Influence of aquatic vegetation on flow structure under wind-driven waves: a case study in Lake Taihu (China) with two typical submerged vegetations
摘要
To study the influence of aquatic vegetation on flow structure under wind-driven waves, field experiments were conducted with two types of typical submerged vegetation (i.e., Vallisneria natans and Potamogeton malaianus) in Lake Taihu in China by measuring flow velocity inside and outside the vegetation patches. By decomposing the wave velocity and turbulent velocity from the spectra of the instantaneous velocity, the influence of vegetation on the distributions of time-averaged velocity, wave velocity and turbulent kinetic energy (ETK) was analyzed in this paper. For each case, a current in a direction consistent with the direction of near-surface wind occurred. The wave velocity was dominated by the vertical component and decreased from water surface to bed bottom. ETK reached its maximum near the water surface and decreased toward the bed bottom. Compared with bare bed, the presence of Vallisneria natans and Potamogeton malaianus decreased the time-averaged velocity, wave velocity, and ETK, and the differences in morphology between these two types of vegetation led to discrepancies in flow alteration. For Vallisneria natans, the canopy frontal area reached a maximum at the middle reach of plant, making the decrease of time-averaged and wave velocities largest near the middle of canopy. With blades concentrated at the top of canopy, the reduction in the time-averaged and wave velocities caused by Potamogeton malaianus was largest near the water surface.