小浪底水库运行后黄河下游水沙过程发生明显变化，为量化小浪底水库在其中发挥的作用，将研究时段划分为三门峡水库单独运行时段（简称“单库时段”）和三门峡水库、小浪底水库联合调度时段（简称“双库时段”），对比2个时段黄河下游水沙过程变化，采用趋势检验、突变点分析、数值模拟等方法，定量评估小浪底水库在水沙过程变化中发挥的作用。结果显示：与单库时段相比，双库时段黄河下游花园口、高村和利津3个断面小于预警流量的天数减少90%以上，超过2 000 m3/s的大流量及关键期高流量脉冲持续时间延长；含沙量降幅超过72%，河道被持续冲刷。其中，小浪底水库通过泄放生态流量、调水调沙等措施，发挥了减少预警天数、增加大流量及高流量脉冲持续时间、年均减少黄河下游河道泥沙淤积量1.58亿t的作用。水沙过程变化提高了生态基流保证率与栖息地稳定性，有利于淡水鱼类多样性恢复。

The construction of cascade reservoirs is a trend and inevitable way for efficient utilization of water resources in the basin. At the same time, the construction and operation of reservoirs have led to the redistribution of non-biological elements such as water and sediment, resulting in changes in the structure and function of river ecosystems. Multiple reservoirs often produce various effects such as summation, synergy, and antagonism along with a complex ecological impact especially in cascade development. The impact of adding new reservoirs has become a key factor in the planning of river cascade development. The river ecosystem is influenced by multiple factors such as water conservancy engineering conditions, climate change, land use, and water intake, which raises difficulty for scientifically quantitfying the role of newly added reservoirs. Xiaolangdi Reservoir is a critical project for controlling the water and sediment processes in the lower reaches of the Yellow River, and since its scheduling, it has jointly worked in conjunction with Sanmenxia Reservoir. Since the scheduling of the Xiaolangdi Reservoir, there have been significant changes in the water and sediment processes in the lower reaches of the Yellow River. To quantify the role played by the Xiaolangdi Reservoir in these changes, the changes in water and sediment conditions in the lower reaches of the Yellow River during the single reservoir period of Sanmenxia Reservoir and the dual reservoir period of Sanmenxia Reservoir and Xiaolangdi Reservoir are quantified. The impact of Xiaolangdi Reservoir is quantitatively evaluated through methods such as trend testing, abrupt change point analysis, and numerical simulation. The results show that the single reservoir period compared with the joint scheduling of Xiaolangdi Reservoir and Sanmenxia Reservoir shortened the duration of low flow events in the lower reaches of the Yellow River, prolonged the duration of high flow events, and caused continuous erosion of the river channel. Compared with the single reservoir period, at the three cross-secions of Huayuankou, Gaocun, and Lijin during the dual reservoir period: the average number of days below the warning flow decreased by more than 90%, and the average number of days above3000 m3/s increased by more than 85%; the duration of high flow pulses during the critical period of fish reproduction (April to June) increased by more than 50%; the annual average sediment yield and average sediment concentration have decreased by more than 70%; the main groove of the cross-sections was deepened and the elevation was reduced. The role played by Xiaolangdi Reservoir was consistent with the characteristics of changes in water and sediment processes. The scheduling of Xiaolangdi Reservoir increased the number of days with a flow greater than 3000m3/s by 86%, and reduced the number of days with a flow less than 150 m3/s by 57%. Xiaolangdi Reservoir annually retained an average of 1.50×108m3 of sediment. The sudden change time of sediment concentration at Huayuankou cross-secion is consistent with the operation time of Xiaolangdi Reservoir. Without Xiaolangdi Reservoir, the the lower reaches of the Yellow River would have shifted from an average annual erosion of 130 million t to an average annual sedimentation of 28 million t. After the joint scheduling of Xiaolangdi Reservoir and Sanmenxia Reservoir, the ecological base flow guarantee rate and habitat stability in the lower reaches of the Yellow River have been improved, and the diversity of freshwater fish has been effectively restored.