A New Classification of Fluvial Rivers According to Channel Pla nform and Sediment Characteristics

Key words: 
• fluvial /
• channel /
• pattern /
• sediment

Abstract: There are many fluvial clsaaifications in the world.S ome of them mainly are concerned with the relationship be tween river process and geotectonic evolution.Some of them are impressed the co mbination of predominant mode of sediment transport and channel stability .Some of them are classified only according to channel planforms.Some classifications are considered the relative rates of channel and interchannel accumulations,and so on.However,many of the classification schemes have more or less defects.Furth ermore,some classifications derived by the research workers of one subject can n ot applied in other subjects. Two classification schemes of fluvial rivers derived by Rust^〔12〕 and Qia n^〔17〕 according to channel planform are applied widely in the world.The classification scheme derived by Rust^〔12〕 is given extensive attention b y many sedimentologists,while the other derived by Qian^〔17〕 is given mor e attention by many water engineers and geomorphologists.The former includes bra ided,meandering,anastomosing and straight fluvial channel patterns and the later includes braided,meandiering,anabranched and straight channel patterns.Some wat er engineers and geomorphologists think that the anastomosing and the anabranche d fluvial rivers are the same river types because the other river types in the t wo schemes are the same respectively.So,they consider that the two classificatio n schemes are equivalent.More studies indicate that the anastomosing and the ana branched aren't the same channel type. The definitions and the interchannel subsurface deposits of anastomosing and ana dranched channel patterns are compared in detail,The anastomosing river is stab le,low bedload,multiple channel systems with low gradicnt and moderate sinuosity separated by vegetated islands.The anabranched river is alternation of single a nd double (or mulitple) channels in flow orientation.The former banks are very s table.Mud and silt are the main sediments of its interchannels and floodplains a nd no channel sand bodies exist in these areas.The banks of the later are very stable in the single channel reaches and are unstable in the double (or multiple ) channel reaches.Mud and silt are the main sediments in the floodplains of sin gle channel reaches and the upper mud-silt floodplains of double (or multiple)channel reaches.The autho rs think that the two classification schemes above aren't equivalent because t he anastomosing and the anabranched are the different channel patterns.Thus the study achievements of fluvial systems in one field are difficult to be applied i n other fields.For the sake of convenience to exchange the achievements in diffe rent fields,a new classification scheme of fluvial revers is needed. After discussing the imperfection of some representative river classification sc hemes,a new classification of fluvial rivers is derived according to the planfor m and stability of channels and the sediment characteristics of interchannnels. Fluvial rivers are divided into braided.meandering,anabranched,anastomosing and straight channel patterns in this new classification.The definitions of anastomo sing and anabranched rivers are defined above.The definitions of braided,meander ing and straight rivers are respectively similar to that of defined by Rust in 1978.The main characteristics of the five fluvial channle patterns are compared in fig.1 and table 3.The new classification may be applied in fluvial sedimento logy,fluvial geomorphology and fluvial hydraulics. It is necessary and useful fo r the study of fluvial systems.