: 99%

Interdisciplinary Reservoir Management—A Tool for Sustainable Water Resources Management

et al. 2021

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Reservoirs are a common way to store and retain water serving for a multitude of purposes like storage of drinking and irrigation water, recreation, flood protection, navigation, and hydropower production, and have been built since centuries. Today, few reservoirs serve only one purpose, which requires management of present demands and interests. Since each reservoir project will cause negative impacts alongside desired advantages both on a local, regional and global scale, it is even more urgent to develop a common management framework in an attempt to mitigate negative impacts, incorporate different demands and make them visible within the discourse in order to avoid conflicts from early on. The scientific publications on reservoirs are manifold, yet a comprehensive and integrative holistic tool about management of this infrastructure is not available. Therefore, a comprehensive and integrated conceptual tool was developed and proposed by the authors of this paper that can contribute to the sustainable management of existing reservoirs. The tool presented herein is based on the results from the interdisciplinary CHARM (CHAllenges of Reservoir Management) project as well as the condensed outcome of relevant literature to aid and enhance knowledge of reservoir management. The incorporated results are based on field, laboratory and empirical social research. The project CHARM focused on five different aspects related to existing reservoirs in southern Germany (Schwarzenbachtalsperre, Franconian Lake District), namely: sedimentation of reservoirs, biostabilisation of fine sediments, toxic cyanobacteria(l) (blooms), greenhouse gas emissions from reservoirs and social contestation, respectively consent. These five research foci contributed to the topics and setup of a conceptual tool, put together by the research consortium via delphi questioning, which can be found alongside this publication to provide insights for experts and laymen. Conceptualising and analysing the management in combination with quantitative and qualitative data in one descriptive tool presents a novelty for the case studies and area of research. The distribution within the scientific community and interested public will possibly make a positive contribution to the goal of sustainable water resources management in the future.

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“…Threedimensional (3D) numerical models have been used by various researchers to simulate the flow field and sediment-transportation issues in dam reservoirs [8][9][10][11][12]. Recently, 3D numerical models were used to analyse the sediment dynamics in reservoirs during a flushing operation at both the physical model scale [13][14][15] and prototype scale [6,[16][17][18]. Assessing the performance of 3D numerical models for simulating various sediment management strategies in reservoirs under different boundary conditions will provide valuable outcomes for further development and wider application of these models for integrated sediment management frameworks.…”

Section: Introductionmentioning

confidence: 99%

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

Esmaeili

Takemon

Kantoush

et al. 2021

Water

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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.

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Three-Dimensional Numerical Modelling of Reservoir Flushing to Obtain Long-Term Sediment Equilibrium

Cited by 7 publications

References 0 publications

Methane emissions due to reservoir flushing: a significant emission pathway?

Methane emissions due to reservoir flushing: a significant emission pathway?

Interdisciplinary Reservoir Management—A Tool for Sustainable Water Resources Management

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

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