Analysis of River Pattern Transformations in the Yellow River Basin
黄河流域河型转化现象初探

The Yellow River is famous in the world because of its high-concentrated flow and high sedimentary rate on the channel bed of the lower reach.The study on the Yellow River,hereinto,is mainly on erosion,hydrology,sediment delivery and channel bed evolution in the middle-lower reaches.It has not been sufficient to pay attention to the river pattern transformations in the main or tributary channels of the Yellow River.Frequent,various and complicated transformations of river patterns in different reaches of the Yellow River are scientific problems which cannot be blench for researchers.This study focuses on the river pattern transformations and their influence factors in the selected river reaches: Maqu reach,the first curve in the upper reach,Tuoketuo reach in the end of the upper reach,and Gaocun reach in the lower reach of the Yellow River.The river pattern transformations in the Maqu reach show changes from anastomosing to meandering and from meandering to braiding.The series transformations present a tend from very stable to very unstable channel patterns that is reverse to the normal trend from unstable to stable channel patterns in the world.These transformations are influenced by crustal rise,restriction of the gorges in upper and lower reaches,hydrodynamic characteristics,sediment characteristics of channel boundary and regional distribution of vegetation cover.The river pattern transformations in the Tuoketuo reach show changes from meandering to straight.That is the transformation from relative stable to very stable channel patterns.It is mainly influenced by the sediment characteristics of channel boundary and hydrodynamic characteristics.The river pattern transformations in the Gaocun reach show changes from braiding to meandering channel patterns.It presents a trend from very unstable to relative stable channel patterns.It is mainly influenced by the sediment characteristics of channel boundary and hydrodynamic characteristics.The artificial levees only restrict the maximum range of the lateral migration of the channel but not influence the channel pattern.The reservoirs built in the upper reach of the braiding reach lead to increase of river flow erosion and sediment coarsening in the braiding channel reach,contemporarily,resulting in a great deal of fine muddy sediments deposit in the meandering channel reach.Obviously,the reservoirs facilitate the river pattern transformation.