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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]

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]

The Xiaolangdi Reservoir is the core of the current Yellow River water and sediment regulation system. In order to improve the Yellow River water and sediment regulation mechanism, it is necessary to study the causes and enhancement measures for the insufficient follow-up power for water and sediment regulation in Xiaolangdi Reservoir. Based on the practice of water and sediment regulation in Xiaolangdi Reservoir, this paper analyzed the incoming conditions of water and sediment in the reservoir and the rule of sediment discharge in the reservoir area, and clarified the characteristics and reasons of insufficient power for water and sediment regulation. Also, it studied themeasures to enhance the follow-up power of Xiaolangdi Reservoir, including lowering the water level for erosion, effective storage capacity maintenance, coordination of downstream water?sediment relations, etc., which required sufficient flood processes to achieve effective and rational water-sediment relation of midstream reservoirs. Combined with the current situation and the planning of the Yellow River water-sediment regulation system, the enhancement measures of follow?up power for water and sediment regulation were proposed. It believed that the current projects had major constraints in enhancing the follow-up power for water and sediment regulation in Xiaolangdi Reservoir. The construction of the Guxian Reservoir was the first choice to solve the lack of follow-up power for water and sediment regulation in Xiaolangdi Reservoir, to effectively supply the follow?up power of water and sediment regulation in Xiaolangdi Reservoir. [ABSTRACT FROM AUTHOR]

Ecological protection and high quality development of the Yellow River basin have become a major national strategy，but there are still some outstanding difficulties and issues in the current stage which need to be considered and gradually promoted from a strategic perspec¬tive. This paper systematically analyzed the outstanding difficulties and issues in the current development and utilization of water resources， sediment deposition control，flood control and disaster reduction，ecological environment protection and economic and social development in the Yellow River basin. Combining with the major national strategic requirements of ecological protection and high quality development in the Yellow River basin，according to the general idea of “combining points，lines and areas” and “five water resources with one treatment”，it put forward the key points to supplement the weak links of flood control and water & sand regulation，strengthen the protection of main and branch water environment and water ecosystem，implement comprehensive management of mountains，rivers，forests，fields，lakes and gras¬ses in the basin，for^n the overall layout and strategic pattern of protecting water resources，restoring water ecology，improving water environ¬ment， controlling water disasters，strengthening water supervision，and formulate the system and mechanism framework of basin coordination management，for maintaining the ecological health of the Yellow River and supporting the high quality development of the Yellow River basin. [ABSTRACT FROM AUTHOR]

： Problems in the Yellow River basin are as follows ： the incompatibility between management strategies in the wide reaches of the- Lower Yellow- River and water and sediment condition； the main frame of the water and sediment regulation system has not been formed; the upper and middle basin has poor economic development basis，harsh ecological environment and endures lack of water resources. Based on the previous and present management methods，the countermeasures for the training of the Yellow，River are provided by this paper. a) Com¬bining “two boundaries mode” and ecological management mode in the training of the wide reaches，using the long-distance high concentra¬tion pipeline sediment transport technolog^^ and other methods to rebuild the functional spaces in the “ newdy-fonned floodplains” and the “ highly-formed floodplains”. Functional spaces in the “ newdy-fonned floodplains” are for agricultural production and functional spaces in the “ highly-formed floodplains” are free for resettlement. Using the precast plank-stake combination dyke technology to build high-level river training stmctures and protection embankments in the “first boundary” construction. The “first boundary” can play a role in the flow，path control and sediment transportation. It can also protect the “ newly-for^med floodplains” under designed discharge. The regulation of the stream line is regarded as the sub-objective of the reser^^oir operation in the upper and middle reaches. Guide the stream line and promote the sedi¬ment transport capacity through river training structures. Achieve the benign management target of the effective utilization of the wide flood¬plains and the coadaptation of stream line stability under medium floods and specific floods conveyance. b) Construct the Guxian Project and the Heishanxia Project as soon as possible to establish main reser^^oirs of water and sediment regulation system in the Yellow River. The water and sediment regulation system in the Yellow River is beneficial in the disaster prevention and can promote the coordinated development of the ecological construction and regional economy in the Yellow River basin. It helps to promote the development of poverty-stricken areas，old revolutionary^ base areas and ethnic minority areas. It further promotes the economic revitalization of the west area and the overall situation of national ecology，food security，energy security and social stability. c) Use modern engineering measures to change the erosion datum level. Transfor^m the serious soil and water loss areas on the Loess Plateau to well-arranged plains. Biological measures are supplemented to reduce the amount of sediment transported into the Yellow- River and to exert ecological benefits persistently. d) The West Route of the South-to-North Water Transfer Project and the Water Transfer Project from Tibet can solve the water shortage situation and the trend of serious degra¬dation of the ecological environment in the Yellow River basin and North China, providing water resources guarantee for national water supply security, energy security, food security and ecological security. The “ Water Transfer from Tibet to the Yellow River” project is a fundamental plan for the sustainable development of China. [ABSTRACT FROM AUTHOR]