Effect of vegetation on flow hydraulics in compound open channels with non-prismatic floodplains

Abstract

The present paper aims to evaluate the effect of emergent rigid vegetation density on the flow's turbulence structure and hydraulic parameters at the non-prismatic floodplains. The experiments were performed using the physical model of the asymmetric non-prismatic compound channel. The results show that the velocity distribution in the vegetation flow is more influenced by the drag force caused by the vegetation than by the bed shear stress and does not follow the law of logarithmic velocity distribution throughout the non-prismatic section. The intense velocity gradient at the interface of the main channel and the floodplain leads to the development of strong secondary currents, increased Reynolds shear stresses, apparent shear stresses and momentum exchange in this region. Vegetation also decreases mean kinetic energy in the floodplain and increases it in the main channel. The mean turbulence exchange coefficient for the non-prismatic compound channels without vegetation was 0.23 and for the divergent and convergent compound channels was 0.035 and 0.020, respectively. The comparison of the local drag coefficient results shows that the fluctuations of this parameter are greater in the divergent section than in the convergent section due to the strong secondary currents in the interface. HIGHLIGHTS This paper is the result of original research in the field of river engineering.; Its innovation is in the field of compound open channel and flow turbulence structure.; The Acoustic Doppler Velocimeter (ADV) profiler has been used with high accuracy to understand the flow structure.; Vegetation on flood plains and its effects on flow hydraulic is novel.; Comparison has been made between the effects of divergence and convergence on flow hydraulics.;

Keywords

• momentum exchange
• non-prismatic compound channels
• secondary current
• turbulence structure
• vegetation density