Experimental Study On The Flow Characteristics Of Compound Meandering Channels With Overbank Flow

The flow in compound meandering channels with overbank flow has the characteristics of the curved river, which is affected by many factors. The floodplain and main channel is an interactive system, the changes of floodplain directly affect the evolution of river channel and the adjustment of main channel also constitutes a significant effect on the stability of floodplain. Therefore it is the complicated boundary conditions that leading to the complexity of the flow structure. Currently, such research is still less and it has important reference value to the natural river channel evolution and governance. This paper first summarizes the research results of flow and sediment transport characteristics in straight and meandering compound channels, then it presented the research needs to be further study and described the experimental procedure.Flume experiment carried out in the generalized compound meander channels, the research focus on flow structure in the condition of overbank flow. It analyzed the flow velocity distribution, the basic characteristics of flow turbulence and the anisotropic characteristics of flow turbulence in typical section were analyzed in detail. Finally, momentum exchange of flow between floodplain and main channel were analyzed from the Reynolds equation. Preliminary the following conclusions: 1. Velocity distribution.? In the overbank condition, the amplitude of water level along the meander channel in the floodplain and the interaction zones is larger than in the main channel. The highest point of water level in the main channel down toward in the overbank condition still near the top of the bend and up toward in the high overbank flow.? The main flow area near the bend top toward the floodplain with the increase level of overbank flow. Reflux flow structure near the left bank of straight transition in the bend developed in the condition of momentum exchange has "narrowed" river channel effect, and in the left floodplain zone the negative longitudinal velocity has a larger dispersion characteristics along the water depth, also the flow velocity of the right bank of the region increased and more uniform.? The interaction of floodplain and main channel flow affects the secondary flow and the intensity and scope of the flow interaction changes accordingly along with different overbank flow depths. 2. Turbulent characteristics? Three-dimensional turbulence intensity distribution along the vertical depth of the overall increases rapidly to a maximum value near the bottom and then up to the vicinity of the surface tends to decrease. The Interaction floodplain and main channel flow causes turbulence intensity reaches the maximum deviation of the position shift from the bottom.? The main area of the large turbulence energy is mainly in the floodplain area and slope area which affected by floodplain and main channel flow interaction, the turbulence kinetic energy increase along the bend with the development of the secondary flow.? The section distribution of Reynolds stress is related to the longitudinal velocity gradients. Opposite in sign of the core area of extreme Reynolds stress value near the junction reflecting flow momentum transfer.? The interaction of floodplain and main channel flow increases flow turbulence degree of anisotropy and floodplain and slope zone is the main area of flow interaction. 3. The floodplain and main channel flow momentum exchangePositive and negative extreme apparent shear stress values is mainly distributed near the junction, this corresponds well to the extreme values of Reynolds stress. The momentum is mainly transmitted from the main channel into the floodplain in straight compound channels, while in the compound meander channels the flow momentum can transmitted from the floodplain into the main channel in the conditions of complex bend boundary.