Experiments Of Water Flow And Bed Deformation In A Flume With Consecutive Curves

Natural fluvial channels usually consist of a series of bends and straight reaches. Therefore investigations on water flow and sediment movement in an ideal bend can be used as a basis for the study of natural river channels. Bend flow has distinct three-dimensional characteristics, such as water surface superelevations and spiral flows.Flume experiment is a basic method to investigate fluvial processes. Existing experimental results and numerical simulation studies on bend flow were mostly aimed at simple bends. In the study of fully-developed multiple-bend channel with consecutive curves, detailed information of flow structure, sediment transport and bed deformation is also needed for further research.In this study, a conceptual model channel with 6 consecutive bends was built, in which both clear water runs and mobile-bed runs were conducted. Patterns of bend flow and channel bed deformation were measured for various conditions. Comparisons of velocity distribution between the first bend and other bends showed that typical bend flow structure was not fully established in the first channel bend, and the flow structure in the first bend should not be used as a representation of the general condition of bend flows, which suggested there could be limitations in single bend model tests. Therefore, for bend flow study, flume tests with multiple-bends will be necessary.This paper summarized the characteristics of bend flow and channel bed deformation processes based on measurements in the flume with consecutive bends. The results showed that: 1) maximum values of depth-averaged velocity were always found near the convex bank for higher flow discharges, and near the concave bank for lower flow discharges, but offset in space to the downstream direction; 2) distribution of longitudinal velocity over depth changed in both longitudinal and transverse directions. Maximum velocity was found near and below the free surface upstream the top of bend, but near the bottom in the convex banks downstream the top of bend; 3) characteristics of bed load sediment transport were manifested as concave bank erosion and convex bank deposition, and the proportion of movement of same bank was larger than different bank.A 3-D numerical model was also used to simulate each test runs and compare the results with physical model tests. It was shown that the results of numerical simulation equated with measured data.