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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]

Xiaolangdi Reservoir has played a great role in flood control, sediment reduction and profit improvement. This paper systematically analyzed the flood control operation and the function of the Xiaolangdi Reservoir. By analyzing the sediment erosion and sedimentation of the reservoir and the Lower Yellow River, the effect of sediment reduction of the reservoir was proposed. The benefit of flood control and sediment reduction of the reservoir was calculated. The results show that the reservoirs in the middle reaches of the Yellow River can block the flood and cut the peak for 15 times. The average peak cutting rate of Huayuankou Station is 36%, and the maximum peak cutting flow is 7 560 m³/s, which can effectively avoid the flood losses in the downstream beach area. Due to the decrease of sediment load, the sedimentation rate of the reservoir is lower than that in the design stage, and the sediment retention ratio of 1.26 relative to the downstream channel is lower than that of 1.57 in the design sediment retention stage. The sediment reduction effect of the reservoir is better, especially in the reach below the Aishan. According to the 2020 price level, the actual annual benefits of flood control (ice-run prevention) and sediment reduction of the reservoir are 5.927 billion Yuan more than the design value, and the cumulative present value of benefits is 21.873 billion Yuan more than the total investment (including power generation), indicating the economic rationality of the construction of the Yellow River water and sediment regulation backbone project, which provides a successful example for accelerating the construction of Guxian project [ABSTRACT FROM AUTHOR]

Fully tapping the regulating potential of reservoir groups in the middle reaches of the Yellow River and improving the sediment transport capacity of the lower reaches of the Yellow River play an important guiding role on river and beach management in the lower reaches of the Yellow River. Through the analysis of measured data and mathematical models, this paper calculated the influence of combined regulation and control of existing reservoir groups under different water and sediment conditions on sediment transport capacity of the lower reaches of the Yellow River, and further to analyzed the change of sediment transport capacity of the lower reaches of the Yellow River after Guxian and Dongzhuang reservoirs come into effect. The results indicate that by optimizing the joint regulation and control mode of the existing reservoir groups, the flow process with large sediment concentration discharged by the reservoir can increase the sediment carrying capacity of the downstream river by about 10%-12%. The sediment discharge into the downstream river during the sediment retaining period after Guxian and Dongzhuang Reservoirs come into effect are reduced, and the sediment transport capacity can be further improved by 11%-12% during the normal operation period. [ABSTRACT FROM AUTHOR]

The Xiaolangdi Reservoir has been mainly used for sediment trapping and water-sediment regulating in order to reduce sedimentation of the lower Yellow River after operation, which results in lower sediment transport efficiency. At present, a suitable river channel scale of median water with the bankfull discharge capacity of 4 000 m³/s has been formed in the lower Yellow River. Under this riverbed condition, how to maintain the river channel of median water of the lower Yellow River and give full play to the river sediment transport capacity becomes new requirement to the operation of the reservoir. This paper analyzed the sediment transport efficiency at different sediment concentration levels and discharge levels based on the measured data of 306 non-overbank floods in the lower reaches of the Yellow River from 1960 to 2016 and proposed that the downstream river channel had a higher sediment transport efficiency when the large flow with sediment concentration greater than 60 kg/m³, but it was also prone to cause sedimentation in the river channel. The paper further proposed the sediment transport requirement to the operation of the reservoir based on maintaining the river channel of median water of the lower Yellow River. In order to improve the sediment transport capacity of the downstream river, when the bankfull discharge capacity of the downstream river channel was about 4 000 m³/s, the Xiaolangdi Reservoir could discharge large-flow processes with sediment concentration less than 100 kg/m³. When the bankfull discharge capacity of the downstream river channel was greater than 4 500 m³/s, the Xiaolangdi Reservoir could discharge large-flow processes with sediment concentration less than 200 kg/m³. When the bankfull discharge capacity of the downstream river channel was less than 4 000 m³/s in the future, the Xiaolangdi Reservoir would still mainly trap sediment to reinvent the river channel. The calculation results of the mathematical model show that the adjustment of the operation mode of the reservoir can improve the sediment transport capacity of the downstream river, alleviate the sedimentation of the reservoir and the downstream river and maintain the river channel of median water with the bankfull discharge capacity of 4 000 m³/s for a longer period of time. [ABSTRACT FROM AUTHOR]

Since the operation of Xiaolangdi Reservoir, great social and economic benefits have been brought into play in ensuring the flood control and silt reduction, the safety of living, production, irrigation and ecological water use. Based on the measured data, this paper analyzed the outflow conditions of high water level density flow and the influence factors of sediment discharge of Xiaolangdi Reservoir. The results show that during the high water level operation (above 235 m) of Xiaolangdi Reservoir, two conditions shall be met for the density flow to reach the front of the dam. a) The inflow flood process shall not be less than 3 days and the fine sediment content shall be higher than 40%. b) Inflow discharge Qi shall not be less than 4000 m³/s. And meet the sediment concentration shall not be less than 13.0 kg/m³. Alternatively, if inflow discharge Qi is between 1700 m³/s and 4000 m³/s, and meet the sediment concentration Si shall not be less than 86 minus 0.018Qi. Sediment discharge ratio of reservoir η is inversely proportional to the ratio of the water storage body and the outflow discharge and the ratio of the inflow and outflow discharge. The larger the maximum continuous 3-day inflow sediment transport rate, the stronger the flow power and the better the sediment discharge effect. The research results can provide a certain technical support for the high water level density flow sediment discharge operation of Xiaolangdi Reservoir. [ABSTRACT FROM AUTHOR]

The Yellow River key reservoir projects bear on the big picture. The practices of planning, construction, operation and management of these key reservoir projects promote continually the deepening of the understanding of the governance of the Yellow River. Based on the planning and construction backgrounds of the Sanmenxia Reservoir and the Xiaolangdi Reservoir in the middle reaches of the Yellow River and their operation and management practices, this paper briefly reviewed the progress from practice to cognition to practice and cognition again, as well as the development and evolution of river harnessing thought through it. Based on the problems and challenges faced by the Yellow River management in the new era, this paper suggests to speed up the development of the Guxian key reservoir project. [ABSTRACT FROM AUTHOR]

In the flood season of 2019, the rainstorm process in the Yellow River Basin was frequent. In order to deal with the flood and sediment from Weihe River and its upstream, Xiaolangdi Reservoir had implemented scientific regulation of water and sediment and achieved significant flood control and deposition reduction. Based on the measured data, this paper analyzed the operation process of Xiaolangdi Reservoir in 2019, the deposition morphology and distribution, and the influencing factors of sediment discharge. The results show that during the flood season, strong scouring occurs in the main stream of the reservoir. The amount of scouring is 174.3 million m 3, and the thalweg elevation in delta section decreases 4.6 m. The annual sediment discharge of the reservoir is 545.1 million tons, the amount of scouring is 265.4 million tons, and the sediment discharge ratio is 194.9%. During the period of two low water level sediment discharge operations, the sediment discharge is 533.4 million tons, accounting for 97.9% of the total annual sediment discharge, and erosion is 397.8 million tons, and the sediment discharge ratio is 393.4%. The main reasons for the better effect of sediment discharge in flood season in 2019 are that the water level in front of dam is at a lower level for a long time, more sediment is deposited in the early stage and strong inflow flow power in flood season. [ABSTRACT FROM AUTHOR]

In the flood seasons of 2018 and 2019, the inflow of Xiaolangdi Reservoir was higher than before and it was the first time that the operation of low reservoir level, long duration,large discharge, and high sediment concentration was applied for two consecutive years, which effectively scoured the sediment in the reservoir area. This paper analyzed the influencing factor of sediment discharge and established the calculation formula of the reservoir sediment discharge ratio by the regression analysis method, based on the actual sediment discharge operation of the reservoir. The results point out that pondage, lowest water depth and inflow are most closely related to sediment discharging, with a high correlation above 0.80. The calculation formula for the sediment discharge ratio verified by the measured data can simulate the sediment discharge of the reservoir well. Based on the observation data of the topography of the reservoir dam area, the sediment scour and silting change in the dam area were analyzed, and it was proposed that the river bed gradient within 4.5 km of the reservoir area had been stabilized between 4.3‰ and 5.1‰ since 2014, under the influence by the discharge bottom hole. The lowest elevation of sediment deposition in front of the intake tower varies between 176 m and 181 m. On the right bank in front of the dam, the sediment deposition elevation gradually rises and the slope becomes steeper. Currently, a stable slope has not been formed. As the left bank in front of the dam is close to the mountain with a high slope and there is little sediment accumulation. [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]

Preventing sediment siltation in front of intake tower group of the Xiaolangdi Reservoir affects the safety operation and the generation benefits of the project. It is vital to determine a proper operation dispatch scheme of the outlet structures. This paper did the numerical research on the prevention of silt plug in the Xiaolangdi Reservoir by a vertical 2D numerical model. The bed evolution, sediment delivery ratio and generation benefit were discussed under typical water and sediment conditions with the two different dispatch schemes of the outlets. The results of the numerical modeling show that neither of the dispatch schemes will cause the sediment siltation and the scheme I shows a better performance in promoting the generation benefits. The present work provides the technical support for the operation dispatch scheme of outlets in engineering practices. [ABSTRACT FROM AUTHOR]

The sediment concentration in the Yellow River is large and the reservoirs in the mainstream suffer from siltation of different degrees. A new concept and method that combining hydraulic power with strong artificial measure was proposed by this article. This method used pressure air to uplift flow in order to enhance turbulence and improve sediment transport. A flume test was introduced by this paper to study the transport of the prototype sand in the Yellow River. The results show that 28% sediment over the air vent is setting up and carried by flow during a period of deaeration, while only 8% settle down in the down reach of flume, which means 20% is carrying to the outside of flume. Taking Xiaolangdi Reservoir of the Yellow River for an example, the feasibility of applying pneumatic system was analyzed and a preliminary scheme was proposed. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive analysis on the ecological benefit and loss of Xiaolangdi reservoir from its completion in 2000 to 2012. We firstly propose a three-step framework of the ecological benefit–loss evaluation for hydropower projects, in accordance with which an index system of riverine wetland ecosystem services valuation was established originally. Then we make a quantitative valuation on the change of riverine wetland ecosystem services caused by this project. Finally, the ecological benefit and loss of the project in the riverine wetland were evaluated in two aspects of positive impacts and negative impacts. The results showed that (1) the positive impacts of Xiaolangdi reservoir mainly included 9 categories of ecosystem services: flood control, ice prevention, sedimentation reduction, energy substitution, emission reduction benefit, water supply, afforestation, shipping and entertainment; the total ecological benefit of the project in the riverine wetland was 26.2058 billion yuan. (2) The negative impacts of Xiaolangdi reservoir mainly included 5 categories: loss due to land submergence, heritage submergence, water and soil erosion, reservoir sedimentation and immigration; the total ecological loss of the project in the riverine wetland was 24.2167 billion yuan. (3) From 2000 to 2012, the net value of ecological benefit–loss for the project was 1.9891 billion yuan. [ABSTRACT FROM AUTHOR]