Planar changes of upper alluvial reaches of the Yellow River in recent thirty years

Based on the data of remote-sensing images,geomorphologic and geologic maps and hydrological data,the Ningxia-Inner Mongolia reaches is divided into four sections.According to planar characteristics,four sections are corresponding to compound of wandering river pattern and branching river,nearly straight river,braided river and meandering river.Comparison of river channel planform from 1978 to 2010 showed that change of river channel width and mainstream length were not monotone increasing or decreasing.As for river mainstream,the mainstream length of branching and nearly straight river had a little change,wandering river reach was decreased in earlier stage and then gradually increased,meandering channel was increased gradually.With respect to river average width,nearly straight river and sinuosity river were firstly widening and then narrowing,process of wandering river width was opposite,only branching river was narrowing gradually.Central shoal quantity changes of different river channel pattern could be divided into two types: one had a little change including Shizuishan-Bayangaole and Sanhuhekou-Toudaoguai;the other one was increasing firstly and then decreasing including Qingtongxia-Shizuishan and Bayangaole-Sanhuhekou.These changes was closely related to reservoir controls in the upstream of Yellow River.