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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 clear identification and quantification of the factors affecting groundwater systems is crucial for protecting groundwater resources and ensuring safety in agricultural production. The Lower Yellow River (LYR) is a suspended river that replenishes groundwater continuously due to clear differences in the water head, especially in the Xinxiang section. Since its construction, the Xiaolangdi Reservoir has reversed the LYR's deposition. To accurately determine the factors influencing the groundwater level (GWL), the study area was divided into five subzones based on hydrogeology. A dynamic factor model (DFM), variational mode decomposition (VMD), and a multiple linear regression model were used to identify and quantify the factors influencing the GWL. The impact of the suspended river on the ground-water before and after the construction of the Xiaolangdi Reservoir was examined. The results show that: (1) The rate of decrease in the GWL was 8.53 × 10−4 m/month, and the rate of decrease in the Yellow River water level (RWL) was 4.63 × 10−4 m/month. (2) Mountain front recharge (MFR) (scale = 3 months) and precipitation (scale = 9 months) were the dominant factors in subzones I and II, accounting for more than 40% of the fluctuation in the GWL. Subzone III was dominated by exploitation (scale = 7 months) and precipitation (scale = 12 months), accounting for 28.43%, and 23.44% of changes in the GWL, respectively. In subzone IV, agricultural irrigation (scale = 12 months) was the major factor, accounting for 32.47% of GWL changes, while in subzone V, the RWL (scale = 12 months) accounted for 52.52% of these changes. (3) The Xiaolangdi Reservoir has increased the lateral seepage of the suspended river and altered the inter-annual distribution. The results of this study can provide a valuable reference for controlling groundwater overexploitation and ensuring water supply security. [ABSTRACT FROM AUTHOR]