Features of the Velocity Distribution and Secondary Flow in a Compound Channel With Vegetation

Abstract

Aquatic vegetation is an important component of natural river ecosystem, usually growing in riverine, marsh, and coastal areas, interacting with water flow to form complex flow structure, which has an important impact on bank slope stability and flood discharge capacity of river channels. Four sets of indoor flume vegetation-flow experiments were conducted using a typical beach trough structure in the lower section of the Yangtze River. The compound channel was divided into the main channel, side slope and side beach zones, and simulated vegetation such as reeds, sedges and dwarf grass were used. The emphasis was on the hydrodynamic properties under semi-covered emergent rigid vegetation and semi-covered non-submerged rigid vegetation. In this study, the Shiono and Knight equation (SKM model) was used to elucidate the distribution characteristics of ‘the depth-averaged velocity U_d’ and ‘equivalent diameter D’ of vegetation in water gradient, and the Taylor method was used to demonstrate that the proposed ‘equivalent diameter D’ of vegetation has a certain level of accuracy within a reasonable threshold range. In addition, a new secondary flow model was proposed using a genetic algorithm that considers many hydraulic and vegetation parameters. Further, a new secondary flow model was proposed using a genetic algorithm that considers many hydraulic and vegetation parameters. Finally, ‘the depth-averaged velocity U_d’ of the compound channel was accurately predicted by combining the experimental data with the new SKM model. In this study, we investigated the water-blocking ability of gradient vegetation in river water. A method in which the secondary flow law and formula are difficult to determine was solved, which could provide technical support for the design of complex vegetated rivers and the evaluation of the flood discharge capacity of rivers.