5 Conclusions
Field experiments were conducted in floodplains of Poyang Lake, China, to investigate the influence of AV on flow structures under combined current and wind-driven wave conditions. Spectral decomposition was used to decompose the wave and turbulent components from the instantaneous velocity series, and the vertical distributions of time-averaged velocity (Uhoriz ), wave orbital velocity (Uw ) and turbulent kinetic energy (TKE ) with the presence of AV were analyzed separately. WithEw /S (= 0.03 ~ 0.3) < 0.5 for all cases tested here the interaction between waves and vegetation was weak and the vertical profiles ofUhoriz and TKE were more similar to that under pure-current conditions. Without significant wave-induced current generated within canopy, Uhoriz distributed uniformly through the entire water column or increased gradually from bed to water surface for emergent vegetation and in the lower part of submerged vegetation. As Red varied between 3 and 90, no stem-generated turbulence was expected to produce within vegetation, leading to the TKE within canopy was comparable for all cases in present study. Near the top of submerged vegetation,Uhoriz increased rapidly with increasing distance to the bottom, and shear turbulence was expected to be generated near the canopy interface, leading to TKE reaching its maximum near the vegetation interface and decrease toward both bed and water surface. With weak wave-plant interaction, the measured Uwfor the vegetated cases agreed with predictions by linear wave theory through the entire water column, suggesting that the wave velocity was not attenuated by AV. Although the mean and turbulent flow structures within vegetation were not altered by waves with weak wave-plant interaction in present study, the shear turbulence generated at the top of vegetation penetrated a deeper depth within vegetation with the influence of waves than without.