THE RIVER BED RECONFIGURATIONS ON THE MIDDLE AMUR LOWLAND RIVERS

Abstract

It is established that the reconfigurations of the river beds in the Middle Amur lowland are defi ned by irregular flows during the year. Their main intensity occurs during the summer and autumn rain floods. The plan reconfigurations comprise the rise and development of meanders. Free meanders are predominant; they occasionally alternate with the adapted, broken and sometimes embedded ones. The reconfigurations of the river beds occur due to the two main processes. The development of segmented bends is associated with the growth of the curvature of the channel and of the bend deflection. During the development of omega-shaped meanders they are moving gradually downstream without significant change in their shapes and sizes. All the river islands of the middle Amur lowland form 4 groups: 1) the islands confined to the relatively straight section of the riverbed; 2) the islands formed in the points of channel braiding; 3) the bend islands; 4) the islands formed as a result of the floodplain braiding. The results of studies indicate the accumulative origin of the islands (except for the fourth group). Their dynamics consists of seasonal variations of their shape and size at a relatively constant spatial position, and, at the same time, depends on the stages of development of bends and straight portions of the channel.