Sinuous or braiding water flows and formation of meandering and braided river channels

Abstract

The paper demonstrates that the instability of straight movement of river flows causes their sinuosity (meandering) or splitting into branches and is reflected in the evolution of any channel pattern type. In a straight unbraided channel the instability is manifested as a sinuosity of the dynamic axis of river flow which bends round side­bars, i. e. elevated parts of channel relief drying out during the low water, or in braided channel reaches, where each branch of the stream forms further bends. In braided channels the sinuosity of the dynamic axis of the flow causes a specific distribution of flow velocities, circulation currents and particular angles of approaching the banks, thus resulting in bank erosion and sediment accumulation near the islands. Therefore, the channel branches look like gentle bends in single braided reaches, while in conjugated braided reaches the sinuosity of main river flow occurs along a series of the islands, and the branches of anabranching and split channels also form meanders. Thus, meandering is a universal process of different channel patterns formation. In braided channels it occurs in line with the distribution of water flow over the branches, which determine the parameters of bends, as well as the rate and direction of their deformation. Meandering channels of large rivers and bends of branches of split channels are, in their turn, complicated by islands in the wings and the top parts of meanders. However, the distribution of water flow into branches is not characteristic for small and medium-size rivers. The patterns discussed in the paper should be taken into account when substantiating the methods of channel processes management for the solution of practical problems.