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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]

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]

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Changes in streamflow and sediment runoffs would affect the reservoir's functional operation and the construction of soil and water conservation measures in China's Loess Plateau. In this study, the long‐term changes in streamflow and sediment were analyzed for a main stem section of the middle Yellow River where the to‐be‐built large Guxian Reservoir is to be located. Results showed that both streamflow and sediment had significant downward trends with the rates of −9.4 m3 s−1 yr−1 and −16.8 million t yr−1, respectively, during the period of 1961–2017. Using the range of variability approach, the change of streamflow regime in its postimpact period (1986–2017) was subjected to the moderate alteration, whereas the alteration of sediment regime was moderate and severe for the first (1980–1996) and second (1997–2017) postimpact periods. As an example, the attribution analyses of annual streamflow and sediment changes were conducted in a typical tributary catchment (Qingjian River) on the right bank of Guxian Reservoir. For the periods of 1980–2002 and 2003–2016, climate variability occupied the primary and secondary proportions to both streamflow and sediment reductions, respectively. Overall, human activities demonstrated the underlying contribution to the sharp declines of streamflow and sediment, accounting for 68% and 74%, respectively, during the period of 1980–2016. We suggest that, based on the operational life of warping dams (built on gully for mitigating gully erosion by raising the gully‐bed step‐by‐step), there are risks of flash flood and high sediment concentration events in the future because the streamflow/sediment‐reducing infrastructures may be damaged by extreme rainstorms and in turn become the flood and sediment amplifiers. [ABSTRACT FROM AUTHOR]