Abstract

Braided rivers easily form wide and shallow floodplains when there is no constraints on both sides of the river. During floods, rising water level submerges the floodplain of the bifurcated channel, resulting in the Compound-Braided River. The generalized model was established based on statistical data from the braided river reach of Heilongjiang. In this paper, the flow field of the straight compound-braided river was measured in flume experiments, and then the effect of the interaction of floodplain and main channel on the flow pattern, water level, flow structure and resistance force were studied under overbank flow conditions. The split ratio variation trend is further discussed. The results show that hydraulic factors in diverge segment were mainly related to braided reach, with high longitudinal velocity observed in inner floodplain. The exchange flow between floodplain and main channel accelerates transverse flow and promotes sediment transport intensity laterally. Secondary flow of compound section within the influence range of bifurcated flow was obviously inhibited. Boundary shear stress analysis showed that the diversion ratio of the main tributary under overbank condition decreased slightly and would maintain constant values as surface rise.