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How to utilize the joint operation of reservoir groups to maximize sediment discharge efficiency is a key technical challenge in water and sediment regulation. This paper selected the joint operation of Sanmenxia and Xiaolangdi reservoirs in the period of water and sediment regulation in 2023 as the object, analyzed the water and sediment processes of the two reservoirs under different matching opportunities and matching water levels, and quantified the water and sediment regulation effect under different matching opportunities and matching water levels between the two reservoirs. Although the Sanmenxia Reservoir has a smaller water storage capacity and limited water transfer capacity, by changing the discharge time of the reservoir, the scouring effect of Xiaolangdi Reservoir is quite different. As the matching water level decreases, the amount of erosion in the reservoir area gradually increases. With the delay of the relative discharge time of Sanmenxia Reservoir, the erosion amount in the reservoir area shows a trend of first increasing and then decreasing. [ABSTRACT FROM AUTHOR]

Xiaolangdi Reservoir is the key project of flood control and security in the lower reaches of the Yellow River, and the sediment retention period of the reservoir is the most significant period for flood control and sediment reduction benefits. This paper analyzed the new requirements for flood control and security of Xiaolangdi Reservoir under the new situation of the lower reaches of the Yellow River, and pointed out that it was of great strategic significance to extend the sediment retention period of Xiaolangdi Reservoir as much as possible, so as to maintain the effective storage capacity of the reservoir as long as possible, especially the flood control storage capacity. The research shows that the larger reservoir capacity has a strong ability to deal with large floods, which is conducive to the prevention of “black swan” events; after the flood control operation of the reservoir, the loss of the beach storage capacity is small, which is conducive to the long-term maintenance of the reservoir’s strong flood control capacity; the combination of sediment storage capacity and water and sediment regulation capacity can significantly enhance the vitality of water and sediment regulation, and create storage conditions for the Guxian Reservoir to exert the overall joint force of the water and sediment regulation system after putting into operation; the use of the sediment storage capacity for flood control in the downstream beach area is conducive to improving the flood control standard of the beach area and reducing the loss of the beach area in the normal flooding. Optimizing the operation mode of reservoir operation, implementing reservoir dredging and building Guxian Water Control Project as soon as possible are important measures to extend the sediment retention period of Xiaolangdi Reservoir. [ABSTRACT FROM AUTHOR]

Recently suspended river, where formed both in tributary and in main stream of Ningxia-Inner Mongolia reaches in the Upper Yellow River, severely threatens people's lives and property safety downstream. In this paper, taking Ningxia-Inner Mongolia reaches for the example, water and sediment are regulated by cascade reservoirs upstream, which can form artificial controlled flood, to improve the relationship of water-sediment and slow down the speed of sedimentation rate. Then, multi-objective optimal operation model of cascade reservoirs is established with four objectives: ice and flood control, power generation, water supply, water and sediment regulation. Based on optimization technique of feasible search space, the non-dominated sorting genetic algorithm (NSGA-II) is improved and a new multi-objective algorithm, Feasible Search Space Optimization-Non-dominated Sorting Genetic Algorithm (FSSO-NSGA-II) is innovatively proposed in this paper. The best time of water and sediment regulation is discussed and the regulation index system and scenarios are constructed in three level years of 2010, 2020 and 2030. After that regulation efforts and contribution to sediment transportation are quantified under three scenarios. Compared with history data in 2010, the accuracy and superiority of multi-objective model and FSSO-NSGA-II are verified. Even more, four-dimensional vector coordinate systems are proposed innovatively to represent each objective and sensitivity of three scenarios are analyzed to clarify the impact on regulation objectives by regulation indexes. At last, relationships between four objectives are revealed. The research findings provide optimal solutions of multi-objectives optimal operation by FSSO-NSGA-II, which have an important theoretical significance to enrich the methods of water and sediment optimal operation by cascade reservoirs, guiding significance to water and sediment regulation implementation and construct water and sediment control system in the whole Yellow River basin. Research Highlights: We establish an multi-objective optimal operation model with four regulation objectives. We proposed a improved multi-objective algorithm (FSSO-NSGA-II) based on feasible search space optimization. Regulation index system and three scenarios are constructed. Four-dimensional vector coordinate systems are proposed to represent each objective and sensitivity of scenarios are analyzed. Relationships between four objectives are revealed. [ABSTRACT FROM AUTHOR]

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Copyright of Yellow River is the property of Editorial Board of Yellow River and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Yellow River is the property of Editorial Board of Yellow River and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The joint operation of Xiaolangdi Reservoir with Sanmenxia Reservoir and tributary reservoirs after the completion of Xiaolangdi Reservoir marks the basic completion of the downstream flood control and disaster reduction project system. However, for the Yellow River beach area, which has always been emphasized as the space for flood detention and sediment deposition, the reservoir flood control operation has set the goal of ensuring that the beach area is not filled with water for many years. Taking the autumn flood in recent four years, including 2021, as an example, this paper showed that it was more difficult to block and stagger the peak of the reservoir after the superposition of a variety of adverse factors, especially when the inflow of trunk tributaries was encountered. In order to solve this problem, it was considered that under the specific restriction of Huayuankou flow. Sanmenxia Reservoir should be allowed to stop the flood, transition to the non flood season pool level in advance, help Xiaolangdi Reservoir reserve the storage capacity under the maximum allowable water level, and skillfully stagger the flood discharge. When necessary, the temporary storage water level of Sammenxia Reservoir could break through to reduce the safe ty risk of high water level of Xiaolangdi dam. In addition, under the current situation that the amount of sediment entering the reservoir de creased greatly. The operation mode of Sanmenxia Reservoir should be adjusted and improved, strive to make this pearl of the Yellow River shine again, improve the downstream flood control engineering system, give play to the role of optimizing the allocation of water resources, and provide safety guarantee for downstream flood control, disaster reduction and high-quality development. [ABSTRACT FROM AUTHOR]

Sediment trap efficiency (TE), defined as the sediment trapped in a reservoir divided by the sediment flowing into the reservoir, or the sediment delivery ratio (SDR=100%-TE), has been studied for small or ponded reservoirs, but for large reservoirs it is still not well understood even though it is important for predicting and managing reservoir sedimentation. In this case study, we analyzed the changes in water and sediment regime caused by the operation of two cascade dams (the Sanmenxia and Xiaolangdi Dams just upstream of the lower Yellow River) during 2000–2020. We found that more than 50% of the water discharge (Q) entering and flowing out of the reservoirs was smaller than 1,000 m3/s , while over 85% of the sediment was transported by larger discharges. Among different ranges of Q , the range 2,000–3,000 m3/s transported the most sediment (30%–50%). Due to the Water and Sediment Regulation Scheme of the dams, the maximum sediment concentration of floods tended to lag behind the maximum water discharge. The longer the lag time, the greater the water volume released to the downstream, resulting in a higher SDR of floods. A calculation method for the SDR at the Xiaolangdi Reservoir during floods and flood seasons was proposed by considering the water retention time in the reservoir. The sedimentation delta in the Xiaolangdi Reservoir changed rapidly after the dam closure and gradually became stable, and its geometric changes also impacted sediment transport through the reservoir. This study may shed light on sediment transport through large reservoirs under the operation of water and sediment regulation. [ABSTRACT FROM AUTHOR]