近30年苦水河水沙变化特征及成因分析

苦水河是宁夏境内重要的黄河一级支流，河流含沙量高，为了探究近30年来流域内水沙变化情势及其驱动机制，文章选取1989—2019年苦水河流域郭家桥控制站水文数据、吴中气象站降雨数据和Lansat系列卫星遥感数据，采用Mann-Kendall趋势检验、集中度分析、构建水沙关系曲线和土地利用转移矩阵等统计分析方法，分析了近30年苦水河流域水沙序列和水沙关系的变化特征。结果表明：(1)苦水河年径流(p<0.1)和输沙量(p<0.05)均显著减少。年径流和泥沙集中在5—8月，且输沙集中度很高。(2)分析水沙关系曲线，参数a有显著下降的趋势，表明流域内侵蚀程度降低。洪水场次下，顺时针和正“8”字滞回类型增加，显示河流输沙能力减弱，由短而急促渐渐转向平缓长久的输沙模式。(3)近30年苦水河流域内径流量和输沙量的减少，人类活动都是首要驱动因素，贡献度分别达到73.65%和95.67%。综上，流域南部山区大范围的农田转变为草地有效降低了苦水河流域上游来沙量，退耕还草措施对促进水土保持、协调水沙关系具有积极意义。

Analysis of Characteristics and Causes of Water and Sediment Changes in Recent 30 Years

Kushui River with high sediment content is an important tributary of the Yellow River in Ningxia. In order to explore the variation of water and sediment in the basin in the past 30 years and its driving mechanism, we selected the hydrological, meteorological and remote sensing data of Kushui River Basin from 1989 to 2019, and used Mann-Kendall trend test, concentration analysis, construction of land use transfer matrix and other statistical analysis methods to analyze the variation characteristics of water-sediment sequence and water-sediment relationship in the past 30 years. The results showed that:(1)the annual runoff(p<0.1)and sediment transport volume(p<0.05)of the Kushui River had decreased significantly; annual runoff and sediment concentrated between May and August and had a high sediment transport concentration:(2)by analyzing the water-sediment relationship curve, the parameter indicating the erosion degree in the basin had a significant downward trend; during floods, the clockwise and positive ‘8' hysteresis types increased, indicating that sediment transport capacity had weakened, and it had gradually shifted from short and rapid to a gentle and long-lasting sediment transport model;(3)human activities had always been the primary driving factors for the decrease in runoff and sediment transport in the Kushui River Basin in the past 30 years, with contributions reaching 73.65% and 95.67%, respectively. The conversion of large-scale farmland to grassland in the mountainous areas of the southern part of the basin effectively reduced the amount of sediment coming from the upper reaches of the Kushui River. The measures of returning farmland to grassland had positive effects on promoting soil and water conservation and coordinating the relationship between water and sediment.