受气候变化和大规模水土保持措施等因素共同作用下,黄河水沙情势发生剧烈变化。以黄河宁夏段面积最大、侵蚀最为严重的清水河流域为研究对象,基于1955—2016年实测水沙资料,解析水沙对关键影响因素的响应规律,探究水土保持作用下流域水沙关系演变特征。结果表明:清水河流域整体上呈现水沙减少趋势,人类活动引发的下垫面剧烈改变是水沙变化的主要因素,加快了流域水沙关系的演变;2000年后流域水沙关系发生明显转变,具体表现为水沙关系曲线系数a的显著降低,流域下游指数b明显上升。本研究认为流域水沙关系受到大规模水土保持措施实施的驱动而发生演变,基于泥沙的“储存-释放”效应,在新水沙条件下,强输沙事件出现的概率仍旧存在,因此需要加强预防措施。

[Objective] Current studies on the causes of water-sediment variation in the Yellow River mainly focus on the middle reaches’ hyperconcentrated sediment region or the Hekou-Longmen reach. Fewer studies have addressed the evolution of water-sediment relationships in typical tributaries of the upper reaches. Most existing research focuses on influencing factors of total water-sediment changes, with limited investigations on the driving factors behind water-sediment relationship evolution. The basin’s water-sediment effects under large-scale ecological restoration measures urgently need to be revealed. [Methods] This study took the Qingshui River Basin (QRB), the largest and most severely eroded tributary in the Ningxia section of the Yellow River, as the research object. Based on the actual water and sand data measured in the research area from 1955 to 2016, trend analysis and water-sediment relationship curves were used to reveal the characteristics of water-sediment changes. Multi-source data were employed to analyze the response of water and sediment to key influencing factors, ultimately exploring the evolution of basin water-sediment relationships under soil and water conservation. [Results] The interannual variations in runoff and sediment transport in the QRB were drastic. Annual runoff and sediment transport in Guyuan showed a significant downward trend. Annual runoff in Hanfuwang exhibited a significant decline, while annual sediment transport showed a non-significant decrease. Annual runoff and sediment transport in Quanyan Mountain showed no significant changes. Significant abrupt change years were observed in both annual runoff and sediment transport in the QRB. The abrupt change in annual runoff occurred in the 1990s, while that in annual sediment transport occurred after 2000. The periods of strong soil and water conservation measures in the Loess Plateau were close to the above abrupt change years of water-sediment factors. Sediment production in the QRB was jointly influenced by climate change (precipitation) and human activities. Drastic changes in the underlying surface caused by human activities were the primary factor leading to the sharp reduction in water and sediment in the QRB, further driving the evolution of basin water-sediment relationships. After 2000, the basin’s water-sediment relationship underwent a distinct transformation, specifically manifested as a significant decrease in the coefficient “a” of the water-sediment relationship curve and a notable increase in the downstream index “b”. Drastic changes in the underlying surface caused by human activities remained the primary factor driving water-sediment changes and the evolution of basin water-sediment relationships. [Conclusions] The water-sediment relationships in the basin have evolved as a result of large-scale soil and water conservation measures. Based on the sediment “storage-release” effect, the probability of strong sediment transport events still exists under new water-sediment conditions, necessitating strengthened preventive measures.