黄河内蒙古段洪峰特征及水沙关系变化

A Study on Characteristics and Sediment Rating Curves of Floods in the Inner Mongolian Reach of the Yellow River

本文通过黄河头道拐站1950-2009年水沙年系列进行突变点分析,识别出1969年、1986年、1996年3个突变点,将黄河内蒙古段水文过程划分为4个时期。在此基础上,利用内蒙古段6个水文站长系列日流量、日含沙量及泥沙组成数据,划分了各站的夏汛洪峰,并统计分析了分期洪峰的水沙分布特征和洪峰水沙关系,揭示出夏汛洪峰流量和输沙率逐渐减少的规律:1996-2006年与1954-1968年相比,夏汛洪峰水沙量占全年水沙的比例都减少了约一半,流量级频率与输沙率乘积的峰值对应的流量也降低了约一半。分析认为,黄河内蒙古段夏汛洪峰特征阶段性变化既有大型水库的影响,又有气候变化及人类活动的影响,而且后者的作用越来越大。分析发现,20世纪90年代以前,黄河上游水沙变化只是改变了内蒙古段来沙中粗颗粒泥沙的水沙关系,显示出大流量输送粗颗粒泥沙能力相对增强的趋向;进入内蒙段后,通过泥沙冲淤调整,分粒径组泥沙水沙关系变化比较复杂。近期在水沙条件巨大变化下,河流的输沙特性并没有发生根本变化,但是无论全沙还是分组沙,水沙关系曲线变陡,大流量输送泥沙能力相对增强。

In the series of annual runoff and sediment load recorded at Toudaoguai station in the period of 1950-2009, three abrupt changes in the years 1969, 1986 and 1996 were identified. According to the three abrupt changes, the hydrological series in the Inner Mongolian reach were divided into four periods. Summer flood peaks were identified from the series of daily water discharge and sediment concentration recorded at six hydrological stations along the Inner Mongolian reach, and statistical analysis was carried out on the frequency distribution of water discharge and sediment load as well as the sediment rating curves of the flood peaks. It was revealed that the water discharge and sediment load of the flood peaks decreased gradually from the earlier to the later periods, with both their percentages in the annual total and the water discharge corresponding to the peaks of product of the water discharge frequency and sediment load being reduced by about two times from the period 1954-1968 to 1996-2006. These changes could be attributed to the flow regulation by large dams and to the flow reduction by climate change, water diversion in the Ningxia-Inner Mongolian reach and other human interferences. It was found that changes in water and sediment input before the 1990s only altered the relation between water discharge and sediment load coarser than 0.005 mm at the entrance of the Inner Mongolian reach, with a tendency of coarser sediment being entrained by the larger flows. In the Inner Mongolian reach, no tendency was identified in the changes of relation of water discharge and sediment load due to the adjustment of sediment scour and deposition before the 1990s. As a result of the great variations of water and sediment inputs in recent years, although there was not an observable change in the sediment transport regime, the sediment rating curves of either the total load or the load of each particle size group became steep, showing an increasing tendency of sediment transport capacity of the larger flows.