Keywords: 
• hydrological and sediment characteristics /
• anastomosing river pattern /
• channel formation and evolution /
• lower xijiang and beijiang Rivers

Abstract: The relationships of velocity and discharge,water level elevation， sediment concentration and widthdepth ratio of xijiang and beijiang River channels on the zhujiang Delte area are analyzed and some differences between the two rivers are revealed. one of the differences is that the channel cross sections are different between the two rivers either in width- dept h ratio or in channel evolution despite the planf or mof the two rivers appears multiple channel system. The author considered that all the xijiang River channels and the beijiang channels at b and C belts on the Delta area are anastomosi ng pattern,but the beijiang River channels at A belt are not anastomosing river pattern. The xijiang anastomosing channels are typical and developed,and the beijiang anastomosing channels still are at the primary developing stage. The anastomosing channel for mation follows the channel avulsion mechanismduring flooding as Smith (1989)stated. However,the freCuency of channel avulsion is veryrare， so the anastomosi ng channel for mation has a long history. The anastomosing channels have cohesive natural levees that were consisted of fine grain sediment such as clay or mud. Artificial levees did not the for mation cause of the anastomosing channel pattern. Nevertheless it not only restrained the migration of the channels and maintained the channel stability but also partly prevented flooding. This human behavior resulted the high sedimentary ratio in the anastomosing channels and lower sedimentary ratio on the interchannel lands. So the relative rising velocity of the anastomosing channel beds is greater than that of the interchannel lands.